Amido Complexes Research Articles

Rare‐Earth Amido and Borohydrido Complexes Supported by Tetradentate Amidinate Ligands: Synthesis, Structure, and Catalytic Activity in Polymerization of Cyclic Esters

Amido [ButC(NC6H4‐2‐OMe)2]2LnN(SiMe3)2 (Ln = Y (3), Nd (4)) and borohydrido complexes [ButC(NC6H4‐2‐OMe)2]2LnBH4 (Ln = Y (5), Nd (6)) coordinated by new amidinate ligand bearing two pendant anisolyl groups are synthesized. According to X‐ray analysis in complexes 3 and 4 one amidinate ligand is coordinated to the Ln3+ cation in a bidentate fashion (κ2‐NN), while the second one is tetradentate (κ4‐NNOO). At the same time in borohydrido neodymium complex 6 the amidinate ligands demonstrate κ4‐NNOO and κ3‐NNO coordination modes. Complexes 3–6 proved to be efficient initiators for ring‐opening polymerization of rac‐lactide and allow for achieving quantitative conversion of 500 equivalents of monomer into polymer in 0.3–4.5 h at 25 °C. The polymerization of ε‐caprolactone initiated by 3–6 proceeds much faster under similar conditions.

Fully renewable limonene‐derived polycarbonate as a high‐performance alkyd resin

AbstractLimonene‐derived polycarbonate‐based alkyd resins (ARs) have been prepared by copolymerization of limonene dioxide with CO2, catalysed by a β‐diiminate zinc–bis(trimethylsilyl)amido complex, and subsequent chemical modification with soybean oil fatty acids using triphenylethylphosphonium bromide as the catalyst. This quantitative partial modification was realized via epoxy–carboxylic acid chemistry, affording ARs with higher oil lengths, lower polydispersities and higher glass transition temperatures (Tg) in comparison to a conventional polyester AR based on phthalic acid, multifunctional polyol pentaerythritol and soybean fatty acid. The novel limonene polycarbonate AR and the conventional polyester AR were evaluated as coatings and both the physical drying (without the presence of the oxidative drying accelerator Borchi® Oxy Coat) and chemical curing (with Borchi® Oxy Coat) processes of these coatings were monitored by measuring the König hardness and complex modulus development with time. A better performance was obtained for the alkyd paint containing polycarbonates modified with fatty acids (FA‐PCs), which showed a faster chemical drying, a higher König hardness and a higher Tg in coating evaluation, demonstrating that the fully renewable FA‐PCs are promising resins for alkyd paint applications. © 2019 Society of Chemical Industry

Parent Cyclopentadienyl Ruthenium(II) Chloride Synthon: Derivatization to CpRu Amido, Imido, and Oxo Complexes

The complex salt [CpRu(η6-C10H8)][(CpRu)2(μ-Cl)3] ([1][2]) was synthesized and found to be a useful CpRuCl synthon. The ions [1]+ and [2]− cleanly comproportionate into monomeric CpRuCl(L)2 complexes with liberation of naphthalene upon treatment with donor ligands L such as DMSO, tBuNH2, 1,5-cycloctadiene, and CO. The amine adduct [CpRuCl(NH2tBu)2] allows access to the coordinatively unsaturated dimeric amido complex [CpRu(NHtBu)]2, which is subsequently transformed into the bridging imido complexes [(CpRu)2(μ-NtBu)(μ-CH2)] and [(CpRu)2(μ-NtBu)(μ-CH)]+. The imido methylidyne complex shows enhanced electrophilicity at the methylidyne carbon compared to its bulkier C5Me5 congener and also allows access to a less hindered parent Cp version of the diruthenocarbene ligand in the form of the Ru2Cu μ3-carbido complex [(CpRu)2(μ-NtBu)(μ3-C)Cu{N(SiMe3)2}]. The salt [1][2] also gives a novel tetranuclear μ4-oxo cluster [(CpRuCl)4(μ4-O)] upon oxidation in air or by N-methylmorpholine N-oxide.

