Turning on red and near-infrared phosphorescence in octahedral complexes with metalated quinones

We report the synthesis of π-bonded ruthenium, rhodium, and iridium o-benzoquinones [Cp*M(o-C(6)H(4)O(2))](n) [M = Ru (2), n = 1-; Rh (3), n = 0; Ir (4), n = 0] following a novel synthetic procedure. Compounds 2-4 were fully characterized by spectroscopic methods and used as chelating organometallic linkers, "OM-linkers", toward luminophore bricks such as Ru(bpy)(2)(2+), Rh(ppy)(2)(+), and Ir(ppy)(2)(+) (bpy = 2,2'-bipyridine; ppy = 2-phenylpyridine) for the design of a novel family of octahedral bimetallic complexes of the general formula [(L-L)(2)M(OM-linkers)][X](m) (X = counteranion; m = 0, 1, 2) whose luminescent properties depend on the choice of the OM-linker and the luminophore brick. Thus, dinuclear assemblies such as [(bpy)(2)Ru(2)][OTf] (5-OTf), [(bpy)(2)Ru(2)][Δ-TRISPHAT] (5-ΔT) {TRISPHAT = tris[tetrachlorobenzene-1,2-bis(olato)]phosphate}, [(bpy)(2)Ru(3)][OTf](2) (6-OTf), [(bpy)(2)Ru(4)][OTf](2) (7-OTf), [(bpy)(2)Ru(4)][Δ-TRISPHAT](2) (7-ΔT), [(ppy)(2)Rh(2)] (8), [(ppy)(2)Rh(3)][OTf] (9-OTf), [(ppy)(2)Rh(4)][OTf] (10-OTf), [(ppy)(2)Rh(4)][Δ-TRISPHAT] (10-ΔT), [(ppy)(2)Ir(2)] (11), [(ppy)(2)Ir(3)][OTf] (12-OTf), [(ppy)(2)Ir(4)][OTf] (13-OTf), and [(ppy)(2)Ir(4)][Δ-TRISPHAT] (13-ΔT) were prepared and fully characterized. The X-ray molecular structures of three of them, i.e., 5-OTf, 8, and 11, were determined. The structures displayed a main feature: for instance, the two oxygen centers of the OM-linker [Cp*Ru(o-C(6)H(4)O(2))](-) (2) chelate the octahedral chromophore metal center, whether it be ruthenium, rhodium, or iridium. Further, the carbocycle of the OM-linker 2 adopts a η(4)-quinone form but with some catecholate contribution due to metal coordination. All of these binuclear assemblies showed a wide absorption window that tailed into the near-IR (NIR) region, in particular in the case of the binuclear ruthenium complex 5-OTf with the anionic OM-linker 2. The latter feature is no doubt related to the effect of the OM-linker, which lights up the luminescence in these homo- and heterobinuclear compounds, while no effect has been observed on the UV-visible and emission properties because of the counteranion, whether it be triflate (OTf) or Δ-TRISPHAT. At low temperature, all of these compounds become luminescent; remarkably, the o-quinonoid linkers [Cp*M(o-C(6)H(4)O(2))](n) (2-4) turn on red and NIR phosphorescence in the binuclear octahedral species 5-7. This trend was even more observable when the ruthenium OM-linker 2 was employed. These assemblies hold promise as NIR luminescent materials, in contrast to those made from organic 1,2-dioxolene ligands that conversely are not emissive.     

Rate and mechanism of the reversible formation of cationic (eta3-allyl)-palladium complexes in the oxidative addition of allylic acetate to palladium(0) complexes ligated by diphosphanes

