Direct dehydrogenative silylation of pyridyl and iminyl substrates with triethylsilane was achieved using (L)Ir(cod)(X) (1) (L = a perimidine-based carbene ligand, X = OAc and OCOPh) complexes as ...catalysts under toluene refluxing conditions in the presence of norbornene as a hydrogen scavenger, and the silylated products were obtained in good yields. The isolated bis(cyclometalated)iridium complexes, (C∧C:)(C∧N)IrOAc (2) (C∧C: = a cyclometalated perimidine-carbene ligand and C∧N = a cyclometalated pyridyl- and iminyl-ligated aromatic substrate), were key intermediates, where cyclometalated five-membered metallacycles of substrates such as phenylpyridine were selectively formed before yielding mono-ortho-silylation products. The bis(cyclometalated)iridium complex (XyC∧C:)(C∧N)IrOAc (2d) (XyC∧C: = a cyclometalated N-xylyl-N′-methylperimidine-carbene ligand and C∧N = a 2-pyridylphenyl ligand), reacted with 2 equiv of Et3SiH to give an iridium hydride complex, (L4)(C∧N)Ir(H)(SiEt3) (8d) (L4 = N-CH3, N-3,5-(CH3)2C6H3 perimidine), via demetalation of a N-3,5-xylyl ring of the carbene ligand of 2d. The formation of 8d was confirmed by isolating the corresponding chloro complex (L4)(C∧N)Ir(Cl)(SiEt3) (8d-Cl) by treatment with CCl4. The N-methyl moiety of the carbene ligand coordinated to 8d was cyclometalated in the presence of norbornene at room temperature to afford (MeC∧C:)(C∧N)Ir(SiEt3) (10d) (MeC∧C: = a cyclometalated N-xylyl-N′-methylperimidine-carbene), while at high temperature 8d reacted with norbornene and Et3SiH to afford the silylated product, 2-(2-triethylsilyl)phenylpyridine (3a) and norbornane. A deuterium labeling experiment using 2d and Et3SiD (excess) revealed the incorporation of deuterium atoms at two ortho-positions of the N-xylyl group (>90%) and at the 3-position of 2-pyridylphenyl ligand (ca. 40%) within 3 h at room temperature, indicating that the cyclometalation/demetalation of the N-xylylperimidine carbene and 2-phenylpyridine ligands were reversible processes. Isolation of these cyclometalated iridium complexes under controlled conditions and D-labeling experiments thus revealed a dual function of the N-aryl group bound to the perimidine-carbene ligand, which acted as both a neutral carbene ligand and a monoanionic ortho-metalated aryl-carbene ligand through reversible C–H bond activation and Ir–C bond cleavage of the N-aryl group during the catalytic cycle.
A new family of heterometallic catalysts based on trimetalated macrocyclic tris(salen) ligands and rare‐earth metals was prepared and structurally characterized. The LaZn3 system containing anionic ...ligands such as acetate plays a critical role in catalyzing the alternating copolymerization of cyclohexene oxide (CHO) and CO2 with a high proportion of carbonate linkages. Among the lanthanide metals, the CeZn3 system exhibits high catalytic activity with a turnover frequency (TOF) of over 370 h−1. NMR analysis of the complex and end‐group analysis of the polymer suggest that the acetate ligands are rapidly exchanged, not only among coordinated acetates, but also between coordinated acetates and added carboxylate anions. These unique properties make this the first example of telomerization for the copolymerization of CHO and CO2.
Homogeneous heterometallic complexes based on the trizincated macrocycle trisaloph and a rare‐earth metal showed high catalytic activity for the alternating copolymerization of cyclohexene oxide and CO2 with a high proportion of carbonate repeat units. The carboxylate anion of the ammonium salt initiates the telomerization, providing the polycarbonate with the corresponding carboxylate.