Calcium Amido Complexes Coordinated by Tridentate Amidinate Ligands: Synthesis, Structures and Catalytic Activity in Olefin Hydrophosphination and Polymerization of Cyclic Esters

The reactions of [(Me3Si)2N]2Ca(thf)2 with amidines 2‐(Ph2P=NPh)C6H4NHC(tBu)=N(2,6‐R2C6H3) {R = iPr (L1H); R = Me (L2H)} afford heteroleptic calcium amido complexes [2‐(Ph2P=NPh)C6H4NC(tBu)=N(2,6‐R2C6H3)]Ca[N(SiMe3)2](thf) {R = iPr (1); R = Me (2)} featuring tridentate coordination of the amidinate ligands. Complexes 1 and 2 proved to be efficient catalysts for intermolecular hydrophosphination of styrene, α‐methylstyrene, divinylbenzene and phenylacetylene with Ph2PH and PhPH2. Compounds 1 and 2 exhibit high catalytic activity in the ring‐opening polymerization of ε‐caprolactone and enable quantitative conversion of 500 equiv. of monomer in 5 seconds (22 °C). Polymerization of rac‐lactide initiated by 1 and 2 proceeds much slower: 52–72 % conversion ([M]0/[Ca]0 = 100) was reached in 12 h (20 °C). The obtained polymers are characterized by narrow polydispersities (Mw/Mn = 1.22–1.28). Catalytic activity of complexes 1 and 2 in rac‐lactide polymerization increases significantly in the presence of 1–3 equiv. of iPrOH. Nearly quantitative (86–98 %) conversion of 100 equiv. of monomer was reached in 1 h and the obtained polymer samples were characterized by relatively narrow polydispersity (Mw/Mn = 1.51–1.68).

Monomeric, Divalent Vanadium Bis(arylamido) Complexes: Linkage Isomerism and Reactivity

Divalent complexes of vanadium were synthesized employing bulky silyl(aryl)amido ligands −N(SiiPr3)DIPP and −N(SitBu2Me)DIPP (DIPP = 2,6-iPr2C6H3). Solid-state structural characterization revealed that although the ligand −N(SiiPr3)DIPP supports a monomeric, bis(amido) complex of vanadium, its constitutional isomer −N(SitBu2Me)DIPP affords a homoleptic complex in which the vanadium center is sandwiched between the arene rings, an unusual binding mode for arylamido ligands. Magnetometry studies indicate that V[N(SiiPr3)DIPP]2 and V[(η5-DIPP)N(SitBu2Me)]2 have similar high-spin d3 electron configurations. However, spectroscopic methods, including electron paramagnetic resonance, nuclear magnetic resonance, infrared, and UV–visible spectroscopies, in addition to cyclic voltammetry and reactivity studies, suggest that V[N(SiiPr3)DIPP]2 is stereochemically nonrigid in solution, while V[(η5-DIPP)N(SitBu2Me)]2 is not. This nonrigidity explicitly impacts the reactivity of V[N(SiiPr3)DIPP]2, which can be used to a...

The Hafnium-Pyridyl Amido-Catalyzed Copolymerization of Ethene and 1-Octene: How Small Amounts of Ethene Impact Catalysis

Copolymerization of ethene and 1-octene is catalyzed by the Hf-pyridyl amido complex used in chain-shuttling polymerization. Active site counts and the molar mass distribution of catalyst-bound polymeryls are determined by chromophore quench-labeling. Catalytic data for copolymerization (1-octene consumption, active site counts, molar mass distributions of polymers, and I2-labeling of Zn-polymeryls) are compared with similar data for the homopolymerization of 1-octene. Such comparisons reveal that small amounts of ethene have a significant impact on catalysis. The rate of 1-octene consumption increases in a copolymerization ∼3-fold compared to a homopolymerization; this likely results from in situ ligand modification. The first insertion of alkene occurs into the Hf–naphthyl bond of the Hf-pyridyl amido catalyst; in copolymerization, competition between ethene and 1-octene for this insertion creates multiple active species. We propose that ethene insertion into the Hf–naphthyl bond leads to a faster polym...

Zinc-Mediated Chain Transfer from Hafnium to Aluminum in the Hafnium-Pyridyl Amido-Catalyzed Polymerization of 1-Octene Revealed by Job Plot Analysis

This report applies a Job plot analysis to demonstrate that dialkyl Zn reagents mediate chain transfer between Hf-pyridyl amido polymerization catalysts and AlR3 chain-transfer agents. Polyoctene produced in the presence of both ZnEt2 and AlEt3 is lower in molecular weight and has a narrower distribution than polyoctene produced in the presence of ZnEt2 alone. I2 labeling and NMR analysis of polymer chain ends enable quantification of the amount of Zn- and Al-polymeryls produced during polymerization. A Job plot of the number of Zn and Al polymer chains produced versus the mole fraction of ZnEt2 at constant moles of Zn + Al reveals a nonlinear relationship. The nonlinearity of the Job plot indicates cooperative exchange between Zn and Al. The chain-transfer agent, AlEt3, inhibits initiation, but not propagation, of polymerization as catalyzed by the Hf-pyridyl amido complex. This inhibition can be obviated by a two-step polymerization protocol. AliBu3 does not inhibit initiation or propagation and can be ...

