Isomerization tetraphosphines

Valence Isomerism. Restricted Rotation and Permutational Isomer i sm. - The variable temperature spectra of bicyclic tetraphosphines (29) has been analysed in terms of valence isomerism involving the corresponding two coordinate open-chain isomers.62 A report on ab initio MO calculations of the inversion barriers for a series of methyl phosphines includes a discussion of the electronic consequences of steric effects.63 Inversion barriers of 1,2-diphosphinobenzenes are in the range 100 - 110 kJ mol". 66 The ring inversion barrier for a dibenzophosphorin has also been measured.63... 

There are numerous possibilities for both positional and optical isomerism amongst the polyphosphines (Chapter 4.4), and the existence of many examples of these has been demonstrated by NMR techniques. There are, for example, two positional isomers of tetraphosphine, P4Hg. 

In the hydroformylation of terminal olefins, superior results in comparison to BISBI at higher temperature were noted l/b = 54.2 in comparison to BISBI Hb = 2.4) [66]. Moreover, with these tetraphosphines more than 95% linear selectivity and up to 94% yield of total aldehydes starting from 2-alkenes (2-pentene, 2-hexene, 2-octene) were observed in isomerizing hydroformylation [67]. The M-regioselectivity increased in relation to the nature of Ar in the following order, indicating a remarkable electronic effect ... 

Ar = p-M C0H4 < Ph m-CF3C0H4 — 3,5-(CF3)2 6 13 3,5-F2C0H3 < p-CF3C0H4 Figure 5.4 Tetraphosphines and their graded suitability for isomerization-hydroformylation. 

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