Synthesis and Reactivity of the Rare-Earth Metal Complexes Bearing the Indol-2-yl-Based NCN Pincer Ligand.

The pincer rare-earth dialkyl complexes [-RE(CHSiMe) (RE = Lu(), Yb(), Er(), Y(), Dy())] with the indol-2-yl-based NCN pincer ligand were synthesized by the reactions of the proligand ( = 1-MeNCHCH-3-(2-PrCHN═CH)CHN) with RE(CHSiMe)(THF). These complexes exhibited a variety of reactivities toward organic compounds such as amines, triphenylphosphine ylide, -phenylimidazole, pyridine derivatives, and -carborane leading to -bond metathesis, migration insertion, and redox reaction products. The reactions of the dialkyl rare-earth metal complexes with -carborane afforded the novel NCN pincer-ligated carboryne-based metallacyclopropanes which reacted with diphenyl ketone to give insertion products of the RE-C and one of the RE-C bonds, while the reaction of the carboryne-based metallacyclopropanes with diphenyldiazomethane produced the di--metallacyclopentanes via the insertions of the N═N bond of the diphenyldiazomethane into two RE-C bonds and the RE-C bond.

Reactivity of Rare Earth Metal Alkyl Complexes with Nitriles or Isonitrile: Versatile Ways toward Multiply Functionalized β-Diketiminato, (Iso)indolyl, and Imidazolyl Chelating Rare Earth Metal Complexes.

The reactivity of the rare earth metal alkyl complexes RE(CHSiMe)(THF) () [RE = Y (), Yb (), Lu (); = 2,5-[(2-pyrrolyl)CPh](-methylpyrrole)] with various nitriles and isonitriles has been fully developed. Treatment of the yttrium monoalkyl complex () with 2 equiv of aromatic nitriles afforded the symmetric trisubstituted β-diketiminato yttrium complexes (, , and through successive cyano group insertion into the RE-C bond and 1,3-H shift or the unsymmetric trisubstituted β-diketiminato yttrium complex () unexpectedly via a 1,3-SiMe shift when 4-(trifluoromethyl)benzonitrile was used in this reaction under the same conditions. By treating with 2 equiv of tolyl acetonitrile, an activation of the C-H bond occurred to form the corresponding β-aryl keteniminato complexes and .

Aryl C-H bond functionalization with diphenyldiazomethane induced by rare-earth metal alkyl complexes.

The first examples of regioselective aryl -C-H functionalization with diphenyldiazomethane for the construction of C-N bonds were accomplished the activation of C-H bonds and the subsequent reaction of diphenyldiazomethane with the RE-C bond. The reactions of rare-earth metal monoalkyl complexes LRE(CHSiMe)(THF) (L = 2,5-[(2-pyrrolyl)CPh](-Me-pyrrole)) supported by a neutral -methylpyrrole anchored dipyrrolyl ligand with 2 equiv. of PhCN gave irreversibly unprecedented hydrazonato-functionalized imino rare-earth metal complexes LRE(PhCNNCH-(-CNHPh) (RE = Y (2a), Lu (2a')) in good yields involving a rather complex process including the interaction of a diazo unit with a RE-C bond, a β-H elimination, a N-N cleavage, 1,4-hydrogen transfer and the subsequent C-N coupling with another diphenyldiazomethane.

Rare-Earth Metal Complexes Supported by 1,3-Functionalized Indolyl-Based Ligands for Efficient Hydrosilylation of Alkenes.

