Scandium terminal imido complex [(NNNN)Sc═NDIPP] (2; NNNN = [MeC(N(DIPP))CHC(Me)(NCH2CH2NMeCH2CH2NMe2)]−, DIPP = 2,6-iPr2C6H3) reacts with 9-borabicyclononane (9-BBN) to give scandium borohydride [(NNNN(B)H)Sc(N(H)DIPP)] (3; NNNN(B)H = [MeC(N(DIPP))CHC(Me)(NCH2CH2NMeCH2CH2N(Me)CH2(BBN)]2–), and C(sp3)–H bond borylation of the NNNN ligand occurs during this reaction. In contrast, the reaction between complex 2 and catecholborane (CatBH) gives scandium catecholate [(NNNN)Sc(Cat)] (4), and B–O bond cleavage happens during this reaction. Both 3 and 4 have been well-characterized including the single-crystal X-ray diffraction analysis. Reaction of 2 with bis(catecholato)diboron (CatB–BCat) also gives a B–O bond cleavage product.

The first scandium phosphinoalkylidene complex was synthesized and structurally characterized. The complex has the shortest Sc–C bond lengths reported to date (2.089(3) Å). DFT calculations reveal the presence of a three center π interaction in the complex. This scandium phosphinoalkylidene complex undergoes intermolecular C–H bond activation of pyridine, 4-dimethylamino pyridine and 1,3-dimethylpyrazole at room temperature. Furthermore, the complex rapidly activates H2 under mild conditions. DFT calculations also demonstrate that the C–H activation of 1,3-dimethylpyrazole is selective for thermodynamic reasons and the relatively slow reaction is due to the need of fully breaking the chelating effect of the phosphino group to undergo the reaction whereas this is not the case for H2.

The reactions of rare-earth metal benzyl complexes supported by silicon-bridged boratabenzene fluorenyl ligands with PhSiH3 in toluene gave the corresponding dinuclear hydrides [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}Ln(μ-H)(THF)]2 (3-Ln; Ln = La, Nd, Gd), wherein the rare-earth metal ions are linked by both silicon-bridged boratabenzene fluorenyl ligands and hydrido ligands. The reactivity of these hydrides toward unsaturated substrates was studied. Among these, alkynides [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}Ln(μ-CCPh)]2 (4-Ln; Ln = La, Nd) were obtained via the σ-bond metathesis reaction, when 3-Ln (Ln = La, Nd) was treated with phenylacetylene. While reacting with 3-hexyne, the mono-addition product [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}Ln]2(μ-H)[μ-C(Et)C(H)Et] (5-Ln; Ln = La, Nd) was formed. Further investigations on the reactivity of 3-La displayed that benzonitrile and tert-butyl isonitrile readily inserted into the La–H bonds, affording an azomethine complex [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}La{μ-NC(H)Ph}]2 (6-La) and an N-tert-butylformimidoyl complex [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}La{μ,η2-C(H)NtBu}]2 (7-La), respectively. The reaction with N,N′-diisopropylcarbodiimide at room temperature or at 75 °C gave a dimeric complex [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}La]2(μ-H)[μ-N(iPr)CHN(iPr)] (8-La) or a monomeric complex [Me2Si(C13H8)(C5H4BNEt2)]La[N(iPr)CHN(iPr)] (9-La), respectively.

Three types of trivalent rare-earth-metal complexes supported by a monoanionic tris(pyrazolyl)methanide ligand were synthesized and structurally characterized, and the catalytic activity of the dialkyl derivatives for isoprene polymerization was investigated. Reactions of the lithium salt of tris(3,5-dimethylpyrazolyl)methanide LLi(THF) with 1 equiv of ScCl3(THF)3, YCl3, or LuCl3 in THF provided the ion-pair complexes [LLnCl3][Li(THF)4] (Ln = Sc (1), Y (2), Lu (3)). Dialkyl complexes LLn(CH2SiMe3)2(THF) (Ln = Y (4), Lu (5)) were prepared by salt metathesis of LLi(THF) with 1 equiv of [Y(CH2SiMe3)2(THF)3][BPh4] or [Lu(CH2SiMe3)2(THF)3][BPh4] in toluene. Reaction of 5 with PhSiH3 provided the unexpected alkylidene-bridged dinuclear complex L2Lu2(μ-η1:η1-3,5-(CH3)C3HN2)2(μ-CHSiMe3) (6). Complexes 1–6 were structurally characterized by single-crystal X-ray diffraction, showing that the tris(pyrazolyl)methanide ligand acts as a κ3-coordinating six-electron donor in all complexes. The dialkyl complexes catalyzed 1,4-cis polymerization of isoprene with high selectivity upon activation with borate and alkylaluminum.

