Iron homo- and heterobimetallic complexes supported by a symmetrical dinucleating ligand.

The selective synthesis of biomimetic Fe/Mn complexes able to mimic the geometry and catalytic activity of enzymes possessing this cofactor is still a challenge. Herein, we discuss the stepwise synthesis, characterization, and magnetic properties of a Fe(II)/Mn(II) species and related Fe(II)/Fe(II) complexes.

Cluster dynamics of heterometallic trinuclear clusters during ligand substitution, redox chemistry, and group transfer processes.

Stepwise metalation of the hexadentate ligand LH (LH = 1,3,5-CH(NHCH--NHSiMeBu)) affords bimetallic trinuclear clusters (L)FeZn(thf) and (L)FeZn(py). Reactivity studies were pursued to understand metal atom lability as the clusters undergo ligand substitution, redox chemistry, and group transfer processes. Chloride addition to (L)FeZn(thf) resulted in a mixture of species including both all-zinc and all-iron products.

A [CoSiH] Silylene Synthon Provides Modular Access to Homo- and Heterobimetallic [Co═Si═M] (M = Co, Fe) Silicide Complexes.

Base-stabilized [BP](H)CoSiH(DMAP) (, [BP] = PhB(CHPPr); DMAP = 4-dimethylaminopyridine) is a rare instance of a synthon for the simplest "parent" silylene complex (LM═SiH). Complex was accessed in high yields via double Si-H bond activation in SiH by [BP]Co(DMAP), and in solution, it undergoes rapid exchange between bound and free DMAP by an associative mechanism (as determined by variable-temperature H NMR dynamic studies). The DMAP ligand of is readily displaced by metal-based fragments that bind silicon and cleave the Si-H bonds of the SiH moiety to produce bimetallic [Co═Si═M] (M = Co, Fe) molecular silicides.

Tetracopper σ-Bound μ-Acetylide and -Diyne Units Stabilized by a Naphthyridine-based Dinucleating Ligand.

Reactions of a dicopper(I) tert-butoxide complex with alkynes possessing boryl or silyl capping groups resulted in formation of unprecedented tetracopper(I) μ-acetylide/diyne complexes that were characterized by NMR and UV/Vis spectroscopy, mass spectrometry and single-crystal X-ray diffraction. These compounds possess an unusual μ -η :η :η :η coordination mode for the bridging organic fragment, enforced by the rigid and dinucleating nature of the ligand utilized. Thus, the central π system remains unperturbed and accessible for subsequent reactivity and modification.

Dimetalloylene (M-E-M) Complexes of Heavier Main Group Elements Ge, Sn, Pb, Bi via Cleavage of E-X Bonds (X=N(SiMe ) , OtBu) with an Iridium Hydride.

Reactions of the Ir hydride [ BDI ]IrH {BDI=(Dipp)NC(Me)CH(Me)CN(Dipp); Dipp=2,6-iPr C H } with E[N(SiMe ) ] (E=Sn, Pb) afforded the unusual dimeric dimetallotetrylenes ([ BDI ]IrH) (μ -E) in good yields. Moreover, ([ BDI ]IrH) (μ -Ge) was formed in situ from thermal decomposition of [ BDI ]Ir(H) Ge[N(SiMe ) ] . These reactions are accompanied by liberation of HN(SiMe ) and H through the apparent cleavage of an E-N(SiMe ) bond by Ir-H.

Direct Transformation of SiH to a Molecular L(H)Co═Si═Co(H)L Silicide Complex.

The synthesis of bimetallic molecular silicide complexes is reported, based on the use of multiple Si-H bond activations in SiH at the metal centers of 14-electron LCo fragments (L = Tp″, HB(3,5-diisopropylpyrazolyl); [BPPz], PhB(CHPBu)(pyrazolyl)). Upon exposure of (Tp″Co)(μ-N) () to SiH, a mixture of (Tp″Co)(μ-H) () and (Tp″Co)(μ-H) () was formed and no evidence for Si-H oxidative addition products was observed. In contrast, [BPPz]-supported Co complexes led to Si-H oxidative additions with the generation of silylene and silicide complexes as products.

Expanded [23]-Helicene with Exceptional Chiroptical Properties via an Iterative Ring-Fusion Strategy.

Expanded helicenes are an emerging class of helical nanocarbons composed of alternating linear and angularly fused rings, which give rise to an internal cavity and a large diameter. The latter is expected to impart exceptional chiroptical properties, but low enantiomerization free energy barriers (Δ) have largely precluded experimental interrogation of this prediction. Here, we report the syntheses of expanded helicenes containing 15, 19, and 23 rings on the inner helical circuit, using two iterations of an Ir-catalyzed, site-selective [2 + 2 + 2] reaction.

Robust dicopper(i) μ-boryl complexes supported by a dinucleating naphthyridine-based ligand.

