Mixed chloride/amine complexes of dimolybdenum(II,II). 3. Preparation, characterization, and crystal structure of Mo2Cl4(NH2R)4 (R = Et, Prn, But, Cy): First quadruply-bonded dimolybdenum compounds with primary amine ligands

Article abstract of DOI:10.1021/ic981289c

Four new quadruply-bonded dimolybdenum(II) complexes of the formula Mo₂Cl₄(NH₂R)₄ (R = Et (1), Pr_n (2), Bu^t (3), Cy (4)) have been prepared in excellent yield by reduction of the dimolybdenum(III) complex Mo₂Cl₆-(THF)₃ with 2 equiv of sodium amalgam in the presence of the appropriate primary amine. The molecular structures of 2-4 have been investigated by X-ray crystallography. Crystal data are as follows: for 2, orthorhombic space group Ccca with a = 13.328(3) ?, b = 26.639(5) ?, c = 6.774(2) ?, and Z = 4; for 3, monoclinic space group P2₁/c with a = 19.165(1) ?, b = 20.858(1) ?, c = 14.1400(8) ?, β = 99.002(5)°, and Z = 8; for 4, tetragonal space group P4₂2₁2 with a = 15.556(4) ?, c = 6.9368(8) ?, and Z = 2. All of the non-centrosymmetric molecules 2-4 possess the same structure characterized by a Mo₂Cl₄N₄ core with D_2d virtual symmetry and slight deviation from the eclipsed geometry. The Mo-Mo bond lengths for 2, 3, and 4 are 2.118(2), 2.1322(6), and 2.117(1) ?, respectively, which are consistent with the Mo-Mo quadruple bond. In addition to the structural data, IR, UV-vis, and ¹H NMR spectroscopy have been used to characterize the complexes 1-4. Without amalgam, the reactions of the starting material with amines also produce the reduced species but with low yields (not exceeding 25%). The main products of these interactions have been found to be mononuclear molybdenum(III) complexes MoCl₃-(NH₂R)₃. This has been confirmed by a single-crystal X-ray diffraction study for mer-MoCl₃(NH₂Pr_n)₃·1/6THF (2a·1/6THF) with the following crystal data: triclinic space group P1?, a = 12.370(2) ?, b = 17.977(2) ?, c = 25.498(6) ?, α = 95.32(1)°, β= 103.21(2)°, γ = 103.48(1)°, and Z = 12.