First structurally characterized triazinyl palladium complexes via oxidative addition of cyanuric chloride derivatives

The reaction of cyanuric chloride and two disubstituted derivatives with [Pd(PPh₃)₄] is described, leading to the trans-triazinyl complexes [(PPh₃)₂Pd(C₃N₃R₂)Cl] 2a-c (R = Ph (a), t-Bu (b), Cl (c)) in good to excellent yield via oxidative addition. The complexes were fully characterized including X-ray structure determination.     

Selenoether ligand assisted Heck catalysis

Selenoether ligands, 2,2′-methylenebis(selanediyl)bis(2,1-phenylene)dimethanol (5), (2,2′-(ethane-1,2-diylbis(selanediyl))bis(2,1-phenylene))dimethanol (6) and (2-(benzylselanyl)phenyl)methanol (7) have been synthesized by reducing di-o-formylphenyl diselenide and reacting the in situ generated selenolate with dibromomethane, 1,2-dibromoethane and benzyl chloride, respectively. The ligands, bis(2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenylselanyl)methane (8) and 1,2-bis(2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenylselanyl)ethane (9) have been synthesized similarly from bis[2-(4,4-dimethyl-2-oxazolinyl)phenyl] diselenide using electrophiles dibromomethane and 1,2-dibromoethane, respectively. Activity of ligands 5-9 along with 2-(2-(benzylselanyl)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (10) and 1-(2-(benzylselanyl)phenyl)-N,N-dimethylmethanamine (11) were examined for the Heck reaction of aryl halides with olefins. Bidentate Se,N ligand 11 was found to be the best one in the series and constitutes an efficient phosphine-free catalytic system with PdCl₂. The catalytic system showed moderate activity for the coupling of activated aryl chlorides in the presence of tetra-n-butyl ammonium bromide (TBAB). Complexes [10-PdCl₂] (12) and [11-PdCl₂] (13) have shown marginally better activity in comparison to the in situ generated catalysts from PdCl₂ and 10 and 11, respectively in the coupling of 4-bromoacetophenone with n-butylacrylate. Ligand 9 and complex 13 have been characterized by single crystal X-ray diffraction analysis.     

Synthesis and structure of mono- and di-nuclear complexes of ortho-palladated derived from phosphorus ylides

The phosphorus ylides Ph₃PCHC(O)C₆H₄R (R = 4-Me 1a, 4-Br 1b) react with PdCl₂ in equimolar ratios to give the C,C-orthopalladated [Pd{CHP(C₆H₄)Ph₂CO-C₆H₄-R)}(μ-Cl)]₂ (R = 4-Me 2a, 4-Br 2b) which react with NaClO₄/dppe, NaClO₄/dppm, py and PPh₃ to give the mononuclear derivatives [Pd{CH{P(C₆H₄)Ph₂}COC₆H₄-R}(dppe-P,P′)[(ClO₄) (R = 4-Me 3a, 4-Br 3b), [Pd{CH{P(C₆H₄)Ph₂}COC₆H₄-R}(dppm-P,P′)[(ClO₄ ( (R = 4-Me 4a, 4-Br 4b), [Pd{CH{P(C₆H₄)Ph₂}COC₆H₄-R}Cl(L)] (L = py, R = 4-Me 5a, 4-Br 5b, L = PPh₃, R = 4-Me 6a, 4-Br 6b). The C, C-metalated chelate are demonstrated by an X-ray diffraction study of 3a and 4a. Characterization of the obtained compounds was also performed by elemental analysis, IR, ¹H, ³¹P, and ¹³C NMR.     

Synthesis and characterizations of N,N,N′,N′-tetrakis (diphenylphosphino)ethylendiamine derivatives: Use of palladium(II) complex as pre-catalyst in Suzuki coupling and Heck reactions

Oxidation of N,N,N′,N′-tetrakis(diphenylphosphino)ethylendiamine (1) with elemental sulfur and selenium gives the corresponding sulfide and selenide, respectively, [(Ph₂P(E))₂NCH₂CH₂N(P(E)Ph₂)₂] (E: S 1a, Se 1b). Complexes of 1 [(M₂Cl₄){(Ph₂P)₂NCH₂CH₂N(PPh₂)₂}] (M: Ni(II) 1c, Pd(II) 1d, Pt(II) 1e) were prepared by the reaction of 1 with NiCl₂ or [MCl₂(COD)] (M = Pd, Pt). The new compounds were characterized by NMR, IR spectroscopy and elemental analysis. The catalytic activity of Pd(II) complex 1d was tested in the Suzuki coupling reaction and Heck reaction. The palladium complex 1d catalyses the Heck reaction between styrene and aryl bromides as well as Suzuki coupling reaction between phenylboronic acid and arylbromides affording stilbenes and biphenyls in high yield, respectively.     

