η1:η2-P-Pyrazolylphosphaalkene Complexes of Ruthenium(0)

An extended range of novel ruthenium phosphaalkene complexes of the type [Ru{η-N:η-P,C-P(pz)=CH(SiMe2R)}(CO)(PPh3)2] (R = Tol, C6H4CF3-p; pz = pzMe2, pzCF3, pzMe,CF3; R = Me, C6H4CF3-p; pz = pzPh) have been prepared from the respective ruthenaphosphaalkenyls [Ru{P=CH(SiMe2R)}Cl(CO)(PPh3)2] upon treatment with Lipz. Where R = C6H4CF3-p and pz = pzMe2 the complex is characterized by single crystal X-ray diffraction, only the second example of such species being structurally characterized. This indicates enhanced pyramidalisation of the alkenic carbon center when compared with precedent data (R = Me, pz = pz) implying an enhanced Ru→π*PC contribution, which can be correlated with the greater donor power of pzMe2. This is similarly reflected in spectroscopic data that reveal significant influence of the pyrazolyl substituents upon the phosphaalkene, stronger donors imparting significantly enhanced shielding to phosphorus; in contrast, a much lesser influence if noted for the silyl substituents.