Dimolybdenum–µ-cyanide complexes supported by N-tert-butylanilide ligation: in pursuit of cyanide reductive cleavage

Abstract

The red cyanide complex (NC)Mo(N[R]Ar)_3 (R=C(CD_3)_2CH_3, Ar=3,5-C_6H_3Me_2) was prepared in 77% yield by reaction of iodide IMo(N[R]Ar)_3 with tetra-n-butyl ammonium cyanide. By reaction of cyanide (NC)Mo(N[R]Ar)_3 with the three-coordinate molybdenum(III) complex Mo(N[R]Ar)_3 was prepared the dimolybdenum-μ-cyanide complex (μ-CN){Mo(N[R]Ar)_3}_2 as a violet solid in 80% yield. Reduction of μ-cyanide (μ-CN){Mo(N[R]Ar)_3}_2 by one electron would give a cyanide-bridged anion isoelectronic with the known μ-N_2 complex (μ-N_2){Mo(N[R]Ar)_3}_2, an intermediate in dinitrogen cleavage to two equivalents of nitride NMo(N[R]Ar)_3 by Mo(N[R]Ar)_3. Instead of undergoing an analogous cleavage of cyanide upon one-electron reduction, μ-cyanide (μ-CN){Mo(N[R]Ar)_3}_2 was found to undergo expulsion of a ligand C(CD_3)_2CH_3 substituent upon exposure to reducing conditions, the product isolated in 50% yield being imido–μ-cyanide (Ar[R]N)_2(ArN)Mo(μ-NC)Mo(N[R]Ar)_3. By reaction of [N^nBu_4][CN] with the 1-adamantyl-substituted molybdenum complex Mo(N[Ad]Ar)_3, the blue salt [N^nBu_4][(NC)Mo(N[Ad]Ar)_3] was obtained in 91% yield. Reaction of ferrocenium triflate or silver triflate with [N^nBu_4][(NC)Mo(N[Ad]Ar)_3] gave ferrocene or silver along with the neutral cyanide complex (NC)Mo(N[Ad]Ar)_3, isolated in 74% yield. While reaction of (NC)Mo(N[Ad]Ar)_3 with Mo(N[R]Ar)_3 gave in 53% yield a burgundy-colored dimolybdenum–μ-cyanide complex (Ar[Ad]N)_3Mo(μ-CN)Mo(N[R]Ar)_3. the 1-adamantyl-substituted cyanide did not exhibit any reaction with the 1-adamantyl-substituted tricoordinate complex Mo(N[Ad]Ar)_3. The latter results indicate that cyanide is too small to serve as a bridge for two equivalents of the highly sterically encumbered Mo(N[Ad]Ar)_3 fragment. A metathetical route to a heterodinuclear cyanide-bridged complex was explored involving addition of [N^nBu_4][(NC)Mo(N[Ad]Ar)_3] to the vanadium iodide complex IV(N[R]Ar_F)_2. By this reaction was obtained the orange–brown μ-cyanide complex (Ar_F[R]N)_2V(μ-NC)Mo(N[Ad]Ar)_3 in 30% recrystallized yield. The latter was characterized by X-ray crystallography. The cyanide chemistry reported here is interpreted with the aid of bonding considerations and cyclic voltammetry studies on the new complexes.