Unsymmetrical complexes containing the linear tetraphosphine ligand DPPEPM

The tetraphosphine DPPEPM reacts with [PtMe₂(cod)] to produce [PtMe₂(DPPEPM-PP)] (1) in near quantitative yield. On standing in solution, the free P atoms become oxidized to give [PtMe₂(DPPEPM(O)₂-PP)] (1a), which has been characterized by X-ray crystallography. In contrast, reactions of DPPEPM with [MCl₂(cod)] (M = Pd, Pt) yield ionic products of the form [M(DPPEPM-PP)₂]MCl₄ (3, 4). When a solution of the platinum complex was allowed to stand, crystals of [Pt(μ-Cl)(μ-DPPEPM)₂]Cl₃ (5) were obtained. In a third set of reactions, treatment of [PtClR(cod)] (R = Me, Ph) or [PdClMe(cod)] with DPPEPM gives species of the type [MR(DPPEPM-PPP)]Cl (6-8), in which one of the internal P atoms is uncoordinated. Reactions of [PtR₂(DPPEPM-PP)] with or [MCl₂(cod)] (M = Pd, Pt), or of [PtR(DPPEPM-PPP)]Cl with [MCl₂(cod)], lead to unsymmetrical bimetallic complexes. [PtMe₂(μ-DPPEPM)PdCl₂] (11) and [PtClPh(μ-DPPEPM)PdCl₂] (14) have been characterized crystallographically. Trimetallic complexes of the form [{PtR₂(μ-DPPEPM)}₂M][MCl₄] (M = Pd, Pt, 15-17) are produced by reaction of [PtR₂(DPPEPM-PP)] with [MCl₂(cod)].     

Rh-complexes of ditopic bis(pyrazol-1-yl)borate ligands: Assessment of their catalytic activity towards phenylacetylene polymerization

Two dinuclear Rh^I-cyclooctadiene complexes [1,4-(cod)Rh(B(R’)pz₂)-C₆H₄-(B(R’)pz₂)Rh(cod)], linked by a ditopic scorpionate ligand, have been prepared and fully characterized (R′ = Ph (2), C₆F₅ (2^F); pz = pyrazolide). Both compounds were tested as catalysts for phenylacetylene polymerization but showed no catalytic activity. Attempts at the synthesis of corresponding complexes of the sterically more demanding ligands (R′ = Ph (4), C₆F₅ (4^F); pz^Ph = 3-phenylpyrazolide) resulted in B-N bond cleavage and formation of the dinuclear complex [(cod)Rh(μ-pz^Ph)₂Rh(cod)] (5). Complex 5 proved to be an efficient catalyst for the preparation of highly stereoregular head-to-tail cis-transoidal poly(phenylacetylene).     

Effect of ortho-substituents on the stereochemistry of 2-(o-substituted phenyl)-1H-imidazoline-palladium complexes

Palladium complexes composed of [Pd(Ln)₂Cl₂] (n = 1, 2, 3, 4, 6), [L5a]₂[PdCl₄] and [Pd(L5b)₂], where L1 = 4,5-dihydro-2-phenyl-1H-imidazole (=2-phenyl-1H-imidazoline), L2 = 2-(o-fluorophenyl)-1H-imidazoline, L3 = 2-(o-methylphenyl)-1H-imidazoline, L4 = 2-(o-tert-butylphenyl)-1H-imidazoline, L5a = 2-(o-hydroxyphenyl)-1H-imidazolinium, L5b = 2-(1H-imidazolin-2-yl)phenolate, and L6 = 2-(o-methylphenyl)-1H-imidazole, were synthesized. Molecular structures of the isolated palladium complexes were characterized by single crystal X-ray diffraction analysis. The effect of ortho-substituents on the phenyl ring on trans-chlorine geometry was noted for complexes [Pd(L1)₂Cl₂] 1a and 1b, [Pd(L2)₂Cl₂] 2 and [Pd(L6)₂Cl₂] 6, whereas cis-chlorine geometry was observed for [Pd(L3)₂Cl₂] 3 and [Pd(L4)₂Cl₂] 4. PdCl₂ reacts with 2-(o-hydroxyphenyl)-1H-imidazoline in DMF to give [L5a]⁺ and [L5b]^- so that [L5a]₂[PdCl₄] 5a and [Pd(L5b)₂] 5b were obtained. In complex 5b, as an N,O-bidentate ligand, two ligands L5b coordinated with the central Pd(II) ion in the trans-form. The coordination of PdCl₂ with 2-(o-hydroxyphenyl)-1H-imidazolines in solution was investigated by NMR spectroscopy.     

