AMINE ADDITION TO COORDINATED NITRILES IN TUNGSTEN(II) ALKYNE COMPLEXES

Reaction of [Tp'(CO) (PhC=CR'')W(N=CR)][BF4] with NH2R' generates cationic amidine complexes of the type [Tp'(CO) (PhC=CR'')W(NH=C(R)NHR')][BF4] (R = Me, R' = H, R'' = Me (1), H (2); R = Me, R'' = Me, R' = Ph (3), C(CH3)3 (4); R'' = H, R' = Ph, R = Me (5), Ph (6)). These reactions reflect net addition of H-NHR' across the nitrile triple bond. NMR spectra and a single crystal X-ray structure of 2 indicate that the alkyne ligand remains as a four-electron donor. Crystals of 2 belong to the monoclinic space group P2(1)/n, Z = 4, with unit cell dimensions of a = 12.919(3) angstrom, b = 18.550(4) angstrom, c = 15.989(4) angstrom, and beta = 99.08(2)-degrees. Refinement of 433 variables over 3974 reflections led to an R value of 3.4 % with R, = 4.7 %. Deprotonation of the a-nitrogen of [Tp'(CO)(PhC=CH)W(NH=C(Ph)NHPh)][BF4] (6) with ammonia results in the formation of a neutral azavinylidene alkyne complex, Tp'(CO)(PhC=CH)W-N=C(Ph)NHPh (9). NMR spectra of 9 indicate that the alkyne ligand adopts a ''three-electron donor'' role. Reaction of [Tp'(CO)(PhC=CH)W(N=CR)][BF4]with either gaseous or aqueous ammonia produces neutral metallocycle complexes of the type Tp'(CO)W=C(Ph)-C(H)=N-C-(R) = N (R = Me (7), Ph (8)). An X-ray structure of 8 indicates that the six-membered metal-ligand ring is planar. The two metal-ligand bond distances in the ring are surprisingly short (W=C(Ph), 2.08(1) angstrom; W=N, 1.769(8) angtrom). The large W-N-C angle of 146.1(7)-degrees in the ring is compatible with the two-bond tungsten-carbon coupling of 22 Hz here, which characterizes nearly linear W-N-C linkages. Complex 8 crystallized in the monoclinic space group P2(1)/c with unit cell dimensions of a = 12.946(6) angstrom, b = 14.259(5) angstrom, c = 16.476(4) angstrom, and beta = 98.50(3)-degrees, with Z = 4. Refinement of 380 variables over 3293 reflections led to R = 5.0 % and R(w) = 5.4 %.