Two different 1,3-functionalized indolyl-based proligands 1-(2-CHO)CH-3-(2-BuCHN═CH)CHN () and 1-MeNCHCH-3-(2-PrCHN═CH)CHN () were designed, prepared in high yields, and successfully applied to rare-earth metal chemistry showing different reactivities and different bondings with the central metals. The reactions of with RE(CHSiMe)(THF) provided two types of rare-earth metal complexes: the pincer type mononuclear complexes κ-()RE(CHSiMe) [ = 1-(2-CHO)CH-3-(2-BuCHN═CH)CHN, RE = Lu(), Yb()], and the dinuclear rare-earth metal alkyl (per alkyl/per metal) complexes having the ligand in novel coordination modes {(η:(μ-η:η):η-1-(2-CHO)CH-3-[2-BuCHNCH-(CHSiMe)]CHN)RECHSiMe} [RE = Er(), Y(), Dy(), and Gd()]. Meanwhile, the reactions of with RE(CHSiMe)(THF) led to the isolation and characterization of only the mononuclear rare-earth metal dialkyl complexes κ-()RE(CHSiMe) [ = 1-MeNCHCH-3-(2-PrCHN═CH)CHN, RE = Lu(), Gd()] bearing the ligand in the pincer chelate form.

Indolyl-based Copper(I) Complex-Catalyzed Intermolecular Trifluoromethylazolation of Alkenes via Radical Process.

Herein, we synthesized and characterized a binuclear copper(I) complex supported by the indolyl-based ligand. Employing this complex as catalyst, we have developed a three-component intermolecular trifluoromethylazolation of alkenes to deliver various trifluoromethylated azole derivatives. The method features exclusive chemo- and regioselectivity, a broad scope of alkenes and oxazoles, thiazoles, and good tolerance of functional groups under mild conditions.

Halide-bridged tetranuclear organocopper(I) clusters supported by indolyl-based pincer ligands and their catalytic activities towards the hydrophosphination of alkenes.

Novel tetranuclear organocopper(I) clusters bridged by two halides and two indolyl-based pincer ligands were synthesized through the reactions of Cu(I) halides with lithiated ligands. Single-crystal X-ray diffraction revealed that the structure of these complexes included a [CuX] cluster unit wherein the four copper ions were stabilized by multiple Cu-Cu interactions, arranged in a distorted tetrahedral fashion and the halide anions μ-bridged with metal centers. Meanwhile, these clusters displayed excellent catalytic activities towards the hydrophosphination of alkenes under solvent-free conditions with wide functional group tolerance.

Synthesis of rare-earth metal complexes with a morpholine-functionalized β-diketiminato ligand and their catalytic activities towards C-O and C-N bond formation.

Unusual tridentate β-diketiminato rare-earth metal chlorides LRECl(μ-Cl)Li(THF) (RE = Y (1a), Yb (1b), and Lu (1c); L = MeC(NDipp)CHC(Me)N(CH)NCHO; Dipp = 2,6-PrCH) and the corresponding dialkyl complexes LRE(CHSiMe) (RE = Y (2a), Yb (2b), and Lu (2c)) were prepared by reaction of a morpholine-functionalized β-diketiminato proligand HL with anhydrous RECl and rare-earth metal trialkyl complexes RE(CHSiMe)(THF), respectively. In 1 and 2, the morpholine moiety displayed a stable chair conformation and the resulting ligand coordinated to the rare-earth metal ion in a [NNN]-tridentate chelating fashion. Further studies demonstrated that these dialkyl complexes showed high activity towards the catalytic formation of C-O and C-N bonds in the alcoholysis of isothiocyanates and aminolysis of epoxides.

Phosphinoamido ligand supported heterobimetallic rare-earth metal-palladium complexes: versatile structures and redox reactivities.

Heterobimetallic Ln(III)-Pd(0) complexes (Ln = Y, Sm, Gd, Yb) featuring tetranuclear structures with COD as bridges were obtained the metallation of tris(phosphinoamido) rare-earth metal complexes [PhPNAd]Ln (Ad = adamantyl) with (COD)Pd(CHSiMe). Notably, the Sc(III)-Pd(0) complex possesses a -symmetry with a very short Sc-Pd bond length of 2.432(2) Å, while the tetranuclear complexes exhibited versatile structures both in solution and in the solid state.

Rare-Earth-Metal-Complex-Catalyzed Hydroalkoxylation and Tandem Hydroalkoxylation/Cyclohydroamination of Isocyanates: Synthesis of Carbamates and Oxazolidinones.

