•An efficient insertion reaction of pyridyl-/quinolyl-lithium with nitriles for preparing pyridyl-/quinolyl-ketone compounds was reported.•The tautomeric equilibria were affected by the substituent in the molecule and characterized by standard methods like NMR, IR or SCXRD.We describe an efficient for the synthesis of compounds of tautomeric β-pyridyl/quinolyl-enol, -ketone, -enaminone, which were finally characterized by standard methods like NMR, IR or SCXRD. The addition reaction of lithiated intermediates of picoline, 2-ethylpyridine and 2-methylquinoline, respectively, with nitriles followed by acid hydrolysis afforded the corresponding tautomeric compounds of enol, ketone and emaminone. Interestingly, treatment of 2-methylpyridine or 2-ethylpyridine with nitriles, respectively, yielded mostly β-pyridyl ketone and enol tautomers without enaminones, while 2-methylquinoline with nitriles gave β-quinolyl ketone and enaminone tautomers without enols. The reaction of 2-benzylpyridine with nitriles was not available under the same conditions.

A family of zinc β-pyridylenolates with varying α,β-substituents has been synthesized. A direct reaction of β-pyridyl ketone ligands with ZnEt2 in toluene afforded dimeric [LZnEt]2 (L = (2-C5H4N)–C(R1)C(R2)–O–). X-ray structural data revealed that all the [LZnEt]2 complexes exist as μ-O-bridged dimers in the solid state, although they adopt a different geometry. Each of the [LZnEt]2 complexes is a highly active catalyst for the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and racemic lactide (rac-LA), respectively. The donating group on the enolate ligand can accelerate the ROP reaction and control the polymerization process well. All complexes also showed different abilities in the block and random copolymerization of ε-CL and L-LA. Diblock PCL-b-PLLA and PLLA-b-PCL copolymers were easily prepared via sequential addition of ε-CL and L-LA by using complex 10, respectively. Random copolymers of PCL-ran-PLLA were also synthesized from complex 10. The copolymers of PCL-ran-PLLA were shown to possess monomer contents which matched well with their composition in the monomer feed. NMR and DSC characterization confirmed a highly random structure of these copolymers, resulting in closely average lengths of the caproyl and lactidyl sequences (LCL = 2.1; LLA = 1.9). All zinc complexes as efficient single-component initiators in both homo- and copolymerizations showed that polymers were probably susceptible to chain transfer and transesterification due to the close Zn⋯Zn proximity in the dimer. The polymers initiated by [LZnEt]2 in the absence of BnOH showed high molecular weight and narrow molecular weight distributions.

•Insertion reaction of 2-benzylpydidyl lithium with nitriles has been investigated.•C-C coupling is proceed via a carbanion attack.•Possible mechanism for the formation of different products is been speculated.This work investigated the reactivity of 2-benzylpyridyl lithium (2-Pyr)C(Ph)(R)Li (R = SiMe3, Li1; R = H, Li2) toward benzonitrile derivatives. Based on the different products, the reaction between lithium salts and nitriles might involve in addition, elimination and bimolecular coupling pathways, respectively. Treatment of Li1 with ArCN (Ar = Ph, p-Tolyl, o-Tolyl, p-OMePh) yielded an addition intermediate pyridyl-1-aza-allyl-lithium [{(2-Pyr)C(Ph)C(Ar)N(SiMe3)}Li]2 (1, Ar = Ph) and its corresponding hydrolysis product 2-benzylpyridyl-ketone 2–5, respectively, in which the reaction involved in a 1,3-shift of -SiMe3 group to form a dimeric pyridyl-1-aza-allyl-lithium then followed by acidic hydrolysis. The MeOLi elimination reaction between Li2 and p-MeO(C6H4)CN resulted in formation of 4-(2-benzylpyridyl)benzonitrile 6. The reaction of Li2 with p-Me(C6H4)CN in the presence of TMEDA generated a 1:2 hydrolysis adduct 2-benzylpyridyl-enaminone 7, however, in the absence of TMEDA it afforded a coupling product of bimolecular nitriles, 1-(4-methylphenyl)-2-cyanophenyl-ethanone 8. We speculated the reaction mechanisms in sequence. The crystal structures of 1 and 5–8 were analyzed.The reaction of Li1, Li2 with ArCN followed by acid hydrolysis give addition, elimination and bimolecular coupling products.Download high-res image (145KB)Download full-size image

