A series of N-protected 3-imino-functionalized indolyl ligands 1-R-3-(R′N═CH)C8H5N [R = Bn, R′ = 2,6-iPr2C6H3 (HL1); R = CH3, R′ = 2,6-iPr2C6H3 (HL2); R = Bn, R′ = tBu (HL3)] and 1-CH3-2-(2,6-iPr2C6H3N═CH)C8H5N (HL4) 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 HL1–HL3 afforded the carbon σ-bonded indolyl-ligated rare-earth metal monoalkyl complexes. Reactions of RE(CH2SiMe3)3(thf)2 with 2 equiv of HL1 or HL2 gave the carbon σ-bonded indolyl-ligated rare-earth metal monoalkyl complexes L12RECH2SiMe3 (RE = Y(1), Er(2), Dy(3)) and L22RECH2SiMe3 (RE = Y(5), Er(6), Dy(7), Yb(8)), while reaction of Yb(CH2SiMe3)3(thf)2 with 2 equiv of HL1 afforded the ytterbium dialkyl complex L1Yb(CH2SiMe3)2(thf)2 (4). Reactions of RE(CH2SiMe3)3(thf)2 with HL3 gave the tris(heteroaryl) rare-earth metal complexes L33RE (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%).

Reactions of rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with different equiv. of 2-(2,6-diisopropylphenylimino)-8-hydroxyquinoline (1) afforded different heterometallic rare-earth metal complexes, and catalytic activity of the resulting complexes was investigated. Reactions of rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (RE = Y, Er, Dy) with 1 equiv. of compound 1 afforded the heterobimetallic rare-earth metal and lithium complexes 2–4 bridged by the oxygen atom of 2-(2,6-diisopropylphenylimino)-8-hydroxyquinoline and the nitrogen atom of N(SiMe3)2. However, the treatment of rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (RE = Sm, Er, Yb) with 2 equiv. of compound 1 gave different heterobimetallic rare-earth metal and lithium complexes 5–7 bridged by the oxygen atoms of 2-(2,6-diisopropylphenylimino)-8-hydroxyquinoline. Complex 6 can also be prepared by the treatment of 3 with 1 equiv. of 1. Complexes 2–7 were fully characterized using spectroscopic methods, elemental analyses and single crystal X-ray diffraction. Investigation of the catalytic properties of the complexes indicated that all complexes exhibited a high catalytic activity towards the addition of diphenylphosphine oxide to trans-β-nitroalkenes to afford β-nitrophosphonates under mild conditions.

The reactions of AlMe3 or AlEt3 with 2-pyridyl- or indolyl-substituted imines were studied, leading to the formation of different organoaluminum complexes. While the reactions of the iminopyridine Cy[N═CMe-2-(C5H4N)]2 (L1) derived from 1-(pyridin-2-yl)ethanone and trans-1,2-cyclohexanediamine with AlEt3 gave the aluminum complex Cy[NC(Me)(Et)-2-(C5H4N)AlEt2]2 (1), in which the two ketimine groups of the ligand were transformed into the amido functionality through the addition of two ethyl groups, the reaction of L1 with AlMe3 afforded the aluminum complex Cy[NC(═CH2)-2-(C5H4N)AlMe2]2 (2) via a sp3 C–H activation with elimination of two methane molecules. The reactions of indolyl-2-aldimines (2-(RN═CH)C8H5NH (R = tBu (L2H), C6H5 (L3H), 2,6-Me2C6H3 (L4H)) with AlMe3 or AlEt3 afforded only the deprotonated indolyl aluminum complexes [2-(RN═CH)C8H5N]AlMe2 (R = tBu (3), C6H5 (4), 2,6-Me2C6H3 (5)) and [2-(2,6-Me2C6H3N═CH)C8H5N]AlEt2 (6), respectively. The structures of complexes 2–6 were characterized by spectral methods and X-ray crystallographic analyses. These aluminum complexes showed a high catalytic activity in the addition of amines to carbodiimides to form guanidines. The mechanism of the catalytic process was studied by control experiments and 1H NMR monitoring. Together with the isolation of the complex [2-(2,6-Me2C6H3N═CH)C8H5N][CyN═C(4-MeC6H3N)(NHCy)]AlMe (7), a probable mechanism for the guanylation reaction was proposed.

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.

