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Antonio D. Brathwaite University of the Virgin Islands, St Thomas, USVI Cation-π and CH-π Interactions in the Coordination and Solvation of Cu+(acetylene)n Complexes Antonio D. Brathwaite1 Timothy B. Ward2, Richard S. Walters2 and Michael A. Duncan2 1College of Science and Mathematics, University of the Virgin Islands, St Thomas, USVI, 00802 2Department of Chemistry, University of Georgia, Athens, GA, 30602 maduncan.myweb.uga.edu/ [email protected] [email protected] Transition metal- Complexes • Play an important role in catalysis – Intermediates in alkene polymerization reactions catalyzed by Ziegler-Natta catalysts – Intermediates in alkene hydrogenation reactions catalyzed by Wilkinson’s catalyst • Prototypical models for bonding in organometallic chemistry – Transition metal – benzene – Transition metal – ethylene – Transition metal – acetylene • Identification of reactive species • We use mass spectrometry, IR spectroscopy and DFT to investigate the structure, coordination and bonding interactions of Cu(C2H2)n+ Transition Metal- Bonding Dewar-Chatt-Duncanson complexation model Ligands donate electron density from their HOMO into σ –type d orbitals on the metal Metals donate electrons from -symmetry d orbitals into the antibonding * orbitals on ligands Combined effect weakens the C-C bond as well as the C-H bonds Results in red-shifted C-H stretching frequencies M+ s-type forward donation M+ -type back donation Previous Investigations Larger complexes to investigate coordination and structures Previous work showed evidence for an intracluster cyclization in large Ni(C2H2)n+ complexes Walters, Schleyer, Corminboeuf, Duncan. J. Am. Chem. Soc. 2005, 127, 1100. Experimental Set Up Mass Spectrum Cu(C2H2)n+ complexes produced by laser ablation in an expansion of 10% acetylene in argon. Investigation of Coordination Weakly bound external ligands are easily eliminated Ligands coordinated directly to metal are strongly bound Sequential C2H2 ligand elimination terminating at n=3 Investigation of Coordination Weakly bound external ligands are easily eliminated Ligands coordinated directly to metal are strongly bound Sequential C2H2 ligand elimination terminating at n=3 Cu(C2H2)3+ - Coordination number of three What is the meaning of this? Comparison to theory B3LYP/Wachters+f Comparison to theory B3LYP/Wachters+f Comparison to theory B3LYP/Wachters+f Comparison to theory B3LYP/Wachters+f core free symmetric stretch core free asymmetric stretch single donor in-phase symmetric stretch external asymmetric stretch single donor out-of-phase symmetric stretch core free symmetric stretch core free asymmetric stretch double donor asymmetric stretch single donor in-phase symmetric stretch external asymmetric stretch single donor out-of-phase symmetric stretch core free symmetric stretch core free asymmetric stretch double donor asymmetric stretch single donor in-phase symmetric stretch external asymmetric stretch single donor out-of-phase symmetric stretch core free symmetric stretch core free asymmetric stretch Conclusion The Cu(C2H2)3+ complex with D3 symmetry is the fully coordinated species Three additional C2H2 ligands, bound at bifurcated CH- binding sites, completes the first solvation sphere This appealing Cu(C2H2)6+ (3C+3) has with D3h symmetry All complexes have IR-active bands that are red-shifted relative to C-H vibrations in acetylene All Cu(C2H2)n+ complexes were found to have d10 singlet ground states DFT is effective at unravelling the complex IR spectra of these species Acknowledgements • Prof. Michael Duncan • Tim Ward • Richard Walters • Members of the Johnson lab