1-Selenolato-2-phenyl-o-carborane complexes of palladium(II) and platinum(II): Synthesis, spectroscopy and structures

The reactions of PhCb^oSeNa (Cb^o = o-C₂B₁₀H₁₀), prepared by reductive cleavage of Se-Se bond in (PhCb^oSe)₂ by NaBH₄ in methanol, with Na₂PdCl₄, MCl₂(PR₃)₂ and [M₂Cl₂(μ-Cl)₂(PR₃)₂] afforded a variety of complexes, viz., [Pd(SeCb^oPh)Cl] (1), [M(SeCb^oPh)₂(PR₃)₂], [M₂Cl₂(μ-SeCb^oPh)(μ-Cl)(PR₃)₂] (M = Pd, Pt) and [Pd₂Cl(SeCb⁰Ph)(μ-Cl)(μ-SeCb^oPh)(PEt₃)₂] (7) have been isolated. These complexes were characterized by elemental analyses and NMR (¹H, ³¹P, ⁷⁷Se, ¹⁹⁵Pt) spectroscopy. The structures of [Pd(SeCb^oPh)₂(PEt₃)₂] (2), [Pt(SeCb^oPh)₂(PMe₂Ph)₂] (3), [Pd₂Cl₂(μ-SeCb^oPh)(μ-Cl)(PMe₂Ph)₂] (5) and [Pd₂Cl(SeCb^oPh)(μ-Cl)(μ-SeCb^oPh)(PEt₃)₂] (7) were established by X-ray crystallography. The latter represents the first example of asymmetric coordination of selenolate ligands in binuclear bis chalcogenolate complexes of palladium and platinum. Thermolysis of [Pd(SeCb^oPh)₂(PEt₃)₂] (2) in HDA (hexadecylamine) at 330 °C gave nano-crystals of Pd₁₇Se₁₅.     

Interaction of copper(II) and palladium(II) with linked 2,2′-dipyridylamine derivatives: Synthetic and structural studies

Interaction of copper(II) salts with 2,2′-dipyridylamine (1), N-cyclohexylmethyl-2,2′-dipyridylamine (2), di-2-pyridylaminomethylbenzene (3), 1,2-bis(di-2-pyridylaminomethyl)-benzene (4), 1,3-bis(di-2-pyridylaminomethyl)benzene (5), 1,4-bis(di-2-pyridylaminomethyl)benzene (6), 1,3,5-tris(di-2-pyridylaminomethyl)benzene (7) and 1,2,4,5-tetrakis(di-2-pyridylaminomethyl)benzene (8) has yielded the following complexes: [Cu(2)(μ-Cl)Cl]₂, [Cu(3)(μ-Cl)Cl]₂ · H₂O, [Cu₂(4)(NO₃)₄], [Cu₂(5)(NO₃)₄] · 2CH₃OH, [Cu₂(6)(CH₃OH)₂(NO₃)₄], [Cu₄(8)](NO₃)₄] · 4H₂O while complexation of palladium(II) with 1, 4, 5 and 6 gave [Pd(1)₂](PF₆)₂ · 2CH₃OH, [Pd₂(4)Cl₄], [Pd₂(4)(OAc)₄], [Pd₂(5)Cl₄], [Pd₂(6)Cl₄] and [Pd₂(6)(OAc)₄] · CH₂Cl₂, respectively. X-ray structures of [Cu(2)(μ-Cl)Cl]₂, [Cu(3)(μ-Cl)Cl]₂ · 2C₂H₅OH, [Cu₂(6)(CH₃OH)₂(NO₃)₄], [Pd(1)₂](PF₆)₂ · 2CH₃OH, [Pd₂(4)(OAc)₄] · 4H₂O and [Pd₂(6)(OAc)₄] · 2CH₂Cl₂ are reported. In part, the inherent flexibility of the respective ligands has resulted in the adoption of a diverse range of coordination geometries and lattice arrangements, with the structures of [Pd₂(4)(OAc)₄] · 4H₂O and [Pd₂(6)(OAc)₄] · 2CH₂Cl₂, incorporating the isomeric ligands 4 and 6, showing some common features. Liquid–liquid (H₂O/CHCl₃) extraction experiments involving copper(II) and 1–3, 5, 7and 8 show that the degree of extraction depends markedly on the number of dpa-subunits (and concomitant lipophilicity) of the ligand employed with the tetrakis-dpa derivative 8 acting as the most efficient extractant of the six ligand systems investigated.     

