(Arylimido)vanadium(V)–Alkylidene Complexes Containing Fluorinated Aryloxo and Alkoxo Ligands for Fast Living Ring-Opening Metathesis Polymerization (ROMP) and Highly Cis-Specific ROMP

Benzimidazole-diamide (bida) Pincer Chromium Complexes: Structures and Reactivity

Serendipitous discovery of bida (i.e., N1-Ar-N2-((1-Ar-1-benzo[d]imidazol-2-yl)methyl)benzene-1,2-diamide; Ar = 2,6-iPr-C6H3), a potentially redox noninnocent, hemilabile pincer ligand with a methylene group that may facilitate proton/H atom reactivity, prompted its investigation. Chromium was chosen for study due to its multiple stable oxidation states. Disodium salt (bida)Na2(THF)n was prepared by thermal rearrangement of (dadi)Na2(THF)4 (i.e., (N,N'-di-2-(2,6-diisopropylphenylamine)phenylglyoxaldiimine)-Na2(THF)4). Salt metathesis of (bida)Na2(THF)n (generated in situ) with CrCl3(THF)3 or Cl3V═NAr (Ar = 2,6-iPr2C6H3) afforded (bida)CrCl(THF) (1-THF) and (bida)ClV═NAr, respectively. Substitutions provided (bida)CrCl(PMe2Ph) (1-PMe2Ph) and (bida)CrR(THF) (2-R, where R = Me, CH2CMe2Ph (Nph)). Oxidation of 1-THF with ArN3 (Ar = 2,6-iPr2C6H3) or AdN3 (Ad = 1-adamantyl) generated (bida)ClCr═NAr (3═NAr) and (bida)ClCr═NAd (3═NAd) and subsequent alkylation converted these to (bida)R'Cr═NR (R' = Me, R = Ad, Ar, 5═NR; R' = CH2CMe2Ph (Nph), R = Ad, Ar, 6═NR). In contrast, the addition of AdN3 to 2-Nph gave the insertion product (bida)Cr(κ2-N,N-ArN3Nph) (7). Addition of N-chlorosuccinimide to 1-THF produced (bia)CrCl2(THF) (8), where bia is the pincer derived via hydrogen atom loss from bida methylene. A similar HAT afforded (bia)ClCr(CNAr')2 (9, Ar' = 2,6-Me2C6H3) when 3═NAd was exposed to Ar'NC. An empirical equation of charge was applied to each bida species, whose metric parameters are unchanging despite formal oxidation state conversions from Cr(III) to Cr(V). Calculations and Mulliken spin density assessments reveal several situations in which antiferromagnetic (AF) coupling and admixtures of integer ground states (GSs) describe a complicated electronic structure.

Synthesis of Bottlebrush Polymers by Z-/E-Specific Living Ring-Opening Metathesis Polymerization, Exhibiting Different Thermal Properties

Synthesis of bottlebrush polymers (BBPs) and block copolymers by Z-/E-specific living ring-opening metathesis polymerization (ROMP) of N-substituted-norbornene-2,3-dicarboximides containing long alkyl chains (n-octadecyl, n-tetradecyl, etc.) has been attained by the vanadium(V)-alkylidene catalysts V(CHSiMe3)(ArN)[OC(CF3)3](PMe3)2 [Ar = 2,6-Cl2C6H3 (1), C6F5 (2)] and V(CHSiMe3)(2,6-F2C6H3N)(OC6Cl5)(PMe3)2 (3). The ROMPs using 1 afforded the BBPs with exclusive Z selectivity (98 to >99% cis) even at high temperature (up to 80 °C) in the presence of PMe3, whereas the ROMPs using 3 gave the BBPs with high E selectivity (90% trans). These ROMPs proceeded in a living manner (even at 80 °C using 1), affording various (amphiphilic) block copolymers while maintaining high E/Z selectivity. The resultant Z- and E-selective BBPs especially prepared from N-(n-octadecyl)norbornene-2,3-dicarboximide possessed different melting temperatures due to different degrees of interpolymer alkyl side chain interaction (side chain crystallization).

