Stable exo-nido-Metallacarboranes (M = OsIV) that Incorporate meta-Carborane-Based Dicarbollide Ligands

• Published in: Journal of the American Chemical Society 2007-03, Vol.129 (12), p.3745-3753
• Main Authors: Balagurova, Elena V, Cheredilin, Dmitri N, Kolomnikova, Galina D, Tok, Oleg L, Dolgushin, Fedor M, Yanovsky, Alexander I, Chizhevsky, Igor T
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja067838s

Reactions of the [K]+ salts of the [nido-7,9-C2B9H12]- anion (2) and its C-phenylated derivative [7-Ph-nido-7,9-C2B9H11]- (4) with [OsCl2(PPh3)3] (3) proceed in benzene at ambient temperature with the formation of 16-electron chlorohydrido-Os(IV) exo-nido complexes, [exo-nido-10,11-{(Ph3P)2OsHCl}-10,11-(μ-H)2-7-R-7,9-C2B9H8] (5:  R = H; 6:  R = Ph), along with the small amounts of the charge-compensated nido-carboranes [nido-7,9-C2B9H11PPh3] (7) and [7-Ph-nido-7,9-C2B9H10PPh3] (8) as byproducts. However, when carried out under mild heating in ethanol, the reaction of 2 with 3 selectively afforded a 16-electron dihydrido-Os(IV) exo-nido complex [exo-nido-10,11-{(Ph3P)2OsH2}-10,11-(μ-H)2-7,9-C2B9H9] (9). Structures of both complexes 5 and 9 have been confirmed by single-crystal X-ray diffraction studies, which revealed that nido-carboranes in these species function as a bidentate dicarbollide ligands [7-R-nido-7,9-C2B9H10]2- linked to the Os(IV) center via two B−H···Os bonds involving adjacent B−H vertices in the upper CBCBB belt of the carborane cage. Thus, compounds 5 and 9 represent the first structurally characterized exo-nido-metallacarboranes based on meta-dicarbollide-type ligands. Variable-temperature 1H and 31P{1H} NMR experiments indicate that complex 9 is fluxional in solution and shows an unusual exchange between terminal Os−(H)2 and bridging {B−H}2···Os hydrogen atoms. Upon heating in d 8-THF at 65 °C, complex 9 converts irreversibly to its closo isomer [2,2-(PPh3)2-2,2-H2-closo-2,1,7-OsC2B9H11] (13), which could thus be obtained as a pure crystalline solid. The structure of 13 has been established on the basis of analytical and multinuclear NMR data and a single-crystal X-ray diffraction study.