Lanthanide Complexes Coordinated by a Dianionic Bis(amidinate) Ligand with a Rigid Naphthalene Linker

Twisted and Disconnected Chains: Flexible Linear Tetracuprous Arrays and a Decanuclear CuI Cluster as Blue- and Green/Yellow-Light Emitters

Defined arrays of transition metal ions embedded in tailored polydentate ligand scaffolds allow for a systematic design of their physical properties. Such molecular strings of closed-shell transition metal centers are particularly interesting for Group 11 metal ions in the oxidation state +1 if they undergo metallophilic d10···d10 contact interactions since these clusters are oftentimes efficient photoluminescence (PL) emitters. Copper is particularly attractive as a sustainable earth-abundant coinage metal source and because of the ability of several CuI complexes to serve as powerful thermally activated delayed fluorescence (TADF) emitters in molecular/organic light-emitting devices (OLEDs). Our combined synthetic, crystallographic, photophysical, and computational study describes a straight tetracuprous array possessing a centrally disconnected CuI2···CuI2 chain and a continuous helically bent CuI4 complex. This molecular helix undergoes a facile rearrangement in diethyl ether solution, yielding an unprecedented nanosized CuI10 cluster (2.9 × 2.0 nm) upon crystallization. All three clusters show either bright blue phosphorescence, TADF, or green/yellow multiband phosphorescence with quantum yields between 6.5 and 67%, which is persistent under hydrostatic pressure up to 30 kbar. Temperature-dependent PL investigations in combination with time-dependent density-functional theory (TD-DFT) calculations and void space analyses of the crystal packings complement a comprehensive correlation between the molecular structures and photoluminescence properties.

Stannylenes and Germylenes Stabilized by Tetradentate Bis(amidine) Ligands with a Rigid Naphthalene Backbone

An unusual series of germylenes and stannylenes stabilized by new tetradentate bis(amidine) ligands RNC(R')N-linker-NC(R')NR with a rigid naphthalene backbone has been prepared by protonolysis reaction of Lappert's metallylenes [M(HMDS)2] (M = Ge or Sn). Germylenes and stannylenes were fully characterized by NMR spectroscopy and X-ray diffraction analysis. DFT calculations have been performed to clarify the structural and electronic properties associated with tetradentate bis(amidine) ligands. Stannylene L1Sn shows reactivity through oxidation, oxidative addition, and transmetalation reactions, affording the corresponding gallium and aluminum derivatives.

Hydrogen bonds and dispersion forces serving as molecular locks for tailored Group 11 bis(amidine) complexes

A flexible polydentate bis(amidine) ligand LH2 operates as a molecular lock for various coinage metal fragments and forms the dinuclear complexes [LH2(MCl)2], M = Cu (1), Au (2), the coordination...

Synthesis, structure, and coordination chemistry of a neutral pyrrolyl-functionalized amidinate ligand

A new o-phenylene-bridged ligand incorporating neutral pyrrolyl and amidino moieties was designed and synthesized. The reactivity of the ligand was investigated and showed versatile coordination modes towards alkali- and rare-earth metals.

Calcium and Magnesium Bis(β-diketiminate) Complexes: Impact of the Alkylene Bridge on Schlenk-Type Rearrangements

Dinuclear heteroleptic alkaline-earth-metal complexes are interesting synthetic targets because the close proximity of two metals allows for cooperative effects. However, these complexes are also prone to undergoing Schlenk-type rearrangements, affording less-active homoleptic complexes. Here we present the metalation of bis(β-diketimine) ligands possessing flexible bridging groups, i.e., 1,2-ethylene, 1,3-propylene, and trans-1,2-cyclohexylene, using calcium and magnesium precursors. Four mononuclear homoleptic calcium complexes were obtained, highlighting the pronounced tendency of calcium to undergo Schlenk-like redistributions. In the case of magnesium, however, the bridging group plays a crucial role, yielding seven dinuclear heteroleptic complexes but also one mononuclear and one dinuclear homoleptic complexes. In addition, a trinuclear mixed heteroleptic-homoleptic magnesium complex, which is a rare example of an intermediate of the Schlenk equilibrium, was isolated.

