Analogous Palladium Research Articles

The mechanism of olefin exchange in platinum(0) pyridyl–methanimine and pyridyl–thioether complexes. A kinetic study

The complexes of type [Pt(η2-ol1)(L–L′)] (ol1 = dimethylfumarate (dmf), naphthoquinone (nq); L–L′ = pyridyl–methanimine (N-N′R′; R′ = But, 4-MeOC6H4), pyridyl–thioether (N-SR; R = But, Ph) ligands) were synthesised and fully characterised by means of spectrometric and spectroscopic techniques and elemental analysis. At variance with analogous palladium complexes which display a more complicated solution behaviour, the fluxional rearrangement of pyridyl–thioether platinum(0) olefin substrates occurs via inversion at sp3 sulfur only (L–L′ = N-SR). Moreover, the exchange olefin reactions between [Pt(η2-ol1)(L–L′)] complexes and the entering olefin ol2 [ol2 = maleic anhydride (ma), fumaronitrile (fn), naphthoquinone (nq) and tetramethylethylenetetracarboxylate (tmetc)] were studied in CHCl3 either under pseudo-first order or second order conditions. On the basis of the ensuing results and of the activation parameters, an associative reaction mechanism is proposed and a novel reactivity scale for the electron poor olefins acting as entering species is determined. The crystal structures of the complexes [Pt(η2-ol)(L–L′)] (ol = fn, ma, dmf) were also determined and compared with those of analogous platinum(0) and palladium(0) species.

Palladium Analog of Gros Salt: A Simple Method of Preparation and Some of Its Properties

A method for the preparation of [Pd(NH3)4Cl2]Cl2 through the oxidation of [Pd(NH3)4]Cl2 with a mixture of HCl and HNO3 acids (3 : 1) in an aqueous-ammonia solution was proposed. The composition of the product was confirmed by X-ray diffraction and chemical analyses and IR and Raman spectroscopy. The yield of the product was higher than 90%, and the content of the main substance was estimated as at least 95%. The crystallographic parameters of [Pd(NH3)4Cl2]Cl2 were determined. The salt was found to be isostructural to Gros salt [Pt(NH3)4Cl2]Cl2.

M 2E 2 four-member ring structure, M 2(μ-EH 2) 2(P2) 2 (M=Pd or Pt; E=Si or Ge; P2=(PH 3) 2 or H 2PCH 2CH 2PH 2) versus μ-disilene and μ-digermene-bridged structures, M 2(μ-E 2H 4)(P2) 2. A theoretical study

M 2(EH 2) 2(P2) 2 (M=Pd or Pt; E=Si or Ge; P2=(PH 3) 2 or diphosphinoethane (H 2PCH 2CH 2PH 2; dipe)) was theoretically investigated with the DFT method. Natural bond orbital (nbo) analysis and the laplacian of electron density indicate that Pt 2(SiH 2) 2(P2) 2 and Pt 2(GeH 2) 2(P2) 2 are characterized to be di(μ-silylene)- and di(μ-germylene)-bridged complexes, respectively, which involve M 2Si 2 and M 2Ge 2 four-member ring structures, respectively. In other words, they should be represented as Pt 2(μ-SiH 2) 2(P2) 2 and Pt 2(μ-GeH 2) 2(P2) 2. On the other hand, the palladium(0) analogs are understood in terms of μ-disilene- and μ-digermene-bridged complexes in which the SiSi and GeGe bonding interactions are maintained. Thus, they should be represented as Pd 2(μ-Si 2H 4)(P2) 2 and Pd 2(μ-Ge 2H 4)(P2) 2. The difference between platinum(0) and palladium(0) complexes is interpreted in terms of the difference in the strength of π-back donation interaction; in the platinum(0) complex, the π-back donation interaction is so strong that the SiSi and GeGe bonds are almost broken, while in the palladium(0) complex the π-back donation interaction is not so strong and thereby the SiSi and GeGe bonding interactions are still maintained. Also in the mononuclear disilene and digermene complexes, M(E 2H 4)(P2) (M=Pd or Pt; E=Si or Ge), a similar difference between platinum(0) and palladium(0) complexes is observed; platinum(0) complexes are characterized to be a three-member metallacycle complex which involves an EE single bond and two ME covalent bonds, whereas the palladium(0) analogs are characterized to be the usual disilene and digermene complexes in which the SiSi and GeGe double bonds are maintained. This is because the π-back-donating interaction is stronger in platinum(0) complexes than in palladium(0) complexes. In M(C 2H 4)(P2) and M 2(μ-C 2H 4)(P2) 2, the CC double bond is maintained, since the π-back donation is much weaker than those of Si and Ge analogs even in platinum(0) complexes. Thus, these complexes are characterized to be the ethylene complex in which the CC double bond coordinates with the Pt(0) and Pd(0) centers and not the three-member metallacycle complex.

