Andrew W. Maverick

Reduction of carbon dioxide to oxalate by a binuclear copper complex

Reduction of carbon dioxide to products such as oxalate (C2O4(2-)) is an active area of research, as the process converts an environmental pollutant into more useful organic compounds. However, carbon dioxide reduction remains a major challenge. Here we demonstrate a three-step reaction sequence in which a copper complex converts carbon dioxide to oxalate under mild conditions. The copper(II) complex is reduced to copper(I) in solution, either electrochemically or using sodium ascorbate. The reduced complex selectively reacts with carbon dioxide from air and fixes it into oxalate, with the oxalate ion bridging between two copper atoms. The bound oxalate ion is released as oxalic acid on treatment with mineral acids, regenerating the original copper(II) complex. This completes the process for conversion of carbon dioxide into oxalate using a binuclear copper complex and a mild reducing agent.

Synthesis and metal-complexing ability of m-xylylenebis(β-diketones)

The preparation of the bis(β-diketone) XBAH2 (3,3′-[1,3-phenylenebis(methylene) bis(2,4-pentanedione)]) and five of its derivatives, and a study of their complexation reactions with Cu2+, is reported. Of these ligands (LH2), only sterically unhindered derivatives of acetylacetone readily yield binuclear copper(II) complexes, Cu2L2. The introduction of bulkier groups (Ph, t-Bu) into the 2,4-pentanedione portions of the ligands inhibits the complex-forming reaction, resulting in lower yields (XBBH2; see ligand abbreviations in Fig. 1), no reaction (XBPH2) or decomposition (XBDH2). The copper complex of Cl4XBAH2 appears to be polymeric; this is probably due to the steric effects of the bulky chlorine atom in the two-position.

Solution Delivery of Cu ( hfac ) 2 for Alcohol‐Assisted Chemical Vapor Deposition of Copper

The authors have applied the liquid delivery technique for the thermally activated chemical vapor deposition of copper using a solution of Cu(hfac){sub 2} in isopropanol [H(hfac) = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione]. Using a substrate temperature of 300 C and reactant partial pressures of 1.8 Torr Cu(hfac){sub 2}, 12 Torr isopropanol, and 40 Torr H{sub 2}, the authors obtained a maximum growth rate of 6.7 {+-} 0.5 mg/cm h (ca. 125 nm/min). There is an induction time of about 5 min, which correlates with the time required for the initial copper clusters to grow into contact with each other (i.e., as judged from scanning electron microscope images). Film resistivities lie in the range 2.5--5.0 {micro}{Omega} cm (vs. 1.68 {micro}{Omega} cm for bulk Cu). The scanning electron microscope images suggest these high values are caused by residual void volume between the clusters. Growth rates and resistivities can be improved by eliminating H{sub 2}O from the starting Cu(hfac){sub 2}/isopropanol solution, by wet-etching the substrate or by increasing the substrate pretreatment time.

Flexible cofacial binuclear metal complexes derived from α, α-bis(salicylimino)-m-xylene

The tetradentate Schiff-base ligand SIXH2 (alpha,alpha-bis(salicylimino)-m-xylene), prepared from salicylaldehyde and m-xylylenediamine, forms cofacial binuclear complexes with Pd and Cu. Of the two isomers possible (trans-syn and trans-anti) for M2(SIX)2, these complexes crystallize exclusively as the trans-anti isomer. In ansolvous Pd2(SIX)2, the metal-containing planes are approximately parallel, with PdPd 4.416(1) A. Pd2(SIX)2 also forms a crystalline solvate, in which the molecules adopt a more open conformation with longer metal-metal distances (5.109(1) and 5.112(1) A). The M...M distance is significantly longer in Cu2(SIX)2 (6.653(1) A), because of conformational changes in the m-xylylene moieties and substantial tetrahedral distortion about Cu.

Alcohol-assisted growth of copper CVD films

Abstract We report the effect of various alcohols on the transport mechanism and reaction kinetics of Cu(hfac) 2 reduction for copper CVD. A variety of transport experiments are performed, all of which indicate that the presence of alcohol does nothing to increase the vapor phase transport rate of Cu(hfac) 2 . In contrast, steady-state kinetic measurements reveal a significant increase in CVD growth rates upon addition of an alcohol co-reactant, which we therefore attribute to an alcohol-assisted enhancement of the intrinsic kinetics of Cu(hfac) 2 reduction. For the series of alcohols studied, the enhancement factor increases in the order: MeOH i -PrOH; this correlates with the p K a values of the alcohols. The dependence of the growth rate on alcohol partial pressure is first-order, which can be described using a simple modification of our earlier Langmuir–Hinshelwood rate expression for H 2 reduction of Cu(hfac) 2 . The revised expression is consistent with a mechanism in which the rate limiting step involves H + transfer between an adsorbed alcohol molecule and the first dissociated (hfac) ligand from an adsorbed Cu(hfac) 2 molecule.