The oxidative addition of the allylic acetate, CH2=CH-CH2-OAc, to the palladium(o) complex [Pd0(P,P)], generated from the reaction of [Pd(dba)2, with one equivalent of P,P (P,P = dppb = 1,4-bis(diphenylphosphanyl)butane, and P,P = dppf = 1,1'-bis(diphenylphosphanyl)ferrocene), gives a cationic (eta3-allyl)palladium(II) complex, [(eta3-C3H5)Pd(P,P)+]. with AcO as the counter anion. This reaction is reversible and proceeds through two successive equilibria. The overall equilibrium constants have been determined in DMF. Compared with PPh3, the overall equilibrium lies more in favor of the cationic (eta3-allyl)palladium(II) complex when bidentate P,P ligands are considered in the order: dppb > dppf > PPh3. The reaction proceeds via a neutral intermediate complex [(eta2-CH=CH-CHCH2-OAc)Pd0(P,P)], which has been kinetically detected. The rate constants of the successive steps have been determined in DMF by UV spectroscopy and conductivity measurements. The overall complexation step of the Pd0 by the allylic acetate C=C bond is faster than the oxidative addition/ionization step which gives the cationic (eta3-allyl)palladium(II) complex.     

Cationic Pd(II)-catalyzed enantioselective cyclization of aroylmethyl 2-alkynoates initiated by carbopalladation of alkynes with arylboronic acids

A cationic palladium(II)-catalyzed enantioselective intramolecular addition of vinylpalladium species to ketones initiated by the carbopalladation of alkynoates under mild conditions without a Pd(II)/Pd(0) redox system was developed with high yield and enantioselectivity. This cascade reaction provides an efficient method for the construction of optically active hydroxylactones.     

Molecular Structures and Catalytical Performance in Suzuki-coupling Reaction of Novel Dipalladium Clip-shaped Complexes with Bifunctional Pyrazolate Ligands

A series of clip-shaped cationic molecular corners C1～C4(C1 = [(bpy)_2Pd_2(L~1)_2]~(2+), C2 =[(dmbpy)_2Pd_2(L~1)_2]~(2+), C3 =(bpy)_2 Pd_2(L~2)_2]~(2+), C4 =(dmbpy)_2 Pd_2(L~2)_2]~(2+), bpy = 2,2-bipyridine, dmbpy =4,4?-dimethyl-2,2-bipyridine) were synthesized through dipalladium complexes [(bpy)_2Pd_2(NO_3)_2](NO_3)_2,[(dmbpy)_2Pd_2(NO_3)_2](NO_3)_2 and bifunctional pyrazole ligands 4-(3,4-dimethoxyphenyl)-3,5-dimethyl-1H-pyrazol(HL~1) and 4,4?-(5-(1H-pyrazol-4-yl)-1,3-phenylene)dipyridine(HL~2). Complexes C1～C4 were characterized by ~1 H and ~(13)C NMR, electrospray ionization mass spectrometry(ESI-MS), elemental analysis, and IR spectroscopy. The X-ray diffraction analysis of C1?2 NO_3~- revealed a Pd_2 dimetallic clip-shaped structure which was synthesized by two bifunctional ligands doubly bridged by the [(bpy)Pd]_2 dimetal units. Additionally, all of the complexes with NO_3~- as counter anions exhibited high-efficiency catalytical performance in the Suzuki-coupling reaction attributed to the tunable impact and weak dinuclear Pd(Ⅱ)···Pd(Ⅱ) intramolecular bonding interaction.     

Synthesis,Characterization, and Catalysis of Water-Soluble Trimeric and Monomeric Palladium Complexes of 8-Aminoquinolines

New water soluble neutral and cationic palladium complexes were synthesized using 8-aminoquinoline (8-AQ) and 2-methyl 8-aminoquinoline (2-Me 8-AQ) ligands and their catalytic properties were evaluated. The neutral trimeric complexes having a Pd₃N₃ core were found to form when Pd(OAc)₂ was reacted with 8-AQ or 2-Me 8-AQ irrespective of the stoichiometry between the 2 reagents. Controlled addition of triflic acid to the neutral trimeric complex resulted in the formation of a trimeric cationic palladium complex as well as a monomeric cationic complex. A cationic palladium complex having two units of 2-Me-8AQ ligand was also synthesized from the cationic monomeric complex. Crystal structures of the new palladium complexes are reported in this study. The water-soluble neutral palladium complex showed catalytic activity for the oxidation of benzyl alcohols to benzaldehydes, while the cationic palladium complexes were found to be efficient catalysts for the oxidation of styrenes to methyl ketones.     

