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

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, NCBut 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 CNBut and CF3SO3Me to give a mixture of isomers of [2,2,2-(CO)3-2-PPh3-7-{N(But)C(H)Me}-closo-2,1-MCB10H10] (M = Mo or W) with E and Z configurations for the BN(But)C(H)Me group.