W₂Cl₄(NHR)₂(PR′₃) ₃ Molecules. 3. Bidentate Phosphine Complexes of Bis(tert-butylamido)tetrachloroditungsten. Preparation and Structural Characterization of cis,cis-W₂Cl₄(NHCMe₃)₂(L-L) (L-L = dmpm, dmpe, dppm, dppe)

Four new triply-bonded ditungsten complexes of the formula cis,cis-W2Cl4(NHCMe3)2(L-L) (L-L = dmpm (1), dmpe (2), dppm (3), dppe (4)) have been prepared by reaction of W2Cl4(NHCMe3)2(NH 2CMe3)2 with the appropriate bidentate phosphines (L-L) in hydrocarbon solvents. These complexes are the first triply-bonded complexes of the form W2Cl4(NHR)2(L-L) where L-L groups are bidentate phosphines. The molecular structures have been investigated by X-ray crystallography. Crystal data are as follows: for 1, monoclinic space group P21/n, a = 13.807(1) Å, b = 11.835(2) Å, c = 15.348(1) Å, β= 109.19(2)°, Z = 4; for 2, P21/n, a = 14.144(2) Å, b = 11.991(1) Å, c = 15.662(2) Å, β= 109.50(1)°, Z = 4; for 3-CH2Cl2, P21/c, a = 18.777(6) Å, b = 10.273(2) Å, c = 21.082(3) Å, β= 94.11(6)°, Z = 4; for 4, P21/n, a = 11.938(1) Å, b = 18.583(3) Å, c = 17.606(2) Å, β = 106.54(6)°, Z = 4. The W-W bond lengths for 1, 2, 3-CH2Cl2 and 4 are 2.3247(4), 2,3274(5), 2.328(1), and 2.3452(5) Å, respectively, which are consistent with a formal W≡W bond. The W-P and W-Cl distances are similar in all of the complexes reported. The average W-N distance of 1.905(7) Å is indicative of a W-N double bond having some N → W π character. No orientational disorder of the central ditungsten units was observed. While strong N-H⋯Cl hydrogen bonding is retained in these diphosphine complexes, each molecule deviates from an eclipsed geometry with torsion angles involving the hydrogen-bonded N and Cl atoms being in the range 12.8-22.0°. It is also noteworthy that all complexes are highly twisted and display exceptionally large torsional angles for the bridging diphosphines across the W≡W bond (1, 46.2°; 2, 59.9°; 3-CH2Cl2, 43.6°; 4, 56.8°). As far as the stereochemistry of each molecule is concerned, the structure analyses reveal that the final product in each case was the cis,cis isomer of W2Cl4(NHCMe3)2(L-L) with the P and N atoms mutually cis on each W atom. In addition to the structural data for these complexes, IR, 31P{1H} and 1H NMR spectroscopy, and mass spectrometry have been used to characterize the complexes.