ETC and thermal ligand substitution in PhCCo3(CO)9 with 2,3-bis(diphenylphosphino)-N-phenylmaleimide(bppm).: X-ray diffraction structure of Co3(CO)6[μ2,η2,η1-C(Ph)(C=C(PPh2)C(O)NPhC)over-bar(O)](μ2-PPh2)

The reactivity of the bidentate ligand 2,3-bis(diphenylphosphino)-N-phenylmaleimide (bppm) with the tetrahedrane cluster PhCCo3(CO)(9) under thermolysis and ETC conditions has been studied and found to ultimately give Co-3(CO)(6)[mu(2),eta(2),eta(1)-C(Ph)C=C(PPh2)C(O)NPhC(O)](mu(2)-PPh2) as the final product. The intermediate cluster compound PhCCo3(CO)(7)(bppm), which was observed by IR and P-31 NMR spectroscopies, readily and rapidly transforms into the product cluster under the reactions conditions. The solid-state structure of Co-3(CO)(6)[mu(2),eta(2),eta(1)-C(Ph)C=C(PPh2)C(O)NPhC(O)](mu(2)-PPh2) was unequivocally determined by X-ray crystallography. Co-3(CO)(6)[mu(2),eta(2),eta(1)-C(Ph)C=C(PPh2)C(O)NPhC(O)](mu(2)-PPh2) crystallizes in the monoclinic space group P2(1)/n; a=11.825(5) Angstrom, b=31.20(1) Angstrom, c=11.831(5)Angstrom, beta=108.720(7)degrees, V=4134(7)Angstrom(3), Z=4, d(calc)=1.567 Mg/m(3); R=0.0350, R-w=0.0817 for 4747 observed reflections with I>2sigma(I). The X-ray structure confirms the coupling of the benzylidyne ligand with the bppm ligand in Co-3(CO)(6)[mu(2),eta(2),eta(1)-C(Ph)C=C(PPh2)C(O)NPhC(O)](mu(2)-PPh2). The course of the thermolysis reaction is identical to those reactions carried out with the related diphosphine ligands bma and bpcd. The utility of electron-transfer catalysis (ETC) in the preparation of PhCCo3(CO)(7)(bppm) is discussed relative to the reduction potential of the bppm ligand and the tricobalt cluster PhCCo3(CO)(9).