Use of Manganese(II)−Schiff Base Complexes for Carrying Polar Organometallics and Inorganic Ion Pairs

This report concerns the carrier properties of [Mn(acacen)]-derived compounds toward polar organometallics, inorganic ion pairs, and salts. Such properties are the consequence of Mn(II) behaving as a Lewis acid and the O asymptotic to O bite of the bidentate Schiff base ligand toward alkali cations. The starting compounds, which occur in a dimeric form, [Mn(acac-L-en)](2) [L' = CH2CH2 (1); L '' = C6H10 (2); L''' = R,R-C6H10(3)] have been synthesized either via a metathesis reaction from MnCl2 or using [Mn(3)Mes(6)]. The reaction of 1-3 with lithium organometallics allowed the isolation of [Mn(acac-L-en)(R)Li(DME)] [R = Me, L = L' (4); R = Ph, L = L' (5); R = Mes, L = L' (6); R = Me, L = L '' (7); R = Me, L = L''' (8)] as metalated forms, where the alkyl or aryl group is sigma-bonded to Mn(II), while the lithium cation is anchored to the Schiff base ligand. The metalated forms 4-8 react with PhCHO to give the corresponding lithium alkoxide, which remains bound in its ion-pair form to the [Mn(acacen)] skeleton in [Mn-2(acac-L'-en)(2)Li-2(OCH(Ph)Me)(2)]n (4). The use of 8, which has a chiral bridge across two nitrogen atoms, did not lead to a significant asymmetric induction in the reaction with PhCHO, because of the long separation between the lithium cation and the stereogenic center. The metalated form 4 was able to transfer the methyl group to the nitrile function to give the corresponding lithium-imide which then remains bonded to [Mn(acacen)] as the ion pair in a dimeric structure, as revealed for [Mn-2(acac-L'-en)(2)Li-2(DME){N=C(Ph)Me}(2)](n) (10). Their reaction with 1 appears to depend on the steric bulkiness of the alkyl group in WaOR, resulting in either monomeric adducts, i.e. in [Mn(acac-L'-en)(2,6-Bu'2C6H3O)Na(DME)(2)] (11 . 2DME), or polymeric structures, like in [Mn(acac-L'-en)Na(DME)(mu-OEt)](n) (13). All the dimeric units reported in this paper show a slight antiferromagnetic coupling between the two Mn(II) assisted by bridging alkoxo groups.