Synthesis, Substitution, and Oxidation of Imidazole‐2‐thione Based Tricyclic 1,4‐Dihydro‐1,4‐diphosphinines

• Published in: European journal of inorganic chemistry 2018-02, Vol.2018 (7), p.904-916
• Main Authors: Koner, Abhishek, Sauerbrey, Susanne, Schnakenburg, Gregor, Bauzá, Antonio, Frontera, Antonio, Streubel, Rainer
• Format: Article
• Language: English
• Subjects: Adducts; Chemical synthesis; Derivatives; Electrostatic interactions; Imidazole; Inorganic chemistry; Methylation; Oxidation; Phosphorus heterocycles; P–borane adduct; S methylation; Substituent effects; Substitution reactions
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201701338

Herein, the synthesis and chemistry of P‐functional tricyclic 1,4‐dihydro‐1,4‐diphosphinines is described, following a recent communication on their use as precursors of 1,4‐diphosphinines. In particular, ring formation of imidazole‐2‐thione‐based tricyclic 1,4‐dihydro‐1,4‐diphosphinines 4a,b {–[P(Me2N)IMSR,R]2–; IMSR,R = 1,3‐dialkylimidazole‐2‐thione‐4‐yl}, first detected as side products, has been optimized to access 4d–f {–[P(Et2N)IMSR,R]2–; IMSR,R = 1,3‐dialkylimidazole‐2‐thione‐4‐yl}. The 1,4‐dihydro‐1,4‐dichloro‐1,4‐diphosphinines 8a,b {–[P(Cl)IMSR,R]2–; IMSR,R = 1,3‐dialkylimidazole‐2‐thione‐4‐yl}, easily obtained from 4, are ideal starting materials for P‐substituted products 9a–c (P–R; R = nBu, TMSC2–). The P‐diorganoamino derivatives 4d–f are used to synthesize bis(P–oxides) 10a–c and bis(P‐sulfides) 11a–c, and similarly, the bis(P–borane) adducts 13a–c. The first examples of bis(spirophosphorane) derivatives 12a–c, featuring two benzodioxaphosphole units, are synthesized by the reaction of 4d–f with o‐chloranil. Attempts to access bis(phosphonium) derivatives using methyl trifluoromethanesulfonate have resulted in S‐methylation of 4d–f, and hence, have furnished the first examples of tricyclic 1,4‐dihydro‐1,4‐diphosphinines possessing two imidazolium units 14a,b {[–{P(Me2N)‐IMSMeR,R}2–](CF3SO3)2; IMSMeR,R = 1,3‐dialkyl‐2‐thiomethyl‐imidazolium‐4‐yl}. Imidazole‐2‐thione‐based tricyclic 1,4‐dihydro‐1,4‐diphosphinines II were synthesized by LDA‐induced cyclization starting from moncyclic 1,4‐dihydro‐1,4‐diphosphinines ; the molecular electrostatic potential indicates competing nucleophilic centers.