Showing papers on "Pincer movement published in 2020"
TL;DR: The combination of well-established meridionally coordinating, tridentate pincers ligands with group 15 elements affords geometrically constrained non-trigonal pnictogen pincer compounds that show remarkable activity in challenging element–hydrogen bond scission reactions, such as the activation of ammonia.
Abstract: The combination of well-established meridionally coordinating, tridentate pincer ligands with group 15 elements affords geometrically constrained non-trigonal pnictogen pincer compounds These species show remarkable activity in challenging element–hydrogen bond scission reactions, such as the activation of ammonia The electronic structures of these compounds and the implications they have on their electrochemical properties and transition metal coordination are described Furthermore, stoichiometric and catalytic bond forming reactions involving B–H, N–H and O–H bonds as well as carbon nucleophiles are presented
41 citations
39 citations
TL;DR: The bis(silylene)-based SiC(sp3)Si pincer ligand N,N′-bis(LSi:)dipyrromethane [SiCH2Si] (L1; L = PhC(NtBu)2) with a C(sp 3) atom anchor was synthesized, and its coordination chemistry to iron was st...
35 citations
TL;DR: Reversible heterolytic N–H and H–H bond activation by MLC is shown, in which hemilability of the phosphorus linkers plays a key role, and base-free catalytic hydrogenation of imines and ketones is demonstrated.
Abstract: A series of PNP zinc pincer complexes capable of bond activation via aromatization/dearomatization metal-ligand cooperation (MLC) were prepared and characterized. Reversible heterolytic N-H and H-H bond activation by MLC is shown, in which hemilability of the phosphorus linkers plays a key role. Utilizing this zinc pincer system, base-free catalytic hydrogenation of imines and ketones is demonstrated. A detailed mechanistic study supported by computation implicates the key role of MLC in facilitating effective catalysis. This approach offers a new strategy for (de)hydrogenation and other catalytic transformations mediated by zinc and other main group metals.
30 citations
TL;DR: In this paper, the synthesis and characterization of a pincer-nickel complex of the type (iPr2NNN)NiCl2(CH3CN) is reported.
28 citations
TL;DR: The synthesis of the first PCNHCP functionalized iron complex and the reactivity of the corresponding trans-dihydride iron(II) dinitrogen complex [(PCNHCP)Fe(H)2N2)] is reported.
Abstract: Earth-abundant metal pincer complexes have played an important role in homogeneous catalysis during the last ten years. Yet, despite intense research efforts, the synthesis of iron PCcarbeneP pincer complexes has so far remained elusive. Here we report the synthesis of the first PCNHCP functionalized iron complex [(PCNHCP)FeCl2] (1) and the reactivity of the corresponding trans-dihydride iron(II) dinitrogen complex [(PCNHCP)Fe(H)2N2)] (2). Complex 2 is stable under an atmosphere of N2 and is highly active for hydrogen isotope exchange at (hetero)aromatic hydrocarbons under mild conditions (50 °C, N2). With benzene-d6 as the deuterium source, easily reducible functional groups such as esters and amides are well tolerated, contributing to the overall wide substrate scope (e.g., halides, ethers, and amines). DFT studies suggest a complex assisted σ-bond metathesis pathway for C(sp2)-H bond activation, which is further discussed in this study.
28 citations
TL;DR: In this paper, simple syntheses of a new class of palladium(II) pincer complexes having NNN and CNN coordination modes were described with the help of 1H and 13C.
27 citations
TL;DR: The electrochemical characterization of [ReCl2(L2)] and comparison with the previously reported platform [Recl2 (L1)] {L1 = N(CH2CH2PtBu2)2 –} provides mechanistic insight to rationalize the dependence of nitride yield on the reductant.
Abstract: The splitting of N2 into well-defined terminal nitride complexes is a key reaction for nitrogen fixation at ambient conditions. In continuation of our previous work on rhenium pincer mediated N2 splitting, nitrogen activation and cleavage upon (electro)chemical reduction of [ReCl2(L2)] {L2 = N(CHCHPtBu2)2 -} is reported. The electrochemical characterization of [ReCl2(L2)] and comparison with our previously reported platform [ReCl2(L1)] {L1 = N(CH2CH2PtBu2)2 -} provides mechanistic insight to rationalize the dependence of nitride yield on the reductant. Furthermore, the reactivity of N2 derived nitride complex [Re(N)Cl(L2)] with electrophiles is presented.
26 citations
TL;DR: A series of iridium complexes supported by N-linked pincer ligands, with the other linker being O- linkage, is described.
