Synthesis, Structure, and Reactivity of β-Diketiminato Aluminum Complexes

Abstract

The preparation and reaction chemistry of β-diketiminato aluminum complexes are described. (TTP)AlCl2 (1) (TTPH = 2-(p-tolylamino)-4-(p-tolylimino)-2-pentene) is formed by the treatment of AlCl3 with LiTTP. Sequential alkylation of 1 with CH3Li results in the formation of the mono- and dimethyl aluminum complexes (TTP)AlMeCl (2) and (TTP)AlMe2 (3), respectively. Only monoalkyl complexes are produced when more hindered alkyllithium reagents are used. Compounds 2 and 3 are more conveniently prepared by treating Al(CH3)3 with TTPH·HCl and TTPH, respectively. The more sterically hindered β-diketimine ligand 2-((2,6-diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pentene (DDPH) also reacts smoothly with Al(CH3)3 to yield (DDP)Al(CH3)2 (4). Compound 3 undergoes methyl abstraction reactions upon addition of B(C6F5)3 or AgOTf. Cationic species formed from 3 and B(C6F5)3 are unstable and decompose to (TTP)Al(CH3)(C6F5) and MeB(C6F5)2. In contrast, (TTP)Al(CH3)(OTf) (6) is thermally stable, but the triflate group is surprisingly inert toward displacement by Lewis bases. Compounds 1, 3, 4, and 6 were crystallographically characterized. The structures all indicate that the β-diketiminato backbone is essentially planar. The pseudotetrahedral aluminum center is displaced from the plane formed by the ligand backbone in 4 by 0.72 Å.

Paramagnetic aluminium β-diketiminate

“…11 A 55 survey of the published data revealed that a straightforward metathetical reaction between the lithiated ligand 1 and group 13 halides fails to proceed beyond 1:1 stoichiometry. 12 Taking into account the scarcity of published works on spirocyclic complexes of the NacNac ligand with group 13 60 elements, we turned our attention to computational pre-screening of 3-6 in order to determine the best possible candidates for synthesis (Electronic Supporting Information, ESI). Geometry optimizations and subsequent frequency analyses carried out using density functional theory (DFT) revealed that the majority 65 of the investigated systems are stable minima on the potential energy hypersurface, thereby confirming their viability as synthetic targets.…”

A New Entry into Aluminum Chemistry: [L1AlMe]⋅THF, a Versatile Building Block for Bimetallic and Polymetallic Complexes

“…The zinccarbon bond lengths average to 1.978 and the average aluminum-methyl bond lengths (Al À C 1.972 , Al À C 1.9675 ) are comparable to those reported for [LAlMe 2 ] (Al À C1 1.955(4) , Al À C2 1.961(3) ). [12] Complex 5 is soluble in various aromatic and polar solvents. …”

Aluminium Complexes of a Phenoxyimine Ligand with a Pendant Imidazolium Moiety: Synthesis, Characterisation and Evidence for Hydrogen Bonding in Solution

“…The 1 H NMR spectrum exhibited a triplet at δ = 0.05 ppm (J HF = 1.4 Hz) characteristic of an Al-Me resonance coupled to the α-fluorines of a coordinated C 6 F 5 group. [17] The resonances of the phim fragment were generally shifted downfield with respect to the relative resonances of the precursor 1. Two quintets in the same 1 H NMR spectrum at 1.33 and 0.96 ppm indicated the presence of MeB(C 6 F 5 ) 2 and Me 2 B(C 6 F 5 ) in a 4:1 molar ratio.…”

“…Treatment of dialkylaluminium complexes bearing bidentate N,N-or N,O-ligands with B(C 6 F 5 ) 3 leads to unstable tricoordinate alkylaluminium cations, which react quite rapidly by abstracting a C 6 F 5 group from the MeB-(C 6 F 5 ) 3 -anion to form neutral LnAlR(C 6 F 5 ) products. [17] Several studies have shown that the presence of a Lewis base (L 1 ) can stabilise the aluminium cation through the formation of {LX}Al(R)(L 1 ) + adducts. [18] Gibson et al showed that a pendant donor group that in the neutral aluminium complexes is weakly bonding or nonbonding becomes a normal donor group in the cationic derivatives upon treatment with B(C 6 F 5 ) 3 , thus stabilising these species.…”