Facile Access to Cationic Methylstannylenes and Silylenes Stabilized by E-Pt Bonding and their Methyl Group Transfer Reactivity.

We describe a family of cationic methylstannylene and chloro- and azidosilylene organoplatinum(II) complexes supported by a neutral, binucleating ligand. Methylstannylenes MeSn:+ are stabilized by coordination to PtII and are formed by facile Me group transfer from dimethyl or monomethyl PtII complexes, in the latter case triggered by concomitant B-H, Si-H, and H2 bond activation that involves hydride transfer from Sn to Pt. A cationic chlorosilylene complex was obtained by formal HCl elimination and Cl- removal from HSiCl3 under ambient conditions. The computational studies show that stabilization of cationic methylstannylenes and cationic silylenes is achieved through weak coordination to a neutral N-donor ligand binding pocket. The analysis of the electronic potentials, as well as the Laplacian of electron density, also reveals the differences in the character of Pt-Si vs. Pt-Sn bonding. We demonstrate the importance of a ligand-supported binuclear Pt/tetrel core and weak coordination to facilitate access to tetrylium-ylidene Pt complexes, and a transmetalation approach to the synthesis of MeSnII :+ derivatives.

Bulky PNP Ligands Blocking Metal-Ligand Cooperation Allow for Isolation of Ru(0), and Lead to Catalytically Active Ru Complexes in Acceptorless Alcohol Dehydrogenation.

We synthesized two 4Me-PNP ligands which block metal-ligand cooperation (MLC) with the Ru center and compared their Ru complex chemistry to their two traditional analogues used in acceptorless alcohol dehydrogenation catalysis. The corresponding 4Me-PNP complexes, which do not undergo dearomatization upon addition of base, allowed us to obtain rare, albeit unstable, 16 electron mono-CO Ru(0) complexes. Reactivity with CO and H2 allows for stabilization and extensive characterization of bis-CO Ru(0) 18 electron and Ru(II) cis and trans dihydride species that were also shown to be capable of C(sp2 ) -H activation. Reactivity and catalysis are contrasted to non-methylated Ru(II) species, showing that an MLC pathway is not necessary, with dramatic differences in outcomes during catalysis between i Pr and t Bu PNP complexes within each of the 4Me and non-methylated backbone PNP series being observed. Unusual intermediates are characterized in one of the new and one of the traditional complexes, and a common catalysis deactivation pathway was identified.

H2 , B-H, and Si-H Bond Activation and Facile Protonolysis Driven by Pt-Base Metal Cooperation.

We report a series of heterobimetallic Pt/Zn and Pt/Ca complexes to study the effect of proximity of a dicationic base metal on the organometallic Pt species. Varying degrees of Pt⋅⋅⋅Zn and Zn interaction with the bridging Me group are achieved, showcasing snapshots of a hypothetical process of retrotransmetalation from Pt to Zn. In contrast, only weak interactions were observed for Ca with a Pt-bound Me group. Activation of H2 , B-H and Si-H bonds leads to the formation of hydride-bridged Pt-H-Zn complexes, which is not observed in the absence of Zn, pointing out the importance of metal-metal cooperation. Reactivity of PtMe2 /M2+ with terminal acetylene, water and methanol is also studied, leading to facile protonation of one of the Me groups at the Pt center only when Zn is present. This study sheds light on various ways in which the presence of a 2+ metal cation significantly affects the reactivity of a common organoplatinum complex.

Photoinduced Trifluoromethylation of Arenes and Heteroarenes Catalyzed by High-Valent Nickel Complexes.

We describe a series of air-stable NiIII complexes supported by a simple, robust naphthyridine-based ligand. Access to the high-valent oxidation state is enabled by the CF3 ligands on the nickel, while the naphthyridine exhibits either a monodentate or bidentate coordination mode that depends on the oxidation state and sterics, and enables facile aerobic oxidation of NiII to NiIII . These NiIII complexes act as efficient catalysts for photoinduced C(sp2 )-H bond trifluoromethylation reactions of (hetero)arenes using versatile synthetic protocols. This blue LED light-mediated catalytic protocol proceeds via a radical pathway and demonstrates potential in the late-stage functionalization of drug analogs.

