HIGH-VALENT ORGANOMANGANESE CHEMISTRY .1. SYNTHESIS AND CHARACTERIZATION OF MANGANESE(III) AND MANGANESE(IV) ALKYLS

A new manganese (IV) alkyl, the hexamethylmanganate salt [Li(tmed)]2[MnMe6], has been prepared by treatment of MnMe4(PMe3)2 with methyllithium followed by addition of N,N,N',N'-tetramethylethylenediamine (tmed). The X-ray structure of the hexamethyl complex reveals an octahedral geometry for this d3 ion with the lithium atoms capping opposite faces in an asymmetric fashion: Mn-C = 2.12 (1) angstrom, Li-C = 2.20 (1), 2.35 (2) angstrom. Addition of excess methyllithium to Mn(acac)3 followed by treatment with tmed gives the pentamethylmanganate [Li(tmed)]2[MnMe5]. This trivalent species can also be obtained by a comproportionation reaction of the manganese(IV) complex [Li(tmed)]2[MnMe6] with 1 equiv of the manganese(II) complex [Li(tmed)]2[MnMe4] in diethyl ether. Interestingly, conducting the same comproportionation reaction in toluene leads to a different trivalent product, the tetramethylmanganate [Li(tmed)2][MnMe4]. The X-ray crystal structure of [Li(tmed)2][MnMe4] reveals a square-planar geometry about manganese that is slightly distorted tetrahedrally: Mn-C = 2.078 (5) angstrom, C-Mn-C(trans) = 161.3 (2)degrees, C-Mn-C(cis) = 91.5 (2)degrees. Crystal data (Mo K alphaBAR, lambdaBAR = 0.71073 angstrom): [Li(tmed)]2[MnMe6], space group Pbca, with a = 12.386 (4) angstrom, b = 13.358 (7) angstrom, c = 15.349 (7) angstrom, V = 2540 (4) angstrom 3, Z = 4, T = 173 K, R(F) = 0.051, and R(wF) = 0.058 for 115 variables and 909 data; [Li(tmed)2][MnMe4], space group P2(1)/n, with a = 9.818 (2) angstrom, b = 15.573 (2) angstrom, c = 15.245 (9) angstrom, beta = 98.24 (4)degrees, V = 2307 (3) angstrom 3, Z = 4, T = 198 K, R(F) = 0.044, and R(wF) = 0.044 for 321 variables and 2491 data. The nonexistence of the quadruply bonded dimanganese(III) complex [Mn2Me8(2-)] is also discussed.