Novel N,N,N-tridentate β-diketiminato rare-earth-metal dialkyl complexes RE(CHSiMe) [RE = Y (), Gd (), Yb (), Lu (); = MeC(NDipp)CHC(Me)N(CH)NCH, where Dipp = 2,6-PrCH] have been conveniently synthesized by one step from reactions of the rare-earth-metal trialkyl complexes RE(CHSiMe)(THF) (THF = tetrahydrofuran) with a pyrrolidine-functionalized β-diketiminate H, and their catalytic behaviors toward hydroalkoxylation and tandem hydroalkoxylation/cyclohydroamination of isocyanates have been described. These rare-earth-metal catalysts exhibited high efficiency in the hydroalkoxylation of isocyanates, providing a variety of -alkyl and -aryl carbamate derivatives under mild reaction conditions with a rather low catalyst loading (0.04 mol %).

Synthesis and characterization of rare-earth metallate amido complexes bearing the 2-amidate-functionalized indolyl ligand and their application in the hydroboration of esters with pinacolborane.

The reactions of 2-amidate-functionalized indolyl proligand 2-(2,6-PrCHNHCO)CHNH (HL) with [(MeSi)N]RE(μ-Cl)Li(THF) were studied leading to the synthesis and characterization of a series of novel discrete trinuclear rare-earth metallate amido complexes containing the anion [{η:(μ-η:η):η-LREN(SiMe)}(μ-Cl)] and cation Li(THF) (RE = Y(1a), Nd (1b), Sm (1c), Gd (1d), Dy (1e), Er (1f), and Yb (1g)) in good yields by silylamine elimination. All of the complexes were characterized by spectroscopic methods, elemental analyses and single-crystal X-ray diffraction, and complexes 1a and 1c were additionally characterized by NMR spectroscopy. As proof of principle of their activity, these complexes were used as precatalysts for the hydroboration of esters using HBpin as the hydride source displaying high activity under neat and room temperature conditions.

Transformation of the sp Carbanion to Carbene with Subsequent 1,1-Migratory Insertion and Nucleophilic Substitution in Rare-Earth Metal Chemistry.

The development of Fischer-type electrophilic carbene chemistry with early transition metals has been a great challenge due to the fact that such metals in their high oxidation states lack the d electrons to stabilize the electrophilic carbene. Herein, we disclose the first experimental and theoretical findings of transformation of an sp carbanion to a Fischer-type electrophilic carbene with rare-earth metals in their high oxidation state with a d electron via electron transfer. The carbene may undergo 1,1-migratory insertion into an adjacent RE-C(sp) bond, and an unprecedented ring opening of the indole ring of the ligand occurs when the carbenes undergo nucleophilic substitution with a special organolithium reagent -MeNCHCHLi.

Three-Coordinate Pd(0) with Rare-Earth Metalloligands: Synergetic CO Activation and Double P-C Bond Cleavage-Formation Reactions.

Metalation of β-diketiminato rare-earth metal complexes LLn(PhNCHPPh) (Ln = Y, Yb, Lu) with (COD)Pd(CHSiMe) afforded three-coordinate Pd(0) complexes supported by two sterically less bulky phosphines and a Pd → Ln dative interaction. The Pd(0) center is prone to ligation with isonitrile and CO; in the latter case, the insertion of a second CO with the Y-N bond was assisted via a precoordination of CO on the Pd(0) center, which led to the formation of an anionic Pd(0) carbamoyl. The reaction of the Pd-Y complex with iodobenzene showed a remarkable double P-C bond cleavage-formation pathway within the heterobimetallic Pd-Y core to afford (PhP)PdI(Ph), imine PhNCH, and a β-diketiminato yttrium diiodide.

Dehydrogenative Coupling of Terminal Alkynes with O/N-Based Monohydrosilanes Catalyzed by Rare-Earth Metal Complexes.

