Synthesis and investigation of phosphorus peri-substituted acenaphthenes

Abstract

The work presented in this thesis builds upon previous investigations by the Kilian group into dealkacoupling reactions of phosphorus peri-substituted acenaphthenes. The focus of this thesis was to investigate the effect of introducing different aryl substituents into the peri region on dealkacoupling and to determine the switching behaviour of these compounds. The effect of introducing other pnictogens (As, Sb) was also investigated.

Previously the Kilian group has reported a novel method for the synthesis of ferrocenyl and dichloroferrocenylphosphine via a dithiadiphosphetane. This synthetic route was expanded beyond ferrocene to allow access to both novel and known primary/dichlorophosphines in good yields and without the need for purification.

A series of novel bis(phosphine) peri-substituted acenaphthene compounds with aryl substituents bearing differing steric and electronic properties was synthesised. These compounds were investigated for their ability to undergo dealkacoupling under conditions previously used by the Kilian group (75°C in the presence of a radical initiator (AIBN) and by exposure to sunlight). Results from both the thermal and light induced dealkacoupling reactions indicate that sterics play an important role as a greater steric profile may impede any free rotation necessary. In addition, light induced dealkacoupling reactions revealed the formation of both cis and trans isomers in varying ratios dependant on the nature of the aryl substituent. Introduction of arsenic into the peri region showed favourable results with dramatic reductions in reaction time compared with comparable P/P systems. P/Sb peri-substituted compounds displayed interesting reactivity forming Sb-Sb bonds through dehydrocoupling and the double activation of C-Cl bonds in DCM, which has never been seen in peri-substituted acenaphthenes previously.

Investigations into the molecular switching behaviour of the P/P and P/As systems demonstrated that peri-substituted acenaphthenes do possess molecular switch like properties. The effectiveness of these compounds as molecular switches relies heavily on the nature of the substituents, with low steric profile high electron rich moieties giving the most favourable results. Interestingly, the P/As system showed improved switching properties in comparison to the P/P. Full conversion to the relevant cis isomers was unfortunately not achieved and this should be an area of significant research in the future.

Date of Award	3 Jul 2025
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Petr Kilian (Supervisor)