Treatment of tautomers of β-quinolyl ketone-enaminones 1a–6a with AlMe3 afforded β-quinolyl enolato dialkylaluminium complexes LAlMe21b–6b (L = [(2-C9H6N)–CHC(R)–O–], R = CH3 (1b), tBu (2b), Ph (3b), o-tolyl (4b), p-tolyl (5b), p-OMePh (6b)), respectively. 2b reacted with benzyl alcohol to generate the corresponding LAl(OBn)2 complex 2c. Complexes 1b–6b and 2c were characterized by 1H and 13C NMR spectroscopy, elemental analyses and single crystal X-ray diffraction analyses. All complexes were tested as catalyst precursors for ring-opening polymerization of ε-caprolactone (ε-CL). The results indicated that LAlMe2 (1b–6b) exhibited good activity towards the ROP of ε-CL in the presence of benzyl alcohol at 80 °C, and LAl(OBn)22c exhibited higher catalytic activity in the absence of alcohol than 1b–6b for the ROP of ε-CL. However, both polymerizations were less controlled. Kinetic studies showed that the polymerization reaction catalyzed by 1b–6b and 2c proceeded with first-order dependence on the monomer and took place through coordination–insertion.

Insertion of LiCH(SiMe3)2 into the CN bond of the appropriate nitriles RCN afforded dimeric β-diketiminato lithium complexes [Li{N(SiMe3)C(R)C(H)C(R′)N(SiMe3)}]2 (1a, R = R′ = NMe2; 1b, R = But, R′ = o-C5H4N). Lithium salt 1a was used as a precursor to react with SnCl2 and GeCl4, respectively, and complexes [ClSn{N(SiMe3)C(NMe2)C(H)C(NMe2)N(SiMe3)}] (2) and [Cl2Ge{NC(NMe2)C(H)C(NMe2)N(GeCl3)}] (3) were obtained in good yields. By β-diketiminato lithium 1b ligand transfer, the cyclo-1,3-diazasilane heterocyclic complex (4) was prepared using 1b and ZrCl4. Unexpectedly, the chelating β-diketiminato backbone in 3 acts as a dianionic ligand, whereas in 4, the ligand acts as a neutral cyclo-1,3-diazasilane heterocyclic ring to coordinate with the Zr center. The X-ray structures of 2–4 are presented, and reaction pathways for each complex are proposed. Upon activation with methylaluminoxane, complex 4 exhibits good activity for ethylene polymerization.

•The azaallyl- and diazaallyl-amino metal complexes were prepared by insertion reactions.•Three complexes have been structurally characterized.•The formation involved 1,3- and 1,5 shift of the bulky silyl group.•A mechanism of the halogenations has presumably been proposed.Four new azaallylamino metallic complexes have been prepared. The insertion reactions of Li{CH[SiN(Me2)Me2]2}(1) with ButCN or PhCN generated azaallyla-mino-lithium Li{[N(Me2)Si(Me2)C(H)C(But)]N[Si(Me2)N(Me2)]·ButCN} (2) or 1,3- diazaallylamino-lithium Li{[N(Me2)Si(Me2)C(H)C(Ph))]N[C(Ph)NSi(Me2)N(Me2)]} (3), respectively. Further transmetalation reaction of 2 with ZrCl4 afforded complex Cl3Zr{[N(Me2)Si(Me2)C(H)C(But)]N[Si(Me2)N(Me2)]}(4), and 3 with SnCl4 yielded Cl3Sn{[N(Me2)Si(Me2)C(H)C(Ph)]N[C(Ph)N(Si(Cl)(Me2))]} (5). The crystal structures of 2, 4 and 5 were reported. Their formation involved 1,3- and 1,5-shift of the bulky silyl group [-Si(NMe2)Me2]. A mechanism of the halogenation reaction is proposed based on the structural parameters of 5.

