Evidence for a SN2-type pathway in the exchange of phosphines at a [PhSe]+ centre

Chris Russell, Michael Green, Laura Forfar, Mairi Haddow, Jason Lynam, John Slattery, Sharifa Hussein

Research output: Contribution to journalArticle (Academic Journal)

Abstract

A range of thio- and seleno-phosphonium cationic complexes [RE(PR’3)]+[X]− (R = Me, Ph; E = S, Se; X = GaCl4, SbF6) have been synthesised and structurally characterised. Reaction of [PhSPPh3][GaCl4] and [PhSePPh3][GaCl4] with PtBu3 results in the ready transfer of the “RS+” and “RSe+” fragments from PPh3 to the stronger electron donor PtBu3. NMR experiments combined with an Eyring analysis on the corresponding degenerate phosphine exchange reaction allowed the thermodynamic values for the phosphine exchange reaction of the sulfuration (ΔH‡ 18.7 ± 12.0 kJ mol−1; ΔS‡ −99.3 ± 36.3 J mol−1 K−1) to be
compared with the corresponding values (ΔH‡ 2.4 ± 1.1 kJ mol−1 and ΔS‡ 58.1 ± 5.0 J mol−1 K−1) for the[PhSePPh3]+ system. Importantly, the large negative entropy of activation and linear dependence on the rate of exchange are compatible with an SN2-type exchange process. This conclusion is supported by
DFT calculations which confirm that the phosphine exchange process occurs via an associative mechanism. The rate of exchange was found to increase from sulfur to selenium and those with aryl substituents underwent exchange faster than those with alkyl substituents.
Original languageEnglish
JournalDalton Transactions
Volume44
Issue number110
DOIs
Publication statusPublished - 2 Oct 2015

    Fingerprint

Cite this