Arene complexes electronic spectra

The only example of P.E. spectra of a mixed arene-carbonyl metal complex is that of Cr(bz)(CO)3 reported by Guest et al. (76). In the latter compound, the two d-bands observed in the spectrum of Cr(bz)2 merge into a single band, with maximum at 7.42 eV, containing the ionizations of all six -electrons. A second band, at 10.70 eV, is related to a benzene orbital, while a third band, at 12.70 eV, has both carbonyl and benzene character. The assignment is supported by theoretical calculations and by comparison between He(I) and He(II) spectra (76). 

The intermediate cyclooctene complex appears to be more reactive with respect to CS coordination and more sensitive to oxidation when the arene ring bears electron-withdrawing groups (e.g., C02CH3). Dicarbonyl(methyl rj6-benzoate)-thiocarbonyl)chromium is air stable in the solid state and reasonably stable in solution.9 The infrared spectrum exhibits metal carbonyl absorptions at 1980 and 1935 cm"1 and a metal thiocarbonyl stretch at 1215 cm"1 (Nujol) (these occur at 1978, 1932, and 1912 cm"1 in CH2C12 solution).10 Irradiation of the compound in the presence of phosphite or phosphine leads to slow substitution of CO by these ligands, whereas the CS ligand remains inert to substitution. The crystal structure has been published."... 

The electronic spectra of Lu(III) 10 and In(III) 11 complexes of calix[4]arene ball-type Pcs in Fig. 3 are worthy of being cited, Fig. 15. It can be seen from the electronic absorption spectrum of 10 that Q band splits into two, with maxima 708 and 673 nm, as a result of exciton coupling between two Pc units. Coumpond 11 exhibits a broadened Q band indicating additional amount of aggregation of that compound, and a weak band around 630 nm due to exciton coupling [42,52-57]. 

Most organometallic EDA complexes of arenes with titanium tetrachloride [116] in solution also follow the general reaction scheme in Eq. 15 in that no net chemical reaction is observed upon charge-transfer irradiation due to rapid back electron transfer (A et 10 ° s ). For example, the transient absorption spectrum of bro-moanthracene (BrAnt) cation radical generated by 532-nm laser excitation of the [BrAnt, TiCU] complex in cyclohexane (see Figure 7) decays completely to the spectral baseline within about 1 ns (see inset) due to back electron transfer [116], (Eq. 18) ... 

The reduction of chlorinated arenes to arenes represents an important chemical transformation because of the deleterious environmental and health impact of these compounds, and nickel reagents have shown higher efficiencies in this reaction compared to other metals. Fort and co-workers reported the first use of NHC-Ni for the reduction of C-Cl bonds. In this approach, stable [(NHC)2Ni ] species were formed in situ, by NaH-induced reduction of [Ni(acac)2]. Interestingly, transmission electron microscopy of the obtained mixture revealed a homogeneous distribution of uniformly sized amorphous and subnanometric (<0.5 nm) Ni nanoparticles (NPs). NMR analysis of the reaction medium revealed a spectrum comparable to the reported spectra for [(IPr)2Ni ] prepared from [Ni(COD)2]. This procedure was recently adapted by Matsubara to prepare free [(IPr)2Ni] and [(IPr)Ni(acac)2] complexes in the absence of NaOt-Bu. This structural study also showed... 

Fullerenes are also known to form the inclusion complexes with calixarenes. In the case of the water-soluble inclusion complex of Qo and calixarene (cationic homoox-acalix[3]arene), substantial interaction between fullerenes and the calixarene was observed in the ground state absorption spectrum [76]. Increase in the absorption intensity around 400-500 nm of C q in calixarene can be attributed to the charge-transfer complex formation due to the n -electron system of calixarene. Strong interaction between the calixarene and fullerenes was also observed in the excited states. The triplet absorption peak of 60 in the calixarene appeared at 545 nm, which is largely blueshifted compared to that of pristine Cgg- The triplet lifetime is as short as 50 ns. The substantial interaction between calixarene and included Qo was also observed in the singlet excited state as a large blueshift of the fluorescence peak. 

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