Archive for the ‘News’ Category

Hierarchical functionality in MOF structures

Yanfeng Yue and co-workers have developed a novel method for introducing mesoporosity into a series of metal–organic framework (MOF) materials by using “perturbation-assisted nanofusion”, as described in their recent Dalton Transactions paper. The authors exemplified the importance of their work by showing that large dye molecules can be encapsulated in the mesopores for luminescent sensing of volatile organic compounds (see also the image below, from Yue and co-workers).

Encapsulation of large dye molecules in hierarchically superstructured metal-organic frameworks, for ratiometric sensing

Introducing mesoporosity into microporous frameworks has been of interest to materials chemists for several years, in an effort to expand the functionality and widen the potential applications of nanoporous materials.

Microporous materials have proved to be great tools for achieving precision in catalysis, separations and sensing (among others), by using internal surfaces or porosity in a multitude of ways. However, by introducing mesoporosity, one can overcome certain limitations, such as diffusion or small molecule selectivity, and one can even introduce multifunctionality by using the properties of both the micropores and the mesopores within a structure.

Typical procedures for the fabrication of mesopores in MOF structures involve the use of wasteful techniques such as etching or organic templates. However, rather than building mesopores into single crystals of MOFs, Yue and co-workers take a different approach by constructing mesopores from fused MOF nanocrystals that are formed through a highly agitated synthesis procedure (that is, perturbation-assisted nanofusion). The result is the formation of a robust hierarchical superstructure through an inexpensive and economical process.

This out-of-the-box thinking allows the authors to exploit their new ‘bottom-up’ approach to introduce functional mesoporosity into MOF materials, for the sensing of volatile organic compounds.

It is easy to see how this method would be useful to researchers not only in sensing but also in any of the myriad established and emerging MOF applications.

Read the full article now at:

Encapsulation of large dye molecules in hierarchically superstructured metal–organic frameworks
Yanfeng Yue, Andrew J. Binder, Ruijing Song, Yuanjing Cui, Jihua Chen, Dale K. Hensley and Sheng Dai
Dalton Trans., 2014, 43, 17893-17898


Christopher Hinde obtained his Masters degree in Chemistry from the University of Southampton, UK in 2011. He is currently doing research towards a Ph.D. in the area of materials chemistry and catalysis under the supervision of both Dr Robert Raja at the University of Southampton and Professor T. S. Andy Hor at the Institute of Materials Research and Engineering (IMRE), part of Singapore’s Agency for Science Technology and Research (A*STAR).
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December’s HOT articles

Enjoy a read of our end of year HOT articles which are free to access for 4 weeks only!

Our HOT articles have also been compiled into a collection and are available for viewing on our website.

Application of three-coordinate copper(I) complexes with halide ligands in organic light-emitting diodes that exhibit delayed fluorescence
Masahisa Osawa, Mikio Hoshino, Masashi Hashimoto, Isao Kawata, Satoshi Igawa and Masataka Yashima
Dalton Trans., 2015, Advance Article
DOI: 10.1039/C4DT02853H

Graphical Abstract

Free to access until 6th January 2015


Na0.3WO3 nanorods: a multifunctional agent for in vivo dual-model imaging and photothermal therapy of cancer cells
Yuxin Zhang, Bo Li, Yunjiu Cao, Jinbao Qin, Zhiyou Peng, Zhiyin Xiao, Xiaojuan Huang, Rujia Zou and Junqing Hu
Dalton Trans., 2015, Advance Article
DOI: 10.1039/C4DT02927E

 

Graphical Abstract

Free to access until 6th January 2015


Transmetalation from B to Rh in the course of the catalytic asymmetric 1,4-addition reaction of phenylboronic acid to enones: a computational comparison of diphosphane and diene ligands
You-Gui Li, Gang He, Hua-Li Qin and Eric Assen B. Kantchev
Dalton Trans., 2015, Advance Article
DOI: 10.1039/C4DT03147D

 

Graphical Abstract

Free to access until 1st January 2015


A contribution to the rational design of Ru(CO)3Cl2L complexes for in vivo delivery of CO
João D. Seixas, Marino F. A. Santos, Abhik Mukhopadhyay, Ana C. Coelho, Patrícia M. Reis, Luís F. Veiros, Ana R. Marques, Nuno Penacho, Ana M. L. Gonçalves, Maria J. Romão, Gonçalo J. L. Bernardes, Teresa Santos-Silva and   Carlos C. Romão
Dalton Trans., 2015, Advance Article
DOI: 10.1039/C4DT02966F

Graphical Abstract

 

Free to access until 1st January 2015

 

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Molecular Memory in a Long-Lasting Mixed Spin State Fe(III) Complex

From early on, we are taught to look at linear mathematical relationships as dependent variables that are determined by the value of an independent variable.

The reason that I find the phenomenon of hysteresis fascinating is that it is the violation of the above concept. By definition, the value of a dependent variable showing hysteresis depends not only on the value of the independent variable but also on whether the independent variable has been increasing or decreasing before it arrives at the value at which a measurement is taken. The dependent variable has a ‘memory’ of its path.

Examples of hysteresis are rare on a molecular level. One of several fascinating aspects of the recent Dalton Transactions paper by Guy Jameson and colleagues is that the (temperature-dependent) magnetism exhibited by the authors’ Fe(III) spin-crossover (SCO) complex shows two hysteresis loops; an example from Jameson and colleagues is shown below.

