Radical-initiated P, P-metathesis reactions of diphosphanes: evidence from experimental and computational studies. Issue 20 (5th May 2021)

• Record Type: Journal Article
• Authors: Branfoot, Callum; Young, Tom A.; Wass, Duncan F.; Pringle, Paul G.
• Is Part Of: Dalton transactions. Volume 50:Issue 20(2021)
• Page Start: 7094
• Page End: 7104
• Publication Date: 2021-05-05
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d1dt01013a
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : The mechanism by which P, P-exchange reactions can occur rapidly under ambient conditions has been investigated and the experimental evidence, combined with computational studies, support a radical process. Abstract : By combining the diphosphanes Ar2 P–PAr2, where Ar = C6 H5, 4-C6 H4 Me, 4-C6 H4 OMe, 3, 5-C6 H3 (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 Z2 P–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 Ar2 P˙ 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)2 P–P( o -Tol)2 are anomalously slow and, in the absence of photolysis, were only observed to take place in CHCl3 and CH2 Cl2 . The role of the chlorinated solvent is ascribed to the formation of Ar2 PCl which catalyses the P, P-metathesis. The slow kinetics observed with ( o -Tol)2 P–P( o -Tol)2 is tentatively attributed to the o -CH3 groups quenching the ( o -Tol)2 P˙ radicals or inhibiting the metathesis reaction sterically.