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. Brathwaite 1 Timothy B. Ward 2, Richard S. Walters 2 and Michael A. Duncan 2 1 College of Science and Mathematics, University of the Virgin Islands, St Thomas, USVI, Department of Chemistry, University of Georgia, Athens, GA, maduncan.myweb.uga.edu/

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(C 2 H 2 ) 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  -type forward donation  -type back donation M+M+ M+M+

Previous Investigations  Larger complexes to investigate coordination and structures  Previous work showed evidence for an intracluster cyclization in large Ni(C 2 H 2 ) n + complexes Walters, Schleyer, Corminboeuf, Duncan. J. Am. Chem. Soc. 2005, 127, 1100.

Experimental Set Up

Mass Spectrum  Cu(C 2 H 2 ) n + complexes produced by laser ablation in an expansion of 10% acetylene in argon.

Investigation of Coordination Sequential C 2 H 2 ligand elimination terminating at n=3 Ligands coordinated directly to metal are strongly bound Weakly bound external ligands are easily eliminated

Investigation of Coordination Cu(C 2 H 2 ) Coordination number of three Sequential C 2 H 2 ligand elimination terminating at n=3 Ligands coordinated directly to metal are strongly bound Weakly bound external ligands are easily eliminated

What is the meaning of this?

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(C 2 H 2 ) 3 + complex with D 3 symmetry is the fully coordinated species  Three additional C 2 H 2 ligands, bound at bifurcated CH-  binding sites, completes the first solvation sphere  This appealing Cu(C 2 H 2 ) 6 + (3C+3) has with D 3h symmetry  All complexes have IR-active bands that are red-shifted relative to C-H vibrations in acetylene  All Cu(C 2 H 2 ) n + complexes were found to have d 10 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