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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