From P‐Functional Thiazol‐2‐thione Derivatives to Phosphaalkenes

Abstract

A facile synthetic methodology is reported that permits access to the backbone (Et2N)2P‐substituted thiazol‐2‐thione 2 [(Et2N)2P‐THSMe; THSMe = 3‐methylthiazol‐2‐thione‐5‐yl]. Starting from 2, Et2N(Cl)P‐substituted thiazol‐2‐thione 3 [Et2N(Cl)P‐THSMe] was formed using chloride scrambling with PCl3. Subsequently, nucleophilic substitution using Ph2CHLi afforded [Et2N(Ph2CH)P‐THSMe] (4) which, via reaction with PCl3, afforded [Ph2CHP(Cl)THSMe] (5). Conversion of 4 into phosphaalkene [Ph2C=P‐THSMe] (6) was achieved, but its thermal instability precluded isolation. Complex [κP‐W(CO)5{Ph2CH(Cl)P}‐THSMe] (7) was then synthesized and used to access end‐on complex [W(CO)5(Ph2C=P‐THSMe)] (8); the 1,2‐addition product of 8 with H2O, complex [Ph2CH(OH)P‐THSMe] (10), was confirmed by X‐ray crystallography. The head‐to‐tail dimers of 8, the diastereomeric dinuclear 1,3‐diphosphetane complex 9 were assigned based on NMR results. In contrast, DFT calculations of all regio‐ and stereochemical isomers of 9 revealed a slight energetic preference for the head‐to‐head dimer. However, since transition states could not be localized, a detailed computational rationale for these experimental findings remains open.