Hydrogenolysis of [(TpAd,iPr)Sr{CH(SiMe3)2}] (1) (TpAd,iPr = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate) in hexane solution under 20 atm of H2 allowed for the isolation of strontium hydride [(TpAd,iPr)Sr(μ-H)]2 (2) in good yield. Complex 2 exhibits the dimeric nature in solid state, featuring two different bond modes between the Sr center and TpAd,iPr ligand. Treatment of complex 2 with PhC(H)═NtBu or PhCH2Bpin (Bpin = pinacolateborane) afforded the strontium amide complex [(TpAd,iPr)Sr{N(CH2Ph)(tBu)}] (4) and hydroborate complex [(TpAd,iPr)Sr{μ-HBpin(CH2Ph)}] (5), respectively. Reactions of complex 2 with 2-picoline, 2-phenylquinoline, or 2-phenylpyridine led to the formation of strontium 2-pyridylmethylene/2-picoline complex [(TpAd,iPr)Sr(2-CH2-Py)(2-picoline)] (6), reductively coupling diphenyl-biquinolide complex [{(TpAd,iPr)Sr}2(2,2'-Ph2-4,4'-dihydro-4,4'-biquinolide)] (7), and diphenyl-bipyridyl radical complex [(TpAd,iPr)Sr(6,6'-Ph2-2,2'-bipyridyl)] (8), separately. All of the complexes have been well characterized, including NMR spectrum and single-crystal X-ray analysis.

Molecular thorium complexes are dominated by stable tetravalent thorium, while subvalent thorium and the relevant synthons are very limited. Herein, we report that hydrogenolysis of the half-sandwich penta-arylcyclopentadienyl-supported thorium tribenzyl complex [(CpAr5)Th(p-CH2-C6H4-Me)3] (1) (CpAr5 = C5Ar5, Ar = 3,5-iPr2-C6H3) affords the double-sandwich bimetallic hydride complex [(CpAr5)Th(μ-H)]2 (2), in which one of the five aryl groups in the CpAr5 ligand is selectively reduced to a puckered di-anionic 1,4-cyclohexadienyl. Complex 2 can be regarded as a thorium(ii) hydride synthon, and exhibits unique redox-active reactivity towards various substrates. Complex 2 not only serves as the six-electron transfer reagent in the reduction of Te and N3SiMe3, leading to the formation of [(CpAr5)Th(THF)]2(μ-Te)3 (3) and [(CpAr5)Th(μ-N3)(μ-NSiMe3)]2 (4), but also promotes the four-electron reductive coupling of CS2 and benzonitrile accompanied by Th-H addition, resulting in the isolation of [(CpAr5)Th(μ-η2:η2-CS3)(μ-S)(μ-η4:η1-SCH[double bond, length as m-dash]CHS)Th(CpAr5)] (5) and [(CpAr5)Th(PhCN)2(μ-NCH2Ph){η1,κ3-NC(Ph)[double bond, length as m-dash]C(Ph)NC(Ph)[double bond, length as m-dash]NC(Ph)[double bond, length as m-dash]N}Th(CpAr5)] (6) respectively.

A series of bridged beta-pyridyl-enamino dinuclear aluminum complexes 1-6 were prepared in high yields, where complexes 1, 2, 3, 5 and 6 were characterized by single-crystal X-ray diffraction. The distance between two Al centers in 1-3 was in the range of 3.7-5.8 & Aring;, which is far shorter than that in 5 and 6 (about 8.0 & Aring;). All of these aluminum complexes were used as initiators for the ring-opening polymerization of epsilon-caprolactone in the presence of benzyl alcohol. Complexes 1-3 exhibited higher catalytic activity compared to complexes 4-6 under the same conditions, indicating that the distance between the Al atoms affects the catalytic activity. Complexes 3 and 5 with Al-Me groups exhibited higher catalytic activity than complexes 4 and 6 with Al-Et groups. This is likely due to the larger steric hindrance or the electron-donating group, which weakens the Lewis acidity of aluminum and results in a reduced reaction rate between the complexes and benzyl alcohol. Herein, two factors affect the polymerization activity in the ROP of epsilon-caprolactone: one is the distance between the two Al centers in bimetallic systems and the other is the alkyl groups on the Al atoms. The MALDI-TOF mass spectra of the polymers revealed that the ring-opening polymerization of epsilon-caprolactone catalyzed by these catalysts yields linear polycaprolactones with controlled molecular weights, narrow distributions and end-group fidelity.

