Rare Earth Metal Complexes Supported by Ancillary Imidazolin‐2‐iminato Ligands

Abstract

The coordination chemistry of imidazolin‐2‐iminato ligands towards rare earth metal atoms is reviewed. The structural characterization of a large number of mono‐, bis‐ and tris(imidazolin‐2‐iminato) complexes – in most cases scandium, yttrium, gadolinium, and lutetium complexes – reveals almost exclusively the formation of mononuclear complexes with very short metal–nitrogen bonds, which confirms the ability of imidazolin‐2‐iminato ligands to efficiently act as imido‐type 2σ,4π‐electron donors. In particular, mono(imidazolin‐2‐iminato) metal dichlorides proved to be excellent starting materials for the introduction of alkyl, amido, cyclopentadienyl, cyclooctatetraenyl, and carboranyl ligands and also for the preparation of efficient pre‐catalysts for ring‐opening, hydroamination and hydrosilylation reactions, which allow to establish imidazolin‐2‐iminato ligands as novel valuable members of the growing family of ancillary ligands in organo rare earth metal and organolanthanide chemistry. In addition, the coordination chemistry of several imidazolin‐2‐imine‐hybrid ligands such as cyclopentadienyl‐imine and pincer‐type diimine ligands is described, and the structural characterization of the resulting complexes indicates that also neutral imidazolin‐2‐imines act as strong amido‐type donor ligands towards rare earth metal ions.

Recent advances in the development of alkyne metathesis catalysts

“…In recent years, our group has significantly expanded the use of these 2σ,4π-electron donor ligands in organometallic chemistry and homogeneous catalysis [56–67]. Their synthesis starts from N -heterocyclic carbenes 1 which react with trimethylsilyl azide to afford 2-trimethylsilyliminoimidazolines 2 .…”

Successive Protonation of an N‐Heterocyclic Imine Derived Carbonyl: Superelectrophilic Dication Versus Masked Acylium Ion

“…[8] In their anionic form these systems harness the strongly electron-releasing properties of the NHC moiety;t he exocyclicC =Nd ouble bond is highly polarized in ylidic fashion (C d+ À N dÀ ), rendering the iminato ligand very electron-rich. [8] In their anionic form these systems harness the strongly electron-releasing properties of the NHC moiety;t he exocyclicC =Nd ouble bond is highly polarized in ylidic fashion (C d+ À N dÀ ), rendering the iminato ligand very electron-rich.…”

“…[9f] Given that protonation of [3] + leads exclusively to [4] 2+ , we pursued another pathway to access the alternative product derived from putative Path B( i.e.aL ewis base free acylium cation). [5] (7), C1-N1 1.219 (8), N1-C2 1.372 (6); O1-C1-N1:1 73.1(9), C1-N1-C2:1 35.9 (8). Recrystallization from dichloromethane at À30 8 8Ca ffords single crystals and X-ray crystallography confirms chloride abstraction to generate the desired cation [5] + as the [SbF 6 ] À salt (Scheme 5a nd Figure 2).…”

“…N-Heterocyclic imines (NHIs) constitute ac lass of imino ligand based on the well-known N-heterocyclic carbene (NHC) scaffold (Scheme 2). [8] In their anionic form these systems harness the strongly electron-releasing properties of the NHC moiety;t he exocyclicC =Nd ouble bond is highly polarized in ylidic fashion (C d+ À N dÀ ), rendering the iminato ligand very electron-rich. NHIs are capable of acting as 2s,4p donors (Scheme 2, top), and as such, have been exploited to stabilize low coordinate,highly electron-deficient main group systems.…”

Synthesis and characterization of homoleptic imidazolin-2-iminato rare earth metal complexes

“…In the course of these studies, a number of mono-and bis(imidazolin-2-iminato) scandium, yttrium, gadolinium and lutetium complexes of the types [(Im Dipp N)MCl 2 (THF) 3 ] [15] and [(Im Dipp N) 2 -MCl(THF) 2 ] [16] containing the Im Dipp N ligand (R ¼ Dipp ¼ 1,3-diisopropylphenyl, R 0 ¼ H, Scheme 1) were prepared, which proved to be versatile starting materials for the preparation of cyclooctatetraenyl, cyclopentadienyl, amido and alkyl complexes by chloride substitution [15]. In continuation of this work, we aimed at the synthesis of tris-(imidazolin-2-iminato) rare earth metal complexes, which might be regarded as isolobal to tris(cyclopentadienyl) complexes [(Cp) 3 M] [2] and to homoleptic tris(phosphoraneiminato) complexes [M(NPR 3 ) 3 ] [6].…”