The Milstein Bipyridyl PNN Pincer Complex of Ruthenium Becomes a Noyori-Type Catalyst under Reducing Conditions.

Hydrogenation of the dearomatized PNN ligand of the Milstein bipyridyl complex RuH(CO)[PNN] (2) gives a square-pyramidal Ru(II) product RuH(CO)[pPNN] (5). The central ring of the pPNN ligand is a piperidine. A minor byproduct of the hydrogenation reaction is complex 6 which has a dimeric structure made of two Ru(II) fragments each possessing a partly hydrogenated PNN ligand. The structures of 5 and 6 have been elucidated by NMR spectroscopy and X-ray crystallography. The PNN ligand of 2 is also hydrogenated under the conditions of the catalytic dehydrogenative coupling of ethanol to ethyl acetate. No direct evidence of the aromatized dihydride RuH2(CO)[PNN] (4) was found in this study. However, treating RuHCl(CO)[PNN] with Li[HBEt3] or reacting 2 with H2 at low temperature resulted in a structurally characterized hydride-bridged dimer (7) bearing intact aromatized bipyridyl ligands. M06-L/def2-QZVP DFT calculations provided insights into the thermodynamics of the stoichiometric reactions of this work and into the nature of the intermediates of the catalytic ester hydrogenation facilitated by RuH2(CO)[pPN(H)N] (8) formed from 5 under H2.

Facile methyl group transfer from PtII to gallium and indium.

Facile transmetalation is observed from a d8 metal, platinum(II), to indium and gallium leading to the extrusion of methylated gallate and indate anions representing a rare case of the "reverse" transmetalation from a d8 metal to a main group metal. The Pt-Ga and Pt-In bonding in the bimetallic complexes was analyzed through bosonic and fermionic potentials, QTAIM, and NBO.

Oxygen transfer reactivity mediated by nickel perfluoroalkyl complexes using molecular oxygen as a terminal oxidant.

Nickel perfluoroethyl and perfluoropropyl complexes supported by naphthyridine-type ligands show drastically different aerobic reactivity from their trifluoromethyl analogs resulting in facile oxygen transfer to perfluoroalkyl groups or oxygenation of external organic substrates (phosphines, sulfides, alkenes and alcohols) using O2 or air as a terminal oxidant. Such mild aerobic oxygenation occurs through the formation of spectroscopically detected transient high-valent NiIII and structurally characterized mixed-valent NiII-NiIV intermediates and radical intermediates, resembling O2 activation reported for some Pd dialkyl complexes. This reactivity is in contrast with the aerobic oxidation of naphthyridine-based Ni(CF3)2 complexes resulting in the formation of a stable NiIII product, which is attributed to the effect of greater steric congestion imposed by longer perfluoroalkyl chains.

Ligand-free nickel catalyzed perfluoroalkylation of arenes and heteroarenes.

We describe a "ligand-free" Ni-catalyzed perfluoroalkylation of heteroarenes to produce a diverse array of trfiluoromethyl, pentafluoroethyl and heptafluoropropyl adducts. Catalysis proceeds at room temperature via a radical pathway. The catalytic protocol is distinguished by its simplicity, and its wide scope demonstrates the potential in the late-stage functionalization of drug analogues and peptides.

Ethylene binding in mono- and binuclear CuI complexes with tetradentate pyridinophane ligands.

