Synthesis of Highly Cis, Syndiotactic Polymers via Ring-Opening Metathesis Polymerization Using Ruthenium Metathesis Catalysts

The first example of ruthenium-mediated ring-opening metathesis polymerization generating highly cis, highly tactic polymers is reported. While the cis content varied from 62 to >95% depending on the monomer structure, many of the polymers synthesized displayed high tacticity (>95%). Polymerization of an enantiomerically pure 2,3-dicarboalkoxynorbornadiene revealed a syndiotactic microstructure

Highly Active Ruthenium Metathesis Catalysts Exhibiting Unprecedented Activity and Z‑Selectivity

A novel chelated ruthenium-based metathesis catalyst bearing an N-2,6-diisopropylphenyl group is reported and displays near-perfect selectivity for the Z-olefin (>95%), as well as unparalleled TONs of up to 7400, in a variety of homodimerization and industrially relevant metathesis reactions. This derivative and other new catalytically active species were synthesized using an improved method employing sodium carboxylates to induce the salt metathesis and C–H activation of these chelated complexes. All of these new ruthenium-based catalysts are highly Z-selective in the homodimerization of terminal olefins

Control of cis-selectivity and tacticity in ring opening metathesis polymerization using ruthenium metathesis catalysts

A series of ruthenium metathesis catalysts contg. a cyclometalated N- heterocyclic carbene (NHC) ligand were examd. in the ring opening metathesis polymn. (ROMP) of norbornene- and norbornadiene- derived monomers. In general, the resulting polymers were found to be highly cis with syndiotactic- biased cis and trans regions, while blockiness calcns. showed that trans double bonds occurred randomly throughout the polymers. These structural trends suggest that the controlling factor in cis selectivity and tacticity is the combined influence of the stereogenic ruthenium center and the steric environment surrounding the alkylidene on monomer approach. These conclusions are further supported by preliminary computational studies, which are ongoing and will also be discussed. It is expected that these results will provide invaluable insight into the mechanism and mode- of- action of cyclometalated ruthenium metathesis catalysts and will be instrumental in the design of future catalysts for cis- selective metathesis transformations

Milder routes to chelated ruthenium complexes for Z-selective metathesis

A novel method to effect the salt metathesis and C-H activation of ruthenium-based, Z-selective metathesis catalysts contg. a chelated N-heterocyclic carbene (NHC) ligand using sodium carboxylates is reported. This method allows for the successful formation of stable chelated species contg. a variety of alterations to the NHC ligand that had decompd. under the previous approach. As such, several new, chelated metathesis-active ruthenium complexes are described, including a catalyst system exhibiting >95% Z-selectivity and record TONs (up to 8100) in homodimerization reactions of terminal olefins. Moreover, a catalyst has been synthesized that gives highly cis, highly tactic polymers via ring opening metathesis polymn. of strained, cyclic olefins, marking the first time tactic polymers have been made using a ruthenium-based metathesis catalysts

Synthesis of Highly Cis, Syndiotactic Polymers via Ring-Opening Metathesis Polymerization Using Ruthenium Metathesis Catalysts

The first example of ruthenium-mediated ring-opening metathesis polymerization generating highly cis, highly tactic polymers is reported. While the cis content varied from 62 to >95% depending on the monomer structure, many of the polymers synthesized displayed high tacticity (>95%). Polymerization of an enantiomerically pure 2,3-dicarboalkoxynorbornadiene revealed a syndiotactic microstructure

Synthesis of Highly Cis, Syndiotactic Polymers via Ring-Opening Metathesis Polymerization Using Ruthenium Metathesis Catalysts

The first example of ruthenium-mediated ring-opening metathesis polymerization generating highly cis, highly tactic polymers is reported. While the cis content varied from 62 to >95% depending on the monomer structure, many of the polymers synthesized displayed high tacticity (>95%). Polymerization of an enantiomerically pure 2,3-dicarboalkoxynorbornadiene revealed a syndiotactic microstructure

Highly Active Ruthenium Metathesis Catalysts Exhibiting Unprecedented Activity and <i>Z</i>‑Selectivity

A novel chelated ruthenium-based metathesis catalyst bearing an <i>N</i>-2,6-diisopropylphenyl group is reported and displays near-perfect selectivity for the <i>Z</i>-olefin (>95%), as well as unparalleled TONs of up to 7400, in a variety of homodimerization and industrially relevant metathesis reactions. This derivative and other new catalytically active species were synthesized using an improved method employing sodium carboxylates to induce the salt metathesis and C–H activation of these chelated complexes. All of these new ruthenium-based catalysts are highly <i>Z</i>-selective in the homodimerization of terminal olefins

A step beyond the Feltham-Enemark notation: spectroscopic and correlated ab initio computational support for an antiferromagnetically coupled M(II)-(NO)- description of Tp*M(NO) (M = Co, Ni)

