Nucleophilic substitution reactions of (η6-fluorotoluene)Cr(CO)3 and (η6-fluoroanisole) Cr(CO)3 toward phenylacetylide, fluorenyl, indolinyl and carbazolinyl lithium

Article abstract of DOI:10.1016/0022-328X(96)06131-1

Tricarbonyl [η⁶-(1,2-diphenylethynyl)benzene]chromium (8a) was obtained along with tricarbonyl[η⁶-(2-phenylethynyl)anisole]chromium (7b) and tricarbonyl[η⁶-(3-phenylethynyl)anisole]chromium (7a) from the reaction of tricarbonyl(η⁶-2-fluoroanisole)chromium (4c) with lithium phenylacetylide (3). The formation of ortho-and meta-products, 7b, 8a and 7a, produced in the above reaction demonstrates that the reaction was by no means through a straightforward nucleophilic substitution mechanism. These results provided support for the mechanism proposed by Pauson and Brookhart, in which the nucleophile attacked the carbon atom of the phenyl ring not bearing the leaving group, followed by hydrogen migration and finally elimination of the leaving group to achieve aromaticity. 8a was obtained presumably from the reaction of 7b with excess 3. Compounds were characterized by mass, infrared, ¹H, ¹³C NMR spectra. The molecular structure of 8a has been determined by X-ray diffraction studies. Crystal data are as follows: orthorhombic, P_BCA, a = 18.690(2) A, b = 10.666(2) A, c = 20.463(2) A, V = 4079.3(8) A³, Z = 8, R = 4.41%, R_w = 5.56%. Tricarbonyl(η⁶-4-fluorenyltoluene)chromium (10) was obtained as the only separated product from the reaction of tricarbonyl(η⁶-4-fluorotoluene)chromium (5) with fluorenyl lithium. The X-ray crystal structure of 10 was determined: monoclinic, P2₁/c, a = 12.318(1) A, b = 11.498(1) A, c = 13.585(2) A, β = 100.35(1)°, V = 1892.8(5) A³, Z = 4, R = 3.63%, R_w = 5.65%. Tricarbonyl(η⁶-4-fluorenylanisole)chromium (11a), tricarbonyl(η⁶-3-fluorenylanisole)chromium (11b) and tricarbonyl(η⁶-2-fluorenylanisole)chromium (11c) were also produced in moderate to good yields. Moreover, tricarbonyl(η⁶-4-indolinyltoluene)chromium (12) and tricarbonyl(η⁶-4-carbazolinyltoluene)chromium (14) were synthesized from the reaction of 5 with indolinyl and carbazolinyl lithium, respectively. Tricarbonyl(η⁶-4-indolinylanisole)chromium (13a), tricarbonyl(η⁶-3-indolinylanisole)chromium (13b) and tricarbonyl(η⁶-2-indolinylanisole)chromium (13c) were obtained in high yields from the direct nucleophilic substitution reactions of related compounds.