Radical-initiated P,P-metathesis reactions of diphosphanes: evidence from experimental and computational studies

Callum Branfoot, Paul G Pringle*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

9 Citations (Scopus)
44 Downloads (Pure)

Abstract

By combining the diphosphanes Ar2P–PAr2, where Ar = C6H5, 4-C6H4Me, 4-C6H4OMe, 3,5-C6H3(CF3)2, it has been shown that P,P-metathesis generally occurs rapidly under ambient conditions. DFT calculations have shown that the stability of unsymmetrical diphosphanes Z2P–PZ′2 is a function of the difference between the Z and Z′ substituents in terms of size and electronegativity. Of the mechanisms that were calculated for the P,P-metathesis, the most likely was considered to be one involving Ar2P˙ radicals. The observations that photolysis increases the rate of the P,P-metatheses and TEMPO inhibits it, are consistent with a radical chain process. The P,P-metathesis reactions that involve (o-Tol)2P–P(o-Tol)2 are anomalously slow and, in the absence of photolysis, were only observed to take place in CHCl3 and CH2Cl2. The role of the chlorinated solvent is ascribed to the formation of Ar2PCl which catalyses the P,P-metathesis. The slow kinetics observed with (o-Tol)2P–P(o-Tol)2 is tentatively attributed to the o-CH3 groups quenching the (o-Tol)2P˙ radicals or inhibiting the metathesis reaction sterically.
Original languageEnglish
Pages (from-to)7094-7104
Number of pages11
JournalDalton Transactions
Volume50
Issue number20
DOIs
Publication statusPublished - 28 May 2021

Bibliographical note

Funding Information:
This research was funded by the Engineering and Physical Sciences Research Council through the EPSRC Centre for Doctoral Training in Advanced Composites for Innovation and Science (grant number EP/L0160208/1). We thank the Department of Chemistry at Oxford and the Centre for Computational Chemistry in Bristol for access to computing facilities.

Publisher Copyright:
© 2021 The Royal Society of Chemistry.

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