Synthesis and characterization of palladium amido complexes containing pincer CNO ligands through nitrene insertion

Synthesis and characterization of palladium amido complexes containing pincer CNO ligands through nitrene insertion

Experimental and Computational Mechanistic Studies of the β-Diketiminatoiron(II)-Catalysed Hydroamination of Primary Aminoalkenes.

A comprehensive mechanistic study by means of complementary experimental and computational approaches of the exo-cyclohydroamination of primary aminoalkenes mediated by the recently reported β-diketiminatoiron(II) complex B is presented. Kinetic analysis of the cyclisation of 2,2-diphenylpent-4-en-1-amine (1 a) catalysed by B revealed a first-order dependence of the rate on both aminoalkene and catalyst concentrations and a primary kinetic isotope effect (KIE) (kH /kD ) of 2.7 (90 °C). Eyring analysis afforded ΔH≠ =22.2 kcal mol-1 , ΔS≠ =-13.4 cal mol-1 K-1 . Plausible mechanistic pathways for competitive avenues of direct intramolecular hydroamination and oxidative amination have been scrutinised computationally. A kinetically challenging proton-assisted concerted N-C/C-H bond-forming non-insertive pathway is seen not to be accessible in the presence of a distinctly faster σ-insertive pathway. This operative pathway involves 1) rapid and reversible syn-migratory 1,2-insertion of the alkene into the Fe-Namido σ bond at the monomer {N^N}FeII amido compound; 2) turnover-limiting Fe-C σ bond aminolysis at the thus generated transient {N^N}FeII alkyl intermediate and 3) regeneration of the catalytically competent {N^N}FeII amido complex, which favours its dimer, likely representing the catalyst resting state, through rapid cycloamine displacement by substrate. The collectively derived mechanistic picture is consonant with all empirical data obtained from stoichiometric, catalytic and kinetics experiments.

Magnetic anisotropy in trigonal planar Fe(ii) bis(trimethylsilyl)amido complexes of the type [Fe{N(SiMe3)2}2L]-experiment and theory.

Systematic ac (alternating current) magnetic investigations on four new trigonal planar high-spin Fe2+ complexes [Fe{N(SiMe3)2}2L] reveal that complexes which comprise a phosphine or arsine type ligand (L = PPh3, PMe3 and AsPh3) display slow magnetic relaxation at temperatures below 8 K under applied dc (direct current) fields, whereas a complex with a phosphine oxide ligand (L = OPPh3) does not. Accordingly, the parameters characteristic for magnetic anisotropy, derived both from dc magnetic measurements and quantum chemical calculations, reveal distinct differences for these two types of complexes. Extensive ab initio calculations of multi-reference wave function type were performed on the four new complexes listed above and the related reported ones with L = py, thf and PCy3 in order to get a reasonable description of the local electronic states involved in the magnetic relaxation. These calculations confirm that strong spin-orbit effects generate the magnetic anisotropy of complexes with L = PPh3, PMe3, AsPh3 and PCy3. On the other hand, the complexes with L = OPPh3, py and THF exhibit only small spin-orbit splittings, consistent with the fast relaxation found experimentally.

Development and mechanistic investigation of the manganese(iii) salen-catalyzed dehydrogenation of alcohols.

The first example of a manganese(iii) catalyst for the acceptorless dehydrogenation of alcohols is presented. N,N'-Bis(salicylidene)-1,2-cyclohexanediaminomanganese(iii) chloride (2) has been shown to catalyze the direct synthesis of imines from a variety of alcohols and amines with the liberation of hydrogen gas. The mechanism has been investigated experimentally with labelled substrates and theoretically with DFT calculations. The results indicate a metal-ligand bifunctional pathway in which both imine groups in the salen ligand are first reduced to form a manganese(iii) amido complex as the catalytically active species. Dehydrogenation of the alcohol then takes place by a stepwise outer-sphere hydrogen transfer generating a manganese(iii) salan hydride from which hydrogen gas is released.

Aminofluoroalkoxide amido and boryloxo lead(ii) complexes.

