MECHANISTIC STUDY OF THE ADDITION OF PYRROLIDINE TO ALPHA,BETA-UNSATURATED FISCHER CARBENE COMPLEXES - THE STRUCTURE OF PENTACARBONYL[(2E)-3-PHENYL-3-N-PYRROLIDINO-1-ETHOXY-PROPEN-1-YLIDENE]TUNGSTEN(0)

The addition of pyrrolidine to pentacarbonyl[ethoxy(phenylethynyl)carbene]metal(0) (metal = Cr, Mo, W) gives in good yield yellow compounds which can be characterized as pentacarbonyl-[(2E)-3-phenyl-3-N-pyrrolidino-1-ethoxypropen-1-ylidene]metal(0). The X-ray structure of the tungsten product was determined. [C2OH19NO6W] Crystallizes in the triclinic space group P1BAR with a = 10.031(3) angstrom, b = 10.629(3) angstrom, c = 11.548(3) angstrom, alpha = 63.82(2)-degrees, beta = 76.57(2)-degrees, gamma = 67.99(2)-degrees, and Z = 2. The refinement of the structure converged to R (R(w)) = 0.0243 (0.0300) for 4173 observed reflections (I > 2sigma-(I)). The temperature, pressure, and solvent dependence of this addition reaction was studied, and the corresponding activation parameters are reported. These data are used to discuss the intimate nature of the addition process in comparison to related data reported for organic reactions in the literature. The data clearly reflect that the investigated reactions proceed via a two step process with a polar transition state for the rate-determining addition step. This is further supported by the absence of a significant deuterium isotope effect.