Preparation and Properties of Molybdenum and Tungsten Dinitrogen Complexes. 44. Preparation of Molybdenum and Tungstcn Diazoalkane-Aminocarbene Complexes cis,trans-(MX2(NN=CMePh){=C(Me)NHBut}(PMe2Ph)2) (M = Mo, W; X = Cl, Br) from Dinitrogen Complexes cis-(M(N2)2(PMe2Ph)4).