Electrochemical properties of palladium(0) complexes coordinated by quinone derivatives

The polagrophic and cyclic voltammetric behavior of quinone derivatives (Q) and their palladium(0) complexes, (Q)₁ or ²Pd(PPh₃)₂, has been studied. All free quinone derivatives except 5,8,9,10-tetrahydro-1,4-naphthoquinone (THNQ) showed two reversible waves, and all palladium(0) complexes showed irreversible waves. The reduction half-wave potentials for free quinone derivatives lie in the following order:7,7,8,8-tetracyanoquinodimethane (TCNQ) ? p-benzoquinone (BQ) ? 5,8-dihydro-1,4-naphthoquinone (DHNQ) ? 1,4-naphthoquinone (NQ) ? THNQ. The reduction potentials for quinone derivatives shifted toward the negative or coordination to palladium(0). The extents of the shifts depended on the electron-withdrawing ability of the free quinone derivatives. On the other hand, the oxidation potentials for the central palladium(0) in their complexes showed more positive values in comparison with the potential for Pd(PPh₃)₄. However, the oxidation potentials were almost constant for all complexes of the quinone derivatives. On the basis of these facts, the phenomena of charge transfer in the complexes are discussed.     

Strongly luminescent palladium(0) and platinum(0) diphosphine complexes

The synthesis, structure, and photoluminescence of palladium(0) and platinum(0) complexes containing biarydiphosphines, biphep (biphep = 2,2'-bis(diphenylphosphino)-1,1'-biphenyl) and binap (binap = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) have been studied. X-ray structure analysis of [Pt(biphep)(2)] revealed the distorted-tetrahedral geometry of the complex. The photophysical properties of the three complexes [Pd(biphep)(2)], [Pt(biphep)(2)], and [Pd(binap)(2)] were investigated and compared with that of the previously reported [Pt(binap)(2)] complex. The [Pd(biphep)(2)] complex shows the strongest luminescence with a high quantum yield (38%) and a long lifetime (3.2 micros) in a toluene solution at room temperature. The luminescence should be due to metal-to-ligand charge transfer excited states. At room temperature, radiative rate constants of the four complexes show similar values. The difference in the luminescent properties should reflect the different nonradiative rate constants of the complexes. The temperature-dependence of the luminescence spectra and lifetime of the complexes were also discussed.     

Ir(I) complexes with oxazoline-thioether ligands: nucleophilic attack of pyridine on coordinated 1,5-cyclooctadiene and application as catalysts in imine hydrogenation

Oxazoline-thioether ligands 6-11 react with [Ir(η⁴-COD)Py₂]PF₆ (COD=C₈H₁₂=1,5-cyclooctadiene) to give [Ir(σ-η²-C₈H₁₂Py⁺)L] PF₆ (L=oxazoline-thioether ligand) (12a-d) complexes resulted from the coordination of ligand to the metal and subsequent nucleophilic attack of pyridine to one of the double carbon bond of COD with concomitant iridium-carbon bond formation. When [Ir(η⁴-COD)₂]BF₄ was used as starting material, the reaction with ligands 7, 9 afforded the complexes [Ir(η⁴-COD)L]BF₄. Application of these iridium complexes to the reduction of N-(α-methyl)benzylidenbenzylamine gave low or negligible enantioselectivity.     

EPR study of (η5-cyclopentadienyl)nickel(I) complexes with P-and N-Donor ligands and 1,5-cyclooctadiene

Mononuclear (η⁵-cyclopentadienyl)nickel(I) complexes with triphenylphosphine, triethylphosphite, 2,2’-bipyridyl, and 1,5-cyclooctadiene formed in the course of reduction of nickelocene were studied by EPR method. Monocyclopentadienyl Ni(I) complexes of the composition CpNiL₂ were shown to form during nickelocene reduction irrespective of the method applied (the use of organometallic compound, alkali metal, thermal conditions) in the presence of stabilizing ligands L (L = PPh₃, P(OEt)₃, Bipy/2, COD/2) and in the course of contradisproportionation reaction between nickelocene and the corresponding NiL₄ complex. It was found that in the structure of these CpNiL₂ complexes (L = PPh₃, P(OEt)₃, Bipy/2), the main molecular axis is perpendicular to the L-Ni-L plane and these complexes should be considered as derivatives of trigonal structures of D _3h symmetry distorted by Cp ligand. In CpNi(COD) complex, the main axis passes through the Cpring center and this complex should be treated as a derivative of pentagonal structure of C _5v symmetry distorted by COD ligand. Nonequivalence of ³¹P nuclei results from vibronic interaction effect in tricoordinate structures in pseudodegenerate electron state (Jahn-Teller effect).     

