Pieter Schipper

Selectivity in Reactions of Tricyclic Phosphatranes

Five-coordinated phosphorus compounds are known to adopt the trigonal bipyramidal (TBP) configuration, in which the apical positions are preferred by electron-withdrawing groups, whereas electron-donating groups are situated in equatorial positions (1). In addition, the apical bonds are longer and weaker than the equatorial bonds originating apical entry and departure of groups (phosphorylation) (2). Little attention has been paid to reactions in which external nucleophiles discriminate between pseudo-equatorial and pseudo-apical carbon atoms in a TBP configuration. The observation of such selective reactions is hampered by the occurrence of pseudo-rotation which brings about ligand exchange in the TBP (3). In order to obtain a definite answer with respect to equatorial vs. apical reactivity for nucleophiles we have synthesized the rigid tricyclic phosphatranes 1-4 in which a transannular N ? P bond brings phosphorus in a TBP configuration. Previously the characterization of the related compound 5 was published by Verkade et al.

3,3,3′,3′-Tetramethyl-1,1′-spirobi[3H-2,1-benzoxaphosph(v)ole]-1-yl radical: evidence of a correlation between pseudorotation and stereoisomerisation

It is shown that the factors which determine the stereoisomerisation of phenylphosphoranyl-radicals are similar to those determining the pseudorotation of PV phosphoranes.

Single crystal e.s.r. study of the 1,6-dioxa-4,9-diaza-5-phospha(V)spiro[4.4]nonan-5-yl and the 1,6-dioxa-4,9-diaza-2,3,7,8-dibenzo-5-phospha(V)spiro[4.4]nona-2,7-dien-5-yl radicals

The unpaired electron in two oriented phosphoranyl radicals (title) with trigonal bipyramial geometry is located in an equatorial position.

Single crystal e.s.r. study of the octahydro-2a,4a,6a,8a-tetra-aza-8b-phospha(V)pentaleno[1,6-cd]pentalen-8b-yl radical. Evidence of ligand exchange via a Berry pseudorotation mechanism

The nitrogen ligands of the title phosphoranyl radical interconvert pairwise via an M-1 Berry pseudo-rotation mechanism in the solid state.

Stereoisomerization of the P(OCH2CH2)3N+BF4– radical: a single-crystal e.s.r. study

The [graphic omitted]+BF4– radical with the unpaired electron in an apical position of the trigonal-bipyramidal (TBP) structure is generated by X-irradiation via an intermediate TBP structure in which the unpaired electron is located in an equatorial position.

Stereospecific quenching of the bicyclo[5.4.1]dodecapentaenyl cation. Evidence of orbital symmetry control

Quenching of the title cation (3) with lithium methoxide results in stereo- and regio-specific incorporation of the methoxy group to give (4); the high specificity of the quench reaction is controlled by orbital symmetry.

Evidence of prevailing strain effects on the valence state of the 5-phenyl-4,6-dioxa-1-aza-5-phospha(V)bicyclo[3.3.0]octan-5-yl radical

The valence state of phenylphosphoranyl radicals, which has been shown to depend on the electro-negativity of the other ligands, appears also to be influenced by incorportion of the phosphorus within a rigid skeleton, which forces the unpaired electron of the bicyclic title compound to be centred on phosphorus in contrast to the behaviour of its acyclic analogue, in which the unpaired electron is preferentially located on the aromatic ring.

Generation of a pentaco-ordinated protonated oxyphosphorane in equilibrium with the isomeric enol phosphonium ion and unprotonated oxyphosphorane

Reaction of 2,2,2-trimethoxy-4,5-dimethyl-2,2-dihydro-1,3,2-dioxaphospholen with FSO3H in CH2Cl2 at low temperatures gives the corresponding protonated oxyphosphorane.