Palladium(II) complexes containing a bulky pyridinyl N-heterocyclic carbene ligand: Preparation and reactivity

Coordination chemistry of a pyridine imidazole-2-ylidene ligand (pyN ˆC) with sterically hindered substituents toward palladium(II) metal ions has been investigated. The palladium carbene complex [(C-pyN ˆC)Pd(η³-allyl)Cl] (3) is prepared via the transmetallation from the corresponding silver carbene complexes with [ClPd(η³-allyl)]₂. Upon the abstraction of chloride, coordination of pyridinyl-nitrogen becomes feasible to form [C,N-(pyN ˆC)Pd(η³-allyl)](BF₄) (4). Ligand substitution reaction of 4 with triphenylphosphine results in the formation of [(C-pyN ˆC)Pd(PPh₃)(η³-allyl)](BF₄)], which the pyridinyl-nitrogen donor is substituted by the phosphine. This palladium complex appears to be base sensitive. Treatment of 4 with t-butoxide causes the decomposition to yield the metal nano-particles. Furthermore, de-complexation of 4 takes place under hydrogen atmosphere to generate the carbene precursor, 1-(6-mesityl-2-picolyl)-3-mesitylimidazolium salt. Nevertheless, the palladium complex 4 shows good catalytic activity on the Suzuki-Miyaura and Mizoroki-Heck reactions.     

Syntheses and coordination chemistry of methylpyridylphosphine oxide ligands with copper(II)

The coordination properties of three heterofunctional phosphine oxide ligands, 2-methylpyridyldiphenylphosphine oxide (L1), phenylphosphino-bis-2-methylpyridine oxide (L2) and phenylphosphino-bis-2-methylpyridine N,N′,P-trioxide (L3) with Cu(II) is described. The X-ray crystal structures of the compounds display a distorted octahedral geometry, which exhibit Jahn–Teller distortions. In compounds 1 and 2, the L1 and L2 ligands react with Cu(BF₄)₂ in a 2:1 ligand to metal ratio, respectively, with the BF₄ anions interacting with the metal center. L3 reacts with Cu(BF₄)₂ in 1:1 and 2:1 ligand/metal ratios to form compounds 3 and 4, respectively. Addition of either 2,2′-bipyridine or 4,4′-bipyridine to reaction solutions containing Cu(BF₄)₂ and L3 produces a discrete molecule (5) and a polymeric structure (7), respectively. The reaction of both bipyridines in the presence of Cu(BF₄)₂ and L3 gives rise to a discrete molecule (6) characterized by two octahedral coppers interconnected by the 4,4′-bipyridine. The electrochemical and photophysical properties of all compounds were investigated by cyclic voltammetry (CV) and UV–Vis, as they exhibited no emission or excitation in fluorimetric experiments.     

Palladium complexes of 8-(di-tert-butylphosphinooxy) quinoline

The preparation of the new ligand 8-(di-tert-butylphosphinooxy)quinoline (1) and the palladium derivatives [PdCl₂(1)] (2), [Pd(η³-all)(1)]⁺ [all = C₃H₅ (3a), 1-PhC₃H₄ (3b) and 1,3-Ph₂C₃H₃ (3c)] and [Pd(η²-ol)(1)] [ol = dimethyl fumarate (4a) and fumaronitrile (4b)] is reported. The cationic species 3a-3c have been isolated as salts. The complex 3a(BF₄) is obtained either from the reaction of 1 with [Pd(μ-Cl)(η³-C₃H₅)]₂ or from the reaction of ClP(CMe₃)₂ with [Pd(η³-C₃H₅)(8-oxyquinoline)], followed in both cases by chloride abstraction with NaBF₄. In the complexes, the ligand 1 is P,N chelated to the central metal, as shown by the X-ray structural analysis of 3a(BF₄). At 25 °C in solution, 3a(BF₄) and 3b(BF₄) undergo a fast η³−η¹−η³ dynamic process which brings about a syn-anti exchange only for the allylic protons cis to phosphorus, while for 4a and 4b a slow rotation of the olefin around its bond axis to palladium takes place. The complexes 2 and 3a(BF₄) are efficient catalyst precursors in the coupling of the phenylboronic acid with aryl bromides and chlorides.     

