NON-OXO CHEMISTRY OF MANGANESE IN HIGH OXIDATION-STATES .1. MONONUCLEAR TERT-BUTYLIMIDO COMPOUNDS OF MANGANESE-(VII) AND MANGANESE-(VI)

The interaction of manganese(III) chloride in acetonitrile with NHR(SiMe3) (R = Bu(t) or CMe2CH2Me) gave the manganese(VII) species Mn(NR)3Cl as thermally and air-stable green crystals. The chlorine atom in Mn(NBut)3Cl 1 has been substituted by Br, OC(O)R (R = Me or CF3), OC6X5 (X = F or Cl), OCH(CF3)2, SC6F5, C6F5 or NHBu(t) by use of SiMe3Br and the silver, thallium or lithium salts of other reagents. Interaction of compound 1 with Ag(O3SCF3) or AgPF6 and NH2But gave the salts of the cation [Mn(NBut)3(NH2But)]+, with Li(NHBu(t)) under selected conditions gave the paramagnetic manganese(vi) analogues of the manganate(vi) anion, [LiL]2[Mn(NBut)4] [L = 1,2-dimethoxyethane (dme) or N,N,N',N'-tetramethylethylenediamine (tmen)], and with HCl gave Mn(NBut)2(NHBut)Cl2, the reaction being reversed by addition of pyridine. Unstable compounds, e.g. Mn(NBut)3(C6F5) and Mn(NBut)3(NHBut), were characterised spectroscopically. The mechanism of the formation of 1 is discussed together with a mechanism accounting for the instability of compounds where the X-group has beta-H atoms as in Mn(NBut)3[OCH(CF3)2]. Beta-Hydrogen transfer to a NBu(t) group to give a manganese(V) dimer [Mn(NBut)2(NHBut)]2 occurs with the formation of ketones from alkoxides; for alkyls decomposition appears to involve homolysis of the Mn-C bond and a radical pathway. The crystal structures of the compounds Mn(NBut)3X, X = OC(O)Me, OC6F5, SC6F5, [Mn(NBut)3(NH2But)]Y, Y = CF3SO3 or PF6 and [Li(dme)]2[Mn(NBut)4] have been determined. In all the compounds the manganese atom has distorted tetrahedral geometry. In the first three the Mn-N(imido) bond lengths are 1.664(3)-1.673(9) angstrom and the Mn-N-C angles 139.9(2) to 144.6(3)-degrees, indicating partial multiple-bond character. The Mn X distances, 1.91(3), 1.896(2) and 2.289(1) angstrom respectively indicate single bonds. In the cationic compounds the Mn-N(imido) distances are 1.531(8)-1.655(8) angstrom, with Mn-N-C angles of 135.8(6)-170.2(9)-degrees, suggesting more uneven distribution of the Mn-N multiple bonding, although these structures were less precisely determined due to disorder. In the manganate(VI) anion the Mn-N(imido) lengths are longer, 1.746(3)-1.749(3) angstrom, as expected.