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 MCl 2 precursors (M=Mn, Fe, Co) with 2 equiv. of the lithium alkynylamidinates Li[ c ‐C 3 H 5 −C≡C−C(NR′) 2 ] ⋅ THF (R′= i Pr (2), Cy (cyclohexyl) ( 2 )) afforded a series of binuclear complexes of the type M 2 [ c ‐C 3 H 5 −C≡C−C(NR) 2 ‐κ N :κ N′ ] 2 [ c ‐C 3 H 5 −C≡C−C(NR) 2 ‐κ 2 N , N′ ] 2 ( 3 : M=Mn, R=Cy; 4 a : M=Fe, R= i Pr; 4 b : M=Fe, R=Cy; 5 : M=Co, R= i Pr) with no significant metal‐metal bonding. In marked contrast, a similar reaction of CrCl 2 with 2 equiv. of 1 afforded the homoleptic dinuclear chromium(II) complex Cr 2 [ c ‐C 3 H 5 −C≡C−C(N i Pr) 2 ‐κ N :κ 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‐κ O :κ O′ ) 2 ([ c ‐C 3 H 5 −C≡C−C(N i Pr) 2 ‐κ N :κ N′ ] 2 ( 7 ) and Mo 2 (OAc‐κ O :κ O′ )([ c ‐C 3 H 5 −C≡C−C(N i Pr) 2 ‐κ N :κ N′ ] 3 ( 8 ). All title compounds were structurally characterized through single‐crystal X‐ray diffraction and spectroscopic techniques (NMR, IR, Raman).