Synthesis and characterization of tricarbonyl[eta(6)-(phenylethynyl) arene]chromium complexes: Crystal structure of tricarbonyl[eta 6-(3-phenylethynyl)anisole]chromium

Tricarbonyl(eta(6)-diphenylacetylene)chromium (4) was prepared from the reaction of tricarbonyl(eta(6)-fluorobenzene)chromium (3) with lithium phenylacetylide (2) at a low temperature using hexamethylphosphoric triamide as cosolvent. A concomitant tricarbonyl(eta(6)-butoxylbenzene)chromium (6) was also obtained in this reaction probably owing to both the air oxidation of n-BuLi and the ring opening of tetrahydrofuran by n-BuLi. The overwhelming abundance of meta and ortho products 9b and 10b produced in the substitution reaction of tricarbonyl(eta(6)-4-fluoroanisole)chromium (8b) by lithium phenylacetylide demonstrates that the reaction was by no means through the straightforward SNAr mechanism. The results provide support for the mechanism proposed by Pauson and Brookhart, in which the nucleophile attacked a carbon of the phenyl ring not bearing the leaving group, followed by hydrogen migration and finally elimination of the leaving group to achieve aromaticity. In addition, compounds were characterized by mass, IR,H-1 and C-13 NMR spectra, and elemental analysis. The molecular structure of tricarbonyl[eta(6)-(3-phenylethynyl)anisole]chromium (9b) has been determined by X-ray diffraction studies. Crystal data are as follows: <P(1)over bar>; a = 7.782(2) Angstrom, b = 8.910(2) Angstrom and c = 12.688(3) Angstrom; alpha = 108.46(3)degrees, beta = 96.05(3)degrees and gamma = 103.19(3)degrees; V = 797.3(4) Angstrom(3); Z = 2; R = 3.23%; R(w) = 4.37%.