Applications of Vanadium, Niobium, and Tantalum Complexes in Organic and Inorganic Synthesis

Organometallic catalysis is a powerful strategy in chemical synthesis, especially with the cheap and low toxic metals based on green chemistry principle. Thus, the selection of the metal is particularly important to plan relevant and applicable processes. The group VB metals have been the subject of exciting and significant advances in both organic and inorganic synthesis. In this Review, we have summarized some reports from recent decades, which are about the development of group VB metals utilized in various types of reactions, such as oxidation, reduction, alkylation, dealkylation, polymerization, aromatization, protein synthesis, and practical water splitting.

Olefin Metathesis by First-Row Transition Metals

Catalytic olefin metathesis based on the second- and third-row transition metals has become one of the most powerful transformations in modern organic chemistry. The shift to first-row metals to produce fine and commodity chemicals would be an important achievement to complement existing methods with inexpensive and greener alternatives. In addition, those systems can offer unusual reactivity based on the unique electronic structure of the base metals. In this Minireview, we summarize the progress of the development of alkylidenes and metallacycles of first-row transition metals from scandium to nickel capable of performing cycloaddition and cycloreversion steps, crucial reactions in olefin metathesis. In addition, we will discuss systems capable of performing olefin metathesis; however, the nature of active species is not yet known.

Predicting Bond Dissociation Energies and Bond Lengths of Coordinatively Unsaturated Vanadium-Ligand Bonds

Understanding the electronic structure of coordinatively unsaturated transition-metal compounds and predicting their physical properties are of great importance for catalyst design. Bond dissociation energy D_e and bond length r_e are two of the fundamental quantities for which good predictions are important for a successful design strategy. In the present work, recent experimentally measured bond energies and bond lengths of VX diatomic molecules (X = C, N, S) are used as a gauge to consider the utility of a number of electronic structure methods. Single-reference methods are one focus because of their efficiency and utility in practical calculations, and multireference configuration interaction (MRCISD) methods and a composite coupled cluster (CCC) method are a second focus because of their potential high accuracy. The comparison is especially challenging because of the large multireference M diagnostics of these molecules, in the range 0.15-0.19. For the single-reference methods, Kohn-Sham density functional theory (KS-DFT) has been tested with a variety of approximate exchange-correlation functionals. Of these, MOHLYP provides the bond dissociation energies in best agreement with experiments, and BLYP provides the bond lengths that are in best agreement with experiments; but by requiring good performance for both the D_e and r_e of the vanadium compounds, MOHLYP, MN12-L, MGGA_MS1, MGGA_MS0, O3LYP, and M06-L are the most highly recommended functionals. The CCC calculations include up to connected pentuple excitations for the valence electrons and up to connected quadruple excitations for the core-valence terms; this results in highly accurate dissociation energies and good bond lengths. Averaged over the three molecules, the mean unsigned deviation of CCC bond energies from experimental ones is only 0.4 kcal/mol, demonstrating excellent convergence of theory and experiments.

cis-Specific ring opening metathesis polymerisation (ROMP) of cyclic olefins using (pentafluorophenylimido)vanadium(v)-alkylidene, V(CHSiMe3)(NC6F5)[OC(CF3)3](PMe3)2

Highly cis-specific (Z selective) ring opening metathesis polymerisation of cycloheptene has been demonstrated using V(CHSiMe₃)(NC₆F₅)[OC(CF₃)₃](PMe₃)₂.