Magnetic Susceptibility vs Temperature Showing Hysteresis

In transition metal complexes where both high spin and low spin states are possible, SCO occurs when a complex switches from one spin state to the other. Unsurprisingly, this is temperature-dependent, hence the temperature dependence of the magnetism. Hysteresis in magnetic measurements of SCO compounds is known, but Jameson and colleagues report a number of rare properties for the Fe(III) compound that they investigate, [Fe(qsal-Br)2]NO3•2MeOH (where qsal-Br denotes the (N-8-quinolyl)-5-bromo-salicylaldimate ligand).

The vast majority of complexes in which SCO occurs exhibit the phenomenon in a single step — at a certain temperature, all of the molecules in a bulk sample will convert from one spin state to the other. This is only the fifth example of a mononuclear Fe(III) complex that shows full SCO that occurs in two or more discrete increments where symmetry is lost within the molecular structure. In the case of this Fe(III) complex, the temperature range over which some metal nuclei are high spin, and some are low spin (in this case 50% each), is the largest ever reported for a mixed spin-state Fe(III): that is, 96 K.

Here, both steps exhibit hysteresis. The spin-state transitions occur at different temperatures when the authors start with the complex at 300 K and cool it, versus when they warm the complex from 4 K.

Read the full article at:

Abrupt two-step and symmetry breaking spin crossover in an iron(III) complex: an exceptionally wide [LS–HS] plateau
David J. Harding, Wasinee Phonsri, Phimphaka Harding, Keith S. Murray, Boujemaa Moubaraki and Guy N. L. Jameson
Dalton Trans., 2015, DOI: 10.1039/C4DT03184A


Ian Mallov Ian Mallov is currently a Ph.D. student in Professor Doug Stephan’s group at the University of Toronto. His research is focused on synthesizing new Lewis-acidic compounds active in Frustrated Lewis Pair chemistry. He grew up in Truro, Nova Scotia and graduated from Dalhousie University and the University of Ottawa, and worked in chemical analysis in industry for three years before returning to grad school.
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November’s HOT articles

Enjoy a read of our latest HOT articles which are free to access for 4 weeks only! 

Our HOT articles have also been compiled into a collection and are available for viewing on our website. 

Redox activity and π bonding in a tripodal seven-coordinate molybdenum(VI) tris(amidophenolate)
Travis Marshall-Roth and Seth N. Brown
Dalton Trans., 2015, Advance Article
DOI: 10.1039/C4DT02936D 

 

Graphical Abstract 

Free to access until 28th December 2014 


FIrpic: archetypal blue phosphorescent emitter for electroluminescence
Etienne Baranoff and Basile F. E. Curchod
Dalton Trans., 2015, Advance Article
DOI: 10.1039/C4DT02991G

Graphical Abstract 

Free to access until 28th December 2014


Optimizing the high-field relaxivity by self-assembling of macrocyclic Gd(III) complexes
Dale Lawson, Alessandro Barge, Enzo Terreno, David Parker, Silvio Aime and Mauro Botta
Dalton Trans., 2015, Advance Article
DOI: 10.1039/C4DT02971B

Graphical Abstract

 

Free to access until 28th December 2014


 

Copper(I), silver(I) and gold(I) complexes of N-heterocyclic carbene-phosphinidene
Venkata A. K. Adiraju, Muhammed Yousufuddin and H. V. Rasika Dias
Dalton Trans., 2015, Advance Article
DOI: 10.1039/C4DT03285C

Graphical Abstract

Free to access until 28th December 2014

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October’s HOT articles

Enjoy a read of our latest HOT articles which are free to access for 4 weeks only!

Our HOT articles have also been compiled into a collection and are available for viewing on our website.

A strong steric hindrance effect on ground state, excited state, and charge separated state properties of a CuI-diimine complex captured by X-ray transient absorption spectroscopy
J. Huang, M. W. Mara, A. B. Stickrath, O. Kokhan, M. R. Harpham, K. Haldrup, M. L. Shelby, X. Zhang, R. Ruppert, J.-P. Sauvage and L. X. Chen
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT02046D

Graphical Abstract

Free to access until 26th November 2014


On the coordination chemistry of organochalcogenolates RNMe2^Eand RNMe2^E^O(E = S, Se) onto lead(II) and lighter divalent tetrel elements
Alexandra Pop, Lingfang Wang, Vincent Dorcet, Thierry Roisnel, Jean-François Carpentier, Anca Silvestru and Yann Sarazin
Dalton Trans., 2014, 43, 16459-16474
DOI: 10.1039/C4DT02252A

Graphical Abstract

Free to access until 26th November 2014


Niobium(V) and tantalum(V) halide chalcogenoether complexes – towards single source CVD precursors for ME2 thin films
Sophie L. Benjamin, Yao-Pang Chang, Chitra Gurnani, Andrew L. Hector, Michelle Huggon, William Levason and Gillian Reid
Dalton Trans., 2014, 43, 16640-16648
DOI: 10.1039/C4DT02694B

Graphical Abstract

Free to access until 26th November 2014


The crystal structure of paramagnetic copper(II) oxalate (CuC2O4): formation and thermal decomposition of randomly stacked anisotropic nano-sized crystallites
Axel Nørlund Christensen, Bente Lebech, Niels Hessel Andersen and Jean-Claude Grivel
Dalton Trans., 2014, 43, 16754-16768
DOI: 10.1039/C4DT01689K