Abstract: A series of iridium complexes (RPOCR′NP)–HCl (4–HCl) and (RPSCR′NP)Ir–HCl (5–HCl) (R = substituent on P; R′ = substituent on N) supported by N-linked pincer ligands, with the other linker being O- ...
25 citations
TL;DR: Cyclic phosphine-free "head to tail" N,N,N pincer-like (pincer complexes mimicking) N-(pyrimidin-2-yl)-1,2-azole-3-carboxamide Pd(II) complexes with deprotonated amide groups as high-turnover catalysts for cross-coupling reactions on the background of up to quantitative yields under Green Chemistry conditions are reported.
Abstract: We report for the first time cyclic phosphine-free "head to tail" N,N,N pincer-like (pincer complexes mimicking) N-(pyrimidin-2-yl)-1,2-azole-3-carboxamide Pd(II) complexes with deprotonated amide groups as high-turnover catalysts (TON up to 106, TOF up to 1.2 × 107 h-1) for cross-coupling reactions on the background of up to quantitative yields under Green Chemistry conditions. The potency of the described catalyst family representatives was demonstrated in Suzuki-Miyaura, Mizoroki-Heck, and Sonogashira reactions on industrially practical examples. Corresponding ligands could be synthesized based on readily available reagents through simple chemical transformations. Within the complex structures, a highly unusual 1,3,5,7-tetraza-2,6-dipalladocane frame could be observed.
24 citations
TL;DR: In this paper, the Mn(I)−PNP pincer type complexes were tested as non-precious transition metal catalysts for the selective reduction of CO2 to boryl-protected MeOH in the presence of hydroboranes (HBpin, 9BBN) and borates as Lewis acids (LA) additives.
Abstract: Well‐defined Mn(I)‐PNP pincer‐type complexes were tested as non‐precious transition metal catalysts for the selective reduction of CO2 to boryl‐protected MeOH in the presence of hydroboranes (HBpin, 9‐BBN) and borates as Lewis acids (LA) additives. The best performance was obtained under mild reaction conditions (1 bar CO2, 60 °C) in the presence of the hydridocarbonyl complex [MnH(PNPNH–iPr)(CO)2] and B(OPh)3 as co‐catalyst. Preliminary mechanistic studies suggest that the initial activation step may occur by cationization of the metal center by the strong LA, and that both metal‐catalyzed and metal‐free steps are present in the overall catalytic system.
TL;DR: In this paper, a tandem approach to synthesize symmetrical azines from alcohols and hydrazine hydrate catalyzed by synthesized arene Ru(II) complexes of aroylthiourea ligand is presented.
TL;DR: In this article, the authors showed that a Mn hydride formed by H2 activation in the presence of a base is the catalytically active species for hydrogenation of substituted styrenes and unactivated aliphatic alkenes.
Abstract: Hydrogenation of substituted styrenes and unactivated aliphatic alkenes by molecular hydrogen has been achieved using a Mn catalyst with a non‐pincer, picolylphosphine ligand. This is the second reported example of alkene hydrogenation catalyzed by a Mn complex. Mechanistic studies showed that a Mn hydride formed by H2 activation in the presence of a base is the catalytically active species. Based on experimental and DFT studies, H2 splitting is proposed to occur via a metal‐ligand cooperative pathway involving deprotonation of the CH2 arm of the ligand, leading to pyridine dearomatization.
TL;DR: Ruthenium PNP pincer complexes bearing supplementary cyclometalated C,N‐bound ligands have been prepared and fully characterized for the first time and it is revealed that during catalysis, Ru carboxylate complexes are predominantly formed whereas neither the PNP nor the CN ligand are released from the catalyst in significant amounts.
Abstract: Ruthenium PNP pincer complexes bearing supplementary cyclometalated C,N-bound ligands have been prepared and fully characterized for the first time. By replacing CO and H- as ancillary ligands in such complexes, additional electronic and steric modifications of this topical class of catalysts are possible. The advantages of the new catalysts are demonstrated in the general α-alkylation of ketones with alcohols following a hydrogen autotransfer protocol. Herein, various aliphatic and benzylic alcohols were applied as green alkylating agents for ketones bearing aromatic, heteroaromatic or aliphatic substituents as well as cyclic ones. Mechanistic investigations revealed that during catalysis, Ru carboxylate complexes are predominantly formed whereas neither the PNP nor the CN ligand are released from the catalyst in significant amounts.
TL;DR: In this paper, the acidine-based PNP pincer complexes have been previously utilized for several environmentally benign catalytic processes, such as base-metal catalysis, in light of the recent growth in interest in base metal catalysis.
