Ionic rare-earth metal complexes 1–4 bearing an imidazolium cation were synthesized, which, as single-component catalysts, showed good activity in catalyzing cyclic carbonate synthesis from epoxides and CO2. In the presence of 0.2 mol % catalyst, monosubstituted epoxides bearing different functional groups were converted into cyclic carbonates in 60–97% yields under atmospheric pressure. In addition, bulky/internal epoxides with low reactivity yielded cyclic carbonates in 40–95% yields. More importantly, the readily available samarium complex 2 was reused for six successive cycles without any significant loss in its catalytic activity. This is the first recyclable rare-earth metal-based catalyst in cyclic carbonate synthesis.

In situ generated cationic zirconium complexes stabilized by amine-bridged bis(phenolato) ligands have been developed to catalyse C(sp3)–H addition of alkyl pyridines to olefins, which are the first examples of group 4 metal based catalysts in this transformation. Ligand-controlled regioselectivity was observed, which was verified by DFT study.

Novel rare earth metal–zinc heterotrinuclear complexes have been synthesized, which showed high efficiency and selectivity in initiating the copolymerization of CO2 and cyclohexene oxide under mild conditions. Significant cooperation between rare earth metal and zinc centres that account for the good performance is observed. Copolymers of high polycarbonate content (up to 99%) as well as high molecular weight (up to 295800 g mol−1) were obtained at 25 °C under 0.7 MPa pressure of CO2.

Dinuclear aluminum methyl complexes stabilized by piperidyl–phenolato ligands were prepared and characterized. The ring-opening polymerizations of cyclohexene oxide (CHO) and propylene oxide (PO) initiated by dinuclear complexes and mononuclear analogues were investigated and compared. Enhanced activity of dinuclear complexes compared to that of mononuclear analogues in both the ring-opening polymerization of CHO and PO proves the synergistic interaction of two Al centers in the former. End-group analysis of oligomers by MALDI-TOF mass spectrometry confirms the role of methyl groups as initiating groups. A bimetallic mechanism is proposed, in which the cooperation of two Al centers are involved in polymerization processes.

Zirconium complexes stabilized by piperazidine- and imidazolidine-bridged bis(phenolato) ligands have been synthesized and characterized. Their activities in catalyzing intramolecular hydroamination reactions have been tested and compared, which reveals the significant role that the ancillary ligands play in influencing catalytic activities. Cationic species derived from zirconium dibenzyl complexes showed good activities in catalyzing intramolecular hydroamination reactions of both primary and secondary amines, and afforded the respective N-heterocycles in 85% to 99% yields. Moreover, this catalytic system also catalyzed sequential cyclization of primary aminodienes, and generated bicyclic tertiary amines in 94–99% yields.

A series of dinuclear aluminum complexes 1–4 stabilized by amine-bridged poly(phenolato) ligands have been synthesized, which are highly active in catalyzing the cycloaddition of epoxides and CO2. In the presence of 0.3 mol % complex 3 and 0.9 mol % NBu4Br at 1 bar CO2 pressure, terminal epoxides bearing different functional groups were converted to cyclic carbonates in 60–97% yields. Complex 3 is one of the rare examples of Al-based catalysts capable of promoting the cycloaddition at 1 bar pressure of CO2. Moreover, reactions of more challenging disubstituted epoxides also proceeded at an elevated pressure of 10 bar and afforded cyclic carbonates in 52–90% yields.

An in situ generated cationic zirconium complex stabilized by an n-butylamine-bridged bis(phenolato) ligand has been developed to catalyse hydroamination reactions of secondary amines, which is the first example of group 4 metal based catalysts capable of mediating intermolecular hydroamination reactions of N-aryl/alkyl amines.

