Palladium phosphinothiolato complexes. Syntheses and crystal structures of mononuclear [PdCl(SC<inf>2</inf>H<inf>4</inf>PPh<inf>2</inf>)PPh<inf>3</inf>] and binuclear [Pd<inf>2</inf>Cl<inf>2</inf>(μ-SC<inf>3</inf>He<inf>6</inf>PPh <inf>2</inf>)<inf>2</inf>] and their performance in catalytic carbonylation

Nuria Brugat, Alfonso Polo, Ángel Álvarez-Larena, J. Francesc Piniella, Julio Real

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Abstract

The phosphinothiolato complexes [PdCl(dppet)PPh3] (3), [Pd(dppet)2] (4), and [Pd2Cl2(dpppt-P μ-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 (31P NMR, δP 66.8 (dppet), 24.1 (PPh3); 2JPP = 459 Hz) and 5 (13C NMR) are trans-P,P. Crystals of 3·CH2Cl2 are orthorhombic (P212121), 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-PPh2R) and 2.343(2) Å (Pd-PPh3). Crystals of 6·CH2Cl2 are monoclinic (P21/n) with a = 12.701(3) Å, b = 12.040(4) Å, c = 22.495(2) Å, and β = 97.36(1)°. The structure of 6 consists of two Pd(dpppt)Cl moieties meeting at an angle of 105.81(3)°, linked by asymmetric thiolato bridges in a syn-endo configuration. The difference in the chelate angles of dppet (85.98(9)°) and dpppt (96.60(3)° and 97.42(3)°) 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°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. © 1999 American Chemical Society.
Original languageEnglish
Pages (from-to)4829-4837
JournalInorganic Chemistry
Volume38
Issue number21
Publication statusPublished - 1 Dec 1999

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