A novel dinuclear double-stranded helical complexes of bis(terdentate) N4O2 donor ligand with silver(I) and zinc(II) d metal ions

Reaction of the hexadentate N₄O₂-donor ligand 6,6′-bis(3-hydrazonobutan-2-one)-2,2′-bipyridine (L) with Ag^(I) and Zn^(II) affords a dinuclear double stranded helicate species [Ag₂L₂]²⁺ (1a) and [Zn₂L₂]²⁺ (1b), in which partitioning of the ligand into two bis-tridentate pyridyl-ketoimine chelating units allow each ligand to bridge both metal centres. X-ray crystallography, ESI-MS and UV–Vis spectrophotometric titration experiments reveal that the complex (1a) retains its solid-state structure in solution. The crystal structure of (1a) provides the first example of dinuclear silver(I) complex in which both of the metal centres can be approximated as a seven coordinate distorted mono-capped trigonal prism in which the Ag?Ag close contact of 3.034(4) Å is taken into account and forms the cap. The counter-ions do not interact with metal centres but hydrogen bond to N–H protons of the hydrazonic arms from the separate strands. The adjacent helical units are cross-linked together via NH?O_keto hydrogen bonding to maintain the supramolecular structure.     

Au(I) and Au(III) complexes of a sterically bulky benzimidazole-derived N-heterocyclic carbene

The reaction of [AuCl(SMe₂)] with in situ generated [AgCl(ⁱPr₂-bimy)] (ⁱPr₂-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene), which in turn was obtained by the reaction of Ag₂O with 1,3-diisopropylbenzimidazolium bromide (ⁱPr₂-bimyH⁺Br⁻, A), afforded the monocarbene Au(I) complex [AuCl(ⁱPr₂-bimy)] (1). Subsequent reaction of 1 and the ligand precursor ⁱPr₂-bimyH⁺BF₄⁻, (B) in acetone in the presence of K₂CO₃ yielded the bis(carbene) complex [Au(ⁱPr₂-bimy)₂]BF₄ (2) as a white powder in 80% yield. The oxidative addition of elemental iodine to complex 2 gave the bis(carbene) Au(III) complex trans-[AuI₂(ⁱPr₂-bimy)₂]BF₄ (3) as an orange-red powder in 92% yield. All complexes 1-3 have been fully characterized by multinuclear NMR spectroscopies, ESI mass spectrometry, elemental analysis, and X-ray single crystal diffraction. Complexes 1 and 2 adopt a linear geometry around metal centers as expected for d¹⁰ metals. The geometry around the Au(III) metal center in 3 is essentially square-planar with two carbene ligands in trans-position to each other. Complex 3 shows absorption and photoluminescence properties owing to a ligand to metal charge transfer.     

Mononuclear zinc(II) and mercury(II) complexes of Schiff bases derived from pyrrolealdehyde and cysteamine containing intramolecular NH?S hydrogen bonds

Two neutral group 12 metal complexes, bis(pyrrol-2-ylmethyleneaminoethylthio)zinc(II) (1) and bis(pyrrol-2-ylmethyleneaminoethylthio)mercury(II) (2), with the (N_imine)₂S₂ coordination mode were synthesized by using metal-templated Schiff base condensation, and their molecular structures were determined by X-ray diffraction analysis. Complex 1 exhibits a distorted tetrahedral geometry around the metal, whereas the metal center has a bisphenoidal configuration in complex 2. Both mononuclear complexes possess intramolecular NH?S hydrogen bonds, as evidenced by IR, ¹H NMR and X-ray crystallography. The hydrogen-bond donor (H-N_pyrrole) and acceptor (S atom) are coming from different ligands within a single molecule. Complex 2 represents the first example of a mercury complex in the N₂S₂ coordination mode with intramolecular NH?S hydrogen-bond interactions. An investigation of the effects of the NH?S hydrogen bonding on the stability of 1 and 2, using an N-methyl pyrrolyl analogue, demonstrated that the N-H hydrogen-bond donor from the pyrrolyl moiety probably played a role in the stability of 1, but not 2.     

