Metallacarboranes compounds

SPh boron detenuination in form of complex with Azomethine-H is the reliable microanalytical method for boronorganic compounds, carboranes, metallacarboranes, etc. Before boron determination the samples should be melted with KOH at 900°C. 

Many novel cluster compounds have now been prepared in this way, including mixed metal clusters. Further routes involve the oxidative fusion of dicarbon metallacarborane anions to give dimetal tetracarbon clusters such as (103) and (104) O (jjg insertion of isonitriles into inetallaborane clusters to give monocarbon meiallacarboranes such as (105) and the reaction of small ii/t/o-carboranes with alane adducts such as Et3NAlH3 to give the commo species (106) ... 

Serendipitous insertion of CsHs- into the metallaborane Cp 2Cr2B4Fl8 gave the triple-decker sandwich 122 in low yield.140 This compound can be described as an eight-vertex Cr2C2B4 c/ara-metallacarborane cluster, and its preparation is notable as one of the few examples of metallacarborane synthesis from a metallaborane precursor (rather than by the usual metal insertion into a carborane), an approach first demonstrated by Grimes and co-workers in the 1970s.34,141,141a... 

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... 

The synthesis of new materials having novel electronic or optical properties is of great current interest. One approach to the synthesis of such materials is to systematically link small sandwich units together to form an extended multi-decker sandwich system. Immediately following the discovery of the triple-decker structure of the Cp3Ni2+ complex in early 1970s,181 Grimes and co-workers synthesized the first neutral triple-decker metallacarborane sandwich compound. Most of the subsequent research in this field, some of which has been described... 

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. 

More remarkably, the reaction forming the Mn-Pt species is unique among the compounds 144-149 in that three other metallacarborane products were also isolated from this system alone. These are two 12-vertex species, [l-Ph-2,2,2-(CO)3-7-X-8,8-dppe-/iyperc/oAo-8,2,l-PtMnCBgHg] pC = H (150), OEt (151)], and the complex [3,6,7- Mn(CO)3 -3,7-(p-H)2-l-Ph-6,6-dppe-c/oio-6,l-PtCBgH6] (152) formed by cluster contraction. Subsequent studies confirmed that the ethoxylated compound 151 is formed by reaction of 146 with adventitious EtOH present in the precursor 129. Indeed, treatment of 146 with other alcohols ROH afforded similar species [l-Ph-2,2,2-(CO)3-7-OR-8,8-dppe-/z3y crc/oA o-8,2,l-PtMnCBgHg] [R = Me (153), (CH2)20H (154), (CH2)40H (155)] with, surprisingly, only mono-cage products observed when diols were used as substrates. All of the alkoxy-substituted compounds 151 and 153-155 are relatively stable and do not react further, whereas... 

Transition-Metal Metallacarboranes. The first demonstration of the insertion of a transition metal into an open face of a borane cage was with the iron sandwich compound [common-Fe(C2B9H11)12]2 [12541 -50-3] (188). This product is readily air-oxidized to [rt /W 0 -(C2B9Hn)2Fe]- ... 

Many structures are possible for the smaller metallacarboranes and various synthetic strategies are available. Especially noteworthy is the occurrence of triple- and tetradecker sandwich compounds (214). The polyhedral expansion synthetic strategy can also be used with small carboranes (212). For instance, the small metallacarborane f/ojo-l,l,l-(CO)3-l,2,3-FeC2B4H6 [3276140-3] (212) is obtained from C2B4Hg upon treatment with Fe(CO)5. 

---