The thermal reaction of 1-phenyl-4,5-dihydroborepin (I) with Mn2(CO)10 produces the triple-decked complex (OC)3Mn(μ-L)Mn(CO)3 (III) where L is 2-ethyl-1-phenylborole. The analogous system I/[(C5H5)Fe(CO)2]2 inter alia yields the triple-decked sandwich complex (C5H5)Fe(μ-L)Fe(C5H5) (VI) and the borabenzene derivative (C5H5)Fe(2-CH3C5H4BC6H5) (VIII). The structures of the 30-electron compounds III and VI have been determined by X-ray analyses.