Activation of propargylic alcohols by dimolybdenum tris(μ-thiolate) complexes: Influence of the substituents R in HCCCR2(OH)-vinylidene/allenylidene transformation. Reactivity of allenylidene complexes

Reaction of the bis(nitrile) complex [Mo₂Cp₂(μ-SMe)₃(NCMe)₂](BF₄) (1) with dimethylpropargylic alcohol, HCCCMe₂(OH), at room temperature in dichloromethane produced good yields of the μ-alkynol species [Mo₂Cp₂(μ-SMe)₃{μ-CHCCMe₂(OH)}](BF₄) (2a) through replacement of the two acetonitrile ligands in 1 by the alkynol. The NMR spectra of 2a indicate a μ-η¹:η¹ coordination mode for the alkyne which is thereby incorporated into a dimetallacyclobutene ring like that found here by X-ray diffraction (XRD) analysis of the related complex [Mo₂Cp₂(μ-SMe)₃(μ-η¹:η¹-CHCCO₂Me)](BPh₄) (2b). When 2a was stirred with Et₃N at room temperature in dichloromethane, deprotonation gave high yields of the μ-3-hydroxyalkynyl derivative [Mo₂Cp₂(μ-SMe)₃{μ-η¹:η²-CCCMe₂(OH)}] (3), together with small amounts of the already-known vinylacetylide [Mo₂Cp₂(μ-SMe)₃{μ-η¹:η²-CCC(Me)CH₂}] (4) resulting from dehydration of 3. Treatment of 3 with 1 equiv. of HBF₄ · OEt₂ in diethyl ether at room temperature gave the 3-hydroxyvinylidene derivative [Mo₂Cp₂(μ-SMe)₃{μ-η¹:η²-CCHCMe₂(OH)}](BF₄) (5) as the major product, together with other minor products [Mo₂Cp₂(μ-SMe)₃{μ-η¹:η²-CCHC(Me)CH₂}](BF₄) (6), [Mo₂Cp₂(μ-SMe)₃(μ-η¹:η²-CCCMe₂)](BF₄) (7), [Mo₂Cp₂(μ-SMe)₃(μ-η¹:η²-CCH₂)](BF₄) (8), [Mo₂Cp₂(μ-SMe)₃{μ-η¹:η²-CCH(CHMe₂)}](BF₄) (9) and [Mo₂Cp₂(μ-SMe)₃(μ-O)](BF₄) (10). The vinylidene (6) and allenylidene (7) species resulted from dehydration of the 3-hydroxyvinylidene complex 5 whereas the vinylidene derivative 8 was formed by deketonisation of 5. When 3 reacted with a large excess of HBF₄ · OEt₂ in dichloromethane, the 3-isopropylvinylidene complex 9 was obtained nearly quantatively via a H radical process. When left for several days CD₂Cl₂ solutions of 5 afforded mainly the vinylidene species 8 by deketonisation and the side-oxoproduct [Mo₂Cp₂(μ-SMe)₃(μ-O)](BF₄) (10) by hydrolysis or reaction with oxygen. Addition of nucleophiles (H⁻, OMe⁻, OH⁻, SMe⁻) to the allenylidene complex [Mo₂Cp₂(μ-SMe)₃(μ-η¹:η²-CCCPh₂)](BF₄) (11) resulted in the formation of the corresponding μ-acetylide derivatives [Mo₂Cp₂(μ-SMe)₃(μ-η¹:η²-CCCRPh₂)] [R = H (12), OMe (16a), OH (17), SMe (16b)], which by further reaction with tetrafluoroboric acid afforded either the vinylidene species [Mo₂Cp₂(μ-SMe)₃{μ-η¹:η²-CCH(CRPh₂)}](BF₄) when R = H (13), or the starting complex 11 when R is a leaving group (OMe). Reaction of 13 with Na(BH₄) gave the μ-alkylidyne complex [Mo₂Cp₂(μ-SMe)₃(μ-η¹-CCH₂CPh₂H)] (14) by nucleophilic attack of H⁻ at the C_β carbon atom of the vinylidene chain. Proton addition at C_α in 14 led to the formation of a μ-vinylidene compound 15 containing an agostic C-H bond. New complexes have been characterised by elemental analyses and spectroscopic methods, supplemented for 2b and 3 by X-ray diffraction studies.     

