Oxidative Addition of Water, Alcohols, and Amines in Palladium Catalysis

The homolytic cleavage of O−H and N−H or weak C−H bonds is a key elementary step in redox catalysis, but is thought to be unfeasible for palladium. In stark contrast, reported here is the room temperature and reversible oxidative addition of water, isopropanol, hexafluoroisopropanol, phenol, and aniline to a palladium(0) complex with a cyclic (alkyl)(amino)carbene (CAAC) and a labile pyridino ligand, as is also the case in popular N‐heterocyclic carbene (NHC) palladium(II) precatalysts. The oxidative addition of protic solvents or adventitious water switches the chemoselectivity in catalysis with alkynes through activation of the terminal C−H bond. Most salient, the homolytic activation of alcohols and amines allows atom‐efficient, additive‐free cross‐coupling and transfer hydrogenation under mild reaction conditions with usually unreactive, yet desirable reagents, including esters and bis(pinacolato)diboron

Carbamoyl Derivatives of a Pyridine-Based Tetraamine

The reaction of four equivalents of phenyl or tert-butyl isocyanate with the pyridine-derived tetraamine 2,6-C3H3N[CMe(CH2NH2)2]2 in toluene gives high yields of the quadruply ureido substituted products 2,6-C5H3N[CMe(CH2R)2]2 [R = -NH(CO)NHPh and -NH(CO)NHtBu]. Full spectroscopic data for both compounds are given. A single crystal X-ray structure determination of the phenyl derivative reveals an intricate network of both intra- and intermolecular hydrogen bonds involving the C=O and both NH functionalities in all ureido groups.DFG, SPP 1118, Sekundäre Wechselwirkungen als Steuerungsprinzip zur gerichteten Funktionalisierung reaktionsträger Substrat

Bond activation in iron(II) and nickel(II) complexes of polypodal phosphanes

A pyridine-derived tetraphosphane ligand (donor set: NP4) has been found to undergo remarkably specific C-P bond cleavage reactions, thereby producing a ligand with an NP3 donor set. The reaction may be reversed under suitable conditions, with regeneration of the original NP4 ligand. In order to investigate the mechanism of this reaction, the NP3 donor ligand C5H3N[CMe(CH2PMe2)2][CMe2(CH2PMe2)] (11) was prepd., and its iron(II) complex 4 generated from Fe(BF4)2·6 H2O, with Me diethylphosphinite (7) as an addnl. monodentate ligand. Ligand 11 has, in addn. to the NP3 donor set, one Me group in close contact with the iron center, reminiscent of an agostic M···H-C interaction. Depending on the stoichiometric amt. of iron(II) salt, a side product 15 is formed, which has a diethylphosphane ligand instead of the phosphinite 7 coordinated to iron(II). While attempts to deprotonate the metal-coordinated Me group in 4 were unsuccessful, the reaction was shown to occur in an alternative complex (18), which is similar to 4 but has a trimethylphosphane ligand instead of the phosphinite 7. The reaction of complex 15 with CO gave two different products, which were both characterized by single-crystal X-ray diffraction. One (19) is the dicarbonyl iron(II) complex of the triphosphane ligand 11, the other (3) is the carbonyl iron(II) complex of the tetraphosphane C5H3N[CMe(CH2PMe2)2]2 (1). This suggests an intermol. mechanism for the C-P bond formation in question. [on SciFinder(R)

Selective oxidative conversion of triaryldihydro[C59N]fullerenes: a model case for oxygenation of carbon allotropes

The photooxidation of triaryldihydro[C59N]fullerenes was achieved by treatment with air and light leading to a new selective core functionalization of azafullerenes, which serves as a model case for oxygenation of carbon allotropes

Swift C–C bond insertion by a 12-electron palladium(0) surrogate

The selective activation of C–C bonds holds vast promise for catalysis. So far, research has been primarily directed at rhodium and nickel under harsh reaction conditions. Herein, we report C–C insertion reactions of a 12-electron palladium(0) surrogate stabilized by a cyclic(alkyl)(amino) carbene (CAAC) ligand. Benzonitrile (1), biphenylene (2), benzocyclobutenone (3), and naphtho[b]cyclopropene (4) were studied. These substrates allow elucidation of the effect of ring strain as well as hybridization encompassing sp3 , sp2 and sp hybridized carbon atoms. All reactions proceed quantitatively at or below room temperature. This work therefore outlines perspectives for mild C–C bond functionalization catalysis

Reactivity of uranium(IV) bridged chalcogenido complexes UIV–E–UIV (E = S, Se) with elemental sulfur and selenium: synthesis of polychalcogenido-bridged uranium complexes

