Mechanism of the formation of palladium complexes serving as catalysts in hydrogenation reactions : I. Reactions of complexes with molecular hydrogen

The interaction of Ph₃PPD(OAc)₂₂ with molecular H₂ yields a binuclear complex of zero-valent palladium, (Ph₃P)₂Pd₂. This complex interacts reversibly with H₂ in CH₂Cl₂, yielding (Ph₃P)₂Pd₂H₂. In argon atmosphere (Ph₃P)₂Pd₂ reacts with [Ph₃PPd(OAc)₂₂ to form a binuclear complex of Pd^I with a metal—metal bond. These data, as well as the results of kinetic studies of the reactions between [Ph₃PPd(OAc)₂₂ and H₂, are in agreement with an autocatalytic mechanism for the process, including catalysis of the reduction of Pd^II complexes by the Pd⁰ compounds. It has been established that the synthesized compound of Pd^II, Pd^I and Pd⁰ with the ratio P/Pd?1, are inactive in the hydrogenation of unsaturated compounds. The catalytically active complex (PPh)₂Pd₅ is formed when palladium acetate reacts with (Ph₃P)₂Pd₂ in the presence of H₂. The same compound is formed when a solution of (Ph₃P)₂Pd₂ is treated with a mixture of H₂ and O₂ (or H₂O₂ in an atmosphere of H₂). (PPh)₂Pd₅ is an effective catalyst for the hydrogenation of olefins, dienes, acetylenes, aldehydes, organic peroxides, quinones, O₂, Schiff bases, and nitro, nitroso, and azo compounds.     

Polynuclear nitrosyl carbonyl ReI complexes with thiolate and sulfide bridges

The reaction of the complex Re₂(CO)₄(NO)₂Cl₄ (1) with NaSCMe₃ (2) (in THF or MeCN, 65–80°C, 24 h) was studied at different ratios of the reagents (from 1∶2 to 1∶6). At the reagent ratio of 1∶2, the binuclear complex Re₂(CO)₄(NO)₂Cl₂(μ-SCMe₃)₂ (3) was obtained as a mixture ofsyn andanti isomers (3a and3b, respectively) containing Re₂S₂ fragments with different structures (the butterfly-like structure in3a and the planar fragment in3b). When the initials were taken in ratios from 1∶4 to 1∶6, two compounds were isolated: the binuclear complex Re₂(CO)₄(NO)₂(μ-SCMe₃)₂(μ-S)4 (cocrystallized as a mixture ofsyn andanti isomers,4a and4b, respectively) and the triangular cluster Re₃(CO)₃(NO)₃(μ-SCMe₃((μ₃-S)(μ₃-Cl) (5). Apparently, complex4 is formed in the course of isolation as a result of elimination of SR₂ from the unstable tetrathiolate dimer Re₂(CO)₄(NO)₂(SCMe₃)₂(μ-SCMe₃)₂ (6). Cluster5 is the product of the reaction between compounds3 and4. Products of interaction of compound6 with silica gel upon column chromatography of the reaction mixture were studied. Four complexes containing hydroxy and oxo bridging groups, (CO)₂(NO)Re(μ-SCMe₃)₂(μ-OH)Re(SCMe₃)(CO)(NO) (7), (CO)₃(NO)₃RE₃(μ-SCMe₃)₃(μ₃-SCME₃)(μ₃-O) (8), [(CO)₂(NO)₂Re₂(SCMe₃)₂(μ-SCMe₃)₂(μ-OH)][Na(THF)(Et₂O)] (9), and [(CO)₂(NO)₂Re₂(SCMe₃)₂(μ-SCMe₃)₂(μ-OH)]₂−[Na(H₂O)₆][H₅O₂] (10), were isolated. The structures of complexes3, 4, 5, 7, 8, 9, and10 were established by X-ray diffraction study. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1030–1044, May, 1998.     

