Amine–nitrile coupling in amino-monocarbollide complexes of molybdenum
Abstract
The Mo0 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 CH2CHCH2Br gives the MoII complex [1,2-μ-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-μ-{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-μ-{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 I2 in the presence of CNBut gives the MoIV derivatives [1,2-μ-{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.