A Systematic ab Initio Study of the Hydration of Selected Palladium Square-Planar Complexes. A Comparison with Platinum Analogues

The hydration surface of four palladium square-planar complexes (neutral cis-dichlorodiamminepalladium PdCl2(NH3)2, neutral trans-dichlorodiamminepalladium PdCl2(NH3)2, tetraamminepalladium cation [Pd(NH3)4]2+, and tetrachloropalladium anion [PdCl4]2-) has been examined by advanced quantum-chemical calculations. Preliminary geometry optimizations were carried out using the second-order Møller−Plesset level of theory with frozen core approximation, utilizing the 6-31G* basis set for H, N, O, and Cl atoms. Pd was described with the Stuttgart relativistic pseudopotential with a basis set of corresponding quality for the explicitly treated electrons. Final reoptimization of all the species considered in the hydration scheme was done at the MP2 (full) level. Then, the reaction surfaces of the structures localized by optimizations were constructed utilizing the MP4 single-point evaluations with additional inclusion of diffuse functions. The computed results were compared with corresponding data of analogous platinum complexes. The Pd and Pt energy surfaces resemble each other to a surprisingly large extent. Practically all qualitative trends, such as cis/trans energy ordering, are identical, and the solvation energies of Pd and Pt species differ only by a few (at most 10) kcal/mol. Concerning the markedly different biochemical and pharmacological roles of Pt- and Pd-based compounds, our basic conclusion is that the difference between cisplatin and analogous palladium complexes cannot be rationalized considering the energetics (thermodynamic properties) of hydration because these properties do not differ significantly.

Potential energy surface for activation of methane by Pt(+): a combined guided ion beam and DFT study.

A guided-ion beam tandem mass spectrometer is used to study the reactions of Pt(+) with methane, PtCH(2)(+) with H(2) and D(2), and collision-induced dissociation of PtCH(4)(+) and PtCH(2)(+) with Xe. These studies experimentally probe the potential energy surface for the activation of methane by Pt(+). For the reaction of Pt(+) with methane, dehydrogenation to form PtCH(2)(+) + H(2) is exothermic, efficient, and the only process observed at low energies. PtH(+), formed in a simple C-H bond cleavage, dominates the product spectrum at high energies. The observation of a PtH(2)(+) product provides evidence that methane activation proceeds via a (H)(2)PtCH(2)(+) intermediate. Modeling of the endothermic reaction cross sections yields the 0 K bond dissociation energies in eV (kJ/mol) of D(0)(Pt(+)-H) = 2.81 +/- 0.05 (271 +/- 5), D(0)(Pt(+)-2H) = 6.00 +/- 0.12 (579 +/- 12), D(0)(Pt(+)-C) = 5.43 +/- 0.05 (524 +/- 5), D(0)(Pt(+)-CH) = 5.56 +/- 0.10 (536 +/- 10), and D(0)(Pt(+)-CH(3)) = 2.67 +/- 0.08 (258 +/- 8). D(0)(Pt(+)-CH(2)) = 4.80 +/- 0.03 eV (463 +/- 3 kJ/mol) is determined by measuring the forward and reverse reaction rates for Pt(+) + CH(4) right harpoon over left harpoon PtCH(2)(+) + H(2) at thermal energy. We find extensive hydrogen scrambling in the reaction of PtCH(2)(+) with D(2). Collision-induced dissociation (CID) of PtCH(4)(+), identified as the H-Pt(+)-CH(3) intermediate, with Xe reveals a bond energy of 1.77 +/- 0.08 eV (171 +/- 8 kJ/mol) relative to Pt(+) + CH(4). The experimental thermochemistry is favorably compared with density functional theory calculations (B3LYP using several basis sets), which also establish the electronic structures of these species and provide insight into the reaction mechanism. Results for the reaction of Pt(+) with methane are compared with those for the analogous palladium system and the differences in reactivity and mechanism are discussed.

