Structural and magnetic insights into the trinuclear ferrocenophane and unexpected hydrido inverse crown products of alkali-metal-mediated manganation(ii) of ferrocene

摘要

With the aim of introducing the diisopropylamide [NiPr2]- ligand to alkali-metal-mediated manganation (AMMMn) chemistry, the temperature-dependent reactions of a 1:1:3 mixture of butylsodium, bis(trimethylsilylmethyl)manganese(II), and diisopropylamine with ferrocene in hexane/toluene have been investigated. Performed at reflux temperature, the reaction affords the surprising, ferrocene-free, hydrido product [Na2Mn2 (-H)2{N(iPr)2}4]2 toluene (1), the first Mn hydrido inverse crown complex. Repeating the reaction rationally, excluding ferrocene, produces 1 in an isolated crystalline yield of 62 %. At lower temperatures, the same bimetallic amide mixture leads to the manganation of ferrocene to generate the first trimanganese, trinuclear ferrocenophane, [{Fe(C5H4)2}3{Mn3Na2(NiPr2)2 (HNiPr2)2}] (2) in an isolated crystalline yield of 81 %. Both 1 and 2 have been characterised by X-ray crystallographic studies. The magnetic properties of paramagnetic 1 and 2 have also been examined by variable-temperature magnetisation measurements on powdered samples. For 1, the room-temperature value for T is 3.45 cm3 K mol-1, and on lowering the temperature a strong antiferromagnetic coupling between the two Mn ions is observed. For 2, the room-temperature value for T is 4.06 cm3 K mol-1, which is significantly lower than the expected value for three isolated paramagnetic MnII ions.