A silicon-bridged boratabenzene fluorenyl ligand [Me2Si(C13H8)(C5H4BNEt2)]2– (L2–) was designed and synthesized. By employment of this ligand, two divalent rare-earth metal complexes [Me2Si(C13H8)(C5H4BNEt2)]Ln(THF)2 (Ln = Sm (1), Yb (2)) were obtained from salt metathesis of K2[Me2Si(C13H8)(C5H4BNEt2)] (K2L) with LnI2(THF)2 in THF. Complex 2 undergoes redox reaction with cyclooctatetraene to give a trivalent Yb complex [(C8H8)Yb]2[μ-{Me2Si(C13H8)(C5H4BNEt2)}2] (3), accompanied with oxidative coupling of two fluorenyl groups. A series of chloro-bridged trimeric trivalent rare-earth metal complexes [Li(THF)4]2[{[Me2Si(C13H8)(C5H4BNEt2)]Ln(μ-Cl)Li(THF)3}3(μ-Cl)3(μ3-Cl)2] (Ln = Nd (4), Sm (5), and Gd (6)) were synthesized by reactions of Li2[Me2Si(C13H8)(C5H4BNEt2)] (Li2L) with LnCl3 in THF. Treatment of K2[Me2Si(C13H8)(C5H4BNEt2)] (K2L) with LnI3(THF)n gave the monomeric complexes [Me2Si(C13H8)(C5H4BNEt2)]LnI(THF) (Ln = La (7), Nd (8), Sm (9), and Gd (10)). These iodides were subsequently reacted with K[CH2C6H4-o-NMe2] to afford THF coordinated benzyl complexes [Me2Si(C13H8)(C5H4BNEt2)]Ln(CH2C6H4-o-NMe2)(THF) (Ln = La (11), Nd (12), and Gd (13a)) and non-THF coordinated complex [Me2Si(C13H8)(C5H4BNEt2)]Gd(CH2C6H4-o-NMe2) (13b).

Four mono(boratabenzene) rare-earth metal dialkyl complexes, [(3,5-Me2-C5H3BR)Ln(CH2SiMe3)2(THF)] (1: R = NEt2, Ln = Sc; 2: R = NEt2, Ln = Lu; 3: R = Ph, Ln = Sc; 4: R = Ph, Ln = Lu), were synthesized efficiently via a one-pot strategy with Li[3,5-Me2-C5H3BR] (R = NEt2, Ph), LnCl3(THF)x (Ln = Sc, x = 3; Ln = Lu, x = 0), and LiCH2SiMe3. The solid-state structures of 1 and 2 were determined by single-crystal X-ray diffraction. Variable-temperature NMR studies indicated that the energy barrier for the rotation of aminoboratabenzene in 1 (ΔG‡ ≈ 71 kJ mol−1) is higher than that of phenylboratabenzene in 3 (ΔG‡ ≈ 59 kJ mol−1). These mono(boratabenzene) rare-earth metal dialkyl complexes’ catalytic behaviors for styrene polymerization were investigated, and found that mono(boratabenzene) scandium dialkyl complexes show high catalytic activities for syndiotactic polymerization upon activation with cocatalysts.

Rare-earth metal phosphido methyl complexes, [LLn(Me){P(H)Ar}] (L = [MeC{N(DIPP)}CHC(Me)(NCH2CH2NMe2)]−, DIPP = 2,6-iPr2C6H3; 1: Ln = Sc, Ar = 2,4,6-tBu3C6H2; 2: Ln = Sc, Ar = 2,6-iPr2C6H3; 3: Ln = Sc, Ar = 2,6-Me2C6H3; 4: Ln = Lu, Ar = 2,4,6-tBu3C6H2; 5: Ln = Lu, Ar = 2,6-iPr2C6H3), were synthesized and characterized. Complexes 1–5 reacted with triphenylphosphine oxide (Ph3PO) to give [LLn(Ph){CH2P(O)Ph2}] (Ln = Sc(6), Lu(7)), by a mechanism that includes C(alkyl)–P bond formation and C(aryl)–P bond cleavage. The molecular structures of 1, 3 and 7 were determined by single-crystal X-ray diffraction. A pathway for the formation of 6 and 7 was suggested.

The scandium complex bearing both methylidene and phosphinidene ligands, [(LSc)2(μ2-CH2)(μ2-PDIPP)] (L = [MeC(NDIPP)CHC(NDIPP)Me]−, DIPP = 2,6-(iPr)2C6H3) (2), has been synthesized, and its reactivity has been investigated. Reaction of scandium methyl phosphide [LSc(Me){P(H)DIPP}] with 1 equiv of scandium dimethyl complex [LScMe2] in toluene at 60 °C provided complex 2 in good yield, and the structure of complex 2 was determined by single-crystal X-ray diffraction. Complex 2 easily undergoes nucleophilic addition reactions with CO2, CS2, benzonitrile, and tert-butyl isocyanide. In the above reactions, the unsaturated substrates insert into the Sc–C(methylidene) bond to give some interesting dianionic ligands while the Sc–P(phosphinidene) bond remains untouched. The bonding situation of complex 2 was analyzed using DFT methods, indicating a more covalent bond between the scandium ion and the phosphinidene ligand than between the scandium ion and the methylidene ligand.

