Metallacarborane chemistry

Structurally, metallacarborane chemistry is the most fully documented area of carborane chemistry. There is not enough space here for a comprehensive survey, but Tables 3.2 and 3.3 and Figure 3.22 show the formulae and skeletal structures of some representative examples. More comprehensive compilations of structural data are to be found in References 1-3 and 199. Metals have been incorporated into the whole range of known carborane deltahedra, and indeed their presence has allowed supraicosahedral systems to be made that are without precedent among metal-free carboranes or boranes, as outlined below. 

We showed above that metal atoms have been incorporated in the whole range of closo borane/carborane deltahedra, and also in many nido and some arachno systems. Indeed, metallacarborane chemistry has become far too large a branch of organometalhc chemistry to discuss in detail here. Excellent surveys of the area are available in specialist texts. There is, however, one particular category of metallacarborane worthy of brief consideration to illustrate how the presence of boron atoms in otherwise familiar organometalhc sandwich compounds can enrich their chemistry. The compounds in question are metal... 

A breakthrough in 2003 into supraicosahedral carborane chemistry (as distinct from supraicosahedral metallacarborane chemistry) came from the use of external tethers to hold together the two cage carbon atoms during syntheses. - - Hie groups of A. J. Welch - - - and Z. have... 

B3.5 Cluster-forming and cage fusion in metallacarborane chemistry... 

Despite the recent proliferation of transition metal carbollide (metallacarboranes) chemistry merely three such compounds comprising a poly(pyrazolyl)borate ligand are known within group 9, viz. c/oyo-3-(K -Tp)-3,l,2-RhC2B9Hii (716), ... 

Although metallaborane and metallacarborane chemistry is extensive, little information is available on metal nuclear shielding in these compounds, and is essentially limited to some nice work on Be, some isolated Pt chemical shifts, " a ( Y) datum for [(thf)2YBjHi2], and a ( Zr) datum for [ZrB4Hie]. Very recent work has included 295 (193-195) 453 (188) H9sn.(i 5)... 

Chemistry and structure of semi-sandwich platinum metal metallacarboranes derived from nido-Ci39Hi2 97JOM(536/537)51. 

Because this chapter is restricted to results published since 1993, when the chemistry of the d- and /-block metallacarboranes has experienced an upsurge, general research trends will be emphasized and no attempt will be made to cover the literature exhaustively. A sense of the scope of the research in this field can be obtained from perusing Table 1. 

Our discussion will be restricted to metallacarboranes in which the r/-block metal is incorporated into the polyhedral framework of the carborane. No attempt will be made to cover those compounds where the transition metal atom is in a bridging group linking several carborane polyhedra together or is involved solely as a member of a substituent group. Since much of the insight into the chemistry of the metallacarboranes is obtained from structural and bonding... 

It is apparent from the above discussions that recent synthetic, structural, bonding, and reactivity studies have established transition metal containing metallacarborane complexes as an important area of study in organometallic chemistry. 

The material reviewed in this Chapter hitherto has focused on metallacarboranes in which the metal atom is a vertex in an icosahedral cage framework. Until recently, monocarbollide metal compounds with core structures other than 12 vertexes were very rare since suitable carborane precursors were not readily available." However, Brellochs recent development of the reaction of decaborane with aldehydes to give 10-vertex monocarboranes permits a considerable expansion in this area of boron cluster chemistry. As a consequence, several intermediate-sized monocarboranes are now easily accessible and we have recently begun to exploit the opportunities that these present. In particular, we have focused thus far on complexes derived from the C-phenyl-substituted species [6-Ph- zJo-6-CBgHii] It is clear from these initial studies that a wealth of new chemistry remains to be discovered in this area, not only from among the metal derivatives of PhCBg car-boranes such as those discussed in this section, but also in the metal complexes of other newly available carboranes. 

Metallacarboranes, 801-802 Metallocenes, 669-686 Metalloporphyrins, and respiration, 891-895 MetaJJoihioreins, 932 Metals, 27-28 descriptive chemistry of,... 

Linear polarization, and NLO properties, 12, 102 Linear polymers, siloxanes, synthesis, 3, 660 Linkage isomerism, for photochromic behavior, 1, 245 Linked cages, metallacarboranes, 3, 245 Linkers, traceless, chromium carbonyls as, 5, 251 Lipids, in bioorganometallic chemistry, 1, 904 Liquefied noble gases, in low-temperature infrared studies, 1, 264... 

A large number of metallacarboranes and polyhedral metallaboranes of s-, p-, d-, and f-block elements are known. In these compounds, the carboranes and boranes act as polyhapto ligands. The domain of metallaboranes and metallacarboranes has grown enormously and engenders a rich structural chemistry. Some new advances in the chemistry of metallacarboranes of f-block elements are described below. 

In contrast to the rather rich and varied chemistry reported for aluminacarboranes, only limited information is available on the heavier group 13 metallacarboranes. The preparation of closo-l-C2H5-GaC2B9Hn by Hawthorne and co-workers (18,19) was described earlier [see Eq. (2)]. Grimes et al. (30) have reported the synthesis of c/oso-l-(CH3)-l,2,3-GaC2B4H6 and l-(CH3)-l,2,3-InC2B4H6 by the gas-phase reaction of Ga(CH3)3 and In(CH3)3 with C2B4H8. Reaction conditions and yields are... 

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