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Homolytic organometallic reactions. Part IX. An electron spin resonance study of the mechanism of β-scission of tetra-alkoxyphosphoranyl radicals. Formation of trialkoxy(methyl)phosphoranyl radicals

1972; Royal Society of Chemistry; Issue: 15 Linguagem: Inglês

10.1039/p29720002224

2050-8239

Alwyn G. Davies, D. Griller, B. P. ROBERTS,

Metal complexes synthesis and properties

The rate of β-scission of the tetra-alkoxyphosphoranyl radicals (RO)4P·, where the alkyl groups may be the same or different, is determined by configurational, steric, electronic, and solvent effects. The rate of C–O cleavage increases along the series Rp < Rs < Rt < PhCH2. In the distorted trigonal bipyramidal radical (RO)4P·, alkyl groups in apical or equatorial positions are not lost at the same rate, probably those in the equatorial position under-going more rapid β-scission. As a result of this configurational selectivity, bulkyl alkyl groups are retained preferentially when (RO)4P· decomposes. The rate of scission of (EtO)3POBut increases somewhat with the solvent polarity, but there appears to be little steric acceleration when (RO)4P· contains bulky alkyl groups. Methyl radicals react with trialkyl phosphites to give the radicals (RO)3[graphic omitted]Me at a rate which is governed primarily by steric effects. PhCH2O[graphic omitted](OEt)2Me undergoes rapid β-scission to give a benzyl radical.