Although significant breakthroughs in stereoselective polymerization of polar styrene derivatives have been achieved during the past decades by using well-defined rare-earth catalysts, the isospecific polymerization of aminostyrenes still faces formidable challenges from the scarcity of highly isoselective catalysts and the poison effect of amino groups. Here we report the isospecific polymerization of a bulky silyl-protected aminostyrene 4-(CH2=CH)-C6H4-N[Me2Si(CH2)-](2) (p-DSAS) by using a single-component racemic ansa-bridged bis(indenyl) yttrium catalyst [{(Ind)(2)CMe2}Y(CH2SiMe3)(THF)] (1) to gave poly(p-DSAS) with perfect isoselectivity (mmmm > 99 %). The first isotactic polystyrene containing primary amino groups and its hydrochloride derivative were successfully achieved by deprotection of poly(p-DSAS). Additionally, deprotection of poly(p-DSAS) with glacial acetic acid followed by thermal treatment afforded the isotactic polystyrene bearing N-acetamido groups. Through the diazotization-mediated post-functionalization, we successfully transformed the isotactic poly(4-vinylaniline) hydrochloride derivative to isotactic polystyrenes containing a variety of functional groups such as cyanide, azide and hydrazonide via the reaction of a diazonium salt intermediate with diverse substrates.

Neutral inverse-sandwich lanthanum arene complexes with the parent benzene tetraanion are still limited. Here, we report the neutral inverse-sandwich lanthanum benzene complexes [(CpAr5)La(THF)n]2(μ-η6:η6-C6H6) (CpAr5 = η5-C5Ar5, Ar = iPr2-C6H3-3,5; n = 0, 2; n = 1, 2-THF) supported by a superbulky penta-arylcyclopentadienyl ligand. Complex 2 was isolated from the reduction of the half-sandwich lanthanum diiodide precursor [(CpAr5)LaI2(THF)2] (1) in benzene by the K/KI reductant, yielding 69%. The reaction of complex 2 with 0.5 equiv of (HBBN)2 enabled C-H bond functionalization of the benzene tetraanion, generating a novel borylated product [(CpAr5)La]2(μ-η6:η6-C6H5BBN) (3). NMR analyses, single-crystal X-ray diffraction, and UV-vis spectroscopic studies demonstrated that complexes 2, 2-THF, and 3 share a [La3+-(arene)4--La3+] electronic structure, which was further confirmed by density functional theory (DFT) calculations. Moreover, treatment of complex 2 with Me3SiN3 afforded a product [(CpAr5)La{N(SiMe3)2}]2(μ-N3)2 (4) via four-electron reduction and subsequent Si-N bond activation. Additionally, the dimeric peroxo complex [(CpAr5)La(THF)]2(μ-η2:η2-O2)2 (5) was detected in the reaction of 2 with O2. The redox reactivity of 2 shows its great potential in the multielectron reduction of unsaturated substrates, functioning as a La(I) synthon.