A series of tris(boratabenzene) lanthanum complexes were synthesized and structurally characterized. Salt elimination of anhydrous LaCl3 with Li[C5H5BR] (R = H, NEt2) provided tris(boratabenzene) lanthanum complexes [C5H5BH]3LaLiCl (1) and [C5H5BNEt2]3LaLiCl(THF) (2) in high yields. Hydroboration of 1-hexene or 3-hexyne with 1 gave the alkyl- or alkenyl-functionalized boratabenzene lanthanum complexes, [C5H5B(CH2)5CH3]3LaLiCl(THF) (3) and [C5H5BC(C2H5)═CH(C2H5)]3LaLiCl(THF) (4), in good yields. Hydroboration of N,N′-diisopropylcarbodiimide with 1 gave the monohydroboration product [C5H5BN(iPr)CHN(iPr)][C5H5BH]2La (5) due to the steric bulk of the [C5H5BN(iPr)CHN(iPr)]− ligand. Complex 5 can undergo further hydroboration with 3-hexyne or dehydrogenative coupling with phenyl acetylene to afford [C5H5BN(iPr)CHN(iPr)][C5H5BC(C2H5)═CH(C2H5)]2La (6) or [C5H5BN(iPr)CHN(iPr)][C5H5BC≡CPh)]2La (7).

A stable scandium-terminal imido complex is activated by borane to form an unsaturated terminal imido complex by removing the coordinated Lewis base, 4-(dimethylamino)pyridine, from the metal center. The ensuing terminal imido intermediate can exist as a THF adduct and/or undergo cycloaddition reaction with an internal alkyne, C–H activation of a terminal alkene, and dehydrofluorination of fluoro-substituted benzenes or alkanes at room temperature. DFT investigations further highlight the ease of C–H activation for terminal alkene and fluoroarene. They also shed light on the mechanistic aspects of these two reactions.

The four-coordinate scandium phosphinidene complex, [LSc(μ-PAr)]2 (L = (MeC(NDIPP)CHC(Me)(NCH2CH2N(iPr)2)), DIPP = 2,6-(iPr)2C6H3; Ar = 2,6-Me2C6H3) (1), has been synthesized in good yield, and its reactivity has been investigated. Although 1 has a bis(μ-phosphinidene)discandium structural unit, this coordinatively unsaturated complex shows high and versatile reactivity toward a variety of substrates. First, two-electron reduction occurs when substrates as 2,2′-bipyridine, elemental selenium, elemental tellurium, Me3P═S, or Ph3P═E (E = S, Se) is used, resulting in the oxidative coupling of two phosphinidene ligands 2[PAr]2– into a diphosphene ligand [ArP-PAr]2–. Complex 1 easily undergoes nucleophilic addition reactions with unsaturated substrates, such as benzylallene, benzonitrile, tert-butyl isocyanide, and CS2. This complex also shows a peculiar reactivity to CO and Mo(CO)6, that includes C–P bond formation, C–C coupling and C–O bond cleavage of CO, to afford novel phosphorus-containing products. In the last two types of reactivity, reaction profiles have been computed (for the insertion of tBuNC and the CO activation by 1) at the DFT level. The unexpected/surprising sequence of steps in the latter case is also revealed.

The synthesis, structural characterization, and reactivity of the first example of a scandium -substituted nitrilimine are presented. This unique complex exhibits high thermal stability but shows a rich reactivity toward a variety of unsaturated substrates, including aldehyde, ketone, nitrile, and allene derivatives. The versatility of the complex was further highlighted by density functional theory mechanistic studies.

Catalytic activity of rare-earth metal complexes for dehydrocoupling of Me2NH·BH3 is deeply ligand- and metal ion-dependent, and 1-methyl boratabenzene yttrium alkyl shows very high activity for the reaction (TOF > 1000 h–1). The transformation of Me2NH·BH3 into [Me2N–BH2]2 proceeds through an intermediate Me2NH–BH2–NMe2–BH3.Keywords: boratabenzene; dehydrocoupling; N,N-dimethylamine borane; rare-earth metal

The facile and reversible addition of the Si–H bond of phenylsilane to the Sc═N bond of the scandium terminal imido complex [LSc═NDIPP(DMAP)] (1; L ═ [MeC(N(DIPP))CHC(Me)(NCH2CH2NMe)]−, DIPP = 2,6-iPr2C6H3) is reported. The reaction gives the scandium anilido hydride [LSc(H)(N(DIPP)(SiH2Ph))] (2), and a labeling experiment shows a rapid σ-bond metathesis between Sc–H of the formed scandium anilido hydride and Si–H of phenylsilane during the reaction. 2 was trapped by an insertion reaction with diphenylcarbodiimide, giving the stable scandium anilido amidinate [LSc(N(DIPP)(SiH2Ph))(κ2(N,N′)-PhNCHNPh)] (3). Furthermore, the scandium terminal imido complex can efficiently catalyze the hydrosilylation of N-benzylidenepropan-1-amine. The reaction was completed within 2 h at 50 °C with 5 mol % of catalyst loading and highly selectively produced the monoaminosilane.

