Synthesis and reactivity of icosahedral molybdenum-monocarbaborane complexes containing one or two intramolecular amino bridges

The room-temperature reaction of Li2[7-NMe3-nido-7-CB10H10] with [Mo(CO)4{NH(CH2)5}2] in THF (THF = tetrahydrofuran), followed by oxidation with CF3SO3Me or CH2CHCH2Br, gives the anion [2,3-µ-{N(CH2)5}-2,2,2-(CO)3-closo-2,1-MoCB10H10]−, isolated as the [N(PPh3)2]+ salt 3a. This salt may similarly be isolated following the direct reaction of 7-NMe3-nido-7-CB10H12 with [Mo(CO)4{NH(CH2)5}2] in refluxing THF. An X-ray diffraction study confirmed the absence of the C–NMe3 group in the anion and formation of an intramolecular piperidinyl bridge between molybdenum and boron. The related compound [N(PPh3)2][1-NH2-2,3-µ-{N(CH2)5}-2,2,2-(CO)3-closo-2,1-MoCB10H9] 4 is obtained from Li[7-NH2-nido-7-CB10H12] with [Mo(CO)4{NH(CH2)5}2] in refluxing THF. Treatment of 3a or 4 with {M(PPh3)}+ (M = Cu, Ag) yields heterobimetallic complexes containing direct Mo–M bonds, of which [2,7,11-{Cu(PPh3)}-7,11-(µ-H)2-2,3-µ-{N(CH2)5}-2,2,2-(CO)3-closo-2,1-MoCB10H8] has been studied by X-ray diffraction analysis. In THF solution, 4 is oxidized by iodine or N-chlorosuccinimide affording the MoIV species [1,2-µ-NH2-2,3-µ-{N(CH2)5}-2,2-(CO)2-2-X-closo-2,1-MoCB10H9] (X = I, Cl, respectively). An X-ray diffraction study of the iodo derivative showed that it contained two intramolecular amino bridges between cage vertices and molybdenum. Treatment of these species with PEt3 in refluxing THF leads to displacement of a carbonyl ligand rather than an amino bridge.