Toward gaining insight into the behavior of bimetallic catalysts for olefin polymerization, a series of structurally related binuclear zirconium catalysts with bisamine bisphenolate and pyridine ...bisphenolate ligands connected by rigid teraryl units were synthesized. Anthracene-9,10-diyl and 2,3,5,6-tetramethylbenzene-1,4-diyl were employed as linkers. Bulky Si i Pr3 and SiPh3 substituents were used in the position ortho to the phenolate oxygen. Pseudo-C s and C 2 symmetric isomers are observed for the binuclear complexes of bisamine bisphenolate ligands. In general, binuclear catalysts show higher isotacticity compared to the monozirconium analogues, with some differences between isomers. Amine bisphenolate-supported dizirconium complexes were found to be moderately active (up to 1.5 kg mmolZr –1 h–1) for the polymerization of 1-hexene to isotactically enriched poly-1-hexene (up to 45% mmmm) in the presence of stoichiometric trityl or anilinium borate activators. Moderate activity was observed for the production of isotactically enriched polypropylene (up to 2.8 kg mmolZr –1 h–1 and up to 25.4% mmmm). The previously proposed model for tacticity control based on distal steric effects from the second metal site is consistent with the observed behavior. Both bisamine bisphenolate and pyridine bisphenolate supported complexes are active for the production of polyethylene in the presence of MAO with activities in the range of 1.1–1.6 kg mmolZr –1 h–1 and copolymerize ethylene with α-olefins. Little difference in the level of α-olefin incorporation is observed between mono- and dinuclear catalysts supported with the pyridine bisphenolate catalysts. In contrast, the size of the olefin affects the level of incorporation differently between monometallic and bimetallic catalysts for the bisamine bisphenolate system. The ratio of the incorporation levels with dinuclear vs mononuclear catalysts decreases with increasing comonomer size. This effect is attributed to steric pressure provided by the distal metal center on the larger olefin in dinuclear catalysts.
Singlet fission has the potential to surpass current efficiency limits in next-generation photovoltaics and to find use in quantum information science. Despite the demonstration of singlet fission in ...various materials, there is still a great need for fundamental design principles that allow for tuning of photophysical parameters, including the rate of fission and triplet lifetimes. Here, we describe the synthesis and photophysical characterization of a novel bipentacene dipyridyl pyrrole (HDPP-Pent) and its Li- and K-coordinated derivatives. HDPP-Pent undergoes singlet fission at roughly 50% efficiency (τSF = 730 ps), whereas coordination in the Li complex induces significant structural changes to generate a dimer, resulting in a 7-fold rate increase (τSF = 100 ps) and more efficient singlet fission with virtually no sacrifice in triplet lifetime. We thus illustrate novel design principles to produce favorable singlet fission properties, wherein through-space control can be achieved via coordination chemistry-induced multipentacene assembly.
C–H bond activation of terminal alkynes by Tp′Rh(CNneopentyl) (Tp′ = hydridotris-(3,5-dimethylpyrazolyl)borate) resulted in the formation of terminal C–H bond activation products ...Tp′Rh(CNneopentyl)(CCR)H (R = t-Bu, SiMe3, hexyl, CF3, p-MeOC6H4, Ph, and p-CF3C6H4). A combination of kinetic selectivity determined in competition reactions and activation energy for reductive elimination has allowed for the calculation of relative Rh–Calkynyl bond strengths. The bond strengths of Rh–Calkynyl products are noticeably higher than those of Rh–Caryl and Rh–Calkyl analogues. The relationship between M–C and C–H bond strengths showed a linear correlation (slope R M–C/H–C = 1.32), and follows energy correlations previously established for unsubstituted sp2 and sp3 C–H bonds in aliphatic and aromatic hydrocarbons.