Amidino-boratabenzenes represent a type of L3X ligand and can be regarded as the monoanionic analogues of the linked amido-cyclopentadienyl ligands. By employment of this type of ligand, 19 constrained-geometry complexes, including Sc(III), Y(III), Lu(III), Zr(IV), and Cr(III) derivatives, have been successfully prepared, and some of them showed excellent catalytic activity for ethylene polymerization upon activation.

Reactions of scandium terminal imido complexes with CuI and [M(COD)Cl]2 (M = Rh, Ir) show two interesting reaction patterns, and the formed heterobimetallic complexes have intriguing structural features and show promising catalytic properties.

Four multitopic Schiff-base ligand precursors were synthesized via condensation of 4,4′-diol-3,3′-diformyl-1,1′-diphenyl or 1,3,5-tris(4-hydroxy-5-formylphenyl)benzene with 2,6-diisopropylaniline or 2,6-dimethylaniline. Amine elimination reactions of Ln[N(SiMe3)2]3 (Ln = La, Nd, Sm or Y) with these multitopic ligand precursors gave ten heterogeneous rare-earth metal catalysts. These heterogeneous rare-earth metal catalysts are active for intramolecular hydroalkoxylation of alkynols, and the catalytic activities are influenced by the ligand and metal ion. The recycling experiment on the most active heterogeneous catalyst showed the catalyst has a good reusability.

Reactions of the yttrium anilido hydride [LY(NH(DIPP))(μ-H)]2 (1; L = [MeC(N(DIPP))CHC(Me)(NCH2CH2NMe2)]−, DIPP = 2,6-iPr2C6H3)) with three phosphine oxides and two phosphine sulfides are reported. The reaction of 1 with Ph3P═O gives C–P bond cleavage and an yttrium anilido phosphinoyl complex, while those with R2MeP═O (R = Me, Ph) result in C–H bond cleavage and two yttrium anilido alkyl complexes. 1 also reacted with R3P═S (R = Me, Ph), which demonstrated P–S bond cleavage via hydride-based reduction and gave an yttrium anilido sulfide.

The reaction between scandium terminal imido complexes and elemental selenium showed an unprecedented C–H bond selenation and the formation of an Sc–Se bond.

A series of pyridyl-1-azaallyl ligand precursors (HL1–HL5) were synthesized via condensation of pyridine ketones with anilines. The alkane elimination reactions between Y(CH2SiMe3)3(THF)2 and HL4 or HL5 gave the monoalkyl complexes (L4–H)YCH2SiMe3(THF) (1) and (L5–H)YCH2SiMe3(THF) (2) supported by new tridentate pyridyl-1-azaallyl dianionic ligands. The reactions of monoalkyl complexes, 1 and 2, with one equivalent of 2,6-diisopropylaniline produced the corresponding monoanilide complexes, (L4–H)YNHAr(THF) (3) and (L5–H)YNHAr(THF) (4) (Ar = 2,6-(iPr)2C6H3), via highly selective protonolysis of the terminal alkyl Y–CH2SiMe3 bond. Complexes 1–4 are active for intramolecular hydroamination of aminoalkenes.

Reactions of the ansa-heteroborabenzene divalent ytterbium amide [C5H5BCH2(CH3)2P→BC5H5]YbN(SiMe3)2 (1) with alkali-metal salts (KC5Me5, NaOiPr, NaOAr, LiNHAr, LiN(SiMe3)2, LiNEt2, and KCH2Ar) were studied. The reaction of 1 with KC5Me5 caused a ligand displacement of neutral borabenzene by KC5Me5 at the Yb ion to give a heterometallic Yb−K boratabenzene complex with a polymeric structure, while that with NaOiPr caused a ligand displacement of the anionic amido ligand at the Yb ion by an isopropoxyl ligand to give a heterometallic Yb−Na boratabenzene complex with a polymeric structure. When LiNEt2 or KCH2Ar was employed as the reagent, the [NEt2]− or [CH2Ar]− group underwent nucleophilic attack at the B atom on the neutral borabenzene to cause the disassociation of the P→B coordination bond and the generation of new boratabenzene ligands.

The hydroboration of alkenes, alkynes, imines, and carbodiimides using the anionic 1-H-boratabenzene ligand bound to rare-earth (RE = Y, Lu), transition (Zr and Rh), and main-group (Li) metals is reported. This hydroboration is metal ion dependent; in the case of 1-H-boratabenzene transition metal complexes, the reactivity follows the trend RE > Zr > Rh. Hydroboration with 1-H-boratabenzene rare-earth metal complexes works well for a range of unsaturated substrates, including 1-hexene, allyl propyl ether, allyl ether, 3-hexyne, benzylidene-n-propylamine, and N,N′-diisopropylcarbodiimide, thus generating a series of new alkyl-, alkenyl-, amino-, or amidino-functionalized boratabenzene rare-earth metal complexes in high yields. The reactions are highly anti-Markovnikov selective, and the mechanism has been investigated by deuterium-labeling experiments. In comparison, a 1-H-boratabenzene Zr complex reacts with benzylidene-n-propylamine and N,N′-diisopropylcarbodiimide, and a 1-H-boratabenzene Rh complex reacts with N,N′-diisopropylcarbodiimide. In contrast, the 1-H-boratabenzene lithium salt reacts only with the activated substrate benzylidene-n-propylamine at elevated temperature to give the corresponding hydroboration product. Boratabenzene Y complexes undergo ligand redistribution with Rh chlorides to give boratabenzene Rh complexes. Studies of the novel monoanionic amidino-boratabenzene ligand by X-ray diffraction and DFT calculations have revealed interesting structural features.