Synthesis and catalytic activity of rhodium diene complexes bearing indenyl-type fullerene η-ligand

Rhodium η⁵-complexes bearing an indenyl-type fullerene ligand, Rh[C₆₀(PhCH₂)₂Ph](cod) (2), Rh[C₆₀(PhCH₂)₂Ph](nbd) (3) and Rh(C₇₀Ph₃)(cod) (4), have been synthesized from the corresponding fullerene tri-adducts in 93-96% yields. X-ray crystallographic analysis of 4 indicated that the structure of 4 is similar to that of Rh(Ind)(cod). The rhodium complex 2 catalyzes alkyne trimerization reactions and hydroboration reactions.     

Construction of optically active multimetallic systems of rhodium(I), palladium(II), and ruthenium(II) with a P-chiral tetraphosphine ligand

The treatment of optically P-chiral tetraphosphine, (3S,6R,9R,12S)-6,9-di-tert-butyl-2,2,3,12,13,13-hexamethyl-3,6,9,12-tetraphosphatetradecane (1), with rhodium(I), palladium(II), and ruthenium(II) complex precursors led to the selective formation of mono-, di-, or trinuclear homo- or heterometallic complexes, [Rh(1)]SbF₆ (4), [{Rh(nbd)}₂(1)](SbF₆)₂ (3), [{Pd(η³-allyl)}₂(1)](SbF₆)₂ (5), [{RuCl(η⁵-C₅(CH₃)₅)}₂(1)] (6), and [{RuCl₂(η⁶-benzene)}₂(PdCl₂)(1)] (8). These complexes were characterized by NMR and X-ray crystallographic analysis.     

Reactions of benzyldiphenylphosphine with Pd(II) sources on silica gel

Depending on the conditions used, reactions of benzyldiphenylphosphine (HL¹) with Na₂PdCl₄ on silica gel or with Pd(OAc)₂ on the same absorbent followed by treatment with LiCl provide one or more of the four compounds: the cyclopalladated binuclear complex [(μ-Cl)PdL¹]₂ (1), cis and trans isomers of the coordination complex PdCl₂(HL¹)₂ (3), the binuclear coordination complex [(μ-Cl)PdCl(HL¹)]₂ (4), and compound PdCl₂(HL¹)₃ (5). The 56% yield of complex 1 achieved using the reaction with Na₂PdCl₄ and NaOAc on SiO₂ is higher than that reported for the direct cyclopalladation of PBnPh₂ with Pd(OAc)₂ in AcOH. X-ray diffraction studies of the cyclopalladated dimer 1 and the coordination complex cis-3 are reported.     