Graphical Abstract

Free to access until 26th November 2014


Lithiated sulfoxides: α-sulfinyl functionalized carbanions
Gerd Ludwig, Tobias Rüffer, André Hoppe, Till Walther, Heinrich Lang, Stefan G. Ebbinghaus and Dirk Steinborn
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT02238F

Graphical Abstract

Free to access until 26th November 2014


Encapsulation of large dye molecules in hierarchically superstructured metal–organic frameworks
Yanfeng Yue, Andrew J. Binder, Ruijing Song, Yuanjing Cui, Jihua Chen, Dale K. Hensley and Sheng Dai
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT02516D

Graphical Abstract

Free to access until 26th November 2014

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The influence of Michael Lappert on the chemistry landscape

Introduction

Michael F. Lappert, one of the giants of 20th century organometallic chemistry, passed away suddenly at the age of 85 on March 28, 2014. His storied career and status as a leader in the field have been commemorated elegantly elsewhere. Prof. Lappert published prolifically over his lengthy career, leaving the global community a legacy of almost 800 scholarly articles on original chemical research in organometallic chemistry from across the Periodic Table.

More than half of those papers, including many of his most highly cited articles, were published in Royal Society of Chemistry journals. To honour his memory and body of work, we have put together this web collection of selected contributions from the RSC Lappert canon (http://rsc.li/lappert). Together, these papers paint a picture of a chemist with extraordinarily broad interests and an uncanny knack for pursuing seminal research that has stood the test of time and influenced the field in significant ways.

The selected papers are grouped by Lappert’s major areas of interest and have been chosen by members of the Editorial Boards of Dalton Transactions and ChemComm, where much of Lappert’s work appeared over the years. They are available for viewing free of charge to interested chemists around the globe. We believe this is a fitting tribute to Prof. Lappert and hope the readers of Royal Society of Chemistry journals enjoy revisiting some of these seminal contributions.

Early contributions

Lappert’s very first paper in the chemical literature “Interaction of boron trichloride with optically active alcohols and ethers”, published in 1951 with his Ph. D. supervisor W. Gerrard, was followed in short order by a remarkable and prolific series of papers exploring the chemistry of boron halides with alcohols, ethers, pyridine, thioethers, extending into the chemistry of boronic acids, boronic esters, borinic acids, borinate esters and borates.

Indeed, almost every imaginable reaction of boron compounds with small organic molecules, and every combination of boron with halide, oxygen, nitrogen, sulfur, alkyl and aryl substituents and the corresponding Lewis acid–base complexes appear in these early papers.

Boronic acids feature in modern applications as diverse as the palladium-catalysed Suzuki–Miyaura cross-coupling reaction and as saccharide sensors; the foundation for these highly significant developments lies in the detailed, systematic work on the properties and chemistry of boron compounds reported in Lappert’s early papers.

All the more remarkably, this work was done on the basis of careful isolation and characterisation of products via melting and boiling points, refractive indices, elemental analyses and optical rotations, but without the aid of the routine spectroscopic techniques we now take for granted.

By the late 1950s, IR spectroscopy was becoming more widely used and a 1958 paper reports and assigns B–O, B–Cl, B–aryl, B–H3, B–N and B–H vibrational frequencies. Both IR and 1H NMR spectroscopy were used to determine whether organic amide complexes of BCl3 and TiCl4 were N-bound or O-bound, concluding that the latter was favoured, and also observing restricted rotation about the amide C–N bond. Almost all of Lappert’s 80 or so papers published from 1951 to 1965 were concerned with the chemistry of boron.

The paper on amide complexes also shows his interest in the Lewis acid properties of boron halides extending to other elements. This theme quickly extended to a range of metals, for example using IR (and to a limited extent, 1H NMR) spectroscopy to investigate complexes of ethylacetate with a wide range of metal halides (boron, aluminium, silicon, germanium, tin, gallium, indium, titanium, zirconium and iron), commenting on the donor ability of the esters, stereochemistry and group trends for both the metals and the halides.

Now established as a leader in exploring the systematic preparative and descriptive chemistry of elements across the periodic table, Lappert began to report new reaction types that were to set the stage for organometallic chemistry into the present. After preparing a range of new tin amine compounds, in 1965 Lappert reported the first well-established aminostannylation reactions, in which an unsaturated substrate inserts into a tin-nitrogen bond. For example, CO2 inserts into Me3SnNMe2 to give the carbamato complex Me3SnOC(O)NMe2.

This paper described the aminostannylation reaction for CO2, CS2, ketene, PhNCO, PhNCS, PhCN, SO2 and other unsaturated small molecules. We now accept, of course, such main group addition reactions such to be of central importance in both academic and industrial chemistry. As well as establishing a major new reaction paradigm, this chemistry also illustrated Lappert’s early success in tin and, more broadly, group 14 chemistry, as his next major set of papers demonstrates.