Synthesis, structure, and catalytic activity of dinuclear aluminium bis(amidinate) and bis(guanidinate) complexes

The ring-opening polymerization grand prix: Bis(amidinate)s outpaced their bis(guanidinate) competitors and won the race, while the drivers’ engines using acidic co-initiators collapsed before take-off.

Ditopic bis(N,N',N'-substituted 1,2-ethanediamine) ligands: synthesis and coordination chemistry

The synthesis of two different types of bis(N,N',N'-substituted 1,2-ethanediamine)s, bridged either through the secondary (type 1) or tertiary (type 2) amine groups is reported. Selected protio-ligands have been applied in subsequent metallation reactions using aluminium, magnesium, tin, and zinc sources allowing to isolate five mononuclear and eight dinuclear complexes. All complexes have been fully characterized and their solid-state structures have been studied by means of single-crystal X-ray diffraction analysis. Nine of the 13 complexes carry reactive alkyl, amide or hydride groups, which indicates their potential as catalysts or supports for (transition) metals.

Magnesium bis(amidinate) and bis(guanidinate) complexes: impact of the ligand backbone and bridging groups on the coordination behaviour

A library of ten dinucleating bis(amidine) and bis(guanidine) ligands, in which the bridging groups, terminal rests, and backbone substituents were systematically altered, has been synthesized and subsequently applied in metallation reactions using three different magnesium sources. Eight Mg complexes could be isolated and fully characterized, and in seven cases their solid-state structure could be determined by means of single crystal X-ray diffraction analysis. The results evidence a versatile coordination behaviour, which ranges from the first dinuclear heteroleptic magnesium iodide complex to dinuclear homoleptic complexes. These findings indicate the crucial impact of both the ligand and the magnesium source not only on the accessibility of well-defined dinuclear complexes but also on the aggregation in solution and in the solid state.

Ligands with Two Monoanionic N,N-Binding Sites: Synthesis and Coordination Chemistry

Polytopic ligands have become ubiquitous in coordination chemistry because they grant access to a variety of mono- and polynuclear complexes of transition metals as well as rare-earth and main-group elements. Nitrogen-based ditopic ligands, in which two monoanionic N,N-binding sites are framed within one molecule, are of particular importance and are therefore the primary focus of this review. In detail, bis(amidine)s, bis(guanidine)s, bis(β-diimine)s, bis(aminotroponimine)s, bis(pyrrolimine)s, and miscellaneous bis(N,N-chelating) ligands are reviewed. In addition to the general synthetic protocols, the application of these ligands is discussed along with their coordination chemistry, the multifarious binding modes, and the ability of these ligands to bridge two (or more) metal(loids).

Rare-earth complexes supported by an ansa-bis(amidinate) ligand with a rigid o-phenylene linker: synthesis, structure, and catalytic activity for polymerization of cyclic esters

A bis(amidinate) ligand with a rigid o-phenylene linker C₆H₄-1,2-[NC(^tBu)NH(C₆H₅)]₂ (1) was successfully employed for the syntheses of rare-earth amides 2-5 in good yields. The structures of the amides were established by X-ray diffraction analysis and revealed that the ligand framework coordinated to the lanthanide atoms in different fashions depending on the central ion size. Larger lanthanide metal ions La³⁺ and Nd³⁺ prefer to form dinuclear complexes with one linked bis(amidinate) ligand as a bridge, while the smaller sized Y³⁺ and Er³⁺ favor the formation of mononuclear complexes. These complexes exhibited good catalytic activity for ring-opening polymerization of ε-caprolactone and l-lactide and the mononuclear complexes display higher activity.

Mono- and bimetallic amidinate samarium complexes - synthesis, structure, and hydroamination catalysis

In order to investigate the difference between mono- and bimetallic systems in the catalytic hydroamination/cyclization reaction two mono- and bimetallic amidinate samarium catalysts, featuring comparable coordination environments, were synthesized. Both systems comprise two {N(SiMe₃)₂}^- leaving groups to minimize the steric influence of the corresponding amidinate ligand. The bimetallic system is based on a bis(amidinate) 4,6-dibenzofuran derivative, while N,N'-bis(2,6-diisopropylphenyl)benzamidinate was employed as ligand for the monometallic catalyst. For the hydroamination/cyclization reaction five different substrates were investigated. Additionally, kinetic studies were carried out to gain deeper understanding of the mechanism.

