W₂Cl₄(NR₂)₂(PR′₃)₂molecules: 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, Buⁿ).

The reactions of W2Cl4(NR2)2(NHR2)2(R=Et, Bun) 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=Bun(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) Å, β=113.57(1)°, V=7884(2) Å3, Z=8, R=0.026, wR2=0.055; 2, monoclinic, space group P21/n, a=14.4962(5), b=18.6305(8), c=17.1667(6) Å, β=97.974(4)°, V=4591.4(3) Å3, Z=4, R=0.043, wR2=0.102. Both molecules are characterized by a W26+core with a σ2π4bond of order three and the W-W distances are 2.3350(3) and 2.3463(4) Å, 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 W26+complexes containing bis(diphenylphosphino)amine (dppa) ligands and complexes of the type W2Cl4(NR2)2(dppa) (R=Et (3), R=Bun(4)) have been characterized by31P{1H} 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 temperature31P{1H} NMR spectroscopic method. In all cases, the trans,trans-isomers of W2Cl4(NR2)2(L-L) (R=Et, Bun; 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 P1̄, a=11.269(2), b=12.020(5), c=18.182(2) Å, α=93.27(1), β=89.72(1), γ=93.275(2)°, V=2455(1) Å3, Z=2, R=0.068, wR2=0.153. The W-W distance in 5 is 2.3030(8) Å and the molecule consists of an anionic bridging ligand [N(OPPh2)PPh2]-, forming a six-membered metallacycle with the ditungsten unit.