Facile Activation of Dihydrogen by a Phosphinito-Bridged Pt(I)−Pt(I) Complex

摘要

The phosphinito-bridged Pt(I) complex [(PHCy2)Pt(μ-PCy2){κ2P,O-μ-P(O)Cy2}Pt(PHCy2)](Pt-Pt)n(1) reversibly adds H2 under ambient conditions, giving cis-[(H)(PHCy2)Pt1(μ-PCy2)(μ-H)Pt2(PHCy2){κPP(nO)Cy2}](Pt-Pt) (2). Complex 2 slowly isomerizes spontaneously into the corresponding more stable isomerntrans-[(PHCy2)(H)Pt(μ-PCy2)(μ-H)Pt(PHCy2){κP-P(O)Cy2}](Pt-Pt) (3). DFT calculations indicate that thenreaction of 1 with H2 occurs through an initial heterolytic splitting of the H2 molecule assisted by thenphosphinito oxygen with breaking of the Pt-O bond and hydrogenation of the Pt and O atoms, leading tonthe formation of the intermediate [(PHCy2)(H)Pt(μ-PCy2)Pt(PHCy2){κP-P(OH)Cy2}](Pt-Pt) (D), where thentwo split hydrogen atoms interact within a six-membered Pt-H· · ·H-OsP-Pt ring. Compound D is a labilenintermediate which easily evolves into the final dihydride complex 2 through a facile (9-15 kcal mol-1,ndepending on the solvent) hydrogen shift from the phosphinito oxygen to the Pt-Pt bond. Informationnobtained by addition of para-H2 on 1 are in agreement with the presence of a heterolytic pathway in the 1nf 2 transformation. NMR experiments and DFT calculations also gave evidence for the nonclassicalndihydrogen complex [(PHCy2)(η2-H2)Pt(μ-PCy2)Pt(PHCy2){κP-P(O)Cy2}](Pt-Pt) (4), which is an intermediatenin the dehydrogenation of 2 to 1 and is also involved in intramolecular and intermolecular exchangenprocesses. Experimental and DFT studies showed that the isomerization 2 f 3 occurs via an intramolecularnmechanism essentially consisting of the opening of the Pt-Pt bond and of the hydrogen bridge followednby the rotation of the coordination plane of the Pt center with the terminal hydride ligand.