N-heterocyclic carbene (NHC) based ligands and related methods

Polydentate macrocyclic NHCs (NHC ligands) and related methods are disclosed. Such ligands advantageously facilitate a variety of ligand coordination modes and stabilize oxidation states of metal complexes with a number of coordination environments and shapes. The NHC ligands described herein comprise pendant groups configured to facilitate a variety of reactions including: cis-trans isomerization, proton shuttling and facilitating changes in coordination environments as a result of redox reactions

Five-Coordinate Rearrangements of Metallacyclobutane Intermediates during Ring-Opening Metathesis Polymerization of 2,3-Dicarboalkoxynorbornenes by Molybdenum and Tungsten Monoalkoxide Pyrrolide Initiators

Addition of rac-DCENBE (2,3-dicarboethoxynorbornene) or rac-DCBNBE (2,3-dicarbo-tert-butoxynorbornene) to Mo(NAd)(CHCMe[subscript 2]Ph)(Pyr)(OHMT) (1a) (Ad = 1-adamantyl, OHMT = 2,6-dimesitylphenoxide, Pyr– = NC[subscript 4]H[subscript 4]–) led to the formation of polymers that have a cis,syndiotactic,alt structure analogous to the structure observed for the polymer obtained from rac-DCMNBE (2,3-dicarbomethoxynorbornene). The PDI of cis,syndio,alt-poly(DCBNBE) is low and decreases as the polymer length increases, and there is a linear relationship between the number of equivalents of monomer employed and the molecular weight of the polymers measured in THF versus polystyrene standards. In contrast, polymerization of (+)-DCMNBE by 1a at 25, 0, −25, and −40 °C yields a polymer that contains ~25% trans,isotactic dyads and 75% cis,syndiotactic dyads. A similar polymerization by Mo(NAd)(CHCMe[subscript 2]Ph)(Pyr)(OHIPT) (1b) (OHIPT = 2,6-(2,4,6-i-Pr[subscript 3])[subscript 2]C[subscript 6]H[subscript 3]) gives a polymer that contains cis,syndiotactic and trans,isotactic dyads in a ratio of ~8:92, respectively. This is the first report of synthesis of a norbornene polymer that has primarily a trans,isotactic structure. Addition of 100 equiv of (+)-DCMNBE, (−)-DCENBE, or (−)-DCBNBE to a toluene solution of W(O)(CH-t-Bu)(2,5-Me[subscript 2]NC[subscript 4]H[subscript 2])(OHMT)(PMe[subscript 2]Ph) (5) led to formation of ~99% cis,syndiotactic polymer. Cis,syndiotactic dyads arise through a mechanism that consists of a syn approach of the monomer to a syn alkylidene isomer followed by inversion of configuration at the metal center as a consequence of an exchange of aryloxide and pyrrolide ligands. The mechanism for formation of trans,isotactic dyads is one in which the monomer approaches in an anti fashion to the syn isomer followed by a “turnstile” rotation in the five-coordinate intermediate metallacyclobutane that allows the metallacylic ring to open productively with retention of configuration at the metal center. The metallacyclobutane intermediate that gives rise to trans,isotactic dyads in the copolymer could be regarded as a relatively high energy species with a “nonideal” structure compared to a trigonal bipyramidal or a square pyramidal structure.United States. Dept. of Energy (DE-FG02-86ER13564

High Oxidation State Molybdenum Imido Heteroatom-Substituted Alkylidene Complexes