Newly synthesized rare-earth metal alkyl complexes bearing a tripyrrolyl ligand act as excellent precatalysts for the cross-dehydrogenative coupling between various terminal alkynes and O/N-based monohydrosilanes of HSi(OEt)/HSi(NMe), leading to the formation of a variety of alkoxysilylalkyne and aminosilylalkyne derivatives in good to high yields. The precatalysts RE(CHSiMe)(thf) (RE = Y(), Er(), Yb(), = 2,5-[(2-CHN)CPh](CHNMe), thf = tetrahydrofuran) were easily prepared in high yields via the reactions of RE(CHSiMe)(thf) with the proligand H in a single step. Mechanistic studies reveal that treatment of with phenylacetylene could generate the active catalytic species: dinuclear rare-earth metal alkynides ((thf)[RE(μ-C≡CPh)]) (RE = Y(), = 1; Yb(), = 0), which could react with HSi(OEt) to produce the coupling product and the dinuclear rare-earth metal hydrides ( (thf)[RE(μ-H)]) (RE = Y(); Yb()).

Heterobimetallic Pd(0) complexes with Pd→Ln (Ln = Sc, Y, Yb, Lu) dative bonds: rare-earth metal-dominated frustrated Lewis pair-like reactivity.

A series of heterobimetallic Pd-Ln complexes with Pd→Ln (Ln = Sc, Y, Yb, Lu) dative bonds were synthesized via sequential reactions of phosphinoamine Ph2PNHAd with (Me3SiCH2)3Ln(THF)2 and (Ph3P)4Pd or (COD)Pd(CH2SiMe3)2. These complexes were characterized by NMR spectroscopy, X-ray diffractions, and computational as well as electrochemical studies, which revealed Pd→Ln dative interactions that vary according to the ionic radii of Ln3+. Furthermore, the notable dynamic structural features of the Pd-Ln complexes in solution and their unexpected frustrated Lewis pair-like reactivity toward aryl halides and ketene were also studied.

Syntheses of Dianionic α-Iminopyridine Rare-Earth Metal Complexes and Their Catalytic Acitivities toward Dehydrogenative Coupling of Amines with Hydrosilanes.

Reactions of [(MeSi)N]RE(μ-Cl)Li(THF) with aminomethylene-substituted pyridine 2-[O(CHCH)NCHCHNCH]CHN () gave the dianionic α-iminopyridine rare-earth metal amido complexes {μ-η:σ:κ:κ-2-[O(CHCH)NCHCHNCH]CHN}RE[N(SiMe)] (RE = Y(), La(), Pr(), Nd(), Sm(), Dy(), Er(), and Lu ()). However, reaction of [(MeSi)N]Y(μ-Cl)Li(THF) with pyridin-2-ylmethyl-substituted amines such as 2-(RNHCH)CHN (R = Bu () and 2,6-PrPh ()) or benzyl-substituted amine O(CHCH)NCHCHNHCHCH () afforded the corresponding yttrium complexes containing monoanionic ligands [2-(RNCH)CHN]YN(SiMe) (R = Bu () and 2,6-PrPh ()) or [O(CHCH)NCHCHNCHCH][(MeSi)N)]Y(μ-Cl)(μ-η-O(CHCH)NCHCHNCHCH)Li(THF) (). Dianionic α-iminopyridine rare-earth metal amido complexes showed high catalytic activities for the dehydrogenation coupling reaction of hydrosilanes and amines providing a variety of silylamines in high yields.

Heterobimetallic scandium-group 10 metal complexes with LM → Sc (LM = Ni, Pd, Pt) dative bonds.

Heterobimetallic scandium complexes with whole group 10 metals were synthesized. All Sc-LM complexes were characterized by NMR spectroscopy, X-ray diffraction analysis and computational studies, which revealed notable LM → Sc (LM = Ni, Pd, Pt) dative bonding interactions in these heterobimetallic systems. Versatile coordination modes toward apical donors were observed in these heterobimetallic Sc-LM complexes, among which the Sc-Ni complexes 2 and 3 were reversibly bound to N and the Sc-Pt complex 5 was coordinated to an additional PPh ligand, while in the Sc-Pd complex 4 no apical donor was ligated.

Aluminum complexes with Schiff base bridged bis(indolyl) ligands: synthesis, structure, and catalytic activity for polymerization of rac-lactide.

