The Lewis acidity of [(eta5-C5R5)Fe(CO)2(BX2)] (1: R = H, X = Cl) and the robust nature of the constituent Fe--B bond have been demonstrated by reaction with 4-methylpyridine to yield the corresponding Lewis acid-base adduct. These properties have subsequently been utilised in the construction of heterodinuclear bridging borylene, bridging boryl and mu(2)-boride complexes from analogues 3 (R = Me, X = Br) and 5 (R = Me, X = Cl). All the bimetallic species so formed exhibited unprecedented coordination modes for boron.