Tridentate Assembling Ligands Based on Oxazoline and Phosphorus Donors in Dinuclear Pd(I)−Pd(I) Complexes

The Stability of Diphosphino-Boryl PBP Pincer Backbone: PBP to POP Ligand Hydrolysis

Since moisture may frequently be present in many solvents, it is important to know the reactivity of a catalyst against water for catalytic reactions. In order to explore the stability and understand the transformation process of diphosphino-boryl-based PBP pincer platform, [PdCl{B(NCH₂ P^t Bu₂ )₂ -o-C₆ H₄ }] (1) was treated with PdCl₂ , HB(NCH₂ PPh₂ )₂ -o-C₆ H₄ was reacted with [PdCl₂ (cod)] (cod=cyclo-octa-1,5-diene) and [Pd₂ (dba)₃ ] (dba=dibenzylideneacetone), respectively, in the presence of water. Some novel palladium POP complexes, [Pd₂ Cl₂ (μ-Cl){μ-κ³ -P,O,P-OB(NCH₂ P^t Bu₂ )₂ -o-C₆ H₄ }] (2 a), [Pd₄ (μ-Cl)₂ (μ-O)₂ {μ-κ³ -P,O,P-OB(NCH₂ PPh₂ )₂ -o-C₆ H₄ }₂ ] (2 b), [Pd₂ {μ-κ⁴ -P,P,P,P-O(B(NCH₂ PPh₂ )₂ -o-C₆ H₄ )₂ }{μ-κ² -P,P-(NHCH₂ PPh₂ )₂ -o-C₆ H₄ }] (3), were obtained. It was found that the PBP pincer backbone can easily be converted into a POP backbone in the presence of water. From the crystal structures of the resultant palladium complexes, possible pincer backbone transformation pathways were discussed.

Coordination of bis(azol-1-yl)methane-based bisphosphines towards RuII, RhI, PdII and PtII: synthesis, structural and catalytic studies

This paper describes the transition metal chemistry of three bis(X-diphenylphosphino-azol-1-yl)-based bisphosphines: bis(2-Ph₂P-imidazol-1-yl)methane (1), bis(5-Ph₂P-pyrazol-1-yl)methane (2) and bis(5-Ph₂P-1,2,4-triazol-1-yl)methane (3). These show versatility in their coordination behaviour.

Two Triazole-Based Phosphine Ligands Prepared via Temperature-Mediated Li/H Exchange: Cu(I) and Au(I) Complexes and Structural Studies

The kinetically favored triazole-based phosphine 1-(2-(diphenylphosphino)phenyl)-4-phenyl-1H-1,2,3-triazole (2, L1) and its thermodynamically preferred isomer, 5-(diphenylphosphino)-1,4-diphenyl-1H-1,2,3-triazole (3, L2), were obtained by the temperature-controlled lithiation of 2-bromotriazole followed by the reaction with chlorodiphenylphosphine. The structures of phosphines 2 and 3 were determined by X-ray diffraction. Upon reaction with late transition-metal derivatives (Cu(I), Ag(I), and Au(I)), phosphines 2 and 3 form complexes with monodentate (Cu(I), Ag(I), and Au(I); κ(1)-P), chelate (Cu(I); κ(2)-P,N), bridged bidentate (Cu(I); μ(2)-P,N), and tridentate (Cu(I); μ(2),κ(2)-P,N,N) modes of coordination. Reactions with copper(I) halides produced mono-, di-, and tetranuclear complexes, whereas the reaction of 2 with [Cu(NCCH3)4]BF4 yielded the binuclear complex [Cu2(CH3CN)2{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(H)}-μ-(κ-P,κ-N),κ-N}2](BF4)2 (10) with the ligand acting as a six-electron donor involving phosphorus and two triazole nitrogen atoms. The copper complexes of 2 and 3 containing rhomboid Cu2X2 units, [(Cu)2(μ-X)2{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(H)}-κ-P}2] (4, X = Cl; 5, X = Br), on treatment with 1,10-phenanthroline and 2,2'-bipyridine gave mixed-ligand complexes of the type [(CuX)(N∩N-κ(2)-N,N){o-Ph2P(C6H4){1,2,3-N3C(Ph)C(H)}-κ-P}] (N∩N = 1,10-phen and 2,2'-bipy; X = Cl, Br, and I).