Copper boryl species have been widely invoked as reactive intermediates in Cu-catalysed C-H borylation reactions, but their isolation and study have been challenging. Use of the robust dinucleating ligand DPFN (2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine) allowed for the isolation of two very thermally stable dicopper(i) boryl complexes, [(DPFN)Cu(μ-Bpin)][NTf] (2) and [(DPFN)Cu(μ-Bcat)][NTf] (4) (pin = 2,3-dimethylbutane-2,3-diol; cat = benzene-1,2-diol). These complexes were prepared by cleavage of the corresponding diborane reaction with the alkoxide [(DPFN)Cu(μ-O Bu)][NTf] (3).

A sequential cyclization/π-extension strategy for modular construction of nanographenes enabled by stannole cycloadditions.

The synthesis of polycyclic aromatic hydrocarbons (PAHs) and related nanographenes requires the selective and efficient fusion of multiple aromatic rings. For this purpose, the Diels-Alder cycloaddition has proven especially useful; however, this approach currently faces significant limitations, including the lack of versatile strategies to access annulated dienes, the instability of the most commonly used dienes, and difficulties with aromatization of the [4 + 2] adduct. In this report we address these limitations the marriage of two powerful cycloaddition strategies.

Copper(III) Metallacyclopentadienes via Zirconocene Transfer and Reductive Elimination to an Isolable Phenanthrocyclobutadiene.

Despite the widespread use of copper catalysis for the formation of C-C bonds, debate about the mechanism persists. Reductive elimination from Cu(III) is often invoked as a key step, yet examples of its direct observation from isolable complexes remain limited to only a few examples. Here, we demonstrate that incorporation of bulky mesityl (Mes) groups into the α-positions of a phenanthrene-appended zirconacyclopentadiene, CpZr(2,5-Mes-phenanthro[9,10]C), enables efficient oxidative transmetalation to the corresponding, formal Cu(III) metallacyclopentadiene dimer.

Versatile Fe-Sn Bonding Interactions in a Metallostannylene System: Multiple Bonding and C-H Bond Activation.

The metallostannylene Cp*(PrMeP)(H)Fe-SnDMP (; Cp* = η-CMe; DMP = 2,6-dimesitylphenyl), formed by hydrogen migration in a putative Cp*(PrMeP)HFe[Sn(H)DMP] intermediate, serves as a robust platform for exploration of transition-metal main-group element bonding and reactivity. Upon one-electron oxidation, expels H to generate the coordinatively unsaturated [Cp*(PrMeP)Fe═SnDMP][B(CF)] (), which possesses a highly polarized Fe-Sn multiple bond that involves interaction of the tin lone pair with iron. Evidence from EPR and Fe Mössbauer spectroscopy, along with DFT studies, shows that is primarily an iron-based radical with charge localization at tin.

C-H Activation by RuCoO Oxo Cubanes: Effects of Oxyl Radical Character and Metal-Metal Cooperativity.

High-valent multimetallic-oxo/oxyl species have been implicated as intermediates in oxidative catalysis involving proton-coupled electron transfer (PCET) reactions, but the reactive nature of these oxo species has hindered the development of an in-depth understanding of their mechanisms and multimetallic character. The mechanism of C-H oxidation by previously reported RuCoO cubane complexes bearing a terminal Ru-oxo ligand, with significant oxyl radical character, was investigated. The rate-determining step involves H atom abstraction (HAA) from an organic substrate to generate a Ru-OH species and a carbon-centered radical.

Scalable, Divergent Synthesis of a High Aspect Ratio Carbon Nanobelt.

Carbon nanobelts are molecules of high fundamental and technological interest due to their structural similarity to carbon nanotubes, of which they are molecular cutouts. Despite this attention, synthetic accessibility is a major obstacle, such that the few known strategies offer limited structural diversity, functionality, and scalability. To address this bottleneck, we have developed a new strategy that utilizes highly fused monomer units constructed via a site-selective [2 + 2 + 2] cycloaddition and a high-yielding zirconocene-mediated macrocyclization to achieve the synthesis of a new carbon nanobelt on large scale with the introduction of functional handles in the penultimate step.

Expanded Helicenes as Synthons for Chiral Macrocyclic Nanocarbons.

Expanded helicenes are large, structurally flexible π-frameworks that can be viewed as building blocks for more complex chiral nanocarbons. Here we report a gram-scale synthesis of an alkyne-functionalized expanded [11]helicene and its single-step transformation into two structurally and functionally distinct types of macrocyclic derivatives: (1) a figure-eight dimer via alkyne metathesis (also gram scale) and (2) two arylene-bridged expanded helicenes via Zr-mediated, formal [2+2+] cycloadditions. The phenylene-bridged helicene displays a substantially higher enantiomerization barrier (22.

Structure and Bonding in a Diamond-Shaped Tin Cluster Possessing a cyclo-Sn Core.