Recent years have witnessed great achievements in the coordination polymerization of various olefins catalyzed by rare-earth metal catalysts. However, the ubiquitous monomers containing a benzocyclobutene (BCB) group, which have excellent thermal properties, remain unexplored yet. Here, we report the coordination (co)polymerization of 4-vinylbenzocyclobutene (4-VBCB) by using tetraphenylcyclopentadienyl supported scandium alkyl complex [(Cp-Ph4H)Sc(CH2SiMe3)(2)(THF)] (1) as a precatalyst. The high syndioselectivity (rrrr > 99%) was observed in both the resultant poly(4-VBCB)s and poly(St-co-VBCB)s, which are soluble in most common solvents, sharply in contrast to the typical sPS. Copolymerization of 4-VBCB with styrene afforded a gradient copolymer due to the dramatically different reactivity of the two monomers (r(VBCB)/r(St) = 84.3). Moreover, copolymerization of 4-VBCB with ethylene (2 atm) proceeded smoothly to yield ethylene-VBCB random copolymers with a variety of VBCB contents (5.2-22.7%). In the presence of maleimide, cross-linked functional polyethylene was obtained through the Diels-Alder reaction and intermolecular cross-link. More interestingly, nanoparticles based on polyethylene were successfully synthesized under ultralow concentration via intramolecular cross-linking of the ethylene-VBCB copolymer.

Well-defined low-valent molecular rare-earth metal hydrides are rare, and limited to Yb2+ and Eu2+ centers. Here, we report the first example of the divalent samarium(ii) hydrido complex [(CpAr5)SmII(μ-H)(DABCO)]2 (4) (CpAr5 = C5Ar5, Ar = 3,5-iPr2-C6H3; DABCO = 1,4-diazabicyclooctane) supported by a super-bulky penta-arylcyclopentadienyl ligand, resulting from the hydrogenolysis of the samarium(ii) alkyl complex [(CpAr5)SmII{CH(SiMe3)2}(DABCO)] (3). Complex 4 exhibits multi-electron redox reactivity toward a variety of substrates. Exposure of complex 4 to CO2 results in the formation of the trivalent samarium(iii) mixed-bis-formate/carbonate complex [(CpAr5)SmIII(μ-η2:η1-O2CH)(μ-η2:η2-CO3)(μ-η1:η1-O2CH)SmIII(CpAr5)(DABCO)] (8), mediated by hydride insertion and reductive disproportionation reactions. Complex 4 shows four-electron reduction toward four equivalents of CS2 to afford the trivalent samarium(iii) bis-trithiocarbonate complex [(CpAr5)SmIII(μ-η2:η2-CS3)(DABCO)]2 (9). A mechanistic study of the formation of complex 8 was carried out using DFT calculations.

Bi- and tetra-lithium quinolyl/pyridyl-amino complexes 1–4 were synthesized and characterized. These lithium complexes were capable of initiating the polymerization of rac-lactice (rac-LA) and ε-caprolactone (ε-CL) with high catalytic activity, respectively, whether in the presence or absence of BnOH. Both number of metal centers and ligand structures are identified as the crucial factors that determine the reactivity of a catalyst in the ROP. Their kinetic analyses indicated that tetrametallic complex 3 showed a more cooperativity comparable to that achieved with bimetallic analogues in the ring-opening polymerization (ROP) of ε-CL, however, number of metal centers has no obvious effect on catalytic activity for the ROP of rac-LA. Polymer end-group analysis by 1H NMR and MALDI-TOF MS support the reaction initiated by Li complexes without or with BnOH switching mechanism from a coordination-insertion to an active monomer in the ROP processes reasonably. The diblock copolymer PCL-b-PLA can be effectively prepared by polymerizing ε-CL firstly followed by addition of rac-LA. However, the formation of PLA-b-PCL or PLA-random-PCL is limited, and the resulting copolymers only contain a short sequence of PCL moieties which produced by the transesterification between PLA and ε-CL, whether the two monomers are added sequentially or simultaneously. Interestingly, these Li complexes not only exhibit a high activity for the polymerization of PLA, but also can fully degrade the resultant PLA into methyl lactate (Me-La) in the presence of MeOH, which is a rare example of making or breaking polymer for chemical recycling.

