A study of the reactions of t-butyl phosphorus compounds.

The preparation and reactions of mono- and di-t-butyl phosphorus (III) compounds have been investigated in order to assess the importance of steric factors in nucleophilic and electrophilic reactions at tervalent phosphorus. In general, while the nucleophilic properties were unaffected by the presence of one or two t-butyl groups, di-t-butyl phosphorus (III) compounds are resistant to attack by all but the smallest nucleophiles. Four co-ordinate phosphorus bearing two t-butyl groups is also resistant to nucleophilic attack and several compounds of extraordinary stability have been obtained, e.g. di-t-butylmethylphenoxy-phosphonium iodide and benzy1-di-t-butylphenoxyphosphonium bromide. A series of t-butyl oxyphosphoranes has been prepared and the variable temperature 1H n.m.r. spectra of these compounds have been investigated. The t-butyl group preferentially occupies the equatorial position, Phosphoranes derived from ethylene phosphonothioites decompose readily to give thiiran and phosphonate or phosphinate esters. A synthesis of t-butylphosphine involving the acid catalysed addition of phosphine to isobutylene has been developed and the reactions of this phosphine investigated. The primary oxide and sulphide were prepared and characterized. t-butylphosphine reacts with only one molecule of a variety of carbonyl compounds to give stable secondary phosphine oxides.