Synthesis and decomposition of neutral palladium(IV) complexes containing fac-PdMe2R groups, including reductive elimination by η-propenylpalladium(IV) complexes to form η-propenylpalladium(II) species

Oxidative addition of ethyl iodide to PdMe₂(2,2′-bipyridyl) in (CD₃)₂CO gives the unstable “PdIMe₂Et(bpy)”, which undergoes reductive elimination to form PdIR(bpy) (R = Me, Et), ethane, and propane. Ethene and palladium metal are also formed, and are attributed to decomposition of PdIEt(bpy) via β-elimination. Similar results are obtained with n-propyl iodide, although a palladium(IV) intermediate was not detected, but CH₂=CHCH₂X (X = Br, I) and PhCH=CHCH₂Br give isolable complexes fac-PdXMe₂(CH₂CH=CHR)(L₂) (R = H, Ph; L₂ = bpy, phen). The propenyl complexes decompose at ambient temperature to form ethane, a trace of PdXMe(L₂), and mixtures of [Pd(η³-C₃H₅)(L₂)]X and [Pd(η³-C₃H₅)(L₂)]-[Pd(η³-C₃H₅)X₂]; for fac-PdBrMe₂(CH₂CH=CH₂)(bpy) the major palladium(II) product is [Pd(η³-C₃H₅)(bpy)]Br.     

Diimine supported group 10 hydroxo, oxo, amido, and imido complexes

A series of L(2) = diimine (Bian = bis(3,5-diisopropylphenylimino)acenapthene, Bu(t)(2)bpy = 4,4'-di-tert-butyl-2,2'-bipyridine) supported aqua, hydroxo, oxo, amido, imido, and mixed complexes have been prepared. Deprotonation of [L(2)Pt(mu-OH)](2)(2+) with 1,8-bis(dimethylamino)naphthalene, NaH, or KOH yields [(L(2)Pt)(2)(mu-OH)(mu-O)](+) as purple (Bian) or red (Bu(t)(2)bpy) solids. Excess KOH gives dark blue [(Bian)Pt(mu-O)](2). MeOTf addition to [(Bu(t)(2)bpy)(2)Pt(2)(mu-OH)(mu-O)](+) gives [(Bu(t)(2)bpy)(2)Pt(2)(mu-OH)(mu-OMe)](2+) while [(Bian)Pt(mu-O)](2) yields [(Bian)(2)Pt(2)(mu-OMe)(mu-O)](+). Treatment of [(Bian)Pt(mu-O)](2) with "(Ph(3)P)Au(+)" gives deep purple [(Bian)(2)Pt(2)(mu-O)(mu-OAuPPh(3))](+) while (COD)Pt(OTf)(2) gives a low yield of [(Bian)Pt(3)(mu-OH)(3)(COD)(2)](OTf)(3). Ni(Bu(t)(2)bpy)Cl(2) and [(Ph(3)PAu)(3)(mu-O)](+) in a 3 : 2 ratio yield red [Ni(3)(Bu(t)(2)bpy)(3)(mu-O)(2)](2+). M(Bu(t)(2)bpy)Cl(2) (M = Pd, Pt) and [(Ph(3)PAu)(3)(mu-O)](+) give [M(Bu(t)(2)bpy)(mu-OAuPPh(3))](2)(2+) and [Pd(4)(Bu(t)(2)bpy)(4)(mu-OAuPPh(3))](3+). Addition of ArNH(2) to [M(Bu(t)(2)bpy)(mu-OH)](2)(2+) (M = Pd, Pt) gives [Pt(2)(Bu(t)(2)bpy)(2)(mu-NHAr)(mu-OH)](2+) (Ar = Ph, 4-tol, 4-C(6)H(4)NO(2)) and [M(Bu(t)(2)bpy)(mu-NHAr)](2)(2+) (Ar = Ph, tol). Deprotonation of [Pt(2)(Bu(t)(2)bpy)(2)(mu-NH-tol)(mu-OH)](2+) with 1,8-bis(dimethylamino)naphthalene or NaH gives [Pt(2)(Bu(t)(2)bpy)(2)(mu-NH-tol)(mu-O)](+). Deprotonation of [Pt(Bu(t)(2)bpy)(mu-NH-tol)](2)(2+) with KOBu(t) gives deep green [Pt(Bu(t)(2)bpy)(mu-N-tol)](2). The triflate complexes M(Bu(t)(2)bpy)(OTf)(2) (M = Pd, Pt) are obtained from M(Bu(t)(2)bpy)Cl(2) and AgOTf. Treatment of Pt(Bu(t)(2)bpy)(OTf)(2) with water gives the aqua complex [Pt(Bu(t)(2)bpy)(H(2)O)(2)](OTf)(2).     