Reactions of homobinuclear platinum and palladium complexes with carbon monoxide

The reactivity of homobimetallic complexes of platinum(II) and palladium(II) containing diethyl(diphenylphosphinomethyl)amine (ddpa = (C₆H₅)₂PCH₂N(C₂H₅)₂) as a bridging ligand has been investigated. Carbon monoxide reacts reversibly with these complexes. The species formed are binuclear carbonyl-bridged derivatives, which can isomerize to ionic terminal carbonyl complexes. Reaction of [PtCl₂(CO)]₂[(C₂H₅)₄N]₂ with ddpa in dichloromethane gives the ionic platinum(I) complex [Pt(ddpa)Cl₂]₂[(C₂H₅)₄N]₂, which reacts with carbon monoxide. Still, homobimetallic derivatives of palladium(I) are unstable, and none have been isolated.     

Mesogens based on palladium orthometallated complexes with carboxylato bridges: tuning and shaping a non-planar molecule

The binuclear cyclopalladated compounds [Pd₂(μ-OH)₂(Lⁿ)₂] (1) derived from imines HLⁿ = p-C_nH_2n + 1O-C₆H₄-CHN-C₆H₄-OC_nH_2n + 1-p (n = 6,10) react with carboxylic acids to give the derivatives [Pd₂(μ-ox)₂(Lⁿ)₂] (2) with a planar core for oxalic acid, and [Pd₂(μ-OOCR)₂(Lⁿ)₂] (3-7) compounds with a non-planar ridge tent structure for other RCOOH acids: (3) R = C_mH_2m + 1 (m = 1, 3, 5, 7, 9, 11, 13, 15, 17); (4) R = CH₂(OCH₂CH₂)_pOCH₃ (p = 1, 2); (5) R = CH₂-C₆H₄-OC_qH_2q + 1-p (q = 2, 4, 6, 8, 10, 12); (6) R = C₆H₄-OC_rH_2r + 1-p (r = 4, 10); (7) R = C*H(OH)CH₃. The acids used were designed to explore the effect on the thermal properties of the compounds prepared of systematic variations in the type of carboxylato ligand, which induce structure, packing, and polarity changes, and in the length of the carboxylato chain. Most of the complexes prepared, even when far from planar, show liquid crystal behavior and display nematic, smectic A and smectic C phases.     

Reactions of terminal acetylenes with aryl iodides catalyzed by palladium complexes under interfacial conditions

Conclusions It was shown that in reactions of aryl iodides with terminal acetylenes catalyzed by palladium complexes, potash or alkali can be used as a base in the interfacial system.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 604–606, March, 1988.     

Reactions of organic halides with organometallic compounds and terminal acetylenes catalyzed by palladium complexes

The results of the investigation of the cross-coupling of organometallic compounds and terminal acetylenes with organic halides catalyzed by transition metal complexes are generalized and analyzed. The influence of different factors on the rate and selectivity of catalytic cross-coupling is discussed. A detailed mechanism of the cross-coupling of Grignard reagents with organic halides is suggested. The cross-coupling reaction involving organotin compounds proceeds under very mild conditions in the presence of a ligand-free Pd catalyst. Examples of using catalytic cross-coupling of organic halides with organomagnesium, organozinc, and organotin compounds are presented.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2148–2167, September, 1996.     

Rotating disk electrode study of the kinetics of formation of palladium(II) ethylenediaminechloride complexes from palladium(II) bis-ethylenediamine complexes

The kinetics of substitution of chloride ions for ethylendiamine in a bis-ethylenediamine complex of palladium(II) is studied in solutions with pH 0.3–2.0 and the ionic strength of 0.11–1.0 M by measuring the transients of limiting diffusion currents of the electroreduction of palladium(II) ethylenediamine complexes on a rotating disk electrode. The first reaction orders in hydrogen and chloride ions are found at the ionic strength of 1 M (NaClO₄). The activation energy of the homogeneous reaction under study is determined from the temperature dependence of its rate constant. The mechanism of substitution of chloride ions for ethylenediamine is discussed.     