The synthesis, structure, and reactivity of the yttrium anilido hydride [LY(NH(DIPP))(μ-H)]2 (3; L = [MeC(N(DIPP))CHC(Me)(NCH2CH2NMe2)]−, DIPP = 2,6-iPr2C6H3)) are reported. The protonolysis reaction of the yttrium dialkyl [LY(CH2SiMe3)2] (1) with 1 equiv of 2,6-diisopropylaniline gave the yttrium anilido alkyl [LY(NH(DIPP))(CH2SiMe3)] (2), and a subsequent σ-bond metathesis reaction of 2 with 1 equiv of PhSiH3 offered the yttrium anilido hydride 3. The structure of 3 was characterized by X-ray crystallography, which showed that the complex is a μ-H dimer. 3 shows high reactivity toward a variety of unsaturated substrates, including imine, azobenzene, carbodiimide, isocyanide, ketone, and Mo(CO)6, giving some structurally intriguing products.

The first rare earth metal terminal imido complex has been isolated and structurally characterized. The complex has an extremely short M–N bond length and a nearly linear M–N–C angle. DFT studies showed two p orbitals of Nimido atom form two bonds with two d orbitals of rare earth metal ion.

Synthesis of new neodymium(III) phosphinidene complexes from a neodymium(III) phosphinidene iodide [(μ-PC6H3-2,6-iPr2)Nd(I)(THF)3]2 (1) was studied. The metathesis reaction of 1 with KC5Me5 (KCp*) gave a neodymium(III) pentamethylcyclopentadienyl phosphinidene complex [(μ-PC6H3-2,6-iPr2)(C5Me5)Nd(THF)]2 (2), and that with potassium hydrotris(pyrazolyl)borate KHB(3-phenylpz)3 (KTpPh) generated a neodymium(III) hydrotris(pyrazolyl)borate phosphinidene complex [(μ-PC6H3-2,6-iPr2)(TpPh*)Nd(THF)]2 (3) and a C–H bond activation byproduct [κ4(N,N′,N″,CPh)-TpPh]TpPhNd (4). Complexes 2–4 have been characterized by single-crystal X-ray diffraction analysis.

A new β-diketimine bearing the pendant pyridyl group, CH3C(2,6-(iPr)2C6H3NH)CHC(CH3)(NCH2–C5NH4) (L1), was synthesized. The reaction of L1 with one equivalent of Sc(CH2SiMe3)3(THF)2 at room temperature gave a singly deprotonated product (L1−H)Sc(CH2SiMe3)2 (1). Y(CH2SiMe3)3(THF)2 under the same conditions led to the unexpected dimer [(L1−H3)Y(THF)]2 (2), in which the ligand precursor L1 was triply deprotonated. The reaction of L1 with Y(CH2SiMe3)3(THF)2 at −35 °C provided a mixture of singly deprotonated product (L1−H)Y(CH2SiMe3)2 (3) and doubly deprotonated product (L1−H2)Y(CH2SiMe3)(THF)2 (4). The reactions of L1 with Ln[N(SiMe3)2]3 gave only singly deprotonated products (L1−H)Ln[N(SiMe3)2]2 (5: Ln = Y; 6: Ln = La). The complexes 1, 2 and 4–6 have been characterized by single-crystal X-ray diffraction.

A series of solvent-free boratabenzene rare-earth metal alkyl complexes (C5H5BR)2LnCH(SiMe3)2 (9: R = NEt2, Ln = Y; 10: R = NPh2, Ln = Y; 11: R = CH3, Ln = Y; 12: R = NPh2, Ln = Sm; 13: R = NPh2, Ln = Dy; 14: R = NEt2, Ln = Lu; 15: R = NPh2, Ln = Lu; 16: R = Me, Ln = Lu) were synthesized. The solid-state structures of 10, 13, and 15 were determined by single-crystal X-ray diffraction. The crystal structures of 10, 13, and 15 feature highly unsymmetrical coordination of the alkyl ligands and short Ln−C(alkyl) distances. The diamagnetic yttrium and lutetium alkyl complexes, 9−11 and 14−16, were characterized by (1H, 13C, 11B) NMR spectroscopy. The Ln−CαHα (1H NMR: δ 0.68−0.99 ppm) and Ln−CαHα (13C NMR: δ 33.9−39.1 ppm) resonances of these boratabenzene rare-earth metal alkyl complexes are rather downfield in comparison with those of the bis-Cp rare-earth metal alkyl complexes. 89Y NMR spectra of the boratabenzene yttrium alkyl complexes 9−11 and the Cp complex (C5H4Me)2YCH(SiMe3)2 were recorded. The 89Y NMR chemical shifts for 9, 10, and 11 are 176.1, 170.0, and 162.2 ppm, respectively, which are significantly downfield in comparison with that of (C5H4Me)2YCH(SiMe3)2 (44.0 ppm).

