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

The reactivity of the rare earth metal alkyl complexes LRE(CH2SiMe3)(THF)2 (1RE) [RE = Y (1Y), Yb (1Yb), Lu (1Lu); L = 2,5-[(2-pyrrolyl)CPh2]2(N-methylpyrrole)] with various nitriles and isonitriles has been fully developed. Treatment of the yttrium monoalkyl complex (1Y) with 2 equiv of aromatic nitriles afforded the symmetric trisubstituted ß-diketiminato yttrium complexes (2Y(H), 2Y(Me), and 2Y(F)) through successive cyano group insertion into the RE-C bond and 1,3-H shift or the unsymmetric trisubstituted ß-diketiminato yttrium complex (3Y) unexpectedly via a 1,3-SiMe3 shift when 4-(trifluoromethyl)benzonitrile was used in this reaction under the same conditions. By treating 1Y with 2 equiv of tolyl acetonitrile, an activation of the sp3 C-H bond occurred to form the corresponding ß-aryl keteniminato complexes 4Y(p-tol) and 4Y(m-tol). Remarkably, a heteroleptic cleavage of the CO-CN bond took place in the reaction of 1Y with benzoyl nitrile, affording the unsymmetric trinuclear yttrium complex 5Y bridged by three cyanide groups. Dinuclear ytterbium and lutetium complexes 6Yb and 6Lu containing a functionalized isoindole fragment were synthesized from the reactions of 1 with phthalonitrile by tandem insertion and cyclization. Further studies indicated that the temperature and stoichiometric ratio have a great influence on the reactivity patterns between the reactions of 1RE with benzylisonitrile: two tetrasubstituted ß-diketiminato complexes 8 and 9 were obtained at -30 °C, and tetrasubstituted imidazolyl yttrium and lutetium complexes 7 were isolated at elevated temperature, respectively. In addition, the tetrasubstituted ß-diketiminato complexes 8 and 9 could be irreversibly converted to the cyclization products 7 by elevating the reaction temperature not only on the NMR scale but also on the preparative scale. Notably, when the phenyl isonitrile instead of benzyl isonitrile was reacted with 1Yb, a 2,3-functionalized indolyl ytterbium complex 10Yb was isolated.

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

The pincer rare-earth dialkyl complexes [κ3-LRE(CH2SiMe3)2 (RE = Lu(1a), Yb(1b), Er(1c), Y(1d), Dy(1e))] with the indol-2-yl-based NCN pincer ligand were synthesized by the reactions of the proligand HL (L = 1-Me2NCH2CH2-3-(2-iPrC6H5N═CH)C8H4N) with RE(CH2SiMe3)3(THF)2. These complexes exhibited a variety of reactivities toward organic compounds such as amines, triphenylphosphine ylide, N-phenylimidazole, pyridine derivatives, and o-carborane leading to σ-bond metathesis, migration insertion, and redox reaction products. The reactions of the dialkyl rare-earth metal complexes with o-carborane afforded the novel NCN pincer-ligated carboryne-based metallacyclopropanes which reacted with diphenyl ketone to give insertion products of the RE-C2-ind and one of the RE-Ccage bonds, while the reaction of the carboryne-based metallacyclopropanes with diphenyldiazomethane produced the di-aza-metallacyclopentanes via the insertions of the N═N bond of the diphenyldiazomethane into two RE-Ccage bonds and the RE-C2-ind bond. The reactions of the dialkyl complexes with 2 equiv of 2,2'-bipyridine afforded the pincer-ligated bis(2,2'-bipyridyl monoanionic radical) complexes via the homolytic redox reaction.