A new synthesis for thermolabile low-valent palladium complexes by electron transfer reactions from nickel(0) to palladium(II) compounds

The nickel(0) complex [Ni(bpy)(cod)] (bpy: 2,2′-bipyridine, cod: cycloocta-1,5-diene) was used as a mild reducing reagent for the synthesis of the extremely reactive low-valent palladium complexes [Pd₂X₂(cod)₂] (1: X = Cl, 2: X = Br), Pd(cod)₂ (3) and Pd(norbornene)₃ (4). The X-ray analysis of 1 showed that the two [Pd(cod)(Cl)] moieties are only connected by a short Pd(I)-Pd(I) bond (bond length: 2.5379(4) Å) with the chloride ions as monodentate ligands. The X-ray structure of 3 which is also known to be an extremely reactive compound could be determined by X-ray diffraction. As expected, the Pd(0) centre is surrounded by the two cod ligands to form a PdC₄ tetrahedron with typical Pd-C bond lengths. The crystal structure of 3 shows it to be very similar to the closely related complexes M(cod)₂ (M: Ni, Pt). The X-ray structure of 4 displays that the Pd(0) centre is in a trigonal planar environment of the three olefin groups. According to ¹H NMR measurements the complexes have the same structure in solution as found in the solid state.     

New cationic palladium (II) and rhodium (I) complexes of [Ph2PCH2C(Ph)N(2,6-Me2C6H3)]

Treatment of the bulky iminophosphine ligand [Ph₂PCH₂C(Ph)N(2,6-Me₂C₆H₃)] (L) with [M(CH₃CN)₂(ligand)]⁺ⁿ, where for M = Pd(II): ligand = η³-allyl, n = 1, and for M = Rh(I), ligand: 2(C₂H₄), 2(CO) or cod, n = 0, yields the mono-cationic iminophosphine complexes [Pd(η³-C₃H₅)(L)][BF₄] (1), [Rh(cod)(L)][BF₄] (2), [Rh(CO)(CH₃CN)(L)][BF₄] (3), and cis-[Rh(L)₂][BF₄] (4). All the new complexes have been characterised by NMR spectroscopy and X-ray diffraction. Complex 1 shows moderate activity in the copolymerisation of CO and ethene but is inactive towards Heck coupling of 4-bromoacetophenone and n-butyl acrylate.     

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.     

Palladium and platinum complexes of chiral and achiral calix[4]arene bisphosphite ligands

Chiral and achiral p-tert-butyl-calix[4]arene bisphosphites (L¹–L³) have been synthesized by the reaction of p-tert-butyl-calix[4]arene and the phosphorodichloridites, ROPCl₂ [R = (1S,2R,5R)-(+)-iso-menthyl (L¹), (1R,2S,5R)-(−)-menthyl (L²) or C₆H₄Bu^t-4 (L³)]. These bisphosphites function as chelating ligands in palladium(II) and platinum(II) complexes which are formed in good yields by the reaction of PdCl₂(PhCN)₂, MCl₂(COD) (M = Pd or Pt) or PdMeCl(COD) with the respective calix[4]arene bisphosphite. Single crystal X-ray diffraction studies performed on the complexes [PdCl₂(L¹)], [PdCl₂(L²)], [PdCl₂(L³)] and [PtCl₂(L³)] reveal a near square planar geometry around the metal with the two chloride ligands in a cis disposition. The crystal packing in the complexes [PdCl₂(L¹)] and [PdCl₂(L²)], which crystallize in the chiral (P6₁22) space group, shows different hydrophobic channels with intermolecular C–H?Cl hydrogen bonding. The complexes [PdCl₂(L³)] and [PtCl₂(L³)] are isostructural and the molecules in the crystal lattice are linked by intermolecular C–H?Cl and C–H?O hydrogen bonds.     

Rhodium(III) and palladium(II) complexes of some P-heterocycles; synthesis and X-ray structures

Deoxygenation of the syn-3-phosphabicyclo[3.1.0]hexane 3-oxides bearing a 3-phenyl or a 3-(4-methylphenyl) substituent (1a,b) by trichlorosilane took place already at mild condition and resulted in the corresponding phosphines (2a,b) with retention of configuration at phosphorus, while in the case of 3-(2-methylphenyl)-3-phosphabicyclo[3.1.0]hexane (2c), the inversion of the phosphorus atom was observed in solution under ambient conditions that was evaluated by quantum chemical calculations. A further phosphine ligand (5) was obtained by the reduction of 4-dichloromethylene-1,4-dihydrophosphinine oxide (4). The phosphine ligands (2 and 5) were used in the preparation of Rh(III) complexes (3 and 6). A Pd(II) complex of type PdCl₂(5)₂ (7) was also prepared. The stereostructures of a series of Rh(III) complexes of 3-aryl-3-phosphabicyclo[3.1.0]hexanes (3b-syn, 3c-syn and 3c-anti) were elucidated by single crystal X-ray analysis confirming the relative position of the dichlorocyclopropane and the P-substituent.     