Crystal structures and coordination-site exchange reactions of palladium(II) and platinum(II) complexes containing tris[2-( tert-butylthio)ethyl]amine

Palladium(II) and platinum(II) complexes, [PdX(NS 3 1 Bu)]BPh 4 (X=Cl, Br, I; NS 3 1 Bu=tris[2-( tert-butylthio)ethyl]amine) and [PtCl(NS 3 1 Bu)]BPh 4, were prepared, and their structures were determined by X-ray analyses. The geometry around the palladium and platinum atoms is square planar. The NS 3 1 Bu ligand functions as a tridentate ligand and one sulfur atom is not coordinated to the metal. The 1H NMR spectrum of [PdCl(NS 3 1 Bu)]BPh 4 in acetone-d 6 exhibited a dynamic behavior. At 20°C the spectrum showed a singlet signal at 1.60 ppm that can be assigned to tert-butyl protons, whereas at −70°C three singlet signals were observed at 1.36, 1.61, and 1.70 ppm with an intensity ratio of 1: 0.25: 2. The signals at 1.36 and 1.70 ppm are assigned to the tert-butyl protons in the square-planar structure, and these signals are consistent with the X-ray structure. The signal at 1.61 ppm can be assigned to the tert-butyl protons in a trigonal-bipyramidal structure where the three tert-butyl groups are magnetically equivalent. Thus, we concluded that the coordination-site exchange occurred via a trigonal-bipyramidal intermediate. The square-planar and trigonal-bipyramidal species of [PdCl(NS 3 1 Bu)]BPh 4 are in equilibrium in acetone-d 6. The equilibrium was shifted toward the square-planar species on decreasing the temperature. The 1H NMR spectra for [PdX(NS 3 1 Bu)]BPh 4 (X=Cl, Br, and I) were similar to one another at the same temperature, suggesting that the site-exchange process is insensitive to the kind of coexisting halogen ligand. The site exchange reaction of [PtCl(NS 3 1 Bu)]BPh 4 seems to occur more slowly than that of the palladium(II) analogue.

Mechanistic Studies of CVD Metallization Processes: Reactions of Rhodium and Platinum β-Diketonate Complexes on Copper Surfaces

The hexafluoroacetylacetonate complexes Rh(hfac)(C2H4)2 and Pt(hfac)2 are known to serve as chemical vapor deposition precursors to Rh and Pt thin films. In the absence of a reducing carrier gas, the depositions are surface-selective and occur preferentially on copper, but under these conditions, the metallization processes are unexpectedly inefficient relative to the rapid deposition of Pd on Cu seen for the palladium analogue Pd(hfac)2. Mechanistic studies of the reactions of Rh(hfac)(C 2H4)2 and Pt(hfac)2 on copper surfaces under ultrahigh vacuum conditions have now been performed in order to elucidate the factors responsible for the differences among these surface-selective metallization processes. The studies demonstrate that adsorption of the rhodium complex Rh(hfac)(C2H4)2 on copper surfaces is accompanied by the loss of the coordinated ethylene groups, even at 100 K. At these low temperatures, the adsorbed Rh(hfac) fragments are oriented in several ways with respect to the surface. Heating the substrate above 150 K causes the hfac ligands to realign to a perpendicular orientation relative to the surface. The platinum precursor Pt(hfac) 2 adsorbs molecularly at 100 K with the molecular planes of the hfac ligands oriented parallel to the copper surface. Heating the substrate to temperatures above 150 K again results in a realignment of the hfac ligands to a perpendicular orientation. This reorientation is accompanied by a partial reduction of the Pt centers (as judged from shifts seen in X-ray photoelectron spectroscopy core level data), a result suggesting that the hfac ligands begin to dissociate from the platinum centers near 150 K. At temperatures above 220 K, the transfer of the hfac ligands from both complexes to the copper surface is complete, as signaled by the reduction of the metal centers to the zero-valent state. The copper-bound hfac ligands are further transformed upon heating, either reacting with copper surface atoms to yield Cu(hfac)2 (which desorbs at temperatures above 250 K) or decomposing (with fragments desorbing above 350 K). The presence of platinum on the copper surface promotes the former reaction as judged by the appearance of a new reaction-limited desorption process for Cu(hfac) 2. The presence of rhodium on the copper surface does not promote the formation of Cu(hfac)2, although autocatalysis is noted in the steady-state reactive scattering data. The inability of the Rh and Pt precursors to engage in a sustained transmetalation reaction with the copper surface is attributed to the slow interdiffusion of copper through the Rh/Cu and Pt/Cu alloys that are produced in the near-surface region.