Architectural formation of a conjugated bimetallic Pd(II) complex via oxidative complexation and a tetracyclic Pd(II) complex via self-assembling complexation

The conjugated homobimetallic palladium(II) complex [(L1)Pd(qd)Pd(L1)] (qd = quinonediimine) was obtained in a one-pot reaction by the in-situ oxidative complexation of 1,4-phenylenediamine with the palladium(II) complex [(L1)Pd(MeCN)] (H2L1 = N,N'-bis(2-phenylethyl)-2,6-pyridinedicarboxamide) while in the absence of an additional ligand [(L1)Pd(MeCN)] was converted to the amide-bridged macrocyclic tetramer [Pd(L1)]4.     

Negishi cross-coupling reaction catalyzed by an aliphatic, phosphine based pincer complex of palladium. biaryl formation via cationic pincer-type Pd(IV) intermediates

The aliphatic, phosphine-based pincer complex [(C(10)H(13)-1,3-(CH(2)P(Cy(2))(2))Pd(Cl)] (1) is a highly active Negishi catalyst, enable to quantitatively couple various electronically activated, non-activated, deactivated, sterically hindered and functionalized aryl bromides with various diarylzinc reagents within short reaction times and low catalyst loadings. Experimental observations strongly indicate that a molecular mechanism is operative with initial chloride dissociation of 1 and formation of the cationic T-shaped 14e(-) complex [(C(10)H(13)-1,3-(CH(2)P(C(6)H(11))(2))(2))Pd](+) (B), which undergoes oxidative addition of an aryl bromide (Ar'Br) to yield the cationic, penta-coordinated aryl bromide pincer complexes of type [(C(10)H(13)-1,3-(CH(2)P(Cy(2))(2))Pd(Br)(aryl')](+) (C) with the metal center in the oxidation state of +IV and the aryl unit in cis position relative to the aliphatic pincer core. Subsequent transmetalation with Zn(aryl)(2) result in the cationic diaryl pincer complexes of type [(C(10)H(13)-1,3-(CH(2)P(Cy(2))(2))Pd(aryl)(aryl')](+) (D), which reductively eliminate the coupling products, thereby regenerating the catalyst. The neutral square planar aryl pincer complex--a possible key intermediate in the catalytic cycle--was found to be reversibly formed in the reaction mixture but is not involved in the catalytic mechanism. Similarly, palladium nanoparticles as the catalytically active form of 1 could have been excluded.     

Efficient addition of alcohols, amines and phenol to unactivated alkenes by Au(III) or Pd(II) stabilized by CuCl2

The nucleophilic addition of alcohols, amines and phenol to unactivated alkenes catalyzed by cationic gold and palladium becomes limited due to the fast reduction into metallic gold under reaction conditions. The presence of CuCl2 retards the reduction of Au(III) and Pd", strongly increasing the turnover number of gold and palladium catalysts. It is shown that new Au(III)-CuCl2 and Pd(II)-CuCl2 catalysts are active and selective for the nucleophilic addition of alcohols, amines and phenol to unactivated alkenes.     

