104115-03-9Relevant academic research and scientific papers
Spectroscopic and chemical properties of nitrogen-15-enriched molybdenum dinitrogen complexes trans ,mer-Mo(N2)2(L)(PMePh2)3
Lazarowych, Natalie J.,Morris, Robert H.,Ressner, Joel M.
, p. 3926 - 3932 (2008/10/08)
Grignard Mg reduction of 0.5 equiv of Mo2Cl10 and 4 equiv of PMePh2 in THF at 0°C under 1 atm of N2 gives trans-Mo-(N2)2(PMePh2)4 (1), which is isolated in 82% yield without contamination by Mo(η6-PhPMePh)(PMePh2)3. Substitution of a PMePh2 ligand in 1 by L gives stable complexes trans,mer-Mo(N2)2(L)(PMePh2)3 when L is a phosphorus or nitrogen donor ligand with a Tolman cone angle that falls in the approximate range 100 L 3, PMe3, N-methylimidazole (N-C-H3C3H3N2), pyridine, or 4-Me-, 4-t-Bu-, 3-Me-, 3-C1-, 3-F-, or 3-PPh2-pyridine. The last coordinates only via the nitrogen donor. The substituted pyridine complexes display intense MLCT absorptions. The chelating ligands PPh2(CH2)nSMe (n = 2 or 3) substitute for two PMePh2 ligands to give trans-Mo(N2)2(chelate)(PMePh2)2 complexes. The dinitrogen ligands of these complexes and also of Mo(N2)(η6-PhPPh2)(PPh2(CH 2)2PPh2) exchange with 15N2 gas at 22°C. Force constants kNN are calculated from the IR spectra of the various 14N2/15N2 isotopomers. There is a poor linear correlation (r = 0.85) of kNN with the E1/2ox (Mo(O) ? Mo(I)) values for these and all other N2 complexes of molybdenum(0): kNN = 2.25E1/2ox + 16.75. The kNN value is sensitive to the other ligands in the complex, especially the one trans to N2. Couplings |1J(Nα,Nβ)| as determined by 15N NMR decrease as constants kNN increase for the trans N2 complexes, which implies that this one-bond coupling is negative and that nonbonding s electron density on Nβ is decreasing as the bond strength increases. The 15N NMR spectra show that the N2 ligands in the complexes trans,mer-Mo(N2)2(3-RC5H 4N)(PMePh2)3 (R = Me, F, PPh2) are inequivalent due to hindrance to rotation about the Mo-heterocycle bond as a result of steric crowding and possibly Mo-N(heterocycle) multiple bonding. The A1 mode of ν(N2) is observed in the IR spectra of these complexes because of this reduction in symmetry. Complexes trans,mer-Mo(N2)2(L)-(PMePh2)3, where L = N-CH3C3H3N2, PMePh2, and P(OMe)3, react with H2SO4 in MeOH to give ammonia. The yield of ammonia is highest (0.70 NH3/Mo) for the most reducing complex with L = N-CH3C3H3N2 and lowest for the most electron-poor complex with L = P(OMe)3 (0.22 NH3/Mo) although there is not a linear relationship between the yield of ammonia and kNN or E1/2ox values.
