Facile One‐Step Access to Pyrrole‐Based 1,4‐Diphosphabarrelenes

Abstract

1,4‐Diphosphabarrelenes are bicyclic diphosphines relevant, for example, for the generation of polymetallic coordination compounds. However, current synthetic protocols either suffer from low yields or require multiple reaction steps. Herein, we report the one‐step synthesis of pyrrole‐based 1,4‐diphosphabarrelenes that are obtained in very good yields from the reaction of 1,2,5‐trimethylpyrrole with 1,2‐bis(dichlorophosphino)ethane or 1,2‐bis(dichlorophosphino)benzene. The new caged diphosphines are strong donor ligands and act as bridging ligand in nickel(0), rhodium(I), iridium(I) and copper(I) coordination compounds.

Application of phosphorus-bridged rigid, bent bis(NHCs) as dipodal ligands in main group and transition metal chemistry

“…1) reveals P-C bond lengths within the range of known 1,4-diphosphabarrelenes. 30,36 As observed for this compound class before, 30,31,36 the phosphorus environment is strongly pyramidalised (∑∠ = 285°) leading to a large s-character of the phosphorus lone pairs. The overall folding angle of the bent structure (∠(C2-P1-P2-C13)) is 125°.…”

“…The 31 P NMR resonances show an expected, significant high-field shift compared to 1 (2a: δ( 31 P) = −86.3 ppm, 2b: δ( 31 P) = −91.4, −87.0 ppm) which puts them in the typical range for 1,4diphosphabarrelenes. 30,31,35,36 2b also displays a 3 J P,P -coupling constant of 17.4 Hz due to the asymmetry of the C 2 bridge. The observed asymmetry and therefore magnetic inequivalence translates outwards to the diastereotopic selenium nuclei whose 77 Se{ 1 H} NMR resonances can be found at 31.2 ppm (2a) and 27.7 ppm and 30.5 ppm (2b).…”

“…32 Historically, the first report of 1,4-diphosphabarrelenes came from Krespan in 1961, 33 a few more examples were published in the following years, 34,35 until Dielmann recently synthesised pyrrole-based 1,4-diphosphabarrelenes and metal complexes thus expanding the field of rigid, caged diphosphane ligands. 36 Herein, we present the synthesis of the first heteroatombridged rigid, bent bis(NHCs) V, obtained from C 2 -saturated 1,4-diphosphabarrelenes, using an optimized reduction protocol. This scaffold presents the unique combination of a bis (NHC) and a caged diphosphane.…”

“…32 Historically, the first report of 1,4-diphosphabarrelenes came from Krespan in 1961, 33 a few more examples were published in the following years, 34,35 until Dielmann recently synthesised pyrrole-based 1,4-diphosphabarrelenes and metal complexes thus expanding the field of rigid, caged diphosphane ligands. 36…”