Mixed Chloride/Amine Complexes of Dimolybdenum(II,II). 3. Preparation, Characterization, and Crystal Structure of Mo₂Cl₄(NH₂R)₄(R = Et, Prⁿ, Bu^t, Cy):  First Quadruply-Bonded Dimolybdenum Compounds with Primary Amine Ligands

Abstract

Four new quadruply-bonded dimolybdenum(II) complexes of the formula Mo 2 Cl 4 (NH 2 R) 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 Mo 2 Cl 6 -(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) Å, b ) 26.639(5) Å, c ) 6.774(2) Å, and Z ) 4; for 3, monoclinic space group P2 1 /c with a ) 19.165(1) Å, b ) 20.858(1) Å, c ) 14.1400(8) Å, β ) 99.002(5)°, and Z ) 8; for 4, tetragonal space group P4 2 2 1 2 with a ) 15.556(4) Å, c ) 6.9368(8) Å, and Z ) 2. All of the non-centrosymmetric molecules 2-4 possess the same structure characterized by a Mo 2 Cl 4 N 4 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) Å, respectively, which are consistent with the Mo-Mo quadruple bond. In addition to the structural data, IR, UVvis, and 1 H 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 MoCl 3 -(NH 2 R) 3 . This has been confirmed by a single-crystal X-ray diffraction study for mer-MoCl 3 (NH 2 Pr n ) 3 ‚ 1 / 6 THF (2a‚ 1 / 6 THF) with the following crystal data: triclinic space group P1 h, a ) 12.370(2) Å, b ) 17.977(2) Å, c ) 25.498(6) Å, R ) 95.32(1)°, β ) 103.21(2)°, γ ) 103.48(1)°, and Z ) 12.

An Electron‐Rich Molybdenum–Molybdenum Quintuple Bond Spanned by One Lithium Atom

“…As illustrated in Scheme 2, two equiv of the lithium amidinate, Li[HC(N-2,6-Et 2 C 6 H 3 )], was added to a mixture of [Mo 2 Cl 6 -(thf) 3 ] and 5 equiv of Zn powder in THF at À35 8C. [14] After Scheme 1. Three possible geometries for quintuply bonded complexes.…”

“…As illustrated in Scheme 2, two equiv of the lithium amidinate, Li[HC(N-2,6-Et 2 C 6 H 3 )], was added to a mixture of [Mo 2 Cl 6 -(thf) 3 ] and 5 equiv of Zn powder in THF at À35 8C. [14] After workup and recrystallization from diethyl ether, the orange diamagnetic trimolybdenum complex [Mo 2 {m-HC(N-2,6- 2) was isolated in 22 % yield. The formulation of 2 was corroborated by single-crystal X-ray diffraction analysis, [15] and its molecular structure is depicted in the Supporting Information, Figure S1.…”

An Electron‐Rich Molybdenum–Molybdenum Quintuple Bond Spanned by One Lithium Atom

“…For example, the groups of Theopold, [6] Tsai, [7] and Kempe [8] reported several type II quintuply bonded Cr 2 and Mo 2 complexes with extremely short metal-metal quintuple bonds spanned by two bidentate nitrogen-based ligands. [14] After Scheme 1. [9] Preliminary reactivity studies on the type II complexes indicate these univalent and low-coordinate dinuclear species are reactive towards unsaturated organic functionalities and small molecules.…”

“…[14] After Scheme 1. As illustrated in Scheme 2, two equiv of the lithium amidinate, Li[HC(N-2,6-Et 2 C 6 H 3 )], was added to a mixture of [Mo 2 Cl 6 -(thf) 3 ] and 5 equiv of Zn powder in THF at À35 8C.…”

“…Selected bond lengths [] and angles [.330(3); N1-Mo1-Mo1A 94.17(6), N2-Mo1-Mo1A 93.80(5), N3-Mo1-Mo1A 92.36(6), N1-Mo1-N2 99.31(8), N2-Mo1-N3 101.56(8), N1-Mo1-N3 157.65(8), Mo1-Li1-Mo1A 45.96(14). Ellipsoids are set at 35 % probability; hydrogen atoms are omitted for clarity.…”