Benzylic C-H Esterification with Limiting C-H Substrate Enabled by Photochemical Redox Buffering of the Cu Catalyst

Copper-catalyzed radical-relay reactions provide a versatile strategy for selective C-H functionalization; however, reactions with peroxide-based oxidants often require excess C-H substrate. Here, we report a photochemical strategy to overcome this limitation by using a Cu/2,2'-biquinoline catalyst that supports benzylic C-H esterification with limiting C-H substrate. Mechanistic studies indicate that blue-light irradiation promotes carboxylate-to-copper charge transfer, reducing resting-state CuII to CuI, which activates the peroxide to generate an alkoxyl radical hydrogen-atom-transfer species. This "photochemical redox buffering" introduces a unique strategy to sustain the activity of Cu catalysts in radical-relay reactions.

Interaction of Cu(+) with cytosine and formation of i-motif-like C-M(+)-C complexes: alkali versus coinage metals

The Watson-Crick structure of DNA is among the most well-known molecular structures of our time. However, alternative base-pairing motifs are also known to occur, often depending on base sequence, pH, or the presence of cations. Pairing of cytosine (C) bases induced by the sharing of a single proton (C-H(+)-C) may give rise to the so-called i-motif, which occurs primarily in expanded trinucleotide repeats and the telomeric region of DNA, particularly at low pH. At physiological pH, silver cations were recently found to stabilize C dimers in a C-Ag(+)-C structure analogous to the hemiprotonated C-dimer. Here we use infrared ion spectroscopy in combination with density functional theory calculations at the B3LYP/6-311G+(2df,2p) level to show that copper in the 1+ oxidation state induces an analogous formation of C-Cu(+)-C structures. In contrast to protons and these transition metal ions, alkali metal ions induce a different dimer structure, where each ligand coordinates the alkali metal ion in a bidentate fashion in which the N3 and O2 atoms of both cytosine ligands coordinate to the metal ion, sacrificing hydrogen-bonding interactions between the ligands for improved chelation of the metal cation.

Square planar Cu(i) stabilized by a pyridinediimine ligand

A set of distorted square planar Cu(i) complexes were synthesized and characterized utilizing the sterically encumbering pyridinediimine ligand, ^iPrPDI (where ^iPrPDI = 2,6-(2,6-ⁱPr₂C₆H₃NCMe)₂C₅H₃N).

A one-pot diastereoselective self assembly of C-stereogenic copper(I) diphosphine clusters

C-chirogenic diphosphine-based clusters with 8-membered "chairlike" Cu4Cl4L2 and 12-membered "drumlike" Cu6Cl6L3 (L = diphosphine) frameworks were prepared in one-pot syntheses from chiral diphosphines, which were generated in situ via the double hydrophosphination reaction in excellent enantio- and diastereoselectivity. Excellent control over the final molecular architecture of the cluster (drum vs chair) could be achieved by the judicious selection of the source of the copper atoms employed in the synthetic protocol. Each cluster was characterized by single-crystal X-ray crystallography, (1)H, (13)C, and (31)P{(1)H} NMR spectroscopy. The synthesized clusters were found to exhibit catalytic activity in the hydroboration reaction of α,β-unsaturated enones with excellent yields albeit with low enantioselectivity.

Redox reactions in palladium catalysis: on the accelerating and/or inhibiting effects of copper and silver salt additives in cross-coupling chemistry involving electron-rich phosphine ligands

Challenging a catalytic cycle: Pd(0) catalysts are readily oxidized by Cu and Ag salts to give dinuclear Pd(I) complexes and Cu(I) or Ag(I) cubanes (see scheme). The reactivities of the resulting Pd(I) dimers are consistent with several observations of additive effects in cross-coupling chemistry. The results indicate the possibility for alternative catalytic cycles involving dinuclear Pd(I) complexes over the currently accepted synergistic cycles involving Pd(0)/Pd(II) intermediates and Cu or Ag.

