Hydridic reactivity of W(CO)(H)(NO)(PMe3)(3) - Dihydrogen bonding and H-2 formation with protic donors

Abstract

The hydridic reactivity of the complex W(CO)(H)(NO)(PMe3)(3) (1) was investigated applying a variety of protic donors. Formation of organyloxide complexes W(CO)(NO)(PMe3)(3)(OR) (R = C6H5 (2), 3,4,5-Me3C6H2 (3), CF3CH2 (4), C6H5CH2 (5), Me (6) and iPr (7)) and H-2 evolution was observed. The reactions of 1 accelerated with increasing acidity of the protic donor: Me2CHOH (pK(a) = 17) < MeOH (pK(a) = 15.5) < C6H5CH2OH (pK(a) = 15) < CF3CH2OH (pK(a) = 12.4) < C6H2Me3OH (pK(a) = 10.6) < C6H5OH (pK(a) = 10). Regioselective hydrogen bonding of 1 was probed with two of the protic donors furnishing equilibrium formation of the dihydrogen bonded complexes ROH center dot center dot center dot HW(CO)(NO)(PMe3)(3) (R = 3,4,5-Me3C6H2, 3a and iPr, 7a) and the O-NO hydrogen bonded species ROH center dot center dot center dot ONW(CO)(H)(PMe3)(3) (R = C6H2Me3, 3b and iPr, 7b) which were studied in hexane and d(8)-toluene solutions using variable temperature IR and NMR spectroscopy. Quantitative IR experiments at low temperatures using 3,4,5-trimethylphenol (TMP) confirmed the two types of competitive equilibria: dihydrogen bonding to give 3a (Delta H-1 = -5.8 +/- 0.4 kcal/mol and Delta S-1 = -15.3 +/- 1.4 e.u.) and hydrogen bonding to give 3b (Delta H-2 = -2.8 +/- 0.1 kcal/mol and Delta S-2 = -5.8 +/- 0.3 e.u.). Additional data for the hydrogen bonded complexes 3a,b and 7a,b were determined via NMR titrations in d(8)-toluene from the equilibrium constants K-(Delta delta) and K-(Delta R1) measuring either changes in the chemical shifts of H-W((Delta delta)) or the excess relaxation rates of H-W (Delta R-1) (3a,b: Delta H-(Delta delta) = -0.8 +/- 0.1 kcal/mol; Delta S-(Delta delta) = -1.4 +/- 0.3 e.u. and Delta H-(Delta R1) = -5.8 +/- 0.4 kcal/mol; Delta S-(Delta R1) = -22.9 +/- 1.9 e.u) (7a,b: Delta H-(Delta delta) = -2.3 +/- 0.2 kcal/mol; Delta S-(Delta delta) = -11.7 +/- 0.9 e.u. and Delta H-(Delta R1) = -2.9 +/- 0.2 kcal/mol; Delta S-(Delta R1) = -14.6 +/- 1.0 e.u). Dihydrogen bonding distances of 1.9 angstrom and 2.1 angstrom were derived for 3a and 7a from the NMR excess relaxation rate measurements of H-W in d(8)-toluene. An X-ray diffraction study was carried out on compound 2. (C) 2009 Elsevier B.V. All rights reserved.