Synthesis, structure and solution studies on mixed aryl/alkyl lithium zincates

Roberts, Andrew J. and Kennedy, Alan R. and McLellan, Ross and Robertson, Stuart D. and Hevia, Eva (2016) Synthesis, structure and solution studies on mixed aryl/alkyl lithium zincates. European Journal of Inorganic Chemistry. pp. 4752-4760. ISSN 1434-1948

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Abstract

Novel homo- and heteroleptic lithium zincates have been prepared by cocomplexation reactions of Zn(CH2SiMe3)2 and PhLi in low-polarity hydrocarbon solvents. X-ray crystallographic studies of products obtained by reacting the organometallic reagents in benzene or toluene yield the novel solvent-free solid-state arrangement [Li4Zn3Ph5(CH2SiMe3)5]⋡ (1). Combining Zn(CH2SiMe3)2 and PhLi in hexane in the presence of the polydentate N-donors PMDETA (N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) or TMEDA (N,N,N′,N′-tetramethylethylenediamine) reveals monomeric heteroleptic [(PMDETA)LiZn(CH2SiMe3)2Ph] (2) and homoleptic [(TMEDA)LiZn(CH2SiMe3)3] (3), the result of a disproportionation process, respectively. NMR spectroscopic studies suggest that 2 and 3 retain their discrete contacted ion-pair solid-state structures in benzene solution. Variable-temperature NMR spectroscopic studies of 2 in [D8]THF reveal a complex equilibrium also including [LiZn(CH2SiMe3)3], [LiZn(CH2SiMe3)Ph2] and [LiZnPh3], an equilibrium process analogous to that of 1 in THF. This study further highlights the complexity of these reactions, which at first would appear simple.