An efficient one-pot synthesis of carbazole fused benzoquinolines and pyridocarbazoles

Cobalt­(II), in the presence of acetate and nitrate, quantitatively adds to the manganese–cobalt oxido cubane Mn^IVCo^III₃O₄(OAc)₅(py)₃ (<b>1</b>) to furnish the pentametallic dangler complex Mn^IVCo^III₃Co^IIO₄(OAc)₆(NO₃)­(py)₃ (<b>2</b>). Complex <b>2</b> is structurally reminiscent of photosystem II’s oxygen-evolving center, and is a rare example of a transition-metal “dangler” complex. Superconducting quantum interference device magnetometry and density functional theory calculations characterize <b>2</b> as having an <i>S</i> = 0 ground state arising from antiferromagnetic coupling between the Co^II and Mn^IV ions. At higher temperatures, an uncoupled state dominates. The voltammogram of <b>2</b> has four electrochemical events, two more than that of its parent cubane <b>1</b>, suggesting that addition of the dangler increases available redox states. Structural, electrochemical, and magnetic comparisons of complexes <b>1</b> and <b>2</b> allow a better understanding of the dangler’s influence on a cubane

Sterically Controlled Functionalization of Carbon Surfaces with −C₆H₄CH₂X (X = OSO₂Me or N₃) Groups for Surface Attachment of Redox-Active Molecules

Glassy carbon electrodes were modified by electrochemical reduction of a diazonium molecule (^<i>i</i>Pr₃SiOCH₂­C₆H₄N₂⁺BF₄^–) featuring a triisopropylsilyl-protected benzylic hydroxyl group. This electrochemical process introduced a monolayer of ^<i>i</i>Pr₃Si­OCH₂C₆H₄– groups onto the surface of the electrode. The bulky −Si^<i>i</i>Pr₃ protecting group not only prevents the uncontrolled growth of structurally ill-defined and electronically blocking polyphenylene multilayers, but also separates the phenyl groups in the monolayer. Thus, the void spaces between these aryl units should allow a better accommodation of sizable molecules. Removal of the −Si^<i>i</i>Pr₃ protecting groups by ^<i>n</i>Bu₄NF exposed the reactive benzylic hydroxyl functionalities that can undergo further transformations to anchor functional molecules. As an example, redox-active ferrocene molecules were grafted onto the modified electrode via a sequence of mesylation, azidation, and copper-catalyzed [3 + 2] cycloaddition reactions. The presence of ferrocenyl groups on the surface was confirmed by X-ray photoelectron spectroscopic and electrochemical studies. The resulting ferrocene-modified glassy carbon electrode exhibits cyclic voltammograms typical of surface-bound redox active species and remarkable electrochemical stability in an acidic aqueous environment

Base-Free Iron Hydrosilylene Complexes via an α‑Hydride Migration that Induces Spin Pairing

Two new base-free hydrosilylene complexes of iron were synthesized using the novel starting material Cp*­(^<i>i</i>Pr₂MeP)­FeMes. These Cp*­(^<i>i</i>Pr₂MeP)­Fe­(H)­SiHR (R = DMP, Trip) complexes are in equilibrium with the corresponding iron silyl complexes, Cp*­(^<i>i</i>Pr₂MeP)­FeSiH₂R, which can be trapped and characterized for R = Trip. Unlike the Ru analogues, the Fe silylene complex with R = DMP is observed to undergo an intramolecular CH activation involving formal addition of a benzylic CH bond across the FeSi bond. This increased activity for bond activations is also observed for reactions with hydrogen, where Fe reacts faster than a Ru analog to form the hydrogenation product, Cp*­(^<i>i</i>Pr₂MeP)­H₂FeSiH₂DMP

Silane–Isocyanide Coupling Involving 1,1-Insertion of XylNC into the Si–H Bond of a σ‑Silane Ligand

