Gerald Henkel

Phenolate Hydroxylation in a Bis(μ-oxo)dicopper(III) Complex : Lessons from the Guanidine/Amine Series

A new hybrid permethylated-amine-guanidine ligand based on a 1,3-propanediamine backbone (2L) and its Cu-O2 chemistry is reported. [(2L)CuI(MeCN)]1+ complex readily oxygenates at low temperatures in polar aprotic solvents to form a bis(mu-oxo)dicopper(III) (O) species (2b), similar to the parent bis-guanidine ligand complex (1b) and permethylated-diamine ligand complex (3b). UV-vis and X-ray absorption spectroscopy experiments confirm this assignment of 2b as an O species, and full formation of the 2:1 Cu-O2 complex is demonstrated by an optical titration with ferrocene-monocarboxylic acid (FcCOOH). The UV-vis spectra of 1b and 2b with guanidine ligation show low-intensity visible features assigned as guanidine pi --> Cu2O2 core transitions by time-dependent density functional theory (TD-DFT) calculations. Comparison of the reactivity among the three related complexes (1b-3b) with phenolate at 195 K is particularly insightful as only 2b hydroxylates 2,4-di-tert-butylphenolate to yield 3,5-di-tert-butylcatecholate (>95% yield) with the oxygen atom derived from O2, reminiscent of tyrosinase reactivity. 1b is unreactive, while 3b yields the C-C radical-coupled bis-phenol product. Attenuated outer-sphere oxidative strength of the O complexes and increased phenolate accessibility to the Cu2O2 core are attributes that correlate with phenolate hydroxylation reactivity observed in 2b. The comparative low-temperature reactivity of 1b-3b with FcCOOH (O-H BDE 71 kcal mol(-1)) to form the two-electron, two-proton reduced bis(mu-hydroxo)dicopper(II,II) complex is quantitative and presumably precedes through two sequential proton-coupled electron transfer (PCET) steps. Optical titrations along with DFT calculations support that the reduced complexes formed in the first step are more powerful oxidants than the parent O complexes. These mechanistic insights aid in understanding the phenol to bis-phenol reactivity exhibited by 2b and 3b.

Die Tetracyanoborate M[B(CN)4], M = [Bu4N]+, Ag+, K+

Erstmals wird das Tetracyanoborat-Anion in Form seines Tetrabutylammonium-Salzes durch Umsetzung von [NBu4]BX und BX3 (X = Br, Cl) in Toluol mit KCN erhalten. Nach Aufarbeitung des Rohproduktes und Umkristallisation aus CHCl3 fallen farblose, stabchenformige Einkristalle [Bu4N][B(CN)4] an. Die Metathese mit AgNO3 ergibt das Silbersalz und aus diesem mit KBr schlieslich das Kaliumsalz. Die drei Salze werden durch Rontgenbeugung an Einkristallen (Ag[B(CN)4] P 43m, a = 5.732(1) A, V = 188.3 A3, Z = 1, R1 = 0.75%; K[B(CN)4] I41/a, a = 6.976(1), c = 14.210(3) A, V = 691.5 A3, Z = 4, R1 = 1.90%; [Bu4N][B(CN)4] Pnna, a = 17.765(3), b = 11.650(2), c = 11.454(2) A, V = 2370.5 A3, Z = 4, R1 = 6.09%) und NMR-, IR-, Raman- sowie UV-Spektroskopie charakterisiert.

