Para-Hydrogen conversion and hydrogen-deuterium equilibration catalyzed by diamagnetic iridium, platinum, and ruthenium complexes in nonaqueous solution (1)

Abstract

Homogeneous solutions of several tertiary phosphine complexes of Ir, Pt, Ru, and Rh have been tested for their catalytic activity for (1) para-hydrogen conversion, p − H 2 ⇄ o − H 2, and (2) hydrogen-deuterium equilibration, H 2 + D 2 → 2 HD. The experiments were carried out in toluene under 1 atm of hydrogen and between 25 and 65°C. The following results were obtained. (1) para-H 2 conversion: (a) active complexes: trans-[Ir(A)(CO)(Ph 3P) 2] (A = Cl, Br, or I), [Pt(Ph 3P) 4], {Pt(Ph 3P) n }, [Pt(O 2)(Ph 3P) 2], [Pt(Cl) 2(Bu 3P) 2], and [Ru(Cl) 2(Ph 3P) 3]; (b) inactive complexes: [Pt(PC 2P) 2], [Pt(PCCP) 2], and [Fe(DPGH) 2(py) 2]. (2) H 2-D 2 equilibration: (a) active complexes: trans-[Ir(A)(CO)(Ph 3P) 2], {Pt(Ph 3P) n }, and [Pt(O 2)(Ph 3P) 2]; (b) inactive complexes [Pt(Ph 3P) 4], [Pt(Cl) 2(Bu 3P) 2], and trans-[Rh(Cl)(CO)(Ph 3P) 2]. The H 2-D 2 catalysis by the iridium complexes was accompanied by an exchange between D 2 and some bound hydrogens in the reaction system. It is proposed that the para-H 2 conversion proceeds via a chemical mechanism through a dihydrido intermediate M(H) 2. The H 2-D 2 equilibration is tentatively proposed to involve a tetra-(hydrido-deuterio) species, M(H, D) 4, representing a labile intermediate or an activated complex. Alternate mechanisms for the H 2-D 2 equilibrium are considered, and their relative merits are discussed.