Palladium phosphinothiolato complexes.: Syntheses and crystal structures of mononuclear [PdCl(SC2H4PPh2)PPh3] and binuclear [Pd2Cl2(μ-SC3H6PPh2)2] and their performance in catalytic carbonylation

The phosphinothiolato complexes [PdCl(dppet)PPh3] (3), [Pd(dppet)2] (4), and [Pd2Cl2(dpppt-P, mu-S)(2)] (6) (Hdppet = HSC2H4PPh2; Hdpppt = HSC3H6PPh2) have been synthesized in good yield by various base-free ligand exchange reactions on Pd(II), but [Pd(dpppt)(2)] (5) could only be obtained as a pure product employing an oxidative route from Pd(0). Both complexes 3 (P-31 NMR, delta(P) 66.8 (dppet), 24.1 (PPh3); (2)J(PP) = 459 Hz) and 5 (C-13 NMR) are trans-P,P. Crystals of 3 . CH2Cl2 are orthorhombic (P2(1)2(1)2(1)), With a = 9.247(3) Angstrom, b = 17.956(9) Angstrom, c = 19.869(9) Angstrom. In 3 the Pd-S distance of 2.270(2) Angstrom is short compared to the very different Pd-P distances of 2.280(2) (Pd-PPh2R) and 2.343(2) Angstrom (Pd-PPh3). Crystals of 6 . CH2Cl2 are monoclinic (P2(1)/n) with a 12.701(3) Angstrom, b = 12.040(4) Angstrom, c = 22.495(2) Angstrom, and beta = 97.36(1)degrees. The structure of 6 consists of two Pd(dpppt)Cl moieties meeting at an angle of 105.81(3)degrees linked by asymmetric thiolato bridges in a syn-endo configuration. The difference in the chelate angles of dppet (85.98(9)degrees) and dpppt (96.60(3)degrees and 97.42(3)degrees) seems to be crucial for palladium to form an unusual mononuclear complex (3) or a binuclear complex (6). Bischelate complexes 4 and 5 are inactive, but 3 and 6 catalyze the hydroesterification of styrene with CO (30 bar) and MeOH at moderate temperatures (60 and 80 degrees C) with no additives. The velocities are slow, but with 6 and with 3 at the lower temperature no decomposition to Pd metal is observed. Only esters are produced and regioselectivities of ca. 84% toward 2-phenylpropanoic acid methyl ester are achieved.