Oligophosphine boranes

The diboronated BisP diphosphines contain two methyl groups amenable to be deprotonated and oxidatively oligomerised to afford C2-oligophosphine boranes with an even number of phosphorus atoms. This chemistry has been extensively studied by Chujo and co-workers (Scheme 5.37). ... 

Scheme 5.37 Preparation of P-stereogenic oligophosphine boranes from t-Bu-BisP (BH3)2- Decaphosphine borane 89 has not been reported but is included for the sake of completeness.

Oligophosphine boranes t-Bu-BisP, 86, 87 and 90 have been also prepared in optically inactive form, i.e. synthesised without the presence of sparteine. Comparison of these diastereomeric mixtures with the corresponding optically active oligophosphine boranes revealed that the latter are more crystalhne. For example, the optically inactive tetraphosphine borane exhibits DSC thermograms and XRD profiles similar to the optically pure hexaphosphine borane 87. 

During the preparation of oligophosphine boranes, the principal side reaction is the intramolecular oxidative coupling of the dianions to produce cyclic compounds." These reactions have been studied in more detail and constitute a stereoselective route to several interesting cyclic (but achiral) polyphosphine boranes. The simplest one is the 1,4-diphosphacyclohexane borane (Scheme 5.39). ... 

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See also in sourсe #XX -- [ , , , , ]

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