Structure,biological and electrochemical studies of transition metal complexes from N,S,N′ donor ligand 8-(2-pyridinylmethylthio)quinoline

The semirigid tridentate 8-(2-pyridinylmethylthio)quinoline ligand (Q1) is shown to form the structurally characterized transition metal complexes [Cu(Q1)Cl₂] (1), [Co(Q1)(NO₃)₂] (2), [Cd(Q1)(NO₃)₂] (3), [Cd(Q1)I₂] (4). [Cu(Q1)₂](BF₄)₂·(H₂O)₂ (5), [Cu(Q1)₂](ClO₄)₂·(CH₃COCH₃)₂ (6), [Zn(Q1)₂](ClO₄)₂(H₂O)₂ (7), [Cd₂(Q1)₂Br₄] (8), [Ag₂(Q1)₂(ClO₄)₂] (9), and [Ag₂(Q1)₂(NO₃)₂] (10). Four types of structures have been observed: ML-type in complexes 1–4, in which the anions Cl⁻, NO₃⁻ or I⁻ also participate in the coordination; ML₂⁻ type in complexes 5–7 without direct coordination of the anions BF₄⁻ or ClO₄⁻ and with more (Cu²⁺) or less (Zn²⁺) distorted bis-fac coordinated Q1; M₂L₂-type in complex 8, in which two Br⁻ ions act as bridges between two metal ions; and M₂(μ-L)₂-type in complexes 9 and 10, in which the ligand bridges two anion binding and Ag–Ag bonded ions. Depending on electron configuration and size, different coordination patterns are observed with the bonds from the metal ions to N_pyridyl longer or shorter than those to N_quinoline. Typically Q1 acts as a facially coordinating tridentate chelate ligand except for the compounds 9 and 10 with low-coordinate silver(I). Except for 6 and 8, the complexes exhibit distinct constraining effects against both G(+) and G(-) bacteria. Complexes 1, 3, 4, 5, 7 have considerable antifungal activities and complexes 1, 5, 7, and 10 show selective effects to restrain certain botanic bacteria. Electrochemical studies show quasi-reversible reduction behavior for the copper(II) complexes 1, 5 and 6.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.     

Palladium complexes containing ligands with hydrogen-bonding functionalities. Reactivity and catalytic studies with CO and olefins

The synthesis of the new bidentate N-N ligand 1-(2-(1-(pyridin-2-yl)ethylideneamino)ethyl)-3-ethylurea (PyUr) with a urea substituent attached to the imine nitrogen is reported. This ligand has been used to form palladium complexes and study the potential influence of the urea group (as a hydrogen bonding unit and a hemilabile ligand) in the insertion of CO and olefins into Pd-C bonds. The reaction of PyUr with [Pd(CH₃)(Cl)(COD)] to yield [Pd(CH₃)Cl(PyUr)] (1) is reported. A crystallographic study of this complex was carried out showing that the urea moieties are involved in a series of intermolecular hydrogen bonding interactions. Upon removal of the chloride from the coordination sphere of 1 (by addition of AgBF₄) the urea group of PyUr coordinates to the palladium centre stabilizing an otherwise coordinatively unsaturated complex. The reaction of these complexes with CO to yield [Pd{C(O)CH₃}Cl(PyUr)] (3) and [Pd{C(O)CH₃}(PyUr)][BF₄] (4) is also discussed. Following on from these reactions, the copolymerization of CO and styrene using 1 as a catalyst was studied and is herein reported. The copolymers synthesized using 1 as a catalyst were obtained in moderate yields and showed to have a narrow size distribution. The same reaction was performed using a palladium complex coordinated by an analogous pyridine ligand but without a hydrogen bonding substituent. The results of the copolymerization reactions showed that, although slightly better yields and larger molecular weights were obtained with the PyUr-containing catalyst, the hydrogen bonding groups in PyUr have little influence on the course of the reaction. To explore further the reactivity of the palladium complexes, the reaction between [Pd(CH₃)Cl(PyUr)][BF₄] (2) and CH₂CHCH₂OH was carried out to yield the allyl complex [Pd(η³-CH₂CHCH₂)(PyUr)] (6). The crystal structure of this complex is also reported.     

