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.

Open-Shell Early Lanthanide Terminal Imides

Group 3- and 4f-element organometallic chemistry and reactivity are decisively driven by the rare-earth-metal/lanthanide (Ln) ion size and associated electronegativity/ionicity/Lewis acidity criteria. For these reasons, the synthesis of terminal "unsupported" imides [Ln═NR] of the smaller, closed-shell Sc(III), Lu(III), Y(III), and increasingly covalent Ce(IV) has involved distinct reaction protocols while derivatives of the "early" large Ln(III) have remained elusive. Herein, we report such terminal imides of open-shell lanthanide cations Ce(III), Nd(III), and Sm(III) according to a new reaction protocol. Lewis-acid-stabilized methylidene complexes [Tp^tBu,MeLn(μ₃-CH₂){(μ₂-Me)MMe₂}₂] (Ln = Ce, Nd, Sm; M = Al, Ga) react with 2,6-diisopropylaniline (H₂NAr^iPr) via methane elimination. The formation of arylimide complexes is governed by the Ln(III) size, the Lewis acidity of the group 13 metal alkyl, steric factors, the presence of a donor solvent, and the sterics and acidity (pK_a) of the aromatic amine. Crucially, terminal arylimides [Tp^tBu,MeLn(═NAr^iPr)(THF)₂] (Ln = Ce, Nd, Sm) are formed only for M = Ga, and for M = Al, the Lewis-acid-stabilized imides [Tp^tBu,MeLn(NAr^iPr)(AlMe₃)] (Ln = Ce, Nd, Sm) are persistent. In stark contrast, the [GaMe₃]-stabilized imide [Tp^tBu,MeLn(NAr^iPr)(GaMe₃)] (Ln = Nd, Sm) is reversibly formed in noncoordinating solvents.

Reversible addition of tin(II) amides to nitriles

Lappert's stannylene (Sn[N(SiMe₃)₂]₂) has been reacted with various nitriles, dinitriles and trinitriles with the formation of heteroleptic amidotin(II) amidinates of the general formulae [RC(NSiMe₃)₂]SnN(SiMe₃)₂, R'{[C(NSiMe₃)₂]SnN(SiMe₃)₂}₂ and R''{[C(NSiMe₃)₂]SnN(SiMe₃)₂}₃, where R = Ph (1), 2-(CN)-C₆H₄ (2), 3-(CN)-C₆H₄ (3); R' = 1,3-C₆H₄ (4), 1,4-C₆H₄ (5) and R'' = 1,3,5-C₆H₃ (6). The reactions of amidotin(II) benzamidinate 1 with an excess of benzonitrile proceed to homoleptic tin(II) bis(benzamidinate) [PhC(NSiMe₃)₂]₂Sn, which reversibly eliminates benzonitrile and 1 when warmed. The premise of reversibility has been supported by a multinuclear time-dependent NMR study and a theoretical (DFT) description. On the other hand, magnesium(II) bis(benzamidinate) [PhC(NSiMe₃)₂]₂Mg (8) and lanthanum(II) tris(benzamidinate) [PhC(NSiMe₃)₂]₃La (7) have been synthesised from appropriate metal hexamethyldisilazides and benzonitrile.

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...

Nitrile formation via dichlorocarbene insertion into the Si–N bond of Ln(iii) bis(trimethylsilyl)amide complexes

Reactions of bis(trimethylsilyl)amino lanthanides and chloroform unprecedently generate the Me3SiCN complexes where the nitrile ligand is formed via insertion of dichlorocarbene into the Si–N bond of the lanthanide precursor.

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.

Synthesis of Boronated Amidines by Addition of Amines to Nitrilium Derivative of Cobalt Bis(Dicarbollide)

A series of novel cobalt bis(dicarbollide) based amidines were synthesized by the nucleophilic addition of primary and secondary amines to highly activated B-N+≡C-R triple bond of the propionitrilium derivative [8-EtC≡N-3,3'-Co(1,2-C2B9H10)(1',2'-C2B9H11)]. The reactions with primary amines result in the formation of mixtures of E and Z isomers of amidines, whereas the reactions with secondary amines lead selectively to the E-isomers. The crystal molecular structures of E-[8-EtC(NMe2)=HN-3,3'-Co(1,2-C2B9H10)(1',2'-C2B9H11)], E-[8-EtC(NEt2)=HN-3,3'-Co(1,2- C2B9H10)(1',2'-C2B9H11)] and E-[8-EtC(NC5H10)=HN-3,3'-Co(1,2-C2B9H10)(1',2'-C2B9H11)] were determined by single crystal X-ray diffraction.

Calcium mediated efficient synthesis of N-arylamidines from organic nitriles and amines

Amidines are a preeminent group of organic compounds having wide applications in various industries. Here, we have developed a simple one-step reaction protocol for the facile synthesis of N-arylamidines catalysed by calcium bis(hexamethyldisilazide) [Ca{N(SiMe3)2}2(THF)2]. The amidine synthesis was readily achieved from organic nitriles and amines which provided a broad substrate scope ranging from electron-withdrawing to electron-donating substitutions as well as heterocyclic substitution. The reaction was carried out in a solvent-free medium under ambient conditions. The nucleophilic addition of aromatic amines to aryl nitriles led to good to excellent yields of the corresponding amidines. The reactivity of the amidines was further examined and the respective urea derivatives were achieved in excellent yields. The plausible mechanism involves the generation of an active calcium amido pre-catalyst that helps in the activation of nitriles in the reaction course.

Amido rare-earth(iii) and Ca(ii) complexes coordinated by tridentate amidinate ligands: synthesis, structure, and catalytic activity in the ring-opening polymerization of rac-lactide and ε-caprolactone

Y(iii), Sm(iii) and Ca(ii) monoamido complexes coordinated by tridentate amidinate ligand were synthesized and evaluated as initiators of ring-opening polymerization of rac-lactide and ε-caprolactone.

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.

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.