Nicholas D. R. Barnett

X-ray crystallographic studies and comparative reactivity studies of a sodium diisopropylamide (NDA) complex and related hindered amides

Two related sodium amide complexes derived from secondary amines with bulky organic substituents have been synthesised and crystallographically characterised. Both [(Pr-i)(2)NNa(TMEDA)](2) and [Cy(Pr-i)NNa(TMEDA)](2) adopt dimeric crystal structures with a central, planar (nitrogen-metal)(2) azametallocycle, a now familiar feature in both lithium amide and sodium amide chemistry. TMEDA ligands chelate in their usual bidentate manner making the Na+ cations four-coordinate with a distorted tetrahedral geometry. In the latter complex, the amido substituents are disposed in a trans conformation with respect to the (NNa)(2) ring plane. The deprotonating ability of the former complex has been tested against that of the parent amide [(Pr-i)(2)NNa](infinity) and the lithium congener [(Pr-i)(2)NLi](infinity) (LDA) in a series of simple organic reactions: selective enolate formation from 2-octanone and 2-methylcyclohexanone; synthesis of diphenylacetic acid via diphenylmethane. In general, the performance of the sodium reagents compares favourably with that of the lithium reagent.

Crystallographic characterisation of binary alkali metal alkoxide-magnesium bis(alkyl) mixtures: differential binding of Na^+ and K^+ to a common dinuclear diorganomagnesiate

Relevant to mixtures studied in solution and utilised in styrene polymerisation but hitherto not characterised in the solid, two crystal structures of alkali metal alkoxide-magnesium bis(alkyl) co-complexes have been determined, revealing that in binding to the C2O tripodal face of a common organomagnesiate anion, Na+ prefers O-coordination, whereas K+ prefers C-coordination.

Synthesis and crystal structure of the mixed lithium sodium guanidide [Li4Na2{NC(NMe2)2}6]: A stack of three (metal-nitrogen)2 dimeric rings with additional intramolecular (tertiary amine) nitrogen-lithium coordinations

The tetralithium disodium guanidide [Li4Na2{N=C(NMe2)2}6], crystallized from a 1 : 1 : 2 Bu(n)Li : Bu(n)Na : HN=C(NMe2)2 mixture, has been studied by X-ray crystallography and found to be related to the ketimide [Li4Na2{N=C(Ph)But}6], reported earlier as having a stacked-core of three (metal-nitrogen)2 ring dimers with Li+ and Na+ cations in end rings and the central ring, respectively. However, it also displays a unique feature: intramolecular donor-acceptor interactions which connect dimethylaminonitrogen atoms project from the central ring to Li+ cations in the end rings. Although these interactions are long range (average length 2.304 angstrom, cf. 2.139 angstrom for Li-N core bonds), they still significantly influence the core bonding as evidenced by an analysis of bond lengths and bond angles.

Novel octameric structure of the lithium primary amide [{Bu(t)N(H)Li}(8)] and its implication for the directed synthesis of heterometallic imide cages

The crystalline lithium primary amide derived from tert-butylamine, [{ButN(H)Li}n], is structurally characterised by an X-ray diffraction study and shown to be a novel octameric (n= 8) ladder conformation, the cyclic, ‘double-crown’ nature of which implies molecules of this design could direct the synthesis of heterobimetallic (i.e. lithium and another metal) imide cage constructions.