The insertion reactions of lithium silylquinolylamide dimers [{8-(2-R-C9H5N)N(Me3Si)}Li·OEt2]2 (R = H, 1a; R = Me, 1b) with dimethylcyanamide afforded dimeric lithium 8-quinolylguanidinates [{8-(2-R-C9H5N)NC(NMe2)N(SiMe3)}Li]2 (R = H, 2a; R = Me, 2b) with a cisoid arrangement of the ligands. Further reaction of 2b with MCl2 (M = Co or Fe) formed the eight-membered binuclear metallic 8-quinolylguanidinate complexes [{8-(2-CH3-C9H5N)NC(NMe2)N(SiMe3)}MCl]2 (M = Fe, 3; Co, 4). The reaction of 2a with (MeC5H4)TiCl3 afforded a centrosymmetric dimeric titanium(IV) complex [{8-(C9H6N)NC(NMe2)N}Ti(MeC5H4)Cl]2 (5) via a metathesis reaction and the elimination of SiMe3Cl. The guanidinate ligand 2b was hydrolyzed with an equimolar amount of water, and reacted with (MeC5H4)TiCl3 forming a monoligated half-titanocene compound {8-(2-CH3-C9H5N)N(H)C(NMe2)N}Ti(MeC5H4)Cl2 (6). Therefore lithium silylquinolylamide dimers provided various coordinative multi-dentate ligands and resulted in a family of metal complexes.

A series of N-(5,6,7-trihydroquinolinylidene)-2-benzhydrylbenzenamine ligands was synthesized and characterized by 1H/13C NMR and IR spectroscopy, and by elemental analysis. These ligands reacted with NiCl2 or NiBr2(DME) to form the title halide complexes, which were also characterized by IR spectroscopy and elemental analysis. Single crystal X-ray diffraction revealed that the representative nickel complexes crystallized as centro-symmetric dimers with chloro-bridges linking distorted octahedral nickel centers. On activation with either methylaluminoxane (MAO) or diethylaluminium chloride (Et2AlCl), all nickel pre-catalysts showed high activities for ethylene polymerization, producing polyethylene with narrow molecular weight distribution, consistent with single-site catalysis. The nature of the ligands and reaction parameters were investigated and discussed in terms of their influence on the catalytic behavior of these nickel pre-catalysts.

The reaction of 9-trimethylsilylfluorenyllithium (C13H8SiMe3)Li (1) with α-hydrogen-free nitriles gave highly sensitive lithium compounds, (η3-C13H8SiMe3)Li(tBuCN)(Et2O) (2), [η3-(C13H8)C(NMe2)N(SiMe3)]Li (Et2O)2 (3) and [η3,η6-(C13H8)C(Ph)N(SiMe3)Li]2 (4), illustrating bonding features of η3-allyl, η3-azaallyl, and η6-arene interactions.The reaction of 9-trimethylsilylfluorenyl lithium with α-hydrogen-free nitriles was carried out to obtain the highly sensitive lithium compounds, which showed a bonding library of lithium with ligands acting as η3-fluorenyl, η3-azaallyl, and η6-arene interactions, and donating bonding.Research Highlights► The 9-trimethylsilylfluorenyllithium (C13H8SiMe3)Li reacted with three α-hydrogen-free nitriles. ► The lithium intermediates were isolated and characterized. ► The different bonding features of η3-allyl, η3-azaallyl, and η6-arene interactions were observed between lithium and ligands.

Treatment of tautomers of β-quinolyl ketone-enaminones 1a–6a with AlMe3 afforded β-quinolyl enolato dialkylaluminium complexes LAlMe21b–6b (L = [(2-C9H6N)–CHC(R)–O–], R = CH3 (1b), tBu (2b), Ph (3b), o-tolyl (4b), p-tolyl (5b), p-OMePh (6b)), respectively. 2b reacted with benzyl alcohol to generate the corresponding LAl(OBn)2 complex 2c. Complexes 1b–6b and 2c were characterized by 1H and 13C NMR spectroscopy, elemental analyses and single crystal X-ray diffraction analyses. All complexes were tested as catalyst precursors for ring-opening polymerization of ε-caprolactone (ε-CL). The results indicated that LAlMe2 (1b–6b) exhibited good activity towards the ROP of ε-CL in the presence of benzyl alcohol at 80 °C, and LAl(OBn)22c exhibited higher catalytic activity in the absence of alcohol than 1b–6b for the ROP of ε-CL. However, both polymerizations were less controlled. Kinetic studies showed that the polymerization reaction catalyzed by 1b–6b and 2c proceeded with first-order dependence on the monomer and took place through coordination–insertion.