A series of rare-earth metal monoalkyl complexes supported by N,N′-di(2,6-dialkylphenyl)formamidinate ligand (L)2RECH2SiMe3·thf [L1 = HC(N-2,6-Me2C6H3)2, RE = Y (1), L2 = HC(N-2,6-iPr2C6H3)2, RE = Y (2), Er (3), Dy (4), Sm (5), and Nd (6)] were synthesized by alkyl elimination reaction or by salt metathesis reaction in good yields. All complexes were characterized by elemental analyses, FT-IR spectroscopy and single crystal X-ray diffraction. In combination with [Ph3C][B(C6F5)4] and alkylaluminium, these complexes displayed a good activity towards isoprene polymerization to give polyisoprenes with high molecular weight (Mn > 104) and narrow molecular distribution (PDI < 2.0). The influence of alkylaluminium, central metal, temperature, sequence of addition of alkylaluminium and [Ph3C][B(C6F5)4] on the polymerization of isoprene was studied. It was interesting to find that addition of the cocatalysts sequence has a great influence on the regioselectivity of the polymerization. High 1,4-regioselectivity polymerizations of isoprene (as high as 98%) were observed when the catalysts were added in the order [RE]/[alkylaluminum]/[borate].

An efficient method for synthesis of useful biaryl building blocks containing 2-thienyl, 3-thienyl, 2-pyridyl, and 3-pyridyl moieties was provided through cross-coupling reactions of aryl bromides or benzyl halides with heteroaryl aluminum reagents in the presence of Pd(OAc)2 and (o-tolyl)3P. The coupling reaction also worked efficiently with heteroaryl bromides affording series of heterobiaryl compounds. The reaction of phenylbromide with in situ prepared 3-pyridyl aluminum was demonstrated to afford the product 8a in high yield. Additionally, the catalytic system was also suited well for the coupling reaction of benzyl halides with pyridyl aluminum reagents to afford series of pyridyl-arylmethane.

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: {η5:η1:η5:η1-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 {η5:η1:η5:η1-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 {η5:η1:η5-Me2Si(C9H5CH2CH2OMe)2NdCl}2 (17), whereas the reaction of Me2Si(C9H5CH2CH2NMe2)2Li2 with SmCl3 afforded a racemic dinuclear samarium chloride bridged by lithium chloride {η5:η1:η5:η1-Me2Si(C9H5CH2CH2NMe2)2SmCl}2(μ-LiCl) (18). Further reaction of complex 18 with LiCH2SiMe3 provided an unexpected rare-earth metal alkyl complex {η5:η1:η5:η1:σ-Me2Si(C9H5CH2CH2NMe2)[(C9H5CH2CH2N(CH2)Me]}Sm (19) through the activation of an sp3 C–H bond α-adjacent to the nitrogen atom. Complexes 19 and {η5:η1:η5:η1: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.

The dehydrogenation of pyrrolyl-functionalized secondary amines initiated by rare-earth metal amides was systematically studied. Reactions of the rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with pyrrolyl-functionalized secondary amines 2-tBuNHCH2-5-R-C4H2NH (R = H (1), R = tBu (2)) led to dehydrogenation of the secondary amines with isolation of imino-functionalized pyrrolyl rare-earth metal complexes [2-tBuNCH-5-R-C4H2N]2REN(SiMe3)2 (R = H, RE = Y (3a), Dy (3b), Yb (3c), Eu (3d); R = tBu, RE = Y (4a), Dy (4b), Er (4c)). The mixed ligands erbium complex [2-tBuNCH2-5-tBu-C4H2N]Er[2-tBuNCH-5-tBuC4H2N]2ClLi2(THF) (4c′) was isolated in a short reaction time for the synthesis of complex 4c. Reaction of the deuterated pyrrolyl-functionalized secondary amine 2-(tBuNHCHD)C4H3NH with yttrium amide [(Me3Si)2N]3Y(μ-Cl)Li(THF)3 further proved that pyrrolyl-amino ligands were transferred to pyrrolyl-imino ligands. Treatment of 2-(tBuNHCH2)C4H3NH (1) with excess (Me3Si)2NLi gave the only pyrrole deprotonated product {[η5:η2:η1-2-(tBuNHCH2)C4H3N]Li2N(SiMe3)2}2 (5), indicating that LiN(SiMe3)2 could not dehydrogenate the secondary amines to imines and rare-earth metal ions had a decisive effect on the dehydrogenation. The reaction of the rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 1 equiv. of more bulky pyrrolyl-functionalized secondary amine 2-[(2,6-iPr2C6H3)NHCH2](C4H3NH) (6) in toluene afforded the only amine and pyrrole deprotonated dinuclear rare-earth metal amido complexes {(μ–η5:η1):η1-2-[(2,6-iPr2C6H3)NCH2]C4H3N]LnN(SiMe3)2}2 (RE = Nd (7a), Sm (7b), Er (7c)), no dehydrogenation of secondary amine to imine products were observed. On the basis of experimental results, a plausible mechanism for the dehydrogenation of secondary amines to imines was proposed.

