Mechanism of the Iridium-Catalyzed Silylation of Aromatic C–H Bonds

<p>The iridium-catalyzed silylation of aromatic C–H bonds has become a synthetically valuable reaction because it forms aryl silanes with high sterically derived regioselectivity with silane reagents that are produced and consumed on large scales. Many groups, including our own, have reported iridium complexes of phenanthroline or bipyridine ligands as catalysts for this reaction. Yet, little is known about the mechanism by which the iridium-catalyzed silylation of arenes occurs. Indeed, no iridium-silyl complexes have been prepared that react with C-H bonds to form C-Si bonds in a fashion that is chemically and kinetically competent to be part of the catalytic cycle. </p><p><br></p> <p>In this manuscript, we report the synthesis and reactivity of iridium-silyl compelexes of the 2,9-Me₂Phen ligand that generates the most active known catalyst for the silylation of aromatic C-H bonds. We show by experiment and computation that the most stable and most reactive silyl complex of this ligand contains two silyl and one hydride ligands and by kinetic analysis of the catalytic reaction determine the rate-limiting step for arenes with varying electronic properties. Computational studies indicate that the steric encumberance of the phenanthroline ligand controls the number of silyl ligands bound to iridium and that the difference in the number of silyl ligands leads to large differences to the rates of the reaction. These studies provide insight into the origins of the high activity of the catalyst containing the 2,9-Me₂Phen ligand.</p>

Mechanism of the Iridium-Catalyzed Silylation of Aromatic C–H Bonds

<p>The iridium-catalyzed silylation of aromatic C–H bonds has become a synthetically valuable reaction because it forms aryl silanes with high sterically derived regioselectivity with silane reagents that are produced and consumed on large scales. Many groups, including our own, have reported iridium complexes of phenanthroline or bipyridine ligands as catalysts for this reaction. Yet, little is known about the mechanism by which the iridium-catalyzed silylation of arenes occurs. Indeed, no iridium-silyl complexes have been prepared that react with C-H bonds to form C-Si bonds in a fashion that is chemically and kinetically competent to be part of the catalytic cycle. </p><p><br></p> <p>In this manuscript, we report the synthesis and reactivity of iridium-silyl compelexes of the 2,9-Me₂Phen ligand that generates the most active known catalyst for the silylation of aromatic C-H bonds. We show by experiment and computation that the most stable and most reactive silyl complex of this ligand contains two silyl and one hydride ligands and by kinetic analysis of the catalytic reaction determine the rate-limiting step for arenes with varying electronic properties. Computational studies indicate that the steric encumberance of the phenanthroline ligand controls the number of silyl ligands bound to iridium and that the difference in the number of silyl ligands leads to large differences to the rates of the reaction. These studies provide insight into the origins of the high activity of the catalyst containing the 2,9-Me₂Phen ligand.</p>

Selective N-formylation/N-methylation of amines and N-formylation of amides and carbamates with carbon dioxide and hydrosilanes: promotion of the basic counter anions of the zinc catalyst

A Zn(OAc)2 catalyst bearing the 1,10-phenanthroline (phen) ligand was efficient in the N-formylation of organic amine derivatives (e.g., amines, amides, and carbamates) using carbon dioxide (CO2) and hydrosilanes.

Synthesis and structural characterization of the complexes of 2-(menthoxycarbonyl)ethyltin chloride

The complexes of 2-(menthoxycarbonyl)ethyltin chloride, MenOCOCH2CH2SnCl3⋅L (Men = Menthyl, L = benzyl phenyl sulfoxide (bpSO), 1; 2,2’-bipyridine (bpy), 2; 1,10-phenanthroline (phen), 3) and [MenOCOCH2CH2SnCl2(OCH3)]2 (4), have been synthesized and characterized by means of elemental analysis, FT-IR, NMR (1H, 13C and 119Sn) spectra. The crystal structures of 1, 3 and 4 have been determined by single crystal X-ray diffraction. The tin atoms in 1-4 are all hexa-coordinated. The tin atom in 1 adopts a distorted [CSnCl3O2] octahedral geometry with an oxygen atom of the ligand and an intramolecular coordination of the oxygen atom from the carbonyl group to the tin atom. Complex 3 possesses a distorted [CSnCl3N2] octahedral geometry with two nitrogen atoms of a chelating phen ligand. The carbonyl oxygen atom of the ester moiety is not coordinating. Compound 4 is a centrosymmetric dimer with a four-membered Sn2O2 ring, and the tin atom has a distorted [CSnCl2O3] octahedral geometry with an intramolecular C=O→Sn coordination and intermolecular methoxy bridging.

