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

Reaction of [Pt<sub>2</sub>Cl<sub>2</sub>(μ-dppm)<sub>2</sub>], dppm = Ph<sub>2</sub>PCH<sub>2</sub>PPh<sub>2</sub>, with PhC⋮CH in methanol gives [Pt<sub>2</sub>Cl<sub>2</sub>(μ-dppm)<sub>2</sub>(μ-PhCCH)], <b>1</b>, or, in the presence of base, [Pt<sub>2</sub>(C⋮CPh)<sub>2</sub>(μ-dppm)<sub>2</sub>], <b>2</b>, or [Pt<sub>2</sub>(C⋮CPh)<sub>2</sub>(μ-dppm)<sub>2</sub>(μ-PhCCH)], <b>4</b>. Complex <b>2</b> reacts with chlorinated solvents to re-form [Pt<sub>2</sub>Cl<sub>2</sub>(μ-dppm)<sub>2</sub>], but in the presence of base, [Pt<sub>2</sub>(C⋮CPh)<sub>2</sub>(μ-dppm)<sub>2</sub>(μ-OH···Cl)], <b>3</b>, may be formed. Complexes <b>1</b> and <b>3</b> have been characterized by X-ray structure determinations, and the conditions for formation of <b>2</b> have been optimized as a model reaction for polymer formation by using diacetylenes. Reaction of [Pt<sub>2</sub>Cl<sub>2</sub>(μ-dppm)<sub>2</sub>] with HC⋮CArC⋮CH in methanol in the presence of base gives insoluble oligomers characterized as Cl-[Pt<sub>2</sub>(μ-C⋮CArC⋮C)<sub>2</sub>(μ-dppm)<sub>2</sub>]<i><sub>x</sub></i>[Pt<sub>2</sub>Cl(μ-dppm)<sub>2</sub>], <b>5</b>, that is as a diacetylide bridged oligomer with chloride end groups; depending on the diacetylide used <i>x</i> varies from <i>ca.</i> 3−12. Cationic polymers [Pt<sub>2</sub>(μ-dppm)<sub>2</sub>(μ-L-L)]<i><sub>x</sub></i>(BF<sub>4</sub>)<sub>2</sub><i><sub>x</sub></i>, <b>6</b> or <b>7</b>, are formed by reaction of [Pt<sub>2</sub>Cl<sub>2</sub>(μ-dppm)<sub>2</sub>] with diisocyanide ligands C⋮NArN⋮C or with the diphosphine ligand Ph<sub>2</sub>PC<sub>6</sub>H<sub>4</sub>PPh<sub>2</sub>, respectively. In contrast, the diphosphine ligand <i>i</i>-Pr<sub>2</sub>PC<sub>6</sub>H<sub>4</sub>C<sub>6</sub>H<sub>4</sub>P-<i>i</i>-Pr<sub>2</sub>, having a longer spacer group, gives the cyclic complex [Pt<sub>2</sub>(μ-dppm)<sub>2</sub>(μ-<i>i</i>-Pr<sub>2</sub>PC<sub>6</sub>H<sub>4</sub>C<sub>6</sub>H<sub>4</sub>P-<i>i</i>-Pr<sub>2</sub>)]<sub>2</sub>(BF<sub>4</sub>)<sub>4</sub>. The polymeric complexes <b>5</b>−<b>7</b> 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.