Methanetrisamidines in coordination chemistry - syntheses, structures and CH-NH tautomerism

Methanetrisamidines {HC[C(NR)NHR](3)} (R = i-Pr 1a; Ph 1b) were reacted with different metal complexes. Reaction of 1a with NiCl2(H2O)(6) occurred with protonation of 1a and formation of {[C(C(NHi-Pr)(2))(3)](2+)[NiCl4](2-)} 2, whereas the reaction with CuCl gave [C(C(N(i-Pr)CuCl)NHi-Pr)(2)(C(NHi-Pr)(2))] 3. The formation of 2 and 3, which contain the N-H tautomeric form of 1a, occurred with H-migration from carbon to nitrogen. In contrast, reactions of 1b with [M(NCMe)(3)(CO)(3)] (M = Cr, Mo, W) yielded octahedral complexes fac-[M(CO)(3)CH(C(NHPh)NPh)(3)] (M = Cr 4a, Mo 4b, W 4c), in which the C-H tautomeric form is preserved. 1b is a rather strong sigma-donor ligand as was shown by IR spectroscopy. The structures of 2, 3 and 4a were determined by single crystal X-ray diffraction.