Autoxidation of Heterocyclic Aminals

The autoxidation reactions of 2-acyl-2,3-dihydroquinazolin-4­(1<i>H</i>)-ones <b>4a</b> and <b>5a</b> and 2,2′-bis­(dihydroquinazolinone) <b>6a</b> are described. These reactions generate aminyl radicals that undergo β-C–C cleavage, and subsequent reactions of the resulting C-based radicals with O₂ lead to diverse products with good selectivity, depending on the structure of the substrate. Oxidation of <b>4a</b>, in which the 2-acyl group is part of a cyclic acenaphthenone unit, yields a heterocyclic <i>C</i>-hydroperoxylaminal via 1,2-acyl migration. Oxidation of <b>5a</b>, which contains a 2-acetyl group, yields peracetic acid and a quinazolinone product. Oxidation of <b>6a</b> forms a bis­(quinazolinone) by net dehydrogenation

Hydrogen Bonding Behavior of Amide-Functionalized α‑Diimine Palladium Complexes

A class of (<i>N,N</i>′-diaryl-α-diimine)­Pd complexes bearing amide substituents on the N-aryl rings is described. Hydrogen bonding interactions involving the amide groups influence the structures, isomer distributions, and ligand coordination behavior of these compounds. The amide-functionalized α-diimine ligands (2,6-ⁱPr₂-Ph)­NCMeCMeN­(2-C­(O)­NMe₂-6-ⁱPr-Ph) (<b>4a</b>), (2,6-ⁱPr₂-Ph)­NCMeCMeN­(2,6-(C­(O)­NMe₂)₂-Ph) (<b>4b</b>), and (2-C­(O)­NMe₂-6-ⁱPr-Ph)­NCMeCMeN­(2-C­(O)­NMe₂-6-ⁱPr-Ph) (<b>4c</b>) were prepared by condensation reactions of 2,3-butanedione and the appropriate anilines. The attempted preparation of (2,6-ⁱPr₂-Ph)­NCMeCMeN­(2-C­(O)­NHMe-6-ⁱPr-Ph) (<b>4d</b>) yielded the corresponding 1,2-dihydroquinazolinone derivative <b>4d</b>′ formed by nucleophilic attack of the amide nitrogen at the proximal imine carbon. <b>4a</b> and <b>4b</b> react with (cod)­PdMeCl to yield square planar (α-diimine)­PdMeCl complexes <b>5a</b>,<b>a</b>′ and <b>5b</b>,<b>b</b>′, respectively, which exist as two isomers that differ in the orientation (trans/cis) of the Pd–Me ligand and the amide-substituted arylimine unit. <b>4c</b> reacts with (MeCN)₂PdCl₂ and (cod)­PdMeCl to yield (<b>4c</b>)­PdCl₂ (<b>6c-</b><i><b>anti</b></i>,<i><b>syn</b></i>) and (<b>4c</b>)­PdMeCl (<b>5c-</b><i><b>anti</b></i>,<i><b>syn</b></i>), which exhibit anti/syn isomerism due to hindered rotation of the C_aryl–N bonds. In the solid state, the amide oxygen atoms in <b>6c-</b><i><b>anti</b></i> and <b>5c-</b><i><b>syn</b></i> engage in hydrogen bonding with cocrystallized CH₂Cl₂ solvent molecules. <b>4d</b>′ reacts with (MeCN)₂PdCl₂ via ring-opening metalation to afford the α-diimine complex (<b>4d</b>)­PdCl₂ (<b>6d</b>). Transmetalation of <b>6d</b> with SnMe₄ yields (<b>4d</b>)­PdMeCl (<b>5d</b>,<b>d</b>′) as a mixture of trans and cis isomers. The reaction of <b>5d</b>,<b>d</b>′ with AgOAc yields (<b>4d</b>)­PdMe­(OAc) (<b>7d</b>) as a single isomer in which the Pd–Me group is trans to the amide-functionalized arylimine unit. <b>5d</b>, <b>6d</b>, and <b>7d</b> exhibit intramolecular N–H···Cl and N–H···O hydrogen bonding interactions involving the amide NH units. The reactions of <b>5a</b>,<b>a</b>′, <b>5c-</b><i><b>anti</b></i>, and <b>5d</b>,<b>d</b>′ with AgSbF₆ in the presence of pyrazole yield the corresponding (α-diimine)­PdMe­(pz)⁺SbF₆^– salts (<b>8a</b>,<b>c</b>,<b>d</b>; pz = pyrazole), which exhibit an intramolecular hydrogen bond between the amide oxygen and the pyrazole NH unit. <b>8a</b>,<b>c</b>,<b>d</b> undergo partial dissociation of pyrazole in CD₃CN solution to generate the corresponding CD₃CN complexes <b>9a</b>,<b>c</b>,<b>d</b>. The non-hydrogen-bonded complex {(2,6-ⁱPr₂-Ph)­NCMeCMeN­(2,6-ⁱPr₂-Ph)}­PdMe­(pz)⁺SbF₆^– (<b>8e</b>) and its pyrazole dissociation product {(2,6-ⁱPr₂-Ph)­NCMeCMeN­(2,6-ⁱPr₂-Ph)}­PdMe­(CD₃CN)⁺SbF₆^– (<b>9e</b>) were generated in a similar fashion. The pyrazole dissociation constants, <i>K</i>_eq = [(α-diimine)­PdMe­(CD₃CN)⁺] × [pz] × [(α-diimine)­PdMe­(pz)⁺]⁻¹, vary in the order <b>8e</b> > <b>8d</b> > <b>8a</b> > <b>8c</b>, span more than 2 orders of magnitude, and reflect the enhancement of pyrazole binding in <b>8a</b>,<b>c</b>,<b>d</b> by amide–pyrazole hydrogen bonding. The intramolecular hydrogen bonding in <b>8c</b> strengthens pyrazole binding by a factor of ca. 120 (i.e., ΔΔ<i>G</i> = 2.8(1) kcal mol^–1) relative to the case of <b>8e</b>

