Synthesis and Reactivity of Low Valent Silicon and Phosphorus Compounds

Abstract

The research described in this thesis is focused on studying the use of phosphinoamidinato ligand NP (NP = [ArNC(Ph)NPiPr2]– (Ar = 2,6-iPr2C6H3)) to stabilize low-valent main group element compounds. Reduction of silane (NP)SiCl3 by magnesium allows for the high-yield preparation of base-stabilized disilylene [(NP)Si-]2. Although it is stable at room temperature, upon heating it rearranges via intermolecular N-P activation into an N,Si-heterocyclic silylene supported by a phosphine donor. The reactivity of [(NP)Si-]2 in the single bond activation of pinacolborane, phenylsilane and diphenylphosphine was tested. Additionally, the phosphidosilylene (NP)SiPPh2 that is formed in the last reaction was found to perform P-P coupling when reacted with diphenylphosphine. Experimental pursuits were taken to elucidate the mechanism of formation of disilylene [(NP)Si-]2, and some insights into its fluxionality in solution were obtained. Disilylene [(NP)Si-]2 was reacted with Si(II) and Ge(II) chlorides to yield the products of tetrylene insertion into the Si-Si bond, the low-valent compounds [(NP)Si-Si(Cl)2-Si(NP)], [(NP)Si(Cl)2Si-Si(NP)] and [(NP)Si(Cl)2Ge-Si(NP)]. Compound [(NP)Si-Si(Cl)2-Si(NP)] is the kinetic product of the direct insertion of SiCl2 fragment into Si-Si bond of [(NP)Si-]2. The thermodynamic product of the insertion of silicon dichloride is disilylene [(NP)Si(Cl)2Si-Si(NP)] that is the consequence of migration of chlorides to terminal Si center. The reaction of [(NP)Si-]2 with GeCl2 produced only one compound [(NP)Si(Cl)2Ge-Si(NP)] that is a rear example of germylene-silylene. Interaction of [(NP)Si-]2 with SiCl4 and SiHCl3 produced a new example of acyclic disilyl silylene. Reduction of (NP)PCl2 with potassium graphite allowed isolation of the base-stabilized phosphinidene (NP)P. Its reactivity was studied. The use of substrates with E-H bonds like pinacolborane, phenylsilane and diphenylphosphine yielded compounds (NP)Bpin (pin = (OC(CH3)2)2) and NPH, (NP)SiH2Ph and NPH, NPH-P-PPh2, respectively, which are the result of N-P and E-H bond metathesis. Upon reaction with tetrachlorobenzoquinone both phosphorus atoms of phosphinidene (NP)P underwent oxidation. (NP)P reacted with benzaldehyde and phenylisocyanate as a phospha-Wittig reagent. Additionally, (NP)P was transformed into phosphinidene oxide (NP)P=O, iminophosphine (NP)P=Np-Tol and phosphinidene sulfide (NP)P=S. Transient (NP)P=O and (NP)P=Np-Tol were captured by para-tolyl isocyanate to form compound (NP)P(N,N-(Np-Tol)2CO). All the compounds were fully characterized by NMR and for most of them single crystal X-ray structure was obtained.