Trans-Dichlorobis(triphenylphosphine-P)platinum(II)

Two different crystals (A and B) were used to structurally characterize trans-[PtCl2(PPh3)2] and to study random and systematic errors in derived parameters. The compound is isomorphous with trans-[PdCl2(PPh3)2] and with one of the polymorphs of trans-[PtMeCl(PPh3)2] reported previously. Half-normal probability plot analyses based on A and B show realistic s.u.'s and negligible systematic errors. R.m.s. calculations give very good agreement between A and B, 0.0088 A. Important geometrical parameters are Pt—P = 2.3163 (11) A, Pt—Cl = 2.2997 (11) A, P—Pt—Cl = 87.88 (4) and 92.12 (4)°. Half-normal probability plots and r.m.s. calculations were also used to compare the title compound with the palladium analogue, showing small systematic differences between the compounds. The torsion angles around the Pt—P bond were found to be very similar to those reported for isomorphous complexes, as well as to the torsion angles around the Pt—As bond in trans-[PtCl2(AsPh3)2]. The NMR coupling constants for the title compound are similar to Pt—P coupling constants reported for analogous trans complexes.

Metal Template Synthesis and Coordination Chemistry of Functionalized P-Chiral Phosphanorbornenes

The organopalladium complex containing the (S)-form of ortho-palladated (1-(dimethylamino)ethyl)-naphthylalene has been used successfully as the chiral template to promote the asymmetric cycloaddition reactions between coordinated 3,4-dimethyl-1-phenylphosphole and two dienophiles: N,N-dimethylacrylamide and styrene. The mechanism, the rate and the stereoselectivity of these chiral template promoted reactions are affected by the number of coordination sites available on the palladium template and the coordination potential of the dienophiles. At room temperature, the intramolecular cycloaddition reaction with N,N-dimethylacrylamide gave the corresponding P-chiral (−)-(Sp)-exo-amidophosphanorbornene stereospecifically in 3d. Under similar conditions, the corresponding intermolecular process gave a pair of separable diastereomeric endo-substituted amidophosphanorbornene complexes in 32d. With styrene, the intermolecular cycloaddition reaction at 80°C gave a pair of diastereomeric endo-substituted phenylphosphanorbornene complexes in 3d. No exo-cycloaddition reaction occurred when styrene was used as the dienophile. The first optically active and stable amido-O bonded platinum complex (Rp,Rp)-[Pt(exo-amidophosphanorbornene-P,O)2](ClO4)2 and its palladium analogue have been isolated and characterized by 31PNMR spectroscopy and X-ray crystallography.

New dinuclear diphenylphosphido-bridged palladium(I) derivatives and the X-ray crystal and molecular structures of the mononuclear homoleptic diphenylphosphine complexes Pd(PPh 2H) 4 and [Pd(PPh 2H) 4](BF 4) 2

By reacting CpPd(η 3-C 3H 5) with PPh 2H we isolated the doubly bridged dinuclear complex [Pd 2(μ-PPh 2) 2(PPh 2H) 3] ( 1). This reacts with HBF 4 yielding the mono-phosphido-bridged cationic derivative [Pd 2(μ-PPh 2)(PPh 2H) 4]BF 4 ( 2)BF 4, arising from the protonation of one of the bridging phosphides. Contrary to our previous data on the parent t-butyl systems, a mononuclear homoleptic phosphine complex is not an intermediate in the formation of 1. Pd(PPh 2H) 4 ( 3), was in fact prepared by an independent route and was shown to decompose thermally to another (uncharacterized) polynuclear derivative; fluoboric acid reacts with 3 yielding its palladium(II) analogue [Pd(PPh 2H) 4](BF 4) 2 ( 3)(BF 4) 2, with dihydrogen evolution. We also report the crystal and molecular structures of 3 and ( 3)(BF 4) 2, the first homoleptic transition metal complexes of diphenylphosphine to be structurally characterized.

