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Crystal structures of the phosphorus ligand Ph2P-pC6H4-Gly-OMe and two polymorphs of its nitrogen analogue Me2N-pC6H4-Phe-OEt

Crystal structures of the two pseudo-peptides, Ph2P-pC6H4-Gly-OMe (1) and Me2N-pC6H4-Phe-OEt (2), have been determined by single crystal X-ray diffraction. Compound 1 forms supramolecular complex with Rh(I) which is used as hydrogenation catalyst. Analogs of this complex containing chiral amino acids catalyze this reaction enantioselectively. Compound 2, which does not bind metal atoms on the Me2N-group, crystallizes in two polymorphs - monoclinic (2a) and orthorhombic (2b). In both polymorphs, conformation of the molecules is identical. In all three presented structures, intermolecular hydrogen bonds of the amide group induce formation of the one-dimensional structural chains. In the case of 1, these chains are consistent with glide-plane symmetry, while in both polymorphs of 2 the chains are obtained using translation of the molecules. Polymorphs of 2 have a similar C–H···π interactions involving identical C donor atoms from identical phenyl rings. Analogous hydrogen bonds and C–H···π interactions aggregate molecules of 2 into similar two-dimensional structural layers. The distinction between two polymorphs originates from different orientation of neighboring layers stacked in the third spatial dimension: in the monoclinic form these layers have equivalent orientation, while in the orthorhombic form they have opposite orientation.

crystal structure; pseudo-peptides

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