The W2Cl4(NHCMe3)2(PR 3)2 molecules (R 3=Me3, Et3, Pr n 3, Me2Ph) I. Their isomeric forms,interconversion proeesses,crystalline forms,and detailed molecular structures

A thorough study of compounds with the formula W₂Cl₄(NHCMe₃)2(PR₃)₂, withR₃=Me₃, Et₃, Prgⁿ₃ Me₂,Ph, is reported. In addition to the previously reported crystalline compounds, namely Ia,trans-W₂Cl₄(NHCMe₃)₂(PMe₃)₂ in space group Pmmn;3a,trans-W₂Cl₄(NHCM₃)₂(PEt₃)₂ in space group P2₁/^a (or P2₁/^c); and4,cis-W₂Cl₄(NHCMe₃)₂(PMe₂Ph)₂ in Pna2₁, we have obtained and structurally characterized the following new substances,1b,trans-W₂Cl₄,(NHCMe₃)₂(PMe₂)₂, space group P2₁/^c,a= 12.233 (4) Å,b= 12.872 (4) Å,c=17.095 (5) Å,=93.52 (2)°,Z=4,V=2687 (1) ų2,cis-W₂Cl₄(NHCMe₃)₂(PMe₃)₂, P2₁/^c,a=9.673 (4) Å,b=17.249 (4) Å,c=16.244 (5) Å,=99.63 (3),Z = 4 ,V=2669 (1) Å.3b,trans-W₂Cl₄(NHCMe₃)₂(PEt₃)₂, Pl,a=16.850 (3) Å,b=17.797 (3) Å,c= 11.459 (2)Å,= 101.02 (1),= 103.13°, y=84.23 (1)°,Z=4,V= 3279 (1) Å5,trans-W₂Cl₄(NHCM₃)₂(PMe₂Ph)₂, Fdd2,a=39.563 (8) Å at 20°C; 39.325 (10) Å at -6O°C,b = 57.543 (17) Å at 20°C; 57.186 (16) Å at -60°C,c= 8.810 (1) Å at 20°C; 8.770 (1) Å at - 60°C ,Z=24,V=20057 (7) ų (20°C), 19723 (8) ų ( - 60°C) .6,trans-W₂Cl₄(NHCMe₃₂(PPrⁿ₃)₂, Pl,a= 17.287 (2) Å (20°C); 17.077 (5) Å (-60°C),b= 19.119 (2) Å (20°C); 18.952 (6) Å (-60°C),c= 12.713 (1) Å (20°C); 12.668 (4) Å (-60°C),Z=4,V= 3980 (1) ų (20°C), 3898 (2) ,ų ( - 60°C). In addition, the structure of3a was re-determined and refined so that the disorder ratio was a refined parameter, leading to a value of 0.520:0.480 instead of being arbitrarily fixed at 0.50:0.50. In all of the structures the molecules are held in eclipsed (but very distorted) rotational conformations and the W-W distances are all within the range of 2.305-2.330 Å. As will be shown in a later paper, for all phosphines, thecis andtrans isomers are of similar stability and an equilibrium mixture exists in solution. It is also shown that1a and3a do not contain unexpectedly short W-N bonds as previously reported.