Structural diversity and versatility for organoaluminum complexes supported by mono- and di-anionic aminophenolate bidentate ligands

Synthesis and Structural Characterization of Various N,O,N-Chelated Aluminum and Gallium Complexes for the Efficient ROP of Cyclic Esters and Carbonates: How Do Aluminum and Gallium Derivatives Compare ?

“…In the solid state and as determined by X-ray crystallographic studies (Figure ), compound 5 indeed crystallizes as a dimer and may be seen as two κ 3 - N , O , N -{(C 5 H 9 NC 6 H 4 ) 2 O}Al units being linked to one another via two μ-OBn alkoxide units, which results into a pseudo C 2 -symmetric compound (with a pseudo- C 2 axis of symmetry orthogonal to the Al 2 O 2 quadrilateral and going through its center; Figure ), and with both five-coordinate Al centers adopting nearly ideal trigonal-bipyramidal (tbp) geometries (see, in particular, the angle values in Figure ). The Al–N amido and Al–(μ-O) bond distances (average 1.852(5) and 1.868(4) Å, respectively) are within the expected range for these types of bonds. , Overall, the bonding parameters for species 5 are rather normal and, with the exception of its dimeric nature, comparable to those in the Al methyl and amido analogues 2 and 4 . It is noteworthy that the dimeric vs monomeric nature of the Al benzyloxide species 5 vs compounds 2 and 4 further illustrates the known propensity of group 13 alkoxide species to readily aggregate.…”

“…To probe this issue further, high-temperature 19 F NMR studies of species 6 were performed, resulting in the observation of a coalescence of the two CF 3 signals at 50 °C (C 6 D 6 ) with a subsequent sharpening of the single CF 3 resonance as the temperature is further raised (Figures S2 and S3, Supporting Information). These data also allowed an estimation of the free enthalpy of activation of the dynamic process (Δ G ⧧ = 14(1) kcal mol –1 ), a value in line with energy barriers observed for the ring inversion of heteroatom-containing eight-membered rings . The poor stability of derivative 6 overall suggested that such NTf-ligated group 13 metal alkyl compounds may be of limited efficiency in polymerization catalysis and the coordination chemistry of ligand 1c was not extended to Ga(III).…”

Substituent Controlled Synthesis of Dioxidomolybdenum(VI) Complexes of N,N,N’,N’‐Tetrakis(2‐Hydroxyl‐3,5‐Disubstitutedbenzyl)‐1,2‐Diaminoethane, Their Trans‐Metalation to Oxidovanadium(V) Complexes and Biocatalytic Applications

“…Due to the extended and flexible spacer [−(CH 2 ) n , n=5–9] between two sites of coordination functionalities these ligands behave like bis(H 2 ONO) and form binuclear dioxidomolybenum(VI) complexes exclusively [19] . Controlling the spacer and putting different substituents at the phenol may modify the electronic and steric properties of ligands which may alter their binding mode to the metal ion [32,33] . Therefore, it is very likely to design stable mono‐ as well as bi‐nuclear complexes with these multidentate ligands.…”

Bimetallic Aluminum 5,6-Dihydro-7,7-dimethyl quinolin-8-olates as Pro-Initiators for the ROP of ε-CL; Probing the Nuclearity of the Active Initiator

“…Related bimetallic aluminum complexes incorporating two linked iminophenolate units have also been evaluated in the ROP of cyclic esters [19]. The dialkylaluminum aminophenolate complexes B have been shown as effective (pro-)initiators for the ROP of ε-CL and epoxides [20,21,22,23], while their dinuclear analogues showed higher activity [22,23]; good selectivity for the ROP of rac -LA have also been noted for some B -type systems [24]. Other aluminum phenolates such as dialkylaluminum 2-imidazolylphenolates ( C ) and 2-benzoxazole phenolates ( D ) have also been reported as efficient (pro-)initiators for the ROP of rac -lactide and ε-CL [25,26].…”