The first catalytic cycloamidination of aminoalkenes with nitriles has been achieved by using rare-earth complexes. This reaction is equivalent to the desired intramolecular hydroamination of alkenylamidines, and allows a new direct access to substituted 2-imidazolines and tetrahydropyrimidines in high yields under operationally simple reaction conditions. Moreover, the methodology is also efficient for synthesis of symmetric and unsymmetric bridged diimidazolines. Compared with the traditional stepwise-mediated synthetic approaches, the present method avoids the use of additives and harsh reaction conditions, and thus leads to a completely different product distribution. Mechanistic data suggest that the reaction involves the initial NH activation by lanthanide complex followed by nitrile insertion into a LnN bond to form an amidinate lanthanide intermediate which undergoes the cyclization.

The first catalytic cycloamidination of aminoalkenes with nitriles has been achieved by using rare-earth complexes. This reaction is equivalent to the desired intramolecular hydroamination of alkenylamidines, and allows a new direct access to substituted 2-imidazolines and tetrahydropyrimidines in high yields under operationally simple reaction conditions. Moreover, the methodology is also efficient for synthesis of symmetric and unsymmetric bridged diimidazolines. Compared with the traditional stepwise-mediated synthetic approaches, the present method avoids the use of additives and harsh reaction conditions, and thus leads to a completely different product distribution. Mechanistic data suggest that the reaction involves the initial NH activation by lanthanide complex followed by nitrile insertion into a LnN bond to form an amidinate lanthanide intermediate which undergoes the cyclization.

Unusual chemical transformations such as three-component combination and ring-opening of N-heterocycles or formation of a carbon–carbon double bond through multiple C–H activation were observed in the reactions of Tp^Me2-supported yttrium alkyl complexes with aromatic N-heterocycles. The scorpionate-anchored yttrium dialkyl complex [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with 1-methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24-membered rare-earth metallomacrocyclic compound [Tp^Me2Y(μ-N,C-Im)(η²-N,C-Im)]₆ (1; Im=1-methylimidazolyl) through two kinds of C–H activations at the C2- and C5-positions of the imidazole ring. However, [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with two equivalents of 1-methylbenzimidazole to afford a C–C coupling/ring-opening/C–C coupling product [Tp^Me2Y{η³-(N,N,N)-N(CH₃)C₆H₄NHCHC(Ph)CN(CH₃)C₆H₄NH}] (2). Further investigations indicated that [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C–C coupling/ring-opening product {(Tp^Me2)Y[μ-η²:η¹-SC₆H₄N(CHCHPh)](THF)}₂ (3). Moreover, the mixed Tp^Me2/Cp yttrium monoalkyl complex [(Tp^Me2)CpYCH₂Ph(THF)] reacted with two equivalents of 1-methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [Tp^Me2CpY(μ-N,C-Im)]₃ (5), whereas when the above reaction was carried out at 55 °C for two days, two structurally characterized metal complexes [Tp^Me2Y(Im-Tp^Me2)] (7; Im-Tp^Me2=1-methyl-imidazolyl-Tp^Me2) and [Cp₃Y(HIm)] (8; HIm=1-methylimidazole) were obtained in 26 and 17 % isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a CC bond through multiple C–H activations.

A lanthanide-catalyzed sequential insertion of CN and CC into an NH bond is presented. The convenient reaction, which proceeds under mild conditions, is an efficient method for preparing 1,2,4-trisubstituted imidazoles directly from readily available propargylamines and nitriles.

A series of unusual chemical-bond transformations were observed in the reactions of high active yttriumdialkyl complexes with unsaturated small molecules. The reaction of scorpionate-anchored yttriumdibenzyl complex [Tp^Me2Y(CH₂Ph)₂(thf)] (1, Tp^Me2=tri(3,5-dimethylpyrazolyl)borate) with phenyl isothiocyanate led to CS bond cleavage to give a cubane-type yttrium–sulfur cluster, {Tp^Me2Y(μ₃-S)}₄ (2), accompanied by the elimination of PhNC(CH₂Ph)₂. However, compound 1 reacted with phenyl isocyanate to afford a C(sp³)H activation product, [Tp^Me2Y(thf){μ-η¹:η³-OC(CHPh)NPh}{μ-η³:η²-OC(CHPh)NPh}YTp^Me2] (3). Moreover, compound 1 reacted with phenylacetonitrile at room temperature to produce γ-deprotonation product [(Tp^Me2)₂Y]⁺[Tp^Me2Y(N=CCHPh)₃]⁻ (6), in which the newly formed NCCHPh ligands bound to the metal through the terminal nitrogen atoms. When this reaction was carried out in toluene at 120 °C, it gave a tandem γ-deprotonation/insertion/partial-Tp^Me2-degradation product, [(Tp^Me2Y)₂(μ-Pz)₂{μ-η¹:η³-NC(CH₂Ph)CHPh}] (7, Pz=3,5-dimethylpyrazolyl).

