W2Cl4(NR2)(2)(PR'(3))(2) molecules .6. New triply-bonded ditungsten complexes with bis(diphenylphosphino) methane or bis(diphenylphosphino) amine as a bridging ligand. Crystal structures of cis,cis-W2Cl4(NR2)(2)(dppm) (R=Et, Bu-n) and W2Cl3(NHCMe3)(2)(NH2CMe3)(PPh2NPOPh2)

The reactions of W2Cl4(NR2)(2)(NHR2)(2) (R = Et, Bu-n) with a stoichiometric amount of bis(diphenylphosphino) methane (dppm) readily resulted in the isolation of two new triply-bonded ditungsten(III) compounds cis,cis-W2Cl4(NR2)(2)(dppm) (R= Et (1), R = Bu-n (2)) in moderate yields. The molecular structures of both compounds have been determined by X-ray crystallography and their crystallographic data are as follows: 1 . CH2Cl2, monoclinic, space group C2/c, a = 38.729(5), b = 11.662(1),c = 19.045(2) Angstrom, beta = 113.57(1)degrees, V = 7884(2) Angstrom(3), Z = 8, R = 0.026, wR(2) = 0.055; 2, monoclinic, space group P2(1)/n, a = 14.4962(5), b = 18.6305(8), c = 17.1667(6) Angstrom, beta = 97.974(4)degrees, V = 4591.4(3) Angstrom(3), Z = 4, R = 0.043, wR(2) = 0.102. Both molecules are characterized by a W-2(6+) core with sigma(2) pi(4) bond of order three and the W-W distances are 2.3350(3) and 2.3463 (4) Angstrom, respectively, for 1 and 2. They entail an essentially staggered rotational geometry and exhibit significant torsion angles in the solid state. Similar procedure has also been used to prepare similar W-2(6+) complexes containing bis(diphenylphosphino) amine (dppa) ligands and complexes of the type W2Cl4(NR2)(2)(dppa) (R = Et (3), R = Bu-n (4)) have been characterized by P-31{H-1} NMR spectroscopy at room temperature. In leading to the reaction pathway of complexes of this kind, the time sequences for the formation of 1 and 2 have been followed by variable temperature P-31{H-1} NMR spectroscopic method. In all cases, the trans,trans-isomers of W2Cl4(NR2)(2)(L-L) (R = Et, Bu-n; L-L = dppm, dppa) are the kinetically favored products while the cis,cis-isomers are the thermodynamic products. The corresponding cis,trans compounds are believed to be the likely intermediate complexes. In the course of a synthetic program directed towards the preparation of a dppa substitution complex of W2Cl4(NHCMe3)(2)(NH2CMe3)(2), an unexpected ditungsten compound W2Cl3(NHCMe3)(2)(NH2CMe3) (PPh2NPOPh2) (5) has been prepared and structurally characterized. Compound 5 crystallizes in the triclinic space group P (1) over bar, a = 11.269(2), b = 12.020(5), c = 18.182(2) Angstrom, alpha = 93.27(1), beta = 89.72(1), gamma = 93.275(2)degrees, V = 2455(1) Angstrom(3), Z = 2, R = 0.068, wR2 = 0.153. The W-W distance in 5 is 2.3030(8) Angstrom and the molecule consists of an anionic bridging ligand [N(OPPh2) PPh2](-), forming a six-membered metallacycle with the ditungsten unit.