Carbonyl transition

Liicke et al. have prepared other phosphinated POSS compounds Tg[(CH2)2-PMe2]8 and Tg[(CH2)3-PMe2]8 by treating T8[CH = CH2]8 or T8[CH2-CH = CH2]8 with H-PMe2 under UV irradiation. The former compound has shown to have good coordination properties to carbonyl transition metal complexes such as CpMn(CO)3 (Table 15). 

In spectroscopy we may distinguish two types of process, adiabatic and vertical. Adiabatic excitation energies are by definition thermodynamic ones, and they are usually further defined to refer to at 0° K. In practice, at least for electronic spectroscopy, one is more likely to observe vertical processes, because of the Franck-Condon principle. The simplest principle for understandings solvation effects on vertical electronic transitions is the two-response-time model in which the solvent is assumed to have a fast response time associated with electronic polarization and a slow response time associated with translational, librational, and vibrational motions of the nuclei.92 One assumes that electronic excitation is slow compared with electronic response but fast compared with nuclear response. The latter assumption is quite reasonable, but the former is questionable since the time scale of electronic excitation is quite comparable to solvent electronic polarization (consider, e.g., the excitation of a 4.5 eV n — n carbonyl transition in a solvent whose frequency response is centered at 10 eV the corresponding time scales are 10 15 s and 2 x 10 15 s respectively). A theory that takes account of the similarity of these time scales would be very difficult, involving explicit electron correlation between the solute and the macroscopic solvent. One can, however, treat the limit where the solvent electronic response is fast compared to solute electronic transitions this is called the direct reaction field (DRF). 49,93 The accurate answer must lie somewhere between the SCRF and DRF limits 94 nevertheless one can obtain very useful results with a two-time-scale version of the more manageable SCRF limit, as illustrated by a very successful recent treatment... 

Structural Comparison of Corresponding /l-Methylene and -Carbonyl Transition Metal Complexes... 

Optically active organometallic compounds in which the transition metal is the center of chirality have been known since 1969, when the first manganese compounds were reported1. In the meantime cyclopentadienyl and carbonyl transition metal complexes with 4, 5 and 6 ligands have been obtained in optically active form for the following types of compounds (Scheme 1) ... 

The computations of dipole and rotational strengths for the polymers are carried out using Cartesian coordinates of the C and O atoms of the various carbonyl groups on the purine and pyrimidine bases or the peptide linkages. Furthermore, the transition frequency i>0 of an unperturbed carbonyl transition is needed, and its monomeric dipole strength D, which is proportional to n2. For the conversion between rotational (or dipole) strengths (in esu cm)2 and the extinction coefficients (in LmoHcm1) the approximations... 

For these calculations, the carbonyl transition frequency and intensity were taken from a 1 1 CMP/GMP mixture in D20 (i/Q = 1650 cm"1 emax = 950 Lmob cm 1). Carbonyl coordinates, created by program MacroModel [21] for a canonical, B-form, alternating CG polymer, were used without geometry optimization. Band shapes were employed that are 50 50 mixtures of Lorenzian and Gaussian contours, since it was found that such a mixed composition provides the best fit between observed and computed spectra, although pure Gaussian or pure Lorenzian band shapes give satisfactory results as well. 

Table IV. Cotton effects for the n - t carbonyl transition of 7-keto steroids and their 6-methylated derivatives.

It was shown in Sec. 11.3.4.3 that Aubke, Willner and colleagues [47] recently carbonylated transition metal fluorosulfates and other compounds in neat SbF5 to generate naked transition metal carbonyl cations in association with the very weakly basic anion Sb2Ff,. 

A large fraction of the binuclear mixed chalcogen/carbonyl transition metal complexes of iron and manganese contain the M2E (CO)6 core with the butterfly-type structure (n = 2) or substructure (n — 3, see Section 1.10.3). As an example of a complex with thiolate ligands, the structure of [Fe2(SC3H7)2(CO)6] is shown in... 

The chiroptical properties of pelletierine and anaferine have been studied. They reveal that both molecules are sensitive to conformational changes. The former apparently adopts the tra 5-pseudo-ring conformation (18) in acid solution and the c/5-fused counterpart (19) in neutral solution. The latter, in acid solution, shows a positive ellipticity for the n-ir carbonyl transition, of about the same magnitude as for (- )-pelletierine sulphate but opposite in sign, suggesting major conformational changes of unknown character. ... 

In electronic spectra of metal carbonyls there are bands due to d-d transitions between metal orbitals, transitions within the ligand, charge-transfer transitions M L and L M, and also, in the case of polynuclear carbonyls, transitions between orbitals of metal-metal bonds. Transitions within the CO group probably occur in the vacuum ultraviolet region. 

The answers to these questions and other questions about the cyanide and carbonyl transition-metal complexes can be derived from the idea that the cyanide and carbonyl groups form double bonds with the transition metal atom. 

Numerous 71-cyclopentadienyl and carbonyl transition metal aryl and alkyl complexes are known which also contain tertiary phosphine ligands. These complexes are discussed as 71-cyclopentadienyl- or carbonyl-a-organo complexes, to which they are more closely related. 

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