Hydrogen Bonding Behavior of Amide-Functionalized α‑Diimine Palladium Complexes

A class of (<i>N,N</i>′-diaryl-α-diimine)­Pd complexes bearing amide substituents on the N-aryl rings is described. Hydrogen bonding interactions involving the amide groups influence the structures, isomer distributions, and ligand coordination behavior of these compounds. The amide-functionalized α-diimine ligands (2,6-ⁱPr₂-Ph)­NCMeCMeN­(2-C­(O)­NMe₂-6-ⁱPr-Ph) (<b>4a</b>), (2,6-ⁱPr₂-Ph)­NCMeCMeN­(2,6-(C­(O)­NMe₂)₂-Ph) (<b>4b</b>), and (2-C­(O)­NMe₂-6-ⁱPr-Ph)­NCMeCMeN­(2-C­(O)­NMe₂-6-ⁱPr-Ph) (<b>4c</b>) were prepared by condensation reactions of 2,3-butanedione and the appropriate anilines. The attempted preparation of (2,6-ⁱPr₂-Ph)­NCMeCMeN­(2-C­(O)­NHMe-6-ⁱPr-Ph) (<b>4d</b>) yielded the corresponding 1,2-dihydroquinazolinone derivative <b>4d</b>′ formed by nucleophilic attack of the amide nitrogen at the proximal imine carbon. <b>4a</b> and <b>4b</b> react with (cod)­PdMeCl to yield square planar (α-diimine)­PdMeCl complexes <b>5a</b>,<b>a</b>′ and <b>5b</b>,<b>b</b>′, respectively, which exist as two isomers that differ in the orientation (trans/cis) of the Pd–Me ligand and the amide-substituted arylimine unit. <b>4c</b> reacts with (MeCN)₂PdCl₂ and (cod)­PdMeCl to yield (<b>4c</b>)­PdCl₂ (<b>6c-</b><i><b>anti</b></i>,<i><b>syn</b></i>) and (<b>4c</b>)­PdMeCl (<b>5c-</b><i><b>anti</b></i>,<i><b>syn</b></i>), which exhibit anti/syn isomerism due to hindered rotation of the C_aryl–N bonds. In the solid state, the amide oxygen atoms in <b>6c-</b><i><b>anti</b></i> and <b>5c-</b><i><b>syn</b></i> engage in hydrogen bonding with cocrystallized CH₂Cl₂ solvent molecules. <b>4d</b>′ reacts with (MeCN)₂PdCl₂ via ring-opening metalation to afford the α-diimine complex (<b>4d</b>)­PdCl₂ (<b>6d</b>). Transmetalation of <b>6d</b> with SnMe₄ yields (<b>4d</b>)­PdMeCl (<b>5d</b>,<b>d</b>′) as a mixture of trans and cis isomers. The reaction of <b>5d</b>,<b>d</b>′ with AgOAc yields (<b>4d</b>)­PdMe­(OAc) (<b>7d</b>) as a single isomer in which the Pd–Me group is trans to the amide-functionalized arylimine unit. <b>5d</b>, <b>6d</b>, and <b>7d</b> exhibit intramolecular N–H···Cl and N–H···O hydrogen bonding interactions involving the amide NH units. The reactions of <b>5a</b>,<b>a</b>′, <b>5c-</b><i><b>anti</b></i>, and <b>5d</b>,<b>d</b>′ with AgSbF₆ in the presence of pyrazole yield the corresponding (α-diimine)­PdMe­(pz)⁺SbF₆^– salts (<b>8a</b>,<b>c</b>,<b>d</b>; pz = pyrazole), which exhibit an intramolecular hydrogen bond between the amide oxygen and the pyrazole NH unit. <b>8a</b>,<b>c</b>,<b>d</b> undergo partial dissociation of pyrazole in CD₃CN solution to generate the corresponding CD₃CN complexes <b>9a</b>,<b>c</b>,<b>d</b>. The non-hydrogen-bonded complex {(2,6-ⁱPr₂-Ph)­NCMeCMeN­(2,6-ⁱPr₂-Ph)}­PdMe­(pz)⁺SbF₆^– (<b>8e</b>) and its pyrazole dissociation product {(2,6-ⁱPr₂-Ph)­NCMeCMeN­(2,6-ⁱPr₂-Ph)}­PdMe­(CD₃CN)⁺SbF₆^– (<b>9e</b>) were generated in a similar fashion. The pyrazole dissociation constants, <i>K</i>_eq = [(α-diimine)­PdMe­(CD₃CN)⁺] × [pz] × [(α-diimine)­PdMe­(pz)⁺]⁻¹, vary in the order <b>8e</b> > <b>8d</b> > <b>8a</b> > <b>8c</b>, span more than 2 orders of magnitude, and reflect the enhancement of pyrazole binding in <b>8a</b>,<b>c</b>,<b>d</b> by amide–pyrazole hydrogen bonding. The intramolecular hydrogen bonding in <b>8c</b> strengthens pyrazole binding by a factor of ca. 120 (i.e., ΔΔ<i>G</i> = 2.8(1) kcal mol^–1) relative to the case of <b>8e</b>

Synthesis and Reactivity of Palladium(II) Alkyl Complexes that Contain Phosphine-cyclopentanesulfonate Ligands