The insertion reactions of lithium silylquinolylamide dimers [{8-(2-R-C9H5N)N(Me3Si)}Li·OEt2]2 (R = H, 1a; R = Me, 1b) with dimethylcyanamide afforded dimeric lithium 8-quinolylguanidinates [{8-(2-R-C9H5N)NC(NMe2)N(SiMe3)}Li]2 (R = H, 2a; R = Me, 2b) with a cisoid arrangement of the ligands. Further reaction of 2b with MCl2 (M = Co or Fe) formed the eight-membered binuclear metallic 8-quinolylguanidinate complexes [{8-(2-CH3-C9H5N)NC(NMe2)N(SiMe3)}MCl]2 (M = Fe, 3; Co, 4). The reaction of 2a with (MeC5H4)TiCl3 afforded a centrosymmetric dimeric titanium(IV) complex [{8-(C9H6N)NC(NMe2)N}Ti(MeC5H4)Cl]2 (5) via a metathesis reaction and the elimination of SiMe3Cl. The guanidinate ligand 2b was hydrolyzed with an equimolar amount of water, and reacted with (MeC5H4)TiCl3 forming a monoligated half-titanocene compound {8-(2-CH3-C9H5N)N(H)C(NMe2)N}Ti(MeC5H4)Cl2 (6). Therefore lithium silylquinolylamide dimers provided various coordinative multi-dentate ligands and resulted in a family of metal complexes.

A family of zinc β-pyridylenolates with varying α,β-substituents has been synthesized. A direct reaction of β-pyridyl ketone ligands with ZnEt2 in toluene afforded dimeric [LZnEt]2 (L = (2-C5H4N)–C(R1)C(R2)–O–). X-ray structural data revealed that all the [LZnEt]2 complexes exist as μ-O-bridged dimers in the solid state, although they adopt a different geometry. Each of the [LZnEt]2 complexes is a highly active catalyst for the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and racemic lactide (rac-LA), respectively. The donating group on the enolate ligand can accelerate the ROP reaction and control the polymerization process well. All complexes also showed different abilities in the block and random copolymerization of ε-CL and L-LA. Diblock PCL-b-PLLA and PLLA-b-PCL copolymers were easily prepared via sequential addition of ε-CL and L-LA by using complex 10, respectively. Random copolymers of PCL-ran-PLLA were also synthesized from complex 10. The copolymers of PCL-ran-PLLA were shown to possess monomer contents which matched well with their composition in the monomer feed. NMR and DSC characterization confirmed a highly random structure of these copolymers, resulting in closely average lengths of the caproyl and lactidyl sequences (LCL = 2.1; LLA = 1.9). All zinc complexes as efficient single-component initiators in both homo- and copolymerizations showed that polymers were probably susceptible to chain transfer and transesterification due to the close Zn⋯Zn proximity in the dimer. The polymers initiated by [LZnEt]2 in the absence of BnOH showed high molecular weight and narrow molecular weight distributions.

A series of N-(5,6,7-trihydroquinolinylidene)-2-benzhydrylbenzenamine ligands was synthesized and characterized by 1H/13C NMR and IR spectroscopy, and by elemental analysis. These ligands reacted with NiCl2 or NiBr2(DME) to form the title halide complexes, which were also characterized by IR spectroscopy and elemental analysis. Single crystal X-ray diffraction revealed that the representative nickel complexes crystallized as centro-symmetric dimers with chloro-bridges linking distorted octahedral nickel centers. On activation with either methylaluminoxane (MAO) or diethylaluminium chloride (Et2AlCl), all nickel pre-catalysts showed high activities for ethylene polymerization, producing polyethylene with narrow molecular weight distribution, consistent with single-site catalysis. The nature of the ligands and reaction parameters were investigated and discussed in terms of their influence on the catalytic behavior of these nickel pre-catalysts.