Synthesis, structures and chemistry of the metallaboranes of group 4-9 with M 2 B 5 core having a cross cluster M-M bond

Abstract

In an attempt to expand the library of M 2 B 5 bicapped trigonal-bipyramidal clusters with different transition metals, we explored the chemistry of [Cp*WCl4] with metal carbonyls that enabled us to isolate a series of mixed-metal tungstaboranes with an M 2 [B 4 M'] [M =W; M' = Cr(CO) 4 , Mo(CO) 4 , W(CO) 4 ] core. The reaction of in situ generated intermediate, obtained from the low temperature reaction of [Cp*WCl 4 ] with an excess of [LiBH 4 ·thf], followed by thermolysis with [M(CO) 5 ·thf] (M = Cr, Mo and W) led to the isolation of the tungstaboranes [(Cp*W) 2 B 4 H 8 M(CO) 4 ], 1-3 (1: M = Cr; 2: M = Mo; 3: M = W). In an attempt to replace one of the BH-vertices in M 2 B 5 with other group metal carbonyls, we performed the reaction with [Fe 2 (CO) 9 ] that led to the isolation of [(Cp*W) 2 B 4 H 8 Fe(CO) 3 ], 4, where Fe(CO) 3 replaces a [BH] core unit instead of the [BH] capped vertex. Further, the reaction of [Cp*MoCl 4 ] and [Cr(CO) 5 ·thf] yielded the mixed-metal molybdaborane cluster [(Cp*Mo) 2 B 4 H 8 Cr(CO) 4 ], 5, thereby completing the series with the missing chromium analogue. With 56 cluster valence electrons (cve), all the compounds obey the cluster electron counting rules. Compounds 1-5 are analogues to the parent [(Cp*M) 2 B 5 H 9 ] (M= Mo and W) that seem to have generated by the replacement of one [BH] vertex from [(Cp*W) 2 B 5 H 9 ] or [(Cp*Mo) 2 B 5 H 9 ] (in case of 5). All of the compounds have been characterized by various spectroscopic analyses and single crystal X-ray diffraction studies.