Synthesis and Properties of the Tetrakis(trifluoromethyl)borate Anion, [B(CF3)4]−: Structure Determination of Cs[B(CF3)4] by Single-Crystal X-ray Diffraction

Salts of the tetrakis(trifluoromethyl)borate anion, M[B(CF3)4], M=Li, K, Cs, Ag, have been prepared by two different routes for the first time. The colorless compounds are thermally stable up to 425 C (Cs salt) and soluble in anhydrous HF, water, and most organic solvents. Single crystals of Cs[B(CF3)4] were grown from diethyl ether by diffusion of CH2Cl2 vapor into the solution. The molecular structure was obtained by single-crystal X-ray diffraction. Crystal data: rhombohedral space group R3m (no. 160); a =7.883(1), c=13.847(4) A: V=748.2 A3; Z=3; T=150K; R1=0.0118, wR2=0.0290. The internal bond parameters of the [B(CF3)4] ion were compared to those of the C(CF3)4 molecule. Due to a disorder of the anions in the cesium salt, it is not possible to distinguish between T and Td symmetry by X-ray diffraction experiments alone. However, a comprehensive IR and Raman study demonstrated that in the potassium and cesium salt as well as in aqueous solution, the anion exhibits T symmetry with all CF3 groups rotated off the staggered position required for Td symmetry. The vibrational study is supported by DFT calculations, which provide, in addition to the equilibrium structure and vibrational wavenumbers, estimates of IR and Raman band intensities. The anion is resistant against strong oxidizing (e.g., F2) as well as reducing agents (e.g., Na) and is not affected by nucleophiles like C2H5O or electrophiles such as H3O+. It is very weakly coordinating, as demonstrated by the low-equilibrium CO pressure over the [Ag(CO)x][B(CF3)4] (x=1, 2) co-adducts and the formation of [Ag(CO)x][B(CF3)4] (x=3,4) at higher CO pressure. The 11B, 13C, and 19F NMR data as well as the structural parameters of the anion are compared with those for other borates containing F, CN, and CF3 ligands.

A Halide‐Induced Copper(I) Disulfide/Copper(II) Thiolate Interconversion

Shortly after their discovery as protein active sites, copper sulfur complexes entered the stage of modern synthetic coordination chemistry. In this respect, the combination of copper (II) and potentially reducing thiolate ligands appears especially attractive owing to its relevance to the CuA within cytochrome-c oxidase and N2O reductase. [2] Despite extensive research efforts, dinuclear copper(II) or mixed-valent copper(I/II) thiolate complexes with protein active site properties are rare. This situation can be traced back to the ligands under investigation, which are not capable of preventing Cu from being reduced to Cu along with the formation of organodisulfides. On the other hand, the selective and reversible oxidation of thiols/thiolates to organo-disulfides (e.g., cysteine to cystine) is one of the most important biological reactions resulting in the formation of disulfide bridges within peptides and proteins. In addition, the reaction system thiol– disulfide is an important electron source for a number of redox processes in biological systems, making it an indispensable component of basic regulatory processes during signal transduction and enzyme activity. Nevertheless, disulfide– thiolate redox processes are largely unexplored in an inorganic context, although they were investigated in terms of the participation of copper(II) ions in kinetic studies more than 50 years ago. Quite recently, further reports have been published on this subject, and in 2002 a unique model system was described which—under the influence of copper and controlled by halide ions—is able to shift the thiolate– disulfide equilibrium reversibly and completely from the one side to the other. This surprising discovery indicates an enormous but largely unrecognized potential for such reaction systems to act as novel electron sources and sinks, which has motivated us to explore this topic more deeply. We report herein a previously unknown chloride-induced disulfide–thiolate interconversion, leading from the copper(I) disulfide complex cation [Cu2{(NGuaS-)2}2] 2+ (1) to the electrically neutral copper(II) thiolate species [Cu2(NGuaS)2Cl2] (2 ; there is no longer an S S bond in the NGauS ligands, thus it is no longer written as (NGuaS )2). Both compounds (1 as 1[OTf]2) were characterized by X-ray crystallography. The proposed oxidation states of the Cu ions were confirmed by K-edge measurements. The reverse reaction can be initiated by removal of the chloride ligands from the corresponding thiolate complex (Scheme 1).