Synthesis and structure of dipalladium complexes containing cyclooctatetraene and bicyclooctatrienyl ligands

The reaction of a substitutionally labile dipalladium(I) complex [Pd₂(CH₃CN)₆][BF₄]₂ (1) with 1,3,5,7-cyclooctatetraene (COT) in acetonitrile afforded [Pd₂(μ-η³:η³-C₈H₈)(CH₃CN)₄][BF₄]₂ (2). The reaction of 2 with COT in acetonitrile yielded [Pd₂(μ-η³:η³-C₁₆H₁₆)(CH₃CN)₄][BF₄]₂ (4), where COT is dimerized via C-C bond formation. Complexes 2 and 4 were structurally characterized by X-ray diffraction analyses. In dichloromethane, COT isomerized to styrene at room temperature in the presence of catalytic amount of 1, 2, or 4.     

Synthesis and structural characterisation of the palladium N-heterocyclic carbene cluster complexes [Pd3(μ-CO)3(NHC)3] and [Pd3(μ-SO2)3(NHC)3]

The reduction of trans-[Pd(NHC)₂Cl₂] (NHC = IMes, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; IⁱPr₂ = 1,3-bis-isopropylimidazol-2-ylidene) with potassium graphite under an atmosphere of CO affords the palladium NHC carbonyl clusters [Pd₃(μ-CO)₃(NHC)₃] (NHC = IMes, 1; IⁱPr₂, 3). Treatment of 1 with SO₂ at room temperature yields the bridging SO₂ complex [Pd₃(μ-SO₂)₃(IMes)₃] (4) in quantitative yield. Complexes 1, 3 and 4 have been structurally characterised by X-ray crystallography.     

Preparation,NMR studies and crystal structure of mononuclear and dinuclear Pd(II) and Pt(II) complexes that contain 1,2-bis[3-(3,5-dimethyl-1-pyrazolyl)-2-thiapropyl]benzene

The reaction between 1,2-bis[3-(3,5-dimethyl-1-pyrazolyl)-2-thiapropyl]benzene (bddf) and [MCl₂(CH₃CN)₂] (M = Pd(II), Pt(II)) in a 1:1 M/L ratio in CH₂Cl₂ or acetonitrile solution, respectively, gave the complexes trans-[MCl₂(bddf)] (M = Pd(II) (1), Pt(II) (4)), and in a 2:1 M/L ratio led to [M₂Cl₄(bddf)] (M = Pd(II) (2), Pt(II) (5)). Treatment of 1 and 4 with AgBF₄ and NaBPh₄, respectively, gave the compounds [Pd(bddf)](BF₄)₂ (3) and [Pt(bddf)](BPh₄)₂ (6). When complexes 3 and 6 were heated under reflux in a solution of Et₄NBr in CH₂Cl₂/CH₃OH (1:1) for 24 h, analogous complexes to 1 and 4 with bromides instead of chlorides bonded to the metallic centre were obtained. These complexes were characterised by elemental analyses, conductivity measurements, infrared, ¹H, ¹H{¹⁹⁵Pt}, ¹³C{¹H}, ¹⁹⁵Pt{¹H} NMR, HSQC and NOESY spectroscopies. The X-ray crystal structure of the complex [Pd(bddf)](BF₄)₂ · H₂O has been determined. The metal atom is tetracoordinated by the two azine nitrogen atoms of the pyrazole rings and two thioether groups.     

