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.