Cyclic pyridyltriazole–Cu(II) dimers as supramolecular hosts

Tetradentate bis(pyridyltriazole) ligands containing aromatic spacers of different sizes react with Cu(2+) to produce metallo-supramolecular hosts that bind 1,4-diazabicyclo[2.2.2]octane molecules internally.

Nucleophilic Attack on Dichloromethane. Synthesis and Structure of mer-[Cu(2-(Aminomethyl)Pyridine)3]2+

Abstract Solutions of copper(II) β-diketone complexes in CH2Cl2 or CHCl3 react with 2-(aminomethyl)pyridine (AMP) to produce Cu(AMP)3 2 +, which precipitates as its chloride salt. mer-[Cu(AMP)3]Cl2·CH2Cl2 is monoclinic, space group P21/c; a = 11.072(1), b = 22.306(3), c = 11.388(2) A; β = 117.39(2)°; Z = 4; R = 0.076; R w = 0.068 for 375 parameters and 3477 reflections with I > I σ (I). The mer-Cu(AMP)3 2 + ion has a tetragonally distorted octahedral geometry; distances from Cu to two trans-oriented pyridine N atoms are elongated (2.420(5) and 2.437(5) A), while the third is normal (2.060(4) A). Distances from Cu to the equatorial NH2 N atoms range from 2.012(5) to 2.048(5) A. The chloride ion in this compound is produced by nucleophilic attack of AMP on the CH2Cl2 solvent.

Solvent-dependent 44 square grid and 64.82 NbO frameworks formed by Cu(Pyac)2(bis[3-(4-pyridyl)pentane-2,4-dionato]copper(II))

The title compound crystallizes from anhydrous solvents in a simple square-grid topology, but when water is present, crystals form with an unusual interpenetrated 3D NbO topology whose pores contain hydrogen-bonded solvent molecules.

Photoredox reactions of oxomolybdenum(V) with phosphines

Abstract The fluorescent molybdenum(V)oxo complex MoOCl 4 (H 2 O) − , and oxomolybdenum(V)phosphine complexes derived from it, undergo thermal and photochemical reactions in acetonitrile with the series of phosphines PEt 3 , PEt 2 Ph, PEtPh 2 , and PPh 3 . PEt 3 reacts spontaneously to form several products: crystalline (PPh 4 )[Mo III Cl 4 (PEt 3 ) 2 ] and (PPh 4 ) 2 [Mo V OCl 5 ]·2CH 2 Cl 2 ; and a maroon oil that contains OPEt 3 , Mo IV OCl 2 (PEt 3 ) 3 and Mo IV Cl 4 (PEt 3 ) 2 . The Mo(III) and OPEt 3 products show that oxygen atom transfer has occurred. PEt 2 Ph and PEtPh 2 show no significant redox activity with oxomolybdenum(V) in the dark, but irradiation ( λ >320 nm, CH 3 CN solution) leads to reduction of Mo(V) and production of the corresponding phosphine oxides. The molybdenum(III) product, cis - mer -MoCl 3 (OPEt 2 Ph) 2 (PEt 2 Ph), was isolated from the PEt 2 Ph experiment. PPh 3 is not oxidized under these conditions; instead, spectral evidence suggests that photoinduced ligand substitution occurs, producing MoOCl 3 (PPh 3 ) 2 . Selective irradiation of the longer-wavelength Mo(V) absorption bands leads to similar photoredox reactions, but much more slowly. X-ray analyses of two reaction products, (PPh 4 ) 2 [Mo V OCl 5 ]·2CH 2 Cl 2 and cis - mer -Mo III Cl 3 (OPEt 2 Ph) 2 (PEt 2 Ph), are reported.

ELECTRONIC SPECTRUM AND CRYSTAL STRUCTURE OF FAC-MOOCL3(DPPE)

Abstract X-ray analysis of the oxomolybdenum(V) complex MoOCl 3 (dppe) (dppe = 1,2-bis(diphenylphosphino)ethane) shows that it is the facial isomer. (C 26 H 24 Cl 3 MoOP 2 , space group P 2 1 / n , a = 13.217(1), b = 12.8935(8), c = 16.0578(9) A , β = 99.967(5)°, V = 2695.1(6) A 3 , Z = 4, R = 0.038 for 6228 data with I > 1 σ ( I ).) The electronic absorption spectrum of the title compound is also compared with those of other oxomolybdenum(V) complexes.