Synthesis, spectroscopy and structures of palladium(II) and platinum(II) complexes containing mercapto-o-carborane

The reactions of [M₂Cl₂(μ-Cl)₂(PMe₂Ph)₂] with mercapto-o-carboranes in the presence of pyridine afforded mono-nuclear complexes of composition, [MCl(SCb°R)(py)(PMe₂Ph)] (M = Pd or Pt; Cb° = o-C₂B₁₀H₁₀; R = H or Ph). The treatment of [PdCl₂(PEt₃)₂] with PhCb°SH yielded trans-[Pd(SCb°Ph)₂(PEt₃)₂] (4) which when left in solution in the presence of pyridine gave another substitution product, [Pd(SCb°Ph)₂(py)(PEt₃)] (5). The structures of [PdCl(SCb°Ph)(py)(PMe₂Ph)] (1), [Pd(SCb°Ph)₂(PEt₃)₂] (4) and [Pd(SCb^oPh)₂(py)(PEt₃)] (5) were established unambiguously by X-ray crystallography. The palladium atom in these complexes adopts a distorted square-planar configuration with neutral donor atoms occupying the trans positions. Thermolysis of [PdCl(SCb°)(py)(PMe₂Ph)] (2) in TOPO (trioctylphosphine oxide) at 200 °C gave nanocrystals of TOPO capped Pd₄S which were characterized by XRD pattern and SEM.     

Synthesis, characterization and crystal structures of palladium(II) complexes containing neutral, one and twofold deprotonated 1,2,4-triazine species

The synthesis and characterization of three new palladium(II) complexes of 4-amino-6-ethyl-1,2,4-triazine-3-thion-5-one (AETTO, H₃L), [PdCl₂(H₃L)]·H₂O (1), [Pd₂Cl₂(H₂L)(PPh₃)₃]NO₃·2CH₃CN (2) and [Pd(HL)(PPh₃)₂] (3), are reported. All the synthesized compounds are air-stable and were characterized by elemental analyses, IR, NMR spectroscopy and mass spectrometry. In addition, the molecular structures of the complexes have been determined by X-ray single crystal diffraction. On the basis of the crystallographic data, the neutral ligand in 1 and the deprotonated ligands in 2 and 3 act as bidentate NS donors. The singly deprotonated ligand in 2 acts as a bridging agent between two metal centers in the binuclear Pd^II-complex.     

Cobalt(II), nickel(II) and zinc(II) coordination compounds derived from aromatic amines

The structural and spectroscopic characterization of coordination compounds of four aromatic amines derived from benzimidazole, 2-aminobenzimidazole (L1), 1-(S-methylcarbodithioate)-2-aminobenzimidazole (L2), 2-(2-aminophenyl)-1H-benzimidazole (L3) and 6,6-dimethyl-5H-benzimidazolyl[1,2-c]quinazoline (L4) are reported. Cobalt(II) [Co(L1)₂(CH₃COO)₂] (1) and nickel(II) [Ni(L1)₂(CH₃COO)₂] (2) acetate coordination compounds of L1 are discussed. The synthesis and the X-ray crystal structure of the new 1-(S-methylcarbodithioate)-2-aminobenzimidazole (L2) is informed, together with its cobalt(II) [Co(L2)₂Cl₂] (3), [Co(L2)₂Br₂] (4) and zinc(II) [Co(L2)₂Cl₂] (5), [Zn(L2)₂Br₂] (6) coordination compounds. In these compounds the imidazolic nitrogen is coordinated to the metal center, while the ArNH₂ and the S-methylcarbodithioate groups do not participate as coordination sites. A co-crystal of L1 and L2 is analyzed. Structural analyses of the coordination compounds of L3 showed that this ligand behaves as a bidentate ligand through the aniline and the imidazole groups forming six membered rings in the cobalt(II) [Co(L3)Cl₂] (7) and zinc(II) [Zn(L3)Cl₂] (8) compounds, as well as the nickel(II) nitrate [Ni(L3)₂(H₂O)₂](NO₃)₂ (9). The quinazoline L4 was produced by insertion of one acetone molecule and water elimination in L3, its X-ray crystal diffraction analysis, as well as that of its zinc(II) coordination compound [Zn(L4)₂Cl₂] (10), are discussed.     