Cationic palladium(II)-allyl-complexes containing 2-pyridyldiphenylphosphine: X-ray crystal structure of the binuclear complex [Pd(η-2-Me-allyl)(μ-Ph2PPy)]2(BF4)2. Detection of an intramolecular C(allyl)-H?phenyl ring π-interaction

Reaction of [PdCl(η³-2-Me-allyl)(Ph₂PPy)] (1) with AgBF₄ affords the new dinuclear cationic complex [Pd(η³-2-Me-allyl)(μ-Ph₂PPy)]₂(BF₄)₂ (2). The X-ray structural analysis of 2 shows that the 2-pyridyldiphenylphosphine ligands adopt a binucleating role through the P and N atoms bridging two independent palladium centres to form an eight-membered metallocyclic ring. One of the anti hydrogen atoms of the allyl moiety was located very close to a phenyl ring of Ph₂PPy indicating the occurrence of a CH/π interaction. Addition of one equivalent of Ph₂PPy to complex (2) affords the mononuclear cationic complex [Pd(η³-2-Me-allyl)(Ph₂PPy)₂](BF₄) (3).     

Ruthenium(II), rhodium(III) and iridium(III) based effective catalysts for hydrogenation under aerobic conditions

The new cationic mononuclear complexes [(η⁶-arene)Ru(Ph-BIAN)Cl]BF₄ [η⁶-arene = benzene (1), p-cymene (2)], [(η⁵-C₅H₅)Ru(Ph-BIAN)PPh₃]BF₄ (3) and [(η⁵-C₅Me₅)M(Ph-BIAN)Cl]BF₄ [M = Rh (4), Ir (5)] incorporating 1,2-bis(phenylimino)acenaphthene (Ph-BIAN) are reported. The complexes have been fully characterized by analytical and spectral (IR, NMR, FAB-MS, electronic and emission) studies. The molecular structure of the representative iridium complex [(η⁵-C₅Me₅)Ir(Ph-BIAN)Cl]BF₄ has been determined crystallographically. Complexes 1–5 effectively catalyze the reduction of terephthaldehyde in the presence of HCOOH/CH₃COONa in water under aerobic conditions and, among these complexes the rhodium complex [(η⁵-C₅Me₅)Rh(Ph-BIAN)Cl]BF₄ (4) displays the most effective catalytic activity.     

Synthesis, properties, and oxidizing function of 6-substituted 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrole-8(7H),10(9H)-dionylium tetrafluoroborates