TL;DR: In this paper, the reactivity of unsymmetrical pyrazole-based PCN pincer Ni(II) halides has been tested in the presence of copper(II)-halides as an oxidizing agent as well as with NaBH4 and LiAlH4 as a hydride source.
TL;DR: In this paper, a tridentate diarylmethanido ligand was found to coordinate to the metal centers via central carbon and two nitrogen atoms of NMe2 groups resulting in [NCsp3N] pincer coordination.
Abstract: Ln(II) (Ln = Yb, Sm) and Ca(II) [NCsp3N] pincer type diarylmethanido complexes [2,2′-(4-MeC6H3NMe2)2CH]2M (M = Yb (2), Sm (3), Ca (4)) coordinated by a tridentate diarylmethanido ligand were synthesized through salt metathesis reactions of {[2,2′-(4-MeC6H3NMe2)2CH]K(THF)}2 and MI2(THF)2. X-ray analysis revealed that both diarylmethanido ligands in 2–4 are tridentate and coordinate to the metal centers via central carbon and two nitrogen atoms of NMe2 groups resulting in [NCsp3N] pincer coordination. In one of the five-membered MCCCN metallacycles in each tridentate diarylmethanido ligand, metal–arene interactions were detected and the coordination mode of [NCsp3N] ligands in 2–4 can be classified as κ1-N:η4-CCCN. A dynamic behavior involving the exchange between NMe2 groups and THF molecules in the coordination sphere of the M(II) ion was detected in solution. Complexes 2–4 proved to be catalytically active in a variety of reactions of C–C and C–E (E = Si, P, N, S) bond formation. Yb(II) 2 and Ca(II) 4 complexes catalyze intermolecular hydrobenzylation of styrene with 2-methyl and 2,6-dimethyl pyridines. Complex 2 demonstrates high chemo- and regioselectivities and is the first Ln(II) catalyst for intermolecular C–C bond formation. Complexes 2–4 were found to be efficient and selective precatalysts for intermolecular hydroelementation of olefins and acetylenes with various EH substrates (E = Si, P, N, S). Complexes 2–4 have demonstrated their versatility for intermolecular C–E bond formation and allow the realization of hydroamination, hydrophosphination, hydrosilylation and hydrothiolation of styrene and phenylacetylene. Moreover, 2–4 were found to be active in the catalysis of challenging transformations such as hydrosilylation and hydrophosphination of internal double CC and triple CC bonds.
TL;DR: Attempts to access the three-coordinate aluminyl by abstraction of pyridine with BF3·Et2O unexpectedly led to a B/Al metathesis with the preservation of the pincer structure in the product (PBP)Rh(CO)2.
Abstract: We report the synthesis of PAlP and PBP pincer complexes of Rh with a central bis(N-pyrrolyl)aluminyl or -boryl unit. Complex (PAlpyP)Rh(CO)2 possesses an aluminyl site stabilized by coordination of pyridine, resulting in a four-coordinate Al. Attempts to access the three-coordinate aluminyl by abstraction of pyridine with BF3·Et2O unexpectedly led to a B/Al metathesis with the preservation of the pincer structure in the product (PBP)Rh(CO)2. Abstraction of pyridine was carried out using B(C6F5)3, but the desired (PAlP)Rh(CO)2 underwent dimerization via isocarbonyl bridging.
TL;DR: Light is shed on the electronic influence of the non‐palindromic pincer ligand and reveal non‐radiative relaxation pathways of the different ligands employed as well as investigating the gold(III) complexes’ photophysical properties.
Abstract: We herein report on new synthetic strategies for the preparation of pyridine and imidazole substituted 2,2’‐dihalo biphenyls. These structures are pre‐ligands suitable for the preparation of respective stannoles. The latter can successfully be transmetalated to K[AuCl$_{4}$] forming non‐palindromic [(C^C^D)Au$^{III}$] pincer complexes featuring a lateral pyridine (D=N) or N‐heterocyclic carbene (NHC, D=C’) donor. The latter is the first report on a pincer complex with two formally anionic sp$^{2}$ and one carbenic carbon donor. The [(C^C^D)Au$^{III}$] complexes show intense phosphorescence in solution at room temperature. We discuss the developed multistep strategy and touch upon synthetic challenges. The prepared complexes have been fully characterized including X‐ray diffraction analysis. The gold(III) complexes’ photophysical properties have been investigated by absorption and emission spectroscopy as well as quantum chemical calculations on the quasi‐relativistic two‐component TD‐DFT and GW/Bethe–Salpeter level including spin–orbit coupling. Thus, we shed light on the electronic influence of the non‐palindromic pincer ligand and reveal non‐radiative relaxation pathways of the different ligands employed.
