The M-(eta(2)-BMn) complex [(eta(5)-C5H5)(OC)(2)Mn{mu-B(Cl)(tBu)Au(PPh3)}] (2) can be functionalized via halide substitution reactions to afford isostructural complexes [(eta(5)-C5H5)(OC)(2)Mn{mu-B(R)(tBu)Au(PPh3)}] (R = Ph, CCPh and NCS). It also reacts with coinage metal complexes [ MCl(PPh3)] (M = Au, Ag and Cu) in the presence of halide abstraction reagents to afford borylene-bridged heteromultinuclear complexes [{(eta(5)-C5H5)(OC)(2)Mn}(2){mu(2)-B(tBu)}(2)M][BAr4x] (M = Au, Ag and Cu; Ar-x = 3,5-C6H3Cl2, 3,5-C6H3(CF3)(2)). Experimental characterization as well as computational studies revealed that these complexes are best viewed as transition metal borylene complexes side-on coordinated to monovalent coinage metal cations, thus representing the first boron analogs of Stone's alkylidyne-bridged multinuclear complexes.