New routes to a series of σ-borane/borate complexes of molybdenum and ruthenium

Abstract

A series of agostic σ-borane/borate complexes have been synthesized and structurally characterized from simple borane adducts. A room-temperature reaction of [Cp*Mo(CO)₃Me], 1 with Li[BH₃(EPh)] (Cp*=pentamethylcyclopentadienyl, E=S, Se, Te) yielded hydroborate complexes [Cp*Mo(CO)₂(μ-H)BH₂EPh] in good yields. With 2-mercapto-benzothiazole, an N,S-carbene-anchored σ-borate complex [Cp*Mo(CO)₂BH₃(1-benzothiazol-2-ylidene)] (5) was isolated. Further, a transmetalation of the B-agostic ruthenium complex [Cp*Ru(μ-H)BHL₂] (6, L=C₇H₄NS₂) with [Mn₂(CO)₁₀] affords a new B-agostic complex, [Mn(CO)₃ (μ-H)BHL₂] (7) with the same structural motif in which the central metal is replaced by an isolobal and isoelectronic [Mn(CO)₃] unit. Natural-bond-orbital analyses of 5–7 indicate significant delocalization of the electron density from the filled σ_B—H orbital to the vacant metal orbital.