Reactions between Mo(NAr)(CHR)(Me2Pyr)-(OTPP) (Ar = 2,6-i-Pr2C6H3, R = H or CHCMe2Ph, Me2Pyr = 2,5-dimethylpyrrolide, OTPP = O-2,3,5,6-Ph4C6H) and CH2=CHX where X = B(pin), SiMe3, N-carbazolyl, N-pyrrolidinonyl, PPh2, OPr, or SPh lead to Mo(NAr)(CHX)-(Me2Pyr)(OTPP) complexes in good yield. All have been characterized through X-ray studies (as an acetonitrile adduct in the case of X = PPh2). The efficiencies of metathesis reactions initiated by Mo(NAr)(CHX)(Me2Pyr)(OTPP) complexes can be rationalized on the basis of steric factors; electronic differences imposed as a consequence of X being bound to the alkylidene carbon do not seem to play a major role. Side reactions that promote catalyst decomposition do not appear to be a serious limitation for Mo=CHX species

High Oxidation State Molybdenum Imido Heteroatom-Substituted Alkylidene Complexes

Reactions between Mo(NAr)(CHR)(Me[subscript 2]Pyr)(OTPP) (Ar = 2,6-i-Pr[subscript 2]C[subscript 6]H[subscript 3], R = H or CHCMe[subscript 2]Ph, Me[subscript 2]Pyr = 2,5-dimethylpyrrolide, OTPP = O-2,3,5,6-Ph[subscript 4]C[subscript 6]H) and CH[subscript 2]═CHX where X = B(pin), SiMe[subscript 3], N-carbazolyl, N-pyrrolidinonyl, PPh[subscript 2], OPr, or SPh lead to Mo(NAr)(CHX)(Me[subscript 2]Pyr)(OTPP) complexes in good yield. All have been characterized through X-ray studies (as an acetonitrile adduct in the case of X = PPh[subscript 2]). The efficiencies of metathesis reactions initiated by Mo(NAr)(CHX)(Me[subscript 2]Pyr)(OTPP) complexes can be rationalized on the basis of steric factors; electronic differences imposed as a consequence of X being bound to the alkylidene carbon do not seem to play a major role. Side reactions that promote catalyst decomposition do not appear to be a serious limitation for Mo═CHX species.National Science Foundation (U.S.) (CHE-1111133)National Institutes of Health (U.S.) (Grant GM-59426

High Oxidation State Molybdenum Imido Heteroatom-Substituted Alkylidene Complexes

Reactions between Mo­(NAr)­(CHR)­(Me₂Pyr)­(OTPP) (Ar = 2,6-<i>i</i>-Pr₂C₆H₃, R = H or CHCMe₂Ph, Me₂Pyr = 2,5-dimethylpyrrolide, OTPP = O-2,3,5,6-Ph₄C₆H) and CH₂CHX where X = B­(pin), SiMe₃, <i>N</i>-carbazolyl, <i>N</i>-pyrrolidinonyl, PPh₂, OPr, or SPh lead to Mo­(NAr)­(CHX)­(Me₂Pyr)­(OTPP) complexes in good yield. All have been characterized through X-ray studies (as an acetonitrile adduct in the case of X = PPh₂). The efficiencies of metathesis reactions initiated by Mo­(NAr)­(CHX)­(Me₂Pyr)­(OTPP) complexes can be rationalized on the basis of steric factors; electronic differences imposed as a consequence of X being bound to the alkylidene carbon do not seem to play a major role. Side reactions that promote catalyst decomposition do not appear to be a serious limitation for MoCHX species

High Oxidation State Molybdenum Imido Heteroatom-Substituted Alkylidene Complexes

Reactions between Mo­(NAr)­(CHR)­(Me₂Pyr)­(OTPP) (Ar = 2,6-<i>i</i>-Pr₂C₆H₃, R = H or CHCMe₂Ph, Me₂Pyr = 2,5-dimethylpyrrolide, OTPP = O-2,3,5,6-Ph₄C₆H) and CH₂CHX where X = B­(pin), SiMe₃, <i>N</i>-carbazolyl, <i>N</i>-pyrrolidinonyl, PPh₂, OPr, or SPh lead to Mo­(NAr)­(CHX)­(Me₂Pyr)­(OTPP) complexes in good yield. All have been characterized through X-ray studies (as an acetonitrile adduct in the case of X = PPh₂). The efficiencies of metathesis reactions initiated by Mo­(NAr)­(CHX)­(Me₂Pyr)­(OTPP) complexes can be rationalized on the basis of steric factors; electronic differences imposed as a consequence of X being bound to the alkylidene carbon do not seem to play a major role. Side reactions that promote catalyst decomposition do not appear to be a serious limitation for MoCHX species