Herein we report a series of CuI complexes supported by tetradentate RN4 pyridinophane ligands that coordinate to ethylene forming either mononuclear complexes with ethylene coordinated in an η2-mode or a binuclear complex where ethylene binds to two Cu atoms in a µ-η2-η2-mode, depending on the steric effects of the RN4 ligand and the reaction conditions. In the binuclear complex with bridging ethylene, the CC bond is significantly elongated, with a bond length of 1.444(8) Å according to X-ray diffraction analysis. This complex represents the only examination a µ-η2-η2-coordinated Cu-olefin complex reported to date, featuring one of the longest reported CC bonds. The spectroscopic characterization, structure, electrochemical properties and solution behavior are analyzed in this study. Coordination of ethylene was found to be reversible in these complexes and more favored in less sterically hindered RN4 ligands, so that ethylene binding is observed in a coordinating solvent (MeCN) environment. In the case of the MeN4 ligand, the ethylene complex is photoluminescent in the solid state. The ethylene binding modes in mono- and binuclear complexes are elucidated through Natural Bond Orbital and QTAIM analyses.

Single and double deprotonation/dearomatization of the N,S-donor pyridinophane ligand in ruthenium complexes.

We report a series of ruthenium complexes with a tetradentate N,S-donor ligand, 2,11-dithia[3.3](2,6)pyridinophane (N2S2), that undergo single and double deprotonation in the presence of a base leading to the deprotonation of one or both pyridine rings. Both singly and doubly deprotonated complexes were structurally characterized by single-crystal X-ray diffraction. The NMR spectra are indicative of the dearomatization of one or both pyridine rings upon the deprotonation of the CH2-S arm, similar to the dearomatization of phosphine-containing pincer ligands. The deprotonated (N2S2)Ru complexes did not show appreciable catalytic or stoichiometric reactivity in transfer hydrogenation, hydrogenation and dehydrogenation of alcohols, and attempted activation of H2, CO2, and other substrates. Such a lack of reactivity is likely due to the low stability of the deprotonated species as evident from the structural characterization of one of the decomposition products in which shrinkage of the macrocyclic ring occurs via picolyl arm migration.

Construction of modular Pd/Cu multimetallic chains via ligand- and anion-controlled metal-metal interactions.

The presence of Pd⋯Cu and Pd⋯Pd interactions as well as the order of metal atoms in a chain held by a modular polynucleating ligand is controlled by the coordinating ability of the anions, leading to selective formation of bi- and tetranuclear Pd/Cu and Pd4 chains. Metal-metal cooperative reactivity in these complexes was tested in Ar-O bond formation and alkyne activation.

Preparation and C-X reductive elimination reactivity of monoaryl Pd(IV)-X complexes in water (X = OH, OH2, Cl, Br).

Monohydrocarbyl palladium(IV) complexes bearing OH, OH(2), Br, and Cl ligands at the metal and supported by facially chelating 1-hydroxy-1,1-bis(2-pyridyl)methoxide were readily prepared in water at 0 °C. These complexes reductively eliminate Ar-X (X = OH, Br, Cl) in water at room temperature in high yield, and the corresponding first-order rate constants k(OH), k(Cl), and k(Br) are on the same order of magnitude.

N-H activation of amines and ammonia by Ru via metal-ligand cooperation.

A nonoxidative addition pathway for the activation of NH bonds of ammonia and amines by a Ru(II) complex is reported. The pincer complex 1 cleaves N-H bonds via metal-ligand cooperation involving aromatization of the pincer ligand without a change in the formal oxidation state of the metal. Electron-rich N-H bond substrates lead to reversible activation, while electron-poor substrates result in stable activation products. Isotopic labeling studies using ND(3) as well as density functional theory calculations were used to shed light on the N-H activation mechanism.

Voltage Imaging of Cortical Oscillations in Layer 1 with Two-Photon Microscopy.

