Rapid phosphorus(III) ligand evaluation utilising potassium selenocyanate

Alfred Muller, Stefanus Otto, Andreas Roodt

Research output: Contribution to journalArticlepeer-review

73 Citations (Scopus)


Oxidative addition of SeCN- to tertiary phosphine ligands has been investigated in methanol at 298 K by use of UV-Vis stopped-flow and conventional spectrophotometry. In most cases kobsvs. [SeCN -] plots were linear with zero intercepts corresponding to a rate expression of kobs = k1[SeCN-]. Reactions rates are dependent on the electron density of the phosphorus centre with k 1 varying by five orders of magnitude from 1.34 ± 0.02 × 10-3 to 51 ± 3 mol-1 dm3 s-1 for P(2-OMe-C6H4)3 to PCy3 respectively. Activation parameters range from 27 ± 1 to 49.0 ± 1.3 kJ mol-1 for ΔH and -112 ± 9 to -140 ± 3 J K-1 mol-1 for ΔS supporting a SN2 mechanism in which the initial nucleophilic attack of P on Se is rate determining. Reaction rates are promoted by more polar solvents supporting the mechanistic assignment. Reasonable linear correlations were observed between log k1vs. pKa, 1JP-Se and χd values of the phosphines. The reaction rates are remarkably sensitive to the steric bulk of the substituents, and substitution of phenyl rings in the 2 position resulted in a decrease in the reaction rate. The crystal structures of SePPh2Cy and SePPhCy2 have been determined displaying Se-P bond distances of 2.111(2) and 2.1260(8) respectively.

Original languageEnglish
Pages (from-to)650-657
Number of pages8
JournalDalton Transactions
Issue number5
Publication statusPublished - 2008

ASJC Scopus subject areas

  • Inorganic Chemistry


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