Synthesis and structure of mono- and dinuclear cyclopentadienyl–indenyl complexes of iron(II) and further reactions to mixed tri- and tetranuclear iron–cobalt complexes

The reaction of a mixture of sodium cyclopentadienide and the monolithium salt or dilithium salt of 2,2-bis(indenyl)propane with FeCl2 leads to the mononuclear complex [(η5-C5H5)Fe(η5-ind-C(CH3)2-ind)] (ind = 1-indenyl) (1) and the dinuclear complex [{(η5-C5H5)Fe(η5-ind)}2C(CH3)2] (2), respectively. [(η5-Me5C5)Fe(tmeda)Cl] reacts with dilithium 1,1′-biindenyl under formation of [{(η5-Me5C5)Fe}2(μ-η5:η5-1,1′-biind)] (4). Due to the annelated arene rings of the η5-indenyl ligands, 2 and 4 may act as 4-electron donor ligands, as exemplified by the reaction with the triple-decker complex [{(η5-Me5C5)Co}2(μ-η6:η6-toluene)], which afforded the tetranuclear dimer of triple-decker complexes [{(η5-C5H5)Fe(η5-Me5C5)Co(μ-η5:η4-1-ind)}2C(CH3)2] (3) and the trinuclear complex [{(η5-Me5C5)Fe}2(η5-Me5C5)Co(μ3-η5:η4:η5-1,1′-biind)] · Et2O (5 · Et2O) by replacement of the central toluene deck, respectively. The [(η5-Me5C5)Co] fragments of 3 and 5 are bonded via the six-membered rings of the indenyl ligands in a η4-fashion. Caused by the coordination to the Co atoms the six-membered rings lose their planarity and adopt a butterfly structure. The coordination geometry of the Fe atoms is similar in all five complexes. Each Fe atom is coordinated by the C atoms of one of the five-membered rings of the indenyl ligands in a slightly distorted η5 manner (η3 + η2-coordination) and by a cyclopentadienyl ligand in a regular η5-fashion. The structures of 3 and 5 represent the first examples of slipped triple-decker complexes which comprise indenyl ligands in a μ-η5:η4 coordination mode.

Graphical abstractA series of mixed multidecker compounds of cobalt and iron with bridging indenyl ligands (derived from 2,2-bis(indenyl)propane) is presented. The coordination of [(η5-CpR)Co] ligand fragments is performed under mild conditions using the triple-decker [{(η5-Me5C5)Co}2(μ-η6:η6-toluene)] as [(η5-CpR)Co] transfer agent. The [(η5-CpR)Co] fragments in the new multidecker complexes are bonded via the six-membered rings of the indenyl ligands in a η4-fashion. The first examples of slipped triple-decker complexes which comprise indenyl ligands in a μ-η5:η4 coordination mode are thus given.Figure optionsDownload full-size imageDownload as PowerPoint slide