antonio d. brathwaite university of the virgin islands, st thomas, usvi

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, 008022Department of Chemistry, University of Georgia, Athens, GA, 30602

maduncan.myweb.uga.edu/

antonio.brathwaite@uvi.edumaduncan@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(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

s-type forward donation

-type back donation

M+

M+

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

Sequential C2H2 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(C2H2)3+ - Coordination number of three

Sequential C2H2 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

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