Anionic and cationic Bi- and tri-nuclear tert-butylimido complexes of manganese-(V) and -(VI)

Abstract

Dimeric anionic complexes have been obtained by reduction of MnCl(NBut)3 or [Mn(NBut)2(µ-NBut)]21 with lithium powder in 1,2-dimethoxyethane (dme) to give [Li(dme)]2[{Mn(NBut)2(µ-NBut)}2]2, or with sodium amalgam in tetrahydrofuran (thf) to give [Na(thf)][{Mn(NBut)2(µ-NBut)}2]3 which have oxidation states V,V and V,VI respectively. Interaction of 1 with iodine gave a mixed-valence (VI,V,VI) compound, [{Mn(NBut)2(µ-NBut)2}2Mn]I34. Interaction of 3 with HgCl2 gave [{Mn(NBut)2(µ-NBut)2}2Mn]2[Hg2Cl6]·2CHCl35a and [(ButN)2Mn(µ-NBut)2Mn(NHBut)(NBut)]2[Hg3Cl8]5b. Oxidation of 1 by silver trifluoromethanesulfonate resulted in an unisolable cation in CH2Cl2, presumably [{Mn(NBut)2(µ-NBut)}2]+, the EPR spectrum of which suggests that the single electron is located on one N atom of the terminal imide groups. The interaction of this cation with thf resulted in abstraction of H to give the manganese(VI) amido species [(ButN)(ButNH)Mn(µ-NBut)2Mn(NBut)2]+ which is also formed on protonation of 1 with stoichiometric amounts of CF3SO3H. The amido cation has been isolated with the anions CF3SO3–6 and [B(C6F5)4]–7, but use of [B{C6H3(CF3)2-3,5}4]– produces, after crystallisation from toluene, the salts of the amido cation 8 and of an oxo species [Mn3(µ-O)(µ-NBut)4]+9. Interaction of [{Mn(NBut)2(µ-NBut)}2]+in situ with dry O2 gave a mixture 10 of [{(ButN)2Mn(µ-NBut)2}2Mn]+ and [{(ButN)2Mn(µ-O)(µ-NBut)}2Mn]+ which cocrystallise and cannot be separated. Thermal decomposition of the alkoxide Mn(NBut)3[OCH(CF3)2] gave the manganese(V) dimer [Mn(NBut)(NHBut)(µ-NBut)]2. The structures of compounds 3, 4, 5a, 5b, 7, 9 and the mixture 10 have been confirmed by single-crystal X-ray studies. In all cases the Mn atoms have distorted-tetrahedral geometry. The Mn–N bonds to terminal imide ligands lie in the range 1.554–1.674 A, whilst bridging distances vary considerably from 1.724 to 1.872 A, reflecting differences for Mn atoms which are co-ordinated only by bridging imides and those which are also bonded to terminal ligands. The Mn–O bonds in the oxo-bridged species are slightly longer than the analogous Mn–N (bridging) distances, indicating less multiple bonding. The structure of the [Hg3Cl8]2– ion in 5b shows it to conform quite closely to the ‘composite’ species [(Cl2Hg)(Cl2HgCl2)(HgCl2)]2–