We report here on the utilisation of a readily available bidentate aminofluoroalkoxide in lead(ii) chemistry. Stable heteroleptic three-coordinate complexes can be produced in high yields, including a convenient amido synthetic precursor and a rare case of PbII-boryloxide.

Synthesis and characterization of 2-t-butylimino-functionalized indolyl rare-earth metal amido complexes for the catalytic addition of terminal alkynes to carbodiimides: the dimeric complexes with the alkynide species in the μ-η1:η2 bonding modes.

A series of new rare-earth metal amido complexes bearing a 2-t-butylimino-functionalized indolyl ligand were synthesized via dehydrogenation of a secondary amine, and their reactivities and catalytic performances were investigated. The reactions of 2-(tBuNHCH2)C8H5NH (1) with rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 afforded the complexes [2-(tBuN[double bond, length as m-dash]CH)C8H5N]RE[N(SiMe3)2]2 (RE = Er (2), Y (3), Dy (4), Sm (5), Nd (6)) containing the bidentate ligand via dehydrogenation of the amine to the imine group. Complexes 2-6 exhibited an excellent catalytic activity for the addition of terminal alkynes to carbodiimides affording a series of corresponding N,N'-dialkyl-propiolamidines. The catalysts can also be efficiently used for the preparation of the sterically bulky N,N'-diaryl-propiolamidine. Furthermore, the dimeric complexes {(μ-η1:η2-RC[triple bond, length as m-dash]C)RE[2-(tBuN[double bond, length as m-dash]CH)C8H5N]2}2 (11: RE = Y, R = Ph; 12: RE = Yb, R = SiMe3), with the alkynyl ligand in the μ-η1:η2 haptic modes, were isolated in attempts to study the catalytic mechanism.

Asymmetric transfer hydrogenation of cycloalkyl vinyl ketones to allylic alcohols catalyzed by ruthenium amido complexes.

A chemoselective 1,2-reduction of cycloalkyl vinyl ketones via asymmetric transfer hydrogenation is described. The reduction proceeded smoothly with a chiral diamine ruthenium complex as a catalyst and a HCOOH-NEt3 azeotrope as both a hydrogen source and solvent under mild conditions. A wide range of 1-cycloalkyl chiral allylic alcohols were obtained in good yields and up to 87% ee. It was found that the alkyl group plays an important role in the enantioselectivity.

A Mononuclear Nonheme Iron(IV)-Amido Complex Relevant for the Compound II Chemistry of Cytochrome P450.

A mononuclear nonheme iron(IV)-amido complex bearing a tetraamido macrocyclic ligand, [(TAML)FeIV(NHTs)]- (1), was synthesized via a hydrogen atom (H atom) abstraction reaction of an iron(V)-imido complex, [(TAML)FeV(NTs)]- (2), and fully characterized using various spectroscopies. We then investigated (1) the p Ka of 1, (2) the reaction of 1 with a carbon-centered radical, and (3) the H atom abstraction reaction of 1. To the best of our knowledge, the present study reports for the first time the synthesis and chemical properties/reactions of a high-valent iron(IV)-amido complex.

Cover Feature: CaII, YbII and SmII Bis(Amido) Complexes Coordinated by NHC Ligands: Efficient Catalysts for Highly Regio‐ and Chemoselective Consecutive Hydrophosphinations with PH3 (Chem. Eur. J. 2/2019)

Cover Feature: Ca^II, Yb^II and Sm^II Bis(Amido) Complexes Coordinated by NHC Ligands: Efficient Catalysts for Highly Regio‐ and Chemoselective Consecutive Hydrophosphinations with PH₃ (Chem. Eur. J. 2/2019)

CaII , YbII and SmII Bis(Amido) Complexes Coordinated by NHC Ligands: Efficient Catalysts for Highly Regio- and Chemoselective Consecutive Hydrophosphinations with PH3.

The first example of intermolecular hydrophosphination of styrene, 2-vinylpyridine and phenylacetylene with PH3 catalyzed by bis-(amido) complexes [(Me3 Si)2 N]2 M(NHC)2 (M=Ca, Yb, Sm) coordinated by NHC ligands is described. The reactions of styrene with PH3 proceed under mild conditions in quantitative yields to afford only anti-Markovnikov product and allow for the chemoselective synthesis of primary, secondary and tertiary phosphines. Addition of phenylacetylene to PH3 regardless the initial molar substrates ratio results in the exclusive formation of a tertiary tris-(Z-styryl)-phosphine. Crucial effect of the Lewis base coordinated to the metal ion in precatalyst on catalytic activity in styrene hydrophosphination with PH3 was demonstrated. Free NHCs were also found to be able to promote addition of PH3 to styrene, however they provide much lower reaction rates compared to the metal complexes.