Multiple spectroscopic and computational methods were used to characterize the ground-state electronic structure of the novel {CoNO}9 species Tp*Co(NO) (Tp* = hydro-tris(3,5-Me2-pyrazolyl)borate). The metric parameters about the metal center and the pre-edge region of the Co K-edge X-ray absorption spectrum were reproduced by density functional theory (DFT), providing a qualitative description of the Co–NO bonding interaction as a Co(II) (SCo = 3/2) metal center, antiferromagnetically coupled to a triplet NO– anion (SNO = 1), an interpretation of the electronic structure that was validated by ab initio multireference methods (CASSCF/MRCI). Electron paramagnetic resonance (EPR) spectroscopy revealed significant g-anisotropy in the S = 1/2 ground state, but the linear-response DFT performed poorly at calculating the g-values. Instead, CASSCF/MRCI computational studies in conjunction with quasi-degenerate perturbation theory with respect to spin–orbit coupling were required for obtaining accurate modeling of the molecular g-tensor. The computational portion of this work was extended to the diamagnetic Ni analogue of the Co complex, Tp*Ni(NO), which was found to consist of a Ni(II) (SNi = 1) metal center antiferromagnetically coupled to an SNO = 1 NO–. The similarity between the Co and Ni complexes contrasts with the previously studied Cu analogues, for which a Cu(I) bound to NO0 formulation has been described. This discrepancy will be discussed along with a comparison of the DFT and ab initio computational methods for their ability to predict various spectroscopic and molecular features

A Step beyond the Feltham–Enemark Notation: Spectroscopic and Correlated <i>ab Initio</i> Computational Support for an Antiferromagnetically Coupled M(II)–(NO)⁻ Description of Tp*M(NO) (M = Co, Ni)

Multiple spectroscopic and computational methods were used to characterize the ground-state electronic structure of the novel {CoNO}⁹ species Tp*Co(NO) (Tp* = hydro-tris(3,5-Me₂-pyrazolyl)borate). The metric parameters about the metal center and the pre-edge region of the Co K-edge X-ray absorption spectrum were reproduced by density functional theory (DFT), providing a qualitative description of the Co–NO bonding interaction as a Co(II) (<i>S</i>_Co = ³/₂) metal center, antiferromagnetically coupled to a triplet NO^– anion (<i>S</i>_NO = 1), an interpretation of the electronic structure that was validated by <i>ab initio</i> multireference methods (CASSCF/MRCI). Electron paramagnetic resonance (EPR) spectroscopy revealed significant <i>g</i>-anisotropy in the <i>S</i> = ¹/₂ ground state, but the linear-response DFT performed poorly at calculating the <i>g</i>-values. Instead, CASSCF/MRCI computational studies in conjunction with quasi-degenerate perturbation theory with respect to spin–orbit coupling were required for obtaining accurate modeling of the molecular <i>g</i>-tensor. The computational portion of this work was extended to the diamagnetic Ni analogue of the Co complex, Tp*Ni(NO), which was found to consist of a Ni(II) (<i>S</i>_Ni = 1) metal center antiferromagnetically coupled to an <i>S</i>_NO = 1 NO^–. The similarity between the Co and Ni complexes contrasts with the previously studied Cu analogues, for which a Cu(I) bound to NO⁰ formulation has been described. This discrepancy will be discussed along with a comparison of the DFT and <i>ab initio</i> computational methods for their ability to predict various spectroscopic and molecular features

A Step beyond the Feltham–Enemark Notation: Spectroscopic and Correlated <i>ab Initio</i> Computational Support for an Antiferromagnetically Coupled M(II)–(NO)⁻ Description of Tp*M(NO) (M = Co, Ni)

Multiple spectroscopic and computational methods were used to characterize the ground-state electronic structure of the novel {CoNO}⁹ species Tp*Co(NO) (Tp* = hydro-tris(3,5-Me₂-pyrazolyl)borate). The metric parameters about the metal center and the pre-edge region of the Co K-edge X-ray absorption spectrum were reproduced by density functional theory (DFT), providing a qualitative description of the Co–NO bonding interaction as a Co(II) (<i>S</i>_Co = ³/₂) metal center, antiferromagnetically coupled to a triplet NO^– anion (<i>S</i>_NO = 1), an interpretation of the electronic structure that was validated by <i>ab initio</i> multireference methods (CASSCF/MRCI). Electron paramagnetic resonance (EPR) spectroscopy revealed significant <i>g</i>-anisotropy in the <i>S</i> = ¹/₂ ground state, but the linear-response DFT performed poorly at calculating the <i>g</i>-values. Instead, CASSCF/MRCI computational studies in conjunction with quasi-degenerate perturbation theory with respect to spin–orbit coupling were required for obtaining accurate modeling of the molecular <i>g</i>-tensor. The computational portion of this work was extended to the diamagnetic Ni analogue of the Co complex, Tp*Ni(NO), which was found to consist of a Ni(II) (<i>S</i>_Ni = 1) metal center antiferromagnetically coupled to an <i>S</i>_NO = 1 NO^–. The similarity between the Co and Ni complexes contrasts with the previously studied Cu analogues, for which a Cu(I) bound to NO⁰ formulation has been described. This discrepancy will be discussed along with a comparison of the DFT and <i>ab initio</i> computational methods for their ability to predict various spectroscopic and molecular features