Tertiary phobanes

Scheme 2.5 Pathways to tertiary phobanes (in Ref. [14], exemplified with R = Ph) and typical...

Secondary phosphines can also be prepared by addition of P—H bonds across olefmic double bonds.40 For example, the industrially important bicyclic secondary phosphine phobane (43) can be synthesized from phosphine gas and cycloocta-1,5-diene, albeit as a mixture of two isomers (43a) and (43b) (Scheme 3). These isomers have recently been separated by an elegant sequence of hydrophosphination/dehydrophosphination steps, affording pure isomers which have been used in subsequent tertiary and ditertiary phosphine ligand syntheses.57... 

In a second report, the Bergman and Ellman groups improved on their original procedure for the arylation of heterocycles with aryl halides [103]. The key improvements over the previous method were three-fold (1) the use of the hindered tertiary amine base Pr.NBu in replacement of Et3N (2) microwave irradiation for rapid (<1 h), high temperature (250 °C) reactions in 1,2-dichlorobenzene (3) the use of bulky bicyclic trialkylphosphine ligands of the phobane family in replacement of PCy3 (Scheme 15). Under typical reaction conditions, the heterocycle... 

In turn, Phobane-H may serve as starting material for the construction of a variety of tertiary phosphines (Scheme 2.5). Noteworthy, pathway (a) via the corresponding chlorophosphine and final alkylation also affords some undesired dimeric P-P coupling products. Alternatively, a chloro-free access has been suggested, which circumvents the Phobane-Cl (pathway b). A palladium-catalyzed P-C coupling reaction (with R = Ar) is less sensitive toward moisture and allows also the incorporation of a third P-substituent bearing functional... 

The CT-donor properties of a series of the bicyclic tertiary phosphines known as phobanes have been compared using the fypse values for the PhobP(=Se)Bu derivatives.The compounds studied were the four isomers of 9-butylphosphabicyclo[3.3.1]nonane, s-PhobPBu, where Bu = -butyl, sec-butyl, isobutyl, tert-bufyl, seven isomers of... 

---