Effects of molecular structure and interfacial ligation on the precision of Cu-bound alpha,omega-mercaptoalkanoic acid "molecular ruler" stacks

Nanolithography processes based on designed, precision thickness multilayer thin films (molecular rulers) have been reported that enable patterning of features on surfaces from a few to the hundred nanometer range. These strategies are unique in their potential ability to enable wafer scale patterning of features of just a few nanometers. If these techniques could be developed to be sufficiently precise and generally applicable, they would fill a long-standing need in nanoscience. In this study a systematic and detailed analysis of the growth mechanisms and molecular layer structures has been carried out for the mercaptoalkanoic acid-copper ion multilayer thin film system currently used as the standard nanolithography resist. Our results show these films form via a redox reaction of thiol groups with surface-ligated Cu(II) ions to form adlayers at only approximately 50% coverage with islanding of the alkyl chains, thereby leading to rough topographies and less than theoretical thicknesses based on a 1:1 ideal adlayer. Strategies are suggested to help overcome these issues for molecular resist applications in nanolithographic processing.

Electrochemical Synthesis, Crystal Structure, and Photomagnetic Properties of a Three-Dimensional Cyano-Bridged Copper−Molybdenum Complex

A single crystal of Cs(I)2Cu(II)7[Mo(IV)CN8]4.6H2O was electrochemically prepared on a Pt wire electrode with a constant potential of +500 mV vs Ag/AgCl electrode. X-ray single-crystal structural analysis showed that this compound consists of a three-dimensional cyano-bridged Cu-Mo bimetallic assembly with a tetragonal structure of I4/mmm. The coordination geometry of Mo(IV) is bicapped trigonal prism, and that of Cu(II) is five-coordinate of square pyramidal or four-coordinate of square planar. This compound was also prepared as a 0.2-3.0 microm thick film on a SnO2-coated glass in the same electrochemical manner. When the sample, which shows paramagnetism due to Cu(II) (S = 1/2), was irradiated with 450-500 nm light at 5 K, spontaneous magnetization with a Curie temperature of 23 K was observed. This photoinduced change was recovered by a thermal treatment. In the infrared (IR) and electron spin resonance (ESR) spectra after light irradiation, variations in the stretching IR peak of CN bridged to Mo(IV) and the paramagnetic ESR peak of Cu(II) were observed, respectively. The data indicate that this photomagnetism is caused by the electron transfer from Mo(IV) to Cu(II) and the ferromagnetic ordering between Cu(II) (S = 1/2) and Mo(V) (S = 1/2).

Acrylonitrile Polymerization by Cy3PCuMe and (Bipy)2FeEt2

Cy(3)PCuMe (1) undergoes reversible ligand redistribution at low temperature in solution to form the tight ion pair [Cu(PCy(3))(2)][CuMe(2)] (3). The structure of 3 was assigned on the basis of (i) the stoichiometry of the 1 = 3 equilibrium, (ii) the observation of a triplet for the PCy(3) C1 (13)C NMR resonance due to virtual coupling to two (31)P nuclei, and (iii) reverse synthesis of 1 by combining separately generated Cu(PCy(3))(2)(+) and CuMe(2)(-) ions. Complex 1 and [Cu(PCy(3))(2)][PF(6)] (5) coordinate additional PCy(3) to form (Cy(3)P)(2)CuMe and [Cu(PCy(3))(3)][PF(6)], respectively, while 3 does not. Complex 1, free PCy(3), and (bipy)(2)FeEt(2) (2) each initiate the polymerization of acrylonitrile. In each case, the polyacrylonitrile contains branches that are characteristic of an anionic polymerization mechanism. The major initiator in acrylonitrile polymerization by 1 is PCy(3), which is liberated from 1. A transient iron hydride complex is proposed to initiate acrylonitrile polymerization by 2.

One-Dimensional Copper(I) Coordination Polymers Based on a Tridentate Thioether Ligand

The one-dimensional copper(I) coordination polymers Cu(3){MeSi(CH(2)SMe)(3)}(2)X(3) (X = Cl, Br) and [{MeSi(CH(2)SMe)(3)}Cu(NCMe)]Y (Y = OSO(2)CF(3), BF(4), PF(6)) were readily obtained in very good to excellent yields (80-95%) by reacting CuX or [Cu(NCMe)(4)]Y, respectively, with the tridentate thioether ligand MeSi(CH(2)SMe)(3) in acetonitrile. The new complexes were characterized by a combination of analytical and spectroscopic techniques, including electrospray ionization mass spectrometry and, for the bromo and hexafluorophosphate derivatives, single-crystal X-ray diffraction. Both complexes exhibit one-dimensional chain structures with approximately tetrahedral copper centers and bridging unidentate/bidentate thioether ligands.