Early metal complexes supported by hemilabile, monoanionic di(pyridyl) pyrrolide ligands substituted with mesityl and anthracenyl groups were synthesized to probe the possibility of second ...coordination sphere arene−π interactions with ligands with potential for allosteric control in coordination chemistry, substrate activation, and olefin polymerization. Yttrium alkyl, indolide, and amide complexes were prepared and structurally characterized; close contacts between the anthracenyl substituents and Y-bound ligands are observed in the solid state. Titanium, zirconium, and hafnium tris(dimethylamido) complexes were synthesized, and their ethylene polymerization activity was tested. In the solid state structure of one of the Ti tris(dimethylamido) complexes, coordination of Ti to only one of the pyridine donors is observed pointing to the hemilabile character of the di(pyridyl) pyrrolide ligands.
Eine neue Familie von Heterometallkatalysatoren auf Basis von dreifach metallierten makrocyclischen Tris(salen)‐Liganden und Seltenerdmetallen wurde hergestellt und strukturell charakterisiert. Das ...LaZn3‐System mit seinen anionischen Liganden wie Acetat spielt eine zentrale Rolle bei der katalysierten alternierenden Copolymerisation von Cyclohexenoxid (CHO) und CO2 und liefert ein Produkt mit einem hohen Gehalt an Carbonatverknüpfungen. Bei den Lanthanoiden zeigt das CeZn3‐System eine hohe katalytische Aktivität mit einer Wechselzahl (TOF) von über 370 h−1. Die NMR‐spektroskopische Analyse des Komplexes und die Bestimmung der Endgruppen im Polymer weisen auf einen schnellen Austausch der Acetatliganden hin. Die koordinierten Acetate werden nicht nur untereinander, sondern auch gegen zugesetzte Carboxylat‐Anionen ausgetauscht. Mit solch einzigartigen Eigenschaften ist dieses System das erste Beispiel für eine als Telomerisierung ablaufende Copolymerisation von CHO und CO2.
Homogene Heterometallkomplexe auf Basis des Makrocyclus Trisaloph mit drei Zinkzentren und einem Seltenerdmetall zeigte eine hohe katalytische Aktivität in der alternierenden Copolymerisation von Cyclohexenoxid und CO2 mit einem hohen Anteil an Carbonat‐Wiederholungseinheiten. Das Carboxylat‐Anion in Ammoniumsalzen initiierte die fortschreitende Telomerisierung zu Polycarbonat mit entsprechenden Carboxylaten.
We report the synthesis and structure of iridium(I) complexes with N,N′-disubstituted perimidine carbene ligands and halides or carboxylate ligands. Iodo-, chloro-, and acetate-Ir(carbene)(cod) ...complexes were selectively prepared by changing the bases and silver salts. Intramolecular C−H bond activation to prepare a cyclometalated Ir(III) complex, (C∧C:)2Ir(OAc) (6), where C∧C: is a cyclometalated perimidine carbene ligand, was achieved using a carboxylate-ligated iridium complex; otherwise, C−H activation did not proceed. Acetate-Ir(carbene)(cod) (3c) reacted with benzoic anhydride at room temperature to afford benzoate-Ir(carbene)(cod) (3d). A perimidine-carbene- and phenylpyridine-ligated Ir(III) complex, (C∧C:)(C∧N)Ir(OCOR) (8), where C∧N is a cyclometalated phenylpyridine ligand, was isolated in good yield by mixing 3c or 3d and phenylpyridine under reflux in toluene. On the basis of the formation of 1,3-cyclooctadiene from the reaction mixture, we propose the following reaction mechanism for the intramolecular C−H activation: carboxylate-induced C−H bond activation and subsequent pyridine- or carbene-directed C−H bond oxidative addition, followed by the isomerization of 1,5-cyclooctadiene and reaction with carboxylic acid produces (C∧C:)(N∧C:)Ir(OCOPh). The cyclometalated complex 6 reacts with sodium acetylacetonate to form (C∧C:)2Ir(acac) (11), which exhibits phosphorescent emission at λmax = 555 nm (τ = 0.65 μs, ΦPL = 0.0018) in CH2Cl2 solution at room temperature.
