The heterodinuclear complexes [(CO) 3 M(µ-H)(µ-C 7 H 7 )Co(η-C 5 Me. The X-ray crystal structures of 7 and 8 have been determined. The boat-shaped bridging cycloheptatrienyl ligands adopt the η 4 (M):η 3 (Co) coordination in the crystalline state. The rather long M-Co vectors were found to be bridged by hydrido ligands, making up 3c-2e MHCo bonds. In solution, hindered rotation of the C 7 H 7 ring was observed, which, in the case of 7, could be frozen on the NMR time scale at 200 K. ResultsSyntheses. When equimolar petroleum ether solutions of 2 and the Jonas reagent 5a were allowed to