Synthesis and characterization of aminoborane derivatives of N-silylphosphoranimines

Abstract

A series of novel aminoborane derivatives of N-silylphosphoranimines were prepared by utilizing three reactive sites in N-Silylphosphoranimines. (1) Cleavage of the Si-N bond to eliminate Me$\sb3$SiCl and form the N-B-N=P backbone. (2) Deprotonation at the P-CH$\sb3$ group followed by substitution with a borane functionality to yield N=P-C-B structures. (3) Deprotonation of an aminophosphoranimine followed by treatment with appropriate chloroboranes to afford N=P-N-B compounds.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) In addition to being polymer precursors, some of these compounds exhibited interesting stereochemisty about the B-N bond. For example, in a compound prepared using the first synthetic approach (X = Ph, Y = NMe$\sb2),$ the $\sp1$H NMR spectrum indicated the expected rotational barrier existed about B-N bond. The second synthetic method afforded several new compounds including a novel N=P-C-B (X = Cl, Y = N(SiMe$\sb3)\sb2,$ Z = OCH$\sb2$CF$\sb3$) four-membered ring and bis(C-boryl)-substituted (X = Y = NMe$\sb2$) compounds. The latter showed no hindered rotation about the B-N bonds as a result of the competition between the two nitrogen atoms for the empty p orbital of the boron atom. The other compounds prepared by this method also behaved consistently from the stereochemical point of view. For example, when X = Y = NMe$\sb2,$ a low rotational barrier was observed about the B-N bond, and replacing one of the NMe$\sb2$ groups with Ph enhanced the B-N $\pi$ bond, as demonstrated by $\sp1$H NMR spectroscopy. The third approach yielded a variety of compounds with different substituents on phosphorus, nitrogen and boron atoms, including an analogue with R = Me, R$\sp\prime$ = t-Bu, X = Ph, and Y = OCH$\sb2$CF$\sb3$ which could potentially be a precursor to a hybrid (borazine/phosphazene) polymer upon thermolysis. Another compound with potential as a polymer precursor was prepared where R = Me, R$\sp\prime$ = t-Bu, X = Ph, Y = Cl. However, this compound was not thermally stable toward distillation, due to the presence of the B-Cl bond, and it decomposed to unidentified product(s). Its formation was verified by further reaction with Me$\sb3$SiNMe$\sb2$ which afforded the analogue with X = Ph, Y = NMe$\sb2,$ that was prepared previously using the third synthetic method. Based on the foundation of the work in this dissertation, future studies should ultimately lead to the synthesis of novel BN/PN hybrid polymer systems. (Abstract shortened by UMI.)