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-C4H7O)CH2-3-(2-tBuC6H5N═CH)C8H5N (HL1) and 1-Me2NCH2CH2-3-(2-iPrC6H5N═CH)C8H5N (HL2) 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 HL1 with RE(CH2SiMe3)3(THF)2 provided two types of rare-earth metal complexes: the pincer type mononuclear complexes κ3-(L1)RE(CH2SiMe3)2 [L1 = 1-(2-C4H7O)CH2-3-(2-tBuC6H5N═CH)C8H4N, RE = Lu(1), Yb(2)], and the dinuclear rare-earth metal alkyl (per alkyl/per metal) complexes having the ligand in novel coordination modes {(η1:(µ-η2:η1):η1-1-(2-C4H7O)CH2-3-[2-tBuC6H5NCH-(CH2SiMe3)]C8H4N)RECH2SiMe3}2 [RE = Er(3), Y(4), Dy(5), and Gd(6)]. Meanwhile, the reactions of HL2 with RE(CH2SiMe3)3(THF)2 led to the isolation and characterization of only the mononuclear rare-earth metal dialkyl complexes κ3-(L2)RE(CH2SiMe3)2 [L2 = 1-Me2NCH2CH2-3-(2-iPrC6H5N═CH)C8H4N, RE = Lu(7), Gd(8)] bearing the ligand in the pincer chelate form. The mononuclear complexes were formed through the sp2 C-H activation of the 2-indolyl moiety, while the dinuclear complexes were produced unexpectedly through the tandem 2-indolyl sp2 C-H activation and C═N insertion into the RE-CH2SiMe3 bond. These complexes were fully characterized by spectroscopic methods, elemental analyses, and single-crystal X-ray crystallography. The applications of the synthesized complexes as catalysts for the hydrosilylation of terminal alkenes with phenylsilane are described. Anti-Markovnikov addition products were produced by the hydrosilylation of aliphatic olefins, and Markovnikov addition products were isolated with aromatic olefins with high selectivity in the absence of cocatalysts. It is found that the dinuclear rare-earth alkyl complexes exhibited the best catalytic activity with the advantages of mild reaction conditions, short reaction time, low catalyst loading, and wide substrate applicability in comparison with the synthesized mononuclear complexes and the reported catalysts.

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

Novel N,N,N-tridentate ß-diketiminato rare-earth-metal dialkyl complexes LRE(CH2SiMe3)2 [RE = Y (1a), Gd (1b), Yb (1c), Lu (1d); L = MeC(NDipp)CHC(Me)N(CH2)2NC4H8, where Dipp = 2,6-iPr2C6H3] have been conveniently synthesized by one step from reactions of the rare-earth-metal trialkyl complexes RE(CH2SiMe3)3(THF)2 (THF = tetrahydrofuran) with a pyrrolidine-functionalized ß-diketiminate HL, 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 N-alkyl and N-aryl carbamate derivatives under mild reaction conditions with a rather low catalyst loading (0.04 mol %). More significantly, they can promote a tandem hydroalkoxylation/cyclohydroamination reaction between terminal and internal propargylic alcohols with substituted arylisocyanates, leading to the efficient synthesis of methylene and (Z)-selective arylidene oxazolidinones in good-to-high yields via consecutive C-O and C-N bond formation. The stoichiometric reaction of 1a with p-tolylisocyanate generated an unusual dinuclear yttrium complex, {[η2-(4-MePhNCO)(CH2SiMe3)]Y[µ-η2:η1:η1-(4-MePhNCO)CC(Me)(NDipp)C(Me)N(CH2)2NC4H8]}2 (7a), with two different amidate units, which underwent an sp2 C-H bond activation of the ß-diketiminato backbone, followed by the insertion of isocyanate.

Transformation of the sp2 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 in situ transformation of an sp2 carbanion to a Fischer-type electrophilic carbene with rare-earth metals in their high oxidation state with a d0 electron via electron transfer. The carbene may undergo 1,1-migratory insertion into an adjacent RE-C(sp3) 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 o-Me2NC6H4CH2Li. The key to success is the uniquely tailored novel ligand systems featuring a suitable conjugate building block (-C═C-C═N) bearing an sp2 carbanion connected to the rare-earth metal center.

