Global warming concern has dramatically increased interest in using CO2 as a feedstock for preparation of value-added compounds, thereby helping to reduce its atmospheric concentration. Here, we describe a dinuclear copper(I) complex that is oxidized in air by CO2 rather than O2; the product is a tetranuclear copper(II) complex containing two bridging CO2-derived oxalate groups. Treatment of the copper(II) oxalate complex in acetonitrile with a soluble lithium salt results in quantitative precipitation of lithium oxalate. The copper(II) complex can then be nearly quantitatively electrochemically reduced at a relatively accessible potential, regenerating the initial dinuclear copper(I) compound. Preliminary results demonstrate six turnovers (producing 12 equivalents of oxalate) during 7 hours of catalysis at an applied potential of -0.03 volts versus the normal hydrogen electrode.

Mononuclear iron(III) species with end-on and side-on peroxide have been proposed or identified in the catalytic cycles of the antitumor drug bleomycin and a variety of enzymes, such as cytochrome P450 and Rieske dioxygenases. Only recently have biomimetic analogues of such reactive species been generated and characterized at low temperatures. We report the synthesis and characterization of a series of iron(II) complexes with pentadentate N5 ligands that react with H 2 O 2 to generate transient low-spin Fe III −OOH intermediates. These intermediates have low-spin iron(III) centers exhibiting hydroperoxo-to-iron(III) charge-transfer bands in the 500−600-nm region. Their resonance Raman frequencies, ν O-O , near 800 cm -1 are significantly lower than those observed for high-spin counterparts. The hydroperoxo-to-iron(III) charge-transfer transition blue-shifts and the ν O-O of the Fe−OOH unit decreases as the N5 ligand becomes more electron donating. Thus, increasing electron density at the low-spin Mononuclear iron(III) peroxide species are implicated as intermediates in the mechanisms of oxygen activating biomolecules such as cytochrome P450, 1 heme oxygenase, 2 the antitumor drug bleomycin, 3 and Rieske dioxygenases, 4,5 as well as superoxide reductases from anaerobic bacteria. [6][7][8][9] Experimental evidence for some of these intermediates has

Considerable effort is being devoted to the fabrication of nanoscale devices. Molecular machines, motors and switches have been made, generally operating in solution, but for most device applications (such as electronics and opto-electronics), a maximal degree of order and regularity is required. Crystalline materials would be excellent systems for these purposes, as crystals comprise a vast number of self-assembled molecules, with a perfectly ordered three-dimensional structure. In non-porous crystals, however, the molecules are densely packed and any change in them (due, for example, to a reaction) is likely to destroy the crystal and its properties. Here we report the controlled and fully reversible crystalline-state reaction of gaseous SO2 with non-porous crystalline materials consisting of organoplatinum molecules. This process, including repetitive expansion-reduction sequences (on gas uptake and release) of the crystal lattice, modifies the structures of these molecules without affecting their crystallinity. The process is based on the incorporation of SO2 into the colourless crystals and its subsequent liberation from the orange adducts by reversible bond formation and cleavage. We therefore expect that these crystalline materials will find applications for gas storage devices and as opto-electronic switches.

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The bite angle effect on the rhodium diphosphine catalyzed hydroformylation was investigated in detail. A series of xantphos-type ligands with natural bite angles ranging from 102°to 121°was synthesized, and the effect of the natural bite angle on coordination chemistry and catalytic performance was studied. X-ray crystal structure determinations of the complexes (nixantphos)Rh(CO)H(PPh 3 ) and (benzoxantphos)Rh(CO)H(PPh 3 ) were obtained. In contrast to the natural bite angle calculations, approximately the same diphosphine bite angles were observed in both crystal structures. The solution structures of the (diphosphine)Rh(CO)H(PPh 3 ) and (diphosphine)Rh(CO) 2 H complexes were studied by IR and NMR spectroscopy. The spectroscopic studies showed that all (diphosphine)Rh(CO) 2 H complexes exhibit dynamic equilibria between diequatorial (ee) and equatorial-apical (ea) isomers. The equilibrium compositions could not be correlated with the calculated natural bite angles. In the hydroformylation of 1-octene an increase in selectivity for linear aldehyde formation and activity was observed with increasing natural bite angle. For styrene the same trend in selectivity for the linear aldehyde was found. For the first time CO dissociation rates of (diphosphine)Rh(CO) 2 H complexes were determined using 13 CO labeling in rapidscan high-pressure (HP) IR experiments. The observed CO dissociation rates for three complexes proved to be orders of magnitude higher than the hydroformylation rates and, contrary to the hydroformylation activity, did not reveal a correlation with the natural bite angle. These findings indicate that the bite angle effect on hydroformylation activity is dominated by the rates of reaction of the reactive, unsaturated (diphosphine)Rh(CO)H intermediates with CO and alkene. The bite angle affects the selectivity in the steps of alkene coordination and hydride migration; the structure of the saturated (diphosphine)Rh(CO) 2 H complex has only some circumstantial relevance to the selectivity.

