The cyanoimido ligand as an oxo analogue. Novel approaches to the preparations of cyano(imino)-aza-phosphorus(V) and N-cyanoaziridine

The known Os(IV)-cyanoimido complexes, mer-Et4NOsIV(bpy)(Cl)3(NalphaCNbeta)] (mer-OsIV=N-CN]-) (bpy = 2,2'-bipyridine) and trans-OsIV(tpy)(Cl)2(NalphaCNbeta)] (trans-OsIV=N-CN]) (2,2':6',2' '-terpyridine), have formal electronic relationships with high oxidation state Ru and Os-oxo and -dioxo complexes. These include multiple bonding to the metal, the ability to undergo multiple electron transfer, and the availability of nonbonding electron pairs for donation. Thermodynamic, oxo-like behavior is observed for mer-OsIV=N-CN]- in the pH-dependence of its Os(VI/V) to Os(III/II) redox couples in 1:1 (v/v) CH3CN:H2O. Oxo-like behavior is also observed in the reaction between mer-OsVI(bpy)(Cl)3(NalphaCNbeta)]PF6 and benzyl alcohol to give mer-OsIV(bpy)(Cl)3(NalphaCNbetaH2)]PF6 and benzaldehyde. The reaction is first order in each reactant with kbenzyl(CH3CN, 25.0 +/- 0.1 degrees C) = (8.6 +/- 0.2) x 102 M-1 s-1. Formal NCN degrees transfer, analogous to O-atom transfer, occurs in reactions with tertiary phosphine and hexenes. In CH3CN under N2, a rapid reaction occurs between trans-OsIV=N-CN] and PPh3 (kPPh3(DMF, 25.0 +/- 0.1 degrees C) = 4.06 +/- 0.02 M-1 s-1) to form the nitrilic N-bound Os(II)-(N-cyano)iminophosphorano product, trans-OsII(tpy)(Cl)2(NalphaCNbetaPPh3)] (trans-OsII-NalphaC-Nbeta=PPh3]). It undergoes solvolysis at 45 degrees C after 24 h to give trans-OsII(tpy)(Cl)2(NCCH3)] and (N-cyano)iminophosphorane (NalphaC-Nbeta=PPh3). The analogue to epoxidation, N-cyanoaziridination of cyclohexene and 1-hexene by mer-OsIV=N-CN]- and trans-OsIV=N-CN], occurs at Nbeta to give the Os(IV)-N-cyanoaziridino complexes, mer-Et4NOsII(bpy)(Cl)3(NalphaCNbetaC6H10)] and trans-OsII(tpy)(Cl)2(NalphaCNbetaC6H11)], respectively. Oxidation to mer-OsV(bpy)(Cl)3(NalphaCNbeta)]- greatly accelerates N-cyanoaziridination of cyclohexene, which is followed by slow solvolysis to give mer-OsIII(bpy)(Cl)3(NCCH3)] and N-cyanoaziridine (NC-NC6H10). The Os-(N-cyano)aziridino complexes are the first well-characterized examples of coordinated cyanoaziridines.