Asymmetric Transfer Hydrogenation of Ketones with Well-Defined Manganese(I) PNN and PNNP Complexes

Three new manganese complexes trans-[Mn(P–NH–NH–P)(CO)2][Br], (14) P–NH–NH–P = (S,S)-PPh2CH2CH2NH–CHPhCHPhNHCH2CH2PPh2), fac-[Mn(P′–NH–NH2)(CO)3][Br], (15) P′–NH–NH2 = (S,S)-PPh2(C6H4)NHCHPhCHPhNH2, and syn-mer-Mn(P–NH–NH2)(CO)2Br, (16) P–NH–NH2 = (S,S)-PPh2CH2CH2NHCHPhCHPhNH2 were synthesized and tested for the asymmetric transfer hydrogenation (ATH) of acetophenone in 2-PrOH. The ligands have stereogenic centers derived from the starting diamine, (S,S)-DPEN. Complex 16 was shown by NOE NMR experiments to have Mn–Br syn to the N–H of the secondary amine. Only the precatalyst 16, upon reaction with potassium tert-butoxide (KOtBu) in 2-PrOH, generated an active system at 80 °C for the ATH of acetophenone to 1-phenylethanol in an enantiomeric excess (ee) of 42% and thus was selected for further investigation into the mechanism of transfer hydrogenation. The corresponding amido complex Mn(P–N–NH2)(CO)2 (17), a borohydride complex syn-mer-Mn(P–NH–NH2)(CO)2(BH4) (18), and an ethoxide complex anti-mer-Mn(P–NH–N...

Well-Defined Amidate-Functionalized N-Heterocyclic Carbene -Supported Rare-Earth Metal Complexes as Catalysts for Efficient Hydroboration of Unactivated Imines and Nitriles

Four amidate-functionalized N-heterocyclic carbene (NHC) rare-earth metal amido complexes [(κ2-N,O-κ1-L)2REN(SiMe3)2] (L = 1-(C6H5C═ONCH2CH2)-3-(CH3)3C6H2(N(CH)2NC)) [RE = Er (1), Y (2), Dy (3), Gd (4)] were synthesized by one-pot reactions of 2 equiv of (1-(C6H5C═ONHCH2CH2)-3-(CH3)3C6H2-(N(CH)2NCH))Br (H2LBr) with 5 equiv of KN(SiMe3)3 followed by treatment with 1 equiv of RECl3 in tetrahydrofuran at -40 °C. These complexes were fully characterized, and their catalytic activities toward hydroboration of unactivated imines and nitriles were investigated, and it was found that these complexes displayed excellent activities as well as remarkable functional group compatibility for imine and nitrile substrates such as halo-, alkyl-, hydroxyl-, N, N-dimethylamino-, and nitro- substituents. Among those, the chemoselectivity for this reaction among the common unsaturated functional groups was achieved in the order C═O ≫ C═N > C≡N > CO2Et > C═C in the current catalytic system, which may facilitate their further application in synthetic chemistry.

Benyzl Alcohol Dehydrogenative Coupling Catalyzed by Defined Mn and Re PNP Pincer Complexes – A Computational Mechanistic Study

Density functional theory computations have been carried out to investigate the base free acceptor‐less dehydrogenative coupling of benzyl alcohol to benzyl benzoate catalyzed by defined Mn and Re PNP pincer amido M(CO)2(PNP) and amino HM(CO)2(PNHP) complexes [M = Mn, Re; PNP = N{CH2CH2P(isopropyl)2}2]. Benchmark calculations show that B3PW91 have the best and closest agreement with the experiments than DLPNO‐CCSD(T). Within all proposed elementary steps, the non‐innocent outer‐sphere mechanism incorporating the amido complex and the N–H bond is more kinetically favored than the innocent outer‐sphere mechanism without the amido complex as well as the inner‐sphere mechanism via the de‐coordination of one phosphine ligand to create a vacant site for β‐hydride elimination. The dehydrogenation of hemiacetal to ester represents the rate‐determining step. Both Mn and Re‐based catalysts have close free energy barriers and similar catalytic activity. However, the computed apparent barrier is overestimated on the basis of the experimentally determined TOF for the Mn‐based complexes.