The synthesis of the phosphine-cyclopentanesulfonate pro-ligands Li/K­[2-PPh₂-cyclopentanesulfonate] (Li/K­[<b>2a</b>]), Li/K­[2-P­(2-OMe-Ph)₂-cyclopentanesulfonate] (Li/K­[<b>2b</b>]), and H­[<b>2b</b>], and the corresponding Pd­(II) alkyl complexes (κ²-<i>P</i>,<i>O</i>-<b>2a</b>)­PdMe­(pyridine) (<b>3a</b>) and (κ²-<i>P</i>,<i>O</i>-<b>2b</b>)­PdMe­(pyridine) (<b>3b</b>) is described. The sulfonate-bridged base-free dimer {(<b>2b</b>)­PdMe}₂ (<b>4b</b>) was synthesized by abstraction of pyridine from <b>3b</b> using B­(C₆F₅)₃. The borane-coordinated base-free dimer [{<b>2b·</b>B­(C₆F₅)₃}­PdMe]₂ (<b>5b</b>), in which B­(C₆F₅)₃ binds to a sulfonate oxygen, was prepared by addition of 1 equiv of B­(C₆F₅)₃ per Pd to <b>4b</b> or addition of 2 equiv of B­(C₆F₅)₃ to <b>3b</b>. Compounds <b>3b</b>, <b>4b</b>, and <b>5b</b> polymerize ethylene with low activity (up to 210 kg mol^–1 h^–1 at 250 psi and 80 °C) to linear polyethylene (<i>M</i>_n = 1950–5250 Da) with predominantly internal olefin placements. <b>3b</b> and <b>4b</b> copolymerize ethylene with methyl acrylate to linear copolymers that contain up to 11.7 mol % methyl acrylate, which is incorporated as −CH₂CH­(CO₂Me)­CH₂– (80%) in-chain units and −CH₂CH­(CO₂Me)­Me (8%) and −CH₂CHCH­(CO₂Me) (12%) chain-end units. <b>3b</b> and <b>4b</b> also copolymerize ethylene with vinyl fluoride to linear copolymers that contain up to 0.41 mol % vinyl fluoride, which is incorporated as −CH₂CHFCH₂– (∼80%) in-chain units and −CH₂CF₂H (7%), −CH₂CHFCH₃ (5%), and −CH₂CH₂F (8%) chain-end units. Complexes <b>3b</b> and <b>4b</b> are more stable and active in ethylene polymerization than analogous (PAr₂-<i>CH</i>₂<i>CH</i>₂SO₃)­PdR catalysts, but are less active than analogous (PAr₂-<i>arene</i>sulfonate)­PdR catalysts. Low-temperature NMR studies show that <b>4b</b> reacts with ethylene below −10 °C to form the ethylene adduct <i>cis</i>-<i>P</i>,<i>R</i>-(<b>2b</b>)­PdMe­(ethylene) (<b>7b</b>), which undergoes ethylene insertion at 5 °C. DFT calculations for a model (PMe₂-cyclopentanesulfonate)­Pd­(Pr)­(ethylene) species show that ethylene insertion proceeds by <i>cis</i>-<i>P</i>,<i>R</i>/<i>trans</i>-<i>P</i>,<i>R</i> isomerization followed by migratory insertion, and that the lower activity of <b>3b</b> and <b>4b</b> vis-à-vis analogous (PAr₂-arenesulfonate)­PdR catalysts results from a higher barrier for migratory insertion of the <i>trans</i>-<i>P</i>,<i>R</i> isomer

Reactivity of (Pyridine-Diimine)Fe Alkyl Complexes with Carbon Dioxide

The reaction of CO₂ with (PDI)­FeMe (<b>1</b>), (PDI)­Fe­(Me)­PMe₃ (<b>1-PMe</b>_<b>3</b>) and [(PDI)­FeMe]­[BPh₄] (<b>2</b>, PDI = 2,6-(2,6-^<i>i</i>Pr₂–C₆H₃–NCMe)₂–C₅H₃N) generates (PDI)­Fe­OAc (<b>3</b>), (PDI)­Fe­(OAc)­PMe₃ (<b>3-PMe</b>_<b>3</b>), and [(PDI)­FeOAc]­[BPh₄] (<b>4</b>), respectively. Kinetic data and solvent effects provide evidence that these reactions occur by precoordination of CO₂ to the Fe center regardless of the charge state and thus favor an insertion mechanism for carboxylation. Carboxylation of <b>1-PMe</b>_<b>3</b> requires initial dissociation of PMe₃ to generate <b>1</b>, which reacts with CO₂; <b>1-PMe</b>_<b>3</b> itself does not react directly with CO₂. CO₂ reacts 5 times faster with neutral <b>1</b> than with cationic <b>2</b> (at 0 °C), which is ascribed to the higher nucleophilicity of the Fe–Me group in <b>1</b>

