KINETICS AND MECHANISM OF STYRENE HYDROCARBOXYLATION CATALYZED BY THEPDCL2(PH3P)(2) COMPLEX .3. EFFECT OF SNCL2 ADDITIVES ON REGIOSELECTIVITY

The relationships between the initial rates of formation of 3-phenylpr opionic acid (I) and 2-phenylpropionic acid (II), r(I) and r(II), on t he CO partial pressure and concentrations of Ph3P, water, and styrene were studied in the styrene hydrocarboxylation reaction catalyzed by t he SnCl2-modified PdCl2(Ph3P)(2). The addition of SnCl2 in an equimola r amount to PdCI2(Ph3P)(2) increases the selectivity to I from 30 to 7 0% at the expense of increasing r(I) and decreasing r(II). Kinetic and spectral data were used to account for the SnCl2 effect within the fr amework of the multiroute hydride mechanism of tile reaction, which wa s shown to occur via the displacement of a CO ligand from Pd(II)-conta ining intermediates by the n-acceptor SnCl3-. These processes led to a n increase in the steady-sate concentration of diphosphine hydride com plexes, which are highly selective toward I.