Azavinylidene Complexes from Coupling Reactions of Organonitriles with Phosphines

The reactions of the rhenium­(III)-phosphine
complex ReCl3(PMePh2)3 with organonitriles
(NCR) were studied
and found to give novel addition as well as simple substitution products.
Refluxing ReCl3(PMePh2)3 in acetonitrile
(MeCN) yielded a mixture of the organonitrile rhenium complex ReCl3(PMePh2)2(NCMe) and the rhenium phosphonium-substituted
azavinylidene complex ReCl3(PMePh2)2{NC­(PMePh2)­Me}. Similarly, reactions of
ReCl3(PMePh2)3 with arylnitriles p-R-C6H4CN (R = H, Me, and Br) gave
the corresponding azavinylidene complexes ReCl3(PMePh2)2{NC­(PMePh2)­(p-C6H4R)}. The nitrile complex ReCl3(PPh3)2(NCPh) is unreactive toward external
PPh3, but it reacts with excess PMe3 to produce
the azavinylidene complex ReCl3(PMe3)2{NC­(PMe3)­Ph}. Computational studies reveal
the effect of ligand and substituent of organonitriles on the thermodynamics
and kinetics for the reactions of ReCl3(PR3)2(NCR′) with PR3. Both the experimental and
computational results indicate that nucleophilic addition of phosphines
to coordinated nitriles is more favorable for nitriles with an electron-withdrawing
group and for phosphines which are more electron-donating.