Microwave synthesis of bis(tetrazolato)-Pd complexes with PPh3 and water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA). The first example of C-CN bond cleavage of propionitrile by a Pd Centre

[2 + 3] Cycloaddition reactions of the di(azido)-Pd^II complex trans-[Pd(N₃)₂(PPh₃)₂] (1) with an organonitrile RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N₄CR)₂(PPh₃)₂] (3) [R = Me (3a), Ph (3b), 4-ClC₆H₄ (3c), 4-FC₆H₄ (3d), 2-NC₅H₄ (3e), 3-NC₅H₄ (3f), 4-NC₅H₄ (3g)]. The reaction of trans-[Pd(N₃)₂(PPh₃)₂] (1) with propionitrile (2h) also affords, apart from trans-[Pd(N₄CEt)₂(PPh₃)₂] (3h), the unexpected mixed cyano-tetrazolato complex trans-[Pd(CN)(N₄CEt)(PPh₃)₂] (3h′) which is derived from the reaction of the bis(tetrazolato) 3h with propionitrile, with concomitant formation of 5-ethyl-1H-tetrazole, via a suggested unusual oxidative addition of the nitrile to Pd^II. The [2 + 3] cycloadditions of [Pd(N₃)₂(PTA)₂] (4) (PTA = 1,3,5-triaza-7-phosphaadamantane) with RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N₄CR)₂(PTA)₂] (5) [R = Ph (5a), 2-NC₅H₄ (5b), 3-NC₅H₄ (5c), 4-NC₅H₄ (5d)]. All these reactions are greatly accelerated by microwave irradiation (1 h, 125 °C, 300 W). Taking advantage of the hydro-solubility of PTA, a simple liberation of 5-phenyl-1H-tetrazole from the coordination sphere of trans-[Pd(N₄CPh)₂(PTA)₂] (5a) was achieved. The complexes were characterized by IR, ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectroscopies, ESI⁺-MS, elemental analyses and, for 3b, also by X-ray structure analysis. Weak agostic interactions between the CH groups of the triphenylphosphines and the palladium(II) centre were found.     

Tuning the regioselectivity of (benzimidazolylmethyl)amine palladium(II) complexes in the methoxycarbonylation of hexenes and octenes

Reactions of N-(1H-benzoimidazol-2-ylmethyl-2-methoxy)aniline (L1) and N-(1H-benzoimidazol-2-ylmethyl-2-bromo)aniline (L2) with p-TsOH, Pd(AOc)₂ and two equivalents of PPh₃ or PCy₃ produced the corresponding palladium complexes, [Pd(L1)(OTs)(PPh₃)] (1), [Pd(L2)(OTs)(PPh₃)] (2) and [Pd(L1)(OTs)(PCy₃)] (3), respectively, in good yields. The new palladium complexes 1–3 and the previously reported complexes [Pd(L1)ClMe] (4) and [Pd(L2)ClMe] (5) gave active catalysts in the methoxycarbonylation of terminal and internal olefins to produce branched and linear esters. The effects of complex structure, nature of phosphine derivative, acid promoter and alkene substrate on the catalytic activities and selectivity have been studied and are herein reported.     