Iridium-Catalyzed Silylation of C-H bonds in Unactivated Arenes: A Sterically-Encumbered Phenanthroline Ligand Accelerates Catalysis Enabling New Reactivity

We report a new system for the silylation of aryl C-H bonds. The combination of [Ir(cod)(OMe)]₂ and 2,9-Me₂-phenanthroline (2,9-Me₂phen) catalyzes the silylation of arenes at lower temperatures and with faster rates than those reported previously, when the hydrogen byproduct is removed, and with high functional group tolerance and regioselectivity. Inhibition of reactions by the H₂ byproduct is shown to limit the silylation of aryl C-H bonds in the presence of the most active catalysts, thereby masking their high activity. Analysis of initial rates uncovered the high reactivity of the catalyst containing the sterically hindered 2,9-Me₂phen ligand but accompanying rapid inhibition by hydrogen. With this catalyst, under a flow of nitrogen to remove hydrogen, electron-rich arenes, including those containing sensitive functional groups, undergo silylation in high yield for the first time, and arenes that underwent silylation with prior catalysts react over much shorter times with lower catalyst loadings. The synthetic value of this methodology is demonstrated by the preparation of key intermediates in the synthesis of medicinally important compounds in concise sequences comprising silylation and functionalization. Mechanistic studies demonstrate that the cleavage of the aryl C-H bond is reversible and that the higher rates observed with the 2,9-Me₂phen ligand is due to a more thermodynamically favorable oxidative addition of aryl C-H bonds.

Iridium-Catalyzed Silylation of C-H bonds in Unactivated Arenes: A Sterically-Encumbered Phenanthroline Ligand Accelerates Catalysis Enabling New Reactivity

We report a new system for the silylation of aryl C-H bonds. The combination of [Ir(cod)(OMe)]₂ and 2,9-Me₂-phenanthroline (2,9-Me₂phen) catalyzes the silylation of arenes at lower temperatures and with faster rates than those reported previously, when the hydrogen byproduct is removed, and with high functional group tolerance and regioselectivity. Inhibition of reactions by the H₂ byproduct is shown to limit the silylation of aryl C-H bonds in the presence of the most active catalysts, thereby masking their high activity. Analysis of initial rates uncovered the high reactivity of the catalyst containing the sterically hindered 2,9-Me₂phen ligand but accompanying rapid inhibition by hydrogen. With this catalyst, under a flow of nitrogen to remove hydrogen, electron-rich arenes, including those containing sensitive functional groups, undergo silylation in high yield for the first time, and arenes that underwent silylation with prior catalysts react over much shorter times with lower catalyst loadings. The synthetic value of this methodology is demonstrated by the preparation of key intermediates in the synthesis of medicinally important compounds in concise sequences comprising silylation and functionalization. Mechanistic studies demonstrate that the cleavage of the aryl C-H bond is reversible and that the higher rates observed with the 2,9-Me₂phen ligand is due to a more thermodynamically favorable oxidative addition of aryl C-H bonds.

Dinuclear Lanthanide–Carboxylate Compounds: Field-Induced Slow Relaxation of Magnetization for Dysprosium(III) Analogue

Three chiral dinuclear lanthanide compounds, Ln2(µ2-L)4(L)2(phen)2 (Ln = Dy (1), Gd (2), and Er (3); phen = 1,10-phenanthroline), have been synthesized using the (S)-(+)-2-(6-methoxy-2-naphthyl)propionic acid (HL) ligand. The two lanthanide centres in compound Ln2(µ2-L)4(L)2(phen)2 are bridged by four carboxylate groups to give a dinuclear Ln2(µ2-L)4 core. The square antiprismatic coordination environment for each lanthanide centre is further completed by a chelating carboxylate group from another L– ligand and two nitrogen atoms from the phen ligand. A weak antiferromagnetic interaction between the two GdIII ions is observed in compound 2. The Dy analogue displays field-induced slow magnetic relaxation behaviour with an effective energy barrier Ueff/k of 17.24(2) K and a pre-exponential factor τ0 of 2.7(1) × 10–6 s. However, no slow relaxation phenomenon was observed for the Er derivative even in the presence of 2 kOe applied field.

