CO substitution in PhCCo3(CO)(9) by 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd). Ligand fluxionality, kinetics, and X-ray structures of PhCCo3(CO)(7)(bpcd) and Co-3(CO)(6)[mu(2)-eta(2),eta(1)-C(Ph)C=C(PPh2)C(O)CH2C(O)]-(mu(2)-PPh2)

摘要

The reaction between the tetrahedrane cluster PhCCo3(CO)(9) (1) and the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) leads to the replacement of two CO groups and formation of PhCCo3(CO)(7)(bpcd) (2). Cluster 2 is thermally unstable and readily transforms into the new cluster Co-3(CO)(6)[mu (2)-eta (2) : eta (1)-C(Ph)C(PPh2)C(O)CH2(O)](mu (2)-PPh2) (3). Both clusters 2 and 3 have been isolated and fully characterized in solution by IR and NMR (P-31 and C-13) spectroscopy. VT P-31 NMR data indicate that the bpcd ligand in PhCCo3(CO)(7)(bpcd) is fluxional in solution, with two chelating and one bridging isomer being observed at 176 K in THR The kinetics for the conversion of 2 to 3 followed first-order kinetics in 1,2-dichloroethane (DCE). These data, coupled with the reaction rates being retarded in the presence of added CO, and the activation parameters (DeltaH(double dagger) = 27.1 +/- 0.3 kcal/mol and DeltaS(double dagger) = 9 +/- 1 eu) support a scheme involving a dissociative CO loss as the rate-limiting step. Clusters 2 and 3 have been structurally characterized by X-ray diffraction analyses. PhCCo3(CO)(7)(bpcd) crystallizes in the monoclinic space group P21: a = 10.731(2) Angstrom, b = 21.743(3) Angstrom, c = 17.143(1) Angstrom, beta = 97.522(8)degrees, V = 3965.4(8) Angstrom (3), Z = 4, d(calc) = 1.552 g (.) cm(-3); R = 0.0598, R-w = 0.0671 for 1428 observed reflections with l > 3 sigma (l). Co-3(CO)(6)[mu (2)-eta (2):eta (1)-C(Ph)C=(PPh2)C(O)CH2C(O)](mu (2)-PPh2) crystallizes in the triclinic space group P (1) over bar a = 11.572(1) Angstrom, b = 11.702(1) Angstrom, c = 15.227(1) Angstrom, alpha = 106.716(6)degrees, beta = 90.419(6)degrees, gamma = 103.676(7)degrees, V = 1912.4(3) Angstrom (3), Z = 2, d(calc) = 1.560 g (.) cm(-3); R = 0.0545, R-w = 0.0632 for 3149 observed reflections with l > 3 sigma (l). The chemistry exhibited by clusters 2 and 3 is compared with related clusters containing the diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma). [References: 64]