Alternative (κ1-N:η6-arene vs.κ2-N,N) coordination of a sterically demanding amidinate ligand: are size and electronic structure of the Ln ion decisive factors?

The amine elimination reaction of equimolar amounts of ansa-bis(amidine) C₆H₄-1,2-{NC(tBu)NH(2,6-iPr₂C₆H₃)}₂ (L¹H) and [(Me₃Si)₂N]₂Yb(THF)₂ affords a bis(amidinate) Yb^II complex [C₆H₄-1,2-{NC(tBu)N(2,6-iPr₂C₆H₃)}₂]Yb(THF) (1) in 68% yield. Complex 1 features a rather rare η¹-amido:η⁶-arene coordination of both amidinate fragments to the Yb^II ion, resulting in the formation of a bent bis(arene) structure. Oxidation of 1 by I₂ regardless of the molar ratio of reagents (2 : 1 or 1 : 1) leads to the formation of the Yb^III species [{(2,6-iPr₂C₆H₃)[double bond, length as m-dash]NC(tBu)NH}-C₆H₄-1,2-{NC(tBu)N(2,6-iPr₂C₆H₃)}]YbI₂(THF)₂ (2) in which only one amidinate fragment is coordinated to the ytterbium ion in κ²-N,N'-chelating coordination mode, while the second NCN fragment is protonated in the course of the reaction and is not bound to the metal ion. The outcome of the salt metathesis reaction of LaCl₃ with lithium amidinates [C₆H₄-1,2-{NC(tBu)N(2,6-R₂C₆H₃)}₂Li₂] (R = Me, iPr) is proven to be strongly affected by the substituent 2,6-R₂C₆H₃ on the amidinate nitrogens. When R = iPr, the salt metathesis reaction occurs smoothly and results in the formation of an ate-chloro-amidinate complex [C₆H₄-1,2-{NC(tBu)N(2,6-iPr₂C₆H₃)}₂]La(μ²-Cl)Li(THF)(μ²-Cl)₂Li(THF)₂ (3) in which the La^III ion is coordinated by both amidinate fragments in a "classic"κ²-N,N'-chelating fashion. In the case of R = Me, the reaction requires prolonged heating for completion. Moreover, the salt metathesis reaction is accompanied by the fragmentation of the ligand and affords a trinuclear chloro-amidinate complex [C₆H₄-1,2-{NC(tBu)N(2,6-Me₂C₆H₃)}₂]La{[(tBu)C(N-2,6-Me₂C₆H₃)₂]La(THF)}₂(μ²-Cl)₄(μ³-Cl)₂ (4) containing one dianionic ansa-bis(amidinate) and two monoanionic [(tBu)C(N-2,6-Me₂C₆H₃)₂] amidinate fragments. DFT calculations are conducted to determine the factor that governs this change in coordination mode and, in particular, the effect of the metal oxidation state.

Syntheses and Structures of a Class of Bridged Bis(Amidinate)s and Derivatives

A series of different types of ‘bridge’ linked bis(amidinate)s have been prepared. Reactions of a variety of linked diamines with pivaloyl chloride yielded the corresponding diamides in very high yields. Conversion of the diamides to the diimine chloride is achieved with PCl5 in CH2Cl2. Reactions of the diimine chloride with aniline or t-butyl amine yielded the bis(amidinate)s in good yields, while reaction with pyrrolyl sodium or 2,5-dimethyl pyrrolyl potassium afforded the corresponding derivatives. Their structures were characterised by NMR and HRMS, and some products were further characterised by X-ray crystal structure analysis. It was found that the locations of the hydrogen atoms within the two amidine fragments vary. The structures showed that in the phenylene-linked bis(amidinate)s, the hydrogen atoms were attached to different nitrogen atoms in the amidine groups, and in the cyclohexylene-linked bis(amidinate)s or their derivatives, the C=N of the amidine groups were conjugated with the aromatic rings.