Reactions of 1,3-bis(trimethylsilyl)indene with Ln(CH2SiMe3)3(THF)2 gave half-sandwich rare earth metal complexes (1,3-(SiMe3)2C9H5)Ln(CH2SiMe3)2(THF) (Ln = Y, Lu, Dy). These complexes were characterized by single-crystal X-ray diffraction, which showed the η5 hapticity of indenyl ligands in all of the complexes. The catalytic behaviors of the complexes for intramolecular hydroamination of aminoalkenes were investigated. The catalytic activity increased with increasing the metal ion size, and the Y and Dy complexes showed excellent activities to a variety of aminoalkenes.

Four discrete half-sandwich dialkyl rare earth metal (REM) complexes incorporating a disilylated indenyl ligand, (1,3-(SiMe3)2C9H5)M(CH2SiMe3)2(THF) (M = Sc, Y, Dy, Lu), have been investigated for the coordination−addition polymerization of naturally renewable methylene butyrolactones, α-methylene-γ-butyrolactone (MBL) and γ-methyl-α-methylene-γ-butyrolactone (MMBL). Initial screening for the polymerization of methyl methacrylate highlighted several differences in catalytic behavior between these half-sandwich REM catalysts and well-studied sandwich REM catalysts in terms of reactivity trend, polymer tacticity, and solvent dependence. Most significantly, all four catalysts herein exhibit exceptional activity for polymerization of MMBL in DMF, achieving quantitative monomer conversion in <1 min with a 0.20 mol % catalyst loading and giving a high turnover frequency of >30 000 h−1. Slower polymerizations occur in CH2Cl2, allowing for establishment of the activity trend within this REM series, which follows: Dy (largest ion) ≥ Y > Lu > Sc (smallest ion). The most active and effective Dy catalyst has been examined in detail, demonstrating its ability to control the polymerization for producing PMMBL with high Tg (221 °C) and with molecular weight ranging from a medium Mn of 1.89 × 104 Da to a high Mn of 1.63 × 105 Da, programmed by the [MMBL]/[Dy] ratio. Kinetic experiments have revealed a first-order dependence on [monomer] and a second-order dependence on [REM]. These kinetic results, coupled to catalyst efficiencies, NMR studies, as well as with chain-end group analysis by MALDI-TOF mass spectrometry, have yielded a chain initiation mechanism that involves both alkyl groups on each metal center and a bimolecular chain propagation that involves two metal centers in the rate-limiting C−C bond forming step. The Dy catalyst response to enolizable organo acids, externally added as chain-transfer agents, has also been examined.

A new class of β-diketiminato derivative dianionic ligands was designed, and three ligand precursors [CH3C(ArNH)CHC(CH3)(NCH2CH2-NHR)] (Ar = 2,6-(iPr)2C6H3; R = tBu (H2L1), 2,6-(CH3)2C6H3 (H2L2), 2,6-(iPr)2C6H3 (H2L3)) were synthesized. The alkane elimination reactions between these ligand precursors and Ln(CH2SiMe3)3(THF)n provided eight five-coordinate monoalkyllanthanide complexes, in which the ligand serves as a tridentate dianionic donor, with one −CH2SiMe3 and one THF molecule completing the five-coordinate center. These monoalkyl complexes exhibited low to very high catalytic activities for intramolecular hydroamination of 2,2-dimethyl-1-aminopent-4-ene. The catalytic activity increased with increasing metal ion size. For the Nd complex, 98% yield was obtained in 1 h at 60 °C with 0.5 mol % catalyst loading.

The synthesis and structural characterization of an unprecedented lanthanide phosphinidene species [(THF)3(I)Nd(μ-PC6H3-2,6-iPr2)]2 are described; the phosphinidene moiety in this complex reacts as a carbene.

Three new tridentate NNN ligand precursors, CH3C(2,6-(iPr)2C6H3NH)CHC(CH3)(NCH2CH2−D) (D = NMe2, NEt2, N((CH2CH2)2CH2)), were synthesized. Subsequent metalations with in situ generated Ln(CH2SiMe3)3(THF)n (Ln = Nd, Sm, Y, Lu) provided six solvent-free dialkyllanthanide complexes. Five of the lanthanide complexes were characterized by single-crystal X-ray diffraction, which showed that the pendant arm D bonds to the lanthanide ion in the solid state. The NMR spectra of these complexes in C6D6 showed that such coordination is retained in solution. These dialkyllanthanide complexes show high activities for the ring-opening polymerization of ϵ-caprolactone, in which narrow-polydispersity polymers were produced. The size of the pendant arm has a significant effect on the molecular weight of the polymer obtained. In comparison to the Y complex with a −NMe2 group, the Y complexes with −NEt2 and −N((CH2CH2)2CH2) groups yield much higher molecular weight polymer (60 000 vs 20 000).