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)3/HSi(NMe2)3, leading to the formation of a variety of alkoxysilylalkyne and aminosilylalkyne derivatives in good to high yields. The precatalysts LRE(CH2SiMe3)(thf)2 (RE = Y(1a), Er(1b), Yb(1c), L = 2,5-[(2-C4H3N)CPh2]2(C4H2NMe), thf = tetrahydrofuran) were easily prepared in high yields via the reactions of RE(CH2SiMe3)3(thf)2 with the proligand H2L in a single step. Mechanistic studies reveal that treatment of 1 with phenylacetylene could generate the active catalytic species: dinuclear rare-earth metal alkynides (L(thf)n[RE(µ-C≡CPh)]2L) (RE = Y(5a), n = 1; Yb(5c), n = 0), which could react with HSi(OEt)3 to produce the coupling product 4aa and the dinuclear rare-earth metal hydrides (L (thf)[RE(µ-H)]2L) (RE = Y(6a); Yb(6c)). By contrast, prior treatment of 1c with HSi(OEt)3 proceeds via cleavage of the Si-O bond to produce the dinuclear ytterbium alkoxide (LYb(µ-OEt))2 7c, which is inert in the dehydrogenative coupling reaction. The results of the mechanistic studies are consistent with the observation that the reaction is greatly influenced by the addition sequence of precatalyst/alkynes/silanes.

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

Reactions of [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 with aminomethylene-substituted pyridine 2-[O(CH2CH2)2NCH2CH2NCH2]C5H4N (1) gave the dianionic α-iminopyridine rare-earth metal amido complexes {µ-η2:σ1:κ1:κ1-2-[O(CH2CH2)2NCH2CH2NCH]C5H4N}2RE2[N(SiMe3)2]2 (RE = Y(2a), La(2b), Pr(2c), Nd(2d), Sm(2e), Dy(2f), Er(2g), and Lu (2h)). However, reaction of [(Me3Si)2N]3Y(µ-Cl)Li(THF)3 with pyridin-2-ylmethyl-substituted amines such as 2-(RNHCH2)C5H4N (R = tBu (3a) and 2,6-iPr2Ph (3b)) or benzyl-substituted amine O(CH2CH2)2NCH2CH2NHCH2C6H5 (5) afforded the corresponding yttrium complexes containing monoanionic ligands [2-(RNCH2)C5H4N]2YN(SiMe3)2 (R = tBu (4a) and 2,6-iPr2Ph (4b)) or [O(CH2CH2)2NCH2CH2NCH2C6H5][(Me3Si)2N)]Y(µ-Cl)(µ-η3-O(CH2CH2)2NCH2CH2NCH2C6H5)Li(THF) (6). 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.

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.

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 [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 with the corresponding 1,2-diimino proligands. Reactions of [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 with 2 equiv of trans-1,2-bis(pyrrol-2-ylmethylene)-1,2-diphenylethanediamine (H2L1) afforded the discrete ion-pair rare-earth metal complexes [Li(THF)4]+[(L1)2RE]- (RE = Sm(5), Dy(6), Er(7)). Reactions of [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 with 2 equiv of ( R, R)-1,2-bis(pyrrol-2-ylmethylene)-1,2-diphenylethanediamine (H2L2) gave the heterobimetallic rare-earth metal complexes (L2)2RELi(THF)2 (RE = Sm(8), Y(9)). When the rare-earth metal is Er, the chiral linear rare-earth coordination polymer {(L2)2ErLi} n (10) was obtained. Reactions of [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 with 2 equiv of trans-1,2-bis(pyrrol-2-ylmethyleneamino)cyclohexane (H2L3) gave the heterobimetallic rare-earth metal complexes (L3)2RELi(THF)2 (RE = Pr (11), Sm(12), Eu(13)). Reactions of [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 with 2 equiv of ( R, R)-1,2-bis(pyrrol-2-ylmethyleneamino)cyclohexane (H2L4) also gave the heterobimetallic rare-earth metal complexes (L4)2RELi(THF)2 (Ln = Pr(14), Sm(15)). All complexes were characterized by spectroscopic methods and elemental analyses, and complexes 5-11, 13, and 14 were further determined by single-crystal X-ray diffraction. The catalytic properties of racemic rare-earth metal complexes on cyanosilylation of ketones were examined, and results showed that the above complexes could effectively catalyze the cyanosilylation of ketones. Chiral rare-earth metal complexes as catalysts for the enantioselective epoxidation of α,ß-unsaturated ketones were also examined to afford the chiral epoxides in high yields with moderate enantioselectivities.