Reactions of (Arylimido)vanadium(V)-Trialkyl Complexes with Phenols: Effects of Arylimido Ligands and Phenols for Formation of the Vanadium Phenoxides

Reactions of a series of (arylimido)vanadium(V) trialkyl complexes, V(NAr')(CH₂SiMe₃)₃ (Ar' = C₆H₅, 2-MeC₆H₄, 2,6-Me₂C₆H₃, 2,6-Cl₂C₆H₃), with various phenols (ArOH, Ar = 2,6-F₂C₆H₃, 2,6-Cl₂C₆H₃, 2,6-Me₂C₆H₃, 2,6- ⁱ Pr₂C₆H₃, 2- ^t BuC₆H₄, 2,6- ^t Bu₂C₆H₃; 1.0 equiv) affording V(NAr')(CH₂SiMe₃)₂(OAr) were conducted in C₆D₆ at 25 °C, and the effects of both arylimido ligands and phenols on the substitution rate were explored. Sterically hindered arylimido ligands showed lower reactivity, and the reaction proceeded in the order: Ar' = 2,6-Me₂C₆H₃ < 2,6-Cl₂C₆H₃ < 2-MeC₆H₄ < C₆H₅. This order is somewhat different from that obtained from the chemical shifts in V(NAr')(CH₂SiMe₃)₃ in the ⁵¹V NMR spectra. The conversions with various disubstituted phenols increased in the order: 2,6- ⁱ Pr₂C₆H₃OH < 2,6-Me₂C₆H₃OH < 2,6-Cl₂C₆H₃OH < 2,6-F₂C₆H₃OH, irrespective of the kind of arylimido ligands. The reactions of V(NAr')(CH₂SiMe₃)₃ with 2,6- ^t Bu₂C₆H₃OH (1.0 or 3.0 equiv) did not take place even upon heating at 60 °C. These results suggest that the reactions proceed via coordination of ArOH toward vanadium, and the reactivity is highly dependent on steric bulk of both the arylimido ligand and the phenol.

Norbornene, norbornadiene and their derivatives: promising semi-products for organic synthesis and production of polymeric materials

The methods for synthesis of promising norbornene monomers from norbornadiene and quadricyclane are summarized. A strategy for their synthesis is discussed, combining theoretical and experimental approaches to the selection of catalysts and the conditions for carrying out stereoselective reactions. The mechanisms of catalytic reactions of synthesis of norbornene monomers, as well as the progress in the macromolecular design of functional polymeric materials based on them, are considered. The data on industrial processes of production of polynorbornenes and areas of their use are presented.

The bibliography includes 297 references.

Synthesis of (Arylmido)niobium(V) Complexes Containing Ketimide, Phenoxide Ligands, and Some Reactions with Phenols and Alcohols

Reactions of Nb(NAr)(N=C ^t Bu₂)₃ (3a, Ar = 2,6-Me₂C₆H₃) with 1.0, 2.0, or 3.0 equiv of Ar'OH (Ar' = 2,6- ⁱ Pr₂C₆H₃) afforded Nb(NAr)(N=C ^t Bu₂)₂(OAr'), Nb(NAr)(N=C ^t Bu₂)(OAr')₂, or Nb(NAr)(OAr')₃, respectively (at 25 °C), whereas the reaction with 2.0 equiv of 2,6- ^t Bu₂C₆H₃OH afforded Nb(NAr)(N=C ^t Bu₂)₂(O-2,6- ^t Bu₂C₆H₃) upon heating (70 °C) without the formation of bis(phenoxide) and the reaction of 3a with 2.0 equiv of 2,4,6-Me₃C₆H₂OH afforded Nb(NAr)(N=C ^t Bu₂)(O-2,4,6-Me₃C₆H₂)₂(HN=C ^t Bu₂). Similar reactions of 3a with 1.0 equiv of (CF₃)₃COH or 2.0 equiv of (CF₃)₂CHOH afforded Nb(NAr)(N=C ^t Bu₂)₂[OC(CF₃)₃](HN=C ^t Bu₂) or Nb(NAr)(N=C ^t Bu₂)[OCH(CF₃)₂]₂(HN=C ^t Bu₂), respectively. On the basis of their structural analyses and the reaction chemistry, it was suggested that these reactions proceeded via coordination of phenol (alcohol) to Nb and the subsequent proton (hydrogen) transfer to the ketimide (N=C ^t Bu₂) ligand. The reaction of Nb(NAr)(N=C ^t Bu₂)₂(OAr') with 1.0 equiv of 2,4,6-Me₃C₆H₂OH gave the disproportionation products Nb(NAr)(N=C ^t Bu₂)(OAr')₂ and Nb(NAr)(N=C ^t Bu₂)(O-2,4,6-Me₃C₆H₂)₂(HN=C ^t Bu₂) with 1:1 ratio, clearly indicating the presence of the above mechanism and the fast equilibrium (between the ketimide and the phenoxide). The reaction of 3a with 1.0 or 2.0 equiv of C₆F₅OH afforded Nb(N=C ^t Bu₂)₂(OC₆F₅)₃(HN=C ^t Bu₂) as the sole isolated product, which was formed from once generated Nb(NAr)(N=C ^t Bu₂)₂(OC₆F₅)(HN=C ^t Bu₂) by treating with C₆F₅OH.