A series of mono- and dinuclear aluminum alkyl complexes stabilized by phenolato ligands have been prepared through alkane elimination reactions. Treatment of piperazidine-bridged bis(phenol)s C4H8N2[1,4-(2-OH-3,5-Me2-C6H2CH2)2] (H2[ONNO]1), C4H8N2[1,4-(2-OH-3-tBu-5-Me-C6H2CH2)2] (H2[ONNO]2), and C4H8N2[1,4-(2-OH-3,5-tBu2-C6H2CH2)2] (H2[ONNO]3) with 2.5–3 equiv of AlR3 (R = Me, Et) afforded dinuclear aluminum complexes (AlMe2)2[ONNO]1 (1), (AlMe2)2[ONNO]2 (2), (AlMe2)2[ONNO]3 (3), (AlEt2)2[ONNO]1 (4), (AlEt2)2[ONNO]2 (5), and (AlEt2)2[ONNO]3 (6), respectively. In order to compare the catalytic activities of these bimetallic complexes with their mononuclear counterparts, mono(phenolato) aluminum complexes AlMe2[ON]1 (7), AlMe2[ON]2 (8), AlMe2[ON]3 (9), AlEt2[ON]2 (10), and AlEt2[ON]3 (11) were synthesized from reactions of 1 equiv of AlMe3 or 2 equiv of AlEt3 with phenols that bear piperidine moieties, i.e., [2-(CH2NC5H10)-4,6-Me2-C6H2OH (H[NO]1), 2-(CH2NC5H10)-4-Me-6-tBu-C6H2OH (H[NO]2), and 2-(CH2NC5H10)-4,6-tBu2-C6H2OH (H[NO]3)], respectively. In comparison, reactions of H[NO]n (n = 2, 3) with 0.5 equiv of AlEt3 led to the isolation of mononuclear monoalkyl complexes AlEt[NO]22 (12) and AlEt[NO]32 (13), respectively. All complexes have been characterized by elemental analysis and NMR spectroscopy, and the solid state structures of 5 complexes have been determined by X-ray diffraction analysis. The activities of both binuclear and mononuclear aluminum complexes in initiating the ring-opening polymerization (ROP) of ε-caprolactone have also been investigated and compared. In general, these phenolato-Al complexes showed high activities in initiating the ROP in the absence of alcohols. More importantly, dinuclear complexes have been found to be 2–8 times more active than their mononuclear counterparts, which provides evidence for the cooperation between two metal centers in the former.

A series of zirconium complexes bearing amine-bridged bis(phenolato) ligands of different steric and electronic properties have been synthesized, and their activities in catalyzing intermolecular hydroamination reactions have been studied and compared. In general, hexacoordinate zirconium dibenzyl complexes 1–4 stabilized by [ONNO]- or [ONOO]-type ligands were found to be less active than pentacoordinate complexes 5 and 7 that carry [ONO]-type ligands, which clearly imply that amine-bridged bis(phenolato) ligands play crucial roles in influencing catalytic activities. Complex 5 showed good activities and regioselectivities in catalysing reactions of various primary amines and alkynes. Moreover, reactions of challenging substrates, including secondary amines, internal alkynes, and hydrazines, were achieved with in situ generated cationic species from complex 5 and [Ph3C][B(C6F5)4].

Eight rare-earth metal guanidinates supported by a versatile family of chelating amine-bridged bis(phenolate) ligands were synthesized. Metathesis reactions of rare-earth metal chlorides [LnClL1(THF)] stabilized by amine-bridged bis(phenolate) ligand L1 with in situ generated lithium guanidinates in a 1:1 molar ratio in THF afforded ytterbium guanidinates YbL1 [R2NC(NR1)2] [R1 = –iPr, R2N = –NiPr2 (1), –N(CH2)5 (2)]. Insertion reactions of the yttrium amides bearing bridged bis(phenolate) ligands with 1 equiv of N,N′-diisopropylcarbodiimide (DIC) yielded six yttrium guanidinates YL1 [(SiHMe2)2NC(NiPr)2] (3), YL2[(SiHMe2)2NC(NiPr)2](THF) (4), YL3[(SiHMe2)2NC(NiPr)2] (5), YL4[(SiHMe2)2NC(NiPr)2] (6), YL5 [(SiHMe2)2NC(NiPr)2] (7), YL6[(SiHMe2)2NC(NiPr)2] (8), respectively. The behaviors of complexes 1–8 in the polymerization of rac-lactide (LA) and rac-β-butyrolactone (BBL) were also explored. It was found that complexes 1–8 efficiently initiated the ring-opening polymerization (ROP) of rac-LA and rac-BBL in a controlled manner, providing highly heterotactic polylactide (Pr up to 0.99) and highly syndiotactic poly(3-hydroxybutyrate) (Pr up to 0.82). The framework of the bridge played a significant role in governing the stereoselectivity, while guanidinate groups work as initiating groups.

It was found for the first time that organic alkali metal compounds serve as highly efficient precatalysts for the hydrophosphonylation reactions of aldehydes and unactivated ketones with dialkyl phosphite under mild conditions. For ketone substrates, a reversible reaction was observed, and the influence of catalyst loading and reaction temperature on the reaction equilibrium was studied in detail. Overall, the hydrophosphonylation reactions catalyzed by 0.1 mol % n-BuLi were completed within 5 min for a broad range of substrates and generated a series of α-hydroxy phosphonates in high yields.

