Monocarbollide complexes of molybdenum and tungsten: functionalization through reactions at a cage boron centre

Abstract

Reactions of the salts [N(PPh₃)₂][2,2,2-(CO)₃-2-PPh₃-closo-2,1-MCB₁₀H₁₁] (M = Mo or W) with CF₃SO₃Me or H₂SO₄ in the presence of donor molecules L afford zwitterionic molecules [2,2,2-(CO)₃-2-PPh₃-7-L-closo-2,1-MCB₁₀H₁₀] [L = OEt₂, O(CH₂)₄, cyclo-1,4-O(CH₂)₄O, SMe₂, S(CH₂)₄, cyclo-1,4,7-S₃(CH₂)₆, NCBu^t or CNC₆H₃Me₂-2,6]. The exopolyhedral group L is attached to a β-boron atom in the CBBBB ring coordinated to the metal, a feature confirmed by an X-ray crystallographic study of [2,2,2-(CO)₃-2-PPh₃-7-(CNC₆H₃Me₂-2,6)-closo-2,1-MoCB₁₀H₁₀]. The molecules [2,2,2-(CO)₃-2-PPh₃-7-L-closo-2,1-WCB₁₀H₁₀] [L = OEt₂ or O(CH₂)₄] in THF (tetrahydrofuran) react with Me₃NO, with addition of [PPh₄]Br, to give the salts [PPh₄][2,2,2-(CO)₃-2-PPh₃-7-R-closo-2,1-WCB₁₀H₁₀] [R = OEt or O(CH₂)₃CHO]. These products on treatment with CF₃SO₃Me in CH₂Cl₂ give the zwitterionic molecules [2,2,2-(CO)₃-2-PPh₃-7-{O(Me)R}-closo-2,1-WCB₁₀H₁₀] (R = Et or Buⁿ). Single crystal X-ray diffraction studies established the structures of [PPh₄][2,2,2-(CO)₃-2-PPh₃-7-OEt-closo-2,1-WCB₁₀H₁₀] and [2,2,2-(CO)₃-2-PPh₃-7-{O(Me)Buⁿ}-closo-2,1-WCB₁₀H₁₀]. In NCMe the reagents [N(PPh₃)₂][2,2,2-(CO)₃-2-PPh₃-closo-2,1-MCB₁₀H₁₁] react with CF₃SO₃Me to yield [2,2,2-(CO)₃-2-PPh₃-7-{N(Me)C(H)Me}-closo-2,1-MCB₁₀H₁₀] (M = Mo or W), compounds in which an imine substituent is bonded to the cage system, a feature confirmed by an X-ray diffraction study of the tungsten species. Similarly, the compounds [N(PPh₃)₂][2,2,2-(CO)₃-2-PPh₃-closo-2,1-MCB₁₀H₁₁] react with CNBu^t and CF₃SO₃Me to give a mixture of isomers of [2,2,2-(CO)₃-2-PPh₃-7-{N(Bu^t)C(H)Me}-closo-2,1-MCB₁₀H₁₀] (M = Mo or W) with E and Z configurations for the BN(Bu^t)C(H)Me group.