98702-90-0Relevant academic research and scientific papers
Synthesis, characterization, and reactions of polymer-bound dinitrogen complexes of molybdenum
George, T. Adrian,Kaul, Bharat B.
, p. 4969 - 4974 (2008/10/08)
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)-(PPh2Me)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 hydrazinc 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.
THE INFLUENCE OF THE STERIC PROPERTIES OF THE LIGANDS PR2Ph AND L ON THE FORMATION AND PROPERTIES OF THE COMPLEXES Mo(η6-PhPR2)(L)(PPh2CH2CH2PPh2), R = Et, L = PPhEt2 and R = Ph, L = PPh3, PR'3, CO, CNR, N2, H2
Frizzell, James J.,Luck, Rudy L.,Morris, Robert H.,Peng, Shane H.
, p. 243 - 256 (2007/10/02)
The reduction of MoCl4(DPPE) (DPPE = PPh2CH2CH2PPH2) with Mg or Na/Hg in the presence of 2 PPhR2 under Ar results in the formation of the new complexes Mo(η6-PhPR2)(PPhR2)(DPPE) when R is Ph(Ia) or Et(II).No η6-PhPR2 complex is obtained when R is Me because this small ligand forms strong Mo-P ?-bonds; nor is one obtained for R = Cy because of too much steric crowding.The limits for η6-complexation can be quantified in terms of cone angle sums.Complex Ia is very similar to Mo(η6-PhPMePh)(PMePh2)3 (IIIa) in that both react at similar rates with a variety of small ligands L = PMePh2, PMe2Ph, PMe3, P(OMe)3, N2, CO, CNBut and H2 via dissocation of a labile ?-bonded ligand.Several other less crowded η6-arylphosphinemolybdenum complexes including II do not have labile ligands at 25 degC.The new complexes Mo(η6-PhPPh2)(L)(DPPE) have been characterized by 31P and 1H NMR, IR and gas uptake measurements.Ia has a higher affinity for H2 than IIIa possibly because Mo(η6-PhPPh2)(H)2(DPPE) adopts a non-fluxional trans-configuration.The 31P chemical shift of the η6-bonded ligand in 8 derivatives of Ia and 12 of IIIa correlate with the sum of cone angles of the three ?-bonded ligands in each complex.
