Control of Selectivity in Homogeneous Catalysis through Noncovalent Interactions

Abstract

The regio-, site-, stereo-or chemoselective homogeneous catalytic transformations are extremely important for the growth/success of the current chemical industry. Based on empirical, theoretical or intuitive knowledge, several synthetic strategies, such as ligand design, transient directing group, metal node alternation, metal-ligand cooperation, pore decoration, biomimetic, have already been developed for the selective functionalization of organic substrates. In comparison to the other tactics, the use of noncovalent interactions for the control of selectivity in catalytic transformations of organic compounds may avoid multi-steps, reduce time of synthetic procedure, decrease cost of operation, and increase reactivity of catalyst. In fact, enzymes achieve a high selectivity through noncovalent interactions in biochemical processes in Nature. Guided by the impressive performance of enzymes in biosynthesis and biodegradation reactions, various types of synthetic metal complex or organocatalysts have already been developed, in which the catalyst-substrate noncovalent interactions have a pivotal impact on the distinctive stabilization of the transition states or intermediates, directing selectivity and improving efficiency of homogeneous catalytic reactions. Herein, we highlight several recent and relevant examples of selectivity directing/driving function of noncovalent interactions in the transformation of organic substrate(s) catalyzed by both organocatalysts and metal complex catalysts.

A Family of Cagelike Mn-Silsesquioxane/Bathophenanthroline Complexes: Synthesis, Structure, and Catalytic and Antifungal Activity

“…100 Nevertheless, there are examples of more active Mn catalytic systems, namely based on a Mn(III) meso-tetrakis(2,3dichlorophenyl)porphyrin 101 and a Schiff complex of Mn grafted on a quaternary ammonium salt into SBA-15. 102 The reaction mechanism is expected to be similar to that proposed in previous Mn-catalyzed reports: 97−100 i) the oxygen atom of the epoxide coordinates to a Mn center in 3 to form an intermediate (I in Scheme 4); ii) this activated epoxide ring is attacked by the nucleophilic Br − of TBABr on the β-carbon of the substrate, thereby opening the epoxy ring and generating an anionic intermediate of bromoalkoxide (II in Scheme 4); and iii) the postulated negative charge assisted tetrel bonding 103 interaction of CO 2 with this anionic intermediate leads to a carbonate anion intermediate (III), which forms the cyclic carbonate product through an intramolecular ring closure with elimination of the Br − anion and regeneration of catalyst 3 (Scheme 4).…”

Halogen Bonding in the Decoration of Secondary Coordination Sphere of Zinc(II) and Cadmium(II) Complexes: Catalytic Application in Cycloaddition Reaction of CO2 with Epoxides

“…41 For example, due to the high directionality, these weak forces have been employed as selectivity directing tools in homogeneous catalysis. 42 The application of halogen bonded metal complexes as catalysts in the reaction of CO 2 with epoxides had not yet been reported, whereas there are only two examples of the halogen bond involved organocatalytic version of this reaction. 43,44 Considering all the above points, in this work, we focused on the following aims: (i) to design the secondary coordination sphere of new Zn(II)-arylhydrazone complexes with hydrogen bond and halogen bond donor centers (Schemes 1 and 2); (ii) to study the influence of methylene active fragments (comparing acetylacetone with barbituric acid, see Scheme 1), halogens (comparing isophthalic and 2,4,6-triiodoisophthalic fragments in arylhydrazone ligands, see Scheme 1) and metal centers (comparing Zn with Cd, see Scheme 2) on Zn(II)-or Cd(II)-catalyzed cycloaddition of CO 2 with epoxides. )…”

Chalcogen Bonding in the Decoration of the Secondary Coordination Sphere of Copper(II) Complexes: Activation of Nitriles, the Auxiliary Ligand Substituent Effect

“…Similarly to the function of metalloenzymes in biochemical processes, the environment beyond the primary coordination sphere of metal complexes may play a crucial role in synthetic chemistry. − In fact, the rational design of ligands in metal complexes with noncovalent bond donor or acceptor sites has become a powerful synthetic strategy in the selective C–H activation, − molecular sensing, crystal engineering, − etc. Like the main ligands, the auxiliary ligands can also provide versatile coordination modes and act as H-bond donors or acceptors in E / Z isomerizations, catalytic intermediates, and crystal packing of coordination compounds. , Although the H-bond (HB) donor or acceptor ability of auxiliary ligands has been well explored in coordination chemistry, − to our knowledge, the role of chalcogen bond (ChB) donor center(s) at auxiliary ligands in the decoration of the secondary coordination sphere of metal complexes has not yet been highlighted.…”