Abstraction of a Vinylic Hydrogen to Form Alkynes. Multinuclear and Multidimensional NMR Spectroscopy and Computational Studies Elucidating Structural Solution Behavior of Acetylene and Propyne Complexes of Titanium

The alkyne complexes [(PNP)­Ti­(η²-HCCH)­(CH₂^tBu)] (<b>2</b>) and [(PNP)­Ti­(η²-HCCMe)­(CH₂^tBu)] (<b>3</b>) have been prepared by treatment of [(PNP)­TiCH^tBu­(OTf)] (<b>1</b>) with the Grignard reagents H₂CCHMgCl and MeHCCHMgBr, respectively. Complex <b>3</b> can be also prepared using the Grignard H₂CC­(Me)­MgBr and <b>1</b>. The 2-butyne complex [(PNP)­Ti­(η²-MeCCMe)­(CH₂^tBu)] (<b>4</b>) can be similarly prepared from <b>1</b> and MeHCC­(Me)­MgBr. Complexes <b>2</b> and <b>3</b> have been characterized with a battery of multidimensional and multinuclear (¹H, ¹³C, and ³¹P) NMR spectroscopic experiments, including selectively ³¹P decoupled ¹H­{³¹P}, ¹H–³¹P HMBC, ¹H–³¹P HOESY, and ³¹P EXSY. Variable-temperature ¹H and ³¹P­{¹H} NMR spectroscopy reveals that the acetylene ligand in <b>2</b> exhibits a rotational barrier of 11 kcal mol^–1, and such a process has been corroborated by theoretical studies. Formation of the titanium alkyne ligand in complexes <b>2</b> and <b>3</b> proceeds via the vinyl intermediate [(PNP)­TiCH^tBu­(CHCHR)] followed by a concerted, metal-mediated β-hydrogen abstraction step that has been computed to have a barrier of 20–22 kcal mol^–1. The geometry and rotational mechanism of the alkyne ligand in <b>2</b> are presented and compared with those of the ethylene derivative [(PNP)­Ti­(η²-H₂CCH₂)­(CH₂^tBu)] (<b>5</b>), which does not display rotation of the bound ethylene under the same conditions

[(F₆acac)Pd(μ-HNC₆F₅)]₂, a Large Family of Polymorphs and Solvates with Short F···F Contacts

Highly fluorinated [(F6acac)Pd(μ-HNC6F5)]2 was prepared by the reaction of palladium bis(hexa­fluoro­acetyl­acetonate), Pd(F6acac)2, with pentafluoroaniline. This compound generates a large family of crystalline polymorphs and solvates. In this paper, we present a study on the synthesis, solution phase dynamics, and crystal structures of highly fluorinated [(F6acac)Pd(μ-HNC6F5)]2. Pd3(μ-F6acac)2(μ-HNC6F5)4 is produced as a minor byproduct. We also describe the synthesis and structural characterization of trinuclear Pd3(μ-F6acac)3[μ-(CF3)2CN]3 prepared by the reaction of Pd(F6acac)2 with hexafluoroacetone imine

Basal Plane Fluorination of Graphene by XeF₂ via a Radical Cation Mechanism

Graphene fluorination with XeF₂ is an attractive method to introduce a nonzero bandgap to graphene under mild conditions for potential electro-optical applications. Herein, we use well-defined graphene nanostructures as a model system to study the reaction mechanism of graphene fluorination by XeF₂. Our combined experimental and theoretical studies show that the reaction can proceed through a radical cation mechanism, leading to fluorination and sp³-hybridized carbon in the basal plane

Cyanide Ligand Assembly by Carbon Atom Transfer to an Iron Nitride

The new iron­(IV) nitride complex PhB­(ⁱPr₂Im)₃FeN reacts with 2 equiv of bis­(diisopropyl­amino)­cyclo­propenylidene (BAC) to provide PhB­(ⁱPr₂Im)₃­Fe­(CN)­(N₂)­(BAC). This unusual example of a four-electron reaction involves carbon atom transfer from BAC to create a cyanide ligand along with the alkyne ⁱPr₂N–CC–NⁱPr₂. The iron complex is in equilibrium with an N₂-free species. Further reaction with CO leads to formation of a CO analogue, which can be independently prepared using NaCN as the cyanide source, while reaction with B­(C₆F₅)₃ provides the cyanoborane derivative

