Rigid-Rod Polymers, Oligomers, and Model Complexes with Pt−Pt Bonds in the Backbone

Abstract

Reaction of [Pt2Cl2(μ-dppm)2], dppm = Ph2PCH2PPh2, with PhC⋮CH in methanol gives [Pt2Cl2(μ-dppm)2(μ-PhCCH)], 1, or, in the presence of base, [Pt2(C⋮CPh)2(μ-dppm)2], 2, or [Pt2(C⋮CPh)2(μ-dppm)2(μ-PhCCH)], 4. Complex 2 reacts with chlorinated solvents to re-form [Pt2Cl2(μ-dppm)2], but in the presence of base, [Pt2(C⋮CPh)2(μ-dppm)2(μ-OH···Cl)], 3, may be formed. Complexes 1 and 3 have been characterized by X-ray structure determinations, and the conditions for formation of 2 have been optimized as a model reaction for polymer formation by using diacetylenes. Reaction of [Pt2Cl2(μ-dppm)2] with HC⋮CArC⋮CH in methanol in the presence of base gives insoluble oligomers characterized as Cl-[Pt2(μ-C⋮CArC⋮C)2(μ-dppm)2]x[Pt2Cl(μ-dppm)2], 5, that is as a diacetylide bridged oligomer with chloride end groups; depending on the diacetylide used x varies from ca. 3−12. Cationic polymers [Pt2(μ-dppm)2(μ-L-L)]x(BF4)2x, 6 or 7, are formed by reaction of [Pt2Cl2(μ-dppm)2] with diisocyanide ligands C⋮NArN⋮C or with the diphosphine ligand Ph2PC6H4PPh2, respectively. In contrast, the diphosphine ligand i-Pr2PC6H4C6H4P-i-Pr2, having a longer spacer group, gives the cyclic complex [Pt2(μ-dppm)2(μ-i-Pr2PC6H4C6H4P-i-Pr2)]2(BF4)4. The polymeric complexes 5−7 are insoluble or sparingly soluble in common organic solvents. They represent rare examples of conjugated, rigid-rod oligomers or polymers with metal−metal bonds in the backbone.