Synthesis and characterization of water-soluble palladium(II)-functionalized diphosphine complexes

Water-soluble functionalized bis(phosphine) ligands L (a–h) of the general formula CH₂(CH₂PR₂)₂, where for a: R = (CH₂)₆OH; b–g: R = (CH₂)_nP(O)(OEt)₂, n = 2–6 and n = 8; h: R = (CH₂)₃NH₂ ( Scheme 1), have been prepared photochemically by hydrophosphination of the corresponding 1-alkenes with H₂P(CH₂)₃PH₂. Water-soluble palladium complexes cis-[Pd(L)(OAc)₂] (1–8) were obtained by the reaction of Pd(OAc)₂ with the ligands a–h in a 1:1 mixture of dichloromethane:acetonitrile. The water-soluble phosphine ligands and their palladium complexes were characterized by IR, ¹H and ³¹P NMR. A crystallographic study of complex 1 shows that the Pd(II) ion has a square planar coordination sphere in which the acetate ligands and the diphosphine ligand deviate by less than 0.12 Å from ideal planar.     

Preparation and crystallographic characterization of Pd(II) complexes containing imidobis(diphenylthiophosphinato) ligand

The reactions of PdCI₂(L-L) [L-L = Ph₂PCH₂PPh₂(dppm), Ph₂PCH₂CH₂PPh₂(dppe) and Ph₂PCH₂CH₂CH₂PPh₂(dppp)] with equivalent amount of (Ph₂P(S)NHP(S)Ph₂)(dppaS₂) gave the complexes [Pd(L-L)(dppaS₂-H)]ClO₄ [L-L = dppm (1), dppe (2), dppp (3)]. The different synthetic route was used for complex 2 by using of Pd(dppe)Cl₂ and K[N(PSPh₂)₂] as starting materials (2a). All of these complexes have been characterized ³¹P{¹H} NMR, IR and elemental analyses. The complexes 2, 2a and 3 were crystallographically characterized. The coordination geometry around the Pd atoms in these complexes distorted square planar. Six membered dppaS₂-H rings are twist boat conformations in three complexes.     

Synthesis and coordination properties of palladium(II) and platinum(II) complexes with phosphonated triphenylphosphine derivatives

Two triphenylphosphine derivatives, diethyl [4-(diphenylphosphanyl)benzyl]phosphonate (3a) and tetraethyl {[5-(diphenylphosphanyl)-1,3-phenylene]dimethylene}bis(phosphonate) (3b), and also the corresponding free acids 4a and 4b were prepared. These ligands were characterized by ¹H, ¹³C and ³¹P NMR spectroscopy and mass spectrometry. A full set of their Pd(II) and Pt(II) complexes of the general formula [MCl₂L₂] and one dinuclear complex trans-[Pd₂Cl₄(3a)₂] were synthesized and their isomerization behaviour in solution was studied. The complexes were characterized by ¹H, ¹³C, ³¹P and ¹⁹⁵Pt NMR spectroscopy, mass spectrometry and far-IR spectroscopy. The X-ray structures of all complexes with 3a or 3b have usual slightly distorted square-planar geometry on the metal ion. Salts of phosphonic acids 4a and 4b and their complexes are freely soluble in aqueous solution; therefore, they can be potentially useful in aqueous or biphasic catalysis.     

Synthesis and crystal structures of new palladium catalysts for the hydromethoxycarbonylation of alkenes

The preparation and structural characterization of dimeric Pd(I)-Pd(I) complex [Pd₂{(PPh₃)(OSO₂CF₃)}₂].CH₂Cl₂ (1) and three palladium center [Pd₃{(PPh₃)(OSO₂CF₃)}₂] (2) and [Pd₃(PPh₃)₄](SO3CF₃)₂ (3) complexes are reported. The complexes exhibit coordination in which the phosphine phenyl ring is used to stabilize Pd(I) centers in (1) and, Pd(I) and Pd(0) centers in (2) and (3) by acting as π electron donors. The complexes were characterized by single crystal X-ray crystallography.     