Recent years have witnessed great progress in the application of calcium-based catalysts in a variety of organic transformations, including hydrofuctionalization, dehydrogenative coupling, and C-H activation. However, these efficient protocols in polymer synthesis remain much less explored. Here, we report the selective bis-hydrosilylation of dienes with bis-hydrosilanes in the presence of scorpionate-supported calcium benzyl complex [(Tp(Ad,iPr))Ca(p-CH2-C6H4-Me)(THP)] (Tp(Ad,iPr) = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate, THP = tetrahydropyran) (1) to obtain linear polycarbosilanes containing a reactive SiH2 unit in the main chain. Furthermore, complex 1 can also catalyze the dehydrogenative silylation of terminal alkyne, silylamination of aniline, and C-H activation of 1-methyl-1H-indole, with the Si-H bonds in polycarbosilanes to allow the introduction of 35-65% new side chains in these polymers. The resulting new polymers contain unusual units including SiH-(C equivalent to CPh), SiH-(NHAr), and SiH-(indole), whose presence is confirmed by NMR and IR spectra.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Ring-opening metathesis polymerization (ROMP) is a strategy in which monocyclic or polycyclic olefins undergo ring-opening polymerization to form functionalized polymers. ROMP has been recognized as a powerful synthetic strategy for the synthesis of advanced polymeric materials. Recently, star polymers are receiving intense interests in materials science and nanotechnology in both academic and industrial fields due to the unique structure and property. In this review, the applications of ROMP in the synthesis of star polymers are discussed in terms of methods of polymerization, monomers, initiators and crosslinking agents. Moreover, the application fields and prospects of the ROMP synthesized star polymers, and the advantages and limitations of various ROMP methods are also presented. This work aims to promote development of ROMP in the synthesis of star-shaped polymers, provide a new scientific research approach for the synthesis of functionally complicated star-shaped polymers, and contribute to the acceleration of the commercialization of star-shaped polymer materials.

Treatment of a divalent ytterbium hydride complex [(TpAd,iPr)Yb(H)(THF)] (TpAd,iPr = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate) (1) with CO, CO2 and CS2 resulted in the formation of a divalent ytterbium ethenediolate complex [(TpAd,iPr)Yb]2(cis-OCHCHO) (2), a formate complex [(TpAd,iPr)Yb(κ2-O2CH)(THF)] (3), and a trivalent ytterbium ethenetetrathiolate complex [(TpAd,iPr)YbIII]2(C2S4) (4), respectively. DFT calculations were carried out to elucidate the reaction profiles of complexes 3 and 4.

We report a re-examination of Trofimenko's original protocol for the preparation of the acid form of his hydrotris(pyrazolyl)borates,H(Tp(R),(R)'), by the treatment of M(Tp(R,R)') with glacial acetic acid. It is concluded that the protocol is effective as long as the 3-substituent of the pyrazolyl moiety is sufficiently bulky to provide steric protection to the acidic N-H proton. The solid-state structure of H(Tp(tBu,Me)), the acid form of the popular TptBu,Me ligand is also presented.

The catalytic ortho-regioselective C-H alkylation of a variety of alkoxy-substituted benzene derivatives with alkenes can be achieved by the use of a half-sandwich calcium alkyl complex [(Cp-Ar5)Ca{CH(SiMe3)(2)}-(THF)] (2) (Cp-Ar5 = C5Ar5, Ar = 3,5-Pr-i-C6H3) as the precatalyst. The potential catalytic reaction intermediates, half-sandwich calcium anisyl complexes [(Cp-Ar5)Ca(o-MeO-m-Ph-C6H3) (THF)(2)] (8) and [(Cp-Ar5)Ca-(o-MeO-2-Np) (THF)(2)] (9) (Np = naphthyl), were isolated and X-ray structurally characterized. DFT calculations were carried out to elucidate the different reaction profiles of sp(2) and sp(3) C-H activations.

