(15.VII.Y 1) A thorough IR and 'H-, "C-, ,'P-, '83W-NMR spectroscopic, and X-ray structural study was carried out on complexes of the type trans,trans-[WH(C0)2(NO)(PR3)2], (R = Et, Me, Ph, i-Pro, MeO, and PhO. Linear correlations could be found between Tolman's parameter X and v(CO), v(WH), v(NO), S(13C) (CO), as well as In(k), k being the H/D exchange rate constant for the hydride in CD,OD. The 1J(1"W,3'P), 2J(3'P,'H), and 2J(31P,13C) as well as the 'J('83W,'H) values are related to the electronegativity of the R groups on the phosphorus ligands. This is also indicated by EHT calculations of s-orbital populations of appropiate W model complexes. The X-ray structures of [WH(CO),(NO)(PR,),] (R = Me, Ph, and MeO) were determined. Minor differences were observed in the W-P bond lenghts and in the P-W-P and C-W-C angles. No obvious relationship between X-ray data and spectroscopic parameters could be found. All three structures reveal a bending of both the CO and PR, ligands towards the hydride atom. The total octahedral distortion is remarkably constant (25.6, 29.4, and 27.0" tilt, respectively), although the ligands individually are very different. This is attributed to redistribution of K -electron density between CO and PR, groups toward the central W-atom in the three complexes.Introduction. ~ The correlation of spectral and structural parameters of transitionmetal complexes with the electronic and steric parameters of their ligands on the one hand, and with kinetic and thermodynamic parameters, i.e. reactivity, on the other hand is an important goal in chemistry. A quantization of the electronic and steric parameters of PR, ligands has been achieved by Tolman [2]. The cone angle 0 has been introduced as a measure of the steric requirements, and the frequency of the A, CO mode in [Ni(CO), (PR,)] is now a well-accepted measure ( X ) of the combined electronic 0-donor/ n-acceptor properties of PR, ligands [3]. Recently, a quantitative separation of c and n effects was made by correlating the former with the pK, values of R3PHf [4]. Tolman's parameters have been linearly correlated mainly to CEO stretching frequencies in other transition-metal complexes, but also to I3C-NMR chemical shifts of these carbonyls [5].In our studies on the reactivity of nitrosyl metal hydrides, we recognized that the complex trans, ~~U~~-[WH(CO>,(NO)[P(~-P~O),]~] is remarkably basic, due to the presence of a W-H bond with highly hydridic character [6].This was attributed to the trans-positioned NO ligand, which as a three-electron donor causes a general rise of the SOMO of the metal fragment and a concurrent polarisation of the metal-H bond [6] [7]. To study the cis-influence of the phosphorus ligands on the hydridic character, we set out a thorough spectroscopical and structural
