Ruthenium complexes with the stanna-closo-dodecaborate ligand: Coexistence of η¹ (Sn) and η³(B-H) coordination

Four stanna-closo-dodecaborate complexes of ruthenium have been prepared and characterized by multinuclear NMR studies in solution and in the solid state. The solid-state structures of the dimeric zwitterions [{Ru(dppb)(SnB ₁₁H₁₁)}₂] (2) (dppb = bis(diphenylphosphino) butane), [{Ru-(PPh₃)₂(SnB₁₁H ₁₁)}₂] (3), and the dianionic ruthenium complex [Bu ₃MeN]₂[Ru(dppb){2,7,8-(μ-H)₃-exo-SnB ₁₁H₁₁} SnB₁₁H₁₁)] (4) were determined by X-ray crystal structure analysis; they establish an unprecedented structural motif in the chemistry of heteroboranes and transition-metal fragments with the stanna-closo-dodecaborate moiety as a two-faced ligand that exhibits η¹(Sn) as well as η³(B-H) coordination. The η³-coordinated stannaborate in 4 and in the isostructural compound [Bu₃MeN]₂[Ru(PPh₃)2{2,7,8-(μ-H) ₃-exo-SnB₁₁H₁₁}(SnB₁₁H ₁₁)] (5) shows fluxional behavior, which was studied in detail by using ³¹P{¹H} EXSY and DNMR experiments. The activation parameters for the dynamic process of 5 are given.