We report a re-examination of Trofimenko’s original protocol for the preparation of the acid form of his hydrotris(pyrazolyl)borates, H(TpR,R′), by the treatment of M(TpR,R′) with glacial acetic acid. It is concluded that the protocol is effective as long as the 3-substituent of the pyrazolyl moiety is sufficiently bulky to provide steric protection to the acidic N–H proton. The solid-state structure of H(TptBu,Me), the acid form of the popular TptBu,Me ligand is also presented.

The exploration into challenging scenarios of the application of elementary reactions offers excellent opportunities for the development of unique transformations under organometallic catalysis. As a ubiquitous reaction of metal alkyl complexes, β-hydride elimination plays a crucial role in a number of important catalytic transformations. However, its functions in these catalytic cycles are limited to either releasing alkene products or generating isomerized intermediates through further migratory insertion. Herein, we report that the precise manipulation of β-hydride elimination enables an auto-tandem copper catalysis for the carboxylation of undirected alkenyl C-H bonds with CO2. In this transformation, β-hydride elimination of an alkyl copper intermediate is facilitated, while its reaction with CO2 is suppressed. The resulting copper hydride in turn reacts with CO2 to provide access to a multitasking catalyst, which enables the tandem borylation/carboxylation of C-H bonds in two mechanistically distinct catalytic cycles.

Treatment of mononuclear calcium hydride complex [(Tp Ad, i Pr )Ca(H)(THP)] ( 1 ) (Tp Ad, i Pr =hydrotris(3‐adamantyl‐5‐isopropyl‐pyrazolyl)borate, THP=tetrahydropyran) with 2‐methylthiophene, 2‐methylfuran, and 1‐methyl‐1 H ‐indole in THF/hexane solution led to the formation of calcium thiophenyl ( 2 ), furanyl ( 3 ), and indolyl ( 4 ) complexes, via sp 2 C−H bond activation. The reaction of complex 1 with 2‐methylpyridine and quinoline afforded calcium benzyl pyridinyl ( 5 ) and 1,2‐dihydroquinolide ( 6 ) complexes, through sp 3 C−H bond activation and hydride insertion reaction, respectively. Under mild conditions, the catalytic regioselective sp 2 C−H silylation of a series of aromatic heterocycles with secondary hydrosilane was achieved by the use of complex 1 . This protocol offers a straightforward method for the synthesis of silylated heteroaromatic compounds without a hydrogen acceptor and free of transition metal.

Norbornene macromonomers (MMs) with polystyrene (PS) or poly(tert-butyl acrylate) (PtBA) side chains were synthesized by a combination of atom-transfer radical polymerization (ATRP) and click reactions. A series of amphiphilic linear and star-shaped brush block copolymers were obtained through sequential ring opening metathesis polymerization (ROMP) of MMs by the use of the highly active olefin metathesis Blechert's catalyst and tri-functionalized Blechert's catalyst respectively, followed by hydrolysis reaction. These well-defined diblock molecular brushes can undergo further self-assembly to form spherical micelles in solution, which have been characterized using DLS, AF4-MALLS, AFM, TEM and fluorescence spectra. The dynamic diameter increases as the hydrophilic backbone content increases for the vast majority of the linear and star copolymers. Brush-arm star diblock amphiphilic copolymers have smaller hydrodynamic diameter and aggregation number than the corresponding linear analogues. Moreover, the critical micelle concentration (CMC) values of star diblock copolymers show less sensitive to the variety of composition.

The first mononuclear divalent ytterbium hydride complex [(TpAd,iPr)Yb(H)(THF)] (TpAd,iPr = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate) (2) bearing a terminal hydrido ligand was obtained by hydrogenolysis of the benzyl precursor in hexane. Complex 2 exhibited two different reaction patterns towards allenes: Yb-H addition with cyclohexylallene and deprotonation of 1,1-dimethylallene.