INSERTION AND ALKYNE COUPLING REACTIONS ON EARLY-TRANSITION-METAL CENTERS - STRUCTURES OF CPTA(ME)(ETA-2-ARCCAR)(ETA-2-MECNTBU), CPMETAC(PH)C(PH)C(ME)NTBU, AND CPCLMO(CPH)4 (AR = PARA-TOLYL)

CpTaCl2(η2-ArCCAr) (Ar = phenyl, p-tolyl) reacts with MeLi to give CpTaMe2(η2-ArCCAr) (1) in high yield. Compound 1 reacts withtBuNC to give the η2-acetimidoyl derivatives CpTaMe(η2-ArCCAr)(η2-MeCNtBu) (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(tBu) (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)2 is heated in toluene; one of the products of this reaction is the metallacyclopentatriene CpClMo(CAr)4 (7). The metallacyclic ring in 7 features two Mo═C double bonds (d = 1.94 Å) and the ring is folded (dihedral angle ≃117°). The crystal structures of 4b (Ar = p-tolyl), 5a (Ar = phenyl), and 7a-CH2Cl2 (Ar = phenyl) have been determined: 4b, a = 10.518 (3) Å, b = 12.782 (3) Å, c = 18.816 (6) Å, α = β = γ = 90°, V = 2530 (1) Å3, Z = 4, ρc = 1.48 g/mL, space group P212121, R = 0.027, Rw = 0.026; for 5a, a = 9.540 (3) Å, b= 10.830 (4) Å, c = 11.932 (3) Å, α = 114.77 (2)°, β = 91.47 (2)°, γ = 91.68 (3)°, V = 1117.8 (6) Å3, Z = 2, ρc = 1.59 g/mL, space group P1, R = 0.045, RW = 0.044; 7a·CH2Cl2 a = 10.039 (4) Å, b = 11.760 (3) Å, c = 12.674 (8) Å, α = 92.21 (4)°, β = 87.35 (4)°, γ = 104.05 (3)°, V = 1449 (1) Å3, Z = 2, ρc = 1.46 g/mL, space group P1, R = 0.038, Rw = 0.038. © 1990, American Chemical Society. All rights reserved.