Conversion of (η5-C2B9H10R)TaX3 (X = Me, NMe2) to (η6-C2B9H10R)TaX′ (X′ = NMe2, azaallyl) in the absence of a reducing agent: synthesis and structure of tantallacarboranes incorporating an arachno-η6-C2B94- ligand

Heating a benzene solution of [eta(5)-(Me2NCH2CH2)C2B9H10] Ta(NMe2)(3) (1) in the presence of pyridine gave an unprecedented complex [eta(1):eta(6)-(Me2NCH2CH2)C2B9H10]Ta (NMe2)(NC5H5) (2). On the other hand, reaction of (eta(5)-C2B9H11)TaMe3 with adamantly isonitrile (AdNC) in dimethoxyethane (DME) at room temperature afforded another unexpected complex (eta(6)-C2B9H11)Ta[eta(3)-C,C,N-CH2C(CH3)NAd](DME) (4). These results show that pyridine and DME are essential for the formation of 2 and 4, respectively. It is suggested that the nido-eta(5)-C2B9H10R2- ligand in tantallacarboranes takes up two electrons released by reductive elimination to form an arachno-eta(6)-C2B9H10R4- fragment via the cage C-C bond cleavage.