Room Temperature Dehydrogenation of Ethane, Propane, Linear Alkanes C4–C8, and Some Cyclic Alkanes by Titanium–Carbon Multiple Bonds

The transient titanium neopentylidyne, [(PNP)­TiC<i>^t</i>Bu] (<b>A</b>; PNP^–N­[2-P<i>ⁱ</i>Pr₂-4-methylphenyl]₂^–), dehydrogenates ethane to ethylene at room temperature over 24 h, by sequential 1,2-CH bond addition and β-hydrogen abstraction to afford [(PNP)­Ti­(η²-H₂CCH₂)­(CH₂<i>^t</i>Bu)] (<b>1</b>). Intermediate <b>A</b> can also dehydrogenate propane to propene, albeit not cleanly, as well as linear and volatile alkanes C₄–C₆ to form isolable α-olefin complexes of the type, [(PNP)­Ti­(η²-H₂CCHR)­(CH₂<i>^t</i>Bu)] (R = CH₃ (<b>2</b>), CH₂CH₃ (<b>3</b>), <i>ⁿ</i>Pr (<b>4</b>), and ^<i>n</i>Bu (<b>5</b>)). Complexes <b>1</b>–<b>5</b> can be independently prepared from [(PNP)­TiCH<i>^t</i>Bu­(OTf)] and the corresponding alkylating reagents, LiCH₂CHR (R = H, CH₃(unstable), CH₂CH₃, <i>ⁿ</i>Pr, and ^<i>n</i>Bu). Olefin complexes <b>1</b> and <b>3</b>–<b>5</b> have all been characterized by a diverse array of multinuclear NMR spectroscopic experiments including ¹H–³¹P HOESY, and in the case of the α-olefin adducts <b>2</b>–<b>5</b>, formation of mixtures of two diastereomers (each with their corresponding pair of enantiomers) has been unequivocally established. The latter has been spectroscopically elucidated by NMR via C–H coupled and decoupled ¹H–¹³C multiplicity edited gHSQC, ¹H–³¹P HMBC, and dqfCOSY experiments. Heavier linear alkanes (C₇ and C₈) are also dehydrogenated by <b>A</b> to form [(PNP)­Ti­(η²-H₂CCH<i>ⁿ</i>Pentyl)­(CH₂<i>^t</i>Bu)] (<b>6</b>) and [(PNP)­Ti­(η²-H₂CCH^<i>n</i>Hexyl)­(CH₂<i>^t</i>Bu)] (<b>7</b>), respectively, but these species are unstable but can exchange with ethylene (1 atm) to form <b>1</b> and the free α-olefin. Complex <b>1</b> exchanges with D₂CCD₂ with concomitant release of H₂CCH₂. In addition, deuterium incorporation is observed in the neopentyl ligand as a result of this process. Cyclohexane and methylcyclohexane can be also dehydrogenated by transient <b>A</b>, and in the case of cyclohexane, ethylene (1 atm) can trap the [(PNP)­Ti­(CH₂<i>^t</i>Bu)] fragment to form <b>1</b>. Dehydrogenation of the alkane is not rate-determining since pentane and pentane-<i>d</i>₁₂ can be dehydrogenated to <b>4</b> and <b>4</b>-<i>d</i>₁₂ with comparable rates (KIE = 1.1(0) at ∼29 °C). Computational studies have been applied to understand the formation and bonding pattern of the olefin complexes. Steric repulsion was shown to play an important role in determining the relative stability of several olefin adducts and their conformers. The olefin in <b>1</b> can be liberated by use of N₂O, organic azides (N₃R; R = 1-adamantyl or SiMe₃), ketones (OCPh₂; 2 equiv) and the diazoalkane, N₂CHtolyl₂. For complexes <b>3</b>–<b>7</b>, oxidation with N₂O also liberates the α-olefin

Room Temperature Dehydrogenation of Ethane, Propane, Linear Alkanes C4–C8, and Some Cyclic Alkanes by Titanium–Carbon Multiple Bonds