Interaction of boron trichloride with optically active alcohols and ethers
W. Gerrard and M. F. Lappert
J. Chem. Soc., 1951, 1020-1024

Stability, solvolysis, and co-ordination reactions of esters of boronic acids and their halogen derivatives
L. J. Bellamy, W. Gerrard, M. F. Lappert and R. L. Williams
J. Chem. Soc., 1958, 2412-2415

Infrared spectra of boron compounds
L. J. Bellamy, W. Gerrard, M. F. Lappert and R. L. Williams
J. Chem. Soc., 1958, 2412-2415

Spectra and structure of amide complexes
W. Gerrard, M. F. Lappert, H. Pyszora and J. W. Wallis
J. Chem. Soc., 1960, 2144-215

Co-ordination compounds having carboxylic esters as ligands. Part II. Relative acceptor strengths of some Group III and IV halides
M. F. Lappert
J. Chem. Soc., 1962, 542-548

Amino-derivatives of metals and metalloids. Part II. Aminostannylation of unsaturated substrates, and the infrared spectra and structures of carbamato- and dithiocarbamato-trimethylstannanes and related compounds
T. A. George, K. Jones and M. F. Lappert
J. Chem. Soc., 1965, 2157-2165

Divalent group 14 compounds

The second group of papers concerns Lappert’s longstanding interest in the “carbene analogs” of the heavier group 14 elements. Debuting in 1976 in a pair of articles in J. Chem. Soc., Dalton Trans., the study of these compounds was a major theme in Lappert’s research efforts in the 1970s and 80s. The first paper is one of his most highly cited (>400), and has certainly been quite influential. It summarizes studies on subvalent alkyl and amido derivatives of the group 14 elements Ge, Sn, and Pb, described in earlier communications going back to 1973. These compounds feature bulky –CH(SiMe3)2 and –N(SiMe3)2 groups that stabilize the divalent compounds in their monomeric forms in solution.

These compounds have since been extensively used as synthetic starting points for low-valent group 14 chemistry, and they represent important milestones in the study of main group compounds and heavy element–element bonded compounds. In particular, with the solid-state structure of {Sn[CH(SiMe3)2]2}2, this work provided the first description of the now well-established trans-bent structure for a E2R4 group 14 compound, and offered a simple rationale for the bonding in such species. In the accompanying paper, the utility of the SnR2 compounds as donor ligands for transition metals and as starting materials for tin(IV) derivatives was explored extensively.

Subsequent studies in this area focused on detailed structural studies and culminated in a paper that provides a more complete understanding of E2R4 species, with more extensive structural data, and establishment of key periodic trends in structure and bonding for these subvalent group 14 compounds. Especially with the aid of molecular orbital calculations, this work provided insight into how localized electron density on the group 14 elements increasingly “bends” the E2R4 structure as E becomes heavier: C < Si < Ge < Sn < Pb.

While the above work focused mainly on the heavier elements in the group, in 1995 Lappert also prepared one of the first well-described silylene derivatives, a class of compounds that has become prominent in recent years as ligands in homogeneous catalysis. These silylenes utilized an “N-heterocyclic” strategy for stabilizing the silylene moiety—a widely familiar approach for the stabilization of divalent species in the lightest group 14 element, carbon. Indeed, Lappert was an early adopter of N-heterocyclic carbenes as ligands for transition metals.

In 1974, Lappert’s lab elegantly demonstrated that a wide range of transition metal N-heterocyclic carbenes could be synthesized via C=C bond cleavage of electron-rich olefins by low valent metals. His 1973 review on transition metal carbenes covers the synthesis, electronic properties, and reactivity of carbenes, as well as their potential role in a range of organic reaction mechanisms. Although written in the early days of metal-carbene chemistry, the basic themes and principles discussed in this review remain pervasive in modern Organometallic Chemistry textbooks.

Subvalent Group 4B metal alkyls and amides. Part I. The synthesis and physical properties of kinetically stable bis[bis(trimethysilyl)methyl]-germanium(II), -tin(II), and -lead(II)
P. J. Davidson, D. H. Harris and M. F. Lappert
J. Chem. Soc., Dalton Trans., 1976, 2268–2274

Subvalent Group 4B metal alkyls and amides. Part II. The chemistry and properties of bis[bis(trimethylsilyl)methyl]tin(II) and its lead analogue
J. D. Cotton, P. J. Davidson and M. F. Lappert
J. Chem. Soc., Dalton Trans., 1976, 2275–2286

Molecular structures of the main group 4 metal(II) bis(trimethylsilyl)-amides M[N(SiMe3)2]2 in the crystal (X-ray) and vapour (gas-phase electron diffraction)
T. Fjeldberg, H. Hope, M. F. Lappert, P. P. Power and A. J. Thorne
J. Chem. Soc., Chem. Commun., 1983, 639–641

Chemistry, including the X-ray structure, of bis[bis(trimethylsilyl)methylgermanium(II)], R2GeGeR2[R = CH(SiMe3)2], a stable compound having a metal–metal ‘double bond,’ a dimetallene
P. B. Hitchcock, M. F. Lappert, S. J. Miles and A. J. Thorne
J. Chem. Soc., Chem. Commun., 1984, 480–482

Subvalent Group 4B metal alkyls and amides. Part 9. Germanium and tin alkene analogues, the dimetallenes M2R4[M = Ge or Sn, R = CH(SiMe3)2]: X-ray structures, molecular orbital calculations for M2H4, and trends in the series M2R′4[M = C, Si, Ge, or Sn; R′= R, Ph, C6H2Me3-2,4,6, or C6H3Et2-2,6]
D. E. Goldberg, P. B. Hitchcock, M. F. Lappert, K. M. Thomas, A. J. Thorne, T. Fjeldberg, A. Haaland and B. E. R. Schilling
J. Chem. Soc., Dalton Trans., 1986, 2387–2394

Synthesis, structures and reactions of new thermally stable silylenes
B. Gehrhus, M. F. Lappert, J. Heinicke, R. Boese and D. Blaser,
J. Chem. Soc., Chem. Commun., 1995, 1931–1932

