# _inorganics_
## 2 Results and Discussion
### Spectroscopic Features and Trends  
The key NMR spectroscopic data for all compounds 2, 3, 4 and 5, along with 6a and 6d are summarized in Table 1. As one would anticipate, the \(\mathrm{p}\mathrm{z}\mathrm{{}^{Me2}}\) derivatives impart significant shielding to the phosphacarbon \"P\" center, which resonates around 25 ppm to lower frequency than for the \(\mathrm{p}\mathrm{z}\) systems; conversely, the presence of an electron-withdrawing CF\({}_{3}\) substituent leads to appreciable deshielding of this site (\(\Delta\mathrm{\text{$\delta$}_{P}}\)\(\sim\)+20), though this is moderated in the \(\mathrm{p}\mathrm{z}\mathrm{{}^{Me,CF3}}\) derivatives by competitive induction from the methyl. All complexes featuring a methyl substituent proximal to the metal also exhibit additional shielding of one \(\mathrm{P}\mathrm{P}\mathrm{h}_{3}\) ligand (\(\Delta\mathrm{\text{$\delta$}_{P}}\)\(-\)3) compared to their non-alkylated analogues; significantly, the extent of this effect is quantitatively comparable whether the second substituent is methyl or trifluoromethyl, which would imply a localized effect, and also offers further support for the isomeric assignment. The presence of a methyl proximal to the metal also leads to an appreciable decrease in the magnitude of the alkenic C-H coupling constant. This implies reduced \(s\)-character in this linkage, consistent with an increased contribution from \(d_{\pi}\)\(\rightarrow\)\(\pi^{*}_{\text{(CP)}}\) retrodonation (the result of increased electron density at the metal) and thus greater pyramidalization; indeed, this concurs with structural data for 3d (_vide supra_).  
Influence of the pyrazole upon the alkenic carbon center is also apparent, but exhibits a less defined trend; in contrast, the nature of the silyl substituent clearly holds significance, the SiMe\({}_{3}\) derivatives being notably more deshielded than their SiMe\({}_{2}\)Ar analogues, distinctions between the latter being ill defined. This is consistent with \({}^{13}\)C-NMR studies of vinyl- [49] and aryl-silanes [50], for which enhanced deshielding of the \(\alpha\)-carbon follows from increasing methyl substitution at silicon, presumably reflecting the relative \"inductive effect\", given the greater electronegativity of carbon relative to silicon. While carbocentric systems show the reverse shielding trend for the \(\beta\)-center, in the case of 2-6 enhanced deshielding of phosphorus is again noted for the SiMe\({}_{3}\) derivatives. Though the relatively lower electronegativity of phosphorus (_cf._ carbon) might reasonably be invoked in accounting for this disparity, indirect effects via the syneric metal-ligand binding mode (such complexes have not been considered for the carbocentric silanes) cannot be discounted. Indeed, it is noted that analogues of **2** and **3** featuring a _tert_-butyl [29], rather than silyl, substituent exert a significant shielding effect upon the phosphorus center (\(\delta\)p 38.8 (pz); 14.2 (pzMe2)), yet deshield the \(\alpha\)-carbon nucleus (\(\delta\)c 81.6 (pz), 79.8 (pzMe2)) even more effectively than does SiMe\({}_{3}\), which would appear counter-intuitive on the basis of purely electronegativity arguments. The relative contributions of ligand\(\rightarrow\)metal \(\sigma\) donation, and \(d_{\pi}\)\(\rightarrow\)\(\pi\)\({}^{\prime\prime}\)(CP) retrodonation for each center must thus be considered contributory, though inadequate data are currently available to quantify this.