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)C8H5N [R = Bn, R' = Dipp (HL1); R = Bn, R' = tBu (HL2); R = CH3OCH2, R' = Dipp (HL3); Dipp = iPr2C6H3] with Me3SiCH2Li or nBuLi in hydrocarbon solvents (toluene or n-hexane) produced 1,3-disubstituted-2-indolyl lithium complexes [η1:(µ2-η1:η1)-1-Bn-3-(DippN═CH)C8H4NLi]2 (1), {[η1:(µ3-η1:η1:η1)-1-Bn-3-(tBuN═CH)C8H4N][η2:η1:(µ2-η1:η1)-1-Bn-3-(tBuN═CH)C8H4N][η1:(µ2-η1:η1)-1-Bn-3-(tBuN═CH)C8H4N]Li3} (2), and [η1:η1:(µ2-η1:η1)-1-CH3OCH2-3-(DippN═CH)C8H4NLi]2 (3), respectively. The bonding modes of the indolyl ligand were kept in 1 by coordination with donor solvent, affording [η1:(µ2-η1:η1)-1-Bn-3-(DippN═CH)C8H4NLi(THF)]2 (4). The trinuclear complex 2 was converted to dinuclear form with a change of bonding modes of the indolyl ligand by treatment of 2 with donor solvent THF, producing [η1:(µ2-η1:η1)-1-Bn-3-(tBuN═CH)C8H4NLi(THF)]2 (5). X-ray diffraction established that compounds 1, 3, 4, and 5 crystallized as dinuclear structures with the carbanionic sp2 carbon atoms of the indolyl ligands coordinated to lithium ions in a µ2-η1:η1 manner, while compound 2 crystallized as a trinuclear structure and the carbanionic atoms of the indolyl moieties coordinated to lithium ions in µ2-η1:η1 and µ3-η1:η1:η1 manners. When the lithiation reaction of HL1 with 1 equiv of nBuLi was carried out in THF, the monomeric lithium complex {η1:η1-1-Bn-3-(DippN═CH)-2-[1'-Bn-3'-(DippNCH)C8H5N]C8H4NLi(THF)} (6) having coupled indolyl moieties was obtained. The compound 6 can also be prepared by the reaction of 1 with 0.5 equiv of HL1 with a higher isolated yield. Accordingly, the lithium complexes [η1:η4-1-Bn-3-tBuN═CH-2-(1'-Bn-3'-tBuNCHC8H5N)C8H4NLi(L)] (L = THF, 7a; L = Et2O, 7b) with the coupled indolyl moieties in η4 mode were isolated by treatment of HL2 with 2 in THF or Et2O. All complexes were characterized by spectroscopic methods, and their structures were determined by X-ray diffraction study.

Dinuclear rare-earth metal alkyl complexes supported by indolyl ligands in µ-η(2) :η(1) :η(1) hapticities and their high catalytic activity for isoprene 1,4-cis-polymerization.

Two series of new dinuclear rare-earth metal alkyl complexes supported by indolyl ligands in novel µ-η(2) :η(1) :η(1) hapticities are synthesized and characterized. Treatment of [RE(CH2 SiMe3 )3 (thf)2 ] with 1 equivalent of 3-(tBuN=CH)C8 H5 NH (L1 ) in THF gives the dinuclear rare-earth metal alkyl complexes trans-[(µ-η(2) :η(1) :η(1) -3-{tBuNCH(CH2 SiMe3 )}Ind)RE(thf)(CH2 SiMe3 )]2 (Ind=indolyl, RE=Y, Dy, or Yb) in good yields. In the process, the indole unit of L1 is deprotonated by the metal alkyl species and the imino C=N group is transferred to the amido group by alkyl CH2 SiMe3 insertion, affording a new dianionic ligand that bridges two metal alkyl units in µ-η(2) :η(1) :η(1) bonding modes, forming the dinuclear rare-earth metal alkyl complexes. When L1 is reduced to 3-(tBuNHCH2 )C8 H5 NH (L2 ), the reaction of [Yb(CH2 SiMe3 )3 (thf)2 ] with 1 equivalent of L2 in THF, interestingly, generated the trans-[(µ-η(2) :η(1) :η(1) -3-{tBuNCH2 }Ind)Yb(thf)(CH2 SiMe3 )]2 (major) and cis-[(µ-η(2) :η(1) :η(1) -3-{tBuNCH2 }Ind)Yb(thf)(CH2 SiMe3 )]2 (minor) complexes. The catalytic activities of these dinuclear rare-earth metal alkyl complexes for isoprene polymerization were investigated; the yttrium and dysprosium complexes exhibited high catalytic activities and high regio- and stereoselectivities for isoprene 1,4-cis-polymerization.

