Heterometathesis of diphosphanes (RP-PR) with dichalcogenides (R'E-ER', E = O, S, Se, Te).

The reactions of RP-PR with R'E-ER', (where E = Se, S, O, Te) to give RP-ER' have been explored experimentally and computationally. The reaction of PhP-PPh with PhSe-SePh gives PhP-SePh (1) rapidly and quantitatively. The P-P/Se-Se reaction is inhibited by the addition of the radical scavenger TEMPO which is consistent with a radical mechanism for the heterometathesis reaction. Compound 1 has been fully characterised, including by X-ray crystallography. A range of other ArP-SeR (R = Ph, Bu or CHCHCOH) have also been prepared and characterised. The reaction of 1 with [Mo(CO)(nbd)] (nbd = norbornadiene) gives two products which, from their characteristic P NMR data, have been identified as -[Mo(CO)(PhPSePh-)] (8) and the mixed-donor complex -[Mo(CO)(PhP-SePh-)(PhP-SePh-)] (9). It is deduced that the P and Se atoms in ligand 1 have comparable capacity to coordinate to Mo(0). The reaction of PhP-PPh with PhS-SPh gives PhP-SPh (2) quantitatively but no reaction was observed between PhP-PPh and PhTe-TePh. Heterometathesis between PhP-PPh and BuO-OBu does not occur thermally but has been observed under UV irradiation to give PhP-OBu along with P(V) oxidation by-products. DFT calculations have been carried out to illuminate why heterometatheses with dichalcogenides R'E-ER' occur readily when E = S and Se but not when E = O and Te. The calculations show that heterometathesis is predicted to be thermodynamically favourable for E = O, S and Se and unfavourable for E = Te. The fact that a metathesis reaction between PhP-PPh with BuO-OBu is not observed in the absence of UV radiation, is therefore due to kinetics.