Azomethine derivatives of some metals and metalloids

Abstract

This thesis describes the preparation of some methyleneamino derivatives of beryllium, zinc, gallium and silicon. The structural, implications of their infra-red spectra and nuclear magnetic resonance spectra are discussed. As a background to the work, the characteristics of such compounds are discussed in the Introduction, and in greater detail in each chapter. Di-t-butylmethyleneaminolithium reacts with beryllium chloride giving dimeric di-t-butylmethyleneaminoberyllium chloride, (Bu(^t)(_2)C:NBeCl)(_2), and the lithium beryllates Li(_n)Be(N:CBu(^t)(_2))(_2+n) (n = 1,2). Bis(di-t-butylmethyl-eneamino)beryllium, [(Bu(^t)(_2)C:N)(_2)Be](_2) was inaccessible by this route but was prepared by reacting di-t-butylmethyleneamine with di-isobutylberyllium (2:1). The crystal structure of this compound shows that the terminal CNBe unit is nearly linear and that the Be-N bond is relatively short, appropriate for N →Be (p → p) π-bonding. The structure determination supports the postulate that a high azomethine stretching frequency, v(C=N) is indicative of a linear CNBe unit and Be-N multiple bonding. Attempts to prepare adducts with trimethylamine and tetramethylethylene-diamine were unsuccessful. Reaction between methyleneamines and dialkylberylliums afford the derivatives (R(^2)C:NBeR’)(_2) (R = Bu(^2), Ph; R' = Bu(^i) and R = Ph; R' = Bu(^t)). A new monomeric compound, di-t-butylmethyleneamino-bis(trimethylsilyl)-aminoberyllium, Bu(^t)(_2)C:NBeN(SiMe(_3))(_2) was prepared and characterised. Reactions of zinc chloride with one or two moles of di-t-butylmethyl-eneaminolithium give dimeric iminozinc compounds, (Bu(^t)(_2)C:NZnCl)(_2) and [(Bu(^t)(_2)C:N)(_2)Zn](_2). A high azomethine stretching frequency in the latter compound is attributed to significant pπpπ interaction between zinc and nitrogen. Dimethylzinc reacts with one or two moles of di-t-butylmethyl-eneamine giving [(Bu(^t)(_2)CN)(_n)ZnMe(_2-n)])_2) (n = 1,2). Reaction between di-t-butylmethyleneaminolithium and gallium trichloride affords the compounds Li(_n)Ga(N: CBu(^t)(_2))(_3+n) (n = 0,1,2). Bis(di-t-butylmethyleneamino)gallium chloride could not be isolated, presumably through disproportionation to the mono- and tris-derivatives. A high azomethine stretching frequency, v(C=N), for (Bu(^t)(_2)C:N)(_3)Ga, is taken as evidence for a linear C=N-Ga skeleton with appreciable N=Ga π-bonding. The phenyl analogue (Ph(_2)C:N)(_3)Ga was prepared by a similar method. Equimolar proportions of diphenylmethyleneaminolithium and chlorosilanes Me(_n)SiCl(_4-n), (n = 0,1,2) afford the diphenylmethy1eneamino-silanes (Ph(_2)C:N)(_2)-SiM(_n)Cl(_3-n), apparently through disproportionation of the mono-substituted compounds Ph(_2)C:NSiMe(_n)Cl(_3-n), which could only be isolated when n = 2. The spectra of these compounds show that these may have bent C:NSi skeletons. Preliminary investigations into transition metal systems (R(_2)C:N)(_3)M (M = Fe; R = Bu(^t),Ph and M = Cr; R = Bu(^t)) are discussed in an appendix.