A tetrameric cluster composed entirely of (aryl)Sn units, [DMPSn] (DMP=2,6-dimesitylphenyl), has been prepared by reduction of [DMPSnCl] with a variety of reductants. This cluster was characterized in solution by multinuclear NMR spectroscopies, as well as in the solid-state by single crystal X-ray diffraction analysis. This species is stereochemically nonrigid in solution and possesses a cyclo-Sn core whose DMP substituents are equivalent at higher temperatures.

Isolation and Study of Ruthenium-Cobalt Oxo Cubanes Bearing a High-Valent, Terminal Ru-Oxo with Significant Oxyl Radical Character.

High-valent Ru-oxo intermediates have long been proposed in catalytic oxidation chemistry, but investigations into their electronic and chemical properties have been limited due to their reactive nature and rarity. The incorporation of Ru into the [CoO] subcluster via the single-step assembly reaction of Co(OAc)(HO) (OAc = acetate), perruthenate (RuO), and pyridine (py) yielded an unprecedented Ru(O)Co(μ-O)(OAc)(py) cubane featuring an isolable, yet reactive, Ru-oxo moiety. EPR, ENDOR, and DFT studies reveal a valence-localized [Ru( = 1/2)Co( = 0)O] configuration and non-negligible covalency in the cubane core.

Activations of all Bonds to Silicon (Si-H, Si-C) in a Silane with Extrusion of [CoSiCo] Silicide Cores.

The [BP ]Co(I) synthon Na(THF){[BP ]CoI} (1, [BP ] = κ-PhB(CHP Pr)) reacts with PhSiH or SiH to form unusual {[BP ](SiHR)CoH}═Si═{HCo[BP ]} species (R = Ph, 2a; R = H, 2b; [BP ] = κ-PhB(CHP Pr)) that result from activation of all Si-H and Si-C bonds in the starting silanes. Solution-spectroscopic data (multinuclear NMR, IR) for 2a,b, and the solid-state structure of 2a, indicate substantial Co═Si═Co multiple bonding and minimal interaction of the core Si atom with nearby hydride ligands. In the presence of 4-dimethylaminopyridine (DMAP), 1 reacts with PhSiH to give [BP ](H)CoSiHPh(DMAP) (3).

Effects of Coordinating a Hemilabile Ligand to 14e Cp*M(NO) Scaffolds (M = Mo, W).

This article describes the differing chemical properties imparted by the two ligands, hemilabile 2-[(diisopropylphosphino)methyl]-3-methylpyridine (PrPN) and the related 1,2-bis(dimethylphosphino)ethane (dmpe), when attached to the 14e Cp*M(NO) scaffolds (Cp* = η-CMe; M = W, Mo). For instance, the treatment of [Cp*W(NO)Cl] with 2 or 1 equiv of dmpe in CH affords excellent yields of [Cp*W(NO)(κ-dmpe)Cl]Cl (1) or [Cp*W(NO)Cl][μ-dmpe] (2). In contrast, the treatment of [Cp*W(NO)Cl] with 1 equiv of PrPN in CH does not produce the complex analogous to 1 but rather affords orange [Cp*W(NO)(κ-P-N-PrPN)Cl][Cp*W(NO)Cl] (3) in 90% yield.

Cationic and Neutral Cp*M(NO)(κ-PhPCHCHPPh) Complexes of Molybdenum and Tungsten: Lewis-Acid-Induced Intramolecular C-H Activation.

Treatment of CHCl solutions of Cp*M(NO)Cl (Cp* = η-C(CH); M = Mo, W) first with 2 equiv of AgSbF in the presence of PhCN and then with 1 equiv of PhPCHCHPPh affords the yellow-orange salts [Cp*M(NO)(PhCN)(κ-PhPCHCHPPh)](SbF) in good yields (M = Mo, W). Reduction of [Cp*M(NO)(PhCN)(κ-PhPCHCHPPh)](SbF) with 2 equiv of CpCo in CH at 80 °C produces the corresponding 18e neutral compounds, Cp*M(NO)(κ-PhPCHCHPPh) which have been isolated as analytically pure orange-red solids. The addition of 1 equiv of the Lewis acid, Sc(OTf), to solutions of Cp*M(NO)(κ-PhPCHCHPPh) at room temperature results in the immediate formation of thermally stable Cp*M(NO→Sc(OTf))(H)(κ-(CH)PhPCHCHPPh) complexes in which one of the phenyl substituents of the PhPCHCHPPh ligands has undergone intramolecular orthometalation.

Thermal Chemistry of Cp*W(NO)(CHCMe)(H)(L) Complexes (L = Lewis Base).

The complexes trans-Cp*W(NO)(CHCMe)(H)(L) (Cp* = η-CMe) result from the treatment of Cp*W(NO)(CHCMe) in n-pentane with H (∼1 atm) in the presence of a Lewis base, L. The designation of a particular geometrical isomer as cis or trans indicates the relative positions of the alkyl and hydrido ligands in the base of a four-legged piano-stool molecular structure. The thermal behavior of these complexes is markedly dependent on the nature of L.