Reaction of [η1:η5‑(R2NCH2CH2)C2B9H10]TaMe3 with Isonitriles: Effects of Nitrogen Substituents on Product Formation

Tantallacarborane trimethyl complexes show diverse reactivity patterns toward isonitriles. Reaction of [η1:η5-(Me2NCH2CH2)­C2B9H10]­TaMe3 (1) with 1-adamantyl isonitrile (AdNC) led to the clean formation of an imido complex, [σ:η5-(MeNCH2CH2)­C2B9H10]­Ta­(NAd)­(THF) (2) with elimination of methane and 2-methylpropene, whereas treatment of [η1:η5-{(CH2)5NCH2CH2}­C2B9H10]­TaMe3 (3) with AdNC under the same reaction conditions gave the cage B–H activated product {σ:η1:η5-[(CH2)5NCHCH2]­(CHMe2)­C2B9H9}­Ta­(NAd)­(THF) (4). An equimolar reaction of 1 with R1NC (R1 = Cy, Ad), followed by 1 equiv of R2NC (R2 = Xyl, Cy), afforded the imido amido complexes [η1:η5-(Me2NCH2CH2)­C2B9H10]­Ta­(NR1)­[N­(CMeCMe2)­R2] (R1 = Ad, R2 = Cy (5); R1 = Cy, R2 = Xyl (6)). If 2 equiv of 2,6-dimethylphenyl isonitrile (XylNC) was used in the above reaction, the cage B–H alkylation products [η1:η5-(Me2NCH2CH2)­C2B9H9]­Ta­(NR1)­[N­(Xyl)­{CHC­(Me2)­C­(Me)NXyl}] (R1 = Cy (7), Ad (8)) were isolated. On the other hand, η2-iminoacyl imido complexes [η1:η5-(Me2NCH2CH2)­(CHMe2)­C2B9H9]­Ta­(NXyl)­(η2-C,N-MeCNR) (R = iPr (9), Cy (10)) were obtained from an equimolar reaction of 1 with XylNC, followed by 1 equiv of alkyl isonitriles. A double methyl migratory insertion tantallaaziridine species is proposed as a crucial intermediate for all aforementioned reactions, and follow-up steps are dependent upon N-substituents and the type and stoichiometry of isonitriles. All new complexes were characterized by spectroscopic methods and single-crystal X-ray analyses.