[​4+2] versus [​2+2] Homodimerization in P(V) Derivatives of 2,4-Disubstituted Phospholes

Abstract

Phosphole P(V) derivatives are interesting building blocks for various applications from ligand synthesis to material sciences. We herein describe the preparation and characterisation of new 2,4-disubstituted oxo-, thiooxo-, and selenooxophospholes. The nature of the substituents on the phosphole ring determines the reactivity of these compounds towards homodimerization reactions. Aryl and trimethylsilyl substituted oxophospholes undergo selective [4+2] dimerization, whereas, for thiooxo- and selenooxophospholes, light-induced, selective [2+2] head-to-head dimerization occurs in the case of aryl substituents. DFT calculations provide some insights on these differences in reactivity.

Moving on from Silicon to the Heavier Tetrels: Germyl- and Stannyl-Substituted Phosphole Derivatives

“…22 By contrast, a comparison of the 77 Se coupling constants for Se-5b and Se-5c show lower values than for most other phosphole selenides found in the literature. In germyl-substituted Se-1, the value of the coupling constant is 743 Hz which is larger than in bisstannyl-substituted Se-5b (714 Hz) and Se-5c (725 Hz), as well as in already reported 1-phenyl-2,4-bis(trimethylsilyl)phosphole selenide (716 Hz) 29 albeit in a different solvent (CDCl 3 ). This comparison suggests a high basicity of the lone pair at the phosphorus atom in the underlying germyl phosphole 1, which could be interesting regarding its coordination properties in future investigations.…”

“…The used cartridges were filled with spheric silica gel (particle size: 15 or 25 μm). 1 H, 13 C, 31 P, 29 Si, 77 Se, and 119 Sn NMR data were recorded on a Varian VNMRS-500 or MR-400 MHz spectrometer at 25 °C. Chemical shifts were referenced to residual protic impurities in the solvent ( 1 H) or the deuterated solvent ( 13 C) and reported relative to external SiMe 4 ( 1 H, 13 C, 29 Si), H 3 PO 4 ( 31 P), Me 2 Se ( 77 Se) and SnMe 4 ( 119 Sn).…”

Organic Synthesis with Elemental Lanthanides – Going Beyond Samarium and Ytterbium

“…[58] Oxidation of these new phospholes 140 with oxygen led to classical [4 + 2] homodimerization products 143, whereas with sulfur or selenium unexpected photoinduced [2 + 2] reactions occurred to afford products 144 in a highly regio and stereoselective manner (Scheme 29). [59] The above described dehalogenation reactions with La metal (Scheme 19 and 20) further inspired this work to access the unsubstituted zirconacyclopentadiene complex A and zirconacyclopentane complex B (Scheme 30). [60] The reaction of La metal with tetrabromoethane 145 led to the in-situ generation of acetylene which reacted with [Cp 2 Zr] to form complex A.…”

“…Selective access to 1,2,4-trisubstituted phospholes and their reactivity. [58,59] Scheme 30. Concomitant reduction and dehalogenation with the Cp 2 ZrCl 2 / Ln system.…”

“…Oxidation of these new phospholes 140 with oxygen led to classical [4+2] homodimerization products 143 , whereas with sulfur or selenium unexpected photoinduced [2+2] reactions occurred to afford products 144 in a highly regio and stereoselective manner (Scheme 29). [59] …”