Stepwise Expansion of Pd Chains from Binuclear Palladium(I) Complexes Supported by Tetraphosphine Ligands

Reaction of [Pd2(XylNC)6]X2 (X = PF6, BF4) with a linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), afforded binuclear Pd(I) complexes, [Pd2(μ-dpmppm)2]X2 ([2]X2), through an asymmetric dipalladium complex, [Pd2(μ-dpmppm)(XylNC)3](2+) ([1](2+)). Complex [2](2+) readily reacted with [Pd(0)(dba)2] (2 equiv) and an excess of isocyanide, RNC (R = 2,6-xylyl (Xyl), tert-butyl ((t)Bu)), to generate an equilibrium mixture of [Pd4(μ-dpmppm)2(RNC)2](2+) ([3'](2+)) + RNC ⇄ [Pd4(μ-dpmppm)2(RNC)3](2+) ([3](2+)), from which [Pd4(μ-dpmppm)2(XylNC)3](2+) ([3a](2+)) and [Pd4(μ-dpmppm)2((t)BuNC)2](2+) ([3b'](2+)) were isolated. Variable-temperature UV-vis and (31)P{(1)H} and (1)H NMR spectroscopic studies on the equilibrium mixtures demonstrated that the tetrapalladium complexes are quite fluxional in the solution state: the symmetric Pd4 complex [3b'](2+) predominantly existed at higher temperatures (>0 °C), and the equilibrium shifted to the asymmetric Pd4 complex [3b](2+) at a low temperature (∼-30 °C). The binding constants were determined by UV-vis titration at 20 °C and revealed that XylNC is of higher affinity to the Pd4 core than (t)BuNC. In addition, both isocyanides exhibited higher affinity to the electron deficient [Pd4(μ-dpmppmF2)2(RNC)2](2+) ([3F'](2+)) than to [Pd4(μ-dpmppm)2(RNC)2](2+) ([3'](2+)) (dpmppmF2 = meso-bis[{di(3,5-difluorophenyl)phosphinomethyl}phenylphosphino]methane). When [2]X2 was treated with [Pd(0)(dba)2] (2 equiv) in the absence of RNC in acetonitrile, linearly ordered octapalladium chains, [Pd8(μ-dpmppm)4(CH3CN)2]X4 ([4]X4: X = PF6, BF4), were generated through a coupling of two {Pd4(μ-dpmppm)2}(2+) fragments. Complex [2](2+) was also proven to be a good precursor for Pd2M2 mixed-metal complexes, yielding [Pd2Cl(Cp*MCl) (Cp*MCl2)(μ-dpmppm)2](2+) (M = Rh ([5](2+)), Ir ([6](2+)), and [Au2Pd2Cl2(dpmppm-H)2](2+) ([7](2+)) by treatment with [Cp*MCl2]2 and [AuCl(PPh3)], respectively. Complex [7](2+) contains an unprecedented PC(sp(3))P pincer ligand with a PCPCPCP backbone, dpmppm-H of deprotonated dpmppm. The present results demonstrated that the binuclear Pd(I) complex [2](2+) was a quite useful starting material to extend the palladium chains and to construct Pd-involved heteromultinuclear systems.

Soluble polymer-supported hindered phosphine ligands for palladium-catalyzed aryl amination

Two structurally different heptane soluble polymers – polyisobutylene and poly(4-alkylstyrene) – are shown to be good supports for hindered biaryldicyclohexyl phosphine Pd(0) aryl amination catalysts.

Synthesis, structure, and optical properties of Pt(II) and Pd(II) complexes with oxazolyl- and pyridyl-functionalized DPPM-type ligands: a combined experimental and theoretical study

New square-planar complexes [Pt(1(-H))2] (2a) [1(-H) = (oxazolin-2-yl)bis(diphenylphosphino)methanide] and [Pd(1(-H))2] (2b), of general formula [M{(Ph2P)2C---C---NCH2CH2O}2] (M = Pt, 2a; M = Pd, 2b), result from deprotonation of 2-{bis(diphenylphosphino)methyl}oxazoline (1) at the PCHP site. The new, functionalized dppm-type ligand 4-{bis(diphenylphosphino)methyl}pyridine, (Ph2P)2CH(4-C5H4N) (4), was prepared by double lithiation and phosphorylation of 4-picoline. In the presence of NEt3, the reactions of 2 equiv of 4 with [PtCl2(NCPh)2] and [Pd(acac)2] (acac = acetylacetonate) afforded [Pt(4(-H))2] (5a) [4(-H) = bis(diphenylphosphino)(pyridin-4-yl)methanide] and [Pd(4(-H))2] (5b), of general formula [M{(Ph2P)2C(4-C5H4N)}2] (M = Pt, 5a; M = Pd, 5b), respectively. In the absence of base, the reactions of 2 equiv of 4 with [PtCl2(NCPh)2] and [PdCl2(NCPh)2] afforded (5a·2HCl) (6a) and (5b·2HCl) (6b), respectively, in which the PCHP proton of 4 has migrated from carbon to nitrogen to give a pyridinium derivative of general formula [M{(Ph2P)2C(4-C5H4NH)}2]Cl2 (M = Pt, 6a; M = Pd, 6b). The complexes 3a, 5a·2MeOH, and 6b·4CH2Cl2 have been structurally characterized by X-ray diffraction. The absorption/emission properties of the Pt(II) complexes 2a and 5a and the Pd(II) complexes 2b and 5b have been investigated by UV-vis spectroscopy and theoretical analysis based on density functional theory. The UV-vis absorption spectra of the neutral complexes recorded in dilute N,N'-dimethylformamide solutions are dominated by intense spin-allowed intraligand transitions in the region below 350 nm. The complexes exhibit charge-transfer bands between 350 and 500 nm. The experimental and theoretical absorption spectra agree qualitatively and point to two low-lying ligand-to-metal charge transfer states that contribute to the bands observed between 350 and 500 nm. The complexes are emissive in frozen solutions at 77 K, in the pure solid state, and when doped into films of poly(methyl methacrylate) but are nonemissive in solution. A red shift is observed when Pt(II) is replaced by Pd(II).

