Phosphine oxides photolysis

In contrast to the situation on flash pyrolysis, methyleneoxophosphoranes generated by thermolysis or photolysis in the presence of protic nucleophiles can be directly trapped to form corresponding derivatives of phosphinic acid (17- 19) however, the possibility of competing insertion of carbenes into the H/X bond of the additives is always present, giving phosphine oxides with X in the a-position (16- 18). Reaction branching at the carbene 16 was first observed on photolysis of 7 in water 13) and prompted detailed investigations on the phosphorylcarbene/ methyleneoxophosphorane rearrangement. 

The energies of the triplet states of sensitizers TX (ITX) and of Pis TPO (BAPO) are close to each other ( 260 kJ/mol), allowing for slightly exothermic or thermoneutral T-T energy transfer from sensitizer to PI. Direct photolysis of phosphine oxides results in a well-documented initial strong absorptive (A) pattern of ESR spectra (see Fig. 12.2). Sensitization by TX or ITX of the photolysis of phosphine oxides leads evidently to the same radicals, but an initial polarization pattern is quite different, namely, emission/absorption (E/A) pattern (see Fig. 12.3). 

H-CIDNP and ESR techniques. A laser flash photolysis and time-resolved ESR study of the formation of phosphinoyl radicals from benzoyldiphenyl-phosphine oxide and 257 has appeared. The addition of dialkyIphosphoryl radicals to a fullerene system has also been studied. Interest in adducts of phosphine oxides with proton donors, notably phenols and other solvent guests ° has continued. 

The photolysis of a mixture of the alkene RCH=CH2 and (382) afforded (383) in good to high yields. The treatment of a large variety of a-thiomethyl- and a-selenomethyl phosphonates with BusSnH-AIBN results in their desulfurization or deselenation. The deselenation of phosphinoselenoic esters, e.g. (384), occurs imder attack by organometallic reagents, and ensuing reaction with alkyl halides provides phosphine oxides. ... 

It consists of thioxanthone or 2-isopropylthioxanthone in combination with (2,4,6-trimethylbenzoyl)-diphenyl-phosphine oxide or bis(2,4,6-trimethyl-benzoyl)-phenylphosphine oxide. The mechanism of sensitization was reported to involve triplet-triplet energy transfer from the thioxanthones to die phosphine oxides. That is followed by formation of radicals through a-cleavage of the photoinitiators. Direct photolysis of the phosphine oxides results in an absorptive, chemically induced, d)mamic electron polarization due to the triplet mechanism of polarization of the substituted benzoyl. The phosphoras-centered radicals produced by a-cleavage of the photoinitiators are the same radicals that... 

Phosphonyl radicals can be generated by photolysis or radical abstraction from secondary phosphine oxides, alkyl phosphinates or dialkyl phosphonates. They can be obtained from tertiary butoxy radicals and dialkyl phosphites or tetra alkyl diphosphites (13.175) and (13.176). Phosphonyl radicals react with alkyl halides according to (13.177). 

The phosphine complex Ru(dmpe)2 has been studied in matrices [62], Ru(diphos)2 (diphos = depe, dppe, (QFs P F P Fs ) has similarly been formed by photolysis of Ru(diphos)2H2 in low-temperature matrices. They probably have square planar structures and undergo oxidative addition with cobalt, C2H4 and hydrogen [63]. 

Photolysis of the first known cyclic a-diazo-p-oxophosphine oxide 49 is unsuccessful with regard to phosphene formation. There is no evidence for a P/C-phenyl shift, which should lead to 51, nor for a P/C-alkyl shift, which would afford 52 via ring contraction, since none of the expected phosphinic esters could be isolated in methanolM). 

If the assumption of this reaction sequence is correct, the photolysis of tetraphenylphosphonium chloride must then only lead to biphenyl, diphenylphosphine, ethyl diphenyl-phosphinate and triphenylphosphine and its oxidation products. After 2 h of irradiation, biphenyl, diphenylphosphine and its oxidation products, triphenylphosphine and triphenylphosphine oxide, in a ratio of 3 1 5, along with raw material, are obtained. Ethyl diphenylphosphinate was detected in trace amounts7. These results support the postulate of the reversibility of phosphoranyl radical formation in such systems and indicate one-electron transfer processes15 in the formation and decomposition of the tetraarylphosphonium cation. This reaction is comparable to the observation of an electron transfer from halide ions to hydroxyl radicals or hydrogen atoms in aqueous solutions16,... 

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