A series of rare-earth metal amides supported by a cyclohexyl-linked bis(β-diketiminato) ligand were synthesized, and their catalytic activities for hydrophosphonylation of aldehydes and ketones were developed. Reaction of [(Me3Si)2N]3RE(µ-Cl)Li(THF)3 with the cyclohexyl-linked bis(β-diketimine) H2L (1) (L = Cy[NC(Me)CHC(Me)NAr]2, Cy = cyclohexyl, Ar = 2, 6-i-Pr2C6H3) gave the rare-earth metal amides LREN(SiMe3)2 (RE = Nd(2), Sm(3), Dy(4), Er(5), Y(6)). All complexes were fully characterized by elemental, spectroscopic and single-crystal X-ray analyses. Investigation of the catalytic properties of the complexes reveals that these complexes exhibited a high catalytic activity towards the hydrophosphonylation of aldehydes and ketones in the presence of a very low loading of rare-earth metal amides (0.1–1 mol%) at room temperature in a short time.

The dehydrogenation of pyrrolyl-functionalized secondary amines initiated by rare-earth metal amides was systematically studied. Reactions of the rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with pyrrolyl-functionalized secondary amines 2-tBuNHCH2-5-R-C4H2NH (R = H (1), R = tBu (2)) led to dehydrogenation of the secondary amines with isolation of imino-functionalized pyrrolyl rare-earth metal complexes [2-tBuNCH-5-R-C4H2N]2REN(SiMe3)2 (R = H, RE = Y (3a), Dy (3b), Yb (3c), Eu (3d); R = tBu, RE = Y (4a), Dy (4b), Er (4c)). The mixed ligands erbium complex [2-tBuNCH2-5-tBu-C4H2N]Er[2-tBuNCH-5-tBuC4H2N]2ClLi2(THF) (4c′) was isolated in a short reaction time for the synthesis of complex 4c. Reaction of the deuterated pyrrolyl-functionalized secondary amine 2-(tBuNHCHD)C4H3NH with yttrium amide [(Me3Si)2N]3Y(μ-Cl)Li(THF)3 further proved that pyrrolyl-amino ligands were transferred to pyrrolyl-imino ligands. Treatment of 2-(tBuNHCH2)C4H3NH (1) with excess (Me3Si)2NLi gave the only pyrrole deprotonated product {[η5:η2:η1-2-(tBuNHCH2)C4H3N]Li2N(SiMe3)2}2 (5), indicating that LiN(SiMe3)2 could not dehydrogenate the secondary amines to imines and rare-earth metal ions had a decisive effect on the dehydrogenation. The reaction of the rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 1 equiv. of more bulky pyrrolyl-functionalized secondary amine 2-[(2,6-iPr2C6H3)NHCH2](C4H3NH) (6) in toluene afforded the only amine and pyrrole deprotonated dinuclear rare-earth metal amido complexes {(μ–η5:η1):η1-2-[(2,6-iPr2C6H3)NCH2]C4H3N]LnN(SiMe3)2}2 (RE = Nd (7a), Sm (7b), Er (7c)), no dehydrogenation of secondary amine to imine products were observed. On the basis of experimental results, a plausible mechanism for the dehydrogenation of secondary amines to imines was proposed.

A series of rare-earth metal monoalkyl complexes supported by N,N′-di(2,6-dialkylphenyl)formamidinate ligand (L)2RECH2SiMe3·thf [L1 = HC(N-2,6-Me2C6H3)2, RE = Y (1), L2 = HC(N-2,6-iPr2C6H3)2, RE = Y (2), Er (3), Dy (4), Sm (5), and Nd (6)] were synthesized by alkyl elimination reaction or by salt metathesis reaction in good yields. All complexes were characterized by elemental analyses, FT-IR spectroscopy and single crystal X-ray diffraction. In combination with [Ph3C][B(C6F5)4] and alkylaluminium, these complexes displayed a good activity towards isoprene polymerization to give polyisoprenes with high molecular weight (Mn > 104) and narrow molecular distribution (PDI < 2.0). The influence of alkylaluminium, central metal, temperature, sequence of addition of alkylaluminium and [Ph3C][B(C6F5)4] on the polymerization of isoprene was studied. It was interesting to find that addition of the cocatalysts sequence has a great influence on the regioselectivity of the polymerization. High 1,4-regioselectivity polymerizations of isoprene (as high as 98%) were observed when the catalysts were added in the order [RE]/[alkylaluminum]/[borate].