Unusual reactivity of a sterically hindered diphosphazane ligand, EtN{P(OR)(2)}(2), (R = C(6)H(3)(Pr(I))(2)-2,6) towards (eta(3)-allyl)palladium precursors

The reactivity of (eta(3)-allyl)palladium chloro dimers [(1-R-eta(3)-C(3)H(4))PdCl](2) (R = H or Me) towards a sterically hindered diphosphazane ligand [EtN{P(OR)(2)}(2)] (R = C(6)H(3)(Pr(i))(2)-2,6), has been investigated under different reaction conditions. When the reaction is carried out using NH(4)PF(6) as the halide scavenger, the cationic complex [(1-R-eta(3)-C(3)H(4))Pd{EtN(P(OR)(2))(2)}]PF(6) (R = H or Me) is formed as the sole product. In the absence of NH(4)PF(6), the initially formed cationic complex, [(eta(3)-C(3)H(5))Pd{EtN(P(OR)(2))(2)}]Cl, is transformed into a mixture of chloro bridged complexes over a period of 4 days. The dinuclear complexes, [(eta(3)-C(3)H(5))Pd(2)(mu-Cl)(2){P(O)(OR)(2)}{P(OR)(2)(NHEt)}] and [Pd(mu-Cl){P(O)(OR)(2)}{P(OR)(2)(NHEt)}](2) are formed by P-N bond hydrolysis, whereas the octa-palladium complex [(eta(3)-C(3)H(5))(2-Cl-eta(3)-C(3)H(4))Pd(4)(mu-Cl)(4)(mu-EtN{P(OR)(2)}(2))](2), is formed as a result of nucleophilic substitution by a chloride ligand at the central carbon of an allyl fragment. The reaction of [EtN{P(OR)(2)}(2)] with [(eta(3)-C(3)H(5))PdCl](2) in the presence of K(2)CO(3) yields a stable dinuclear (eta(3)-allyl)palladium(I) diphosphazane complex, [(eta(3)-C(3)H(5))[mu-EtN{P(OR)(2)}(2)Pd(2)Cl] which contains a coordinatively unsaturated T-shaped palladium center. This complex exhibits high catalytic activity and high TON's in the catalytic hydrophenylation of norbornene.     

ESI-MS studies on the mechanism of Pd0-catalyzed three-component tandem double addition-cyclization reaction

Four cationic palladium intermediates have been characterized by the high-resolution ESI-FTMS technology, on the basis of which a mechanism was proposed for the Pd0-catalyzed three-component tandem double addition cyclization of organic halides, 2-(2,3-allenyl)malonates, and imines.     

Photochemical and chemical oxidation of alpha-dimine-dithiolene metal complexes: insight into the role of the metal atom

[Pd(bpy)(bdt)], 2 (bpy = 2,2'-bipyridine, bdt = 1,2-benzenedithiolate), was prepared in good yield by the reaction of bdtNa2 with [(bpy)PdCl2] in DMSO. The analogous nickel complex, 1, was prepared in a similar reaction using MeOH/CH2Cl2 and [(bpy)NiCl2.dmf]2. Both 1 (a = 7.9920(1) A, b = 11.4385(1) A, c = 16.1415(1) A, beta = 103.327(1) degrees, V = 1435.86(2) A3, Z = 4) and 2 (a = 8.1631(5) A, b = 11.4379(7) A, c = 16.2475(10) A, beta = 103.7010(10) degrees, V = 1473.84(12) A3, Z = 4) crystallize in the monoclinic space group P2(1)/c and are isostructural with their previously reported platinum analogue. In accord with the results observed for platinum but not nickel, photochemical oxidation of 2 in DMF provides the monosulfinate complex [Pd(bpy)(bdtO2)], 4, along with a minor amount of the corresponding disulfinate [Pd(bpy)(bdtO4)], 5, while chemical oxidation yields only the latter. 4 cocrystallizes with 5 in the monoclinic space group P2(1)/c (a = 8.026(3) A, b = 14.600(6) A, c = 13.371(3) A, beta = 101.80(3) degrees, V = 1533.8(9) A3, Z = 4) as does pure 5 (a = 8.5611(9) A, b = 14.4586(15) A, c = 13.3677(14) A, beta = 108.122(2) degrees, V = 1572.6(3) A3, Z = 4). Comparison of spectroscopic and electrochemical properties of the three complexes, [M(bpy)(bdt)], yields the following ordering for the energy of the HOMO: Pd < Ni < Pt. The observed reactivity patterns and the electronic data suggest that the "anomalous" reactivity of 1 be attributed to the greater relative flexibility of the coordination geometry for nickel(II) complexes rather than electronic differences such as the energies of the frontier orbitals.     