Three new patterns of reactivity of rare-earth metal methylidene complexes have been established and thus have resulted in access to a wide variety of imido rare-earth metal complexes [L₃Ln₃(μ₂-Me)₃(μ₃-Me)(μ-NR)] (L=[PhC(NC₆H₃iPr₂-2,6)₂]⁻; R=Ph, Ln=Y (2 a), Lu (2 b); R=2,6-Me₂C₆H₃, Ln=Y (3 a), Lu (3 b); R=p-ClC₆H₄, Ln=Y (4 a), Lu (4 b); R=p-MeOC₆H₄, Ln=Y (5 a), Lu (5 b); R=Me₂CHCH₂CH₂, Ln=Y (6 a), Lu (6 b)) and [{L₃Lu₃(μ₂-Me)₃(μ₃-Me)}₂(μ-NR′N)] (R′=(CH₂)₆ (7 b), (C₆H₄)₂ (8 b)). Complex 2 b was treated with an excess of CO₂ to give the corresponding carboxylate complex [L₃Lu₃(μ-η¹:η¹-O₂CCH₃)₃(μ-η¹:η²-O₂C-CH₃)(μ-η¹:η¹:η²-O₂CNPh)] (9 b) easily. Complex 2 a could undergo the selective μ₃-Me abstraction reaction with phenyl acetylene to give the mixed imido/alkynide complex [L₃Y₃(μ₂-Me)₃(μ₃-η¹:η¹:η³-NPh)(μ₃-CCPh)] (10 a) in high yield. Treatment of 2 with one equivalent of thiophenol gave the selective μ₃-methyl-abstracted products [L₃Ln₃(μ₂-Me)₃(μ₃-η¹:η¹:η³-NPh)(μ₃-SPh)] (Ln=Y (11 a); Lu (11 b). All new complexes have been characterized by elemental analysis, NMR spectroscopy, and most of the structures confirmed by X-ray diffraction.

A convenient and efficient method for the synthesis of polysubstituted indenes has been developed by the iron(III) trichloride-catalyzed tandem mono- and dibenzylation/cyclization reactions of benzylic alcohols with alkynes. This method is featured with the easily available starting materials, cheap catalyst, simple manipulation and mild conditions.

Unsolvated, trinuclear, homometallic, rare-earth-metal multimethyl methylidene complexes [{(NCN)Ln(μ₂-CH₃)}₃(μ₃-CH₃)(μ₃-CH₂)] (NCN=L=[PhC{NC₆H₄(iPr-2,6)₂}₂]⁻; Ln=Sc (2 a), Lu (2 b)) have been synthesized by treatment of [(L)Ln{CH₂C₆H₄N(CH₃)₂-o}₂] (Ln=Sc (1 a), Lu (1 b)) with two equivalents of AlMe₃ in toluene at ambient temperature in good yields. Treatment of 1 with three equivalents of AlMe₃ gives the heterometallic trinuclear complexes [(L)Ln(AlMe₄)₂] (Ln=Sc (3 a), Lu (3 b)) in good yields. Interestingly, 2 can also be generated by recrystallization of 3 in THF/toluene, thereby indicating that the THF molecule can also induce CH bond activation of 2. Reaction of 2 with one equivalent of ketones affords the trinuclear homometallic oxo–trimethyl complexes [{(L)Ln(μ₂-CH₃)}₃(μ₃-CH₃)(μ₃-O)] (Ln=Sc(4 a), Lu(4 b)) in high yields. Complex 4 b reacts with one equivalent of cyclohexanone to give the methyl abstraction product [{(L)Lu(μ₂-CH₃)}₃(μ₃-OC₆H₉)(μ₃-O)] (5 b), whereas reaction of 4 b with acetophenone forms the insertion product [{(L)Lu(μ₂-CH₃)}₃{μ₃-OCPh(CH₃)₂}(μ₃-O)] (6 b). Complex 4 a is inert to ketone under the same conditions. All these new complexes have been characterized by elemental analysis, NMR spectroscopy, and confirmed by X-ray diffraction determination.

An efficient and highly selective Yb(OTf)₃-catalyzed direct substitution of the hydroxy group at the allylic and propargylic positions with a variety of heteroatom- and carbon-centered nucleophiles, such as alcohols, thiols, amines, amides and active methylene compounds has been developed. The advantages of the present catalytic system are wide availability of the starting materials, especially for tolerance to thiols, no need for dried solvents and additives, mild conditions, short time of reaction, simple manipulation and environmentally friendly catalyst that can be recovered and reused at least ten times without significant reduction of activity.