Synthesis, characterization and reactivity of tribenzylphosphine rhodium and iridium complexes

New rhodium and iridium complexes, with the formula [MCl(PBz₃)(cod)] [M = Rh (1), Ir (2)] and [M(PBz₃)₂(cod)]PF₆ [M = Rh (3), Ir (4)] (cod = 1,5-cyclooctadiene), stabilized by the tribenzylphosphine ligand (PBz₃) were synthesized and characterized by elemental analysis and spectroscopic methods. The molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. The addition of pyridine to a methanol solution of 1or 2, followed by metathetical reaction with NH₄PF₆, gave the corresponding derivatives [M(py)(PBz₃)(cod)]PF₆ [M = Rh (5), Ir (6)]. At room temperature in CHCl₃ solution, 4 converted spontaneously to the ortho-metallated complex [IrH(PBz₃)(cod){η²-P,C-(C₆H₄CH₂)PBz₂}]PF₆ (7) as a mixture of cis/trans isomers via intramolecular C-H activation of a benzylic phenyl ring. The reaction of 3 or 4 with hydrogen in coordinating solvents gave the dihydrido bis(solvento) derivative [M(H)₂(S)₂(PBz₃)₂]PF₆ (M = Rh, Ir; S = acetone, acetonitrile, THF), that transformed into the corresponding dicarbonyls [M(H)₂(CO)₂(PBz₃)₂]PF₆ by treatment with CO. Analogous cis-dihydrido complexes [M(H)₂(THF)₂(py)(PBz₃)₂]PF₆ (M = Rh, Ir) were observed by reaction of the py derivatives 5 and 6 with H₂.     

Aziridine-derived iminophosphine ligands in palladium-catalyzed allylic substitution

New iminophosphines have been synthesized from (R,R)-1-amino-2-diphenylphosphino cyclohexane (R.R)-1 in good to excellent yields. The catalysts obtained from iminophosphines 3a-g and [Pd(C₃H₅)Cl]₂ promote the enantioselective allylic substitution of 1,3-diphenyl-2-propenyl acetate (6) with diethyl malonate with good enantioselectivity. The air-stable complex PdCl₂[κ²-P,N-(R,R)-2-Ph₂PC₆H₁₀NCHPh] (4) has been prepared and structurally characterized by X-ray crystallography.     

Synthesis, characterization, and catalytic application of a new chiral P,N-indene ligand derived from (R)-BINOL

Lithiation of 2-dimethylaminoindene followed by quenching with [(R)-(1,1′-binaphthalene-2,2′-diyl)]chlorophosphite and treatment with triethylamine afforded the crystallographically characterized enantiopure P,N-indene 3 in 71% isolated yield. In the course of rhodium coordination chemistry studies involving 3, the formation of the isolable complex [(κ²-P,N-3)(κ¹-P,N-3)RhCl] (7) (81%) was observed, thereby confirming the propensity of this new ligand to form L_nRh(3)₂ complexes. Such coordination chemistry behavior may contribute in part to the generally poor catalytic performance exhibited by mixtures of 3 and rhodium precursor complexes in the asymmetric hydrogenation and hydrosilylation studies described herein.     

