Supramolecular Allosteric Cofacial Porphyrin Complexes

Abstract

Nature routinely uses cooperative interactions to regulate cellular activity. For years, chemists have designed synthetic systems that aim toward harnessing the reactivity common to natural biological systems. By learning how to control these interactions in situ, one begins to allow for the preparation of man-made biomimetic systems that can efficiently mimic the interactions found in Nature. To this end, we have designed a synthetic protocol for the preparation of flexible metal-directed supramolecular cofacial porphyrin complexes which are readily obtained in greater than 90% yield through the use of new hemilabile porphyrin ligands with bifunctional ether-phosphine or thioetherphosphine substituents at the 5 and 15 positions on the porphyrin ring. The resulting architectures contain two hemilabile ligand-metal domains (Rh I or Cu I sites) and two cofacially aligned porphyrins (Zn II sites), offering orthogonal functionalities and allowing these multimetallic complexes to exist in two states, "condensed" or "open". Combining the ether-phosphine ligand with the appropriate Rh I or Cu I transition-metal precursors results in "open" macrocyclic products. In contrast, reacting the thioether-phosphine ligand with Rh I or Cu I precursors yields condensed structures that can be converted into their "open" macrocyclic forms via introduction of additional ancillary ligands. The change in cavity size that occurs allows these structures to function as allosteric catalysts for the acyl transfer reaction between X-pyridylcarbinol (where X = 2, 3, or 4) and 1-acetylimidazole. For 3-and 4-pyridylcarbinol, the "open" macrocycle accelerates the acyl transfer reaction more than the condensed analogue and significantly more than the porphyrin monomer. In contrast, an allosteric effect was not observed for 2-pyridylcarbinol, which is expected to be a weaker binder and is unfavorably constrained inside the macrocyclic cavity.

Spontaneous Formation of Heteroligated PtII Complexes with Chelating Hemilabile Ligands

“…Because of the robustness of the Pt complexes with respect to oxygen and moisture and the high selectivity of the rearrangement process, the reaction is expected to become a valuable tool for the "programmed" assembly of complex functional supramolecular structures and allosteric catalysts. [7] The selective reactivity of the complexes with respect to various small molecules suggests potential applications for the development of sensors for small molecules. The interaction of nucleobases as N-donor ligands with respect to hemilabile, homoligated Pt II -P,N complexes [18] indicates that a further extension to biologically relevant analyte molecules may be possible.…”

Oxide‐Bridged Heterobimetallic Aluminum/Zirconium Catalysts for Ethylene Polymerization

“…[1][2][3][4][5][6] Cooperation of two neighboring metals enables attractive new reactivities or physical properties. [7][8][9] Homogeneous olefin polymerization by metallocenes is an interesting playground for such heterobimetallic catalysts: Cp 2 MCl 2 (Cp = C 5 H 5 ; M = Ti, Zr, Hf) type precatalysts are usually activated by a cocatalyst that is generally a compound containing a Lewis acidic boron or aluminum center.…”

“…[31][32][33] These cages [Equation (2)] do not contain highly Lewis acidic low-coordinate Al, but they can activate Cp 2 ZrMe 2 by so-called latent Lewis acidity: two adjoining four-membered rings open to create a three-coordinate Lewis acidic Al site. The reaction product of (tBuAlO) 6 and Cp 2 ZrMe 2 has been characterized by multidimensional NMR spectroscopy [Equation (2)]. (2) Despite studies on self-activating catalysts with built-in Lewis acidic boron functions, [26][27][28][29] only very few approaches towards heterobimetallic Zr/Al catalysts have been reported.…”

Enzymnachbildungen auf der Basis supramolekularer Koordinationschemie

“…[12d, 88,91] Die geschlossene und die offene Rhodium(I)-Zink(II)-Porphyrinstruktur 89 c bzw. 90 c (Abbildung 24) wurden synthetisiert und in Lösung spektroskopisch charakterisiert.…”

“…Zusätzlich wurde für 89 c'DABCO (DABCO = 1,4-Diazabicyclo[2.2.2]octan; das Symbol ' bedeutet Einkapselung) eine Einkristall-Röntgenstrukturanalyse angefertigt, die eine cofaciale Ausrichtung der Porphyrineinheiten mit einer Koordination an beide Stickstoffatome von DABCO zeigt. [88] Die Geschwindigkeit der Acylübertragung von 1-Acetylimidazol (65) [92] katalysieren, nur schwer möglich ist.…”