Synthesis and crystal structures of the gold–carbaborane complexes [9-exo-{Au(PPh3)}-9-(µ-H)-10-endo-{Au(PPh3)}7,8-Me2-nido-7,8-C2B9H8] and [10-exo-{Au2(PPh3)2}-10-endo-{Au(PPh3)}-7,8-Me2-nido-7,8-C2B9H8]

Abstract

Treatment of the salt [NEt₄][10-endo-{Au(PPh₃)}-7,8-Me₂-nido-7,8-C₂B₉H₉] with [AuCl(PPh₃)] in CH₂Cl₂ afforded the digold complex [9-exo-{Au(PPh₃)}-9-(µ– H)-10-endo-{Au(PPh₃)}-7,8-Me₂-nido-7,8-C₂B₉H₈]. Deprotonation of the latter with NaH in tetrahydrofuran followed by addition of [AuCl(PPh₃)] gave the trigold compound [10-exo-{Au₂(PPh₃)₂}-10-endo-{Au(PPh₃)}-7.8-Me₂-nido-7,8-C₂B₉H₉]. The crystal structures of the new compounds have been determined by X-ray diffraction. In the digold species one Au(PPh₃) group is endo-bound to the nido-C₂B₉ cage, primarily through a connectivity [Au–B 2.28(1)Å] with the boron atom which is in the β-site with respect to the two carbons in the open [graphic omitted] face. There is a weaker attachment [Au–B 2.37(1)Å] to one of the α-boron atoms, while the other α-BH unit forms a three-centre two-electron B–H⇀Au bond with the second Au(PPh₃) group [Au–B 2.28(1), Au–µ– H 1.9(1)Å]. The latter gold fragment lies exo with respect to the open face of the carbaborane cage, with an Au–Au separation of 2.875(1)Å. The structure of the trigold complex is formally related to that of its digold precursor by replacement of the µ–H atom in the latter by an Au(PPh₃) moiety. This results in the molecule having an essentially isosceles triangle of gold atoms [Au–Au 2.691(1), 2.922(1), 3.010(1)Å], asymmetrically bridged by the β-boron [Au–B 2.192(9), 2.227(7), 2.307(8)Å] of the open [graphic omitted] face of the C₂B₉ cage. The NMR data (¹H, ¹³C –{¹H}, ³¹P –{¹H} and ¹¹B –{¹H}) of the compounds are reported and discussed.