No abstract

No abstract

No abstract

No abstract

No abstract

No abstract

The phosphinothiolato complexes [PdCl(dppet)PPh(3)] (3), [Pd(dppet)(2)] (4), and [Pd(2)Cl(2)(dpppt-P,&mgr;-S)(2)] (6) (Hdppet = HSC(2)H(4)PPh(2); Hdpppt = HSC(3)H(6)PPh(2)) 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 ((31)P NMR, delta(P) 66.8 (dppet), 24.1 (PPh(3)); (2)J(PP) = 459 Hz) and 5 ((13)C NMR) are trans-P,P. Crystals of 3.CH(2)Cl(2) are orthorhombic (P2(1)2(1)2(1)), with a = 9.247(3) Å, b = 17.956(9) Å, c = 19.869(9) Å. In 3 the Pd-S distance of 2.270(2) Å is short compared to the very different Pd-P distances of 2.280(2) (Pd-PPh(2)R) and 2.343(2) Å (Pd-PPh(3)). Crystals of 6.CH(2)Cl(2) are monoclinic (P2(1)/n) with a = 12.701(3) Å, b = 12.040(4) Å, c = 22.495(2) Å, 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.

The hydroformylation of the differently protected glucal derivatives 3,4,6-tri-O-acetyl-Dglucal, 3,4,6-tri-O-benzyl-D-glucal and 3,4,6-tri-O-methyl-D-glucal was carried out with rhodium catalytic systems, and 2-formyl derivatives were obtained as the main products in yields of 58%, 68%, and 55% respectively, when [Rh 2 (µ-OMe) 2 (COD) 2 ]/P(O-o-t BuC 6 H 4 ) 3 was used. The bulky phosphite needs to be used as auxiliary ligand to achieve the hydroformylation of these highly hindered cyclic olefins. A mechanistic cycle is proposed which explains the regio-and stereoselectivity of the reaction. The mononuclear rhodium complex trans-[RhCl(CO)(P(O-o-t BuC 6 H 4 ) 3 ) 2 ] was isolated at the end of the catalytic reaction by breaking the dinuclear complexes used as catalyst precursors. To confirm the characterization of trans-[RhCl(CO)(P(O-o-t BuC 6 H 4 ) 3 ) 2 ], a separate synthesis was carried out which isolated crystals suitable for an X-ray determination.