- Calorimetric studies of the heats of protonation of the dangling phosphorus in η1-Ph2PCH2PPh2 complexes of chromium, molybdenum, and tungsten
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Titration calorimetry has been used to determine the heats of protonation (ΔHHP) of M(CO)5(η1-dppm) (M = Cr, Mo, W) and fac-M(CO)3(Ndown curve signN)(η1-dppm) (M = Mo, Ndown curve signN = bipy, phen; M = W, Ndown curve signN = bipy) complexes with CF3SO3H in 1,2-dichloroethane solvent at 25.0°C. Spectroscopic studies show that protonation occurs at the uncoordinated phosphorus atom of the η1-coordinated dppm (Ph2PCH2PPh2) ligand. For dppm, its monoprotonated form (dppmH+), and these complexes, the basicity (ΔHHP) of the dangling phosphorus increases from -14.9 kcal/ mol to -23.1 kcal/mol in the order: dppmH+ 5(η1-dppm) 5(η1-dppm) 5(η1-dppm) 3(η2-bipy)(η1-dppm) 3(η2-phen)(η1-dppm) ≈ fac-W(CO)3(η2-bipy)(η1-dppm). In this series, H+ is more electron-withdrawing than M(CO)5 (M = Cr, Mo, W); Mo(CO)3(η2-phen) and W(CO)3(η2-bipy) actually enhance the basicity of the dangling phosphorus as compared with dppm itself. The basicity (ΔHHM) of fac-W(CO)3(η2-bipy)(PPh2Me), which protonates at the metal center to give a seven-coordinate complex, is -18.8 kcal/mol. Thus, the basicity of the dangling phosphorus atom in fac-W(CO)3(η2-bipy)(η1-dppm) is approximately 4.3 kcal/mol more basic than the metal center.
- Rottink, Mary K.,Angelici, Robert J.
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p. 2421 - 2425
(2008/10/08)
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- Molybdenum tricarbonyl complexes containing unidentate diphosphine. NMR study of fac-mer isomers and crystal structure of fac-Mo(CO)3(η2-phen)(η1-dppm)
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The preparation of Mo(CO)3(η2-NN)(η1-dppm) (NN = 2,2'-bipyridyl (bipy), 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (dmp); dppm = bis(diphenylphosphino)methane) by reactions of Mo(CO)4(η2-NN) with dppm have given a fac isomer or a fac-mer mixture depending on the nature of the NN ligand and on the reaction conditions. 1H, 13C and 31P NMR spectroscopy have been used for the characterization of fac and mer isomers.The X-ray structure of one of the phen derivative shows a fac configuration (monoclinic, P21/c, a 16.843(3), b 11.220(2),c 19.358(4) Angstroem, β 111.72(2) deg, V 3398 Angstroem3, Z = 4).A transformation in solution has been observed for both isomers, and the fac judged to be more stable than the mer isomer.
- Cano, M.,Campo, J. A.,Perez-Garcia, V.,Gutierrez-Puebla, E.,Alvarez-Ibarra, C.
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p. 397 - 406
(2007/10/02)
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