Reaction of the Transition Metal Hydrides [Cp*MH2]2 (Cp* = η5-C5Me5; M = Fe, Ru) with BH3·THF to Yield Metallaboranes. Improved Kinetic Control Leads to Novel Ferraboranes

Abstract

The reactions of [Cp*MH2]2, Cp* = η5-C5Me5; M = Fe, Ru, with BH3·THF have been explored. As with [Cp*RuCl2]2, [Cp*RuH2]2 readily reacts with borane to generate nido-1,2-(Cp*RuH)2B3H7. In contrast to the chloride, intermediates are detectible in the hydride reaction and product selectivity is higher. Benefits of the apparently lower reaction barrier appear in the reaction of [Cp*FeH2]2 with BH3·THF. The formation and isolation of the novel hydrogen-rich ferraborane arachno-1-Cp*FeB4H11 from the iron hydride contrasts with the production of pentamethylferrocene from a pentamethylcyclopentadienyl iron halide. This metastable ferraborane has been characterized spectroscopically as well as by reaction with Co2(CO)8 to give a good yield of the more stable derivative nido-1-(Cp*Fe)-2-{Co(CO)3}B4H8 by metal fragment addition. The latter compound has been spectroscopically characterized in solution as well as in the solid state by a single-crystal X-ray diffraction study as an example of a mixed metal dimetallahexaborane.