Metal carbonyl cluster chemistry

The foregoing examples show the relevance to metal-carbonyl cluster chemistry of the borane-oarborane structural and bonding pattern. Its relevance to other areas of chemistry may be explored readily using a systematic skeletal electron-counting procedure (161, 201). 

P. J. Dyson and J. S. Mclndoe, Transition Metal Carbonyl Cluster Chemistry, Gordon and Breach, Amsterdam, 2000. 

The appreciative reader of this text will immediately recognize that compounds II and IV and their inter-conversion have analogs in both carborane and metal-carbonyl cluster chemistry. Thus, B3C2 or M3C2 cores of six-sep davo-lrigonal-bipyramidal clusters can have 1,2- or 1,5-C atom positions with the latter clearly more stable in the carborane. For the Mo compounds in Figure 8.20, the 1,2-isomer (IV, C adjacent) must form from the 1,5-isomer (II, C apart) if it is an intermediate. Another notable difference is that this Mo reaction system takes place in air in water solution. 

These early measurements stimulated my interest in NMR spectroscopy, and, on moving to the University of Kent at Canterbury (1972), we were lucky to be able to buy the first Fourier Transform NMR spectrometer in the UK. This instrument was still based on an electromagnet ( H, 100 MHz) but allowed faster acquisition of NMR spectra and enabled the development of multinuclear NMR spectroscopy. This permitted me to start collaborating with Paolo Chini who had taken up an appointment at the University of Milan where he was developing metal carbonyl cluster chemistry. In Milan, Chini had access only to an IR spectrometer that aided the clean preparation and subsequent crystallisation of clusters, and, importantly, an X-ray diffractometer for their structural characterisation. 

As the field of metal carbonyl cluster chemistry was expanding rapidly many other new classes of clusters joined the fold, in particular, gold phosphine clusters, metal-alkoxide, -thiolate, and -halide clusters of the early transition elements. The theories of bonding in metal clusters rapidly advanced aided by both computational procedures and conceptual ideas. Without a doubt the most significant in the latter... 

The characterization of structure and dynamics in metal carbonyl cluster chemistry has understandably been based around single-crystal X-ray diffraction and NMR spectroscopic studies, respectively. As has been shown in the earlier part of this chapter, these sources of data can be used in conjunction to provide a coherent picture of the possible molecular configurations of a given species and the processes by which they interconvert, at least in favorable cases. In general however, it is not possible to determine the geometric structures of these species in solution, nor to obtain direct experimental evidence to confirm that the same structure(s) obtain in solution as in the solid state. Fortunately the rebirth and exploitation of X-ray absorption spectroscopy (XAS) and in particular the application of synchrotron X-ray sources and improved methods of data analysis to EXAFS (Extended X-ray Absorption Eine Structure) spectroscopy has provided exactly this sort of experimental evidence. In this section we provide selective coverage of such work as relates to the structure and dynamics of metal carbonyl clusters. 

The applications of EXAFS spectroscopy to metal carbonyl cluster chemistry can be subdivided into a number of broad and overlapping areas ... 

Bond Length-Bond Enthalpy Patterns in Metal Carbonyl Cluster Chemistry... 

The adherence to close-packed structural arrangements lends support to the idea that these compounds can be used as models for metal surface chemistry—with respect to chemisorbed species and their mobility and reactions of substrates on these surfaces. It also indicates a marked deviation from the behavior of boranes and their derivatives. Structures based upon some polyhedra favored by boron, such as the pentagonal bipyramid, triangulated dodecahedron, and especially the icosahedron, are absent so far in metal-carbonyl cluster chemistry. In this connection, it has been mentioned that [M(CO)3],g compounds should be the closest analogs to On skeletal electron counting... 

The appearance of tellurium in mixed-metal carbonyl cluster chemistry has been a feature of recent years and the reactions of [Te Feg(CO)24] with dihaloalkanes has now been reported. ... 

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