The boratabenzene derivative of divalent ytterbium complex (C5H5BNPh2)2Yb(THF)2 (1) was synthesized and characterized. Reaction of 1 with α-diimine PhNC(Me)C(Me)NPh in toluene afforded a trivalent ytterbium complex, [C5H5BNPh2]2Yb[PhNC(Me)C(Me)NPh] (2), which was characterized by single-crystal X-ray diffraction. The redox process is solvent sensitive and reversible.

Several solvent-free boratabenzene yttrium chlorides were synthesized and structurally characterized. Their reactions with KN(SiMe3)2 first gave boratabenzene yttrium amides; the latter reacted further with KN(SiMe3)2, which results in π-ligand displacement. The boratabenzene yttrium amides showed good catalytic activities for intramolecular hydroamination.

The preparation and characterization of the complexes (C5H5BXPh2)2Sm(THF)2 (X = N (1), P (2)), the first boratabenzene derivatives of a divalent lanthanide metal, are reported. Their solid-state structures display different structural features arising from the different degrees of B−X π interactions. Complexes 1 and 2 initiate the polymerization of methyl methacrylate (MMA) to a highly syndiotactic and atactic PMMA, respectively.

The reactions of rare-earth metal benzyl complexes supported by silicon-bridged boratabenzene fluorenyl ligands with PhSiH3 in toluene gave the corresponding dinuclear hydrides [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}Ln(μ-H)(THF)]2 (3-Ln; Ln = La, Nd, Gd), wherein the rare-earth metal ions are linked by both silicon-bridged boratabenzene fluorenyl ligands and hydrido ligands. The reactivity of these hydrides toward unsaturated substrates was studied. Among these, alkynides [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}Ln(μ-CCPh)]2 (4-Ln; Ln = La, Nd) were obtained via the σ-bond metathesis reaction, when 3-Ln (Ln = La, Nd) was treated with phenylacetylene. While reacting with 3-hexyne, the mono-addition product [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}Ln]2(μ-H)[μ-C(Et)C(H)Et] (5-Ln; Ln = La, Nd) was formed. Further investigations on the reactivity of 3-La displayed that benzonitrile and tert-butyl isonitrile readily inserted into the La–H bonds, affording an azomethine complex [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}La{μ-NC(H)Ph}]2 (6-La) and an N-tert-butylformimidoyl complex [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}La{μ,η2-C(H)NtBu}]2 (7-La), respectively. The reaction with N,N′-diisopropylcarbodiimide at room temperature or at 75 °C gave a dimeric complex [{μ-[Me2Si(C13H8)(C5H4BNEt2)]}La]2(μ-H)[μ-N(iPr)CHN(iPr)] (8-La) or a monomeric complex [Me2Si(C13H8)(C5H4BNEt2)]La[N(iPr)CHN(iPr)] (9-La), respectively.

A series of new sandwich type lanthanide complexes containing both boratabenzene and cyclooctatetraenyl ligands, [(C5H5BR)Ln(COT)] (1Er: R = H, Ln = Er; 2Er: R = Me, Ln = Er; 3Er: R = NEt2, Ln = Er; 4Dy: R = H, Ln = Dy; 5Dy: R = Me, Ln = Dy; 6Dy: R = NEt2, Ln = Dy; 7Y: R = NEt2, Ln = Y), were synthesized. The structures of 1Er–7Y were all characterized by single crystal X-ray diffraction. Dynamic susceptibility experiments showed that the erbium complexes 1Er–3Er exhibited slow magnetic relaxation under zero dc field while the dysprosium complexes 4Dy–6Dy did not. For the erbium complexes, the magnetic properties were influenced by the substituent on the boron atom. 1Er exhibited hysteresis up to 8 K, and 2Er featured the highest energy barrier (300 cm−1) among all the reported erbium single-ion magnets (SIMs). The influence of the boron substituent on the magnetic properties was highlighted by ab initio calculations.

Reactions of scandium terminal imido complexes with CuI and [M(COD)Cl]2 (M = Rh, Ir) show two interesting reaction patterns, and the formed heterobimetallic complexes have intriguing structural features and show promising catalytic properties.

The reaction between scandium terminal imido complexes and elemental selenium showed an unprecedented C–H bond selenation and the formation of an Sc–Se bond.

The first rare earth metal terminal imido complex has been isolated and structurally characterized. The complex has an extremely short M–N bond length and a nearly linear M–N–C angle. DFT studies showed two p orbitals of Nimido atom form two bonds with two d orbitals of rare earth metal ion.

The synthesis and structural characterization of an unprecedented lanthanide phosphinidene species [(THF)3(I)Nd(μ-PC6H3-2,6-iPr2)]2 are described; the phosphinidene moiety in this complex reacts as a carbene.

