Substitution of η2-Dihydrogen by Toluene and Alkanes in IrXH2(H2)(PPri3)2 Complexes

Abstract

We have found that the equilibrium position is highly solvent dependent. It has also been observed that hydrogen is liberated with vigorous effervescence when solid samples of IrXH{sub 2}(H{sub 2})(PPr{sup i}{sub 3}){sub 2}, X = Cl (1), Br (2), I (3), are dissolved in hydrocarbons. These observations suggest that the five-coordinate complexes establish a rapid equilibrium with solvent coordinated complexes in conjunction with the relatively slow equilibrium with the dihydrogen complex. In order to explore this possibility, we have carried out variable temperature {sup 1}H NMR spectroscopic studies of equilibrated solutions of 1, 2, and 3 and the corresponding five-coordinate complexes, IrXH{sub 2}(PPr{sup i}{sub 3}){sub 2}, X = Cl (4), Br (5), I (6), in toluene-d{sub 8}, methylcyclohexane-d{sub 14}, and n-hexane-d{sub 14}. Our studies demonstrate that the energetics of the reversible loss of H{sub 2} from IrXH{sub 2}(H{sub 2})(PR{sub 3}){sub 2} complexes are highly solvent dependent. Apparently toluene and, in the case of the iodo complex, alkanes can compete with H{sub 2} for binding to the five-coordinate IrXH{sub 2}(PR{sub 3}){sub 2} complexes. The competitive interaction of hydrocarbon solvents has been overlooked in earlier analyses of the factors which influence the stabilization of dihydrogen IrXH{sub 2}(H{sub 2})(PR{sub 3}){sub 2} complexes. Thismore » work illustrates that toluene and alkane complexes can be of major thermodynamic significance. 10 refs., 1 fig., 1 tab.« less