Synthesis and Electronic Structure of Ru<inf>2</inf>(X ap)<inf>4</inf>(Y- gem -DEE) Type Compounds: Effect of Cross- Conjugation

Reported in this Article are the preparation and characterization of a series of new Ru2(II,III) compounds bearing one cross-conjugated σ-geminal-diethynylethene ligand (gem-DEE), namely, Ru2(Xap)4(Y-gem-DEE) (Xap = N,N′-anilinopyridinate (ap) or 2-(3,5-dimethoxy)anilinopyridinate (DiMeOap), and Y = SiiPr3 (1) or H (2)) and [Ru2(ap)4]2(μ-gem-DEE) (3). Compounds 1-3 were characterized by spectroscopic and voltammetric techniques as well as the single crystal X-ray diffraction study of 2a. The X-ray structural data of 2a and the spectroscopic/voltammetric data of compounds 1 and 2 indicate that the gem-DEE ligands are similar to simple alkynyls in their effects on the molecular and electronic structures of the Ru2(Xap)4 moiety. Similar to the previously studied [Ru2(ap)4]2(μ-C2n) type compounds, dimer 3 exhibits pairwise 1e- oxidations and reductions, albeit the potential splits within the pair (ΔE1/2) are significantly smaller than those of [Ru2(ap)4]2(μ-C4). The electronic absorption spectra of the reduced and oxidized derivatives of 1a and 3 were determined using spectroelectrochemistry methods. No discernible intervalence charge transfer transition (IVCT) was detected in the near-IR spectrum for either 3- or 3+, suggesting that the Ru2-Ru2 coupling in these mixed-valence states is weak. DFT calculations on a model compound of 3 yielded six singly occupied molecular orbitals (SOMOs), which have Ru2 contributions similar to those previously calculated for the [Ru2(ap)4]2(μ-C2n) type compounds. Among six SOMOs, SOMO-2 is the only one containing substantial dπ-π(gem-DEE) character across the entire Ru2-μ-gem-DEE-Ru2</in

Synthesis and Electronic Structure of Ru₂(X<i>ap</i>)₄(Y-<i>gem</i>-DEE) Type Compounds: Effect of <i>Cross-</i>Conjugation

Reported in this Article are the preparation and characterization of a series of new Ru₂(II,III) compounds bearing one <i>cross</i>-conjugated σ-<i>geminal</i>-diethynylethene ligand (<i>gem</i>-DEE), namely, Ru₂(X<i>ap</i>)₄(Y-<i>gem</i>-DEE) (X<i>ap</i> = <i>N</i>,<i>N</i>′-anilinopyridinate (<i>ap</i>) or 2-(3,5-dimethoxy)­anilinopyridinate (DiMeO<i>ap</i>), and Y = Si^<i>i</i>Pr₃ (<b>1</b>) or H (<b>2</b>)) and [Ru₂(<i>ap</i>)₄]₂(μ-<i>gem</i>-DEE) (<b>3</b>). Compounds <b>1</b>–<b>3</b> were characterized by spectroscopic and voltammetric techniques as well as the single crystal X-ray diffraction study of <b>2a</b>. The X-ray structural data of <b>2a</b> and the spectroscopic/voltammetric data of compounds <b>1</b> and <b>2</b> indicate that the <i>gem-</i>DEE ligands are similar to simple alkynyls in their effects on the molecular and electronic structures of the Ru₂(X<i>ap</i>)₄ moiety. Similar to the previously studied [Ru₂(<i>ap</i>)₄]₂(μ-C_2<i>n</i>) type compounds, dimer <b>3</b> exhibits pairwise 1e^– oxidations and reductions, albeit the potential splits within the pair (Δ<i>E</i>_1/2) are significantly smaller than those of [Ru₂(<i>ap</i>)₄]₂(μ-C₄). The electronic absorption spectra of the reduced and oxidized derivatives of <b>1a</b> and <b>3</b> were determined using spectroelectrochemistry methods. No discernible intervalence charge transfer transition (IVCT) was detected in the near-IR spectrum for either <b>3</b>^– or <b>3</b>⁺, suggesting that the Ru₂–Ru₂ coupling in these mixed-valence states is weak. DFT calculations on a model compound of <b>3</b> yielded six singly occupied molecular orbitals (SOMOs), which have Ru₂ contributions similar to those previously calculated for the [Ru₂(<i>ap</i>)₄]₂(μ-C_2<i>n</i>) type compounds. Among six SOMOs, SOMO-2 is the only one containing substantial <i>d</i>π–π­(<i>gem</i>-DEE) character across the entire Ru₂-μ-<i>gem</i>-DEE-Ru₂ linkage, which explains the weakened Ru₂–Ru₂ coupling