Potentiometric study of the kinetics and equilibria of formation of chloroglycinate palladium(II) complexes from bis-glycinato palladium(II) complexes

The equilibria and kinetics of the reaction of Pd(gly)₂ complexes with hydrogen ions and chloride ions has been studied by a potentiometric method. The underlying idea of the method is the measurement of solution pH as a function of reaction time t using a glass electrode. The solutions used had the following initial compositions: xM Pd(gly)₂, xM Hgly, and 1 M NaCl with x = 1 × 10^?4, 5 × 10^?4, and 1 × 10^?3; initial pH₀ was from ～3.5 to ～4.4. The experimentally determined pH versus t dependences and the rate equation for a pseudo-second-order reaction were used to determine the equilibrium constant of formation of Pd(gly)(Hgly)Cl complexes from Pd(gly)₂ complexes and the observed rate constant for this reaction, k _obs. The dependence of k _obs on the pH of the acid solutions studied was assigned to a change in the sequence of the reactions of addition of a hydrogen ion and a chloride ion to the complex Pd(gly)₂.     

Reactions of dimethyl- and diphenyl-mercury with dihalobis(isocyanide)palladium(II) complexes

The reaction of cis-[PdCl₂(CNR)₂] (R = Ph, p-MeC₆H₄, p-MeOC₆H₄) and trans-[PdI₂(CNPh)₂] with HgR′₂ (R′ = Me, Ph) followed by addition of PPh₃ (Pd/PPh₃, $\text{1}\text{2}$) gives complexes of the type trans- [PdX {C(=NR)C(R′)=NR}(PPh₃)₂] (X = Cl, I) I as main products. These bis(imino) compounds may result from double insertion of the coordinated isocyanides into a PdR′ σ-bond. NaBPh₄ was also found to act like HgPh₂ as a good phenylating agent towards coordinated isocyanide. The reactions of I with methanolic HClO₄ yield cationic compounds: trans- [PdX{C(NHR)C(R′)=NR}(PPh₃)₂]ClO₄; the protonated bis(imino) group may also be formulated as {C(=NR)C(R′)NHR} and a fast equilibrium between the two forms probably exists in solution. The factors influencing the reaction with HgR′₂ and spectroscopic data (IR and ¹H NMR) for the complexes are reported and discussed.     

Reactions of platinum complexes with spiro compounds. formation of platinospiroalkanes

Spiro[2.nalkanes (n = 2, 4, 5) react with platinum complexes to form compounds of composition PtCl₂(spiroalkane). These materials have been characterized by infrared and nuclear magnetic resonance spectra, and the point of insertion has been shown to be the cyclopropyl carbon—carbon bond opposite the spiro carbon.     

C-S bond formation catalyzed by N-heterocylic carbene palladium phosphine complexes

N-Heterocyclic carbenes (NHCs) are known to be useful ligands for palladium-complex catalysis. It was found that [(NHC)Pd(PPh₃)Cl₂] is an effective pre-catalyst in Pd-catalyzed C-S cross coupling reactions to produce the functionalized sulfides in excellent yields. The turn over frequency (TOF) for the coupling of p-CH₃C₆H₄Br with p-CH₃C₆H₄SH reaches to 6.25 (mol of product) (mole of catalyst)⁻¹ h⁻¹.     