The transient titanium neopentylidyne, [(PNP)­TiC<i>^t</i>Bu] (<b>A</b>; PNP^–N­[2-P<i>ⁱ</i>Pr₂-4-methylphenyl]₂^–), dehydrogenates ethane to ethylene at room temperature over 24 h, by sequential 1,2-CH bond addition and β-hydrogen abstraction to afford [(PNP)­Ti­(η²-H₂CCH₂)­(CH₂<i>^t</i>Bu)] (<b>1</b>). Intermediate <b>A</b> can also dehydrogenate propane to propene, albeit not cleanly, as well as linear and volatile alkanes C₄–C₆ to form isolable α-olefin complexes of the type, [(PNP)­Ti­(η²-H₂CCHR)­(CH₂<i>^t</i>Bu)] (R = CH₃ (<b>2</b>), CH₂CH₃ (<b>3</b>), <i>ⁿ</i>Pr (<b>4</b>), and ^<i>n</i>Bu (<b>5</b>)). Complexes <b>1</b>–<b>5</b> can be independently prepared from [(PNP)­TiCH<i>^t</i>Bu­(OTf)] and the corresponding alkylating reagents, LiCH₂CHR (R = H, CH₃(unstable), CH₂CH₃, <i>ⁿ</i>Pr, and ^<i>n</i>Bu). Olefin complexes <b>1</b> and <b>3</b>–<b>5</b> have all been characterized by a diverse array of multinuclear NMR spectroscopic experiments including ¹H–³¹P HOESY, and in the case of the α-olefin adducts <b>2</b>–<b>5</b>, formation of mixtures of two diastereomers (each with their corresponding pair of enantiomers) has been unequivocally established. The latter has been spectroscopically elucidated by NMR via C–H coupled and decoupled ¹H–¹³C multiplicity edited gHSQC, ¹H–³¹P HMBC, and dqfCOSY experiments. Heavier linear alkanes (C₇ and C₈) are also dehydrogenated by <b>A</b> to form [(PNP)­Ti­(η²-H₂CCH<i>ⁿ</i>Pentyl)­(CH₂<i>^t</i>Bu)] (<b>6</b>) and [(PNP)­Ti­(η²-H₂CCH^<i>n</i>Hexyl)­(CH₂<i>^t</i>Bu)] (<b>7</b>), respectively, but these species are unstable but can exchange with ethylene (1 atm) to form <b>1</b> and the free α-olefin. Complex <b>1</b> exchanges with D₂CCD₂ with concomitant release of H₂CCH₂. In addition, deuterium incorporation is observed in the neopentyl ligand as a result of this process. Cyclohexane and methylcyclohexane can be also dehydrogenated by transient <b>A</b>, and in the case of cyclohexane, ethylene (1 atm) can trap the [(PNP)­Ti­(CH₂<i>^t</i>Bu)] fragment to form <b>1</b>. Dehydrogenation of the alkane is not rate-determining since pentane and pentane-<i>d</i>₁₂ can be dehydrogenated to <b>4</b> and <b>4</b>-<i>d</i>₁₂ with comparable rates (KIE = 1.1(0) at ∼29 °C). Computational studies have been applied to understand the formation and bonding pattern of the olefin complexes. Steric repulsion was shown to play an important role in determining the relative stability of several olefin adducts and their conformers. The olefin in <b>1</b> can be liberated by use of N₂O, organic azides (N₃R; R = 1-adamantyl or SiMe₃), ketones (OCPh₂; 2 equiv) and the diazoalkane, N₂CHtolyl₂. For complexes <b>3</b>–<b>7</b>, oxidation with N₂O also liberates the α-olefin

Addition of Si–H and B–H Bonds and Redox Reactivity Involving Low-Coordinate Nitrido–Vanadium Complexes

In this study we enumerate the reactivity for two molecular vanadium nitrido complexes of [(nacnac)­VN­(X)] formulation [nacnac = (Ar)­NC­(Me)­CHC­(Me)­(Ar)⁻, Ar = 2,6-(CHMe₂)₂C₆H₃); X^– = OAr (<b>1</b>) and N­(4-Me-C₆H₄)₂ (Ntolyl₂) (<b>2</b>)]. Density functional theory calculations and reactivity studies indicate the nitride motif to have nucleophilic character, but where the nitrogen atom can serve as a conduit for electron transfer, thus allowing the reduction of the vanadium­(V) metal ion with concurrent oxidation of the incoming substrate. Silane, H₂SiPh₂, readily converts the nitride ligand in <b>1</b> into a primary silyl–amide functionality with concomitant two-electron reduction at the vanadium center to form the complex [(nacnac)­V­{N­(H)­SiHPh₂}­(OAr)] (<b>3</b>). Likewise, addition of the B–H bond in pinacolborane to the nitride moiety in <b>2</b> results in formation of the boryl–amide complex [(nacnac)­V­{N­(H)­B­(pinacol)}­(Ntolyl₂)] (<b>4</b>). In addition to spectroscopic data, complexes <b>3</b> and <b>4</b> were also elucidated structurally by single-crystal X-ray diffraction analysis. One-electron reduction of <b>1</b> with 0.5% Na/Hg on a preparative scale allowed for the isolation and structural determination of an asymmetric bimolecular nitride radical anion complex having formula [Na]₂[(nacnac)­V­(N)­(OAr)]₂ (<b>5</b>), in addition to room-temperature solution X-band electron paramagnetic resonance spectroscopic studies