Four mono(boratabenzene) rare-earth metal dialkyl complexes, [(3,5-Me2-C5H3BR)Ln(CH2SiMe3)2(THF)] (1: R = NEt2, Ln = Sc; 2: R = NEt2, Ln = Lu; 3: R = Ph, Ln = Sc; 4: R = Ph, Ln = Lu), were synthesized efficiently via a one-pot strategy with Li[3,5-Me2-C5H3BR] (R = NEt2, Ph), LnCl3(THF)x (Ln = Sc, x = 3; Ln = Lu, x = 0), and LiCH2SiMe3. The solid-state structures of 1 and 2 were determined by single-crystal X-ray diffraction. Variable-temperature NMR studies indicated that the energy barrier for the rotation of aminoboratabenzene in 1 (ΔG‡ ≈ 71 kJ mol−1) is higher than that of phenylboratabenzene in 3 (ΔG‡ ≈ 59 kJ mol−1). These mono(boratabenzene) rare-earth metal dialkyl complexes’ catalytic behaviors for styrene polymerization were investigated, and found that mono(boratabenzene) scandium dialkyl complexes show high catalytic activities for syndiotactic polymerization upon activation with cocatalysts.

Synthesis of new neodymium(III) phosphinidene complexes from a neodymium(III) phosphinidene iodide [(μ-PC6H3-2,6-iPr2)Nd(I)(THF)3]2 (1) was studied. The metathesis reaction of 1 with KC5Me5 (KCp*) gave a neodymium(III) pentamethylcyclopentadienyl phosphinidene complex [(μ-PC6H3-2,6-iPr2)(C5Me5)Nd(THF)]2 (2), and that with potassium hydrotris(pyrazolyl)borate KHB(3-phenylpz)3 (KTpPh) generated a neodymium(III) hydrotris(pyrazolyl)borate phosphinidene complex [(μ-PC6H3-2,6-iPr2)(TpPh*)Nd(THF)]2 (3) and a C–H bond activation byproduct [κ4(N,N′,N″,CPh)-TpPh]TpPhNd (4). Complexes 2–4 have been characterized by single-crystal X-ray diffraction analysis.

A new β-diketimine bearing the pendant pyridyl group, CH3C(2,6-(iPr)2C6H3NH)CHC(CH3)(NCH2–C5NH4) (L1), was synthesized. The reaction of L1 with one equivalent of Sc(CH2SiMe3)3(THF)2 at room temperature gave a singly deprotonated product (L1−H)Sc(CH2SiMe3)2 (1). Y(CH2SiMe3)3(THF)2 under the same conditions led to the unexpected dimer [(L1−H3)Y(THF)]2 (2), in which the ligand precursor L1 was triply deprotonated. The reaction of L1 with Y(CH2SiMe3)3(THF)2 at −35 °C provided a mixture of singly deprotonated product (L1−H)Y(CH2SiMe3)2 (3) and doubly deprotonated product (L1−H2)Y(CH2SiMe3)(THF)2 (4). The reactions of L1 with Ln[N(SiMe3)2]3 gave only singly deprotonated products (L1−H)Ln[N(SiMe3)2]2 (5: Ln = Y; 6: Ln = La). The complexes 1, 2 and 4–6 have been characterized by single-crystal X-ray diffraction.

Four multitopic Schiff-base ligand precursors were synthesized via condensation of 4,4′-diol-3,3′-diformyl-1,1′-diphenyl or 1,3,5-tris(4-hydroxy-5-formylphenyl)benzene with 2,6-diisopropylaniline or 2,6-dimethylaniline. Amine elimination reactions of Ln[N(SiMe3)2]3 (Ln = La, Nd, Sm or Y) with these multitopic ligand precursors gave ten heterogeneous rare-earth metal catalysts. These heterogeneous rare-earth metal catalysts are active for intramolecular hydroalkoxylation of alkynols, and the catalytic activities are influenced by the ligand and metal ion. The recycling experiment on the most active heterogeneous catalyst showed the catalyst has a good reusability.

A series of pyridyl-1-azaallyl ligand precursors (HL1–HL5) were synthesized via condensation of pyridine ketones with anilines. The alkane elimination reactions between Y(CH2SiMe3)3(THF)2 and HL4 or HL5 gave the monoalkyl complexes (L4–H)YCH2SiMe3(THF) (1) and (L5–H)YCH2SiMe3(THF) (2) supported by new tridentate pyridyl-1-azaallyl dianionic ligands. The reactions of monoalkyl complexes, 1 and 2, with one equivalent of 2,6-diisopropylaniline produced the corresponding monoanilide complexes, (L4–H)YNHAr(THF) (3) and (L5–H)YNHAr(THF) (4) (Ar = 2,6-(iPr)2C6H3), via highly selective protonolysis of the terminal alkyl Y–CH2SiMe3 bond. Complexes 1–4 are active for intramolecular hydroamination of aminoalkenes.