Reactivity of C(sp)-Pd and C(sp)-Pd bonded palladacycles with diphosphines. Crystal and molecular structure of the novel A-frame complex [{Pd[2,5-Me2C6H2C(H)N(2,4,6-Me3C6H2)-C6]}2(μ-Ph2PCH2PPh2)2(μ-Cl)][PF6]

Treatment of the halogen-bridged complexes [Pd{2,5-Me₂C₆H₂C(H)N(2,4,6-Me₃C₆H₂)-C6,N}(μ-X)]₂ (1a, X = Cl; 2a, X = Br) with the tertiary diphosphine Ph₂PCH₂PPh₂ (dppm), regardless of the molar ratio used, gave a mixture of two complexes: [Pd{2,5-Me₂C₆H₂C(H)N(2,4,6-Me₃C₆H₂)-C6}(μ-Ph₂PCH₂PPh₂)₂(μ-X)]₂[PF₆] (5a, X = Cl; 6a, X = Br), which presents an A-frame structure, and [Pd{2,5-Me₂C₆H₂C(H)N(2,4,6-Me₃C₆H₂)-C6,N}(Ph₂PCH₂PPh₂-P,P)][PF₆], 3a, with the diphosphine as chelating. The mixture could be separated and the corresponding complexes isolated. However, reaction of 1a and 2a with the diphosphine Ph₂PC(CH₂)PPh₂ (vdpp) exclusively gave the mononuclear complex [Pd{2,5-Me₂C₆H₂C(H)N(2,4,6-Me₃C₆H₂)-C6,N}{Ph₂PC(CH₂)PPh₂-P,P}][PF₆], 4a, analogous to 3a. Treatment of the halogen-bridged complexes [Pd{1-CH₂-2-[HCN(2,4,6-Me₃C₆H₂)]-4-MeC₆H₃-C,N}(μ-X)]₂ (1a′, X = Cl; 2a′, X = Br) with dppm or vdpp in a cyclometallated complex/diphosphine 1:2 M ratio, gave mononuclear complexes with the chelating diphospines [Pd{1-CH₂-2-[HCN(2,4,6-Me₃C₆H₂)]-4-MeC₆H₃-C,N}(Ph₂PCH₂PPh₂-P,P)][PF₆], 3a′, and [Pd{1-CH₂-2-[HCN(2,4,6-Me₃C₆H₂)]-4-MeC₆H₃-C,N}{Ph₂PC(CH₂)PPh₂-P,P}][PF₆], 4a′. When the reaction was carried out using a cyclometallated complex/diphosphine 1:1 M ratio the dinuclear complexes [{Pd[1-CH₂-2-{HCN(2,4,6-Me₃C₆H₂)}-4-MeC₆H₃-C,N]}₂(μ-X)(μ-Ph₂PCH₂PPh₂)][Cl], (5a′, X = Cl; 7a′, X = Br) and [{Pd[1-CH₂-2-{HCN(2,4,6-Me₃C₆H₂)}-4-MeC₆H₃-C,N]}₂(μ-Cl){μ-Ph₂PC(CH₂)PPh₂}][Cl], 6a′, were obtained. The molecular structures of complexes 3a, 4a, 5a and 6a′ were determined by X-ray single crystal diffraction.     

Four mono-/bi-nuclear palladium(II) complexes of triphenylphosphine and heterocyclic-N/NS ligands: Synthesis, structural characterization and luminescence properties

The reactions of palladium(II) chloride, PPh₃ and heterocyclic-N/NS ligand in a mixture of CH₃CN (5 ml) and CH₃OH (5 ml) produced [PdCl₂(PPh₃)(L1)]·(CH₃CN) (1) (L1 = ADMT = 3-amino-5,6-dimethyl-1,2,4-triazine), [PdCl₂(PPh₃)(L2)] (2) (L2 = 3-CNpy = 3-cyanopyridine), [PdCl(PPh₃)(L3)]₂·(CH₃CN) (3), [PdCl(PPh₃)₂(HL3)]Cl (4) (HL3 = Hmbt = 2-mercaptobenzothiazole). The coordination geometry around the Pd atoms in these complexes is a distorted square plane. In 3, L3 acts as a bidentate ligand, bridging two metal centers, while in 4, HL3 appears as monodentate ligand with one nitrogen donor atom uncoordinated. Complexes 1-4 are characterized by IR, luminescence, NMR and single crystal X-ray diffraction analysis. All complexes exhibit luminescence in solid state at room temperature.     

