Low-oxidation state cobalt-magnesium complexes: ion-pairing and reactivity

Abstract

Magnesium cobaltates (Arnacnac)MgCo(COD)2(1-3) were synthesised by reacting (Arnacnac)MgI(OEt2) with K[Co(η4-COD)2] (COD = 1,5-cyclooctadiene) [Arnacnac = CH(ArNCMe)2; Ar = 2,4,6-Me3-C6H2(Mes), 2,6-Et2-C6H3(Dep), 2,6-iPr2-C6H3Mes (Dipp)]. Compounds1-3form contact ion-pairs in toluene, while solvent separated ion-pairs are formed in THF. The effect of ion-pairing on the reactivity is illustrated by reaction of2withtert-butylphosphaalkyne, which affords distinct 1,3-diphosphacyclobutadiene complexes. The heteroleptic sandwich complex [(Depnacnac)MgCo(P2C2tBu2)]2(4) is selectively formed in toluene, while the homoleptic bis(1,3-diphosphacyclobutadiene) complex [(Depnacnac)Mg(THF)3][Co(P2C2tBu2)2] (5) is obtained in THF. Complex4is a precursor to further unusual phosphaorganometallic compounds. Substitution of the labile COD ligand in4by white phosphorus (P4) enabled the synthesis of the phosphorus-rich sandwich compound [(Depnacnac)MgCoP4(P2C2tBu2)]2(6). The heterobimetallic complex (Cp*NiP2C2tBu2)Co(COD) (7) was isolated after treatment of4with Cp*Ni(acac) (Cp* = C5Me5, acac = acetylacetonate).