Copper-Catalyzed Electrophilic Amination of Organoaluminum Nucleophiles with O-Benzoyl Hydroxylamines.

A copper-catalyzed electrophilic amination of aryl and heteroaryl aluminums with N,N-dialkyl-O-benzoyl hydroxylamines that affords the corresponding anilines in good yields has been developed. The catalytic reaction proceeds very smoothly under mild conditions and exhibits good substrate scope. Moreover, the developed catalytic system is also well suited for heteroaryl aluminum nucleophiles, providing facile access to heteroaryl amines.

Synthesis and Characterization of Organo-Rare-Earth Metal Monoalkyl Complexes Supported by Carbon σ-Bonded Indolyl Ligands: High Specific Isoprene 1,4-Cis Polymerization Catalysts.

A series of N-protected 3-imino-functionalized indolyl ligands 1-R-3-(R'N═CH)C8H5N [R = Bn, R' = 2,6-(i)Pr2C6H3 (HL(1)); R = CH3, R' = 2,6-(i)Pr2C6H3 (HL(2)); R = Bn, R' = (t)Bu (HL(3))] and 1-CH3-2-(2,6-(i)Pr2C6H3N═CH)C8H5N (HL(4)) was prepared via reactions of N-protected indolyl aldehydes with corresponding amines. The C-H σ-bond metathesis followed by alkane elimination reactions between RE(CH2SiMe3)3(thf)2 and HL(1)-HL(3) afforded the carbon σ-bonded indolyl-ligated rare-earth metal monoalkyl complexes. Reactions of RE(CH2SiMe3)3(thf)2 with 2 equiv of HL(1) or HL(2) gave the carbon σ-bonded indolyl-ligated rare-earth metal monoalkyl complexes L(1)2RECH2SiMe3 (RE = Y(1), Er(2), Dy(3)) and L(2)2RECH2SiMe3 (RE = Y(5), Er(6), Dy(7), Yb(8)), while reaction of Yb(CH2SiMe3)3(thf)2 with 2 equiv of HL(1) afforded the ytterbium dialkyl complex L(1)Yb(CH2SiMe3)2(thf)2 (4). Reactions of RE(CH2SiMe3)3(thf)2 with HL(3) gave the tris(heteroaryl) rare-earth metal complexes L(3)3RE (RE = Y(9), Er(10)). In the presence of cocatalysts, the rare-earth metal monoalkyl complexes initiated isoprene polymerization with a high activity (90% conversion of 1000 equiv of isoprene in 25 min) producing polymers with high regio- and stereoselectivity (1,4-cis polymers up to 99%).

Synthesis of polysubstituted pyrroles via [3 + 2]-annulation of aziridines and ß-nitroalkenes under aerobic conditions.

Polysubstituted pyrroles were regioselectively synthesized in moderate to good yields via the copper acetate-catalyzed [3 + 2] annulation reaction of readily accessible aziridines and nitroalkenes. This reaction was proposed to proceed through a key azomethine ylide intermediate generated by selective C-C bond cleavage of the aziridine followed by annulation with nitroalkenes under aerobic conditions.

Controlled synthesis of racemic indenyl rare-earth metal complexes via the cooperation between the intramolecular coordination of donor atoms and a bridge.

