• Ashoka G Samuelson

      Articles written in Journal of Chemical Sciences

    • Tuning metal-metal distances through ligands

      Santosh P Abraham Ashoka G Samuelson

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      Metal-metal distances in polynuclear metal complexes are often controlled by factors other than favourable metal-metal (M-M) interactions. Recently metal cluster topology has been identified as a major factor in controlling Cu-Cu distances in tetrahedral copper clusters. The more obvious ligand control in M-M distances was shown to play a secondary role. In order to probe ways to tune metal-metal distances in clusters, a study of clusters with similar ligands around the metal has been taken up. Two broad classes were identified: Clusters in which there are two-electron two-centre bonds, and a second class where multicentre multielectron bridging is involved.

      Clusters held together by two-electron two-centre bonds can be analysed fairly effectively using a test electrophile like the proton. This is illustrated by analysing structures available in the literature. The sensitivity of the method to detect M-M interactions will be illustrated with examples from gold clusters where relativistic interactions cause goldd10d10 interactions to be attractive. Among the latter class Cu3P6X2 core makes a specially interesting case study. The capping ligand X determines the extent of Cu-Cu interaction present in the cluster. Simple EHT calculations on the cluster reveal that Cu-Cu reduced overlap populations change significantly with the extent ofπ-donation or acceptance of the ligand.

    • Electronic effects in the insertion reaction of copper(I) aryloxides

      Christina Wycliff Ashoka G Samuelson

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    • Transfer hydrogenation reactions catalyzed by chiral half-sandwich Ruthenium complexes derived from Proline

      ARUN KUMAR PANDIA KUMAR ASHOKA G SAMUELSON

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      Chiral ruthenium half-sandwich complexes were prepared using a chelating diamine made from proline with a phenyl, ethyl, or benzyl group, instead of hydrogen on one of the coordinating arms. Three of these complexes were obtained as single diastereoisomers and their configuration identified by X-ray crystallography. The complexes are recyclable catalysts for the reduction of ketones to chiral alcohols in water. A ruthenium hydride species is identified as the active species by NMR spectroscopy and isotopic labelling experiments.Maximum enantio-selectivity was attained when a phenyl group was directly attached to the primary amine on the diamine ligand derived from proline.

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