Organoplatinum(IV) and Palladium(IV) Complexes Containing Intramolecular Coordination Systems Based on the 8-Methylquinolinyl Group (mq), Including Structures of the Cation [Pt(mq)Me2(bpy)]+(bpy = 2,2‘-bipyridine) and the Palladium(IV) Complexes Pd(mq)MeR{(pz)2BH2} (R = Me, Ph; [(pz)2BH2]-= Bis(pyrazol-1-yl)borate)

Oxidative addition of 8-(bromomethyl)quinoline (mqBr) to PdMeR(bpy) (R = Me, Ph; bpy = 2,2'-bipyridine) and [PdMeR{(pz)2BH2}]- (R = Me, Ph; [(pz)2BH2]- = bis(pyrazol-1-yl)borate]) has given the first isolable palladium(IV) complexes containing an intramolecular coordination system, [Pd(mq)MeR(bpy)]Br [R = Me (1), Ph (2)] and [Pd(mq)MeR{(pz)2BH2}- [R = Me (7), Ph (8)]. The pallada(IV)cyclic complex [Pd(CH2CH2CH2CH2)(mq)(bpy)]Br (6) has also been isolated. The first structural analysis of an arylpalladium(IV) complex, Pd(mq)MePh{(pz)2BH2} (8), is reported. Complex 8 occurs as two isomers and the one examined by X-ray crystallography has the fac-PdC3 configuration with the phenyl group trans to the quinoline nitrogen donor. NMR spectra of 8 indicate that the other isomer has the methyl group trans to the quinoline nitrogen donor. Similar geometric isomerism occurs for [Pd(mq)MePh(bpy)]BF4 (4). Structural studies of the dimethylpalladium(IV) complex Pd(mq)Me2{(pz)2BH2} (7) and the platinum(IV) cation in [Pt(mq)Me2(bpy)]BF4.0.75(CH2Cl2) (5) reveal similar structures. The cation [Pd(mq)Me2(bpy)]+ is less stable than the methyl(phenyl)palladium(IV) analogue (2), decomposing in (CD3)2CO by reductive elimination to form ethane and 8-ethylquinoline in ~1:2 ratio, together with the Pd(II) products [Pd(mq)(bpy)]Br and PdBrMe(bpy). A complex mixture of 8-substituted-quinolines (saturated and unsaturated substituents) were obtained as the major products of decomposition of [Pd(CH2CH2CH2CH2)(mq)(bpy)]Br (6), consistent with mq...CH2 coupling to give Pd(II) species that undergo further decomposition.

Organometallics in Acidic Media: Catalytic Dimerization of Ethylene by (Perfluoroalkyl)phosphine Complexes of Platinum and Palladium in Trifluoroacetic Acid

Catalytic ethylene dimerization by (dfepe)Pt(Me)X complexes in aprotic and trifluoroacetic acid solvents is described. In CH2Cl2, catalyst deactivation due to acid loss and generation of (dfepe)Pt(η2-C2H4) is observed. In contrast, long-term ethylene dimerization activity takes place in trifluoroacetic acid at 80 °C and produces 2-(trifluoroacetato)butane as the sole organic product. Under these reaction conditions, the catalyst resting state is (dfepe)Pt(Et)(O2CCF3). At 20 °C, reversible acid elimination from (dfepe)Pt(Et)(O2CCF3) and ethylene ligand exchange results in catalytic vinylic H+/D+ exchange with CF3CO2D (t1/2 ≈ 40 min). Analogous palladium systems exhibit enhanced dimerization activity at 25 °C (340 turnovers/h, 100 psi C2H4) and form (dfepe)2Pd as a catalyst resting state. Inhibition of catalytic activity in the presence of added dfepe was noted. Comparisons between catalytic runs in CF3CO2H and CF3CO2D gave an apparent solvent kinetic effect of 3.5(2), based on an initial second-order rate ...

