Ion pairs of the type Cp x 2 ZrMe + ‚‚‚Acontaining various ansa-zirconocene methyl cations in contact with Me-B(C 6 F 5 ) 3or B(C 6 F 5 ) 4anions have been studied with regard to their anion exchange kinetics by 2D-NMR methods in benzene or toluene solutions. The resultssacceleration of anion exchange by added Li + ‚‚‚Me-B(C 6 F 5 ) 3 -, substantial nonproductive exchange between added and Zr-bound Me-B(C 6 F 5 ) 3anions, an increase of exchange rates at increased zirconocene concentrations, and the exclusively entropic origin of this rate increasesall indicate that anion exchange occurs by way of ion quadruples or higher ionic aggregates, rather than via dissociation to solvent-separated ions. These findings imply that solvent-separated (i.e. anionfree) alkyl zirconocene cations are unlikely to be relevant intermediates in reaction systems containing Cp x 2 ZrMe + ‚‚‚Aion pairs and, hence, also in zirconocene-based catalyst systems for the polymerization of R-olefins.

N,N 0 -Di(S-phenylethyl)-2-amino-4-iminopent-2-ene, S,S-nacnac CH(Me)Ph H, 1a, and N,N 0 -dibenzyl-2amino-4-iminopent-2-ene, nacnac Bn H, 1b, react with ZnEt 2 to form the corresponding nacnacZnEt complexes 2a and 2b. Neither complex is reactive with 2-propanol or methyl lactate to produce the corresponding alkoxide complexes. In reactions with 2b, ligand redistribution occurs and nacnac Bn 2 Zn was obtained. Reaction of 1a and 1b with Zn(N(SiMe 3 ) 2 ) 2 yielded nacnacZnN(SiMe 3 ) 2 , 6a and 6b. From further reactions with 2-propanol nacnacZnOiPr, 7a and 7b, were obtained. Both complexes were catalytically active for polymerization of rac-lactide with apparent first-order rate constants of k app =0.013-0.019 min -1 and 0.019-0.038 min -1 for 7a and 7b, respectively. Obtained polymers were highly heterotactic, with P r =0.84-0.87 (7a) and 0.65-0.71 (7b). Analysis of remaining monomer after 75% conversion showed negligible ee and indicates that chiral 7a does not show enantioselectivity in rac-lactide polymerization. Complex 7a, but not 7b, catalyzes unselective transesterification of the polymer during and after polymerization. PLA microstructures in polymerizations with 7b were independent of temperature (23 or 0 °C) or monomer/catalyst ratio (100:1 to 400:1). However, slightly higher P r values were obtained in the presence of 10-100 equiv of MeCN or pyridine. Complexes nacnac Bn 2 Zn, 2b, 6b, and 7a were characterized by an X-ray diffraction study.

Copper­(II) pyridyliminoarylsulfonate complexes with chloride or triflate counteranions were employed in Chan–Evans–Lam (CEL) couplings of N-nucleophiles and arylboronic acids. The complexes avoided typical side reactions in CEL couplings, and an excess of boronic acid was not required. Water was tolerated, and addition of neither base nor other additives was necessary. Primary amines, acyclic and cyclic secondary amines, anilines, aminophenol, imidazole, pyrazole, and phenyltetrazole can be quantitatively arylated at either 25 or 50 °C with 2.5 mol % of the catalyst. Reaction kinetics were investigated in detail. Kinetic and spectroscopic studies provide evidence for the formation of unproductive copper–substrate complexes. Formation of an aniline–phenylboronic acid adduct was responsible for the zero-order dependence of reaction rates on phenylboronic acid concentration. Kinetic evidence indicates that the order of reaction steps is transmetalation, nucleophile coordination, and oxidation. Couplings performed poorly with electron-deficient arylboronic acids, due to a slower Cu­(II)/Cu­(III) oxidation in the catalytic cycle. Photoredox catalysis partially resolved this problem, but addition of copper acetate as an external oxidant proved to be more efficient.

Ligands in which multiple metal-binding domains are linked by a metal-containing moiety rather than a conventional organic group are described as "expanded ligands". The use of 4,4'-difunctionalised {Ru(tpy)(2)} units provides a linear spacer between metal-binding domains and we have extended this motif to expanded ligands containing two carboxylic acid metal-binding domains. In this paper, we describe the synthesis and structural characterisation of ruthenium(ii) complexes of 2,2':6',2''-terpyridine-4'-carboxylic acid and 4'-carboxyphenyl-2,2':6',2''-terpyridine. The ability of the ruthenium(ii) centre to charge compensate deprotonation of the carboxylic acid leads to Zwitterionic complexes and three representative compounds have been structurally characterised.