TL;DR: This compound is a strong reducing reagent, as it has been easily oxidized to germyl-palladium derivatives with a gold(i) complex, HCl and Ph2S2 through processes that involve formal addition of a bond of the oxidant across the Ge-Pd bond.
TL;DR: By use of a macrocyclic phosphinite pincer ligand and bulky substrate substituents, it is demonstrated how the mechanical bond can be leveraged to promote the oxidative addition of an interlocked 1,3‐diyne to a rhodium(I) center.
Abstract: By use of a macrocyclic phosphinite pincer ligand and bulky substrate substituents, we demonstrate how the mechanical bond can be leveraged to promote the oxidative addition of an interlocked 1,3-diyne to a rhodium(I) center. The resulting rhodium(III) bis(alkynyl) product can be trapped out by reaction with carbon monoxide or intercepted through irreversible reaction with dihydrogen, resulting in selective hydrogenolysis of the C-C σ-bond.
TL;DR: Ru complexes based on lutidine-derived pincer CNN(H) ligands having secondary amine side donors are efficient precatalysts in the hydrogenation and dehydrogenation of N-heterocycles.
Abstract: Ru complexes based on lutidine-derived pincer CNN(H) ligands having secondary amine side donors are efficient precatalysts in the hydrogenation and dehydrogenation of N-heterocycles. Reaction of a Ru-CNN(H) complex with an excess of base produces the formation of a Ru(0) derivative, which is observed under catalytic conditions.
TL;DR: Monitoring the catalytic borylation of 2-methylfuran and 2,6-lutidine by 1H NMR spectroscopy established the trans-dihydride cobalt(III) boryl as the catalyst resting state at low substrate conversion.
TL;DR: The synthesis of macrocyclic variants of commonly employed phosphine-based pincer ligands derived from lutidine and 2,6-dihydroxypyridine is described, where the P-donors are trans-substituted with a tetradecamethylene linker.
Abstract: The synthesis of macrocyclic variants of commonly employed phosphine-based pincer ligands derived from lutidine (PNP-14) and 2,6-dihydroxypyridine (PONOP-14) is described, where the P-donors are trans-substituted with a tetradecamethylene linker. This was accomplished using an eight-step procedure involving borane protection, ring-closing olefin metathesis, chromatographic separation from the cis-substituted diastereomers, and borane deprotection. The rhodium coordination chemistry of these ligands has been explored, aided by the facile synthesis of 2,2′-biphenyl (biph) adducts [Rh(PNP-14)(biph)][BArF4] and [Rh(PONOP-14)(biph)][BArF4] (ArF = 3,5-(CF3)2C6H3). Subsequent hydrogenolysis enabled generation of dihydrogen, ethylene and carbonyl derivatives; notably the ν(CO) bands of the carbonyl complexes provide a means to compare the donor properties of the new pincer ligands with established acyclic congeners.
TL;DR: A series of chiral NCN pincer iridium(III) complexes 2a–h with bis(imidazolinyl)phenyl ligands were synthesized via the central aryl C2–H bond activation of the 1,3-bis(2′-imidZolinyl )benzene liga.
TL;DR: Analysis of IR data indicated that NHC and phenolate ligands have a similar donor character but which remains lower than that of the phosphonium ylide, which was illustrated in the Pd-catalyzed allylation of aldehydes.
Abstract: The coordinating properties of N-heterocyclic carbene (NHC) (A), phenolate (B), and phosphonium ylide (C) moieties were investigated systematically through the preparation of a family of NHC, phosphonium ylide-based pincer ligands, where the third donor extremity can be either an NHC, a phenolate, or a phosphonium ylide. The overall donor character of such ligands [NHC(AaBbCc)] (a + b + c = 2) was analyzed by comparison of the molecular orbitals (energy and shape), oxidation potentials (Epox), and IR νCO and νCN stretching frequencies of their isostructural pincer Pd(II) complexes [NHC(AaBbCc)PdL][OTf] (L = NCCH3, CO, or CNtBu). The three categories of pincer complexes based on phosphonium ylides were easily obtained by acidic treatment of their highly stable ortho-metalated Pd(II) precursors prepared in a single step from readily available N-phosphonio-substituted imidazolium salts. Analysis of IR data indicated that NHC and phenolate ligands have a similar donor character but which remains lower than that of the phosphonium ylide. The impact on catalytic performance of the incorporation of a second strongly donating phosphonium ylide into the ligand architecture was illustrated in the Pd-catalyzed allylation of aldehydes.