Carbene complexes. Part VIII. Chromium(0), iron(0), rhodium(I), iridium(I), nickel(II), palladium(II), platinum(II), and gold(I) mono- and oligo-carbene species from electron-rich olefins
B. Cetinkay, P. Dixneuf and M. F. Lappert
J. Chem. Soc., Dalton Trans., 1974, 1827–1833

The chemistry of transition-metal carbene complexes and their role as reaction intermediates
D. J. Cardin, B. Cetinkaya, M. J. Doyle and M. F. Lappert,
Chem. Soc. Rev., 1973, 2, 99–144

Metallocenes

Lappert did not restrict himself to the main group part of the Periodic Table! Transition metal metallocenes occupy a central position in Organometallic Chemistry and early in his career, Lappert was active in the development of improved synthetic routes to the group metallocene dihalides and the development of their organometallic chemistry. In “Part 1” of a series on metallocene dihalides, the Lappert group established routes to zirconocenes and hafnocenes of all the halides and provided detailed spectroscopic data.

The crucial role these compounds were to play in “single site” olefin polymerization catalysis was still on the horizon, but these key early studies provided foundational work for these later developments. The Lappert group continued working with metallocenes for several years; subsequent studies on group 4 compounds included the preparation and characterization of a wide variety of alkyl derivatives. In an example from group 5, the report of an η2-CO2 complex of an alkyl niobocene complements the famous nickel complex of Aresta et al. and demonstrated the first such complex for an early transition metal. Remarkably, the CO2 does not insert into the Nb–C bond of the alkyl group. Given the recent intense interest in the chemistry of CO2, this early discovery serves as a fundamental example of M–CO2 bonding.

Lappert was also interested in the organometallic chemistry of the group 3 metals and the lanthanides (vide infra), including metallocene derivatives of these metals. He was among the first to demonstrate that alkyl groups could serve as bridging ligands in these highly Lewis acidic species. Through careful synthesis and structural analysis, the disclosure of these unusual, highly reactive compounds provided fundamental insight into the organometallic chemistry of the lanthanide metals. Finally, in another prescient contribution, the Lappert group highlighted the bis-(trimethylsilyl) cyclopentadienyl ligand as a bulky, solubilizing Cp donor for the preparation of a variety of lanthanocene chlorides. This ligand is a well-utilized alternative to the ubiquitous (pentamethyl) cyclopentadienyl donor, particularly for the lanthanide and actinide elements.

Metallocene halides. Part I. Synthesis, spectra, and redistribution equilibria of di-π-cyclopentadienyldihalogeno-titanium(IV),-zirconium-(IV), and -hafnium(IV)
P. M. Druce, B. M. Kingston, M. F. Lappert, T. R. Spalding and R. C. Srivastava
J. Chem. Soc. A, 1969, 2106–2110

Metallocene derivatives of early transition metals. Part 2. Substituted cyclopentadienyl Group 4A dichloro-metallocene complexes [M(η-C5H4R)2Cl2](M = Zr or Hf; R = Me, Et, Pri, But, or SiMe3), their mono- and di-alkyl derivatives [M(η-C5H4R)2R′X](X = Cl or R′; R′= CH2SiMe3 or CH2CMe3), and their d1 reduction products
M. F. Lappert, C. J. Pickett, P. I. Riley and P. I. W. Yarrow
J. Chem. Soc., Dalton Trans., 1981, 805–813

A novel carbon dioxide complex: synthesis and crystal structure of [Nb(η-C5H4Me)2(CH2SiMe3)(η2-CO2)]
G. S. Bristow, P. B. Hitchcock and M. F. Lappert
J. Chem. Soc., Chem. Commun., 1981, 1145–1146

Alkyl-bridged complexes of the d- and f-block elements. Part 2. Bis[bis(η-cyclopentadienyl)methylmetal(III)] complexes, and the crystal and molecular structure of the yttrium and ytterbium species
J. Holton, M. F. Lappert, D. G. H. Ballard, R. Pearce, J. L. Atwood and W. E. Hunter
J. Chem. Soc., Dalton Trans., 1979, 54–61

Use of the bis(trimethylsilyl)cyclopentadienyl ligand for stabilising early (f0–f3) lanthanocene chlorides; X-ray structure of [(Pr{η-[C5H3(SiMe3)2]}2Cl)2] and of isoleptic scandium and ytterbium complexes
M. F. Lappert, A. Singh, J. L. Atwood and W. E. Hunter
J. Chem. Soc., Chem. Commun., 1981, 1190–1191

Homoleptic compounds of Lewis acidic metals

The use of steric bulk in ligand sets to stabilize reactive species pervades the work of Lappert, and in the development of routes to homoleptic alkyls of the early metals and lanthanides he used this strategy to great effect. In addition to the metallocene work described above, the Lappert group produced a strong body of work concerning homoleptic alkyl and amido derivatives of these elements.

The earliest forays into this area built on the group 4 metallocene chemistry described above. 1973 saw publication of the first of his full papers on trimethylsilylmethyl and trimethylgermylmethyl complexes of group 4 metals, including the homoleptic derivatives. Over a decade later, these complexes inspired some of Arnold’s postdoctoral research with Wilkinson into related homoleptic aryls and their reactivity. As is now well appreciated, alkyl ligands of the type used by Lappert provide a number of important and attractive features: in addition to the stability they impart by virtue of the lack of beta hydrogen atoms, they are easy to prepare and handle and they provide excellent solubility, and crystallinity to the resulting metal complexes.

