Backbone-Substituted β-Ketoimines and Ketoiminate Clusters: Transoid Li2O2 Squares and D2-Symmetric Li4O4 Cubanes. Synthesis, Crystallography and DFT Calculations

Abstract

Abstract:The preparation and crystal structures of four β-ketoimines with bulky aryl nitrogen substituents (2,6-diisopropylphenyl and 2,4,6-trimethylphenyl) and varying degrees of backbone methyl substitution are reported. Backbone substitution "pinches" the chelate ring. Deprotonation with n-butyllithium leads to dimeric Li 2 O 2 clusters, as primary laddered units, with an open transoid geometry as shown by crystal structures of three examples. The coordination sphere of each lithium is completed by one tetrahydrofuran ligand. NMR spectra undertaken in either C 6 D 6 or 1:1 C 6 D 6 /d 8 -THF show free THF in solution and the chemical shifts of ligand methyl groups experience significant ring-shielding which can only occur from aryl rings on adjacent ligands. Both features point to conversion to higher-order aggregates when the THF concentration is reduced. Recrystallization of the materials from hydrocarbon solutions results in secondary laddering as tetrameric Li 4 O 4 clusters with a cuboidal core, three examples of which have been crystallographically characterised. These clusters are relatively insoluble and melt up to 250 • C; a consideration of the solid-state structures indicates that the clusters with 2,6-diisopropylphenyl substituents form very uniform ball-like molecular structures that will only be weakly solvated.

Comprehensive Experimental and Computational Study of η6-Arene Ruthenium(II) and Osmium(II) Complexes Supported by Sulfur Analogues of the β-Diketiminate Ligand

“…Selected δ­( 1 H) and δ­( 13 C) values are provided in Table . For β-ketoiminates and β-diketiminates, δ­(H) of β-H is between 5.0 and 5.5 ppm and δ­(H) N–H is between 11 and 12 ppm. − In contrast, the β-thio- and β-seleno-ketoiminates are strongly deshielded with δ­(H) β-H around 6.35–6.84 ppm, and δ­(H) of N–H is extremely deshielded, i.e., 15.33–15.61 ppm. The similar electronegativity values of S and Se thus imparts greater π-type character to the core atoms of β-thio- or -seleno-ketoiminates.…”

Metal Complexes of Donor‐functionalized Fluorinatedβ‐Ketoiminates – Synthesis, Structure, and CVD Application

“…The formation of trinuclear complexes has been reported for the donor‐functionalized β ‐ketoiminate lithium complex [LiOC(CH 3 )CHC(CH 3 )N(H)CH 2 CH 2 N(CH 3 ) 2 ] 3 ,[19c] which shows slightly elongated Li–O and Li–N bonds. In contrast, dinuclear and tetranuclear lithium β ‐ketoiminate complexes show similar Li–O and Li–N bond lengths compared to 1 and 5 , respectively.…”