Homoleptic chelating N-heterocyclic carbene complexes of palladium and nickel

Homoleptic, dicationic nickel(II) complexes with two cis-chelating N-heterocyclic carbene ligands have been prepared via high yielding, air-stable procedures. Homoleptic and heteroleptic dicationic tetra(carbene) palladium(II) analogues are accessible by the reaction of [ cis-CH 2{ N(H)CC(H)N(Me)C } 2Pd(OAc) 2] with one diazolium diiodide salt precursor or by reacting [ cis-CH 2{ N(H)CC(H)N(Me)C } 2PdI 2] with two equivalents of NaOAc and the corresponding diazolium diiodide salts. 1H- and 13C-NMR as well as X-ray crystallographic data are discussed.

Dinuclear Phosphido-Bridged Derivatives of Platinum(I). Synthesis and Characterization of [Pt2(μ-PBut2)2(PBut2H)(L)] [L = PBut2R (R = H, Li, n-Heptyl), CO, η2-CS2

Contrarily to its palladium analogue, the platinum(II) dihydride [Pt(μ-PBut2)(H)(PBut2H)]2 (3) does not reductively eliminate molecular hydrogen to the corresponding Pt(I) dinuclear derivative. The transformation can, however, be achieved in a two-step procedure, i.e., by oxidant-induced hydride abstraction from 3, which produces the cationic monohydride [Pt2(μ-PBut2)2(H)(PBut2H)2]PF6, (4)PF6, and deprotonation of the latter with a strong base, which produces the desired [Pt(μ-PBut2)(PBut2H)]2 (5). Complex 5 can be used as the precursor of other neutral bis-phosphido bridged platinum(I) derivatives. For example, carbon monoxide substitutes in mild conditions one of the terminally bonded secondary phosphines and yields quantitatively the monocarbonyl [Pt2(μ-PBut2)2(PBut2H)(CO)], (6), whose crystal and molecular structure was determined by X-ray diffraction. Crystal data: monoclinic, space group P21/n (No. 14), Z = 4, a = 9.0910(12) Å, b = 30.527(4) Å, c = 11.903(2) Å, β = 93.78(2)°, R(Fo) = 0.0378, Rw(Fo2) = 0.0826 [I > 2σ(I)]. Complex 6 reacts cleanly with carbon disulfide to give the product of CO substitution [Pt2(μ-PBut2)2(PBut2H)(η2-CS2)] (9). Further modifications of complex 5 can be achieved by deprotonating with n-BuLi/TMEN one of its secondary phosphines, which produces the lithiated derivative [Pt2(μ-PBut2)2(PBut2H)(PBut2Li)] (10). The latter has been alkylated with 1-bromoheptane to the soluble derivative [Pt2(μ-PBut2)2(PBut2H)(PBut2R)] (12) (R = n-heptyl).

SnBrMe 3 and dichalcogenides (ER) 2 as oxidants: Synthesis of platinum(IV) complexes, and C⋯C and C⋯E coupling from pallada(IV)cyclopentane complexes and PdMe 2(EPh){(pz) 3BH} {E=O 2C, S, Se; [(pz) 3BH] −=tris(pyrazol-1-yl)borate}

Oxidation of the platinum(II) species [PtMe 2{(pz) 3BH}] − {[(pz) 3BH] −=tris(pyrazol-1-yl)borate} by SnBrMe 3 and the Group 16 oxidants (ER) 2 results in the formation of a series of stable platinum(IV) complexes PtMe 2(SnMe 3){(pz) 3BH} and PtMe 2(ER){(pz) 3BH} (ER=O 2CPh, SMe, SPh, SeMe, SePh). In contrast, the palladium(II) analogue does not react with SnBrMe 3 and reacts with (O 2CPh) 2 to form a 1:1 ratio of PdMe 3{(pz) 3BH} and a Pd IIMe species. The oxidants (EPh) 2 (E=S, Se) react with [PdMe 2{(pz) 3BH}] − to form unstable but NMR detectable species analogous to the platinum(IV) complexes followed by reductive elimination via C⋯C, C⋯S and C⋯Se bond formation processes. The pallada(II)cyclopentane species [ Pd(CH 2CH 2CH 2C H 2){(pz) 3BH}] − reacts with (ER) 2 to form unstable species Pd(CH 2CH 2CH 2C H 2)(ER){(pz) 3BH} (ER=O 2CPh, SPh, SePh) followed by related decomposition reactions.