Crystal structure of triaqua(1,10-phenanthroline-κ2N,N′)(2,4,5-trifluoro-3-methoxybenzoato-κO1)cobalt(II) 2,4,5-trifluoro-3-methoxybenzoate

The title salt, [Co(C8H4F3O3)(C12H8N2)(H2O)3](C8H4F3O3), was obtained under solvothermal conditions by the reaction of 2,4,5-trifluoro-3-methoxybenzoic acid with CoCl2in the presence of 1,10-phenanthroline (phen). The CoIIion is octahedrally coordinated by two N atoms [Co—N = 2.165 (2) and 2.129 (2) Å] from the phen ligand, by one carboxylate O atom [Co—O = 2.107 (1) Å] and by three O atoms from water molecules [Co—O = 2.093 (1), 2.102 (1) and 2.114 (1) Å]. The equatorial positions of the slightly distorted octahedron are occupied by the N atoms, the carboxylate O and one water O atom. An intra- and intermolecular O—H...O hydrogen-bonding network between the water-containing complex cation and the organic anion leads to the formation of ribbons parallel to [010].

Structural study of new cytotoxic heteroleptic Copper (II) complexes

The widespread success of Cisplatin in the treatment of several neoplasias has arisen the interest in coordination compounds as drugs for the treatment of cancer. In the search for new compounds with antitumor activity, copper coordination complexes are being studied by our group. This work presents the synthesis and structural characterization of four new copper complexes with general stoichiometry [Cu(L-dipeptide)(phen)]·nH2O and their cytotoxicity against tumor cell lines. Single crystal X-ray diffraction experiments show that the copper ion is situated in a distorted squared pyramidal environment. The phen ligand is perpendicular to the plane defined by the coordinated dipeptide, therefore exposed and potentially available for interaction with biological molecules, e.g. DNA. The availability of the phen ligand and the physico-chemical properties of the complexes are modulated by the dipeptide. Complementary techniques (elemental analysis, infrared and UV-vis spectroscopies) were used to further characterize the complexes in solid state and aqueous solution, confirming that the coordination is maintained in solution. Lipophilicity and DNA binding constants were also measured, being able to discriminate between the behavior of even the complexes containing the ala-phe and phe-ala dipeptide. All the complexes induce cell death in the cell lines of human cervical adenocarcinoma, human metastatic breast adenocarcinoma and human lung epithelial carcinoma. Among the six complexes studied, [Cu(ala-phe)(phen)] presents the lowest half maximal inhibitory concentration (IC50) values. In an attempt to increase the activity, studies are presently being carried out using 2,9-dimethyl-10-phenanthroline. X-ray diffraction studies on the latter show slight deviations in the coordination geometries and different results are expected in their biological activities. Acknoledgements: CSIC, CAPES-UdelaR, PEDECIBA.

A two-dimensional CdII coordination polymer with 2,2′-(disulfanediyl)dibenzoate and 1,10-phenanthroline ligands

In poly[[μ3-2,2′-(disulfanediyl)dibenzoato-κ5 O:O,O′:O′′,O′′′](1,10-phenanthroline-κ2 N,N′)cadmium(II)], [Cd(C14H8O4S2)(C12H8N2)] n , the asymmetric unit contains one CdII cation, one 2,2′-(disulfanediyl)dibenzoate anion (denoted dtdb2−) and one 1,10-phenanthroline ligand (denoted phen). Each CdII centre is seven-coordinated by five O atoms of bridging/chelating carboxylate groups from three dtdb2− ligands and by two N atoms from one phen ligand, forming a distorted pentagonal–bipyramidal geometry. The CdII cations are bridged by dtdb2− anions to give a two-dimensional (4,4) layer. The layers are stacked to generate a three-dimensional supramolecular architecture via a combination of aromatic C—H...π and π–π interactions. The thermogravimetric and luminescence properties of this compound were also investigated.