Ag -CO complexes

Deposition of Ag atoms represents the simplest case due to the low-adsorption energy of Ag to MgO and to the absence of reactivity of the deposited Ag atoms. The calculations exclude the formation of stable Ag-CO complexes at any of the surface sites considered (regular sites or point defects like F centers or steps). The small changes in the TDS and FTIR (Fourier Transform Infra-Red) spectra before and after Ag deposition must thus be attributed to indirect effects, like local changes in the surface potential induced by the presence of the Ag atoms or the formation of van der Waals complexes. 

The silver(I) carbonyl complexes [Ag(CO)]+, [Ag(CO)2]+, and the stable [Ag HB[3,5-(CF3)2pz]3 (CO)] (where pz = pyrazolyl) have been characterized spectroscopically and crystal-lographically, they indicate little or no Ag to CO 7r-back bonding. 26... 

The structure of [Ag(CO)2]+ is linear and it weakly bonds to two or more B(OTeF5)4 anions. These complexes decompose at room temperature giving (Ag(CO)(OTeF5)], CO, and B(OTeF5)3. The Zn(OTeF5)42 and Ti(OTeF5)62 adducts are more stable when subjected to subambient pressures of CO. 

Cationic Group 11 carbonyl complexes have been implicated in catalytic carbony-lation reactions of alkenes, arenes, alcohols, saturated hydrocarbons and aldehydes under acidic conditions [106]. While the mono- and di-carbonyls [M(CO)] and [M(C0)2] (M = Cu, Ag, Au) can be formed at atmospheric pressure of CO, only Cu(I) forms a tricarbonyl cation under such conditions [107]. Strauss and co-workers reported the observation of [Ag(CO)3] when a Fluorolube mull of Ag[Nb(OTep5)5] was subjected to 13 bar CO in an HP IR transmission cell [108]. 

Figure 36. A diagram of the mixed-metal Co(III)-Ag(I) complex. (Reproduced by permission from reference 161)...

Reaction of (triars)AgBr (triars = bis(o-dimethylarsinophenyl)methylarsine) with the carbonyl anions Mn(CO)i Fe(CO)4- and Co(CO)4 in THF gave complexes of the type (triars)Ag—Co(CO)4. 0 The crystal structure of the complex with an Ag—Co bond has been determined.211 The silver atom had a distorted tetrahedral arrangement with three Ag—As bonds (262-272 pm) and an Ag—O bond (266 pm). The tetrahedral starting material was prepared by reaction of the triarsine with AgBr in ethanol.210... 

As shown in Fig. 19, the most marked result is that the band frequency remains almost constant for palladium and Pd-Ag alloys, but the relative intensities change in a dramatic manner. The 2060 cm"1 band, which is ascribed to the linear CO complexes and is rather weak for CO on palladium, becomes the most important feature of the spectrum of CO on Pd-Ag alloys, where the bands characteristic of multicenter-adsorbed CO are very faint. Measurement on Cu-Ni alloys (75b) show an almost similar behavior. 

Despite the fact that CO is reversibly bound to Ag(I), Strauss and co-workers1012 succeeded in isolating crystalline silver carbonyl complexes at low temperature under a CO atmosphere and studying the crystal structure of [Ag(CO)]+[B(OTeF5)4] and [Ag(CO)2]+[B(OTeF5)4r. 

A paper dating from 1976 investigated the reaction of olefins or alcohols with cationic copper and silver complexes of carbon monoxide 49 The remarkable outcome of these kinetic measurements is that there is no difference between the catalytic behavior of Cu(CO) + and Ag(CO)2 +. 

There are roughly 421 reports of homoleptic bis(dithiolene) units based on transition metal elements. The approximate tally of the structures as a function of central metal atom is outlined in Fig. 2. The examples predominantly contain late transition metals. The majority of complexes are Ni based, partially because of interest in these complexes for materials applications. Other common central elements are Cu, Pd, Pt, Au, and Zn. There are also a few Fe and Co complexes and a small number of structures based on Cr, Mn, Ag, Cd, and Hg. 

Until recently, isolable CO complexes of silver were unknown. However, if the counteranion possesses only very weak basicity, fairly stable CO adducts are obtained. Carbon monoxide acts in these compounds as a donor ligand only. Back-bonding is virtually absent, and the C—O stretching frequencies are substantially higher than that of free CO (2143 cm"1). The compounds [Ag(CO)]+X" (vqo = 2204 cm"1) and [OC—Ag—CO]+X (vco = 2198 cm-1) [X = B(OTeF5)4] were characterized by X-ray diffraction.21 The [Ag(CO)3]+ ion is formed under CO pressure. 

In contrast to the tricarbonyl halide complexes, it is the exo conformation of () -allyl)FeCp(CO) complexes (163) which is preferred, and at equilibrium only traces of the endo isomer can be observed. Existing crystal structures of members of this class are of the exo conformation.Reasonable percentages of the endo conformer are realized upon low-temperature photolyses of their () -allyl)Fp precursors, however, and the activation barrier to endolexo conversion has been determined to be AG = 100.8kJmol for the 2-methallyl complex. In addition, the anti isomers, which can be prepared stereospecifically from the (j7 -allyl)Fp complexes, isomerize to the syn isomers with brief heating. The Fe NMR spectra are known for several of the complexes where CO has been replaced by a phosphine or phosphite (145) the chemical shift is highly dependent on the nature of the phosphorus ligand. ... 

Silver alkyls and aryls, together with silver(I) complexes of cyclic polyenes and aUcynyl ligands, are generally classified under organometallic compounds. Stable silver(l) carbonyl complexes that have been characterized by X-ray analysis include [Ag(CO) B(OTeF5)4 ], [Ag(CO)2 B(OTeF5)4 ], and [Ag(CO) HB[3,5-(CF3)2pz]3 ]. Silver acetylide (AgzCz) complexes are described in Section 3.6. 

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