Lone-Pair-Induced Topicity Observed in Macrobicyclic Tetra-thia Lactams and Cryptands: Synthesis, Spectral Identification, and Computational Assessment

The synthesis of a rigid macrobicyclic N,S lactam <b>L1</b> and a topologically favored in/in N,S cryptand <b>L2</b> are reported with X-ray structure analysis, dynamic correlation NMR spectroscopy, and computational analysis. Lactam <b>L1</b> exhibits two distinct rotameric conformations (plus their enantiomeric counterparts) at 25 °C, as confirmed via NMR spectroscopy and computational analysis. Coalescence of the resonances of <b>L1</b> was observed at 115 °C, allowing for complete nuclei to frequency correlation. Combining computational investigations with experimental data, topological equilibria and relative energies/strain relating to the perturbation of the pore were determined. Due to the increased conformational strain of the N₂S₂ template, the nitrogen lone pairs in <b>L2</b> elicit a unique transannular interaction, resulting in a thermodynamically favored in/in nephroidal racemate. The combination of preferred topology, steric relief, and electronic localization of <b>L2</b> induces a chiral environment imparted through the amine with a computed inversion barrier of 10.3 kcal mol^–1

Lone-Pair-Induced Topicity Observed in Macrobicyclic Tetra-thia Lactams and Cryptands: Synthesis, Spectral Identification, and Computational Assessment

The synthesis of a rigid macrobicyclic N,S lactam <b>L1</b> and a topologically favored in/in N,S cryptand <b>L2</b> are reported with X-ray structure analysis, dynamic correlation NMR spectroscopy, and computational analysis. Lactam <b>L1</b> exhibits two distinct rotameric conformations (plus their enantiomeric counterparts) at 25 °C, as confirmed via NMR spectroscopy and computational analysis. Coalescence of the resonances of <b>L1</b> was observed at 115 °C, allowing for complete nuclei to frequency correlation. Combining computational investigations with experimental data, topological equilibria and relative energies/strain relating to the perturbation of the pore were determined. Due to the increased conformational strain of the N₂S₂ template, the nitrogen lone pairs in <b>L2</b> elicit a unique transannular interaction, resulting in a thermodynamically favored in/in nephroidal racemate. The combination of preferred topology, steric relief, and electronic localization of <b>L2</b> induces a chiral environment imparted through the amine with a computed inversion barrier of 10.3 kcal mol^–1

Lone-Pair-Induced Topicity Observed in Macrobicyclic Tetra-thia Lactams and Cryptands: Synthesis, Spectral Identification, and Computational Assessment

The synthesis of a rigid macrobicyclic N,S lactam <b>L1</b> and a topologically favored in/in N,S cryptand <b>L2</b> are reported with X-ray structure analysis, dynamic correlation NMR spectroscopy, and computational analysis. Lactam <b>L1</b> exhibits two distinct rotameric conformations (plus their enantiomeric counterparts) at 25 °C, as confirmed via NMR spectroscopy and computational analysis. Coalescence of the resonances of <b>L1</b> was observed at 115 °C, allowing for complete nuclei to frequency correlation. Combining computational investigations with experimental data, topological equilibria and relative energies/strain relating to the perturbation of the pore were determined. Due to the increased conformational strain of the N₂S₂ template, the nitrogen lone pairs in <b>L2</b> elicit a unique transannular interaction, resulting in a thermodynamically favored in/in nephroidal racemate. The combination of preferred topology, steric relief, and electronic localization of <b>L2</b> induces a chiral environment imparted through the amine with a computed inversion barrier of 10.3 kcal mol^–1