The reactions of Me2Si(C9H6CH2CH2-DG)2 (DG = NMe2 (1), CH2NMe2 (2), OMe (3), and N(CH2CH2)2O (4)) with [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 in toluene afforded a series of racemic divalent rare-earth metal complexes: {η(5):η(1):η(5):η(1)-Me2Si(C9H5CH2CH2-DG)2}RE (DG = NMe2, RE = Yb (6) and Eu (7); DG = CH2NMe2, RE = Yb (8), Eu (9), and Sm (10); DG = OMe, RE = Yb (11) and Eu (12); DG = N(CH2CH2)2O, RE = Yb (13) and Eu (14)). Similarly, the racemic divalent rare-earth metal complexes {η(5):η(1):η(5):η(1)-Me2Si(C9H5CH2CH2CH2NMe2)(C9H5CH2CH2OMe)}RE (RE = Yb (15) and Eu (16)) were also obtained. The reaction of Me2Si(C9H5CH2CH2OMe)2Li2 with NdCl3 gave a racemic dimeric neodymium chloride {η(5):η(1):η(5)-Me2Si(C9H5CH2CH2OMe)2NdCl}2 (17), whereas the reaction of Me2Si(C9H5CH2CH2NMe2)2Li2 with SmCl3 afforded a racemic dinuclear samarium chloride bridged by lithium chloride {η(5):η(1):η(5):η(1)-Me2Si(C9H5CH2CH2NMe2)2SmCl}2(µ-LiCl) (18). Further reaction of complex 18 with LiCH2SiMe3 provided an unexpected rare-earth metal alkyl complex {η(5):η(1):η(5):η(1):σ-Me2Si(C9H5CH2CH2NMe2)[(C9H5CH2CH2N(CH2)Me]}Sm (19) through the activation of an sp(3) C-H bond α-adjacent to the nitrogen atom. Complexes 19 and {η(5):η(1):η(5):η(1):σ-Me2Si(C9H5CH2CH2NMe2)[(C9H5CH2CH2N(CH2)Me]}Y (20) were also obtained by one-pot reactions of Me2Si(C9H5CH2CH2NMe2)2Li2 with RECl3 followed by treatment with LiCH2SiMe3. All compounds were fully characterized by spectroscopic methods and elemental analysis. Complexes 6-10 and 14-20 were further characterized by single-crystal X-ray diffraction analysis. All of the prepared rare-earth metal complexes were racemic, suggesting that racemic organo rare-earth metal complexes could be controllably synthesized by the cooperation between a bridge and the intramolecular coordination of donor atoms.

Synthesis, structure, and reactivity of lanthanide complexes incorporating indolyl ligands in novel hapticities.

The chemistry of interactions of 2-(2,6-diisopropylphenylaminomethylene)indole ligand (1) with europium and ytterbium amides is described. Reaction of 2-(2,6-diisopropylphenylaminomethylene)indole 2-(2,6-i-Pr2C6H3NHCH2)C8H5NH (1) with europium amide [(Me3Si)2N]3Eu(III)(µ-Cl)Li(THF)3 afforded a novel europium(II) complex formulated as {[µ-η(6):η(1):η(1)-2-(2,6-i-Pr2C6H3N═CH)C8H5N]Eu[2-(2,6-i-Pr2C6H3N═CH)C8H5N]}2 (2), having a bridged indolyl ligand in the novel µ-η(6):η(1):η(1) hapticities with the reduction of europium(III) to europium(II) and the oxidation of amino to imino group. Reaction of 2-(2,6-diisopropylphenylaminomethylene)indole 2-(2,6-i-Pr2C6H3NHCH2)C8H5NH (1) with ytterbium(III) amide [(Me3Si)2N]3Yb(III)(µ-Cl)Li(THF)3 produced the only deprotonated ytterbium(III) complex formulated as [2-(2,6-i-Pr2C6H3NCH2)C8H5N]Yb[N(SiMe3)2](THF)2 (3), having an η(1) hapticity indolyl ligand. Reaction of 2 with formamidine [(2,6-Me2C6H3)NCHNH(C6H3Me2-2,6)] produced {[µ-η(3):η(1):η(1)-2-(2,6-i-Pr2C6H3N═CH)C8H5N]Eu[(2,6-Me2C6H3)NCHN(C6H3Me2-2,6)](THF)}2 (4), which has a bridged indolyl ligand in the novel µ-η(3):η(1):η(1) hapticities, whereas the reaction of 2 with the more sterically bulky formamidine [(2,6-i-Pr2C6H3)NCHNH(C6H3i-Pr2-2,6)] afforded complex {[µ-η(2):η(1):η(1)-2-(2,6-i-Pr2C6H3N═CH)C8H5N]Eu[(2,6-i-Pr2C6H3)N═CHN(C6H3i-Pr2-2,6)](THF)}2 (5), having the indolyl ligand in the novel µ-η(2):η(1):η(1) hapticities. The results represent the first example of organometallic complexes having indolyl ligands in the novel µ-η(6):η(1):η(1), µ-η(3):η(1):η(1), and µ-η(2):η(1):η(1) bonding modes with metal.

