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

Abstract

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 Mo^IV 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.