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 of mono- and trinuclear palladium(II) complexes via oxidative addition of a bulky hexathioether containing a disulfide bond to palladium(0)

The oxidative addition reactions of a bulky hexathioether containing a disulfide bond, TbtS(o-phen)S(o-phen)SS(o-phen)S(o-phen)STbt (1) (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, o-phen = o-phenylene), to a palladium(0) complex were studied. In the reaction of 1 with 3 molar amounts of [Pd(PPh₃)₄], a trinuclear palladium(II) complex, [Pd₃{S(o-phen)S}₂{(o-phen)STbt}₂(PPh₃)₂] (2), was formed via three-step palladium insertion reaction including unusual C(aryl)-S bond cleavages. On the other hand, the reaction of 1 with an equimolar amount of [Pd(PPh₃)₄] afforded mononuclear palladium(II) complex having a pseudo-octahedral structure, [Pd{S(o-phen)S(o-phen)STbt}₂] (3). The hexa-coordinated geometry for the palladium center in 3 was confirmed by the atoms in molecule (AIM) analysis, which revealed the presence of the bond critical points between the central Pd atom and the S atoms at the axial positions. In contrast to the bulky system, the reaction of Ph-substituted hexathioether, PhS(o-phen)S(o-phen)SS(o-phen)S(o-phen)SPh (4), with an equimolar amount of [Pd(PPh₃)₄] gave a palladium(II) complex having square-planar structure, [Pd{S(o-phen)S(o-phen)SPh}₂] (5). Theoretical calculations revealed that there is no remarkable difference among the energies of isomers of [Pd{S(o-phen)SPh}₂], 6a-syn, 6a-anti, 6b-syn, and 6b-anti. This result suggests that a reason for the preference of the trans-anti-conformation in 3 is the steric repulsion between the bulky Tbt groups, and that of the cis-syn-conformations in 5 and 6 is the intermolecular interactions.     

Palladacycles incorporating a carboxylate-functionalized phosphine ligand: syntheses,characterization and their catalytic applications toward Suzuki couplings in water

A series of acetato-bridged [C^X]-type (C = aryl carbanion, X = N, P) palladacycles (1–5) of the general formula [Pd(μ-CH₃COO)(C^X)]₂ were synthesized as metal precursors via slightly modified procedures. However, in the case of complex 5 with Dpbp (Dpbp = 2′-(diphenylphosphino-κP)[1,1′-biphenyl]-2-yl-κC) as the supporting C^P ligand, an unexpected dinuclear complex [Pd(μ-CO₂)(Dpbp)]₂ (6) was obtained as a by-product and structurally determined by X-ray crystallography. The reactions of complexes 1–4 with 2-(diphenylphosphino)benzoic acid conveniently afforded four carboxylate-functionalized phosphine complexes [Pd(C^N)(Dpb)] (Dbp = 2-(diphenylphosphino-κP)benzoato-κO, 7–10), two of which (9/10) are newly synthesized in the present work and have been fully characterized. A comparative catalytic study revealed that complex [Pd(Ppy)(Dpb)] (7) (Ppy = 2-(2-pyridinyl-κN)phenyl-κC) is the best performer in Suzuki cross-couplings in H₂O. In addition, complex 7 exhibits much better catalytic activity compared to the non-functionalized phosphine equivalent [Pd(OAc)(PPh₃)(Ppy)] (11), which clearly indicates the superiority of incorporating a carboxylate-functionalized phosphine ligand into the palladacycles. A preliminary mechanistic study uncovered a different precatalyst initiation pathway compared to other known analogues of catalyst precursors.     

Nucleophilic substitution reactions at the Si-Cl bonds of the dichloro(methyl)silyl ligand in five- and six-coordinate complexes of ruthenium(II) and osmium(II)

