Amine-nitrile coupling in amino-monocarbollide complexes of molybdenum

The Mo-0 molybdenacarbaborane trianion [1-NH2-2,2,2-(CO)(3)-closo-2,1-MoCB10H10](3-) is formed in situ from the reaction between [7-NH2-nido-7-CB10H10](3-) and [Mo(CO)(4){NH(CH2)(5)}(2)] in THF solution (THF=tetrahydrofuran). In the absence of nitriles, oxidation of this trianion by CH2=CHCH2Br gives the Mo-II complex [1,2-mu-NH2-2,2,2-(CO)(3)-closo-2,1-MoCB10H10](-), isolated as its [N(PPh3)(2)](+) salt. However, in the presence of nitriles NCR, the same oxidation ultimately affords the species [N(PPh3)(2)][1,2-mu-{NHC(R)=NH}-2,2,2-(CO)(3)-closo-2,1-MoCB10H10]in which amidine groups form a bridge between the carbon atom of the cage and the molybdenum, as a consequence of coupling of the nitrile with the cage-bound NH2 group. The acetamidine product [N(PPh3)(2)][1,2-mu-{NHC(Me)=NH}-2,2,2-(CO)(3)-closo-2,1-MoCB10H10] is also formed by reaction of [7-NH2-nido-7-CB10H12](-) with [Mo(CO)(6)] in refluxing NCMe, and its structure was confirmed by an X-ray diffraction study. Further oxidation of this species by I-2 in the presence of CNBut gives the Mo-IV derivatives [1,2-mu-{NHC(Me)=NH}-2,2-(CNBut)(2)-2-L-2-I-closo-2,1-MoCB10H10] (L=CO, CNBut), of which the tris(isocyanide) complex has been studied by X-ray diffraction.