Synthesis, characterization, DNA binding and cytotoxic studies of platinum(II) and palladium(II) complexes of the 2,2'-bipyridine and an anion of 1,1-cyclobutanedicarboxylic acid.

Two neutral complexes of formula [M(bpy)(cbdca)] [where M is palladium(II) (Pd(II)) or platinum(II) (Pt(II)), bpy is 2,2'-bipyridine and cbdca is anion of 1,1-cyclobutanedicarboxylic acid] have been synthesized. These water soluble complexes have been characterized by chemical analysis and conductivity measurements as well as 1H-NMR, ultraviolet-visible and infrared spectroscopy. In these complexes the ligand cbdca coordinates to Pt(II) or Pd(II) as bidentate with two oxygen atoms. They are nonelectrolyte in conductivity water. These complexes inhibit the growth of P388 lymphocytic leukemia cells and their targets are DNA. They invariably show ID50 values less than cisplatin. [Pt(bpy)(cbdca)] and [Pd(bpy)(cbdca)] have been interacted with calf thymus DNA and bind to DNA through coordinate covalent bond. In addition, the influence of binding of these complexes on the intensity of EtBr-DNA have been studied. They bind to DNA via a nonintercalating mode.     

X-ray structure characterization of palladium(II) ternary complexes of pyridinedicarboxylic and phthalic acid with phenanthroline and bipyridine

The crystal structures of the series of four ternary complexes, [Pd(phen)(2,6-PDCA)].4H(2)O (1) (phen=1,10-phenanthroline; 2,6-PDCA=2,6-pyridinedicarboxylic acid), [Pd(bpy)(2,3-PDCA)].3H(2)O (2) (bpy=2,2'-bipyridineand; 2,3-PDCA=2,3-pyridinedicarboxylic acid) and [Pd(phen)(PHT)].2.5H(2)O (3) (PHT=o-phthalic acid ) and [Pd(bpy)(PHT)].1.5H(2)O (4), are determined and the coordination modes of palladium(II) ternary complexes are characterized. All complexes take the mononuclear Pd(II) complexes, in which central Pd(II) atom of each complex has a similar distorted square-planar four coordination geometry. In all complexes, the aromatic heterocyclic compounds, phen and bpy, behave as a bidentate N, N' ligand. In the complex 1 and 2, 2,6-PDCA and 2,3-PDCA behave as a bidentate N, O ligand, and in complex 3 and 4, PHT behaves as a bidentate O, O' ligand.     

Ligand-directed electrochemical functionalization of C(sp<Superscript>2</Superscript>)—H bonds in the presence of the palladium and nickel compounds

The recent achievements of electrochemical functionalization of C—H bonds in aromatic substrates containing the pyridine moiety and acting as a ligand directing substitution to the ortho-position in the presence of the palladium and nickel compounds are analyzed and generalized in the review. Acetoxylation, perfluoroacetoxylation, perfluoroalkylation, and phosphorylation are considered for 2-phenylpyridine (PhPy) as an example. The Pd^II metallocycles with the Pd-bound acetate, perfluoroacetate, and perfluoroheptanoate substituents were isolated and characterized as possible intermediates: binuclear [(PhPy)Pd(µ-OAc)]₂ and [(PhPy)Pd(µ-TFA)]₂ and mononuclear [(PhPy)Pd(TFA)](MeCN), [(PhPy)Pd(TFA)](PhPy), [(PhPy)Pd(PFH)](PhPy), and [(PhPy)Pd(EtO)₂P(O)]₂. Their electrochemical properties were studied. The fluorinated derivatives are in solvent-dependent equilibrium between the mononuclear and binuclear forms. Cyclic voltammetry was used to establish the redox properties of the palladium cycles and routes of their oxidation to the final products. A new approach to CH-substitution products based on the electrochemical generation of Pd or Ni in high oxidation states in the presence of substrate-ligand was proposed.     