Synthesis and Electronic Structure of Ru₂(X<i>ap</i>)₄(Y-<i>gem</i>-DEE) Type Compounds: Effect of <i>Cross-</i>Conjugation

Reported in this Article are the preparation and characterization of a series of new Ru₂(II,III) compounds bearing one <i>cross</i>-conjugated σ-<i>geminal</i>-diethynylethene ligand (<i>gem</i>-DEE), namely, Ru₂(X<i>ap</i>)₄(Y-<i>gem</i>-DEE) (X<i>ap</i> = <i>N</i>,<i>N</i>′-anilinopyridinate (<i>ap</i>) or 2-(3,5-dimethoxy)­anilinopyridinate (DiMeO<i>ap</i>), and Y = Si^<i>i</i>Pr₃ (<b>1</b>) or H (<b>2</b>)) and [Ru₂(<i>ap</i>)₄]₂(μ-<i>gem</i>-DEE) (<b>3</b>). Compounds <b>1</b>–<b>3</b> were characterized by spectroscopic and voltammetric techniques as well as the single crystal X-ray diffraction study of <b>2a</b>. The X-ray structural data of <b>2a</b> and the spectroscopic/voltammetric data of compounds <b>1</b> and <b>2</b> indicate that the <i>gem-</i>DEE ligands are similar to simple alkynyls in their effects on the molecular and electronic structures of the Ru₂(X<i>ap</i>)₄ moiety. Similar to the previously studied [Ru₂(<i>ap</i>)₄]₂(μ-C_2<i>n</i>) type compounds, dimer <b>3</b> exhibits pairwise 1e^– oxidations and reductions, albeit the potential splits within the pair (Δ<i>E</i>_1/2) are significantly smaller than those of [Ru₂(<i>ap</i>)₄]₂(μ-C₄). The electronic absorption spectra of the reduced and oxidized derivatives of <b>1a</b> and <b>3</b> were determined using spectroelectrochemistry methods. No discernible intervalence charge transfer transition (IVCT) was detected in the near-IR spectrum for either <b>3</b>^– or <b>3</b>⁺, suggesting that the Ru₂–Ru₂ coupling in these mixed-valence states is weak. DFT calculations on a model compound of <b>3</b> yielded six singly occupied molecular orbitals (SOMOs), which have Ru₂ contributions similar to those previously calculated for the [Ru₂(<i>ap</i>)₄]₂(μ-C_2<i>n</i>) type compounds. Among six SOMOs, SOMO-2 is the only one containing substantial <i>d</i>π–π­(<i>gem</i>-DEE) character across the entire Ru₂-μ-<i>gem</i>-DEE-Ru₂ linkage, which explains the weakened Ru₂–Ru₂ coupling