Reactivity of cyclooligophosphanes: synthesis and structural characterisation of cyclo-1,4-(BH₃)₂(P₄Ph₄CH₂) and cyclo-1,2-(BH₃)₂(P₅Ph₅)

Abstract

The borane complexes cyclo-1,4-(BH3)2(P4Ph4CH2) (3) and cyclo-1,2-(BH3)2(P5Ph5) (4) were prepared by reaction of cyclo-(P4Ph4CH2) and cyclo-(P5Ph5) with BH3(SMe2). Only the 2:1 complexes 3 and 4 were isolated, even when an excess of the borane source was used. In solution, 3 exists as a mixture of the two diastereomers (R(P)*,S(P)*,S(P)*,R(P)*)-(+/-)-3 and (R(P)*,R(P)*,R(P)*,R(P)*)-(+/-)-3. However, in the solid state the (R(P)*,S(P)*,S(P)*,R(P)*)-(+/-) diastereomer is the major stereoisomer. Similarly, while only one isomer of 4 is observed in its X-ray structure, NMR spectroscopic investigations reveal that it forms a complex mixture of isomers in solution. 3 may be deprotonated with tBuLi to give the lithium salt cyclo-1,4-(BH3)2(P4Ph4CHLi) (3 x Li), though this could not be isolated in pure form.

The unusual coordination chemistry of phosphorus-rich linear and cyclic oligophosphanide anions

“…In these reactions, the ring size is usually retained, but some ring expansions have also been observed. Analogously, compounds such as cyclo-1,2-(BH 3 ) 2 (P 5 Ph 5 ) (1) have been also synthesized by this method (Scheme 1) [14].…”

Cyclotetraphosphinophosphonium Ions: Synthesis, Structures, and Pseudorotation

“…In this context, homoatomic bonding, which is responsible for the extent of organic chemistry, promises a diverse and extensive catena -phosphorus chemistry that has not yet been fully realized. New versatile synthetic methods have enabled the discovery of catena -phosphonium ions − that complement the well-known series of catena -phosphines, − new borane complexes of catena -phosphines, and catena -phosphorus anions, − ,− each featuring phosphorus centers as isolobal analogues of tetrahedral carbon environments. The phosphinophosphonium frameworks 5 , ,, 6 , and 7 7 (Scheme ) derive from the neutral polyphosphines 1 , 2 , and 3 but have been prepared from a variety of starting materials that provide guidelines for the development of larger frameworks.…”

Synthesis and Molecular Structure of [Cp*Ta(Ph)(P6Ph5)]: A Terminal Phosphinidene Complex of the (P6Ph5)3– Ligand (Cp* = C5Me5)

“…Most likely, they can be attributed to the presence of a second diastereomer of 2 in solution, which may be formed by inversion of either of the uncoordinated P atoms (P B or P D ). It is well‐known that catenated oligophosphanes have significantly reduced inversion barriers, as was observed, for example, in the heterocycles cyclo ‐1,4‐(BH 3 ) 2 (P 4 Ph 4 CH 2 )24 and [M{ cyclo ‐(P 4 Cy 4 As)}] (M = Li, Na) 25…”