Synthesis, Structure, Bonding, and Reactivity of Metal Complexes Comprising Diborane(4) and Diborene(2): [{Cp*Mo(CO) } {μ-η :η -B H }] and [{Cp*M(CO) } B H M(CO) ], M=Mo,W.

The reaction of [(CpMo) (μ-Cl) B H ] (1) with CO at room temperature led to the formation of the highly fluxional species [{CpMo(CO) } {μ-η :η -B H }] (2). Compound 2, to the best of our knowledge, is the first example of a bimetallic diborane(4) conforming to a singly bridged C structure. Theoretical studies show that 2 mimics the Cotton dimolybdenum-alkyne complex [{CpMo(CO) } C H ]. In an attempt to replace two hydrogen atoms of diborane(4) in 2 with a 2e [W(CO) ] fragment, [{CpMo(CO) } B H W(CO) ] (3) was isolated upon treatment with [W(CO) ⋅thf]. Compound 3 shows the intriguing presence of [B H ] with a short B-B length of 1.624(4) Å. We isolated the tungsten analogues of 3, [{CpW(CO) } B H W(CO) ] (4) and [{Cp*W(CO) } B H Mo(CO) ] (5), which provided direct proof of the existence of the tungsten analogue of 2.