Lanthanide anilido complexes stabilized by the 2,6-diisopropylanilido ligand have been synthesized and characterized, and their catalytic activity for hydrophosphonylation reaction was explored. A reaction of anhydrous LnCl3 with 5 equivalents of LiNHPh-iPr2-2,6 in THF generated the heterobimetallic lanthanide–lithium anilido complexes (2,6-iPr2PhNH)5LnLi2(THF)2 [Ln = Sm(1), Nd(2), Y(3)] in good isolated yields. These complexes are well characterized by elemental analysis, IR, NMR (for complex 3) and single-crystal structure determination. Complexes 1–3 are isostructural. In these complexes, the lanthanide metal ion is five-coordinated by five nitrogen atoms from five 2,6-diisopropylanilido ligands to form a distorted trigonal bipyramidal geometry. The lithium ion is coordinated by two nitrogen atoms from two 2,6-diisopropylanilido ligands, and one oxygen atom from a THF molecule. It was found that these simple lanthanide anilido complexes are highly efficient for catalyzing hydrophosphonylation reactions of various aldehydes and unactivated ketones to generate α-hydroxyphosphonates in good to excellent yields (up to 99%) within a short time (5 min for aldehydes, 20 min for ketones). Furthermore, the mechanism of hydrophosphonylation reactions has also been elucidated via1H NMR monitoring of reaction.

Zirconium and titanium complexes 1 and 2, bearing an amine-bridged bis(phenolato) ligand, have been synthesized and characterized. Although 1 and 2 were inactive in catalyzing intermolecular hydroamination reactions, cationic complexes generated in situ from treatment of 1 and 2 with borate [Ph3C][B(C6F5)4], respectively, were found to be highly active. In general, excellent yields (up to >99%) and 100% regioselectivity for a broad range of terminal alkynes and anilines were observed within a reaction time of 1 h. Reactions with internal alkynes of moderate sterics also led to good yields and moderate regioselectivity. A kinetic study was also conducted, which provided some insights into the mechanism of hydroamination reactions.

In situ generated cationic zirconium complexes stabilized by amine-bridged bis(phenolato) ligands have been developed to catalyse C(sp3)–H addition of alkyl pyridines to olefins, which are the first examples of group 4 metal based catalysts in this transformation. Ligand-controlled regioselectivity was observed, which was verified by DFT study.

An in situ generated cationic zirconium complex stabilized by an n-butylamine-bridged bis(phenolato) ligand has been developed to catalyse hydroamination reactions of secondary amines, which is the first example of group 4 metal based catalysts capable of mediating intermolecular hydroamination reactions of N-aryl/alkyl amines.

Lanthanide anilido complexes stabilized by the 2,6-diisopropylanilido ligand have been synthesized and characterized, and their catalytic activity for hydrophosphonylation reaction was explored. A reaction of anhydrous LnCl3 with 5 equivalents of LiNHPh-iPr2-2,6 in THF generated the heterobimetallic lanthanide–lithium anilido complexes (2,6-iPr2PhNH)5LnLi2(THF)2 [Ln = Sm(1), Nd(2), Y(3)] in good isolated yields. These complexes are well characterized by elemental analysis, IR, NMR (for complex 3) and single-crystal structure determination. Complexes 1–3 are isostructural. In these complexes, the lanthanide metal ion is five-coordinated by five nitrogen atoms from five 2,6-diisopropylanilido ligands to form a distorted trigonal bipyramidal geometry. The lithium ion is coordinated by two nitrogen atoms from two 2,6-diisopropylanilido ligands, and one oxygen atom from a THF molecule. It was found that these simple lanthanide anilido complexes are highly efficient for catalyzing hydrophosphonylation reactions of various aldehydes and unactivated ketones to generate α-hydroxyphosphonates in good to excellent yields (up to 99%) within a short time (5 min for aldehydes, 20 min for ketones). Furthermore, the mechanism of hydrophosphonylation reactions has also been elucidated via1H NMR monitoring of reaction.

A series of zirconium complexes bearing amine-bridged bis(phenolato) ligands of different steric and electronic properties have been synthesized, and their activities in catalyzing intermolecular hydroamination reactions have been studied and compared. In general, hexacoordinate zirconium dibenzyl complexes 1–4 stabilized by [ONNO]- or [ONOO]-type ligands were found to be less active than pentacoordinate complexes 5 and 7 that carry [ONO]-type ligands, which clearly imply that amine-bridged bis(phenolato) ligands play crucial roles in influencing catalytic activities. Complex 5 showed good activities and regioselectivities in catalysing reactions of various primary amines and alkynes. Moreover, reactions of challenging substrates, including secondary amines, internal alkynes, and hydrazines, were achieved with in situ generated cationic species from complex 5 and [Ph3C][B(C6F5)4].