Uracil-annulated heteroazulenes, 6-substituted 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrole-8(7H),10(9H)-dionylium tetrafluoroborates 7a,b·BF₄⁻, which are the isoelectronic compounds of 5-dezazaflavin, were synthesized. X-Ray crystal analysis and MO calculations were carried out to clarify the structural characteristics of 7a,b·BF₄⁻. The stability of cations 7a,b is expressed by the pK_R+ values which were determined spectrophotometrically to be 10.9 and 11.2, respectively. The electrochemical reduction of 7a,b exhibited high reduction potentials at −0.84 and −0.87 (V vs Ag/AgNO₃) upon cyclic voltammetry (CV). A good linear correlation between the pK_R+ values and reduction potentials (E1_red) of 7a,b·BF₄⁻ and reference compounds 4·BF₄⁻ and 5·BF₄⁻ was obtained. In a search of the reactivity, reactions of 7a,b·BF₄⁻ with some nucleophiles, hydride and diethylamine, were carried out to clarify that the introduction of nucleophiles to give regio-isomers is dependent on the nucleophile. The photo-induced oxidation reactions of 7a,b·BF₄⁻ toward some alcohols under aerobic conditions were carried out to give the corresponding carbonyl compounds in more than 100% yield [based on compounds 7a,b·BF₄⁻], suggesting the oxidizing function of 7a,b·BF₄⁻ toward alcohols in the autorecycling process.     

Group 9 complexes of an N-heterocycle carbene bearing a pentafluorobenzyl substituent: attempted dehydrofluorinative coupling of cyclopentadienyl and N-heterocycle carbene ligands

Treatment of N-methylimidazole with pentafluorobenzyl bromide produces 1-pentafluorobenzyl-3-methylimidazolium bromide (1), which reacts with silver(I) oxide to give the N-heterocycle carbene (NHC) complex 1-pentafluorobenzyl-3-methylimidazolin-2-ylidene silver(I) bromide (2). Complex 2 acts as a carbene transfer reagent giving the complexes [(η⁵-C₅Me₅)MCl₂(NHC)] (3a, M = Rh; 3b M = Ir) on reaction with [(η⁵-C₅Me₅)MCl(μ-Cl)]₂. An attempt to use intramolecular dehydrofluorinative coupling methodology to link the carbene and the pentamethylcyclopentadienyl ligands of [(η⁵-C₅Me₅)RhCl(CN^tBu)(NHC)]BF₄ was unsuccessful.     

New structural motifs of silver and gold complexes of pyridine-functionalized benzimidazolylidene ligands

Reaction of 1,3-bis(picolyl)benzimidazolium chloride ([HL1]Cl) with Ag₂O yields mononuclear complex [Ag(L1)Cl] (2), further reaction of 2 with Au(Et₂S)Cl afforded [Au(L1)Cl] (3). Treatment of 2 with AgBF₄ gave the trinuclear silver cluster [Ag₃(L1)₃](BF₄)₃ (4), whereas the digold complex [Au₂(L1)₂](BF₄)₂ (5) can be easily obtained from the carbene transfer reaction of 4 with Au(Et₂S)Cl. A one-dimensional coordination polymer {[Ag(L2)](BF₄) · CH₃CN}_n (8) was isolated from the reaction of [Ag(L2)Cl] (7, L2 = 1-benzyl-3-picolylbenzimidazolylidene) with additional Ag⁺ in good yield. The dinuclear [Ag₂(L3)₂](PF₆)₂ (12, L3 = 1,4-di(N-benzylbenzimidazolylidene)but-2-yne) is a 18-membered macrocycle. All these complexes have been structurally characterized. Complex 2 shows a dimeric structure because of intermolecular Ag?Cl interactions. Complex 4 consists of a triangular Ag₃ ring with very short Ag-Ag contacts 2.777(1) Å, the Au-Au distance in 5 is 3.206(2) Å showing very weak Au-Au interaction and the macrocyclic cations in 12 are aligned one above another to form channels filled with hexafluorophosphate anions. The complexes 2-5, 8, and 12 are intensely luminescent upon irradiation of uv light, and their emission properties are briefly described.     