A new family of heterometallic catalysts based on trimetalated macrocyclic tris(salen) ligands and rare-earth metals was prepared and structurally characterized. The LaZn
system containing anionic ...ligands such as acetate plays a critical role in catalyzing the alternating copolymerization of cyclohexene oxide (CHO) and CO
with a high proportion of carbonate linkages. Among the lanthanide metals, the CeZn
system exhibits high catalytic activity with a turnover frequency (TOF) of over 370 h
. NMR analysis of the complex and end-group analysis of the polymer suggest that the acetate ligands are rapidly exchanged, not only among coordinated acetates, but also between coordinated acetates and added carboxylate anions. These unique properties make this the first example of telomerization for the copolymerization of CHO and CO
.
Reactions of {Cp*IrCl(μ‐Cl)}2 (Cp* = η5‐pentamethylcyclopentadienyl) with bidentate pyridine–imine ligands such as 2‐(1‐hydrazonoethyl)pyridine (L1‐NH2) and ...4‐({1‐(pyridine‐2‐yl)ethylidenehydrazono}methyl)benzaldehyde (L3‐CHO), followed by salt exchange, afforded the corresponding iridium mononuclear complexes Cp*IrCl(L1‐NH2)PF6 (1a‐PF6) and Cp* IrCl(L3‐CHO)PF6 (6‐PF6) that bear N‐amino and formyl functionalities, whereas the reaction of {Cp*IrCl(μ‐Cl)}2 with butane‐2,3‐diylidenebis(hydrazone) L2‐(NH2)2; 2 equiv. afforded the half‐metallocene iridium complex 2‐PF6 with two free amino groups at the 2,5‐positions of an irida‐2,5‐diazacyclopentene skeleton. Post‐functionalization of the N‐amino groups of 1a‐PF6 and 6‐PF6 was accomplished with 3,5‐dimethoxybenzaldehyde in the presence of a catalytic amount of H2SO4 in CH3CN heated at reflux. The condensation reaction proceeded to form N‐imino‐functionalized iridium mononuclear complexes 3‐PF6 and 4‐PF6. Dinuclearization of complex 1a‐PF6 was achieved by a condensation reaction of 1a‐PF6 with dialdehydes. Reaction of an N‐amino functional group of 1a‐PF6 with terephthalaldehyde and isophthalaldehyde in the presence of a catalytic amount of H2SO4 gave the corresponding homodinuclear iridium complexes m‐5‐PF6 and p‐5‐PF6 in high yield. The molecular structure of p‐5‐PF6, evaluated by X‐ray diffraction study, revealed that two {Cp*IrCl} fragments coordinated to the tetradentate linked hydrazonoethyl skeleton in an anti fashion. Furthermore, treatment of the formyl group of iridium complex 6‐PF6 with the N‐amino group of ruthenium complex 1b‐PF6 resulted in the selective formation of an Irμ2‐(N‐N)Ru heterobimetallic complex (7‐PF6) under similar reaction conditions. The selectivity for the formation of the Ru–Ir heterobimetallic complex was due to the tolerance of the imine moiety to hydrolysis under acidic conditions.
We prepared Cp*Ir (Cp* = η5‐pentamethylcyclopentadienyl) complexes with amino and formyl functionalities at the ligand backbone. Ir2 complexes were isolated by the condensation reaction of an Ir complex with an N‐NH2 group and dialdehydes. Heterodinuclearization was accomplished by the condensation reaction of an Ir complex with a formyl group and a Ru complex with an N‐NH2 moiety.
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![Synthesis of Ir[μ2-(N-N)]M ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1434-1948/small "Synthesis of Ir[μ2-(N-N)]M (M = Ir and Ru) Homo- and Heterobimetallic Complexes through a Condensation Reaction of N-Amino and Formyl Groups Bound to Mononuclear (ηn-CnMen)M Units (n = 5 for M = Ir; n = 6 for M = Ru)")