SYNTHESIS, CHARACTERIZATION, AND PROPERTIES OF [CP-ASTERISK-M(NO)(ETA(2)-CH(2)PH)(NCME)]BF4 SALTS (M=MO, W) AND RELATED COMPLEXES - THE STABILIZING INFLUENCE OF BENZYL LIGANDS

Treatment of orange solutions of CpM(NO)(eta(2)-CH(2)Ph)Cl (M = Mo or W) with an equimolar amount of solid AgBF4 in MeCN affords the salts [CpM(NO)(eta(2)-CH(2)Ph)(NCMe)]BF4 as analytically pure crystals in g ood yields. Both orange complexes have been subjected to single-crysta l X-ray crystallographic analyses in order to establish their molecula r geometries and their intramolecular metrical parameters. Both salts consist of discrete organometallic cations and tetrahedral BF4- anions , the intramolecular dimensions of the two cationic complexes being es sentially the same and resembling those found for related CpM(NO)-con taining compounds. The isolated [CpM(NO)(eta(2)-CH(2)Ph)(NCMe)](+) ca tions are quite electrophilic, being able to abstract Cl- from a NaCl IR cell to revert to their chloro precursors. However, treatment of th e [CpW(NO)(eta(2)-CH(2)Ph)(NCMe)]BF4 salt with various unsaturated su bstrates (e.g., diphenylacetylene, 2,3-dimethyl-1,3-butadiene, carbon monoxide, and acetone) in CDCl3 results in no detectable chemical reac tion. Lewis bases weaker than Cl- evidently cannot displace the aceton itrile ligand from the coordination sphere of the metal or induce the benzyl ligand to diminish its hapticity. Such a diminution does occur for the CH(2)Ph ligand when the MeCN group in the cationic complexes i s replaced by a carboxylate anion to produce neutral Cp'M(NO)(eta(1)-C H(2)Ph)(eta(2)-O(2)CR) complexes. The latter complexes are obtainable by treatment of CpM(NO)(eta(2)-CH(2)Ph)Cl with AgO(2)CR (R = CH(Et)(P h)) in CH2Cl2 and have been fully characterized by conventional spectr oscopic methods.