Hydridic reactivity of W(CO)(H)(NO)(PMe3)3 – Dihydrogen bonding and H2 formation with protic donors

Abstract The hydridic reactivity of the complex W(CO)(H)(NO)(PMe 3 ) 3 ( 1 ) was investigated applying a variety of protic donors. Formation of organyloxide complexes W(CO)(NO)(PMe 3 ) 3 (OR) (R = C 6 H 5 ( 2 ), 3,4,5-Me 3 C 6 H 2 ( 3 ), CF 3 CH 2 ( 4 ), C 6 H 5 CH 2 ( 5 ), Me ( 6 ) and i Pr ( 7 )) and H 2 evolution was observed. The reactions of 1 accelerated with increasing acidity of the protic donor: Me 2 CHOH (p K a  = 17) K a  = 15.5) 6 H 5 CH 2 OH (p K a  = 15) 3 CH 2 OH (p K a  = 12.4) 6 H 2 Me 3 OH (p K a  = 10.6) 6 H 5 OH (p K a  = 10). Regioselective hydrogen bonding of 1 was probed with two of the protic donors furnishing equilibrium formation of the dihydrogen bonded complexes ROH···HW(CO)(NO)(PMe 3 ) 3 (R = 3,4,5-Me 3 C 6 H 2, 3a and i Pr, 7a ) and the O NO hydrogen bonded species ROH···ONW(CO)(H)(PMe 3 ) 3 (R = C 6 H 2 Me 3, 3b and i Pr, 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 (Δ H 1  = −5.8 ± 0.4 kcal/mol and Δ S 1  = −15.3 ± 1.4 e.u.) and hydrogen bonding to give 3b (Δ H 2  = −2.8 ± 0.1 kcal/mol and Δ 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 (Δ δ ) and K ( Δ R 1 ) measuring either changes in the chemical shifts of H W ( Δ δ ) or the excess relaxation rates of H W (Δ R 1 ) ( 3a,b : Δ H (Δ δ )  = −0.8 ± 0.1 kcal/mol; Δ S (Δ δ )  = −1.4 ± 0.3 e.u. and Δ H ( Δ R 1 )  = −5.8 ± 0.4 kcal/mol; Δ S ( Δ R 1 )  = −22.9 ± 1.9 e.u) ( 7a,b : Δ H (Δ δ )  = −2.3 ± 0.2 kcal/mol; Δ S (Δ δ )  = −11.7 ± 0.9 e.u. and Δ H ( Δ R 1 )  = −2.9 ± 0.2 kcal/mol; Δ S ( Δ R 1 )  = −14.6 ± 1.0 e.u). Dihydrogen bonding distances of 1.9 A and 2.1 A 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 .