Electrophile-Induced Nucleophilic Substitution of the nido-Dicarbaundecaborate Anion nido-7,8-C2B9H12- by Conjugated Heterodienes

Substitution of the dicarbaundecaborate anion nido-7,8-C2B9H12- (1) by precise hydride abstraction followed by nucleophilic attack usually leads to symmetric products 10-R-nido-7,8-C2B9H11. However, thioacetamide (MeC(S)NH2) as nucleophile and acetone/AlCl3 as hydride abstractor gave asymmetric 9-[MeC(NHiPr)S]-nido-7,8-C2B9H11 (2), whereas N,N-dimethylthioacetamide (MeC(S) NMe2) gave the expected symmetric 10-[MeC(NMe2)S]-nido-7,8-C2B9H11 (4). For the formation of 2, acetone and thioacetamide are assumed to give the intermediate MeC(S) N(CMe2) (3), which then attacks 1 with formation of 2. Similarly, reaction of acetyliminium chloride [MeC(O)NH(CPh2)]Cl (5) with 1 in THF gave a mixture of 9- and 10-substituted [MeC(NHCHPh2)O]-nido-7,8-C2B9H11 (6 and 7, respectively). These reactions are the first examples in which compounds (here heterodienes) that unite the functionalities of both hydride acceptor and nucleophilic site react with 1 in a bimolecular fashion. Furthermore, the analogous reaction of 1 and 5 (in an equilibrium mixture with acetyl chloride and benzophenone imine) in MeCN afforded 10-[MeC(NCPh2)NH]-nido-7,8-C2B9H11 (8) and MeC(O) NHCHPh2 (9).