Pyrrole-based new diphosphines: Pd and Ni complexes bearing the PNP pincer ligand

A new class of diphosphine PNP pincer ligand, 2,5-bis(diphenylphosphinomethyl)pyrrole 2, was synthesized by the reaction between Ph2PH and 2,5-bis(dimethylaminomethyl)pyrrole in 90% yield. The analogous reaction of Ph2PH with 1,9-bis(dimethylaminomethyl)diphenyldipyrrolylmethane readily afforded a PNNP type diphosphine ligand, 1,9-bis(diphenylphosphinomethyl)diphenyldipyrrolylmethane 5 in 92% yield. These phosphine compounds were oxidized with H2O2 and S8 to give the corresponding phosphoryl and thiophosphoryl compounds 6-9 in very good yields. The reaction of the PNP pincer ligand 2 with [PdCl2(PhCN)2] in the presence of Et3N afforded the mononuclear Pd(II) complex, [PdCl{C4H2N-2,5-(CH2PPh2)2-κ(3)PNP}] 10 in 87% yield. Conversely, treatment of 2 with [PdCl2(PhCN)2] in the absence of Et3N gave the dinuclear Pd(II) complex [Pd2Cl4{μ-C4H3N-2,5-(CH2PPh2)2-κ(2)PP}2], the structure which is proposed based on the spectroscopic data. When 2 was treated with Pd(0) precursor [Pd2(dba)3]·CHCl3 the dinuclear Pd(I) complex [Pd2{μ-C4H2N-2,5-(CH2PPh2)2-κ(2)PN,κ(1)P}2], 12, was obtained in 23% yield. The formation of complex 12 is solvent dependent, which transforms into complex 10 in CDCl3 as studied by variable temperature (1)H and (31)P NMR methods. Treatment of 2 with [Ni(OAc)2]·4H2O gave the mononuclear Ni(II) pincer complex [Ni(OAc){C4H2N-2,5-(CH2PPh2)2-κ(3)PNP}], 13, which upon treatment with an excess of LiCl or LiBr or KI afforded the respective halide ion substituted Ni(II) complexes, [NiX{C4H2N-2,5-(CH2PPh2)2-κ(3)PNP}] (X = Cl, Br, and I), 14-16, in very good yields. The structures of 5, 2,5-bis(diphenylphosphorylmethyl)pyrrole 6, 10, 12, and 14-16 were determined by the single crystal X-ray diffraction method. In the structure of 12, two short contacts between the diagonally positioned Pd and P atoms are observed. To understand these weak interactions, density functional theory (DFT) calculations were done and an interaction MO diagram is presented.

Coordination chemistry with phosphine and phosphine oxide-substituted hydroxyferrocenes

New unsymmetrical hydroxyferrocenes were synthesised from dibromoferrocene. The oxygen heteroatom was introduced via lithiation and quenching with bis-trimethylsilylperoxide followed by hydrolysis to unmask the hydroxyl functionality. The coordination chemistry of 1'-(diphenylphosphino)-1-hydroxyferrocene 2 was explored with palladium and rhodium precursors. A dinuclear palladium methyl complex with bridging ferrocenyloxo groups was obtained from the reaction between 2 and (cyclooctadiene)methylchloropalladium(II). With tetracarbonyldichlorodirhodium(I), two complexes were isolated. The major product was a bis ligand cis phosphine ligated complex with one ligand bound in a chelating mode and one with a pendant hydroxyl group. A minor product was crystallographically characterised as a dinuclear ferrocenyloxo-bridged rhodium carbonyl complex. The coordination chemistry of 2 and the corresponding phosphine oxide 3 was examined with group 4 metals and the resulting complexes examined as ethylene polymerisation catalysts. The ligands were found to bind in either a chelating fashion or with pendant phosphine donors. In all cases, low to moderately active ethylene polymerisation catalysts were found. The catalysts were very unstable and catalyst residues were observed in the isolated polymer indicating a short catalyst lifetime.