Reactions of 2,4-hexadiyne-1,6-diol with [H2Os3(CO)9(PR3)] clusters. Cyclization of the diyne and reversible exchange of the phosphine ligands between different positions of the “Os3C3” framework?

Dalton Transactions Pub Date: 2004-05-05 DOI: 10.1039/B403861B

Abstract

Reactions between unsaturated [H2Os3(CO)9(PR3)] clusters (PR3 = PPh3, P(4-CF3–C6H4)3, PEt3) and 2,4-hexadiyne-1,6-diol have been studied. It was found that the diyne ligand easily reacts with all these complexes to give [HOs3(CO)8(PR3){μ3,η1:η3:η1-(CH3–C–C[double bond, length as m-dash]CH–CH[double bond, length as m-dash]C–O)}] complexes (V, VI and VII, respectively) containing the “Os3C3” pentagonal pyramid cluster framework. This structural pattern is formed through the diyne cyclization, dissociation of a CO ligand and eventual coordination of the cyclized organic moiety to the osmium triangle in the μ3,η1:η3:η1 manner. In the case of the PEt3 substituted cluster the second hydride transfer onto the organic fragment occurs to afford the nonhydride [Os3(CO)8(PR3){μ3,η1:η2:η1-(CH3–CH–C[double bond, length as m-dash]CH–CH[double bond, length as m-dash]C–O)}] cluster, VIII, containing distorted pentagonal pyramid framework with a broken Os–C bond. Heating of V, VI and VII in hexane solutions results in formation of the regioisomers (Va, VIa and VIIa) with the phosphine ligand located at adjacent osmium atoms across the Os–Os bond bridged by the coordinated organic fragment. The most probable mechanism of the isomerization includes reversible phosphine migration between these metal centres. Solid-state structure of V, Va, VI, VIIa and VIII have been established by single crystal X-ray diffraction. A general mechanistic scheme for the diyne ligand cyclization and cluster framework transformations is suggested and discussed.

Graphical abstract: Reactions of 2,4-hexadiyne-1,6-diol with [H2Os3(CO)9(PR3)] clusters. Cyclization of the diyne and reversible exchange of the phosphine ligands between different positions of the “Os3C3” framework
Recommended Literature