by
Jeremy ZIMBRON
Literature Meeting
November 27th, 2012
Cyclopentadienyl ligands (Cp)
Common anionic ancillary ligand in organometallic chemistry
Ferrocene is the classic cyclopentadienyl compound
Discovered and identified by Woodward, Wilkinson and Fischer in the
1950s1
Wilkinson and Fischer dancing at
the final reception of the
Conference on Organometallic
Chemistry in July 1974 in Ettal
Tigger important developments in modern organometallic chemistry
1.
H. Werner, Angew. Chem. Int. Ed. 2012, 51, 6052-6058.
2
Cyclopentadienyl ligands (Cp)
Present in some of the most active catalysts:
Stereospecific
olefin
polymerization2
Hydroacylation of
olefins with
aromatic aldehydes4
Hydroxylation of
alkanes6
Enantioselective
Diels-Alder3
1.
2.
3.
4.
5.
6.
Enantioselective
C-C and C-H Bond
Formation5
H. Werner, Angew. Chem. Int. Ed. 2012, 51, 6052-6058.
Waymouth et al., Angew. Chem. Int. Ed. 1995, 34, 1143-1170.
F. Viton, G. Bernardinelli and E. P. Kündig, J. Am. Chem. Soc., 2002, 124, 4968
A. D. Bolig, M. Brookhart, J. Am. Chem. Soc. 2007, 129, 14544.
A. H. Hoveyda, J. P. Morken, Angew. Chem. Int. Ed. Engl. 1996, 35, 1262.
M. Zhou, N. D. Schley, R. H. Crabtree, J. Am. Chem. Soc. 2010, 132, 12550.
3
About Cp and Cp* ligands
Inert to both nucleophilic or electrophilic reagents
Strong binding to metal centers
Large array of possible structural modifications of the ligand
In asymmetric catalysis Cp ligands have been bypassed by chiral ligands
Only few examples of chiral Cp inducing enantioselection
A. Gutnov et al., Angew. Chem. Int. Ed. 2004, 43, 3795 and A. Gutnov et al., Organometallics 2004, 23, 1002-1009.
4
Designing chiral Cp metal complexes1
Cyclopentadienyl-derived chirality
Combined metal-centered
and Cp-derived chirality
1. R. L. Halterman. Chem. Rev. 1992, 92, 965-994.
Metal-centered chirality
Mono-bidentate chiral ligands
5
Designing chiral Cp metal complexes1
Cyclopentadienyl-derived chirality
Combined metal-centered
and Cp-derived chirality
Metal-centered chirality
No C2 symmetry in chiral Cp
ligands: form diastereomers
during coordination of the
metal
Separate diastereomeric complexes
1. R. L. Halterman. Chem. Rev. 1992, 92, 965-994.
6
Designing chiral Cp ligand
Ligand features to achieve the required selectivity:
1,2-substituted cyclopentadiene with C2-symmetric Cp derivatives
Provides one
chiral complex
7
Designing chiral Cp ligand
Ligand features to achieve the required selectivity:
1,2-substituted cyclopentadiene with C2-symmetric Cp derivatives
Restriction of rotation around the Cp moiety: a single preferential alignment of substrates
8
Designing chiral Cp ligand
Ligand features to achieve the required selectivity:
1,2-substituted cyclopentadiene with C2-symmetric Cp derivatives
Restriction of rotation around the Cp moiety: a single preferential alignment of substrates
A shield from a remote substituent: direct the approach of the incoming reactant
9
Structure of chiral Cpx*Rh(I) complexes
Different backside shielding from the corresponding C2-symmetric Cp precursors
Relatively air-stable and easy to handle
10
Synthesis of chiral Cpx*Rh(I) complexes
Synthesis of the C2-symmetric cyclopentadienes 13
15-crown-5,
THF
54%
11
Synthesis of chiral Cpx*Rh(I) complexes
12
C–H bond functionalization using Rh catalysts1
Cramer: enantioselective [3+2] cycloaddition2
DTBM-MeOBiphep
imine directing group
1.
2.
G. Song, F. Wang, X. Li, Chem. Soc. Rev. 2012, 41, 3651-3678.
D. N. Tran, N. Cramer, Angew. Chem. Int. Ed. 2011, 50, 11098-11102.
13
C–H bond functionalization using Rh catalysts1
Cramer: enantioselective [3+2] cycloaddition2
C-H functionalization using an oxidizing directing group3,4
• Glorius work3
• Excellent directing group
• Fagnou work4
• Internal oxidant
• Mild conditions
• High functional group
compatibility
1.
2.
3.
4.
G. Song, F. Wang, X. Li, Chem. Soc. Rev. 2012, 41, 3651-3678.
D. N. Tran, N. Cramer, Angew. Chem. Int. Ed. 2011, 50, 11098-11102.
S. Rakshit, C. Grohmann, T. Besset, F. Glorius, J. Am. Chem. Soc. 2011, 133, 2350-2353.
N. Guimond, S. I. Gorelsky, K. Fagnou, J. Am. Chem. Soc. 2011, 133, 6449-6457.
14
Optimization of the asymmetric C-H
functionalization
R
R
15
Optimization of the asymmetric C-H
functionalization
R
R
16
Optimization of the asymmetric C-H
functionalization
R
R
17
Optimization of the asymmetric C-H
functionalization
R
R
18
Optimization of the asymmetric C-H
functionalization
R
R
19
Substrate scope: olefin acceptors
Variety of styrenes are competent reaction partners
20
Substrate scope: olefin acceptors
21
Substrate scope: aryl hydroxamates
22
Presumed catalytic cycle for the cyclization
23
Postulated model for the
stereochemical preference
24
Presumed catalytic cycle for the cyclization
25
Presumed catalytic cycle for the cyclization
7-membered rhodacycle is stabilized with the extra coordination of the carbonyl oxygen of BOC
L. Xu, Q. Zhu, G. Huang, B. Cheng, Y. Xia, J. Org. Chem. 2012, 77, 3017.
26
Presumed catalytic cycle for the cyclization
27
Conclusion
A class of chiral Cpx* analogs with low molecular weight
Desymmetrize a Rh(III)-catalyzed directed C–H bond functionalization
Reaction proceeds under mild conditions and is high yielding and
enantioselective
Unlock the potential of chiral Cp ligands in enantioselective catalysis with
half-sandwich complexes
Asymmetric catalytic amination of alcohols
R. Kawahara, K-i. Fujita, R. Yamaguchi, Adv. Synth. Catal. 2011, 353, 1161–1168.
28
How to induce chirality with Cp complexes?
Coordination of chiral ligands: diamines or phosphines
Chiral, non racemic cyclopentadienyl ligands
Biochemical approach: Cp-complex embedded into a chiral protein environment
Biotinylated Cp complex
Sav protein
29
30
31
Oxidizing Directing Groups in
CH Activation Reactions
Cui and Wu previous work1
Quinoline N-oxides:
directing group and
internal oxidant
Fagnou previous work2
Benzhydroxamic acid:
directing group and
internal oxidant
1.
2.
J. Wu, X. Cui, L. Chen, G. Jiang, Y. Wu, J. Am. Chem. Soc. 2009, 131, 13888.
N. Guimond, C. Gouliaras, K. Fagnou, J. Am. Chem. Soc. 2010, 132, 6908
32