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

Abstract

Heating a benzene solution of [η⁵-(Me₂NCH₂CH₂)C₂B₉H₁₀] Ta(NMe₂)₃ (1) in the presence of pyridine gave an unprecedented complex [η¹:η⁶-(Me₂NCH₂CH₂)C₂B₉H₁₀]Ta (NMe₂)(NC₅H₅) (2). On the other hand, reaction of (η⁵-C₂B₉H₁₁)TaMe₃ with adamantly isonitrile (AdNC) in dimethoxyethane (DME) at room temperature afforded another unexpected complex (η⁶-C₂B₉H₁₁)Ta[η³-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-η⁵-C₂B₉H₁₀R²⁻ ligand in tantallacarboranes takes up two electrons released by reductive elimination to form an arachno-η⁶-C₂B₉H₁₀R⁴⁻ fragment via the cage C–C bond cleavage.