Palladium-mediated synthesis of novel meso-chiral porphyrins: cobalt-catalyzed cyclopropanation

Transition Metal Catalysis Controlled by Hydrogen Bonding in the Second Coordination Sphere

Transition metal catalysis is of utmost importance for the development of sustainable processes in academia and industry. The activity and selectivity of metal complexes are typically the result of the interplay between ligand and metal properties. As the ligand can be chemically altered, a large research focus has been on ligand development. More recently, it has been recognized that further control over activity and selectivity can be achieved by using the "second coordination sphere", which can be seen as the region beyond the direct coordination sphere of the metal center. Hydrogen bonds appear to be very useful interactions in this context as they typically have sufficient strength and directionality to exert control of the second coordination sphere, yet hydrogen bonds are typically very dynamic, allowing fast turnover. In this review we have highlighted several key features of hydrogen bonding interactions and have summarized the use of hydrogen bonding to program the second coordination sphere. Such control can be achieved by bridging two ligands that are coordinated to a metal center to effectively lead to supramolecular bidentate ligands. In addition, hydrogen bonding can be used to preorganize a substrate that is coordinated to the metal center. Both strategies lead to catalysts with superior properties in a variety of metal catalyzed transformations, including (asymmetric) hydrogenation, hydroformylation, C-H activation, oxidation, radical-type transformations, and photochemical reactions.

Synthesis and Functionalization of Porphyrins through Organometallic Methodologies

This review focuses on the postfunctionalization of porphyrins and related compounds through catalytic and stoichiometric organometallic methodologies. The employment of organometallic reactions has become common in porphyrin synthesis. Palladium-catalyzed cross-coupling reactions are now standard techniques for constructing carbon-carbon bonds in porphyrin synthesis. In addition, iridium- or palladium-catalyzed direct C-H functionalization of porphyrins is emerging as an efficient way to install various substituents onto porphyrins. Furthermore, the copper-mediated Huisgen cycloaddition reaction has become a frequent strategy to incorporate porphyrin units into functional molecules. The use of these organometallic techniques, along with the traditional porphyrin synthesis, now allows chemists to construct a wide range of highly elaborated and complex porphyrin architectures.

C–C bond forming reactions catalyzed by chiral metalloporphyrins

Porphyrins are abundant in nature facilitating many enzymatic reactions by being present in the active sites of many enzymes. Consequently, over the years, a number of chiral metalloporphyrins have been synthesized and have proved efficient in catalyzing C–C bond forming reactions. Herein, we review the synthesis of chiral metalloporphyrins and their catalytic activity in cyclopropanation, cyclopropenation, and C–H insertion reactions.

Synthetic transformations of porphyrins – Advances 2004-2007

Recent developments in the synthesis and transformation of porphyrins and their derivatives are presented. In connection with the Fifth International Conference on Porphyrins and Phthalocyanines (ICPP-5) a survey of current method developments and reactivity studies is made. The review focuses on synthetic advances in porphyrin chemistry. A brief survey of important developments covers selectively the literature from 2004 to late 2007.

Synthesis and Aggregation Behavior ofmeso-Sulfinylporphyrins: Evaluation of S-Chirality Effects on the Self-Organization to S–Oxo-Tethered Cofacial Porphyrin Dimers

The synthesis and aggregation behavior of meso-sulfinylporphyrins are described. The copper-catalyzed C-S cross-coupling reaction of a meso-iodoporphyrin with benzenethiol and n-octanethiol has proved to be an efficient method for the synthesis of meso-sulfanylporphyrins, which are oxygenated by m-chloroperbenzoic acid to produce the corresponding meso-sulfinylporphyrins. Optically active zinc meso-sulfinylporphyrins were successfully isolated by means of optical resolution of the racemates on a chiral HPLC column. Zinc sulfinylporphyrins readily undergo self-organization through S-oxo-zinc coordination to form cofacial porphyrin dimers in solution, in which the hetero- and homodimers are present as a diastereomeric mixture. The aggregation modes of the S-oxo-tethered porphyrin dimers were fully characterized by 1H NMR, IR, and UV/Vis spectroscopy as well as DFT calculations on their model compounds, thus revealing that the self-aggregation behavior depends on the combination of S chirality. The absolute configurations at the sulfur center can be determined by the exciton-coupled CD method. The observed self-association constant for the S-oxo-tethered dimerization of (S)-phenylsulfinylporphyrin in toluene is larger than that in dichloromethane, which reflects the difference in dipole moments between the homodimer and the monomer. In cyclic and differential pulse voltammetry, the first oxidation process of the cofacial dimers is split into two reversible steps, which indicates that the initially produced pi radical cations are delocalized efficiently between the two porphyrin rings. The present findings demonstrate the potential utility of meso-sulfinyl groups as promising ligands for investigating the effects of peripheral chirality on the structures and optical and electrochemical properties of metal-assisted porphyrin self-assemblies.

Asymmetric cyclopropanation of styrenes catalyzed by metal complexes of D2-symmetrical chiral porphyrin: superiority of cobalt over iron

The cobalt(II) complex of D2-symmetric chiral porphyrin [Co(1)] is an effective catalyst for highly diastereoselective and enantioselective cyclopropanation of a broad range of styrene derivatives under mild conditions. Dimerization of diazo compounds, a common side reaction in metal-mediated carbene transfer processes, is minimized in a cobalt porphyrin-based system, obviating the need to employ excess substrates and slow addition of diazo compounds. The high catalytic activity and selectivity of [Co(1)] evidently resulted from the appropriate combination of the cobalt ion and the chiral porphyrin 1 as the use of iron(III) complex of the same ligand [Fe(1)Cl] afforded the desired cyclopropane products in low yields and poor enantioselectivity.

Synthesis of Novel N-Linked Porphyrin−Phthalocyanine Dyads

[structure: see text] Two types of covalently NH-linked porphyrin-phthalocyanine dyads, connected either through the meso phenyl group or the beta-pyrrolic position of the porphyrin, have been synthesized following statistical condensation methodologies for phthalocyanine preparation and palladium-catalyzed amination methods. Photophysical studies have revealed that energy transfer from the porphyrin to the phthalocyanine prevails regardless of linkage.