W2Cl4(NHR)(2)(PR'(3))(2) molecules .3. Bidentate phosphine complexes of bis(tert-butylamido)tetrachloroditungsten. Preparation and structural characterization of cis,cis-W2Cl4(NHCMe(3))(2)(L-L) (L-L=dmpm, dmpe, dppm, dppe)

Four new triply-bonded ditungsten complexes of the formula cis,cis-W2Cl4(NHCMe(3))(2)(L-L) (L-L = dmpm (1), dmpe (2), dppm (3), dppe (4)) have been prepared by reaction of W2Cl4(NHCMe(3))(2)(NH(2)CMe(3))(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 P2(1)/n, a = 13.807(1) Angstrom, b = 11.845(2) Angstrom, c = 15.348(1) Angstrom, beta = 109.19(2)degrees, Z = 4; for 2, P2(1)/n, a = 14.144(2) Angstrom, b = 11.991(1) Angstrom, c = 15.662(2) Angstrom, beta = 109.50(1)degrees, Z = 4; for 3 . CH2Cl2, P2(1)/c, a = 18.777(6) Angstrom, b = 10.273(2) Angstrom, c = 21.082(3) Angstrom, beta = 94.11(6)degrees, Z = 4; for 4, P2(1)/n, a = 11.938(1) Angstrom, b = 18.583(3) Angstrom, c = 17.606(2) Angstrom, beta = 106.54(6)degrees, 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) Angstrom, 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) Angstrom is indicative of a W-N double bond having some N --> W pi 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 degrees. 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 degrees; 2, 59.9 degrees; 3 . CH2Cl2, 43.6 degrees; 4, 56.8 degrees). 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(NHCMe(3))(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, P-31{H-1} and H-1 NMR spectroscopy, and mass spectrometry have been used to characterize the complexes.