Synthesis and Structural Characterization of Divalent Transition Metal Alkynylamidinate Complexes

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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≡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).