The mechanism and kinetics of the solvolysis of complexes of the type [(L-L)Pd(C(O)CH(3))(S)](+)[CF(3)SO(3)](-) (L-L = diphosphine ligand, S = solvent, CO, or donor atom in the ligand backbone) was studied by NMR and UV-vis spectroscopy with the use of the ligands a-j: SPANphos (a), dtbpf (b), Xantphos (c), dippf (d), DPEphos (e), dtbpx (f), dppf (g), dppp (h), calix-6-diphosphite (j). Acetyl palladium complexes containing trans-coordinating ligands that resist cis coordination (SPANphos, dtbpf) showed no methanolysis. Trans complexes that can undergo isomerization to the cis analogue (Xantphos, dippf, DPEphos) showed methanolyis of the acyl group at a moderate rate. The reaction of [trans-(DPEphos)Pd(C(O)CH(3))](+)[CF(3)SO(3)](-) (2e) with methanol shows a large negative entropy of activation. Cis complexes underwent competing decarbonylation and methanolysis with the exception of 2j, [cis-(calix-diphosphite)Pd(C(O)CH(3))(CD(3)OD)](+)[CF(3)SO(3)](-). The calix-6-diphosphite complex showed a large positive entropy of activation. It is concluded that ester elimination from acylpalladium complexes with alcohols requires cis geometry of the acyl group and coordinating alcohol. The reductive elimination of methyl acetate is described as a migratory elimination or a 1,2-shift of the alkoxy group from palladium to the acyl carbon atom. Cis complexes with bulky ligands such as dtbpx undergo an extremely fast methanolysis. An increasing steric bulk of the ligand favors the formation of methyl propanoate relative to the insertion of ethene leading to formation of oligomers or polymers in the catalytic reaction of ethene, carbon monoxide, and methanol.

Geminal frustrated Lewis pairs (FLPs) are expected to exhibit increased reactivity when the donor and acceptor sites are perfectly aligned. This is shown for reactions of the nonfluorinated FLP tBu(2)PCH(2)BPh(2) with H(2), CO(2), and isocyanates and supported computationally.

The effects of isoelectronic replacement of a neutral nitrogen donor atom by an anionic carbon atom in terpyridine ruthenium(II) complexes on the electronic and photophysical properties of the resulting N,C,N'- and C,N,N'-cyclometalated aryl ruthenium(II) complexes were investigated. To this end, a series of complexes was prepared either with ligands containing exclusively nitrogen donor atoms, that is, [Ru(R(1)-tpy)(R(2)-tpy)](2+) (R(1), R(2) = H, CO(2)Et), or bearing either one N,C,N'- or C,N,N'-cyclometalated ligand and one tpy ligand, that is, [Ru(R(1)-N(/\)C(/\)N)(R(2)-tpy)](+) and [Ru(R(1)-C(/\)N(/\)N)(R(2)-tpy)](+), respectively. Single-crystal X-ray structure determinations showed that cyclometalation does not significantly alter the overall geometry of the complexes but does change the bond lengths around the ruthenium(II) center, especially the nitrogen-to-ruthenium bond length trans to the carbanion. Substitution of either of the ligands with electron-withdrawing ester functionalities fine-tuned the electronic properties and resulted in the presence of an IR probe. Using trends obtained from redox potentials, emission energies, IR spectroelectrochemical responses, and the character of the lowest unoccupied molecular orbitals from DFT studies, it is shown that the first reduction process and luminescence are associated with the ester-substituted C,N,N'-cyclometalated ligand in [Ru(EtO(2)C-C(/\)N(/\)N)(tpy)](+). Cyclometalation in an N,C,N'-bonding motif changed the energetic order of the ruthenium d(zx), d(yz), and d(xy) orbitals. The red-shifted absorption in the N,C,N'-cyclometalated complexes is assigned to MLCT transitions to the tpy ligand. The red shift observed upon introduction of the ester moiety is associated with an increase in intensity of low-energy transitions, rather than a red shift of the main transition. Cyclometalation in the C,N,N'-binding motif also red-shifts the absorption, but the corresponding transition is associated with both ligand types. Luminescence of the cyclometalated complexes is relatively independent of the mode of cyclometalation, obeying the energy gap law within each individual series.