Decomposition of electron-excited molecules of molybdenum and tungsten phosphine hydride and phosphine nitrogen complexes

Abstract

The kinetics and mechanism of photodehydrogenation of the phosphine hydride complexes MH 4 L 4 (M = Mo, W; L are phosphine ligands) and the formation of coordinatively unsaturated species ML 4 were studied by the absorbance of long wavelength bands with λ max at 450-460 nm appeared in the absorption spectra of the photoproducts. The rate constants of the reactions of the coordinatively unsaturated M(DPPE) 2 species (M = Mo, W; DPPE = Ph 2 PCH 2 CH 2 PPh 2 ) with molecular nitrogen in benzene were determined (k W = 200 s -1 , k Mo = 8700 s -1 ).

Detection of Unusual Reaction Intermediates during the Conversion of W(N2)2(dppe)2 to W(H)4(dppe)2 and of H2O into H2

“…Computed binding enthalpies for the first and second N 2 ligands of 1m are 214 and 129 kJ mol –1 , respectively. This is consistent with the experimental observation that the rate of binding of the second N 2 ligand occurs much slower than that of the first . Furthermore, when coupled with the relative thermodynamic instability of the N 2 ortho -metalation product, an explanation emerges for why no net photochemistry is observed for 1 in the absence of H 2 .…”

“…It has previously been reported that UV irradiation of W(H) 4 (dppe-κ 2 P ) 2 under N 2 leads to low yields of ammonia and alkene hydrogenation. It has also been reported that H 2 loss corresponds to the main photochemical process in such systems. , Here we have demonstrated that W(H) 6 (dppe-κ 2 P )(dppe-κ 1 P ) ( 4 ) is formed under UV irradiation which suggests that 16-electron W(H) 4 (dppe-κ 2 P )(dppe-κ 1 P ) and not W(H) 2 (dppe-κ 2 P ) 2 is responsible for these conversions.…”