Treatment of either RuHCl(CO)(PPh₃)₃ or MPhCl(CO)(PPh₃)₂ with HSiMeCl₂ produces the five-coordinate dichloro(methyl)silyl complexes, M(SiMeCl₂)Cl(CO)(PPh₃)₂ (1a, M = Ru; 1b, M = Os). 1a and 1b react readily with hydroxide ions and with ethanol to give M(SiMe[OH]₂)Cl(CO)(PPh₃)₂ (2a, M = Ru; 2b, M = Os) and M(SiMe[OEt]₂)Cl(CO)(PPh₃)₂ (3a, M = Ru; 3b, M = Os), respectively. 3b adds CO to form the six-coordinate complex, Os(SiMe[OEt]₂)Cl(CO)₂(PPh₃)₂ (4b) and crystal structure determinations of 3b and 4b reveal very different Os-Si distances in the five-coordinate complex (2.3196(11) Å) and in the six-coordinate complex (2.4901(8) Å). Reaction between 1a and 1b and 8-aminoquinoline results in displacement of a triphenylphosphine ligand and formation of the six-coordinate chelate complexes M(SiMeCl₂)Cl(CO)(PPh₃)(κ²(N,N)-NC₉H₆NH₂-8) (5a, M = Ru; 5b, M = Os), respectively. Crystal structure determination of 5a reveals that the amino function of the chelating 8-aminoquinoline ligand is located adjacent to the reactive Si-Cl bonds of the dichloro(methyl)silyl ligand but no reaction between these functions is observed. However, 5a and 5b react readily with ethanol to give ultimately M(SiMe[OEt]₂)Cl(CO)(PPh₃)(κ²(N,N-NC₉H₆NH₂-8) (6a, M = Ru; 6b, M = Os). In the case of ruthenium only, the intermediate ethanolysis product Ru(SiMeCl[OEt])Cl(CO)(PPh₃)(κ²(N,N-NC₉H₆NH₂-8) (6c) was also isolated. The crystal structure of 6c was determined. Reaction between 1b and excess 2-aminopyridine results in condensation between the Si-Cl bonds and the N-H bonds with formation of a novel tridentate “NSiN” ligand in the complex Os(κ³(Si,N,N)-SiMe[NH(2-C₅H₄N)]₂)Cl(CO)(PPh₃) (7b). Crystal structure determination of 7b shows that the “NSiN” ligand coordinates to osmium with a “facial” arrangement and with chloride trans to the silyl ligand.     

Three novel bismetallacyclopropa[60]fullerene complexes formed via intermediate monometallacyclopropa[60]fullerene diphosphine ligands

The homodinuclear bismetallacyclopropa[60]fullerene complexes (η²-C₆₀)M(μ-η¹,η¹-trans-Ph₂PCHCH PPh₂)₂M(η²-C₆₀) (1, M = Pt; 2, M = Pd) were prepared by reaction of C₆₀ with M(dba)₂ (dba = dibenzylideneacetone) and trans-1,1′-bis(diphenylphosphino)ethylene in 82% and 92% yield, whereas reaction of C₆₀ with Pd(dba)₂ and trans-dppet followed by treatment with C₆₀ and Pt₂(dba)₃ gave rise to the heterodinuclear complex (η²-C₆₀) Pd(μ-η¹,η¹-trans-Ph₂PCHCH PPh₂)₂Pt(η²-C₆₀) (3) in 65% yield. Mechanistic study showed that these reactions involve the intermediates of monometallacyclopropa[60]fullerene diphosphine ligands (η²-C₆₀)M(η¹-trans-Ph₂PCHCHPPh₂)₂ (4, M = Pt; 5, M = Pd). All the mono- and bismetallacyclopropa[60]fullerene complexes 1-5 have been fully characterized by elemental analysis and spectroscopy, as well as for 2 by X-ray crystallography.     

The Staudinger reaction of platinum(II)- and palladium(II)-coordinated 2-(azidomethyl)phenyl isocyanide. X-ray structure of trans-[PtCl{(H)}(PPh3)2][BF4] · CDCl3 · H2O

