RESUMEN
Reaction of the phenoxytriamine proligands 2,4-dimethyl-6-bis(2-(diethylamino)ethyl)aminomethlyphenol (HL1) and 2,4-di-tert-butyl-6-bis(2-(diethylamino)ethyl)aminomethylphenol (HL2) with Y[N(SiMe2H)2]3(THF)2 in pentane gave the momomeric complexes L1Y[N(SiMe2H)2]2 (1) and L2Y[N(SiMe2H)2]2 (2). X-Ray structural analysis of 2 shows a 5-coordinate yttrium center. The complexes 1 and 2 catalyze the ring opening polymerization of d-l-lactide and epsilon-caprolactone leading to narrow product polydispersities under mild conditions.
RESUMEN
Only one of eight possible diastereomers of the organometallic chiral-at-metal complex [ZrL2(CH2Ph)2] (L = a bidentate, chiral non-racemic pyrdine alcoholate) is observed by NMR spectroscopy in the slow exchange regime.
RESUMEN
Racemic 2,2'-diamino-6,6'-dimethylbiphenyl is resolved using simulated moving bed chromatography, and the absolute configuration of the enantiomers is confirmed via the X-ray crystal structure of a derivative. The diamine is condensed with a range of aldehydes to give bidentate aldimine proligands L. Molecular structures of the complexes formed between L and Cu(I) fall into two classes; bimetallic double helices ([Cu(2)L(2)](2+)) and monometallic ([CuL](+)). The latter are strikingly more efficient in the aziridination of alkenes than are the former in terms of rate, turnover, and enantioselection. In particular, the imine ligand formed from the diamine and 2,6-dichlorobenzaldehyde gives, in combination with Cu(I) or Cu(II), up to 99% ee in the aziridination of 6-acyl-2,2-dimethylchromene and 88-98% ee for a range of cinnamate esters. Styrenic and other alkenes are converted with lower selectivities (5-54%). The catalytic system shows a linear response in product ee to catalyst ee, and the product ee does not vary significantly during the reaction. UV spectrophotometric investigations indicate that conversion of Cu(I) to Cu(II) is not essential for catalysis but that Cu(II) is probably also a competent system.