Rare-earth metal-mediated PhCN insertion into N,N-bis(trimethylsilyl)naphthalene-1,8-diamido dianion – a synthetic approach to complexes coordinated by ansa-bridged amido-amidinato ligand

We report the first example of rare earth metal-mediated insertion of PhCN into Si–N bonds with the formation of an amidinato moiety.

1,8-Bis(silylamido)naphthalene complexes of magnesium and zinc synthesised through alkane elimination reactions

The reactions between magnesium or zinc alkyls and 1,8-bis(triorganosilyl)diaminonaphthalenes afford the 1,8-bis(triorganosilyl)diamidonaphthalene complexes with elimination of alkanes. The reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and one or two equivalents of MgⁿBu₂ affords two complexes with differing coordination environments for the magnesium; the reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and MgⁿBu₂ in a 1 : 1 ratio affords 1,8-C₁₀H₆(NSiMePh₂)₂{Mg(THF)₂} (1), which features a single magnesium centre bridging both ligand nitrogen donors, whilst treatment of 1,8-C₁₀H₆(NSiR₃H)₂ (R₃ = MePh₂, ⁱPr₃) with two equivalents of MgⁿBu₂ affords the bimetallic complexes 1,8-C₁₀H₆(NSiR₃)₂{ⁿBuMg(THF)}₂ (R₃ = MePh₂2, R₃ = ⁱPr₃3), which feature four-membered Mg₂N₂ rings. Similarly, 1,8-C₁₀H₆(NSiⁱPr₃)₂{MeMg(THF)}₂ (4) and 1,8-C₁₀H₆(NSiMePh₂)₂{ZnMe}₂ (5) are formed through reactions with the proligands and two equivalents of MMe₂ (M = Mg, Zn). The reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and two equivalents of MeMgX affords the bimetallic complexes 1,8-C₁₀H₆(NSiMePh₂)₂(XMgOEt₂)₂ (X = Br 6; X = I 7). Very small amounts of [1,8-C₁₀H₆(NSiMePh₂)₂{IMg(OEt₂)}]₂ (8), formed through the coupling of two diamidonaphthalene ligands at the 4-position with concomitant dearomatisation of one of the naphthyl arene rings, were also isolated from a solution of 7.

Bis(amidinate) ligands in early lanthanide chemistry – synthesis, structures, and hydroamination catalysis

Bis(amidinate) ligands attached to rigid dibenzofuran and phenanthrene backbones have been introduced into lanthanide chemistry for the first time.

Amido rare-earth complexes supported by an ansa bis(amidinate) ligand with a rigid 1,8-naphthalene linker: synthesis, structures and catalytic activity in rac-lactide polymerization and hydrophosphonylation of carbonyl compounds

We report the synthesis of rare-earth amides and their catalytic activity in ROP of lactide.

Reactivity of lithium n-butyl amidinates towards group 14 metal(II) chlorides providing series of hetero- and homoleptic tetrylenes

The new class of homo- and heteroleptic n-butyl-N,N'-disubstituted amidinato group 14 metal(II) complexes were prepared by salt elimination from starting lithium amidinates and metal(II) chlorides both in stoichiometric ratio 2:1 and 1:1, respectively. The target amidinates contain less bulky isopropyl or cyclohexyl as well as a sterically demanding aromatic substituent. Desired 1:1 Pb(II) complexes are not accessible by the described procedure. Ligand transfer from Pb to Sn is taking place if homoleptic Pb(II) compounds are reacted with SnCl(2). Prepared tetrylenes were characterized by (1)H, (13)C, (119)Sn and (207)Pb NMR spectroscopy in C(6)D(6) or THF-d(8). X-Ray diffraction studies of one heteroleptic Ge(II) monomeric where the coordination polyhedron of the three coordinated germanium atoms is a trigonal pyramid, two different dimeric structures of heteroleptic Sn(II) complexes, one amidine hydroiodide byproduct and the oxidation product of the heteroleptic chloro Sn(II) amidinate as a tetranuclear species with two Sn(IV) and two Sn(II) atoms in central Sn(2)O(2) planar ring were performed on appropriate single crystals. The dimer of one of the heteroleptic stannylenes reveals a new type of monomeric units connection, weak Sn-Cl contact and an interaction of the tin atom with delocalized N-C(C)-N system of the amidinato ligand of the second molecule.