2-(Azidomethyl)phenyl isocyanide, 2-(CH₂N₃)C₆H₄NC (AziNC), coordinates to some cationic Pt(II) and Pd(II) species to afford isocyanide complexes of the type trans-[MCl(AziNC)(PPh₃)₂][BF₄] (M=Pt, l; Pd, 2). AziNC is coordinated also in some neutral Pt(II) and Pd(II) species such as [MCl₂(AziNC)₂] (M=Pt, 3; Pd, 4) derived from the reactions of 2 equiv. of AziNC with [PtCl₂(COD)] and [PdCl₂(MeCN)₂], respectively. Complexes 1 and 2 react with 1 equiv. of PPh₃ affording the heterocyclic carbene complexes trans-[MCl{(H)}(PPh₃)₂][BF₄] (M=Pt, 5; Pd, 6). Complexes 3 and 4 react with 1 equiv. of PPh₃ displacing the isocyanide with the formation of the complexes cis-[MCl₂(AziNC)(PPh₃)] (M=Pt, 7; Pd, 8). These latter ones react with 2 equiv. of PPh₃ affording as the final products the cationic carbene species trans-[MCl{(H)}(PPh₃)₂][Cl] (M=Pt, 9; Pd, 10). Complex 5 was also characterized by single crystal X-ray diffraction. The carbene complex is square-planar and the angle formed between the platinum square plane and the heterocyclic carbene ligand is 87.9(2)°. The C(1)-N(1) and C(1)-N(2) bond distances in the latter of 1.32(2) and 1.30(2) Å, respectively, are short for a single bond and indicate extensive π-bonding between the nitrogen atoms and the carbene carbon.     

Synthesis and characterization of tris{2-(N,N-bis(diphenylphosphino) aminoethyl} amine derivatives: Application of a palladium(II) complex as a pre-catalyst in the Heck and Suzuki cross-coupling reactions

The polydendate bis(phosphino)amine, tris{2-(N,N-bis(diphenylphosphino)aminoethyl}amine 1 has been prepared in a single step from the reaction of tris(2-aminoethyl)amine with six equivalents of PPh₂Cl in the presence of NEt₃ in THF. Oxidation of 1 with aqueous H₂O₂, elemental sulfur or grey selenium gave the corresponding oxide, sulfide or selenide derivatives. [{(P(E)Ph₂)₂NCH₂CH₂}₃N] (E: 2a O, 2b S, 2c Se), respectively. Reaction of [{(PPh₂)₂NCH₂CH₂}₃N] with 3 equiv. of PdCl₂(cod) or PtCl₂(cod) gave the corresponding chelate complexes, [Pd₃Cl₆1] or [Pt₃Cl₆1]. The new compounds were fully characterized by NMR, IR spectroscopy and elemental analysis. The catalytic activity of the Pd(II) complex was tested in the Suzuki coupling and Heck reactions. The Pd(II) complex catalyzed the Suzuki coupling and Heck reaction affording biphenyls and stilbenes, respectively, in high yields.     

Reactivity differences between nickel and palladium complexes bearing 1,2-diphosphino-1,2-dicarba-dodecaborane ligand

AgOTf (OTf = trifluoromethanesulfonate) shows the reactivity differences when it reacts with carborane complexes [MCl₂{(PPh₂)₂(C₂B₁₀H₁₀)}] (M = Ni (2), Pd (3)). The reaction of AgOTf with the palladium complex 3 affords [Pd₂(μ-OTf)₂{(PPh₂)₂(C₂B₉H₁₀)}₂] (4) in high yields, while corresponding reaction between the nickel complex 2 and AgOTf leads to the formation of binuclear complexes [Ni{(PPh₂)₂(C₂B₉H₁₀)}](μ-Cl)₂[Ag{(PPh₂)₂(C₂B₁₀H₁₀)}] (5) and [Ag₂(μ-Cl)₂ {(PPh₂)₂ (C₂B₁₀H₁₀)}₂] (6). The carborane cage of complexes 4 and 5 were broken to form nido-carboranes. It is believed the group 10 metals themselves play an important role in opening the closo-carborane skeleton. Directly stirring [(PPh₂)₂(C₂B₁₀H₁₀)] with AgOTf afforded [Ag₂(μ-OTf)₂{(PPh₂)₂(C₂B₁₀H₁₀)}₂] (7), which is also used to react with 2 and 3. The reaction between 2 and 7 gives only 4 in high yields, however, stirring the mixture of 3 and 7 affords [Pd₂(μ-Cl)₂{(PPh₂)₂(C₂B₉H₁₀)}₂] (8), [Pd{(PPh₂)₂(C₂B₉H₁₀)}₂] (9) and 6. All these complexes have been characterized by IR, ¹H NMR, ¹¹B NMR and elemental analyses. Complexes 2, 4-9 have also been determined by single-crystal X-ray diffraction analyses.     

