REACTIONS OF COORDINATED DINITROGEN .26. SYNTHESIS, CHARACTERIZATION, AND REACTIONS OF POLYMER-BOUND DINITROGEN COMPLEXES OF MOLYBDENUM

Studies of the reactions of acid with a bis(dinitrogen) complex of molybdenum anchored to a polymer support provide valuable information concerning the mechanism of nitrogen fixation. Two methods have been developed for attaching {Mo(N2)2} to a microreticular resin, PS-diphos, in which -P(Ph)CH2CH2PPh2 (diphos) is covalently bonded to a polystyrene-2% divinylbenzene copolymer, prepared by the reaction of LiP(Ph)CH2CH2PPh2 with chloromethylated (16%) polystyrene. trans-[Mo(N2)2(PS-diphos)(PPh2Me)2] (2) can be prepared either by (i) a phosphine-exchange between PS-diphos and trans-[Mo(N2)2(PPh2Me)4] (1) or (ii) bubbling N2 through a suspension of [MoH4(PS-diphos)(PPh2Me)2] in THF. The latter complex was prepared by reducing MoCl4(PPh2Me)2 with LiBHEt3 in THF in the presence of PS-diphos. Reaction of trans-[Mo(N2)2(PS-diphos)-(PPh2Mc)2] with HBr in THF produced no ammonia whereas reaction of the nonanchored analogue produced significant amounts of ammonia. These data support a hypothesis that ammonia formation occurs as a result of the disproportionation of interacting intermediate hydrazido(2-) (NNH2) complexes: no interaction occurred due to site isolation. A hydrazido(2-) complex of the anchored N2 complex was prepared. Complex 2 reacted with HBr in CH2Cl2 to afford hydrazine but no ammonia, demonstrating that hydrazine is formed at a single metal center. Addition of HBr in THF to a 1:1 mixture of complexes 1 and 2 produced a 33% increase in yield of ammonia/mol of 1. In an analogous experiment with 1 and 2 (15N2 labeled), the presence of 15NH3 (identified as 14N15N and 15N2 when the ammonia formed was oxidized by hypochlorite) indicated that the homogeneous and anchored complexes had interacted, trans-[W(N2)2(PPh2Me)4] was also able to cause 2 to form ammonia in the presence of HBr in THF. The tungsten analogue of 2 was prepared by the phosphine-exchange method, but the loading was not as high. © 1990, American Chemical Society. All rights reserved.