in tetrahydrofuran under Ar, W-complex added to soln. of diphosphine at -65°C, color change to dark yellow, stirred (4 h, -40°C), warmed to 25°C; evapn., extn. (pentane), filtration, evapn., entire yield 14percent, crystn. (THF/Et2O, -30°C); elem. anal.;