CHARACTERIZATION AND THERMOLYSIS REACTIONS OF CO2-BRIDGED IRON-TIN AND RHENIUM-TIN COMPLEXES - STRUCTURE-REACTIVITY CORRELATIONS

The synthesis, characterization, and thermolysis reactions of the CO2-bridged iron-tin complexes CpFe(CO)(PPh(3))(CO2)SnR(3) (1a-c; R = Ph, Me, n-Bu), Cp*Fe(CO)(2)(CO2)SnR(3) (2a-c; R = Ph, Me, n-Bu), Cp*Fe(CO)(PPh(3))(CO2)SnPh(3) (4a), and CpFe(CO)(2)(CO2)SnPh(3) (5a) and the rhenium-tin complexes Cp*Re(CO)(NO)(CO2)SnR(3) (3a,b; R = Ph, Me) are described. Four of the compounds have been structurally characterized. Crystal data for 1b: a = 10.574(3) Angstrom, b = 13.329(8) Angstrom, c = 23.346(9) Angstrom, beta = 94.71(4)degrees, with Z = 4 in space group P2(1)/c. Crystal data for 1c: a = 13.695(10) Angstrom, b = 14.251(9) Angstrom, c = 10.475(5) Angstrom, alpha = 90.99(5)degrees, beta = 90.04(5)degrees, gamma = 83.05(5); with Z = 2 in space group P $$($) over bar 1. Crystal data for 2a: a = 12.318(3) Angstrom, b = 11.907(4) Angstrom, c = 19.399(4) Angstrom, beta = 100.81(2)degrees, with Z = 4 in space group P2(1)/c. Crystal data for 3b: a = 11.072(2) Angstrom, b = 15.403(7) Angstrom, c = 7.108(2) Angstrom, alpha = 92.91(3)degrees, beta = 106.91(2)degrees, gamma = 89.58(3)degrees, with Z = 2 in space group P $$($) over bar 1. All compounds have been characterized by solid-state IR spectral methods which allow a determination of the mu(2)-eta(2) or mu(2)-eta(3) bonding mode in each compound when compared with structural data on representative compounds of each type. Factors which control the ease of thermolysis and the mode of decomposition are the bonding type, the presence of electron-donating or electron-withdrawing groups on the tin atom as well as those on iron or rhenium, metal-carbon bond strength, the orientation of the bridging CO2 Ligand between the two metal centers, and, most importantly, the stability of the corresponding metal (iron or rhenium) anion. Simple decarboxylation takes place with 2a-c, 3b, and 5a; disproportionation takes place with 1a-c and 4a. Extensive degradation occurs with 3a. Reaction mechanisms are proposed which are consistent with structural and electronic differences that lead to separate thermolysis paths.