Stabilisation of a Highly Reactive Bis(μ-oxo)dicopper(III) Species at Room Temperature by Electronic and Steric Constraint of an Unconventional Nitrogen Donor Ligand

Herein we present an innovative combination of EXAFSspectroscopy and resonant Raman scattering for the charac-terisation of the ground state and structural dynamics of athermally stable binuclear bisACHTUNGRE(m-oxo) dicopperACHTUNGRE(III) species.Peralkylated bis(guanidine)-based ligands are used in thesynthesis of this compound.

First intermolecular palladium catalyzed arylation of an unfunctionalized aromatic hydrocarbon

Abstract Azulene is arylated by iodobenzene and by 4-nitro-chlorobenzene under palladium catalysis at the electron-rich 1-position.

C6F5XeCl and [(C6F5Xe)2Cl][AsF6]: The First Isolated and Unambiguously Characterized Xenon(II) Chlorine Compounds

: Xenon(II) chlorine compounds can be obtained as the isolable organo derivatives C(6)F(5)XeCl and [(C(6)F(5)Xe)(2)Cl][AsF(6)] (whose cation is depicted) in 85 and 91 % yield, respectively. These compounds decompose vigorously at 36 degrees C and 100 degrees C, respectively, leading to the formation of C(6)F(5)Cl and Xe gas and of C(6)F(5)Cl, C(6)F(6), and [C(6)F(5)Xe][AsF(6)], respectively.

Preparation, properties and reactions of metal-containing heterocycles ☆: Part C: tetraazatetraphosphadimolybdacyclophanes: synthesis, isolation, characterization, and X-ray crystal structures

The ditopic aminodiphosphines CH 2 (4,4′-Ph 2 PNHC 6 H 4 ) 2 ( 2 ) and CH 2 (4,4′-Ph 2 PCH 2 NHC 6 H 4 ) 2 ( 5 ) are obtained by reaction of 4,4′-diaminodiphenylmethane with ClPPh 2 and (i) (CH 2 O) n /NaOMe/(ii) HPPh 2 , respectively. Treatment of (η 4 -nbd)Mo(CO) 4 with 2 and 5 under high-dilution conditions in CH 2 Cl 2 affords the tetraazatetraphosphadimolybdaclophanes [CH 2 (4,4′-(OC) 4 Mo(Ph 2 PNHC 6 H 4 ) 2 )] 2 ( 3 ) and [CH 2 (4,4′-(OC) 4 Mo(Ph 2 PCH 2 NHC 6 H 4 ) 2 )] 2 ( 6 ) in relatively high yields. The structures of 3 and 6 were investigated by X-ray crystal-structure analyses. Whereas the cavity of the molecular structure of 3 can be described by a parallelogram, that of 6 has the shape of a boat in which the diphenylmethane building blocks form the hull and the cis -(Ph 2 P) 2 Mo(CO) 4 fragments represent the bow and stem, respectively. Because of the formation of only very weak hydrogen bonds in 3 and 6 , no binding to molecules like p -benzoquinone, 1,4-cyclohexanedione, 2,5-piperazinedione and trans -1,4-diaminocyclohexane could be detected.

{Ph2(Carb)P}MCl3 (M = Pd, Pt; Carb = 2,3‐dihydro‐1,3‐diisopropyl‐4,5dimethylimidazol‐2‐ylidene) – a Novel Cationic Phosphane Ligand [1]

The phosphane ligand [Ph2(Carb)P]+ forms neutral complexes {Ph2(Carb)P}MCl3 (Carb = 2,3-dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; M = Pd, Pt) through the reaction of its chloride salt with (PhCN)2MCl2; the triarylphosphane type properties of the ligand are revealed by n.m.r. and structural data.

Palladium-catalyzed arylation of butadiynes

Abstract Diarylbutadiynes 1 undergo a palladium-catalyzed coupling reaction with aryl halides 2 to give tetraarylbutatrienes 3 , which may further react to benzofulvenes 6 depending on the reaction temperature and the type of aryl groups.