Alkylideneamino derivatives of some main group elements

Abstract

This thesis describes the preparation of some alkylideneamino derivatives containing groups R(_2)C:N-attached to lithium, boron, aluminium, gallium, silicon and phosphorus, compounds which were prepared with the object of finding model systems for the study of dative N=M-bonding between nitrogen and these elements. Systems in which R = (^t)Bu proved particularly apt for this purpose. The new compounds di-t-butylmethyleneamine, (^t)BU(_2)C:NH, and its N-lithio and N-trimethylsilyl derivatives, (^t)BU(_2)C:NLi and (^t)Bu(_2)C:NSiMe(_3), were prepared (Chapter I) and used to synthesise di-t-butylmethyleneamino-boranes (Chapter III), -alanes (Chapter IV) and -silanes (Chapter VI), The infrared and (^1)H n.m.r. spectra of the boranes ((^t)Bu(_2)C:N)(_x)BX(_3-x) were consistent with allene-like geometries for these compounds, with the linear C=N=tB skeletons appropriate for significant (p → p) π-interaction between nitrogen and boron. Similar (p →p) and also (p →d) N=Al it-interactions were detected spectroscopically in 3- and 4-co-ordinate aluminium derivatives, and (p →d) N Si n-bonding was apparently indicated by the spectra of some di-t-butylmethyleneaminosilanes, (^t)Bu(_2)C:NSiR(_n)Cl(_3-n). Such interactions have subsequently been confirmed by X-ray crystallographic work on one boron and one aluminium compound. Studies on tetramethylguanidine adducts, (Me(_2)N)(_2)C:NH,AlX(_3) and on derivatives [(Me(_2)N)(_2)C:NAlX(_2)](_2) (X = Et, CI) (Chapter V) showed them to contain only single Al-N bonds, and apparently four-co-ordinate aluminium in each case. The spectroscopic effects of co-ordination of either a proton or boron trifluoride to various alkylideneamines R(^1)R(^2)C:NH, needed as reference systems for interpreting the spectra of derivatives R(^1)R(^2)C:NMX(_n), are described in Chapter II.