Insertion and alkyne coupling reactions on early-transition-metal centers. Structures of CpTa(Me)(.sigma.2-ArCCAr)(.sigma.2-MeCNCMe3), CpMeTaC(Ph)C(Ph)C(Me)NCMe3, CpClMo(CPh)4 (Ar = p-tolyl)

Abstract

CpTaCl{sub 2}({eta}{sup 2}-ArCCAr) (Ar = phenyl, p-tolyl) reacts with MeLi to give a CpTaMe{sub 2}({eta}{sup 2}-ArCCAr) (1) in high yield. Compound 1 reacts with {sup t}BuNC to give the {eta}{sup 2}-acetimidoyl derivatives CpTaMe({eta}{sup 2}-ArCCAr)({eta}{sup 2}-MeCN{sup t}Bu) (4) from the insertion of the isocyanide into one of the Ta-Me bonds. Gentle heating causes a quantitative conversion of 4 into metallacyclopentatriene derivatives, CpMeTaC(Ar)C(Ar)C(Me)N({sup t}Bu) (5), in which the alkyne has coupled to the acetimidoyl ligand with the formation of a new C-C bond. A similar coupling reaction is observed when CpMoCl(ArCCAr){sub 2} is heated in toluene; one of the products of this reaction is the metallacyclopentatriene CpClMo(CAr){sub 4} (7). The metallacyclic ring in 7 features two Mo=C double bonds (d = 1.94 {angstrom}) and the ring is folded (dihedral angle {approx equal}117{degree}). The crystal structures of 4b (Ar = p-tolyl), 5a (Ar = phenyl), and 7a{center dot}CH{sub 2}Cl{sub 2} (Ar = phenyl) have been determined: 4b, a = 10.518 (3) {angstrom}, b = 12.782 (3) {angstrom}, c = 18.816 (6) {angstrom}, {alpha} = {beta} = {gamma} = 90{degree}, V = 2,530 (1) {angstrom}{sup 3}, Z = 4, {rho}{sub c} =1.48 g/mL, space group P2{sub 1}2{sub 1}2{sub 1}, R = 0.027, R{sub w}more » = 0.026; for 5a, a = 9.540 (3) {angstrom}, b = 10.830 (4) {angstrom}, c = 11.932 (3) {angstrom}, {alpha} = 114.77 (2){degree}, {beta} = 91.47 (2){degree}, {gamma} = 91.68 (3){degree}, V = 1117.8 (6) {angstrom}{sup 3}, Z = 2, {rho}{sub c} = 1.59 g/mL, space group P{bar 1}, R = 0.045, R{sub w} = 0.044; 7a{center dot}CH{sub 2}Cl{sub 2} a = 10.039 (4) {angstrom}, b = 11.760 (3) {angstrom}, c = 12.674 (8) {angstrom}, {alpha} = 92.21 (4){degree}, {beta} = 87.35 (4){degree}, {gamma} = 104.05 (3){degree}, V = 1,449 (1) {angstrom}{sup 3}, Z = 2, {rho}{sub c} = 1.46 g/mL, space group P{bar 1}, R = 0.038, R{sub w} = 0.038.« less