Synthesis of electronically and coordinatively unsaturated complexes [Ru2(CO)4(μ-H)(μ-PBu2)(μ-L2)] (L2 = biphosphanes)

A convenient synthesis and the characterization of six new electronically and coordinatively unsaturated complexes of the formula [Ru₂(CO)₄(μ-H)(μ-P^tBu₂)(μ-L₂)] (2b-g) (RuRu) is described exhibiting a close relation to the known [Ru₂(CO)₄(μ-H)(μ-P^tBu₂)(μ-dppm)] (2a). The complexes 2b-g were obtained in a kind of one-pot synthesis starting from [Ru₃(CO)₁₂] and P^tBu₂H in the first step followed by the reaction with the bidentate bridging ligand in the second step. The method was developed for the following bridging ligands (μ-L₂): dmpm (2b, dmpm = Me₂PCH₂PMe₂), dcypm (2c, dcypm = Cy₂PCH₂PCy₂), dppen (2d, dppen = Ph₂PC(=CH₂)PPh₂), dpppha (2e, dpppha = Ph₂PN(Ph)PPh₂), dpppra (2f, dpppra = Ph₂PN(Pr)PPh₂), and dppbza (2g, dppbza = Ph₂PN(CH₂Ph)PPh₂). The molecular structures of all new complexes 2b−g were determined by X-ray diffraction.     

The stereoselective synthesis of (E)-octafluoro-1,3,5-hexatriene and (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene

(E)-(1,2-Difluoro-1,2-ethenediyl)bis[tributylstannane], 3, readily undergoes a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction with iodotrifluoroethene to yield (E)-octafluoro-1,3,5-hexatriene, 4, in high isomeric purity. (1Z,3E,5Z)-(1,2,3,4,5,6-Hexafluoro-1,3,5-hexenetriyl)bis[tributylstannane], 7, was sequentially prepared from (1Z,3E,5Z)-(1,2,3,4,5,6-hexafluoro-1,3,5-hexenetriyl)bis[triethylsilane], 5, which was prepared via a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction of 3 with (E)-1,2-difluoro-1-iodo-2-triethylsilylethene, 6. Pd(PPh₃)₄/CuI cross-coupling of 7 with iodotrifluoroethene gave (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene, 8.     

Cyclopalladated complexes with N-(benzoyl)-N-(2,4-dimethoxybenzylidene)hydrazine: syntheses, characterization and structural studies

Cyclopalladated complexes with the Schiff base N-(benzoyl)-N^′-(2,4-dimethoxybenzylidene)hydrazine (H₂L, 1) have been described. The reaction of 1 with Li₂[PdCl₄] in methanol yields the complex [Pd(HL)Cl] (2). [Pd(HL)(CH₃CN)Cl] (3) has been prepared by dissolving 2 in acetonitrile. In methanol-acetonitrile mixture, treatment of 2 with two mole equivalents of PPh₃ produces [PdL(PPh₃)] (4) and that with one mole equivalent of PPh₃ produces [Pd(HL)(PPh₃)Cl] (5). Crystallization of 2 from dmso-d₆ results into isolation of [Pd(HL)((CD₃)₂SO)Cl] (6). In 2, the monoanionic ligand (HL⁻) is C,N,O-donor and the Cl-atom is trans to the azomethine N-atom. In 3, 5 and 6, HL⁻ is C,N-donor and the Cl-atom is trans to the metallated C-atom. The remaining fourth coordination site is occupied by the N-atom of CH₃CN, the P-atom of PPh₃ and the S-atom of (CD₃)₂SO in 3, 5 and 6, respectively. Thus on dissolution in acetonitrile and dmso and in reaction with stoichiometric PPh₃ the incoming ligand imposes a rearrangement of the coordinating atoms on the palladium centre. On the other hand, in presence of excess PPh₃ deprotonation of the amide functionality in 2 occurs and the Cl-atom is replaced by the P-atom of PPh₃ to form 4. Here the dianionic ligand (L²⁻) remains C,N,O-donor as in 2. The compounds have been characterized with the help of elemental analysis (C, H, N), infrared, ¹H NMR and electronic absorption spectroscopy. Molecular structures of 3, 4, and 6 have been determined by X-ray crystallography.