CO replacement in the tetrahedrane cluster MeC(O)CCo3(CO)9 by the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-l,3-dione (bpcd): Diphosphine ligand isomerization and X-ray structure of the bridged cluster MeC(O)CCo3(CO)7(bpcd)

The tricobalt cluster MeC(O)CCo₃(CO)₉ reacts with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-l,3-dione (bpcd) in the presence of added Me₃NO to furnish the disubstituted cluster MeC(O)CCo₃(CO)₇(bpcd) in good yield. MeC(O)CCo₃(CO)₇(bpcd) has been characterized in solution by IR and NMR (¹H and ³¹P) spectroscopies, and the solid-state structure determined by X-ray crystallography. MeC(O)CCo₃(CO)₇(bpcd) crystallizes in the monoclinic space group P2₁/c, a=14.8421(8), b=16.6162(9), c=14.9363(8) ?, β=99.705(1)°, V=3630.9(3) ?³, Z=4, D _cacl=1.632 Mg/m³; R=0.0288, R _w=0.0683 for 8618 observed reflections with I > 2σ(I). The bridging of adjacent cobalt atoms by the bpcd ligand in MeC(O)CCo₃(CO)₇(bpcd) is crystallographically established, and the facile isomerization of the bridging bpcd to the chelating isomer at low temperature is confirmed by VT ³¹P NMR measurements.