Metal carbonyl complexes structures

AT-heterocyclic carbenes show a pure donor nature. Comparing them to other monodentate ligands such as phosphines and amines on several metal-carbonyl complexes showed the significantly increased donor capacity relative to phosphines, even to trialkylphosphines, while the 7r-acceptor capability of the NHCs is in the order of those of nitriles and pyridine [29]. This was used to synthesize the metathesis catalysts discussed in the next section. Experimental evidence comes from the fact that it has been shown for several metals that an exchange of phosphines versus NHCs proceeds rapidly and without the need of an excess quantity of the NHC. X-ray structures of the NHC complexes show exceptionally long metal-carbon bonds indicating a different type of bond compared to the Schrock-type carbene double bond. As a result, the reactivity of these NHC complexes is also unique. They are relatively resistant towards an attack by nucleophiles and electrophiles at the divalent carbon atom. 

Metal bromides, 4 322-330 Metal can food packaging, 18 37-39 Metal-carbene complexes, 26 926 Metal-carbon compounds, 4 648, 650 Metal-carbon eutectic fixed points, 24 454 Metal carbonyl catalysts, supported, 16 75 Metal carbonyl complexes, 16 73 Metal carbonyls, 15 570 16 58-78 bonding and structure of, 16 59-64 from carbon monoxide, 5 12 in catalysis, 16 72-75 economic aspects of, 16 71 health and safety aspects of, 16 71 heteronuclear, 16 69-71 high nuclearity, 16 66-69 high nuclearity carbonyl clusters, 16 64-66... 

Reaction of (butadiene)ZrCp2 (31/32), and substituted Cp variants, with a wide range of metal-carbonyl complexes, generates the chelated metal-carbene complexes 163 (equation 22)163. The crystal structure of a number of these complexes has been determined... 

Processes for two-electron reductions, two sequential one-electron reductions with a radical anion intermediate, and reactions of dianions with unreduced parents to give radical anions were observed. Structural reorganization is occasionally observed, particularly in the case of Fe(CO)2 and Fe(CO)3 complexes (26). There appears to be little correlation between structure and electrochemical behavior. In general, the presence of metal-metal bonds in the substrate appears to correlate well with the ability to yield a stable radical anion on reduction. The lack of a metal-metal bond correlates, although poorly, with the ability to form radical cations (25). At present, the predictability of results from reduction in metal-carbonyl complexes is very low. The area remains one in which a great deal more work is needed. 

In this chapter we have examined examples of polynuclear metal carbonyl complexes as well as simple metal carbonyl hydrides. Consider now the polynuclear carbonyl hydride complex, H,Os,(CO)i2- Rationalize the formulation of this species. From your application of the 18-electron rule, what can you say about the structure of this molecule1 How is it similar to or different from the complex Os COln shown in Figure 5.9 (See Churchill M. R. Wasserman, H. J. Iticrg, Chen. 1980, 19, 2391-2395.)... 

In contrast to the results described above, experiments with palladium atoms and SiO lead to a different behavior. It is clear that PdSiO is formed, but compared with monomeric SiO the corresponding stretching vibration of PdSiO is shifted to higher wavenumbers (1246 cm-1 in solid argon)118. With the aid of a normal coordinate analysis involving different isotopomers, a linear structure of PdSiO is deduced. Bonding in PdSiO is similar to that in typical transition metal carbonyl complexes. 

Most metal carbonyl complexes exhibit sharp and intense CO bands in the range 1800-2100 cm-1. Since the CO stretch motions are rarely coupled with other modes and CO absorption bands are not obscured by other vibrations, measurement of the CO stretch bands alone often provides valuable information about the geometric and electronic structures of the carbonyl complexes. As we may recall, free CO absorbs strongly at 2155 cm-1, which corresponds to the stretching motion of a C=0 triple bond. On the other hand, most ketones and aldehyde exhibit bands near 1715 cm-1, which corresponds formally to... 

Since there is a direct relationship between the structure of a metal-carbonyl complex and the number of CO stretching bands, it is often possible to deduce the arrangement of the CO groups in a complex when we compare its spectrum with the number of CO stretch bands predicted for each of the possible structures using group theory techniques. As an illustrative example, consider the cis and trans isomers of an octahedral M(CO)4L2 complex. For the trans isomer, with 7 4h symmetry, we have... 

These results strengthen the analogy between molecular and supported metal carbonyl complexes and extend it beyond structure and bonding to reactivity. 

Abstract This work describes the ultrafast processes preceding the photoinduced decarbonylation of the simple metal carbonyl complexes Cr(CO)6, Fe(CO)5, and Ni(CO)4. Models for their electronic structure are presented based on recent ab initio quantum chemical calculations and these models are used to describe initial excited-state dynamics leading to the expulsion of one CO ligand. Experimental support for the proposed excited-state dynamics is presented, as obtained from ultrafast pump-probe experiments using mass-selective detection, ultrafast electron diffraction, and luminescence studies. The results of some steady-state experiments are also presented where they support the proposed dynamic model. 

Subsequent to the initial work outlined above, high field H and NMR studies of 11 and model compounds supported the original suggestion for its structure In terms of model compounds one of the key approaches taken was to use the metal carbonyl complexes of the homotropenylium ion system. Thus the molybdenum, 12, chromium, 13, and... 

The text below describes the force fields and possible v(CO) absorptions of the various types of mononuclear transition metal carbonyl complex. Although it is not an exhaustive survey, most of the important groups are covered. A suimnary of the structures covered is given in Table 7. Where a ligand is denoted as L it is a two-electron donor (e.g., PF3) and where it is X it is a one-electron donor (e.g., Br). 

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