Half sandwich complexes of Ru(II) and complexes of Pd(II) and Pt(II) with seleno and thio derivatives of pyrrolidine: Synthesis, structure and applications as catalysts for organic reactions

The reactions of PhSe⁻, PhS⁻ and Se²⁻ with N-{2-(chloroethyl)}pyrrolidine result in N-{2-(phenylseleno)ethyl}pyrrolidine (L1), N-{2-(phenylthio)ethyl}pyrrolidine (L2), and bis{2-pyrrolidene-N-yl)ethyl selenide (L3), respectively, which have been explored as ligands. The complexes [PdCl₂(L1/L2)] (1/7), [PtCl₂(L1/L2)] (2/8), [RuCl(η⁶-C₆H₆)(L1/L2)][PF₆] (3/9), [RuCl(η⁶-p-cymene)(L1/L2)][PF₆] (4/10), [RuCl(η⁶-p-cymene)(NH₃)₂][PF₆] (5) and [Ru(η⁶-p-cymene)(L1)(CH₃CN)][PF₆]₂·CH₃CN (6) have been synthesized. The L1-L3 and complexes were found to give characteristic NMR (Proton, Carbon-13 and Se-77). The crystal structures of complexes 1, 3-6, 9 and 10 have been solved. The Pd-Se and Ru-Se bond lengths have been found to be 2.353(2) and 2.480(11)/2.4918(9)/2.4770(5) Å, respectively. The complexes 1 and 7 have been explored for catalytic Heck and Suzuki-Miyaura coupling reactions. The value of TON has been found up to 85 000 with the advantage of catalyst’s stability under ambient conditions. The efficiency of 1 is marginally better than 7. The Ru-complexes 3 and 9 are good for catalytic oxidation of primary and secondary alcohols in CH₂Cl₂ in the presence of N-methylmorpholine-N-oxide (NMO). The TON value varies between 8.0 × 10⁴ and 9.7 × 10⁴ for this oxidation. The 3 is somewhat more efficient catalyst than 9.     

The synthesis of palladacyclopentadienyl derivatives from rigid bis-alkynes and their use as precursors in the synthesis of fluoroanthene-like cycles under mild conditions. A reactivity investigation

The palladium(0) derivatives of the type [Pd(η²-ol)(LL′)] (2) (ol = dmfu: dimethylfumarate (a), fn: fumaronitrile (b), tmetc: tetramethylethylenetetracarboxylate (c), LL′ = HNSPh: 2-(phenylthiomethyl)-pyridine (A), BiPy: 2,2′-bipyridyl (B), DPPE: bis-diphenylphosphinoethane (C)) were reacted in CH₂Cl₂ with 1,8-bis(methylpropynoate)naphthalene (1) and 2,2′-bis(methylpropynoate)biphenyl (1′). At variance with the flexible 1′ derivative, the rigid bis-alkyne 1 reacts smoothly to give the corresponding cyclopalladate complexes [PdC₄(COOMe)₂(Ph)₂(LL′)] (3). The rates of reaction were determined and the X-ray diffraction structure of the complex [PdC₄(COOMe)₂(Ph)₂(HNSPh )] (3A) is reported. The reactivity of the complexes [PdC₄(COOMe)₂(Ph)₂(LL′)] (LL′ = HNSPh (3A), BiPy (3B), DPPE (3C)) was studied by reacting these complexes with fn and tetracyanoethylene (tcne), respectively. The ensuing fluoroanthene-like compounds were fully characterized.     

Diruthenium(I,I) saccharinate complexes: Synthesis, molecular structure, and evaluation as catalysts for carbenoid reactions of diazoacetates

The dinuclear ruthenium complexes [Ru₂(μ-sac)₂(CO)₆] (1), [Ru₂(μ-sac)₂(CH₃CN)₂(CO)₄] (3), [Ru₂(μ-sac)₂(CO)₅(PPh₃)] (4) and [Ru₂(μ-sac)₂(CO)₄(PPh₃)₂] (5) as well as the tetranuclear ruthenium complex [Ru₂(μ-sac)₂(CO)₅]₂ (2) (sac = saccharinate, C₇H₄NO₃S⁻) were synthesized starting from Ru₃(CO)₁₂ and saccharin. X-ray crystal structure analysis of 1, 3A × p-xylene, 4 × CH₂Cl₂ and 5 × 3CH₂Cl₂ showed that the core is bridged through the amidate moieties of the two saccharinate ligands, with a head-tail arrangement in complexes 1, 3A and 5, and a head-head arrangement in 4. For complex 3, an equilibrium mixture of the head-head regioisomer 3A and a second species 3b exists in solution. Complexes 1 and 2 are suitable catalysts for the cyclopropanation of nucleophilic alkenes (styrene, cyclohexene and 2-methyl-2-butene) with methyl diazoacetate.     

