40545-00-4Relevant academic research and scientific papers
Calorimetric studies of the heats of protonation of the dangling phosphorus in η1-Ph2PCH2PPh2 complexes of chromium, molybdenum, and tungsten
Rottink, Mary K.,Angelici, Robert J.
, p. 2421 - 2425 (2008/10/08)
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.