Facile in situ generation of highly active (arylimido)vanadium(v)–alkylidene catalysts for the ring-opening metathesis polymerization (ROMP) of cyclic olefins by immediate phenoxy ligand exchange

Remarkably active vanadium(v)–alkylidene catalysts for the ring-opening metathesis polymerization of cyclic olefins can be generated in situ upon addition of C₆F₅OH or C₆Cl₅OH.

Synthesis of vanadium–alkylidene complexes and their use as catalysts for ring opening metathesis polymerization

Synthesis of vanadium–alkylidene complexes and some reactions have been reviewed; highly active, thermally robust, cis specific ROMP of cyclic olefins has been attained by ligand modification in (imido)vanadium(v)–alkylidene catalysts.

Enhancing the emission of hexa-peri-hexabenzocoronene-containing polynorbornene via electron donating, unsymmetric constitution and solvent effects

Hexa-peri-hexabenzocoronene-containing hydrogenated polynorbornene dispersion showed an intensive emission of the 0–0 transition (465 nm) and excellent dispersibility.

Reactions of Ruthenium Complexes Containing Pentatetraenylidene Ligand

Two ruthenium acetylide complexes [Ru]-C≡C-C≡C-C(OR)(C₃ H₅ )₂ (2, R=H and 2 a, R=CH₃ ; [Ru]=Cp(PPh₃ )₂ Ru) each with two cyclopropyl rings were synthesized from TMS-C≡C-C≡C-C(OH)(C₃ H₅ )₂ (1; TMS=trimethylsilyl). Treatments of 2 and 2 a with allyl halide in the presence of KPF₆ afforded the vinylidene complexes 3 and 3 a, respectively. When NH₄ PF₆ was used, instead of KPF₆ , additional ring-opening reaction took place on one of the three-membered ring. Treatment of [Ru]Cl with 1,3-butadiyne (6), bearing an epoxide ring, afforded acetylide complex 7 with a furyl ring. Treatment of 2 a with Ph₃ CPF₆ presumably afforded pentatetraenylidene complex {[Ru]=C=C=C=C=C(C₃ H₅ )₂ }[PF₆ ] (10), which was not isolated. Additions of various alcohols in a solution of 10 generated a number of disubstituted allenylidene complexes {[Ru]=C=C=C(OR)-C=C(C₃ H₅ )₂ }[PF₆ ] (11). Treatment of 11 with K₂ CO₃ afforded the acetylide complex 12 bearing a carbonyl group, characterized by single X-ray diffraction analysis. Addition of a primary amine to 10 caused cleavage of the farthermost C=C bond and several allenylidene complexes {[Ru]=C=C=C(Me)(NHR)}[PF₆ ] (18) were isolated.