Also in 1973, Lappert and Pearce put out a brief report in J. Chem. Soc., Chem. Commun. Concerning the preparation of scandium and yttrium tris(alkyl) complexes as their bis-THF adducts. This simple paper has served as an inspiration for many groups working in this area, and these alkyl complexes are now routinely used to prepare post-metallocene organometallic compounds of these reactive, Lewis acidic metals directly via facile alkane elimination protocols. Use of even bulkier –CH(SiMe2)2 groups (the same groups used to prepare the divalent group 14 metallenes described above) allowed for isolation of truly homoleptic lanthanide(III) alkyls, even those of larger, more kinetically labile lanthanides such as La and Sm. The key to success in this endeavour was addition of a second trimethylsilyl group to the alpha carbon, which provided much needed steric protection along with electronic stabilization. His interest in this area was not just restricted to synthesis; he also went far beyond his usual standard synthesis and characterization techniques to explore the thermochemistry of metal alkyl complexes, establishing standard heats of formation for metal–carbon bonds in homoleptic species.

In addition to homoleptic alkyls, the Lappert group prepared amido and alkoxo derivatives of these metals that have proven useful over time. In a seminal paper from 1968 by Lappert and Chandra a number of such complexes were initially reported. Many working in the area of group 4 chemistry take the protonolysis reactions of metal amides for granted as synthetic routes to metalcyclopentadienyl, -alkoxide and –thiolate derivatives. It is this classic contribution by Lappert which provides the foundation of so much chemistry deriving from the early transition metals, from applications in olefin polymerisation catalysis to CVD precursors to hydroelementation chemistry. In a related communication 15 years later, Lappert and Singh describe new classes of hydrocarbon-soluble group 3 and lanthanoid complexes of bulky aryloxide ligands.

Remarkably, before this time only a handful of three- and four-coordinate rare earth compounds were known. Today, many working in this area of rare earth and alkaline earth (i.e. large and electropositive) metal chemistry accept the use of bulky phenolate-based ligands as a sine qua non for controlling coordination numbers and nuclearity. Not surprisingly, with 183 citations, this is one of the top 3% most cited papers from Lappert’s many contributions.

Silylmethyl and related complexes. Part I. Kinetically stable alkyls of titanium(IV), zirconium(IV), and hafnium(IV)
M. R. Collier, M. F. Lappert and R. Pearce
J. Chem. Soc., Dalton Trans., 1973, 445–451

Stable silylmethyl and neopentyl complexes of scandium(III) and yttrium(III)
M. F. Lappert and R. Pearce
J. Chem. Soc., Chem. Commun., 1973, 126–126

Synthesis and structural characterisation of the first neutral homoleptic lanthanide metal(III) alkyls: [LnR3][Ln = La or Sm, R = CH(SiMe3)2]
P. B. Hitchcock, M. F. Lappert, R. G. Smith, R. A. Bartlett and P. P. Power
J. Chem. Soc., Chem. Commun., 1988, 1007–1009

Standard heats of formation and M–C bond energy terms for some homoleptic transition metal alkyls MRn
M. F. Lappert, D. S. Patil and J. B. Pedley
J. Chem. Soc., Chem. Commun., 1975, 830–831

Amido-derivatives of metals and metalloids. Part VI. Reactions of titanium(IV), zirconium(IV), and hafnium(IV) amides with protic compounds
G. Chandra and M. F. Lappert
J. Chem. Soc. A, 1968, 1940–1945

Three- and four-co-ordinate, hydrocarbon-soluble-aryloxides of scandium, yttrium, and the lanthanoids; X-ray crystal structure of tris(2,6-di-t-butyl-4-methylphenoxo)scandium
P. B. Hitchcock, M. F. Lappert and A. Singh
J. Chem. Soc., Chem. Commun., 1983, 1499–1501

β-Diketiminato (“NacNac”) ligands

Few ancillary ligand classes develop into widely adopted platforms for chemistry. Cyclopentadienyl ligands, phosphine donors, pincer frameworks come to mind when thinking about such ligand sets, and it can be argued that the β-diketiminato ligands deserve to be thought of in these terms. Lappert was again ahead of the curve on this and was among the first to recognize that these ligands should be suitable for supporting a wide range of coordination chemistry, providing the advantage of steric protection of a metal center in comparison to the widely used acetylacetonate, or acac, ligand.

This was amply demonstrated in two closely related communications that were published on the same year (1994) and attracted 114 citations each. They describe straightforward preparation of two highly lipophilic monoanionic ligands, namely azaallyl and β-diketiminate, and introduce these ligands into early transition and main group metal chemistry. Later, β-diketiminate ligands (also more widely known as “NacNac”) became particularly popular ancillary group in various fields of organometallic and coordination chemistry with significant contributions using Lappert’s bis(trimethylsilyl) substituted β-diketiminate.

Lappert himself continued to publish prodigiously in this area until late in his career and, along with Bourget-Merle and Severn, published a definitive review on the subject of NacNac ligands in coordination chemistry. Recent results include the use of the NacNac ligand system to support low valent Ln(II) compounds and the exploration of non-spectator roles for the NacNac ligand in chemical reactivity.

