Synthesis and Reactivity of Monocyclic Homoleptic Oligophosphanes

Abstract

This Minireview outlines the synthesis and reactivity of homoleptic, cyclic oligophosphanes, which have been known for more than 150 years. We will discuss a variety of (PR)n (n = 3,4,5,6) species and outline approaches towards their syntheses in the first part of this review. Then the unique reactivity of these inorganic ring systems will be discussed in detail with a focus on recent findings within the last 20 years. First ring expansion reactions will be described, which are mainly restricted to cyclotriphosphanes. Secondly, ring fragmentation will be highlighted, including phosphinidene transfer reactions. Furthermore, cyclooligophosphanes can be functionalized while retaining the parent ring structures. As oligophosphanes offer multiple donor sites, in a last part the coordination chemistry of these species is highlighted. We hope that this Minireview will spark further interest in this underexplored class of compounds as reagents in inorganic and organic synthesis, as well as the design of new P‐containing materials.

Cyclo‐Dipnictadialanes

“…Tr iphosphiranes (PR) 3 and cyclo-oligophosphanes are,i n general, the formal oligomers of phosphinidenes. [26] Especially (PhP) 5 has been shown to react with NHCs to give NHC phosphinidene adducts of the type NHC=PPh, [27] by formal phosphinidene transfer. We thus hypothesised that the combination of three equiv of Cp 3t Al with (ArP) 3 (Ar = Mes,D ip,T ip) would facilitate formation of Cp 3t Al = PA r, which might exist either in its monomer form or as adimeric cyclo-diphosphadialane (Scheme 3).…”

Cyclische Dipnictadialane

“…Diphosphadialane ausgehend von Cp 3t Al und (PR) 3 /(PAr) 5 Tr iphosphirane (PR) 3 und Cyclooligophosphane im Allgemeinen sind die formalen Oligomere von Phosphinidenen. [26] Insbesondere hat sich gezeigt, dass (PhP) 5 mit NHCs zu NHC-Phosphiniden-Addukten des Ty ps NHC=PPh durch formale Phosphinidenübertragung reagiert. [27] Wirs tellten daher die Hypothese auf,d ass die Kombination von drei ¾quivalenten von Cp 3t Al mit (ArP) 3 (Ar = Mes,Dip,Tip) die Bildung von Cp 3t Al=PA rermçglichen sollte,die entweder in monomerer Form oder als dimere Cyclo-Diphosphadialane vorliegen kçnnten (Schema 3).…”

Phosphine-catalysed reductive coupling of Dihalophosphanes

“…39 Even though a large variety of diphosphenes is known, sterically demanding and therefore kinetically stabilizing groups attached to phosphorus are needed to stabilize the reactive P=P double bond, as formation of larger oligomers, namely cyclooligophosphanes is observed otherwise. [40][41] Our group has shown that aryldihalophosphanes of the type ArPX 2 (Ar = 2,4,6-Me 3 C 6 H 3 , Mes; 2,6-iPr 2 C 6 H 3 , Dip; 2,4,6-iPr 3 C 6 H 2 , Tip; X = Cl, Br) are selectively coupled S4 using a mixture of PMe 3 and Zn to give the corresponding triphosphiranes (PAr) 3 . PMe 3 was identified as the active reductant.…”