CYCLOPALLADATION OF TRIMESITYLARSINE - THE X-RAY CRYSTAL-STRUCTURE FOR [PD(ASMES2C6H2(CH3)2CH2)CL(PPH3)]

The bulky trimesitylarsine ligand, As(mes)3undergoes facile cyclopalladation to yield the dimeric complex, [Pd(Asmes2C6H2 (CH3)2CH2)Cl]2characterized by microanlysis, IR and 1HN MR spectroscopy. This complex is very stable but readily undergoes bridge-cleavage reactions with tertiary phosphine ligands having ligand cone angles less than 170°;. The crystal structure for the PPh3 bridge-cleavage product is reported. This complex, [Pd(Asmes2C6H2(CH3)2CH2)Cl(PPh3 )] is monoclinic, space group P21 / c with a = 20.469(2), b = 12.702(2), c = 15.401(4) Åß= = 98.46(1)°, V = 3961 Å3Z, = 4, R = 0.0284 and Rw = 0.0305. The Pd geometry is distorted square-planar with principal dimensions, Pd-Cl 2.395(1), Pd-P 2.318(1), Pd-C 2.056(3), and Pd-As 2.437(1) Å; As-Pd-Cl 96.5(1), Cl-Pd-P 90.9(1), P-Pd-C 93.7(1), As-Pd-C 78.9(1), As-Pd-P 172.6(1), and CI-Pd-C 171.7(1)°. The average C-P-C angle (104.3(1)°) is smaller than expected and is rationalized on the basis of steric effects operative within the complex.