Chemistry of the azine phosphine ligand Z,E-PPh 2CH 2C(Bu t)=N-N=CMe(C 6H 4NO 2-4): crystal structure of [Mo(CO) 4{PPh 2CH 2C(Bu t)=N-N=CMe(C 6H 4NO 2-4)}

Condensation of Z-PPh 2CH 2C(Bu t)=NNH 2 with 4-nitroacetophenone gave the azine phosphine Z,E-PPh 2CH 2C(Bu t)=N-N=CMe(C 6H 4NO 2-4) ( I). The corresponding phsophine oxide II was prepared by treatment of I with H 2O 2. The phosphine I with [Mo(CO) 4(nbd)] (nbd=norbornadiene) gave [Mo(CO) 4{PPh 2CH 2C(Bu t)=N-N=CMe(C 6H 4NO 2-4)}] ( 1a); the corresponding tungsten 1b and chromium 1c complexes were made similarly. The crystal structure of 1a was determined by X-ray diffraction and showed the presence of a six-membered chelate ring with the bulky 4-nitrophenyl group held close to the metal. Oxidation of 1a with bromine gave the seven-coordinate molybdenum (II) complex 2. Treatment of [PtMe 2(cod)] (cod=cycloocta-1,5-diene) with I at 20°C gave the dimethyl-platinum (II) complex [PtMe 2{PPh 2CH 2C(Bu t)=N-N=CMe(C 6H 4NO 2-4)}] ( 3a) which with MeI gave the iodotrimethylplatinum(IV) complex 4. Treatment of 3a with C≡O opened the chelate ring to give the dimethyl(carbonyl)platinum(II) complex 5 containing a monodentate phosphine ligand. When 3a was heated in toluene solution at 110°C it gave the cyclometallated methylplatinum(II) complex [PtMe{PPh 2CH 2C(Bu t)=N-N=CMe(C 6H 3NO 2-4)}] ( 6). Treatment of 6 with MeI gave the platinum(IV) complex 7. The dichloropalladium(II) complex [PdCl 2{PPh 2CH 2C(Bu t)=N-N=CMe(C 6H 4NO 2-4)}] ( 3b) was prepared by treatment of [PdCl 2(NCPh) 2] with I in CH 2Cl 2. Treatment of [PtCl 2(NCMe) 2] with 2 equiv. of I gave the trans-bis(phosphine) complex 8. When 2 equiv. of I were treated with [PtCl 2(cod)] followed by NH 4PF 6 this gave the salt 9a containing two six-membered chelate rings; the analogous palladium(II) 9b) salt was also prepared. Treatment of 2 equiv. of I with [PtCl 2(cod)] followed by NH 4PF 6 gave the PF 6 salt 10 containing a six-membered chelate ring and a monodentate ligand. When 10 was treated with AgNO 3 followed by NH 4PF 6 this gave the bis-chelate complex 11 containing five- and six-membered chelate rings. Treatment of [IrCl(CO) 2( p-toluidine)] with I gave the cyclometallated iridium(III) hydride complex [IrHClCO{PPh 2CH 2C(Bu t)=N-N=CMe(C 6H 3NO 2-4)}] ( 12). [RuCl 2(PPh 3) 3] with the phosphine I resulted in the Ru(II) complex 13 in which the ortho hydrogens of the 4-nitrophenyl group are agostically interacting with ruthenium. Proton, Phosphorus-31, some carbon-13 NMR and IR data have been obtained. Crystals of 1a are orthorhombic, space group Pna2 1, with a = 1819.3(2), b = 1050.0(1), c = 1614.8(2) pm and Z = 4; final R = 0.0191 for 2616 observed reflections.

Why Do Pt(PR3)2 Complexes Catalyze the Alkyne Diboration Reaction, but Their Palladium Analogues Do Not? A Density Functional Study

The B3LYP hybrid density functional method has been applied to study theoretically the mechanism of the Pd(0)-catalyzed alkyne diboration reaction. It has been found that this reaction proceeds via the same mechanism as the Pt(0)-catalyzed diboration reaction and involves the following steps: (i) coordination of diborane R2B−BR2 to the Pd(0) complex, (ii) oxidative addition of the B−B bond to Pd, (iii) dissociation of one phosphine ligand, (iv) coordination of acetylene, (v) insertion of acetylene into one of the Pd−B bonds, (vi) isomerization of the resultant complex accompanied by recoordination of a phosphine ligand, and (vii) reductive elimination of the alkenyl−diboron products. However, the Pd(0) complex cannot catalyze the alkyne diboration reaction, while its Pt(0) analogue can. The main reason for this difference is found to be in the oxidative addition process of the B−B bond to M(PH3)2. This step takes place for M = Pt with a 14.0 kcal/mol activation barrier and is exothermic, but it does not ...

