Carbon dioxide, complexes

IR spectra, 27 283, 284 oxidized state, 27 289 reflectance speetroscopy, 27 279 sulfided, 27 299 surface area, 27 288 X-ray diffraction, 27 272, 273 calcination, 27 268, 269 -carbon dioxide complex, coordination, 28 127... 

CAMPHOS catalyst, asymmetric hydrogenation of a,p-unsaturated carboxlic acids, 25 107-109, 112 -carbon bond, COj insertion, 28 132-134 -carbon dioxide complex, coordination, 28 125, 126, 128 oxide formation, 28 27 as catalyst, 26 335... 

Carbon dioxide reacts with [Mo(N2)2(PMe2Ph)4] to produce not a carbon dioxide complex, but a carbonato-carbonyl, whose formation involves reductive disproportionation of C02 (equation 16). The structure of the Mo" product [ Mo(CO)(PMe2Ph)3 2( -C03)2] has been determined by X-ray structure analysis.166... 

The other carbon dioxide complex characterized by x-ray crystallography contains two linked C02 molecules in the coordination sphere (116). This complex, [IrCl(C204)(PMe3)3], was prepared by the interaction of C02 with chloro(cyclooctene)[tris(trimethylphosphine)]iridium(I), [IrCl(C8 H j 4)-(PMe3)3], in benzene solution. The structure, (25), shows essentially octahedral coordination about the iridium center, with one metal-carbon bond and a five-membered chelate ring formed with the second C02 molecule. 

Results from the same laboratory have appeared on carbon dioxide complexes with copper(I) compounds (124). Phosphine-containing copper(I) car-boxylate complexes, formed by the insertion of C02 into a copper-alkyl bond, take up additional C02. A complex, formulated as [(RC00)Cu(C02)-(PPh3)J has been isolated and the C02 shown to be labile, i.e., the C02 was lost on attempted recrystallization. The authors speculate that the car-... 

Formation of Carbon Dioxide Complexes. As mentioned in the introduction, our initial interest in synthesizing the PCy3 complexes was in their potential for binding C02. However, except for the formation of peroxycarbonate and carbonato complexes from IrCl(02)(PCy3)2 (44), which is well-established chemistry for some platinum metal peroxide complexes (42) (but, to our knowledge, not with PCy3 systems), we have not been able to isolate any C02 complexes or even carbonate or bicarbonate species which are formed sometimes in the presence of adventitious water (16). 

Less attention has been paid, however, to C02 organometallic chemistry during the past decade. Whilst many reduction or coupling reactions are known to proceed in the presence of stoichiometric or catalytic amounts of transition metal complexes, very few examples remain where the formation of a metal-C02 complex has led to an effective, catalytic reduction reaction of C02. Carbon dioxide complex photoactivation also represents an attractive route to CO bond cleavage, coupled with O-atom transfer. However, progress in the area of C02 utilization requires a better understanding of the reaction mechanisms, of the thermodynamics of reaction intermediates, and of structure-reactivity relationships. 

Five types of fragment structures, typically 68-72 (X = Y = 0) [104,105], are discussed for carbon dioxide complexes ... 

J. Sadlej et al., Ab initio study of energy, structure and dynamics of the water-carbon dioxide complex. J. Chem. Phys. 109, 3919 (1998)... 

The first step in the activation of carbon dioxide by transition metal compounds is the formation of a M-C02 complex, since it is through coordination that the electronic structure of this molecule, and hence its reactivity, can be substantially modified. Transition metal complexes containing carbon dioxide in its intact form have received considable attention in the last decade (Inone et al, 1982), mainly with the aim of finding model systems for the activation of C02 and subsequent transformation into organic chemicals of comercial interest (Aresta et al, 1987). Despite considerable and intensive work in this area, the number of structurally characterized carbon dioxide complexes is stilt very limited, and they have been found to contain side-on (Alvarez et al, 1986), 72 -coordinated and, l2 C-coordinated (Calabrese et al, 1983) C02. 

Interaction of the bis (carbon dioxide) adduct with various isocyanides affords new carbon dioxide complexes of composition trans, mer-Mo(C02) (CNR) (PMe3)3, (R=Me, i-Pr, t-Bu, C6H12, CH2C6H5), as shown in eq. 1. In no case has substitution of a second PMe3 or of a C02 ligands been observed. 

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