Phosphite ligands derived from distally and proximally substituted dipropyloxy calix[4]arenes and their palladium complexes: Solution dynamics, solid-state structures and catalysis

Two bisphosphite ligands, 25,27-bis-(2,2′-biphenyldioxyphosphinoxy)-26,28-dipropyloxy-p-tert-butyl calix[4]arene (3) and 25,26-bis-(2,2′-biphenyldioxyphosphinoxy)-27,28-dipropyloxy-p-tert-butyl calix[4]arene (4) and two monophosphite ligands, 25-hydroxy-27-(2,2′-biphenyldioxyphosphinoxy)-26,28-dipropyloxy-p-tert-butyl calix[4]arene (5) and 25-hydroxy-26-(2,2′-biphenyldioxyphosphinoxy)-27,28-dipropyloxy- p-tert-butyl calix[4]arene (6) have been synthesized. Treatment of (allyl) palladium precursors [(η³-1,3-R,R′-C₃H₄)Pd(Cl)]₂ with ligand 3 in the presence of NH₄PF₆ gives a series of cationic allyl palladium complexes (3a-3d). Neutral allyl complexes (3e-3g) are obtained by the treatment of the allyl palladium precursors with ligand 3 in the absence of NH₄PF₆. The cationic allyl complexes [(η³-C₃H₅)Pd(4)]PF₆ (4a) and [(η³-Ph₂C₃H₃)Pd(4)]PF₆ (4b) have been synthesized from the proximally (1,2-) substituted bisphosphite ligand 4. Treatment of ligand 4 with [Pd(COD)Cl₂] gives the palladium dichloride complex, [PdCl₂(4)] (4c). The solid-state structures of [{(η³-1-CH₃-C₃H₄)Pd(Cl)}₂(3)] (3f) and [PdCl₂(4)] (4c) have been determined by X-ray crystallography; the calixarene framework in 3f adopts the pinched cone conformation whereas in 4c, the conformation is in between that of cone and pinched cone. Solution dynamics of 3f has been studied in detail with the help of two-dimensional NMR spectroscopy.The solid-state structures of the monophosphite ligands 5 and 6 have also been determined; the calix[4]arene framework in both molecules adopts the cone conformation. Reaction of the monophosphite ligands (5, 6) with (allyl) palladium precursors, in the absence of NH₄PF₆, yield a series of neutral allyl palladium complexes (5a-5c; 6a-6d). Allyl palladium complexes of proximally substituted ligand 6 showed two diastereomers in solution owing to the inherently chiral calix[4]arene framework. Ligands 3, 6 and the allyl palladium complex 3f have been tested for catalytic activity in allylic alkylation reactions.     

Synthesis,structure and reactivity of novel palladiumdichloride-2,2′-bipyridine with 4,4′-bis(fluorous-ponytail)

With the readily available fluorous alkanols R_fCH₂OH, a series of novel fluorous-ponytailed bpy ligands, 4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy (1a–e), were prepared and treated with [PdCl₂(CH₃CN)₂] to result in the corresponding novel Pd complexes [PdCl₂(4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy)] (2a–e) where R_f = n-C₃F₇ (a), HCF₂(CF₂)₃ (b), HCF₂(CF₂)₇ (c), n-C₈F₁₇ (d), n-C₁₀F₂₁ (e). The new ligands and Pd complexes were spectroscopically characterized by multi-nuclei NMR (¹H, ¹⁹F and ¹³C), FTIR and high resolution mass (FAB). The structure for the Pd complex 2b, the first with fluorinated ponytails on bpy and not on phosphine, was also established by a single crystal X-ray diffraction study. The TGA data of both ligands and Pd complexes indicated that the Pd-complexes were resistant to higher temperatures than the corresponding ligands. The Pd catalysts derived from 2a–c showed an almost quantitative conversion and could be reused for eight runs with Heck reactions, in that the products and unspent reactants were directly removed by distillation. With the highest fluorine content in the series, Pd complex 2e was successfully applied in the Heck reaction using the fluorous biphasic catalysis strategy.     