Reactivity of (Pyridine-Diimine)Fe Alkyl Complexes with Carbon Dioxide

The reaction of CO₂ with (PDI)­FeMe (<b>1</b>), (PDI)­Fe­(Me)­PMe₃ (<b>1-PMe</b>_<b>3</b>) and [(PDI)­FeMe]­[BPh₄] (<b>2</b>, PDI = 2,6-(2,6-^<i>i</i>Pr₂–C₆H₃–NCMe)₂–C₅H₃N) generates (PDI)­Fe­OAc (<b>3</b>), (PDI)­Fe­(OAc)­PMe₃ (<b>3-PMe</b>_<b>3</b>), and [(PDI)­FeOAc]­[BPh₄] (<b>4</b>), respectively. Kinetic data and solvent effects provide evidence that these reactions occur by precoordination of CO₂ to the Fe center regardless of the charge state and thus favor an insertion mechanism for carboxylation. Carboxylation of <b>1-PMe</b>_<b>3</b> requires initial dissociation of PMe₃ to generate <b>1</b>, which reacts with CO₂; <b>1-PMe</b>_<b>3</b> itself does not react directly with CO₂. CO₂ reacts 5 times faster with neutral <b>1</b> than with cationic <b>2</b> (at 0 °C), which is ascribed to the higher nucleophilicity of the Fe–Me group in <b>1</b>

(α-Diimine)nickel Complexes That Contain Menthyl Substituents: Synthesis, Conformational Behavior, and Olefin Polymerization Catalysis

We describe the synthesis and coordination chemistry of the (1<i>R</i>,2<i>S</i>,5<i>R</i>)-menthyl-substituted <i>N,N</i>′-diaryl-α-diimine ligands <i>N,N</i>′-(2-Men-4-Me-Ph)₂-BIAN (<b>L1</b>, Men = menthyl, BIAN = bis­(imino)­acenaphthene) and <i>N,N</i>′-(2-Men-4,6-Me₂-Ph)₂-BIAN (<b>L2</b>), the conformational properties of these ligands and their metal complexes, and the ethylene and 1-hexene polymerization behavior of the corresponding (α-diimine)­Ni complexes. Free ligands <b>L1</b> and <b>L2</b> and square-planar (<b>L1</b>)­PdCl₂ and (<b>L1</b>,<b>2</b>)­Ni­(acac)⁺ complexes exhibit a preference for the syn conformation, in which the two menthyl units are located on the same side of the NCCN plane, while tetrahedral (<b>L1</b>,<b>2</b>)­MX₂ (MX₂ = ZnCl₂, NiBr₂) complexes exhibit a preference for the <i>anti</i> conformation, in which the menthyl units are located on opposite sides of the NCCN plane. Both the <i>anti</i> and the <i>syn</i> conformers of [(<b>L2</b>)­Ni­(acac)]­[B­(C₆F₅)₄] can be activated by Et₂AlCl to generate highly active ethylene polymerization catalysts (activity (2.5–6.6) × 10⁶ g of PE/((mol of Ni) h) at 15 psi of C₂H₄, room temperature). The polyethylene produced by the <i>syn</i> conformer (<i>syn</i>/<i>anti</i> = 91/9) has a higher molecular weight (2×) and a higher branch density (3×) in comparison to that produced by the <i>anti</i> conformer. The polyhexene produced by the <i>syn</i> conformer (<i>syn</i>/<i>anti</i> = 91/9) contains a higher level of chain straightening (<i>syn</i> 50%, <i>anti</i> 41%) and a higher percentage of Me versus Bu branches (<i>syn</i> 24/26, <i>anti</i> 6/53) in comparison to that produced by the <i>anti</i> isomer. These results are indicative of a greater preference for 2,1-insertion and for chain walking (versus growth) following 1,2-insertion for the <i>syn</i> conformer

