Synthesis and application in asymmetric copper(I)-catalyzed allylic oxidation of a new chiral 1,10-phenanthroline derived from pinene

Fifty Shades of Phenanthroline: Synthesis Strategies to Functionalize 1,10-Phenanthroline in All Positions

1,10-Phenanthroline (phen) is one of the most popular ligands ever used in coordination chemistry due to its strong affinity for a wide range of metals with various oxidation states. Its polyaromatic structure provides robustness and rigidity, leading to intriguing features in numerous fields (luminescent coordination scaffolds, catalysis, supramolecular chemistry, sensors, theranostics, etc.). Importantly, phen offers eight distinct positions for functional groups to be attached, showcasing remarkable versatility for such a simple ligand. As a result, phen has become a landmark molecule for coordination chemists, serving as a must-use ligand and a versatile platform for designing polyfunctional arrays. The extensive use of substituted phenanthroline ligands with different metal ions has resulted in a diverse array of complexes tailored for numerous applications. For instance, these complexes have been utilized as sensitizers in dye-sensitized solar cells, as luminescent probes modified with antibodies for biomaterials, and in the creation of elegant supramolecular architectures like rotaxanes and catenanes, exemplified by Sauvage's Nobel Prize-winning work in 2016. In summary, phen has found applications in almost every facet of chemistry. An intriguing aspect of phen is the specific reactivity of each pair of carbon atoms ([2,9], [3,8], [4,7], and [5,6]), enabling the functionalization of each pair with different groups and leading to polyfunctional arrays. Furthermore, it is possible to differentiate each position in these pairs, resulting in non-symmetrical systems with tremendous versatility. In this Review, the authors aim to compile and categorize existing synthetic strategies for the stepwise polyfunctionalization of phen in various positions. This comprehensive toolbox will aid coordination chemists in designing virtually any polyfunctional ligand. The survey will encompass seminal work from the 1950s to the present day. The scope of the Review will be limited to 1,10-phenanthroline, excluding ligands with more intracyclic heteroatoms or fused aromatic cycles. Overall, the primary goal of this Review is to highlight both old and recent synthetic strategies that find applicability in the mentioned applications. By doing so, the authors hope to establish a first reference for phenanthroline synthesis, covering all possible positions on the backbone, and hope to inspire all concerned chemists to devise new strategies that have not yet been explored.

Metal-catalyzed asymmetric reactions enabled by organic peroxides

As a class of multifunctional reagents, organic peroxides play vital roles in the chemical industry, pharmaceutical synthesis and polymerization reactions. Metal-catalyzed asymmetric catalysis has emerged as one of the most straightforward and efficient strategies to construct enantioenriched molecules, and an increasing number of metal-catalyzed asymmetric reactions enabled by organic peroxides have been disclosed by researchers in recent years. Despite remarkable progress, the types of asymmetric reactions facilitated by organic peroxides remain limited and the catalysis systems need to be further broadened. To the best of our knowledge, there is still no review devoted to summarizing the reactions from this perspective. In this review, we will endeavor to highlight the advances in metal-catalyzed asymmetric reactions enabled by organic peroxides. We hope that this survey will summarize the functions of organic peroxides in catalytic reactions, improve the understanding of these compounds and inspire future developments in this area.

Enantioselective Allylic C-H Bond Oxidation of Olefins Using Copper Complexes of Chiral Oxazoline Based Ligands

This review article discusses historical and contemporary research studies of asymmetric allylic oxidation of olefins using homogeneous and heterogeneous copper complexes of various kinds of oxazoline-based ligands, until the end of 2021. It is revealed that this strategy is a powerful method to form a new stereogenic center bearing an oxygen substituent adjacent to an unchanged C=C bond. Enantioselectivities as well as chemical yields, and also the reactivity, are strongly dependent on the type of substrate, oxidant, the copper salt and its oxidation state, ligand structure, temperature, nature of the solvent, and additives such as phenylhydrazine and porous materials.

A New Dimeric Copper(II) Complex of Hexyl Bis(pyrazolyl)acetate Ligand as an Efficient Catalyst for Allylic Oxidations

A new dimeric copper(II) bromide complex, [Cu(L^OHex)Br(μ-Br)]₂ (1), was prepared by a reaction of CuBr₂ with the hexyl bis(pyrazol-1-yl)acetate ligand (L^OHex) in acetonitrile solution and fully characterized in the solid state and in solution. The crystal structure of 1 was also determined: the complex is interlinked by two bridging bromide ligands and possesses terminal bromide ligands on each copper atom. The two pyrazolyl ligands in 1 coordinate with the nitrogen atoms to complete the Cu coordination sphere, resulting in a five-coordinated geometry—away from idealized trigonal bipyramidal and square pyramidal geometries—which can better be described as distorted square pyramidal, as measured by the τ and χ structural parameters. The pendant hexyloxy chain is disordered over two arrangements, with final site occupancies refined to 0.705 and 0.295. The newly synthesized complex was evaluated as a catalyst in copper-catalyzed C–H oxidation for allylic functionalization through a Kharasch–Sosnovsky reaction without any external reducing agent. Using 0.5 mol% of this catalyst, and tert-butyl peroxybenzoate (Luperox) as an oxidant, allylic benzoates were obtained with up to 90% yield. The general reaction time was only slightly decreased to 24 h but a very significant decrease in the alkene:Luperox ratio to 3:1 was achieved. These factors show relevant improvements with respect to classical Kharasch–Sosnovsky reactions in terms of rate and amount of reagents. The present study highlights the potential of copper(II) complexes containing functionalized bis(pyrazol-1-yl)acetate ligands as efficient catalysts for allylic oxidations.