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.     

Reaction between palladium(II) and gallium(III) halogenides in arenes: influence of halogen nature on the formation of binuclear palladium(I) clusters

Palladium(II) bromide reacts with gallium(III) bromide in the presence of arenes yielding binuclear palladium(I) complexes [Pd₂(GaBr₄)₂(arene)₂], where arene=benzene (1), toluene (2) and p-xylene (3). Reaction of palladium(II) chloride with gallium(III) chloride in p-xylene leads to the analogous palladium(I) compound [Pd₂(GaCl₄)₂(p-xylene)₂] (4); the X-ray structures of 1-4 were determined.     

Synthesis and structure of highly substituted pyrazole ligands and their complexes with platinum(II) and palladium(II) metal ions

Reaction of 3-methoxycarbonyl-2-methyl- or 3-dimethoxyphosphoryl-2-methyl-substituted 4-oxo-4H-chromones 1 with N-methylhydrazine resulted in the formation of isomeric, highly substituted pyrazoles 4 (major products) and 5 (minor products). Intramolecular transesterification of 4 and 5 under basic conditions led, respectively, to tricyclic derivatives 7 and 8. The structures of pyrazoles 4a (dimethyl 2-methyl-4-oxo-4H-chromen-3-yl-phosphonate) and 4b (methyl 4-oxo-2-methyl-4H-chromene-3-carboxylate) were confirmed by X-ray crystallography. Pyrazoles 4a and 4b were used as ligands (L) in the formation of ML₂Cl₂ complexes with platinum(II) or palladium(II) metal ions (M). Potassium tetrachloroplatinate(II), used as the metal ion reagent, gave both trans-[Pt(4a)₂Cl₂] and cis-[Pt(4a)₂Cl₂], complexes with ligand 4a, and only cis-[Pt(4b)₂Cl₂] isomer with ligand 4b. Palladium complexes were obtained by the reaction of bis(benzonitrile)dichloropalladium(II) with the test ligands. trans-[Pd(4a)₂Cl₂] and trans-[Pd(4b)₂Cl₂] were the exclusive products of these reactions. The structures of all the complexes were confirmed by IR, ¹H NMR and FAB MS spectral analysis, elemental analysis and Kurnakov tests.     

Hexapalladium cluster: Unique cluster construction reaction of cyclic Pd3(CNC6H3Me2-2,6)6 and linear [Pd3(CNC6H3Me2-2,6)8]

Reaction of a triangle Pd(0) complex, Pd₃(CNXyl)₆ (1; Xyl = 2,6-C₆H₃Me₂), with a dicationic linear trinuclear complex [Pd₃(CNXyl)₈][PF₆]₂ (3) afforded a dicationic hexapalladium complex [Pd₆(CNXyl)₁₂][PF₆]₂ (4), while the reaction of 1 with a dicationic dinuclear complex [Pd₂(CNXyl)₆][PF₆]₂ (2) resulted in the formation of 3. The molecular structure of the complex 4 was determined by X-ray crystallography and spectroscopic analysis.     

Syntheses of a 2,6-bis-(methylphospholyl)pyridine ligand and its cationic Pd(II) and Ni(II) complexes - application in the palladium-catalyzed synthesis of arylboronic esters

2,6-Bis(2,5-diphenylphospholyl-1-methyl)pyridine (2) was prepared from the reaction of 2,5-diphenylphospholide anion with 2,6-bis(chloromethyl)pyridine. The X-ray crystal structure of 2 was recorded. Reaction of 2 with [Pd(COD)Cl₂] in the presence of AgBF₄ yields the cationic complex [Pd(2)Cl][BF₄] (3). The analogous Ni complex [Ni(2)Br][BF₄] (4) was prepared in a similar way by reacting ligand 2 with [NiBr₂(DME)] in the presence of AgBF₄ and its formulation was confirmed by an X-ray crystal structure study. Complex 3 efficiently catalyzes the coupling between pinacolborane and iodo and bromoarenes with good TON (up to 1 × 10⁵ with iodo derivatives and 8.9 × 10³ with bromo derivatives).