Lewis Acid Modification and Ethylene Oligomerization Behavior of Palladium Catalysts That Contain a Phosphine-Sulfonate-Diethyl Phosphonate Ancillary Ligand

The multifunctional phosphine-sulfonate-diethyl phosphonate ligand [1-(P­(4-^<i>t</i>Bu-Ph)­(2-PO₃Et₂-5-Me-Ph)-2-SO₃-5-Me-Ph]⁻ ([OP-P-SO]⁻) was used to form complexes of type [κ²-(OP-<i>P</i>-S<i>O</i>)]­PdMe­(L) (L = 2,6-lutidine, <b>2b</b>; L = pyridine, <b>2c</b>). B­(C₆F₅)₃ abstracts the Pd-bound sulfonate group of <b>2b</b> and induces a switch to a phosphine-diethyl phosphonate coordination mode, affording [κ²-(<i>O</i>P-<i>P</i>-SO-B­(C₆F₅)₃)]­PdMe­(2,6-lutidine) (<b>3</b>). In contrast, MgCl₂ binds to the sulfonate and diethyl phosphonate units of <b>2b</b>, generating the dipalladium species [{κ²-(OP-<i>P</i>-S<i>O</i>)­PdMe}₂­(μ-Cl)]­[MgCl] (<b>4</b>) by simple self-assembly. AgB­(C₆F₅)₄ reacts with <b>4</b> in the presence of THF to selectively abstract the Mg-<i>Cl</i> to form [{κ²-(OP-<i>P</i>-S<i>O</i>)­PdMe}₂­(μ-Cl)­Mg­(THF)]­[B­(C₆F₅)₄] (<b>5</b>). The ethylene polymerization behaviors of <b>2b</b>, <b>2c</b>, <b>3</b>, and <b>5</b> are quite similar (<i>M</i>_n: 120–1170 Da, activity: 60–290 kg (mol Pd)^–1 h^–1). All of these catalysts produce low-molecular-weight polyethylene with predominantly internal unsaturation, but little branching. The reaction of <b>4</b> with 2 equiv of AgB­(C₆F₅)₄ to abstract both chloride ions generates an active ethylene polymerization catalyst that produces linear polyethylene with a bimodal molecular weight distribution

Synthesis and Reactivity of NHC-Supported Ni₂(μ²‑η²,η²‑S₂)‑Bridging Disulfide and Ni₂(μ-S)₂‑Bridging Sulfide Complexes

The (IPr)Ni scaffold stabilizes low-coordinate, mononuclear and dinuclear complexes with a diverse range of sulfur ligands, including μ²-η²,η²-S₂, η²-S₂, μ-S, and μ-SH motifs. The reaction of {(IPr)­Ni}₂(μ-Cl)₂ (<b>1</b>, IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazolin-2-ylidene) with S₈ yields the bridging disulfide species {(IPr)­ClNi}₂(μ²-η²,η²-S₂) (<b>2</b>). Complex <b>2</b> reacts with 2 equiv of AdNC (Ad = adamantyl) to yield a 1:1 mixture of the terminal disulfide compound (IPr)­(AdNC)­Ni­(η²-S₂) (<b>3a</b>) and <i>trans</i>-(IPr)­(AdNC)­NiCl₂ (<b>4a</b>). <b>2</b> also reacts with KC₈ to produce the Ni–Ni-bonded bridging sulfide complex {(IPr)­Ni}₂(μ-S)₂ (<b>6</b>). Complex <b>6</b> reacts with H₂ to yield the bridging hydrosulfide compound {(IPr)­Ni}₂(μ-SH)₂ (<b>7</b>), which retains a Ni–Ni bond. <b>7</b> is converted back to <b>6</b> by hydrogen atom abstraction by 2,4,6-^tBu₃-phenoxy radical. The 2,6-diisopropylphenyl groups of the IPr ligand provide lateral steric protection of the (IPr)Ni unit but allow for the formation of Ni–Ni-bonded dinuclear species and electronically preferred rather than sterically preferred structures