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Supramolecular Allosteric Cofacial Porphyrin
ComplexesChristopher G. Oliveri, Nathan C. Gianneschi, SonBinh T.
Nguyen,*,Chad A. Mirkin,*, Charlotte L. Stern, Zdzislaw Wawrzak,and
Maren PinkJ. Am. Chem. Soc. 2007, 128, 16286 - 16296 Speaker
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Allosteric RecognitionChad A. Mirkin et. al. Angew. Chem. Int.
Ed. 2006, 45, 941 944The allosteric-effector-mediated shape change
of a macrocycle.
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Introduction-Porphyrin 93
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Supramolecular Coordination ChemistryHolliday, B. J. et. al.
Angew. Chem. Int. Ed. 2001, 40, 2022-2043.Hydrogen bondingp-p
interactionMetal to ligand bindingvan der Waals forces
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The Directional-Bonding ApproachHolliday, B. J. et. al. Angew.
Chem. Int. Ed. 2001, 40, 2022-2043.
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The Symmetry-Interaction Approach The symmetry-interaction
synthetic strategy has granted researchers access to a variety of
elegant shapes andarchitectures (for example, helicates,
tetrahedra, and adamantoidstructures) through the predictable
coordination chemistry of multibranched chelating ligands with
transition and main group metal centers.Holliday, B. J. et. al.
Angew. Chem. Int. Ed. 2001, 40, 2022-2043.
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The Weak-Link Approach A critical feature of this approach is
that themetals used in the assembly process are available
forfurther reactions without destroying the
supramolecularstructure. This approach targets condensed structures
that contain strategically placed strong(metal-phosphine) and weak
(metal-X) bonds.Mirkin, C. A. Acc. Chem. Res. 2005,38,825-837.
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Catalytic Acyl Transfer by a Cyclic Porphyrin TrimerSanders, J.
K. M. et. al. J. Am. Chem. Soc. 1994,116, 3141-3142.
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Design of Allosteric Porphyrin-Based SupramoleculesPPh2 =
diphenylphosphineMES = 1,3,5-trimethylbenzene
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( i ) 1-bromo-2-chloroethane, K2CO3, Acetone, Reflux( ii)
1,3-propanedithiol, Y(OTf)3 (5 mol %), CH3CN(iii) KPPh2, THF(iv)
S8, THF( v) NaNO2,AcCl/H2O, CH2Cl2, 0 C rtSynthesis of Ether-Based
Ligand 7 and Macrocycles 8a and 8b
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( vi ) 5-mesityldipyrromethane, BF3OEt2, DDQ, NEt3, CHCl3, 4
Molecular Sieves(vii ) Zn(OAc)22H2O, 4:1 CHCl3/MeOH, Reflux(viii)
Cp2ZrHCl, THF, 60 C
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(ix) [Rh(CO)2(Cl)]2, CH2Cl2/THF( x) [Cu(CH3CN)4]PF6,
CH2Cl2/THF
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X-ray crystal structure of 8aDABCO as viewed (A) from the side
and (B) from the topGrayCPinkRh, RedO, YellowCl, GreenP, BlueN,
Light BlueZnZn-Zn distance of 7.09 Rh-Rh distance of 24.85 P-Rh-P
distance of 4.64
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X-ray crystal structure of 8cDABCO as viewed (A) from the side
and (B) from the topZn-Zn distance6.99 Cu-Cu distance22.6
GrayCBrownCu, RedO, YellowCl, GreenP, BlueN, Light BlueZn
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( i ) ClCH2CH2PPh2, Cs2CO3, CH3CN, Reflux( ii) S8, THF(iii)
n-BuLi, DMF, THF, -78 C 5-mesityldipyrromethane, BF3OEt2, DDQ,
NEt3,CHCl3, 4 Molecular SievesSynthesis of Thioether-Based Ligand
13 and Macrocycles 14a-b, 15a-b
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( v ) Zn(OAc)22H2O, 4:1 CHCl3/MeOH, Reflux( vi ) Cp2ZrHCl, THF,
60 C( vii) for 14a: [Rh(NBD)Cl]2, AgBF4, CH2Cl2/THF(viii) for 14b:
[Cu(CH3CN)4]PF6, CH2Cl2/THF
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(ix) for 15a: PPNCl/CO (1 atm)( x) for 15b: C5D5N.
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NMR Data of 14a and 14bChad A. Mirkin et. al. Inorg. Chem. 2000,
39, 3432-3433Comp. 2
31P{1H} NMR (CD2Cl2)64 ppm (d,JRh-P=161 Hz)Comp. 14a
31P{1H} NMR (CD2Cl2)64.5 ppm (d,JRh-P=162 Hz)
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X-ray crystal structure of 15aDABCO as viewed (A) from the side
and (B) from the topGrayCPinkRh, RedO, OrangeS,YellowCl, GreenP,
BlueN, Light BlueZnZn-Zn distance7.02 Rh-Rh distance22.59 P-Rh-P
distance4.60 Dihedral angles17.8
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X-ray crystal structure of 15cDABCO as viewed (A) from the side
and (B) from the topGrayCBrownCu, RedO, YellowCl, GreenP, BlueN,
Light BlueZnZn-Zn distance7.05 Cu-Cu distance22.38
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Acyl transfer reactions catalyzed by a closed macrocycle vs. the
corresponding open macrocycle.
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Formation of 4-(acetoxymethyl)pyridine (4-AMP) plotted as
concentration vs. time for 14a and 15a.
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Formation of 4-(acetoxymethyl)pyridine (4-AMP) plotted as
concentration vs. time for [Zn(TPP) + 16a] and [Zn(TPP) + 16b]
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Catalytic efficiency of 4-PC15a14a = 2115amonomer = 141
14a is probably dynamic when in solution and the observed
catalytic activity may originate from the conformational
flexibility around the S atoms.
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Formation of 3-(acetoxymethyl)pyridine (3-AMP) plotted as
concentration vs. time for 14a and 15a.
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Formation of 3-(acetoxymethyl)pyridine (3-AMP) plotted as
concentration vs. time for [Zn(TPP) + 16a] and [Zn(TPP) + 16b]
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Catalytic efficiency of 3-PCDrop slightly with respect to
4-PC
=> the cavities of 14a and 15a are still flexible enough to
accommodate the change in transition state distance for acyl
transfer from acetylimidazole upon binding.
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Formation of 2-(acetoxymethyl)pyridine (2-AMP) plotted as
concentration vs. time for 14a and 15a.
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Formation of 2-(acetoxymethyl)pyridine (2-AMP) plotted as
concentration vs. time for [Zn(TPP) + 16a] and [Zn(TPP) + 16b]
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Catalytic efficiency of 2-PCDrop significantly with respect to
3-PC and 4-PCSimilar to those observed for the monomer
=> Unfavorable transition state (in comparison to those for
3-PC and 4-PC) for productive acyl transfer.
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ConclusionThey have developed a coordination chemistrybased
synthetic approach for the quantitative preparation of flexible
cofacial porphyrin assemblies in which the porphyrins act as
functional sites within an allosteric framework that istunable via
modulation of peripheral structure control domains.
This capability enables the cofacial porphyrin structuresto act
as allosteric catalysts capable of discriminatingdifferent
substrate combinations and selectively transformingthem into the
desired products.
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Table 1. X-ray Crystallographic Data for 8aDABCO and
15aDABCO
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Table 1. X-ray Crystallographic Data for 8cDABCO and
15cDABCO.
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Homework1. paper15a14bAns
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2. Weak-link approach (WLA)transition metalAnsTransition
metalRh()Pd()1macrocycletransition metald8Rh()d10Cu()d6