Complexes [PhBP^Ph₃]­RuH­(η³-H₂SiRR′) (R,R′ = Me,Ph, <b>1a</b>; RR′ = Ph₂, <b>1b</b>) react with XylNC (Xyl = 2,6-dimethylphenyl) to form Fischer carbene complexes [PhBP^Ph₃]­Ru­(H)[C­(H)­(N­(Xyl)­(η²-H–SiRR′))] (<b>2a</b>,<b>b</b>) that feature a γ-agostic Si–H bond. The ruthenium isocyanide complexes [PhBP^Ph₃]­Ru­(H)­(CNXyl)­(η²-HSiHRR′) (<b>6a</b>,<b>b</b>) are not intermediates as they do not convert to <b>2a</b>,<b>b</b>. Experimental and theoretical investigations indicate that XylNC is activated by initial coordination to the silicon center in <b>1a</b>,<b>b</b>, followed by 1,1-insertion into an Si–H bond of the coordinated silane and then rearrangement to <b>2a</b>,<b>b</b>

Silane–Allyl Coupling Reactions of Cp*(^<i>i</i>Pr₂MeP)Fe(η³‑C₃H₅) and Synthetic Access to the Hydrido–Dinitrogen Complex Cp*(^<i>i</i>Pr₂MeP)FeH(N₂)

Herein we report reactions of the iron allyl complex Cp*­(ⁱPr₂MeP)­Fe­(η³-C₃H₅) with sterically demanding silanes. These reactions lead to stoichiometric hydrosilation of the allyl ligand and dehydrocoupling reactions between the silane and the allyl group. Furthermore, this system has allowed access to a novel Si–H oxidative addition–reductive elimination equilibrium involving Cp*­(ⁱPr₂MeP)­FeH₂(SiH₂DMP) and Cp*­(ⁱPr₂MeP)­FeH­(N₂), which was independently synthesized

Silane–Allyl Coupling Reactions of Cp*(^<i>i</i>Pr₂MeP)Fe(η³‑C₃H₅) and Synthetic Access to the Hydrido–Dinitrogen Complex Cp*(^<i>i</i>Pr₂MeP)FeH(N₂)

Herein we report reactions of the iron allyl complex Cp*­(ⁱPr₂MeP)­Fe­(η³-C₃H₅) with sterically demanding silanes. These reactions lead to stoichiometric hydrosilation of the allyl ligand and dehydrocoupling reactions between the silane and the allyl group. Furthermore, this system has allowed access to a novel Si–H oxidative addition–reductive elimination equilibrium involving Cp*­(ⁱPr₂MeP)­FeH₂(SiH₂DMP) and Cp*­(ⁱPr₂MeP)­FeH­(N₂), which was independently synthesized

Silane–Isocyanide Coupling Involving 1,1-Insertion of XylNC into the Si–H Bond of a σ‑Silane Ligand

Complexes [PhBP^Ph₃]­RuH­(η³-H₂SiRR′) (R,R′ = Me,Ph, <b>1a</b>; RR′ = Ph₂, <b>1b</b>) react with XylNC (Xyl = 2,6-dimethylphenyl) to form Fischer carbene complexes [PhBP^Ph₃]­Ru­(H)[C­(H)­(N­(Xyl)­(η²-H–SiRR′))] (<b>2a</b>,<b>b</b>) that feature a γ-agostic Si–H bond. The ruthenium isocyanide complexes [PhBP^Ph₃]­Ru­(H)­(CNXyl)­(η²-HSiHRR′) (<b>6a</b>,<b>b</b>) are not intermediates as they do not convert to <b>2a</b>,<b>b</b>. Experimental and theoretical investigations indicate that XylNC is activated by initial coordination to the silicon center in <b>1a</b>,<b>b</b>, followed by 1,1-insertion into an Si–H bond of the coordinated silane and then rearrangement to <b>2a</b>,<b>b</b>

Silane–Allyl Coupling Reactions of Cp*(^<i>i</i>Pr₂MeP)Fe(η³‑C₃H₅) and Synthetic Access to the Hydrido–Dinitrogen Complex Cp*(^<i>i</i>Pr₂MeP)FeH(N₂)