Coordination properties of N2S (1,5-bis(3,5-dimethyl-1-pyrazolyl)-3-thiapentane) or N2S2 (1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane or 1,2-bis[3-(3,5-dimethyl-1-pyrazolyl)-2-thiapropyl]benzene) donor ligands toward Rh(I)

The 1,5-bis(3,5-dimethyl-1-pyrazolyl)-3-thiapentane ligand (bdtp) reacts with [Rh(COD)(THF)₂][BF₄] to give [Rh(COD)(bdtp)][BF₄] ([1][BF₄]), which is fluxional in solution on the NMR time scale. Its further treatment with carbon monoxide leads to a displacement of the 1,5-cyclooctadiene ligand, generating a mixture of two complexes, namely, [Rh(CO)₂(bdtp)][BF₄] ([2][BF₄]) and [Rh(CO)(bdtp-κ³N,N,S)][BF₄] ([3][BF₄]). In solution, [2][BF₄] exists as a mixture of two isomers, [Rh(CO)₂(bdtp-κ²N,N)]⁺ ([2a]⁺) and [Rh(CO)₂(bdtp-κ³N,N,S)]⁺ ([2b]⁺; major isomer) rapidly interconverting on the NMR time scale. At room temperature, [2][BF₄] easily loses one molecule of carbon monoxide to give [3][BF₄]. The latter is prone to react with carbon monoxide to partially regenerate [2][BF₄]. The ligands 1,2-bis[3-(3,5-dimethyl-1-pyrazolyl)-2-thiapropyl]benzene (bddf) and 1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane (bddo) are seen to react with two equivalents of [Rh(COD)(THF)₂][BF₄] to give the dinuclear complexes [Rh₂(bddf)(COD)₂][BF₄]₂ ([4][BF₄]₂) and [Rh₂(bddo)(COD)₂][BF₄]₂ ([5][BF₄]₂), respectively. In such complexes, the ligand acts as a double pincer holding two rhodium atoms through a chelation involving S and N donor atoms. Bubbling carbon monoxide into a solution of [4][BF₄]₂ results in loss of the COD ligand and carbonylation to give [Rh₂(bddf)(CO)₄][BF₄]₂ ([6][BF₄]₂). The single-crystal X-ray structures of [3][CF₃SO₃], [5][BF₄]₂ and [6][BF₄]₂ are reported.     

Dinuclear copper(I) complexes of tris(3,5-dimethylpyrazol-1-yl)methane: Synthesis, structure, and reactivity

The reaction of [Cu(NCMe)₄](BF₄) with equimolar amounts of the tris(substituted-pyrazolyl)methane ligand HCPz₃ or HC(3,5-Me₂Pz)₃ yields the respective salts [Cu(HCPz₃)(NCMe)](BF₄) (1a) or [Cu(HC(3,5-Me₂Pz)₃)(NCMe)](BF₄) (1). The acetonitrile ligand of 1 can be replaced by prazine, 4,4′-dipyridine or 1,4-diisocyanobenzene to yield related mononuclear complexes [Cu(HC(3,5-Me₂Pz)₃)(pyrazine)](BF₄) (2), [Cu(HC(3,5-Me₂Pz)₃)(4,4′-bipyridine)] (BF₄) (3) or [Cu(HC(3,5-Me₂Pz)₃)(1,4- CNC₆H₄NC)](BF₄) (7), respectively. A series of binuclear copper(I) complexes {[Cu(HC(3,5-Me₂Pz)₃)]₂(μ -BL)}(BF₄)₂ (4, BL = pyrazine; 5, BL = 4,4′-dipyridine; 8, BL = 1,4-diisocyanobenzene) were prepared by treating equal molar ratio of 1 with related mononuclear complexes 2, 3 and 7. In addition, binuclear copper(I) complexes were also prepared from treatment of 2 equiv of 1 with the related bridge ligand. Both of 4 and 5 reformed mononuclear starting complex 1 in acetonitrile solution. However, the more robust complex 8 was stable in acetonitrile solutions. The structure of complexes 1a, 4, 5, and 7 were confirmed by X-ray crystallography. The redox properties of 4 and 8 were examined by cyclic voltammetry and exhibited two quasi-reversible waves suggesting that no significant structural reorganization occurs during the redox process on the electrochemical time scale.     