Transformation of the bis(trimethylsilyl)methyl into a β-diketinimato ligand; the X-ray structure of [Li(L′L′)]2, SnCl(Me)2(L′L′) and SnCl(Me)2(LL), [L′L′= N(R)C(Ph)C(H)C(Ph)NR, LL = N(H)C(Ph)C(H)C(Ph)NH, R = SiMe3)
P. B. Hitchcock, M. F. Lappert and D. S. Liu
J. Chem. Soc., Chem. Commun., 1994, 1699–1700

Transformation of the bis(trimethylsilyl)methyl into aza-allyl and β-diketinimato ligands; the X-ray structures of [Li{N(R)C(But)CH(R)}]2 and [Zr{N(R)C(But)CHC(Ph)N(R)}Cl3](R = SiMe3)
P. B. Hitchcock, M. F. Lappert and D. S. Liu
J. Chem. Soc., Chem. Commun., 1994, 2637–2638

Heteroleptic ytterbium(II) complexes supported by a bulky β-diketiminato ligand
P. B. Hitchcock, A. V. Khvostov, M. F. Lappert and A. V. Protchenko
Dalton Trans., 2009, 2383–2391

New reactions of β-diketiminatolanthanoid complexes: sterically induced self-deprotonation of β-diketiminato ligands
P. B. Hitchcock, M. F. Lappert and A. V. Protchenko
Chem. Commun., 2005, 951–953

Final thoughts

None of us was formally associated with Prof. Lappert, but each has encountered his work again and again as our own careers have developed. In choosing these papers, we have focused on those that we believe to have been the most influential on the field (mostly as measured by the number of citations, but also based on our own experiences) while reflecting the impressive breadth of Lappert’s interests. As such, the selection is somewhat biased towards his early career work and we may have missed some chestnuts from later on in his career.

Realizing that such choices are personal and reflective of our own experiences, it is entirely possible that many of you reading this will have opinions of your own as to what contributions by Mike Lappert should be recognized. In this case, we invite you to add to the conversation by leaving your comments here. In the meantime, we hope you accept this collection in the spirit it is meant: to honour the work and legacy of a fine chemist.

Happy reading!

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The Rare BH5

In fall 2008 I visited Boston, where a good friend gave me a tour of Harvard’s chemical laboratories.  Passing by a small office, I saw through the window a thin elderly man in glasses hunched over a desk.  He was turned away from me but the sign on his office said William N. Lipscomb.

Since Lipscomb’s astonishing groundwork beginning in the 1940’s, boranes have provided fascinating examples of the diversity and possibilities of chemical bonding.  Today, boron’s Lewis acidity is widely exploited in catalysis and Frustrated Lewis Pair (FLP) chemistry.

The BH5 molecule, described as BH3 with sigma-bonded dihydrogen bound in an H2 manner, lies at the confluence of many currents of boron chemistry: the activation of hydrogen by FLP’s using borane Lewis acids; three-centre-two-electron bonding; H2 complexes, and the comparison of main group and transition metal chemistry.

In a recent paper in Dalton Transactions, authors Szieberth, Szpisjak, Turczel and Konczol describe BH5 as “rare.”  This is an understatement.  As they report, its existence was confirmed in 1994 by infra-red spectroscopy in an argon matrix at 10-25K temperatures.

In this paper, they present the modelling of the BH5 complex using Natural Bond Order analysis.  Although this has been reported before, the authors use this paper to discern a unique and significant contribution to the stability of η2 H2 borane complexes: the back-donation of electron density from the B-H (or B-R) s-bonds into the σ* orbital of the bound H2, just as electron density from d-orbitals is donated to the H-H σ* orbital in transition metal H2 complexes.  Their description of the Lewis structure of BH5 as a BH3/H2 adduct featuring a three-centre-two electron bond accounts for 99.1% of the electron density.

William Lipscomb passed away on April 14, 2011 at the age of 91.  But I am sure he would be pleased that work within his research area remains vigorously active.

Read the original paper:

The stability of η2-H2 borane complexes – a theoretical investigation
László Könczöl, Gábor Turczel, Tamás Szpisjaka and Dénes Szieberth
Dalton Trans., 2014,43, 13571-13577


Ian Mallov Ian Mallov is currently a Ph.D. student in Professor Doug Stephan’s group at the University of Toronto. His research is focused on synthesizing new Lewis-acidic compounds active in Frustrated Lewis Pair chemistry. He grew up in Truro, Nova Scotia and graduated from Dalhousie University and the University of Ottawa, and worked in chemical analysis in industry for three years before returning to grad school.
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September’s HOT articles

Enjoy a read of Autumn’s crop of HOT articles which are free to access for 4 weeks only!

Our HOT articles have also been compiled into a collection and are available for viewing on our website.

Metal-mediated coupling of amino acid esters with isocyanides leading to new chiral acyclic aminocarbene complexes
Tatyana B. Anisimova, M. Fátima C. Guedes da Silva, Vadim Yu. Kukushkin, Armando J. L. Pombeiro and Konstantin V. Luzyanin
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT01917B

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Free to access until 27th October 2014


Photoinduced hydrogen evolution by a pentapyridine cobalt complex: elucidating some mechanistic aspects
Elisa Deponti, Alessandra Luisa, Mirco Natali, Elisabetta Iengo and Franco Scandola
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT02269F

Graphical Abstract

Free to access until 27th October 2014


Efficient halogen photoelimination from dibromo, dichloro and difluoro tellurophenes
Elisa I. Carrera and Dwight S. Seferos
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT01751J

