Kinetische und mechanistische untersuchungen von Übergangsmetall-komplex-reaktionen : III. Abhängigkeit des gleichgewichts der addition von tributylphosphan an pentacarbonyl(arylmethoxycarben)wolfram vom substituenten am ring

Abstract

The reaction of pentacarbonyl(arylmethoxycarbene)tungsten, (CO) 5W[C(OCH 3( p-C 6H 4R)] [R = OCH 3 (a), CH 3 (b), H (c), Br (d), CF 3 (e)], with tributylphosphane at low temperatures results in a reversible addition of the phosphane to the carbene carbon atom. The addition—dissoziation equilibrium is not only dependent on the temperature but also to a strong degree on the nature of the substituent R. Δ G, Δ H and the equilibrium constant K increase in the series from R = OCH 3 to R = CF 3. With the exception of R = OCH 3 the substituents b to e form an isentropic class. For all substituents (a to e) a linear dependency from Jaffés σ-constants was observed for Δ H. Good linear correlation for the substituents b to e was also found for log K and σ as well as for log K and the CO-force constants k cis and k trans .