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 [CpMo(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 σB-H orbital to the vacant metal orbital. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.