Herein we report reactions of the iron allyl complex Cp*­(ⁱPr₂MeP)­Fe­(η³-C₃H₅) with sterically demanding silanes. These reactions lead to stoichiometric hydrosilation of the allyl ligand and dehydrocoupling reactions between the silane and the allyl group. Furthermore, this system has allowed access to a novel Si–H oxidative addition–reductive elimination equilibrium involving Cp*­(ⁱPr₂MeP)­FeH₂(SiH₂DMP) and Cp*­(ⁱPr₂MeP)­FeH­(N₂), which was independently synthesized

Base-Free Iron Hydrosilylene Complexes via an α‑Hydride Migration that Induces Spin Pairing

Two new base-free hydrosilylene complexes of iron were synthesized using the novel starting material Cp*­(^<i>i</i>Pr₂MeP)­FeMes. These Cp*­(^<i>i</i>Pr₂MeP)­Fe­(H)­SiHR (R = DMP, Trip) complexes are in equilibrium with the corresponding iron silyl complexes, Cp*­(^<i>i</i>Pr₂MeP)­FeSiH₂R, which can be trapped and characterized for R = Trip. Unlike the Ru analogues, the Fe silylene complex with R = DMP is observed to undergo an intramolecular CH activation involving formal addition of a benzylic CH bond across the FeSi bond. This increased activity for bond activations is also observed for reactions with hydrogen, where Fe reacts faster than a Ru analog to form the hydrogenation product, Cp*­(^<i>i</i>Pr₂MeP)­H₂FeSiH₂DMP

Hypercoordinate Ketone Adducts of Electrophilic η³‑H₂SiRR′ Ligands on Ruthenium as Key Intermediates for Efficient and Robust Catalytic Hydrosilation

The electrophilic η³-H₂SiRR′ σ-complexes [PhBP^Ph₃]­RuH­(η³-H₂SiRR′) (RR′ = MePh, <b>1a</b>; Ph₂, <b>1b</b>; [PhBP^Ph₃]⁻ = [PhB­(CH₂PPh₂)₃]⁻) are efficient catalysts (0.01–2.5 mol % loading) for the hydrosilation of ketones with PhMeSiH₂, Ph₂SiH₂, or EtMe₂SiH. An alkoxy complex [PhBP^Ph₃]­Ru–OCHPh₂ (<b>4b</b>) was observed (by ³¹P­{¹H} NMR spectroscopy) as the catalyst resting state during hydrosilation of benzophenone with EtMe₂SiH. A different catalyst resting state was observed for reactions using PhMeSiH₂ or Ph₂SiH₂, and was identified as a silane σ-complex [PhBP^Ph₃]­RuH­[η²-H–SiRR′(OCHPh₂)] (RR′ = MePh, <b>5a</b>; Ph₂, <b>5b</b>) using variable temperature multinuclear NMR spectroscopy (−80 to 20 °C). The hydrosilation of benzophenone with PhMeSiH₂ and <b>1a</b> was examined by ¹H NMR spectroscopy at −18 °C (in CD₂Cl₂), and this revealed that either <b>1a</b>, <b>5a</b>, or both <b>1a</b> and <b>5a</b> could be observed as resting states of the catalytic cycle, depending on the initial [PhMeSiH₂]:[benzophenone] ratio. Kinetic studies revealed two possible expressions for the rate of product formation, depending on which catalyst resting state was present (rate = <i>k</i>_obs[PhMeSiH₂]­[<b>5a</b>] and rate = <i>k</i>′_obs[benzophenone]­[<b>1a</b>]). Computational methods (DFT, b3pw91, 6-31G­(d,p)/LANL2DZ) were used to determine a model catalytic cycle for the hydrosilation of acetone with PhMeSiH₂. A key step in this mechanism involves coordination of acetone to the silicon center of <b>1a-DFT</b>, which leads to insertion of the carbonyl group into an Si–H bond (that is part of a Ru–HSi 3c–2e bond). This generates an intermediate analogous to <b>5a</b> (<b>5a-i-DFT)</b>, and the final product is displaced from <b>5a-i-DFT</b> by an associative process involving PhMeSiH₂