Amine addition to coordinated nitriles in tungsten(II) alkyne complexes

Abstract

Reaction of [Tp[prime](CO)(PhC[triple bond]CR[double prime])W(N[triple bond]CR)]BF[sub 4]RB with NH[sub 2]R[prime] generates cationic amidine complexes of the type [Tp[prime](CO)(PhC[triple bond]CR[double prime])W(NH=C(R)NHR[prime])][BF[sub 4]] (R = Me, R[prime] = H, R[double prime] = Me (1), H (2); R = Me, R[double prime] = Me, R[double prime] = Ph (3), C(CH[sub 3])[sub 3] (4); R[double prime] = H, R[prime] = Ph, R = Me (5), Ph (6)). These reactions reflect net addition of H-NHR[prime] 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[sub 1]/n, Z = 4, with unit cell dimensions of a = 12.919(3) A, b = 18.550(4) A, c = 15.989(4) A, and [beta] = 99.08(2)[degrees]. Refinement of 433 variables over 3974 reflections led to an R value of 3.4% with R[sub w] = 4.7%. Deprotonation of the [alpha]-nitrogen of [Tp[prime](CO)(PhC[triple bond]CH)W(NH=C(Ph)NHPh)][BF[sub 4]] (6) with ammonia results in the formation of a neutral azavinylidene alkyne complex, Tp[prime](CO)(PhC[triple bond]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[prime](CO)(PhC[triple bond]CH)W(N[triple bond]CR)][BF[sub 4]] with either gaseous or aqueous ammonia producesmore » neutral metallocycle complexes of the type Tp[prime](CO)W=C(Ph)-C(H)=H-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) A; W=N, 1.769(8) A). 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. 24 refs., 2 figs., 6 tabs.« less