REDOX AND CARBONYL CHEMISTRY OF DIRHENIUM COMPLEXES CONTAINING QUADRUPLE AND ELECTRON-RICH TRIPLE BONDS (TRANSITION METAL)
Abstract
Chemical redox reactions of multiply-bonded dirhenium phosphine complexes of the M(,2)L(,8) and M(,2)L(,10) structural types have been carried out using cobaltocene and nitrosonium hexafluorophosphate as the reductant and oxidant, respectively. The systems that were studied are those which were found to exhibit electrochemically reversible oxidations or reductions as determined by the cyclic voltammetry technique. The series Re(,2)Cl(,4)(PMe(,2)Ph)(,4) ('n+) (n = 0, 1, or 2) was prepared using NOPF(,6) and was studied structurally in order to ascertain the relationship between bond distance and formal metal-metal bond order. Another series of dirhenium complexes was prepared by the one-electron oxidation and one-electron reduction of the doubly-bonded complex Cl(,2)Re((mu)-Cl)(,2)((mu)-dppm)(,2)ReCl(,2) to give Re(,2)Cl(,6)(dppm)(,2) ('1+,1-). Both of the latter ions are examples of the rarely encountered M-M bond order of 1.5. The quadruply-bonded complexes Re(,2)Cl(,6)(PR(,3))(,2) (PR(,3) = PEt(,3), P-n-Pr(,3), PMePh(,2) or PEtPh(,2)) and Re(,2)(O(,2)CR)(,4)Cl(,2) (R = C(,3)H(,7), CMe(,3), or C(,6)H(,5)) were reduced by Cp(,2)Co to give the paramagnetic salts ((eta)('5)-C(,5)H(,5))(,2)Co Re(,2)Cl(,6)(PR(,3))(,2) and ((eta)('5)-C(,5)H(,5))(,2)Co Re(,2)(O(,2)CR)(,4)Cl(,2) . The reduction of Re(,2)Cl(,5)- (PMe(,2)Ph(,2))(,3) to give ((eta)('5)-C(,5)H(,5))(,2)Co Re(,2)Cl(,5)(PMePh(,2))(,3) and its oxida- tion to Re(,2)Cl(,5)(PMePh(,2))(,3) PF(,6) have also been accomplished. These results demonstrate that mixed halide-phosphine complexes of Re(,2)('n+) (n = 6, 5, or 4) exhibit the most extensive redox chemistry of any class of multiply-bonded dimetal species. The reactions of carbon monoxide with dirhenium complexes containing monodentate phosphine ligands have been explored. The series Re(,2)Cl(,4)(PMe(,2)Ph)(,4) (PF(,6))(,n) (n = 0, 1, or 2) reacts with CO to yield monomeric ReCl(CO)(,2)(PMe(,2)Ph)(,3), ReCl(CO)(,3)(PMe(,2)Ph)(,2) and ReCl(,3)(CO)(PMe(,2)Ph)(,3), resulting from M-M bond cleavage. The complex Re(,2)Cl(,4)(dppm)(,2), which contains the bridging bidentate phosphine bis(diphenylphosphino)methane, reacts with CO to yield Re(,2)Cl(,4)(dppm)(,2)(CO)(,n) (n = 1 or 2). These results provide, for the first time, evidence as to the nature of the intermediates that are formed in the cleavage of the electron-rich triple bond ((sigma)('2)(pi)('4)(delta)('2)(delta)*('2) configuration) by (pi)-acceptor ligands. The interesting biscarbonyl complex Re(,2)Cl(,4)(dppm)(,2)(CO)(,2) reacts with L = RCN and RNC in the presence of TIPF(,6) to yield Re(,2)Cl(,3)(dppm)(,2)(CO)(,2)(L) PF(,6). These species can be reduced by Cp(,2)Co to give the corresponding neutral compounds. The latter constitute the first examples of complexes that contain the Re(,2)('3+) core.
Degree
Ph.D.
Subject Area
Chemistry
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