Platinum(II) Complexes of Piperazine (and Derivatives):trans-Dichlorobis(N-methylpiperazine-N')platinum(II)

The neutral title complex, trans-[PtCl2(C5H12N2)2], has been synthesized in the course of our studies on piperazine derivative complexes with platinum(II). This complex is square-planar and isomorphous with the analogous palladium(II) complex, and exhibits the same molecular, but not crystallographic, structure as trans-[PtCl2(C5H13N2)2]Cl2.2H2O, [(C5H13N2) is N-methylpiperazinium(+1)]. The six-membered ring is in the chair conformation and binds platinum(II) through the unmethylated N1—H nitrogen, which is sterically less hindered than the methylated one. The molecule has a local pseudo-mirror plane nearly coincident with the square-planar coordination plane and nearly bisecting the piperazine ring.

2-(Phenyltelluromethyl)tetrahydrofuran (L 1) and 2-(2-{4-methoxyphenyl}telluroethyl)-1,3- dioxolane (L 2) and their palladium(II) and platinum(II) complexes

The nucleophile [ArTe −] generated in situ borohydride solution of Ar 2Te 2, reacts with 2-(chloromethyl) tetrahydrofuran and 2-(2-bromoethyl)-1,3-dioxolane resulting in L 1 and L 2, respectively. The complexes of palladium(II) and platinum(II) with L 1/L 2 having stoichiometries [MCl 2·L 2], [ML 2](ClO 4) 2, [(DPPE)ML 2](ClO) 4) 2, [(PPh 3) 2ML 2](ClO 4) 2 and [(phen)ML 2](ClO 4) 2 (where L = L 1/L 2 DPPE = Ph 2PC H 2CH 2PPh 2, phen = 1,10-phenanthroline and M = Pd/Pt) have been synthesized. IR, 1H, 125Te{ 1H} and 31P{ 1H} NMR and UV-vis spectral data of these species in conjunction with their molar conductance and molecular weight data have been used to authenticate the new species. In all complexes ( 1–20) the ligands L 1 and L 2 are coordinated through tellurium and in the complexes of formula [ML 2](ClO 4) 2 (M = Pd, Pt) the ligand is bidentate with the oxygen atom used in complexation. In solution, complexes PtCl 2L 2 exist as a mixture of cis and trans isomers whereas only the trans isomer was observed for the palladium analogues. The [(phen)PdL 2](ClO 4) 2(Q) quenches 1O 2 readily. The plot of log [Q] vs time is linear. Mechanism compatible with the experimental observations is proposed.

Singlet Oxygen and the Production of Sulfur Oxygenates of Nickel(II) and Palladium(II) Thiolates.

The metal dithiolate [1,5-bis(2-mercaptoethyl)-1,5-diazacyclooctane]nickel(II) (Ni-1), a sterically hindered analogue (Ni-1), and the palladium analogue Pd-1 react with (1)Delta O(2) to yield a variety of stable and isolable metallosulfones (MS(O(2))R) and metallosulfoxides (MS(O)R). Singlet oxygen was generated both photochemically with the sensitizer Rose Bengal and thermally by decomposition of the 1,4-endoperoxide of 1,4-dimethylnaphthalene. Increased rates and oxygenation yields are observed upon excitation of O(2) from its ground state, (3)Sigma, to the excited state, (1)Delta. The reactions are both solvent and concentration dependent, with sulfones generally favored in acetonitrile and sulfoxides favored in methanol. There is also a ligand and metal effect. The proposed mechanistic pathways involving a persulfoxide precursor to single sulfur site O(2) addition (producing metallosulfones) and adjacent sulfur site O(2) addition (producing metallosulfoxides) are consistent with product distribution, comparison to the much studied oxygenation of organic sulfides, and previous isotopic labeling experiments (J. Am. Chem. Soc. 1996, 118, 1791; 1992, 114, 4601; Inorg. Chem. 1993, 32, 4171).