Access to and reactions of P-functional 1,4-dihydro-1,4-diphosphinines fused to two TTF units

Abstract

P-Functional phosphanylated tetrathiafulvalenes 3a–f were synthesised via stepwise lithiation and phosphanylation of TTF derivatives, and then reacted with PCl₃ to form the related P-chloro compounds 4a–f. Reactions of 4c–f with LDA resulted in the formation of the corresponding 1,4-dihydro-1,4-diphosphinines 5c–f. As a case in point, P-oxidation reactions of 5d,f with elemental chalcogens were performed, and the former were also converted into 1,4-dichloro-1,4-dihydro-1,4-diphosphinine 9f. The latter was reduced to form the related 1,4-diphosphinine 10f which could not be isolated but formed the corresponding 1,4-diphosphabarrelene 11f in a [4 + 2]-cycloaddition with 1-hexene. All compounds were characterised by multinuclear NMR spectroscopy and mass spectrometry and also by single crystal X-ray diffraction studies in some cases. Intensive cyclic voltammetry studies were performed for all isolated compounds with the special focus on using TTF units as sensors to study the substituent effects on oxidation potentials and, hence, the degree of electronic communication between redox active moieties in the bis-TTF species. E.g., 5d possesses four quasi-reversible one-electron oxidation steps thus forming a tetracation species at highest potential (+0.54 V vs. Fc^+/0). Additionally, high level DFT calculations were undertaken to get a deeper understanding of various aspects of this novel combination of phosphorus and TTF chemistry.