A square-planar oxo-alkyl of manganese(III). Synthesis and X-ray crystal structure of {Li2[MnOMe3]·2Li2(Meacac)·tmed}2

Alkylation of Mn(acac)3 (acac = 2,4-pentanedionato) with five equiv. of methyl-lithium in diethyl ether, followed by addition of N,N,N′,N′-tetramethylethylenediamine (tmed), gives the deep red manganese(III) oxo-alkyl [MnOMe32−], which has been isolated as a lithium double salt with the 4-methyl-2-penten-2,4-diolate (Meacac) dianion. Overall, the molecular formula is {Li2[MnOMe3]·2Li2(Meacac)·tmed}2. Six lithium atoms and six oxygen atoms form a hexagonal prismatic core which is capped on each hexagonal face by Li3(Meacac)2·tmed groups. Two of the oxygen atoms of the Li6O6 core are part of two square-planar [MnOMe32−] centres that are slightly distorted tetrahedrally; this is a rare coordination geometry since manganese(III) is known to adopt a square-planar configuration in only one other case. The oxo group of the [MnOMe32−] unit is bonded to four lithium atoms, and there are Li…HC interactions with two of the methyl groups on manganese. Important bond distances and angles involving the [MnOMe32−] unit are: MnC = 2.040(8) Å (trans to O), MnC = 2.133(8) Å (trans to C), MnO = 1.913(4) Å, OLi = 1.91(2) Å, CMnC = 88.2(3)° (cis), CMnC = 149.1(3)° (trans), CMnO = 98.6(2)° (cis), CMnO = 152.5(3)° (trans). Crystal data for C42H90N4O10Li12Mn2 at −100°C: monoclinic, space group P21/n, a = 10.616(3), b = 18.189(4), c = 14.973(4) Å, β = 95.06(2)°, V = 2880(2) Å3, Z = 2, RF = 0.037, RwF = 0.042 for 2084 data and 317 variables. The present compound is the first oxo-alkyl of manganese and only the third σ-organomanganese(III) complex of any kind.