Membrane voltage oscillations in layer 1 (L1) of primary sensory cortices might be important indicators of cortical gain control, attentional focusing, and signal integration. However, electric field recordings are hampered by the low seal resistance of electrodes close to the brain surface. To study L1 membrane voltage oscillations, we synthesized a new voltage-sensitive dye, di1-ANNINE (anellated hemicyanine)-6plus, that can diffuse into tissue. We applied it with a new surgery, leaving the dura intact but allowing injection of large quantities of staining solution, and imaged cortical membrane potential oscillations with two-photon microscopy depth-resolved (25-100 µm below dura) in anesthetized and awake mice. We found delta (0.5-4 Hz), theta (4-10 Hz), low beta (10-20 Hz), and low gamma (30-40 Hz) oscillations. All oscillations were stronger in awake animals. While the power of delta, theta, and low beta oscillations increased with depth, the power of low gamma was more constant throughout L1. These findings identify L1 as an important coordination hub for the dynamic binding process of neurons mediated by oscillations.

Metal-metal cooperative bond activation by heterobimetallic alkyl, aryl, and acetylide PtII/CuI complexes.

We report the selective formation of heterobimetallic PtII/CuI complexes that demonstrate how facile bond activation processes can be achieved by altering the reactivity of common organoplatinum compounds through their interaction with another metal center. The interaction of the Cu center with the Pt center and with a Pt-bound alkyl group increases the stability of PtMe2 towards undesired rollover cyclometalation. The presence of the CuI center also enables facile transmetalation from an electron-deficient tetraarylborate [B(ArF)4]- anion and mild C-H bond cleavage of a terminal alkyne, which was not observed in the absence of an electrophilic Cu center. The DFT study indicates that the Cu center acts as a binding site for the alkyne substrate, while activating its terminal C-H bond.

Triboluminescence of a new family of CuI-NHC complexes in crystalline solid and in amorphous polymer films.

Triboluminescent compounds that generate emission of light in response to mechanical stimulus are promising targets in the development of "smart materials" and damage sensors. Among triboluminescent metal complexes, rare-earth europium and terbium complexes are most widely used, while there is no systematic data on more readily available and inexpensive Cu complexes. We report a new family of photoluminescent Cu-NHC complexes that show bright triboluminescence (TL) in the crystal state visible in ambient indoor light under air. Moreover, when these complexes are blended into amorphous polymer films even at small concentrations, TL is easily observed. Observation of TL in polymer films overcomes the limitation of using crystals and opens up possibilities for the development of mechanoresponsive coatings and materials based on inexpensive metals such as Cu. Our results may also have implications for the understanding of the TL effect's origin in polymer films.

Highly sensitive mechano-controlled luminescence in polymer films modified by dynamic CuI-based cross-linkers.

Dynamic CuI-based mechanophores used as cross-linkers in polybutylacrylates enable highly sensitive detection of mechanical stress even at small strain (<50%) and stress (<0.1 MPa) values via reversible changes in luminescence intensity. Such sensitivity is superior to previously reported systems based on classical organic mechanophores and it allows for direct visualization of mechanical stress by imaging methods.

Unusual rearrangement of modified PNP ligand based Ru complexes relevant to alcohol dehydrogenation catalysis.

'Hangman-type' PNP pincer ligands and their associated Ru complexes undergo sp2-sp3 C-C bond cleavage and subsequent C-C formation processes to form a new, one carbon unit longer backbone motif. DFT and mechanistic studies suggest a mechanism dependent upon arm pyridine coordination and ligand sterics.

Facile and reversible double dearomatization of pyridines in non-phosphine MnI complexes with N,S-donor pyridinophane ligand.

Single and double dearomatization of pyridine rings was observed in MnI complexes with an N2S2 pyridinophane ligand via deprotonation of one or two CH2 arms, respectively. In contrast to other N,S-donor pincer-like systems, the dearomatized (N2S2)Mn species were found to be stable, with the dearomatization being reversible.

Bidirectional transfer of phenyl and methyl groups between Pt(IV) and boron in platinum dipyridylborato complexes.

In the presence of weakly Lewis basic DMSO methyl group migration between B and PtIV in dipyridylborato trihydrocarbyl PtIV complexes is reversible; the preferred direction of Ph group migration in THF solution is from PtIV to B.