Protonation of palladium(II)-allyl and palladium(0)-olefin complexes containing 2-pyridyldiphenylphosphine

The pendant nitrogen atom of the Ph₂PPy ligand in the Pd(II)-allyl complexes [PdCl(η³-2-CH₃-C₃H₄)(Ph₂PPy)] (1) and [Pd(η³-2-CH₃-C₃H₄)(Ph₂PPy)₂]BF₄ (3) has been protonated with methanesulfonic acid to afford the corresponding pyridinium salts [PdCl(η³-2-CH₃-C₃H₄)(Ph₂PPyH)](CH₃SO₃) (1a) and [Pd(η³-2-CH₃-C₃H₄)(Ph₂PPyH)₂](CH₃SO₃)₂(BF₄) (3a).Protonation strongly influences the ¹H and ¹³C NMR spectral parameters of the allyl moieties of 1a and 3a whose signals resonate at lower fields with respect to the parent species indicating that upon protonation Ph₂PPy becomes a weaker σ-donor and a stronger Π-acceptor. The allyl moiety, which in 1 is static, becomes dynamic in 1a, the observed syn-syn and anti-anti exchange being due to deligation of the protonated phosphine from the metal centre. Treatment of complex 3 with diethylamine in the presence of fumaronitrile gives the new Pd(0)-olefin complex [Pd(η²-fumaronitrile)(PPh₂Py)₂] (4) which has been characterized by elemental analysis and NMR spectroscopy. Low temperature protonation of 4 with methanesulfonic acid leads to the bis-protonated species [Pd(η²-fumaronitrile)(Ph₂PPyH)₂](CH₃SO₃)₂ (4a) which is stable only at temperatures <0 °C.     

Reactions of (1,5-cyclooctadiene)duroquinonenickel with electron donors

Conclusions Electron transfer from the reducing agent to the complex occurs when the electron donors, sodionaphthalene and sodiomalonic ester, act on (1,5-cyclooctadiene)duroquinonenickel, with the formation of the [(C₈H₁₂)(DQ)Ni]^–· anion radicals, which proved to be thermally less stable and more reactive than the anion radicals of bis(duroquinone)nickel.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2320–2322, October, 1975.     

Oxidative addition of palladium(0) complexes generated from

The major complex formed in solution from [[Pd0(dba)2]+1P-N] mixtures is [Pd0(dba)(P-N)] (dba=trans,trans-dibenzylideneacetone; P-N=PhPN, 1-dimethylamino-2-diphenylphosphinobenzene; FcPN, N,N-dimethyl-1-[2-(diphenylphosphino)ferrocenyl]methylamine; OxaPN, 4,4'-dimethyl-2-(2-diphenylphosphinophenyl)-1,3-oxazoline). Each complex consists of a mixture of isomers involved in equilibria: two 16-electron rotamer complexes [Pd0(eta2-dba)(eta2-P-N)] and one 14-electron complex [Pd0(eta2-dba)(eta1-P-N)] observed for FcPN and OxaPN. [Pd0(dba)(PhPN)] and [SPd0(PhPN)] (S solvent) react with PhI in an oxidative addition: [SPd0(PhPN)] is intrinsically more reactive than [Pd0(dba)(PhPN)]. This behavior is similar to that of the bidentate bis-phosphane ligands. When the PhPN ligand is present in excess, it behaves as a monodentate phosphane ligand, since [Pd0(eta2-dba)(eta1-PhPN)2] is formed first by preferential cleavage of the Pd-N bond instead of the Pd olefin bond. [Pd0(eta1-PhPN)3] is also eventually formed. [Pd0(dba)(FcPN)] and [Pd0(dba)(OxaPN)] are formed whatever the excess of ligand used. [SPd0(FcPN)] and [SPd0)(OxaPN)] are not involved in the oxidative addition. The 16-electron complexes [Pd0(eta2-dba)(eta2-FcPN)] and [Pd0(eta2-dba)(eta2-OxaPN)] are found to react with PhI via a 14-electron complex as has been established for [Pd0(eta2-dba)(eta1-OxaPN)]. Once again, the cleavage of the Pd-N bond is favored over that of Pd-olefin bond. This work demonstrates the higher affinity for [Pd0(P-N)] of dba compared with the P-N ligand, and emphasizes once more the important role of dba, which either controls the concentration of the most reactive complex, [SPd0(PhPN)], or is present in the reactive complexes, [Pd0(dba)(FcPN)] or [Pd0(dba)(OxaPN)], and thus contributes to their intrinsic reactivity.     