Immobilization of (l)-valine and (l)-valinol on SBA-15 nanoporous silica and their application as chiral heterogeneous ligands in the Cu-catalyzed asymmetric allylic oxidation of alkenes

Chiral heterogeneous ligands AL*-i-Pr-SBA-15 and AA*-i-Pr-SBA-15 were synthesized and then used in Cu-catalyzed asymmetric allylic oxidation of alkenes. Allylic esters with moderate enantiomeric excess and good yields were obtained.

Luminescent Zn(ii) and Cd(ii) complexes with chiral 2,2′-bipyridine ligands bearing natural monoterpene groups: synthesis, speciation in solution and photophysics

Coordination of chiral ligands containing a 2,2′-bipyridine moiety and natural terpene (+)-limonene or (+)-3-carene groups to zinc(ii) and cadmium(ii) leads to excitation wavelength dependent emission.

Renovation of Optically Active Phenanthrolines as Powerful Chiral Ligands for Versatile Asymmetric Metal Catalysis

In the field of asymmetric synthesis, the development of new chiral ligands has been regarded as an attractive challenge for decades. Novel chiral ligands can often have a great impact on synthetic protocols. In this context, we are currently interested in the application of 1,10-phenanthroline (phen) as an entirely new class of chiral ligand. To handle this issue, we designed a chiral phen ligand that provides the N,N,O-tridentate coordination of the phen moiety and an additional phenolic hydroxyl group. As phen possesses greater coordination ability with various ions, our chiral phen ligand would be valuable as one of the "privileged" chiral ligands applied to a broad range of metal catalysts and new reactions. This account summarizes the results of the application of the chiral phen ligand to various kinds of metal catalysis.

Enantioselective Recognition of Chiral Carboxylic Acids by a β-Amino Acid and 1,10-Phenanthroline Based Chiral Fluorescent Sensor

A novel chiral 1,10-phenanthroline-based fluorescent sensor was designed and synthesized from optical active β-amino acids. It used 1,10-phenanthroline moiety as a fluorescent signaling site and binding site, with optically active β-amino acids as a chiral barrier site. Notably, the optically active β-amino acids were obtained by a Lewis base catalyzed hydrosilylation of β-enamino esters according to our former work. The chiral sensor has been used to conduct the enantioselective recognition of chiral mono and dicarboxylic acids derivatives. Using this fluorescent sensor, a moderate “turn-off” fluorescence-diminishment response towards enantiomer of tartaric acids, and proline was observed. It found that l-enantiomers quench the chiral fluorescence sensor more efficiently than d-enantiomers due to the absolute configuration of the β-amino acid.

Design of novel chiral N,N,O-tridentate phenanthroline ligands and their application to enantioselective addition of organozinc reagents to aldehydes

The novel chiral N,N,O-tridentate ligands (BinThro) containing binaphthyl and phenanthroline units were developed. The enantioselective organozinc addition to aldehydes was performed in the presence of BinThro (S)-1 with up to 95% ee.

Synthesis and application in asymmetric catalysis of camphor-based pyridine ligands

This tutorial review deals with the synthesis and application in asymmetric catalysis of camphor-based pyridine ligands. These ligands can be roughly divided into two groups: those in which the camphor is annulated in the 2,3-positions to the beta-face of the pyridine ring and those in which the pyridine is contained as a pendant on the C2 or C3 of the camphor framework. Camphor-based pyridine ligands can also contain other donor centers located on the pyridine ring or camphor skeleton. Some of these ligands have provided interesting enantioselectivities in several asymmetric reactions, such as S(N)2' reactions, allylic oxidations, carbonyl additions with organozinc reagents and hydrogenations. This review contains a lot of chemistry on ligand synthesis and readers will find it of value and also perhaps an inspiration for the development of more active and improved versions.

Asymmetric allylic oxidation reactions catalyzed by a chiral nonracemic and C2-symmetric 2,2′-bipyridyl copper(i) complex

The evaluation of a chiral, nonracemic and C2-symmetric 2,2'-bipyridyl ligand in copper(I)-catalyzed asymmetric allylic oxidation reactions of a series of cyclic alkenes with tert-butyl peroxybenzoate is reported (up to 91% ee, the highest reported enantioselectivity for a bipyridyl ligand copper(I) complex to date).

Tuneable asymmetric copper-catalysed allylic amination and oxidation reactions

Asymmetric allylic amination or oxidation can be achieved by reaction of an alkene with a peroxycarbamate catalysed by a chiral copper bis-oxazoline complex, and the reaction can be tuned to give either the amination or oxidation product by reagent choice.

Synthesis of new chiral 2,2'-bipyridine ligands and their application in copper-catalyzed asymmetric allylic oxidation and cyclopropanation

A series of modular bipyridine-type ligands 1 and 3-9 has been synthesized via a de novo construction of the pyridine nucleus. The chiral moieties of these ligands originate from the isoprenoid chiral pool, namely, beta-pinene (10 --> 1), 3-carene (14 --> 3 and 5), 2-carene (28 --> 4), alpha-pinene (43 --> 6-8), and dehydropregnenolone acetate (48 --> 9), respectively. Copper(I) complexes, derived from these ligands and (TfO)(2)Cu (1 mol %) upon an in situ reduction with phenylhydrazine, exhibit good enantioselectivity (up to 82% ee) and unusually high reaction rate (typicaly 30 min at room temperature) in allylic oxidation of cyclic olefins (52 --> 53). Copper-catalyzed cyclopropanation proceeded with < or =76% enantioselectivity and approximately 3:1 to 99:1 trans/cis-diastereoselectivity (54 --> 55 + 56). The level of the asymmetric induction is discussed in terms of the ligand architecture that controls the stereochemical environment of the coordinated metal.