Linear homobimetallic palladium complexes

The oxidative addition of C₆H₄-1,4-I₂ (1) to Pd(PPh₃)₄ (2) gives mononuclear trans-(Ph₃P)₂Pd(C₆H₄-4-I)(I) (3), which can be converted to trans-(Ph₃P)₂Pd(C₆H₄-4-I)(OTf) (5) by its reaction with [AgOTf] (4). Complex 5 can be used in the high-yield preparation of a series of unique cationic mono- and dinuclear palladium complexes of structural type [trans-(Ph₃P)₂Pd(C₆H₄-4-I)(L)]⁺ (7, L = C₄H₄N₂; 9a, L = C₅H₄N-4-CN; 9b, L = NC-4-C₅H₄N) and [trans-(C₆H₄-4-I)(Ph₃P)₂Pd ← N^∩N → Pd(PPh₃)₂(C₆H₄-4-I)]²⁺ (14a, N^∩N = C₆H₄-1,4-(CN)₂; 14b, N^∩N = (C₆H₄-4-CN)₂; 14c, N^∩N = 4,4′-bipyridine (=bipy)). Complexes 7, 9 and 14 rearrange in solution to give [trans-(Ph₃P)₂Pd(C₆H₄-4-PPh₃)(L)]²⁺ (10, L = C₄H₄N₂; 12a, L = C₅H₄N-4-CN; 12b, L = NC-4-C₅H₄N) and [trans-(C₆H₄-4-PPh₃)(Ph₃P)₂Pd ← N^∩N → Pd(PPh₃)₂(C₆H₄-4-PPh₃)]⁴⁺ (15a, N^∩N = C₆H₄-1,4-(CN)₂; 15b, N^∩N = (C₆H₄-4-CN)₂) along with {[(Ph₃P)₂(Ph₃P-4-C₆H₄)Pd(μ-I)]₂}²⁺ (11).The solid state structures of 3, 9a, 10, 11 and 15b are reported. Most characteristic for all complexes is the square-planar coordination geometry of palladium with trans-positioned PPh₃ ligands. In 3 the iodide and the 4-iodo-benzene are linear oriented laying with the palladium atom on a crystallographic C₂ axes. In 9a this symmetry is broken by steric interactions of the PPh₃ ligands with the 4-cyanopyridine and 4-iodobenzene groups. Compound 11 contains two μ-bridging iodides with different Pd-I separations showing that the ligand induces a stronger trans-influence than PPh₃. In 15b, the Ph₃PC₆H₄Pd ← NCC₆H₄C₆H₄CN → PdC₆H₄PPh₃ building block is rigid-rod structured with the C₆H₄ units perpendicular oriented to the Pd coordination plane, while the biphenylene connecting moiety is in-plane bound.     

Mononucleotide recognition by cyclic trinuclear palladium(II) complexes containing 4,7-phenanthroline N,N bridges

Reaction of [(dach)Pd(NO3)2] entities (dach = (R,R)-1,2-diaminocyclohexane, (S,S)-1,2-diaminocyclohexane) and 4,7-phenanthroline (phen) providing, respectively, 90 and 120 degrees bond angles, leads to the formation of two novel positively charged homochiral cyclic trinuclear metallacalix[3]arene species [((R,R)-1,2-diaminocyclohexane)Pd(phen)]3(NO3)6 (2a) and [((S,S)-1,2-diaminocyclohexane)Pd(phen)]3(NO3)6 (2b). These species have been characterised by 1)H NMR and X-ray diffraction methods (2b), showing that they possess accessible cavities suited for supramolecular recognition processes. We prove, indeed, from 1H NMR studies the inclusion of mononucleotides inside the cavity of the trinuclear species [(ethylenediamino)Pd(phen)]3(6+) (1), [((R,R)-1,2-diaminocyclohexane)Pd(phen)]3(6+) (2a) and [((S,S)-1,2-diaminocyclohexane)Pd(phen)]3(6+) (2b) in aqueous solution. Association constants (K(ass)) range from 85 +/- 6 M(-1) for the interaction between [(ethylenediamine)Pd(phen)]3(6+) and adenosine monophosphate to 37 +/- 4 M(-1) for the interaction between [(1,2-diaminocyclohexane)Pd(phen)]3(6+) and thymidine monophosphate. We invoke the synergy of electrostatic, anion-pi and pi-pi interactions to explain the recognition of mononucleotides inside the cavity of the metallacalix[3]arenes.