Synthesis, molecular structure and chemistry of p-[CoIII(tren)(2-(dihydroxymethyl)glycinato)]ZnCl4.2H2O

Abstract

regions of the molecule; around the benzo moiety and the phenyl group at C5. Separation of the disordered structures was not straightforward since several of the related disordered atoms were located within 0.5 Á of each other. Nonetheless, smooth convergence was eventually realized by constraining corresponding bond lengths to be equal within = 0.005 Á. The phenyl groups were treated as rigid planar groups with C-C bond lengths 1.395 A and internal angle 120°. Only the hydrogen atoms around the nondisordered phenyl group at Cl, which could be readily located on a difference Fourier map, were included in the refinement with fixed coordinates and temperature factors. The occupancy factors of the disordered structures, constrained to add to 1.0, refined to 50% in each region. This value was fixed in the final stages of structural refinement. A unit weighting scheme was found to be adequate.When all the non-hydrogen atoms in the disordered structure were refined with individual temperature factors, the conventional R factor converged to 0.105. Further structural refinement with anisotropic temperature factors for the atoms of the ozonide ring and the phenyl group at Cl, which were not evidently disordered, produced an R factor of 0.092. The final difference Fourier map contained no feature greater than ±0.36 e" A"3.In addition to the tabulated material already mentioned in the main text, tables of thermal vibrational parameters, calculated least-square planes, and observed and calculated structure factor amplitudes for each determination are available as supplementary material.University) for use of computer programs, and the University of Aberdeen Computer Centre for computer time.

Stereoretentive formylation of (S)-proline: new application of the self-regeneration of stereo-centres (SRS) principle via chelation to cobalt(iii)

“…[14][15][16][17] However, in the present study quaternary carbon centres were created, and the products, rac-p-[Co(tren)- their structures verified by X-ray crystallography. [14][15][16][17] However, in the present study quaternary carbon centres were created, and the products, rac-p-[Co(tren)- their structures verified by X-ray crystallography.…”

“…The feasibility of conducting Vilsmeier-Haack-type formylation reactions at the α-C centre of a chelated amino acidate, hitherto only performed at the glycinate methylene group, [14][15][16][17]27 has been expanded to also incorporate the methine groups of chelated alaninate and prolinate.…”

“…[14][15][16][17][18][19][20][21][22][23][24] The α-C centre of this triply-charged complex (19) is activated towards deprotonation to generate enolate intermediate 20, stabilized by conjugation and the lower charge, but with some strain in the bound pyrrolidine ring. 18,23 Nevertheless, the ee value of 85% testifies that chirality is largely retained in this instance.…”

“…Alkylation at the α-C centre of the lithium enolate intermediate 3 to give 4 also proceeded diastereoselectively. [14][15][16][17][18][19][20][21][22][23][24] However, the extent of concomitant activation of the neighbouring amine has not been elucidated. Hydrolytic removal of the auxiliary centre provided 5.…”

“…In general, bidentate coordination of an amino acidate to a cationic metal centre invariably serves to activate both of these centres, with the amine usually the most acidic, primarily due to the direct binding to the metal. 13 However, enhanced activation of the α-C proton(s) of amino acid chelates by acid halide formation has been implicated for a number of cobalt(III) systems in reactions effecting, overall, formylation, [14][15][16][17] oxidative imine formation 18-23 or oxidation 24,25 of the amino acid chelate. These reactions were typically carried out in DMF with POCl 3 , SOCl 2 or PBr 3 as reagents, and were all interpreted as proceeding via initial conversion of the cobalt(III)-bound amino acidate to the derivative acid halide, thus enhancing activation at the α-C centre.…”