The M-(η²-BMn) complex [(η⁵-C₅H₅)(OC)₂Mn{μ-B(Cl)(tBu)Au(PPh₃)}] (2) can be functionalized via halide substitution reactions to afford isostructural complexes [(η⁵-C₅H₅)(OC)₂Mn{μ-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 [{(η⁵-C₅H₅)(OC)₂Mn}₂{μ²-B(tBu)}₂M][BAr^x₄] (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.