Synthesis and Structural Characterization of Divalent Transition Metal Alkynylamidinate Complexes

A series of new alkynylamidinate complexes of selected first and second row transition metals has been synthesized and fully characterized. Treatment of MCl2 precursors (M=Mn, Fe, Co) with 2 equiv. of the lithium alkynylamidinates Li[c-C3H5-C equivalent to C-C(NR ')(2)] . THF (R ' = Pr-i (2), Cy (cyclohexyl) (2)) afforded a series of binuclear complexes of the type M-2[c-C3H5-C equivalent to C-C(NR)(2)-kappa N:kappa N '](2)[c-C3H5-C equivalent to C-C(NR)(2)-kappa N-2,N '](2) (3: M = Mn, R = Cy; 4 a: M = Fe, R = Pr-i; 4 b: M = Fe, R = Cy; 5: M = Co, R = Pr-i) with no significant metal-metal bonding. In marked contrast, a similar reaction of CrCl2 with 2 equiv. of 1 afforded the homoleptic dinuclear chromium(II) complex Cr-2[c-C3H5-C equivalent to C-C((NPr)-Pr-i)(2)-kappa N:kappa N '](4) (6) which supposedly comprises a Cr-Cr quadruple bond. Complex 6 could also be prepared in a more rational way and in better yield (61 %) by using dichromium(II) tetraacetate, Cr-2(OAc)(4), as starting material. Related reactions employing dimolybdenum(II) tetraacetate, Mo-2(OAc)(4), and 2 or 3 equiv. of 1 afforded the mixed-ligand paddle wheel-type complexes trans-Mo-2(OAc-kappa O:kappa O ')(2)([c-C3H5-C equivalent to C-C((NPr)-Pr-i)(2)-kappa N:kappa N '](2) (7) and Mo-2(OAc-kappa O:kappa O ')([c-C3H5-C equivalent to C-C((NPr)-Pr-i)(2)-kappa N:kappa N '](3) (8). All title compounds were structurally characterized through single-crystal X-ray diffraction and spectroscopic techniques (NMR, IR, Raman).