Synthesis and catalytic activity of tetradentate ß-diketiminato rare-earth metal monoalkyl complexes in tandem Oppenauer oxidation and cross-aldol condensation.

A series of unsymmetric tetradentate ß-diketiminato rare-earth metal monoalkyl complexes were synthesized, and their catalytic behavior has been well developed. Indole-incorporated ß-diketiminato proligands H2L (L = MeC(NDipp)CHC(Me)NCH2CH2-3-(1-R-C8H4N), R = CH2-(2-C4H7O), L1; R = (CH2)2OMe, L2; Dipp = 2,6-iPr2C6H3) were prepared by the reaction of an arylamino-enone with 1-substituted-tryptamine in good yields. Treatment of the proligands with the rare-earth metal trialkyl complexes RE(CH2SiMe3)3(THF)2 generated the corresponding unsymmetric N,N,C,O-tetradentate ß-diketiminato rare-earth metal monoalkyl complexes LRE(CH2SiMe3) (L1, RE = Y (1a), Gd (1b), Yb (1c), Lu (1d); L2, RE = Y (2a), Gd (2b), Yb (2c), and Lu(2d)). During the process, the activation of the sp2 C-H bond at the 2-position of the indole ring led to the formation of an unprecedented ß-diketiminato dianion L2-, bonding to the rare-earth metal ions in a chelating N,N,C,O-tetradentate manner. Further studies indicated that these tetradentate rare-earth metal complexes could initiate the Oppenauer oxidation of secondary alcohols into the corresponding ketones in high yields. In the case of primary alcohols, a tandem Oppenauer oxidation and cross-aldol condensation occurred unexpectedly. Various α-mono-substituted benzylidene acetones, α,α'-bis-substituted benzylidene acetones and cyclohexanones were obtained under mild conditions only by controlling the molar ratio of alcohols to ketones. Notably, all these alkenylation ketones exhibited exclusive E configuration.

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

The first examples of regioselective aryl ortho-C-H functionalization with diphenyldiazomethane for the construction of Caryl-Nhydrazinato bonds were accomplished via the activation of C-H bonds and the subsequent reaction of diphenyldiazomethane with the RE-Caryl bond. The reactions of rare-earth metal monoalkyl complexes LRE(CH2SiMe3)(THF)2 (L = 2,5-[(2-pyrrolyl)CPh2]2(N-Me-pyrrole)) supported by a neutral N-methylpyrrole anchored dipyrrolyl ligand with 2 equiv. of Ph2CN2 gave irreversibly unprecedented hydrazonato-functionalized imino rare-earth metal complexes LRE(Ph2CNNC6H4-(o-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-Calkyl bond, a ß-H elimination, a N-N cleavage, 1,4-hydrogen transfer and the subsequent C-N coupling with another diphenyldiazomethane. More important is that regioselective aryl C-H bond functionalization with diphenyldiazomethane to construct the Caryl-Nhydrazinato bonds can be easily achieved by three-component reactions of rare-earth metal monoalkyl complexes, a wide range of substituted imines (including aldimines, ketimines or analogous 2-phenylpyridine) and diphenyldiazomethane, affording various hydrazonato-functionalized phenyl, thienyl imino or pyridyl rare-earth metal complexes 2b-2j at room temperature. A further study indicated that the substituents on the phenyl ring have a great effect on the reaction pathway and governed the Caryl-Nhydrazinato bond construction. Moreover, the experimental studies show that the formation of the Caryl-Nhydrazinato bonds is thermodynamically facile, which could be realized at room temperature easily.