We report the syntheses, electronic properties, and molecular structures of a series of polychalcogenido-bridged dinuclear uranium species. These complexes are supported by the sterically encumbering but highly flexible, single N-anchored tris(aryloxide) chelator (AdArO)3N3−. Reaction of an appropriate uranium precursor, either the U(III) starting material, [((AdArO)3N)U(DME)], or the dinuclear mono-chalcogenido-bridged uranium(IV/IV) compounds [{((AdArO)3N)U(DME)}2(μ-E)] (E = S, Se), with elemental sulfur or selenium, yields new complexes with a variety of bridging chalcogenide entities μ-Emn− (E = S, m = 2, n = 1 or 2 and E = Se, m = 2, 4; n = 2). Activation of the heavy chalcogens typically requires either a coordinatively unsaturated, strongly-reducing metal complex or a compound with a metal–metal bond. Since uranium complexes in the +IV oxidation state, are generally considered rather unreactive, the observed reaction of the here employed uranium(IV)/(IV) species with elemental chalcogens is fairly remarkable

Well-defined molecular uranium(III) chloride complexes

The first anhydrous molecular complexes of uranium(III) chloride, soluble in polar aprotic solvents, are reported, including the structures of the dimeric [UCl3(py)4]2 and the trimetallic [UCl(py)4(μ-Cl)3U(py)2(μ-Cl)3UCl2(py)3]

Influence of Donor‐Acceptor Interactions on MLCT Hole Reconfiguration in {Ru(bpy)} Chromophores

In MLCT chromophores, internal conversion (IC) in the form of hole reconfiguration pathways (HR) is a major source of dissipation of the absorbed photon energy. Therefore, it is desirable to minimize their impact in energy conversion schemes by slowing them down. According to previous findings on {Ru(bpy)} chromophores, donor‐acceptor interactions between the Ru ion and the ligand scaffold might allow to control HR/IC rates. Here, a series of [Ru(tpm)(bpy)(R‐py)] 2+ chromophores, where tpm is tris(1‐pyrazolyl)methane, bpy is 2,2’‐bipyridine and R‐py is a 4‐substituted pyridine, were prepared and fully characterized employing electrochemistry, spectroelectrochemistry, steady‐state absorption/emission spectroscopy and electronic structure computations based on DFT/TD‐DFT. Their excited‐state decay was monitored using nanosecond and femtosecond transient absorption spectroscopy. HR/IC lifetimes as slow as 568 ps were obtained in DMSO at room temperature, twice as slow as in the reference species [Ru(tpm)(bpy)(NCS)] + .Excited state dynamics of metal‐to‐ligand charge transfer (MLCT) states have been explored in model ruthenium polypyridines. Substitution of ancillary ligands with electron‐donor groups decelerates internal conversion by means of hole reconfiguration, from high‐energy MLCT to the lowest‐energy MLCT, to 600 ps. This is promising in the design of strategies to extract the energy of high‐energy excited states before dissipation. imageCONICET http://dx.doi.org/10.13039/501100002923ANPCyT http://dx.doi.org/10.13039/501100003074CONICET http://dx.doi.org/10.13039/50110000292

A Genuine Trivalent Bis‐Acylphosphide (BAP) Complex of Uranium

The genuine trivalent uranium complex, K[UIII(mesBAP)4], employing four bidentate bis(2,4,6‐trimethylbenzoyl)phosphide (mesBAP) chelating ligands, is reported and obtained by the reduction of the literature‐known tetravalent analog [UIV(mesBAP)4]. Hence, the bis(acyl)phosphide mesBAP ligand allowed to establish a fully reversible redox couple with uranium in the oxidation states +III and +IV. In both complexes [U(mesBAP)4]0/−, the uranium ions are coordinated to four mesBAP ligands in a square antiprismatic geometry. All new compounds have been characterized by single‐crystal XRD analysis, 1H and 31P NMR, and UV/Vis/NIR electronic absorption spectroscopy, as well as SQUID magnetization and electrochemical measurements, and CW X‐band EPR in the case of the trivalent complex.A trivalent uranium complex, K[UIII(mesBAP)4], has been synthesized and spectroscopically, electrochemically, and magnetochemically characterized. An X‐ray diffraction analysis on single‐crystals of [K(2.2.2‐crypt)][UIII(mesBAP)4] reveals the molecular structure, consisting of four bis(acyl)phosphide chelates coordinated to the electron‐rich uranium ion in a distorted tetragonal antiprismatic geometry. [UIII(mesBAP)4]− complements the known [UIV(mesBAP)4], thus providing an isostructural U(III/IV) redox pair with axial cavities for small molecule activation. image German Federal Ministry of Education and ResearchFriedrich-Alexander-Universität Erlangen-NürnbergETH Züric