Chemistry and electrochemistry of pentafluorophenyl molybdenum(0) complexes

The compound PPN[Mo(CO)5(C6F 5)] can be oxidized either chemically or electrochemically by one electron. The electrochemical studies suggest that the oxidation of PPN[Mo(CO) 5(C6F5)] is followed by a chemical reaction responsible for the chemical irreversibility. Digital simulation of cyclic voltammetry experiments in the presence of pyridine support a mechanism in which Mo(CO) 5(C6F5) formed upon oxidation of PPN[Mo(CO) 5(C6F5)] is converted to Mo(CO)5(Py) through an SN2 transition state, Mo(CO)5(C6F 5)(Py), the rate constant for this reaction being 7 (+/-2) x 102 M-1s-1. When tropylium chemically oxidizes [Mo(CO)5(C6F5)] -, the pentafluorophenyl group is released and (C7H 7)(C6F5) is formed. The 1H, 19F NMR and mass spectra of the product show the formation of (C 7H7)(C6F5). When ferrocenium oxidizes [Mo(CO)5(C6F5)]- in the presence of PPh3 the pentafluorophenyl group is replaced by a PPh3 group. The 19F NMR spectrum of the product shows the formation of C6F5H. The 31P NMR spectrum of the product shows the formation of Mo(CO)5(PPh 3).; Previous studies had suggested that CO2 insertion into the Mo-C6F5 bond of [Mo(CO)2(C6F 5){lcub}P(OMe)3{rcub}3]- occurred upon exposure of the Na and PPN salts to CO2 at one atmosphere pressure. The work reported in this dissertation has shown that CO2 insertion is not occurring. Instead, CO2 likely reacts with traces of water to produce carbonic acid. This acid may be capable of protonating the pentafluorophenyl group in both [Mo(CO)2(C6F5){lcub}P(OMe) 3{rcub}3]- and [Mo(CO)2(C 6F5)(CD3CN){lcub}P(OMe)3{rcub}2] -, leading to loss of the C6F5 ligand as C6F5H. Solvent substitution then produces Mo(CO) 2(CD3CN)2{lcub}P(OMe)3{rcub}2 and Mo(CO)2(CD3CN){lcub}P(OMe)3{rcub}3. Mo(CO) 2(CD3CN)2{lcub}P(OMe)3{rcub}2 reacts with previously released free P(OMe)3 to produce Mo(CO)2(CD 3CN){lcub}P(OMe)3{rcub}3 and Mo(CO)2{lcub}P(OMe) 3{rcub}4.; Acetophenone does not seem to do anything. The final products of this experiment in CD3CN were Mo(CO)2(CD3CN){lcub}P(OMe) 3{rcub}3 (major), Mo(CO)2{lcub}P(OMe)3{rcub} 4, C6F5H, and C6F5R (major). There were two unidentified singlets in the 31P NMR spectrum of this reaction mixture. However, in CH2Cl2, the major products were Mo(CO)2{lcub}P(OMe)3{rcub}4 and C 6F5H, the minor ones were Mo(CO)2(CD3CN){lcub}P(OMe) 3{rcub}3 and C6F5R, and there were many unidentified peaks in the 19F NMR spectrum of the final solution. With the reactions in THF-d8 and benzene-d6, the 31P NMR spectra showed only the peaks of Mo(CO)2{lcub}P(OMe) 3{rcub}4.