A series of Schiff base bridged bis(indolyl) ligands were developed for aluminum chemistry. The reactions of AlEt3 or AlMe3 with the Schiff base bridged bis(indolyl) proligands R1(-N[double bond, length as m-dash]CHC8H5NH)2 (R1 = -CH2CH2- (H2L1); -CH2CH2CH2- (H2L2); -CH2CMe2CH2- (H2L3); rac-Cy (H2L4); and R,R-Cy (H2L5)) were studied leading to the synthesis of a series of aluminum alkyl complexes L1AlEt (1)-L5AlEt (5) and L3AlMe (3b) in good yields, while the reaction of H2L3 with Al(OiPr)3 gave the aluminum alkoxide complex L3AlOiPr (3a). These aluminum complexes were characterized by spectroscopic methods and elemental analyses.

Copper Salts/TBAB-Catalyzed Chemo- and Regioselective β-C(sp)-H Acyloxylation of Aliphatic Amides.

An efficient Cu(II)-catalyzed and tetrabutylammonium bromide (TBAB)-promoted strategy for highly regioselective and chemoselective C(sp)-H acyloxylation of aliphatic amides is described. Acyloxylation occurs selectively at the β position with a broad substrate scope of carboxylic acids and aliphatic amides and good functional group compatibility. Notably, the competing reaction of intramolecular dehydrogenative amidation and intermolecular acyloxylation could be efficiently controlled by the amount of copper salt and the addition of TBAB.

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-η:η 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-(BuNHCH)CHNH (1) with rare-earth metal amides [(MeSi)N]RE(μ-Cl)Li(THF) afforded the complexes [2-(BuN[double bond, length as m-dash]CH)CHN]RE[N(SiMe)] (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.

A Scandium Metalloligand-Based Heterobimetallic Pd-Sc Complex: Electronic Tuning Through a Very Short Pd→Sc Dative Bond.

The first heterobimetallic Pd-Sc complex featuring a very short Pd→Sc dative bond has been synthesized and characterized by multinuclear NMR spectroscopy, X-ray diffraction analysis, and electrochemistry. Computational studies elucidated the nature of the Pd→Sc bond as a donor-acceptor interaction, which generates a more electron-deficient Pd metal center as compared to that in the mono Pd complex in their reactions with isonitrile and carbon monoxide. Cooperative reactivity has been demonstrated in the reaction with MeI.

Synthesis, characterization, and reactivity of dinuclear organo-rare-earth-metal alkyl complexes supported by 2-amidate-functionalized indolyl ligands: substituent effects on coordination and reactivity.

Two series of new dinuclear organo-rare-earth-metal alkyl complexes supported by 2-amidate-functionalized indolyl ligands with different haptic modes were synthesized and characterized. The treatment of [RE(CH2SiMe3)3(THF)2] with 1 equiv. of 2-(2,6-iPr2C6H3NHC[double bond, length as m-dash]O)C8H5NH (H2L1) and 2-(2-tBuC6H4NHC[double bond, length as m-dash]O)C8H5NH (H2L2) in toluene yielded the dinuclear organo-rare-earth-metal alkyl complexes {[η1:(μ2-η1:η1)-L1]RE(CH2SiMe3)(THF)2}2 [RE = Gd (1a), Dy (1b), Y (1c), Er (1d), and Yb (1e)] and {[η1:(μ2-η1:η1):η1-L2]RE(CH2SiMe3)(THF)2}2 [RE = Gd (2a), Dy (2b), Y (2c), Er (2d), and Yb (2e)] in good yields.

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 [(κ-N,O-κ-L)REN(SiMe)] (L = 1-(CHC═ONCHCH)-3-(CH)CH(N(CH)NC)) [RE = Er (1), Y (2), Dy (3), Gd (4)] were synthesized by one-pot reactions of 2 equiv of (1-(CHC═ONHCHCH)-3-(CH)CH-(N(CH)NCH))Br (HLBr) with 5 equiv of KN(SiMe) followed by treatment with 1 equiv of RECl 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 > COEt > C═C in the current catalytic system, which may facilitate their further application in synthetic chemistry.