Stabilization of bis(triphenylphosphine)palladium(0) by chloride ions. Electrochemical generation of highly reactive zerovalent palladium complexes

“Pd⁰(PPh³)₂” has been generated by electroreduction of Cl₂Pd(PPh₃)₂ in the absence of PPh₃. Its structure is consistent with [Cl_xPd⁰(PPh₃)₂]_n^nx−, with values of x and/or n depending on the chloride ion concentration. The half-lives of its reactions with PhI or PhBr have been determined, and found to be 350 and 100 times, respectively, as large as those for Pd(PPh₃)₄.     

Mechanistic study on the coupling reaction of aryl bromides with arylboronic acids catalyzed by (iminophosphine)palladium(0) complexes. Detection of a palladium(II) intermediate with a coordinated boron anion

The complexes [Pd(eta2-dmfu)(P-N)] [P-N = 2-(PPh2)C6H4-1-CH=NR, R = C(6)H(4)OMe-4; CHMe2; C6H3Me2-2,6; C6H3(CHMe2)-2,6] react with an excess of BrC6H4R1-4 (R1= CF3; Me) yielding the oxidative addition products [PdBr(C6H4R1-4)(P-N)] at different rates depending on R [C6H4OMe-4 > C6H3(CHMe2)-2,6 > CHMe2 approximately C6H3Me2-2,6] and R1 (CF3> Me). In the presence of K2CO3 and activated olefins (ol = dmfu, fn), the latter compounds react with an excess of 4-R2C6H4B(OH)2 (R2= H, Me, OMe, Cl) to give [Pd(eta2-ol)(P-N)] and the corresponding biaryl through transmetallation and fast reductive elimination. The transmetallation proceeds via a palladium(II) intermediate with an O-bonded boron anion, the formation of which is markedly retarded by increasing the bulkiness of R. The intermediate was isolated for R = CHMe2, R1 = CF3 and R2= H. The boron anion is formulated as a diphenylborinate anion associated with phenylboronic acid and/or as a phenylboronate anion associated with diphenylborinic acid. In general, the oxidative addition proceeds at a lower rate than transmetallation and represents the rate-determining-step in the coupling reaction of aryl bromides with arylboronic acids catalyzed by [Pd(eta2-dmfu)(P-N)].     

Novel trinuclear palladium(0) complexes; tris(tribenzylideneacetylacetone) tripalladium(solvent) complexes and their reactions

In an extension of our studies on palladium(0)dibenzylideneacetone complexes, novel trinuclear palladium complexes with three molecules of tribenzylideneacetylacetone have been obtained and identified by elemental and spectroscopic analyses (IR, UV and NMR).Ligand exchange reactions, oxidative addition reactions and complex formation reaction with maleic anhydride, dimethyl acetylenedicarboxylate and para-quinones were investigated. These were found to be similar to those of palladium (0)dibenzylideneacetone complexes.     

Crystal structure of (5-methylcyclopentadienyl)-(1,5-cyclooctadiene) iridium(I)

XRD is used to determine the structure of Cp′Ir(cod) at a temperature of 150(2) K. Crystallographic data for C₁₄H₁₉Ir are: a = 10.8272(5) ?, b = 9.7746(4) ?, c = 10.9180(5) ?, β = 97.3310(10)°, monoclinic symmetry, space group P2₁/n, V = 1146.02(9) ?³, Z = 4, d _calc= 2.199 g/cm³, R = 0.0246. The structure is molecular, built of neutral molecules. The metal atom coordinates carbon atoms of two cyclic ligands: 5-methylcyclopentadienyl-ion (Cp′) and 1,5-cyclooctadiene (cod). Five Ir-C_Cp′ distances lie in the range of 2.21–2.28 ?; four Ir-C_cod distances differ insignificantly, and their average value is 2.114(13) ?. The C₁₁C₁₂C₁₃C₁₄C₁₅ and C₁C₂C₅C₆ planes of ligand fragments are almost parallel, and the angle between normals is 1.9°. In the crystal, molecules are bonded only by van der Waals interactions; in the structure, the eight shortest Ir...Ir distances are in the range of 5.608–7.257 ?. Original Russian Text Copyright ? 2009 by K. V. Zherikova, N. B. Morozova, and I. A. Baidina __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 591–594, May–June, 2009.     

