Lithium and magnesium complexes by using pyridyl-pendanted unsymmetrical ß-diketiminates: syntheses and application as catalysts for the hydroboration of carbonyl compounds.

The push for environmentally benign and sustainable chemical processes has reinforced the demand to displace transition metals with cheap, nontoxic and naturally abundant metals. To fulfil this requirement, we endeavored to synthesize alkali- and alkaline earth-metal complexes and employ them as catalysts for organic transformations. Two lithium and one magnesium complexes, which are supported by pyridyl-pendanted unsymmetrical ß-diketiminates, have been synthesized and characterized. They are formulated as [Li(L1)]2 (1), [Li(L2)]2 (2) and [Mg(L2)2]·0.5C6H14 (3) (HL1 = N{-4-[(2,6-diisopropylphenylamino)pent-3-en-2-ylidene]-6-methyl}pyridin-2-amine and HL2 = N-{4-[(2,6-diisopropylphenyl)imino]pent-2-en-2-yl}pyridin-2-amine). Complex 1 features two inequivalent Li(I) sites. One Li(I) center exhibits tetrahedral geometry, while the other Li(I) ion adopts a triangular coordination sphere. The catalytic activities of 1-3 toward the hydroboration of aldehydes and ketones by pinacolborane (HBpin) were investigated. Both dinuclear lithium complexes and homoleptic magnesium compound were found to be highly efficient catalysts for the hydroboration of aldehydes and ketones, affording the corresponding borate esters in good yields within a very short time. Synthetic application of the complexes was demonstrated by the gram-scale reduction of ketones via a one-pot two step reaction with only 0.2 mol% loading of 2. Mechanistic details for the hydroboration were revealed by DFT calculations.

Synthesis of Titanium Complexes Supported by Carbinolamide- and Amide-Containing Ligands Derived from Ti(NMe2)4-Mediated Selective Amidations of Carbonyl Groups.

An efficient strategy for the syntheses of a series of titanium complexes has been developed. This protocol features the employment of Ti(NMe2)4 both as the metal center to trigger the deprotonation of the ligands and as an amine source to proceed the amidation reactions of carbonyl functionalities of the ligands. Treatment of Ti(NMe2)4 with a ligand HL1 (HL1 = 2,2'-(((2-hydroxybenzyl)azanediyl)bis(ethane-2,1-diyl))bis(isoindoline-1,3-dione) results in the formation of Ti(L1')(NMe2) (1) (H3L1' = N1-(2-((2-(1-(dimethylamino)-1-hydroxy-3-oxoisoindolin-2-yl)ethyl)(2-hydroxybenzyl)amino)ethyl)-N2,N2-dimethylphthalamide). One important feature regarding the synthesis of 1 is the occurrence of the in situ metal-ligand reaction between Ti(NMe2)4 and HL1, leading to the simultaneous formations of carbinolamide and amide scaffolds. Another prominent feature in terms of the preparation of 1 is the achievement of the selective ring-opening reaction of one of the two phthalimide units of the HL1 ligand, affording carbinolamide and amide functionalities within one ligand set. The developed methodology characterizes an ample substrate scope. The selective amidation reactions of the carbonyl groups have been realized for a series of analogous ligands HL2-HL7. Density functional theory calculations were employed to disclose the mechanisms for the formation of 1-7, and the details for the selective ring-opening reactions of the phthalimide unit were uncovered.