Highly efficient hydrophosphonylation of aldehydes and unactivated ketones catalyzed by methylene-linked pyrrolyl rare earth metal amido complexes.

A series of rare earth metal amido complexes bearing methylene-linked pyrrolyl-amido ligands were prepared through silylamine elimination reactions and displayed high catalytic activities in hydrophosphonylations of aldehydes and unactivated ketones under solvent-free conditions for liquid substrates. Treatment of [(Me(3)Si)(2)N](3)Ln(µ-Cl)Li(THF)(3) with 2-(2,6-Me(2)C(6)H(3)NHCH(2))C(4)H(3)NH (1, 1 equiv) in toluene afforded the corresponding trivalent rare earth metal amides of formula {(µ-η(5):η(1)):η(1)-2-[(2,6-Me(2)C(6)H(3))NCH(2)](C(4)H(3)N)LnN(SiMe(3))(2)}(2) [Ln=Y (2), Nd (3), Sm (4), Dy (5), Yb (6)] in moderate to good yields. All compounds were fully characterized by spectroscopic methods and elemental analyses. The yttrium complex was also characterized by (1)H NMR spectroscopic analyses. The structures of complexes 2, 3, 4, and 6 were determined by single-crystal X-ray analyses. Study of the catalytic activities of the complexes showed that these rare earth metal amido complexes were excellent catalysts for hydrophosphonylations of aldehydes and unactivated ketones. The catalyzed reactions between diethyl phosphite and aldehydes in the presence of the rare earth metal amido complexes (0.1 mol%) afforded the products in high yields (up to 99%) at room temperature in short times of 5 to 10 min. Furthermore, the catalytic addition of diethyl phosphite to unactivated ketones also afforded the products in high yields of up to 99% with employment of low loadings (0.1 to 0.5 mol%) of the rare earth metal amido complexes at room temperature in short times of 20 min. The system works well for a wide range of unactivated aliphatic, aromatic or heteroaromatic ketones, especially for substituted benzophenones, giving the corresponding α-hydroxy diaryl phosphonates in moderate to high yields.

Lanthanide amido complexes incorporating amino-coordinate-lithium bridged bis(indolyl) ligands: synthesis, characterization, and catalysis for hydrophosphonylation of aldehydes and aldimines.

Two series of new lanthanide amido complexes supported by bis(indolyl) ligands with amino-coordinate-lithium as a bridge were synthesized and characterized. The interactions of [(Me(3)Si)(2)N](3)Ln(III)(µ-Cl)Li(THF)(3) with 2 equiv of 3-(CyNHCH(2))C(8)H(5)NH in toluene produced the amino-coordinate-lithium bridged bis(indolyl) lanthanide amides [µ-{[η(1):η(1):η(1):η(1)-3-(CyNHCH(2))Ind](2)Li}Ln[N(SiMe(3))(2)](2)] (Cy = cyclohexyl, Ind = Indolyl, Ln = Sm (1), Eu (2), Dy (3), Yb (4)) in good yields. Treatment of [µ-{[η(1):η(1):η(1):η(1)-3-(CyNHCH(2))Ind](2)Li}Ln[N(SiMe(3))(2)](2)] with THF gave new lanthanide amido complexes [µ-{[η(1):η(1)-3-(CyNHCH(2))Ind](2)Li(THF)}Ln[N(SiMe(3))(2)](2)] (Ln = Eu (5), Dy (6), Yb (7)), which can be transferred to amido complexes 2, 3, and 4 by reflux the corresponding complexes in toluene. Thus, two series of rare-earth-metal amides could be reciprocally transformed easily by merely changing the solvent in the reactions. All new complexes 1-7 are fully characterized including X-ray structural determination. The catalytic activities of these new lanthanide amido complexes for hydrophosphonylation of both aromatic and aliphatic aldehydes and various substituted aldimines were explored. The results indicated that these complexes displayed a high catalytic activity for the C-P bond formation with employment of low catalyst loadings (0.1 mol % for aldehydes and 1 mol % for aldimines) under mild conditions. Thus, it provides a convenient way to prepare both α-hydroxy and α-amino phosphonates.