antonio d. brathwaite university of the virgin islands, st thomas, usvi
DESCRIPTION
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 +TRANSCRIPT
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/
[email protected]@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