Syntheses, Structures, and Catalytic Activities of the Anionic Heterobimetallic Rare-Earth Metal Complexes Supported by Pyrrolyl-Substituted 1,2-Diimino Ligands.

A series of the anionic heterobimetallic rare-earth metal complexes supported by trans- or chiral pyrrolyl-substituted 1,2-diimino ligands were synthesized in good yields via reactions of [(MeSi)N]RE(μ-Cl)Li(THF) with the corresponding 1,2-diimino proligands. Reactions of [(MeSi)N]RE(μ-Cl)Li(THF) with 2 equiv of trans-1,2-bis(pyrrol-2-ylmethylene)-1,2-diphenylethanediamine (HL) afforded the discrete ion-pair rare-earth metal complexes [Li(THF)][(L)RE] (RE = Sm(5), Dy(6), Er(7)). Reactions of [(MeSi)N]RE(μ-Cl)Li(THF) with 2 equiv of ( R, R)-1,2-bis(pyrrol-2-ylmethylene)-1,2-diphenylethanediamine (HL) gave the heterobimetallic rare-earth metal complexes (L)RELi(THF) (RE = Sm(8), Y(9)).

Versatile reactivities of rare-earth metal dialkyl complexes supported by a neutral pyrrolyl-functionalized β-diketiminato ligand.

Herein, rare-earth metal dialkyl complexes supported by a neutral pyrrolyl-functionalized β-diketiminato ligand with the formula LRE(CHSiMe)(thf) (RE = Y (1a), Dy (1b), Er (1c), Yb (1d); L = MeC(NDipp)CHC(Me)NCHCHNCH-2,5-Me, Dipp = 2,6-PrCH) were synthesized via the reactions of the β-diketimine HL with the rare-earth metal trialkyl complexes RE(CHSiMe)(thf) in high yields. The reactivities of 1 with pyridine derivatives, unsaturated substrates, and elemental sulfur were investigated, and some interesting chemical transformations were observed. Ligand exchange and activation of sp and sp C-H bonds occurred during the reactions with pyridine derivatives to afford different types of mononuclear rare-earth metal pyridyl complexes, namely, LEr(CHSiMe)(η-NCH) (2c), LRE(η-CH-2-NCH-4,6-Me) (RE = Y (3a), Er (3c)), and LRE(CHSiMe)(η-(C,N)-2-(2-CHNCH)) (RE = Er (4c), Yb = (4d)).

Reactivity of 1,3-Disubstituted Indoles with Lithium Compounds: Substituents and Solvents Effects on Coordination and Reactivity of Resulting 1,3-Disubstituted-2-Indolyl Lithium Complexes.

Reactivity of 1,3-disubstituted indolyl compounds with lithium reagents was studied to reveal the substituents and solvent effects on coordination modes and reactivities resulting in different indolyl lithium complexes. Treatment of 1-alkyl-3-imino functionalized compounds 1-R-3-(R'N═CH)CHN [R = Bn, R' = Dipp (HL); R = Bn, R' = Bu (HL); R = CHOCH, R' = Dipp (HL); Dipp = PrCH] with MeSiCHLi or BuLi in hydrocarbon solvents (toluene or n-hexane) produced 1,3-disubstituted-2-indolyl lithium complexes [η:(μ-η:η)-1-Bn-3-(DippN═CH)CHNLi] (1), {[η:(μ-η:η:η)-1-Bn-3-(BuN═CH)CHN][η:η:(μ-η:η)-1-Bn-3-(BuN═CH)CHN][η:(μ-η:η)-1-Bn-3-(BuN═CH)CHN]Li} (2), and [η:η:(μ-η:η)-1-CHOCH-3-(DippN═CH)CHNLi] (3), respectively. The bonding modes of the indolyl ligand were kept in 1 by coordination with donor solvent, affording [η:(μ-η:η)-1-Bn-3-(DippN═CH)CHNLi(THF)] (4).