Sterically Constrained Bicyclic Phosphines: A Class of Fascinating Compounds Suitable for Application in Small Molecule Activation and Coordination Chemistry

Abstract

Bicyclic phosphines with two annulated, electronically unsaturated five-membered heterocycles are available through facile routes. In most cases, their phosphorus atoms are bound to heteroatoms such as oxygen or nitrogen (PN or PN O), whereas homoleptic coordination by three sp -hybridized carbon atoms has been reported only recently. Steric strain causes unique reactivity. Oxidative addition of halogens, N-H or O-H bonds have afforded phosphoranes as valuable materials for secondary processes. Ring opening was identified as an important step for the understanding of these reactions and has been observed experimentally with a diphosphorus-based ring system. A PH derivative has been considered as a model system for small molecule activation, and hydrogen transfer to a diazo compound was observed experimentally. Several of these phosphines are excellent ligands for the coordination of transition-metal atoms. The very bulky PC compound has a basicity similar to that of PPh and may allow the synthesis of complexes with unusually low coordination numbers at the metal atoms. These phosphines found recently renewed interest as promising reagents in various secondary transformations such as the activation of σ-bonds or in coordination chemistry.

Dihalides of Sterically Constrained Tricyclic Phosphines, Lewis Acidity and Fluoride Affinity, Chloride Abstraction, and a Phosphonium Cation, Dimethylphosphorane

“…Strained bi‐ or tricyclic phosphines ( 1 and 2 ; Scheme ) show a fascinating reactivity in various transformations, which include oxidative addition to the P atoms, ring opening by P–X bond cleavage or coordination to transition metal atoms. Recently, we reported on the facile synthesis of a new type of such compounds ( 2 ), which had the P atoms bound to three C atoms.…”

“…Sterically constrained bicyclic or tricylic phosphines ( 1 and 2a ; Scheme ) found considerable interest in recent research . In most cases they have two annulated five‐membered heterocyles with the bridgehead P atoms bound to N, O, S or P. Only the tricylic compound 2a has the homoleptic coordination of the central P atom by three C atoms .…”

Sterically constrained tricyclic phosphine: redox behaviour, reductive and oxidative cleavage of P–C bonds, generation of a dilithium phosphaindole as a promising synthon in phosphine chemistry

“…The highly interesting chemical properties of sterically constrained bicyclic or tricyclic phosphines ( 1 to 3 ; Scheme 1 ) have attracted considerable attention in recent research. 1–7 These compounds are accessible through facile routes and have in most cases heteroatoms such as N, O, S or P bound to their central P atoms. Only recently we found facile access to the first derivatives ( 3 ) which had the P atoms coordinated in a homoleptic fashion by three C atoms.…”

“…Only recently we found facile access to the first derivatives ( 3 ) which had the P atoms coordinated in a homoleptic fashion by three C atoms. 1,7,8 The latter compounds were obtained by treatment of the dimeric or trimeric trilithium compounds 4 (ref. 7 and 9 ) with PCl 3 and salt elimination.…”

Synthesis and characterization of a pair of O-fac/O-mer 12-P-6 alkyloxaphosphates with a P–O–C–C four-membered ring

“…In the context of synthetic organic chemistry, pentacoordinate phosphoranes have been the centre of studies related to Wittig reactions5 since the first report of the pentaphenylphosphorane (Ph 5 P),6 revealing their characteristic apicophilicity7–11 and facile stereomutation 12–15. This, subsequently, leads to the later development of geometrically constrained T-shaped phosphorus( iii ) compounds16 for small molecule activation and catalysis,17 as well as the increasing number of applications of phosphonium as Lewis acids in Frustrated Lewis Pair (FLP) chemistry 18,19…”