Synthesis and characterization of palladium(II) complexes with chiral aminophosphine ligands: Catalytic behaviour in asymmetric hydrovinylation. Crystal structure of cis-[PdCl2(PPh((R)-NHCHCH3Ph)2)2]

Optically active ligands of type Ph₂PNHR (R = (R)-CHCH₃Ph, (a); (R)-CHCH₃Cy, (b); (R)-CHCH₃Naph, (c)) and PhP(NHR)₂ (R = (R)-CHCH₃Ph, (d); (R)-CHCH₃Cy, (e)) with a stereogenic carbon atom in the R substituent were synthesized. Reaction with [PdCl₂(COD)₂] produced [PdCl₂P₂] (1) (P = PhP(NHCHCH₃Ph)₂), whose molecular structure determined by X-ray diffraction showed cis disposition for the ligands. All nitrogen atoms of amino groups adopted S configuration. The new ligands reacted with allylic dimeric palladium compound [Pd(η³-2-methylallyl)Cl]₂ to gave neutral aminophosphine complexes [Pd(η³-2-methylallyl)ClP] (2a-2e) or cationic aminophosphine complexes [Pd(η³-2-methylallyl)P₂]BF₄ (3a-3e) in the presence of the stoichiometric amount of AgBF₄. Cationic complexes [Pd(η⁴3-2-methylallyl)(NCCH₃)P]BF₄ (4a-4e) were prepared in solution to be used as precursors in the catalytic hydrovinylation of styrene. ³¹P NMR spectroscopy showed the existence of an equilibrium between the expected cationic mixed complexes 4, the symmetrical cationic complexes [Pd(η³-2-methylallyl)P₂]BF₄ (3) and [Pd(η³-2-methylallyl)(NCCH₃)₂]BF₄ (5) coming from the symmetrization reaction. The extension of the process was studied with the aminophosphines (a-e) as well as with nonchiral monodentate phosphines (PCy₃ (f), PBn₃ (g), PPh₃ (h), PMe₂Ph (i)) showing a good match between the extension of the symmetrization and the size of the phosphine ligand. We studied the influence of such equilibria in the hydrovinylation of styrene because the behaviour of catalytic precursors can be modified substantially when prepared ‘in situ’. While compounds 3 and bisacetonitrile complex 5 were not active as catalysts, the [Pd(η³-2-methylallyl)(η²-styrene)₂]⁺ species formed in the absence of acetonitrile showed some activity in the formation of codimers and dimers. Hydrovinylation reaction between styrene and ethylene was tested using catalytic precursors solutions of [Pd(η³-2-methylallyl)LP]BF₄ ionic species (L = CH₃CN or styrene) showing moderate activity and good selectivity. Better activities but lower selectivities were found when L = styrene. Only in the case of the precursor containing Ph₂PNHCHCH₃Ph (a) ligand was some enantiodiscrimination (10%) found.     

Synthesis and evaluation of substituted pyrazoles palladium(II) complexes as ethylene polymerization catalysts

The substituted pyrazole palladium complexes, (3,5-^tBu₂pz)₂PdCl₂ (1) (3,5-Me₂pz)₂PdCl₂ (2), (3-Mepz)₂PdCl₂ (3) and (pz)₂PdCl₂ (4) (pzH=pyrazole), can be prepared from the reaction of (COD)PdCl₂ with the appropriate pyrazole. The chloromethyl derivative, (3,5-^tBu₂pz)₂PdCl(Me) (5), was prepared from (COD)PdClMe and ^tBu₂pzH. X-ray crystal structure determination of 1 and 5 established their structures in the solid state to be the trans-isomer. After activation of 1-4 and 5 with methylaluminoxane (MAO) the resulting palladium complexes were used as catalysts in ethylene polymerization, yielding linear high-density polyethylene (HDPE). The highest activity was observed for (3,5-^tBu₂pz)PdClMe.