Synthesis and Structural Characterization of Divalent Transition Metal Alkynylamidinate Complexes

Abstract

AbstractA 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≡C−C(NR′)2] ⋅ THF (R′=iPr (2), Cy (cyclohexyl) (2)) afforded a series of binuclear complexes of the type M2[c‐C3H5−C≡C−C(NR)2‐κN:κN′]2[c‐C3H5−C≡C−C(NR)2‐κ2N,N′]2 (3: M=Mn, R=Cy; 4 a: M=Fe, R=iPr; 4 b: M=Fe, R=Cy; 5: M=Co, R=iPr) 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 Cr2[c‐C3H5−C≡C−C(NiPr)2‐κN:κN′]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, Cr2(OAc)4, as starting material. Related reactions employing dimolybdenum(II) tetraacetate, Mo2(OAc)4, and 2 or 3 equiv. of 1 afforded the mixed‐ligand paddle wheel‐type complexes trans‐Mo2(OAc‐κO:κO′)2([c‐C3H5−C≡C−C(NiPr)2‐κN:κN′]2 (7) and Mo2(OAc‐κO:κO′)([c‐C3H5−C≡C−C(NiPr)2‐κN:κN′]3 (8). All title compounds were structurally characterized through single‐crystal X‐ray diffraction and spectroscopic techniques (NMR, IR, Raman).