Selective cleavage by acids of one metal-carbon sigma-bond of a bis(ortho-platinated) triarylphosphane: A P-31 NMR trans-influence series based on the unit pt(kappa(2)-C6H3-5-Me-2-PPh2)(PPh2-4-tol)

Treatment of the bis(chelate) complex cis-[Pt(2-C6H3-5-Me-2-PPh2)2] (1) with strong acids causes selective cleavage of one of the metal-aryl bonds to give cis-[PtX(2-C6H3-5-Me-2-PPh2)(PPh2-4-tol)] [X = Cl (2), Br (3), I (4), ONO2 (5) and OCOCF3 (6)], from which a series of neutral and cationic derivatives can be derived by metathetical reactions. The complexes 2 and 6 rearrange spontaneously to the corresponding trans isomers, this reaction being promoted by CO. The J(Pt-P) values for the phosphorus atom of the four-membered ring can be ordered to establish a trans-influence series of anionic ligands X and neutral ligands L, which correlates well with, but is more extensive than, that based earlier on PtMe(dppe) complexes. Single-crystal X-ray structural analysis of trans-[Pt(1-OCOCF3)(2-C6H3-5-Me-2-PPh2)(PPh2-4-tol)] (trans-6), cis-[PtX(2-C6H3-5-Me-2-PPh2)(PPh2-4-tol)] [X = Cl (2), CN (11), Me (43) and C6F5 (45)], and [Pt(2-C6H3-5-Me-2-PPh2)(PPh2-4-tol)2]BF4 (34) show these complexes to have distorted square-planar geometry. The Pt-P distances to the phosphorus atom of the four-membered ring in 2, 11, 43 and 45 broadly follow the trend of J(Pt-P) values, Cl- being placed near the bottom and Me- near the top of the trans-influence series, but the corresponding Pt-P distance in 34 is out of line. The Pt-P distances to PPh2-4-tol cis to X or L tend to decrease with increasing trans-influence of X or L, in agreement with previous indications of a ligand cis-influence that runs opposite to the trans-influence. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)