Recyclable Palladium Catalysts for the Heck/Sonogashira Reaction under Microwave‐assisted Thermomorphic Conditions

The reaction of allyl palladium(II) chloride dimer and 4,4′‐bis(R_fCH₂OCH₂)‐2,2′‐bpy, 1a–b , in the presence of AgOT_f resulted in the synthesis of cationic palladium complex, [Pd(η³‐allyl)(4,4′‐bis‐(R_fCH₂OCH₂)‐2,2′‐bpy)](OT_f), 2a–b where R_f = C₉F₁₉ ( a ), C₁₀F₂₁ ( b ), respectively. The reaction of [PdCl₂(CH₃CN)] or K₂PdCl₄ with 1b , gave rise to the synthesis of [PdCl₂(4,4′‐bis‐(C₁₀F₂₁CH₂OCH₂)‐2,2′‐bpy)], 3b . The quantitatively determined solubility curves of 2a–b and 3b in DMF indicated dramatic increase of solubility for 2a – b and 3b from ?40 to 90 °C. The catalyst‐recoverable Pd‐catalyzed Heck/Sonogashira reactions were successfully achieved in DMF with microwave‐assistance. The cationic Pd‐catalyzed Heck arylation of methyl acrylate was selected to demonstrate the feasibility of recycling 2a–b using DMF as a solvent under microwave‐assisted thermomorphic conditions. At the end of each cycle, the product mixtures were cooled, and then the catalysts were recovered by decantation. The Heck arylation catalyzed by 2b under microwave‐assisted mode exhibited good recycling results favoring the trans product. To our knowledge, this is the first example of cationic Pd‐catalyzed Heck arylation under microwave‐assisted thermomorphic conditions. Additionally, recoverable 3b ‐catalyzed Sonogashira reactions were also achieved successfully in DMF. The reactions under microwave‐assistance gave much better results in yield and in efficiency than that under conventional thermal heating.     

Synthesis,Characterization, and Theoretical Investigation of Two‐Coordinate Palladium(0) and Platinum(0) Complexes Utilizing π‐Accepting Carbenes

An elegant general synthesis route for the preparation of two coordinate palladium(0) and platinum(0) complexes was developed by reacting commercially available tetrakis(triphenylphosphine)palladium/platinum with π‐accepting cyclic alkyl(amino) carbenes (cAACs). The complexes are characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. The palladium complexes exhibit sharp color changes (crystallochromism) from dark maroon to bright green if the C‐Pd‐C bond angle is sharpened by approximately 6°, which is chemically feasible by elimination of one lattice THF solvent molecule. The analogous dark orange‐colored platinum complexes are more rigid and thus do not show this phenomenon. Additionally, [(cAAC)₂Pd/Pt] complexes can be quasi‐reversibly oxidized to their corresponding [(cAAC)₂Pd/Pt]⁺ cations, as evidenced by cyclic voltammetry measurements. The bonding and stability are studied by theoretical calculations.     

Oxidative addition of allylic carbonates to palladium(0) complexes: reversibility and isomerization

The oxidative addition of a cyclic allylic carbonate to the palladium(0) complex generated from a [Pd(dba)2]+2 PPh3 mixture affords a cationic pi-allylpalladium(II) complex with the alkyl carbonate as the counter-anion. This reaction is reversible and proceeds with isomerization of the allylic carbonate at the allylic position. The equilibrium constant has been determined in DMF. The influence of the precursor of the palladium(0) is discussed.     

Palladium fluoride complexes: one more step toward metal-mediated C-F bond formation

The first molecular complexes of palladium containing a Pd-F bond, both fluorides and bifluorides, were synthesized and fully characterized in the solid state and in solution. Reactivity studies of the Pd fluoride complexes revealed their unexpected stability and unusual chemical properties, different from the hydroxo, chloro, bromo, and iodo analogues. A novel efficient method to generate "naked fluoride" was developed using [(Ph(3)P)(2)Pd(F)Ph]. The naked fluoride from the Pd source fluorinated dichloromethane, deprotonated chloroform, and catalyzed di- and trimerization of hexafluoropropene under uncommonly mild conditions.