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

The red cyanide complex (NC)Mo(N[R]Ar)(3) (R = C(CD3)(2)CH3, Ar = 3,5-C6H3M e2 was prepared in 77% yield by reaction of iodide IMo(N[R]Ar)(3) with tetr a-n-butyl ammonium cyanide. By reaction of cyanide (NC)Mo(NIR]Ar)(3) with t he three-coordinate molybdenum(III) complex Mo(N[R]Ar)(3) was prepared the dimolybdenum-mu-cyanide complex (mu-CN){Mo(N[R]Ar)(3)}(2) as a violet solid in 80% yield. Reduction of mu-cyanide (mu-CN){Mo(N[R]Ar)(3)}(2) by one ele ctron would give a cyanide-bridged anion isoelectronic with the known mu-N- 2 complex (mu-N-2){Mo(N[R]Ar)(3)}(2), an intermediate in dinitrogen cleavag e 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, m u-cyanide (mu-CN){Mo(N[R]Ar)(3)}(2) was found to undergo expulsion of a lig and C(CD,),CH, substituent upon exposure to reducing conditions, the produc t isolated in 50% yield being imido-mu-cyanide (Ar[R]N)(2)(ArN)Mo(mu-NC)Mo( N[R]Ar)(3). By reaction of [(NBu4)-Bu-n][CN] with the 1-adamantyl-substitut ed molybdenum complex Mo(N[Ad]Ar)(3), the blue salt [(NBu4)-Bu-n][(NC)Mo(N[ Ad]Ar)(3)] was obtained in 91% yield. Reaction of ferrocenium triflate or s ilver triflate with [(NBu4)-Bu-n][(NC)Mo(N[Ad]Ar)(3)] gave ferrocene or sil ver 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-mu-cyanide complex (Ar[Ad]N)(3)Mo (mu-CN)Mo(N[R]Ar)(3). the 1-adamantyl-substituted cyanide did not exhibit a ny 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 MoCN[Ad]Ar) (3) fragment. A metathetical route to a heterodinuclear cyanide-bridged com plex was explored involving addition of [(NBu4)-Bu-n][(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 mu-cyanide complex (Ar-F[R]N)(2)V(mu-NC)Mo(N[Ad]Ar)(3) in 30% recrystallized yield. The latter was characterized by X-ray crystallog raphy. The cyanide chemistry reported here is interpreted with the aid of b onding considerations and cyclic voltammetry studies on the new complexes. (C) 1999 Elsevier Science S.A. All rights reserved.