Ferrocenylpyrazole—A versatile building block for hydrogen-bonded organometallic supramolecular assemblies

The crystal architectures of 5-ferrocenylpyrazole (1) and its metal complexes were investigated. Compound 1 can form non-solvated and chloroform-solvated crystals. In both cases, 1 forms a zigzag one-dimensional architecture via NH?N hydrogen bonds. The hydrogen bond exhibits a twofold disorder, which was shown to be static by solid-state ¹³C NMR. In the solvated crystal, the chloroform is released at 415 K, associated with melting of the crystal. The reaction of 1 with metal salts provided metal-centered ferrocenyl clusters [Zn(NO₃)₂(1)₄] (4), [Co(NO₃)₂(1)₄] (5), [CoCl₂(1)₄] (6), [Zn(NCS)₂(1)₂] (7), cis-[Pt(NH₃)₂(1)₂](PF₆)₂ (8), and trans-[Pt(NH₃)₂(1)₄](PF₆)₂ (9). In all of these complexes, 1 acts as a monodentate ligand. In 4, 5, and 7, the multinuclear units are joined via hydrogen bonds to form supramolecular chains. Two polymorphs were found for the crystals of 4. Both are composed of the same hydrogen-bonded chains, but their arrangements are different. 5-Ferrocenyl-1-tritylpyrazole (2) and 4-ferrocenyl-1-methylpyrazole (3) were also crystallographically characterized.     

Dinuclear hexamethylbenzene ruthenium cations containing η:η-2-(ferrocenyl)ethen-1-yl ligands: Synthesis, structure, electrochemistry

The cationic ferrocenyl-containing complexes [(η⁶-C₆Me₆)₂Ru₂(μ-η¹:η²-CH-CHFc)₂(μ-H)]⁺ (3) and [(η⁶-C₆Me₆)₂Ru₂(μ-PPh₂)(μ-η¹:η²-CH-CHFc)(μ-H)]⁺ (4) have been synthesised in ethanol from ethynylferrocene and the dinuclear precursors [(η⁶-C₆Me₆)₂Ru₂(μ-H)₃]⁺ (1) and [(η⁶-C₆Me₆)₂Ru₂(μ-PPh₂)(μ-H)₂]⁺ (2) respectively, and isolated as tetrafluoroborate salts. The spectroscopic data of 3 and 4 as well as the single-crystal X-ray diffraction analysis of [4][BF₄] show that the alkyne function of ethynylferrocene has been converted to a σ/π-ethenyl ligand by transfer of a bridging hydride from the diruthenium backbone onto the α-carbon of the triple bond in ethynylferrocene. The ferrocenyl-containing diruthenium compounds [3][BF₄] and [4][BF₄] as well as their parent compounds [1][BF₄] and [2][BF₄] have been studied by voltammetric techniques: Whereas 1 shows only an irreversible Ru(II)/Ru(III) oxidation, the phosphido-bridged derivative 2 displays two well-separated one-electron redox processes. In the case of 3 and 4, the ferrocenyl substituents give rise to additional reversible ferrocene/ferrocenium waves.     

Syntheses of a 2,6-bis-(methylphospholyl)pyridine ligand and its cationic Pd(II) and Ni(II) complexes - application in the palladium-catalyzed synthesis of arylboronic esters

2,6-Bis(2,5-diphenylphospholyl-1-methyl)pyridine (2) was prepared from the reaction of 2,5-diphenylphospholide anion with 2,6-bis(chloromethyl)pyridine. The X-ray crystal structure of 2 was recorded. Reaction of 2 with [Pd(COD)Cl₂] in the presence of AgBF₄ yields the cationic complex [Pd(2)Cl][BF₄] (3). The analogous Ni complex [Ni(2)Br][BF₄] (4) was prepared in a similar way by reacting ligand 2 with [NiBr₂(DME)] in the presence of AgBF₄ and its formulation was confirmed by an X-ray crystal structure study. Complex 3 efficiently catalyzes the coupling between pinacolborane and iodo and bromoarenes with good TON (up to 1 × 10⁵ with iodo derivatives and 8.9 × 10³ with bromo derivatives).