Graphical Abstract

Free to access until 17th October 2014


Synthesis, structure and catalytic activity of a gold(I) complex containing 1,2-bis(diphenylphosphino)benzene monoxide
Christine Hahn, Leticia Cruz, Amanda Villalobos, Liliana Garza and Samuel Adeosun
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT02116A

Graphical Abstract

Free to access until 17th October 2014


1,3,5-Triferrocenyl-2,4,6-tris(ethynylferrocenyl)-benzene – a new member of the family of multiferrocenyl-functionalized cyclic systems
Ulrike Pfaff, Grzegorz Filipczyk, Alexander Hildebrandt, Marcus Korb and Heinrich Lang
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT02307B

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Free to access until 17th October 2014

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Expanding the Utility of Expanded NHCs

In their recent paper in Dalton Transactions, Stasch, Jones and co-workers describe the use of bulky ring-expanded N-heterocyclic carbenes (NHCs) for the stabilisation of Group 15 trichlorides, ECl3; E = P, As, Sb.

The authors show that mixing 1:1 solutions of the ring-expanded, 2,6-diisopropylphenyl-subsitutied NHC “6-Dipp” with ECl3 (E = P, As, and Sb) affords satisfactory yields of the corresponding [(6-Dipp)ECl3] adduct, noting that the use of the alternatively-substituted mesityl-substituted carbene (6-Mes) led to a mixture of products thus highlighting the importance of the 6-Dipp ligand for stabilising the adducts.

Adduct formation

The group characterised each adduct using standard means, including NMR spectroscopy and electron-impact (EI) mass spectrometry. In the cases of P and Sb, they were able to use X-ray crystallography to determine the solid state structures of those compounds and observed that each pnictogen centre adopted a saw-horse geometry.

When the researchers tried to reduce these adducts using either KC8 or a Mg(I) derivative, they were mostly unsuccessful, however they were able to reduce [(6-Dipp)PCl3] using the former reagent to form a unique dicationic carbene-stabilized P4 unit. Once again, the authors attributed the stability of this species to the steric profile of the 6-Dipp ligand framework. The X-ray crystal structure of the complex shows a P4-butterfly geometry stabilised by two carbene moieties.

P4 compound

During the course of their reactivity studies, the group identified (6-MesH)2 as a byproduct resulting from reaction of in-situ generated [(6-Mes)PCl3] with KC8. With further optimisation, they revealed that this moiety could be accessed from treatment of [6-MesH]Br with KC8 – marking the first successful reductive coupling of cyclic amidinium ions. Along with NMR and X-ray crystal data, a cyclic voltammetry (CV) study was also performed on (6-MesH)2 to fully characterise this unique species.

The successful syntheses of all these p-block NHC complexes pave the way for new discoveries in fundamental reactivity, bonding, and catalysis employing main group elements, further demonstrating the potential of these elements to perform exciting chemistry.

Read the full article to find out more:

Expanded Ring N-Heterocyclic Carbene Adducts of Group 15 Element Trichlorides: Synthesis and Reduction studies
Anastas Sidiropoulos, Brooke Osborne, Alexandr Simonov, Deepak Dange, Alan Bond, Andreas Stasch and Cameron Jones
Dalton Trans., 2014, DOI: 10.1039/C4DT02074J


Marcus Drover is a Ph.D. student, co-supervised by Professors Laurel Schafer and Jennifer Love at the University of British Columbia. His research is focused on the preparation of low-coordinate RhI and IrI complexes for use in small-molecule reactivity. He grew up in St. John’s, Newfoundland and graduated from Memorial University (MUN) before beginning graduate school in 2012.
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August’s HOT papers

Enjoy a read of our fresh batch of HOT articles which are free to access for 4 weeks only!

Our HOT articles have also been compiled into a collection and are available for viewing on our website.

Unusual assembly of lacunary heteropolymolybdates with cyanometalate fragment
Ya Wang, Ning Jiang, Fengyan Li, Yanzhen Zheng, Lin Xu and Minghui Sun
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT01875C

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Free to access until 17th October 2014


Structure, stability and photocatalytic H2 production by Cr-, Mn-, Fe-, Co-, and Ni-substituted decaniobate clusters
Jung-Ho Son, Jiarui Wang and William H. Casey
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT02020K

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Free to access until 17th October 2014


Light-induced spin-state switching in the mixed crystal series of the 2D coordination network {[Zn1−xFex(bbtr)3](BF4)2}: optical spectroscopy and cooperative effects
Pradip Chakraborty, Cristian Enachescu, Arnaud Humair, Leo Egger, Teresa Delgado, Antoine Tissot, Laure Guénée, Céline Besnard, Robert Bronisz and Andreas Hauser
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT01728E

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Free to access until 11th September 2014


Two-photon sensitized visible and near-IR luminescence of lanthanide complexes using a fluorene-based donor–π-acceptor diketonate
Adam W. Woodward, Andrew Frazer, Alma R. Morales, Jin Yu, Anthony F. Moore, Andres D. Campiglia, Evgheni V. Jucov, Tatiana V. Timofeeva and Kevin D. Belfield
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT01507J

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Free to access until 11th September 2014


Low temperature activation of S8, Sered and α-Te with [CpBIGFe(CO)2] radicals
S. Heinl and M. Scheer
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT01764A

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Free to access until 9th September 2014


Large structural changes upon protonation of Fe4S4 clusters: the consequences for reactivity
Ian Dance and Richard A. Henderson
Dalton Trans., 2014, Advance Article
DOI: 10.1039/C4DT01687D

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Free to access until 9th September 2014

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