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Bis(2,6-dinitroaryl)platinum(II) Complexes. Cis/Trans Isomerization

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posted on 28.08.2006, 00:00 by José Vicente, Aurelia Arcas, María-Dolores Gálvez-López, Peter G. Jones
The complexes cis-[Pt(κ2-Aryl)(κ1-Aryl)L] (κ2-Aryl = κ2-(C,O)-C6(NO2)2-2,6-(OMe)3, κ1-Aryl = κ1(C)-C6(NO2)2-2,6-(OMe)3, L = S-dmso (2cis), XyNC (4cis; Xy = 2,6-Me2C6H4), CO (5cis), PPh3 (7cis)) have been obtained by reacting at room temperature cis-[Pt(κ2-Aryl)(κ1-Aryl)(OH2)] (1cis) with dimethyl sulfoxide (dmso; 1:1 or excess), XyNC (1:1), or CO (excess) or cis-(Me4N)[Pt(κ2-Aryl)(κ1-Aryl)Cl] with PPh3 (1:1), respectively. The room-temperature reaction of 1cis with XyNC (1:2), of 5cis with PPh3 (1:1), or of cis-(Me4N)[Pt(κ2-Aryl)(κ1-Aryl)Cl] with PPh3 (1:2) gives cis-[Pt(κ1-Aryl)2LL‘] (L = L‘ = XyNC (3cis), PPh3 (8cis); L = CO, L‘ = PPh3 (6cis)). Complexes 3cis, 4cis, and 5cis isomerize on heating in solution or in the solid state to give 3trans, 4trans, and 5trans, respectively, while 6cis and 8cis decompose to give 7cis instead of their trans isomers; these, however, can be prepared by reacting 5trans or 6trans with PPh3 in molar ratios of 1:1 or 1:2, respectively. When they are heated, 6trans and 8trans also descompose to 7cis, while 2cis and cis-[Pt(κ2-Aryl)(κ1-Aryl)L] (L = H2O (1cis), PhCN, tht) decompose to a mixture of unidentified products (1cis) or are recovered unchanged. These results, and others reported in the literature, on the stability of cis- and trans-diaryl complexes of platinum or palladium can be explained as the result of two competing factors, transphobia and the steric requirements of the ligands. The X-ray crystal structures of 2cis, 3cis, 3trans, 4trans·CHCl3, 5cis·CH2Cl2, 5cis·0.5hexane, 6cis, 6trans·CHCl3, 7cis·Me2CO, and 8trans·0.5CHCl3 have been determined.

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