Kuang S. Chen

An esr study of the reactions of decacarbonyldimanganese, trimethyltinpentacarbonylmanganese and decacarbonyldirhenium with quinones and α-diketones

Abstract The thermal and photochemical reactions of Mn2(CO)10, Me3SnMn(CO)5, and Me2Sn[Mn(CO)5]2 with various quinones and α-diketones were studied by ESR. The results clearly show that with p-quinones the predominant manganese radical adducts are formed via complexation of the metal with the quinonoid π-electron systems. However, a different reaction with o-quinones and α-diketones leads to the formation of manganese radical adducts mainly via metal chelation to the carbonyl oxygens. The photolysis of Re2(CO)10 with o-quinones also yields the analogous rhenium radical adducts.

A comparative esr study of the reactions of group ivb organometallic radicals with 4,4′-dimethoxybenzophenone, 4,4′-dimethoxythiobenzophenone, and 3-ethyl-2-thioxo-4-oxazolidione

Abstract Various reactions of Group IVB organometallic radicals with 4,4′-dimethoxybenzophenone, 4,4′-dimethoxythiobenzophenone, and 3-ethyl-2-thioxo-4-oxazolidione were studied by ESR spectroscopy. The greater involvement of sulfur in comparison with oxygen in spin delocalization is clearly reflected in both the hyperfine coupling constants and the g -factors. In general, thiocarbonyl compounds appear to be more efficient in forming radical adducts than the corresponding carbonyl compounds but the overall reactions depend strongly upon the structure of the thiocarbonyl compounds.

Photolytic generation of radical anions and dianions and Group IVB organometallic adducts of β-diketones. An electron spin resonance study on the effects of fluorine substitution and crown ethers

Using CF3COCH2COCF3, 2-thienyl-COCH2COCF3 and model diketones, we have successfully demonstrated the formation and the observation of the e.s.r. of radical anions by photoreduction with amines and the radical dianions by photochemical reactions with THF and alkali-metal tetraphenylborates. The e.s.r. results shed some light on the reaction mechanisms of these photochemical processes. The chemical selectivity of different organometallic radicals towards the tautomers of CF3COCH2COCF3 is further illustrated by having organosilyl radicals add mainly to the enol form while the organotin radicals co-ordinate only to the keto-form of the diketone.

An electron spin resonance study of the Group IVB organometallic adducts of 2,6-di-t-butylbenzoquinone

2,6-Di-t-butylbenzoquinone can interact with group IVB organometallic compounds to give the stable substituted phenoxyl radicals detectable by e.s.r. The strong bonding between silicon and oxygen atoms together with the unusual stability of the resulting phenoxyl radicals show that 2,6-di-t-butylbenzoquinone is an excellent spin trap of organosilyl radicals. This quinone has also been used successfully to trap both diphenylphosphino and phenylthiyl radicals.