Synthesis, Structure and Bonding of the Tungstaboranes [Cp*W(CO)2B3H8] and [(Cp*W)3(CO)2B4H7]

The structure and bonding of two novel tungstaboranes which were synthesized using diverse synthetic methods are described. (i) The room-temperature photolysis of [Cp*W(CO)(3)Me] with [BH3 & BULL;SMe2] led to the isolation of the hydrogen-rich tungstaborane [Cp*W(CO)(2)B3H8] (1). Its geometry consists of an arachno butterfly core similar to tetraborane(10) and obeys the Wade-Mingos electron counting rules (n vertices, n + 3 skeletal electron pairs (seps)). (ii) Further, the tungstaborane [(Cp*W)(3)(& mu;-H)(2)(& mu;(3)-H)(& mu;-CO)(2)B4H4] (4) was isolated by thermolysis reaction of a tungsten intermediate, obtained by low temperature reaction of [Cp*WCl4] and [LiBH4 & BULL;THF] with [Cr(CO)(5)& BULL;THF]. Compound 4 which seems to have formed by replacement of a BH unit in [(Cp*W)(2)B5H9] by the isoelectronic fragment {Cp*W(CO)(2)}, adopts an oblato-nido hexagonal-bipyramidal core (n vertices, n-1 seps). Both compounds were characterized using multinuclear NMR, IR spectroscopy, mass spectrometry as well as single crystal X-ray diffraction analysis. In addition, density functional theory (DFT) calculations were performed in order to elucidate their bonding and electronic structures.