Synthesis and investigation of platinum-silicon compounds
Description
The synthesis of the platinum hydride complexes (dcpe)PtH$\sb2$ and ((dcpe)Pt($\mu$-H$\sb2$)HPt(dcpe)) $\sp+$ X$\sp-$ (where dcpe = 1,2-bis(dicyclohexylphosphino)ethane and X = OH$\sp-$ or BPh$\sb4\sp-$) was accomplished in high yields via reduction of(dcpe)PtCl$\sb2$ with Na (XB(OMe)$\sb3$) (X = H or D). The platinum complexes (dcpe)Pt(C$\rm \sb2O\sb4$,) and (dcpe)Pt($\rm C\sb4H\sb{11}$)(H) were also synthesized and found to be an excellent source of (dcpe)Pt(0). The X-ray crystal structures of (dcpe)PtCl$\sb2$ and (dcpe)Pt($\rm C\sb2O\sb4$) were determined and illustrate the steric bulk associated with the dcpe ligand Rare examples of mono(hydrosilyl) and bis(hydrosilyl) complexes of platinum have been synthesized and fully characterized from the reaction of low-valent platinum complexes with monosilanes. Direct NMR evidence for an octahedral Pt(IV) intermediate was seen for the reaction of $\rm (Me\sb3Si)\sb2SiH\sb2\ or\ Ph\sb2SiH\sb2\ with\ (dcpe)PtH\sb2\ at\ -80\sp\circ$C. The bis(silyl) complexes of platinum synthesized show significant catalytic activity for both dehydrocoupling and substituent redistribution The reaction of disilane gas with (dcpe)PtH$\sb2$ gave rise to several products, with the relative ratios determined largely by the rate of addition of disilane gas. A slow rate of disilane addition results in the formation of (dcpe)Pt($\mu$-SiH$\sb2$)Pt(dcpe) and (dcpe)Pt(SiH$\sb3)\sb2$. Faster additions result in the formation of (dcpe)Pt(SiH$\sb2$SiH$\sb3)\sb2$ and (dcpe)Pt($\mu$-SiH$\rm\sb2SiH\sb2)\sb2$Pt(dcpe). The most intriguing product formed was (dcpe)Pt(SiH$\sb3)\sb2$ resulting from cleavage of the Si-Si bond. The X-ray crystal structures for (dcpe)Pt($\rm SiH\sb2SiH\sb3)\sb2$, (dcpe)Pt($\mu$-$\rm SiH\sb2SiH\sb2)\sb2)$Pt(dcpe) and (dcpe)Pt($\mu$-SiH$\sb2$)Pt(dcpe) were determined. Monitoring of the reaction of (dcpe)PtH$\sb2$ with the disilanes $\rm H\sb2MeSiSiMeH\sb2$ and $\rm HMe\sb2SiSiMe\sb2H$ between $-80\sp\circ$C and $-25\sp\circ$C by NMR spectroscopy showed the existence of two intermediates, fac-(dcpe)Pt(SiMeRSiMeRH)H$\sb3$ and (dcpe)Pt(SiMeRSiMeRH)(H) (where R = Me or H). No other intermediates were observed. Above $-25\sp\circ$C, the intermediate disilanyl platinum hydride complexes (dcpe)Pt(SiMeRSiMeRH)(H) (where R = Me or H) decompose cleanly to give bis(silyl) complexes. The X-ray crystal structure of (dcpe)Pt(SiMeH$\sb2)\sb2$ was determined Spectroscopic evidence for the rearrangement of the complexes (dcpe)Pt($\rm SiMe\sb2SiMe\sb2R$)(H) (where R = Ph or CD$\sb3$) to give (dcpe)Pt(SiMeRSiMe$\sb3$)(H) via $\alpha$-(silyl) silylene intermediates was given. We also observed that the two complexes are in equilibrium, with the deuteromethyl complex giving a statistical product distribution