Palladium(0) complexes coordinated with substituted olefins and tertiary phosphine ligands

New palladium(0) complexes with a variety of coordinated olefins [Pd(olefin)(PMePh₂)₂] (II) (olefin = styrene, ethyl methacrylate, methyl methacrylate, methyl acrylate, methacrylonitrile, and dimethyl maleate), were prepared by the reactions of [PdEt₂(PMePh₂)₂] (I) with corresponding olefins in toluene. These complexes were characterized by means of elemental analysis, IR and ¹H NMR spectroscopy and the chemical reactions. The dissociation of the coordinated olefin from complex II in solution was confirmed by spectroscopic studies of [Pd(mma)(PMePh₂)₂] (mma = methyl methacrylate). From the variable temperature NMR study, kinetic parameters for the dissociation process were determined as E_a = 7 kcal/mol, and ΔS³ (293 K) = -30 cal/deg · mol. Some new hydrido complexes, [Pd(H)ClL₂] (IV) (L = PMePh₂, PEtPh₂ and PEt₂Ph), were prepared by the reactions of [Pd(olefin)L₂] with dry HCl.     

Preparation and properties of palladium(II) and rhodium(I) complexes containing bidentate phosphine sulphide and selenide ligands

Summary The synthesis and properties of cationic complexes of general formula [ML₂{CH₂(Ph₂PE)₂}]BF₄, where M = Pd^II and Rh^II, L₂ = ³-MeC₃H₄, {P(O)(OR)₂}₂H (R = Me, Et), COD, (CO)₂, (CO)PPh₃ and E = S, Se are described. The methylene proton of the coordinated phosphine sulphide or selenide ligands react with strong bases as BuLi in n-hexane or NaH in THF, to give neutral complexes of the type [ML₂{CH(Ph₂PE)₂}], where M = Pd^II, Rh^I; L₂ = ³-MeC₃H₄, COD and E = S, Se. The complexes have been characterized by elemental analyses, molar conductivities, i.r., ¹H n.m.r. and ³¹P{¹H} n.m.r. spectroscopy.     

Sigma-borane coordinated to nickel(0) and some related nickel(II) trihydride complexes

The reactions of the complexes [(dcype)NiH]2, 1, [(dippe)NiH]2, 2, and [(dtbpe)NiH]2, 3, with a mixture of BEt3 and Super-Hydride (LiHBEt3) afforded sigma-borane nickel(0) compounds of the type [(dcype)Ni(sigma-HBEt2)], 4, [(dippe)Ni(sigma-HBEt2)], 5, [(dtbpe)Ni(sigma-HBEt2)], 6, respectively, with the concomitant formation in each case of [(dcype)2Ni2)(H)3][BEt4], 7, [(dippe)2Ni2(H)3][BEt4], 8 and [(dtbpe)2Ni2(H)3][BEt4], 9, respectively. X-ray crystal structures are reported for 4 and 8.The reaction of BEt3 and LiHBEt3 was also reviewed in detail.     

Preparation and properties of sandwiched trinuclear palladium(II) complexes with tridentate phosphine and phosphine sulfide ligands

The central phosphino group of tripodal tetradentate tris[2-(diphenylphosphino)ethyl]phosphine (pp₃) was selectively oxidized by the reaction with diethyl disulfide to give tridentate phosphine ligand pOp₃. The terminal phosphino groups were reacted with sulfur to give pOp₃ trisulfide (pOp₃S₃). Three palladium(II) ions were sandwiched in the two pOp₃ and pOp₃S₃ ligands to form the trinuclear complexes with three trans(P) and trans(S) PdX₂ (X = Cl, Br, I) moieties, respectively. The tripodal triphosphine, 1,1,1-tris(diphenylphosphinomethyl)ethane (i-p₃), and its mono- and tri-sulfide, which have shorter carbon chains compared with pOp₃, form the mononuclear dichloro palladium(II) complexes with cis(P) and cis(S) geometries. Difference in the catalytic activity for the C–C coupling reaction was discussed in connection with the coordinated groups and geometries of the complexes.