W₂Cl₄(NR₂)₂(PR′ ₃)₂ Molecules. 4. a New Synthetic Route to Products with a Staggered Conformation. Preparations and Characterizations of W₂Cl₄(NR₂)₂(PR′ ₃)₂ (R = Et, Bu, Hex; R′₃ = Me₃, Et₂H).

A new and convenient synthetic route to a series of W≡W compounds with the general formula W2Cl4(NR2)2-(PR′ 3)2 has been developed. The method has been used in the preparation of W2Cl4(NR2)2(PMe3) 2 (R = Et (2), Bu (3), Hex (4)) and W2Cl4(NR2)2(PEt2H) 2 (R = Et (5), Bu (6), Hex (7)). Treatment of W2Cl6(THF)4 with the appropriate dialkylamine NHR2 (R = Et, Bu, Hex) affords an intermediate species having the stoichiometry W2Cl4(NR2)2(NHR2) 2. This has been verified by single-crystal X-ray diffraction studies for W2Cl4(NEt2)2(NHEt2) 2 (1) with the following crystallographic parameters: orthorhombic space group Iba2, a = 11.6704(9) Å, b = 13.336(1) Å, c = 17.321(2) Å, Z = 4. The structure of 1 reveals that the molecule itself deviates from an eclipsed conformation with retention of a strong intramolecular N-H⋯Cl hydrogen bonding and the torsion angle involving the hydrogen bonded N and Cl atoms is 27.0°. Each W atom is coordinated by a cis set of two Cl and two N atoms with a W-W distance of 2.3084(5) Å. There is a 1.6% orientational disorder of the W-W unit. Subsequent addition of the monodentate phosphines (PMe3 and PEt2H) to the intermediate complexes produces a variety of new W26+ complexes W2Cl4(NR2)2(PR′ 3)2, 2-7, in reasonable yields, depending on the choices of the amines and phosphines. The characterization of 2-7 has been accomplished using IR and 1H and 31P{1H} NMR spectroscopy and mass spectrometry. The crystal structures of 2, 3, 6, and 7 are fully described. Crystal data for these compounds are as follows: for 2, triclinic space group P1, a =_9.568(2) Å, b = 17.294(7) Å, c = 17.418(5) Å, α = 111.82(3)°, β = 103.11(2)°, γ = 90.72(3)°, Z = 4; for 3, P1, a = 12.162(6) Å, b= 14.955(4) Å, c = 18.82 (1) Å, α = 95.66(3)°, β = 97.99(4)°, γ = 91.26(3)°, Z = 4; for 6, monoclinic space group P21/n, a = 17.970(3) Å, b = 10.993(2) Å, c = 20.689(4) Å, β = 115.43(1)°, Z = 4; for 7, P21/c, a = 15.3937(7) Å, b = 11.473(2) Å, c = 24.977(3) Å, β = 92.33(1)°, Z = 4. The molecular structures of all these phosphine-containing complexes possess a common metal core unit and each entails an essentially staggered W2Cl4N2P2 conformation with the W atoms united by a triple bond (average W-W distance, 2.322 Å). Each molecule adopts a cis configuration with the P and N atoms mutually cis on each W atom, consistent with the stereochemistry of the intermediate species W2Cl4(NR2)2(NHR2) 2 formed in the first step.