Chelate ring-opening of Pd(II) triphos complexes:: Ligand exchange, selective phosphine oxidation, and X-ray crystal structure of [Pd(Ph2P(CH2)2PPh(CH2)2P(O)Ph2)2Br]Br

P-31 NMR studies show that chelate ring-opening of [Pd(triphos)Cl](+), 4, (triphos = Ph2P(CH2)(2)PPh(CH2)(2)PPh2) can be achieved in solution by reaction with excess of triphos with the formation of [Pd(Ph2P(CH2)(2)PPh(CH2)(2)PPh2-P,P)(2)](2+). In the X-ray crystal structure, [Pd(triphos)Br]Br, 1 has a distorted square-planar geometry, and the oxidation of 1 with H2O2 gives rise to [Pd(Ph2P(CH2)(2)PPh(CH2)(2)P(O)Ph-2-P,P)(2)](2+), 2, which contains two bidentate ligands. The presence of two dangling arm phosphine oxide groups was confirmed by X-ray crystallography for the related complex [Pd(Ph2P(CH2)(2)PPh(CH2)(2)P(O)Ph-2-P,P)(2)Br]Br, 3, which contained square-pyramidal five-coordinated Pd(II). (C) 1998 Elsevier Science Ltd. All rights reserved.