Photochemistry of π-cyclopentadienylcarbonylmetal halides in dimethyl sulphoxide and related solvents

Abstract

The principal product when solutions in dimethyl sulphoxide or pyridine of x-cyclopentadienylcarbonyimetal halides of Fe, Mo, and W are irradiated at long wavelengthsin the case of Fe (indicating loss of halogen) but appears to be [(X-C~H~)M(CO),CJ], for Mo and W; free cyclopentadiene and chloride ion are also produced in the case of Fe. The reactions do not proceed in non-polar solvents. At shorter wavelengths (A > 280 nm) the principal product in all cases is a dimeric species which could not be isolated, but which spectral data suggest to correspond to displacement of one CO molecule by solvent from the dimers obtained at longer wavelengths; moreover i.r. and n.m.r. spectral profiles of the h > 280 nm reaction indicate that the latter are essential intermediates in all three cases. Coventry CV4 7ALTHE primary process dominating the photochemistry of many metal and arenemetal carbonyls is that of elimination of one molecule of CO to leave an unsaturated intermediate, which rapidly co-ordinates with a solvent molecule S,1~2 vix.unless it is prepared either in an inert in which case it can be rendered sufficiently stable for i.r. and U.V. examination, or in a non-co-ordinating solvent, in which case the end-product corresponds to a disproportiona-tionJ6 e.g. GCr(CO), + 5Cr(CO), + Cr which clearly involves a sequence of several steps. Evidence for the unsaturated intermediates has also been obtained from room-temperature flash photolysis

Quantitative Photochemistry of (η5-C5H5)Fe(CO)2I in Solution: Effective Heterolytic Fe−I Dissociation upon Long-Wavelength Excitation

“…First, the energy positions of these bands have been determined to not be particularly solvent dependent (see Table ), which is typical behavior of d → d transitions. , Second, the molar absorptivities of these absorption bands are fairly low, consistent with orbitally forbidden transitions in organometallic complexes . Third, the earlier photochemical studies have demonstrated that these (η 5 -C 5 H 5 )Fe(CO) 2 X (X = halide) complexes undergo highly efficient CO dissociation following excitation at 366 and 458 nm 4b 1 Electronic absorption spectrum of (η 5 -C 5 H 5 )Fe(CO) 2 I in chloroform at room temperature.…”

“…In contrast, other studies have revealed that irradiation of (η 5 -C 5 H 5 )Fe(CO) 2 X can result in the formation of the dimer {[(η 5 -C 5 H 5 )Fe(CO) 2 ] 2 }, together with Fe 2+ , X - , and ferrocene, depending on experimental conditions. 3c,4c Metal−halide heterolysis and metal−metal-bonded dimer formation followed by subsequent disproportionation have been shown to be the main routes for the photochemical formation of ionic products from organometallic halide complexes. In the case of (η 5 -C 5 H 5 )Fe(CO) 2 I, the reaction involves the initial heterolysis of the Fe−I bond, a step which is recognized as being amine base assisted 4b…”

“…Cyclopentadienylmetal carbonyl complexes containing one-electron-donor halide ligands have attracted considerable attention recently as they are known to exhibit a variety of photochemical deactivation pathways. These processes include dissociation of the carbonyl ligand, , homolytic or heterolytic cleavage of the metal−halide bond, intramolecular isomerization, and intraligand rearrangements . For instance, earlier studies have demonstrated that (η 5 -C 5 H 5 )M(CO) 3 X complexes (M = Mo, W; X = Cl, Br, I) undergo photochemistry in solutions containing two-electron-donor ligands to yield either ligand-substituted or ionic products via CO and halide ion displacements. 2e, …”

“…Although quantitative photochemical measurements have demonstrated that the CO dissociative process in (η 5 -C 5 H 5 )Fe(CO) 2 X (X = Br, I) proceeds with high quantum efficiency (Φ cr = 0.14−0.89) at 366 or 458 nm,4b the optimum excitation wavelength conditions and the photoefficiencies for the corresponding heterolytic Fe−X dissociative reaction are not known. Consequently, we present here a determination of this quantitative photochemistry for the dissociation of I from (η 5 -C 5 H 5 )Fe(CO) 2 I (see eq 1) following long-wavelength excitation.…”

Labeling Biomolecules with Radiorhenium - A Review of the Bifunctional Chelators

“…The rhenium diazenido complexes (Re=N=N-R) have been extensively investigated since they were first reported in the early 1970s [92][93][94]. Because there are no stable isotopes of technetium, the structural investigation of the rhenium diazenido complexes [92][93][94][95][96][97][98][99][100] is more comprehensive than that of the technetium analogues at both macroscopic and tracer level [100][101][102][103][104][105][106][107][108][109]. However, a far greater number of reports have been published on 99m Tc compared to radiorhenium labeling of biomolecules with hynic.…”