Exploring Chelating Bis-NHC Ligands

1
Exploring Chelating Bis-NHC Ligands Soraya
Sluijter, Kees Elsevier Van t Hoff Institute
for Molecular Sciences, University of Amsterdam,
Science Park 904, 1098 XH Amsterdam S.N.Sluijter_at_
uva.nl
http//www.science.uva.nl/research/molinc/
Introduction N-heterocyclic carbenes (NHCs) are
useful and versatile ligands in transition metal
catalysis. Recently, our group has developed
zero-valent palladium NHC-complexes that show
high activity and selectivity in the transfer
semihydrogenation of alkynes1. In this project
bidentate biscarbenes A, B and C, are explored as
ligands in late transition metals catalysis

• Advantages
• High stability (chelate effect)
• Fine tuning of steric properties fluxional
  behavior
• Increased donating capacity of bis-expanded ring
  NHC (B)
• NHC-MesoIonicCarbene (C) in synergy ? other
  catalytic properties

Catalytic hydrogenation
Synthesis complexes
Preliminary results
A2
Entry Hydrogen source T (0C) Time (h) Conversion () TOF (h-1) Z-/E-alkene/ alkanec
1 HCO2H/NEt3 70 29 18 / 96/1/3
2 H2 60 3 gt99 72c 89/3/8
a Reaction conditions 2.2 mmol substrate, lt1
mol catalyst for entry 1 5 eq. HCO2H/NEt3 for
entry 2 P(H2) 1 bar b Product distributions
as determined by GC after 2 hours. c Turnover
frequency (TOF) is defined as molsubmolcat-1 h-1
after 1,5-2 h.
B3

• Low yield ligand synthesis A
• Convenient synthetic route ligands B
• No reproducible complexation yet for A B via
• Deprotonation with base Pd-precursor
• Transmetallation via Ag-complex

• Conclusions
• Ligands A, B C synthesized in moderate to good
  yields
• Complexation A , B C underway
• Preliminary results in hydrogenation with A
  (complex 1)
• Promising results in hydrogenation excellent
  activity good selectivity
• Moderate activity in transfer hydrogenation, but
  high selectivity
• Outlook
• Complexation (B C) other metals (first row)
• Further investigation of catalytic properties

C1b,4
Acknowledgements
References
1 a) P. Hauwert, G. Maestri, J. W. Sprengers,
M. Catellani, C. J. Elsevier, Angew. Chem. Int.
Ed., 2008, 3223 3226 b) S. Warsink, R. M.
Drost, M. Lutz, A. L. Spek, C. J. Elsevier,
Organometallics, 2010, 3109-3116 2 Y. A.
Wanniarachchi, M. A. Khan, L. M. Slaughter,
Organometallics, 2004, 58815884 3 B. Alici, I.
Özdemir, N. Gürbüz, E. Çetinkaya, B. Çetinkaya,
2005, Heterocycles, 1439-1445 4 R. Lalrempuia,
N. D. McDaniel, H. Müller-Bunz, S. Bernhard, M.
Albrecht, Angew. Chem. Int. Ed., 2010, 9765 9768
We thank NRSCC project 2009-13 for financial
support.