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.     

Synthesis of [Ru(CO)2(PPh3)(SP)] and [Ru(CO)(PPh3)2(SP)] and their catalytic activities for the hydroamination of phenylacetylene

The reaction of [Ru(CO)₂(PPh₃)₃] (1) with o-styryldiphenylphophine (SP) (2) gave [Ru(CO)₂(PPh₃)(SP)] (3) in 83% yield. This styrylphosphine ruthenium complex 3 can also be synthesized by the reaction of [Ru(p-MeOC₆H₄NN)(CO)₂(PPh₃)₂]BF₄ (4) with NaBH₄ and 2 in 50% yield. When “Ru(CO)(PPh₃)₃” generated by the reaction of [RuH₂(CO)(PPh₃)₃] (8) with trimethylvinylsilane reacted with 2, [Ru(CO)(PPh₃)₂(SP)] (10) was produced in moderate yield as an air sensitive solid. The spectral and X-ray data of these complexes revealed that the coordination geometries around the ruthenium center of both complexes corresponded to a distorted trigonal bipyramid with the olefin occupying the equatorial position and the C-C bonding in the olefin moiety in 3 and 10 contained a significant contribution from a ruthenacyclopropane limiting structure. Complexes 3 and 10 showed catalytic activity for the hydroamination of phenylacetylene 11 with aniline 12. Ruthenium complex 3 in the co-presence of NH₄PF₆ or H₃PW₁₂O₄₀ proves to be a superior catalyst system for this hydroamination reaction. In the case of the reaction using H₃PW₁₂O₄₀ as an additive, ketimines (13) was obtained in 99% yield at a ruthenium-catalyst loading of 0.1 mol%. Some aniline derivatives such as 4-methoxy, 4-trifluoromethyl-, and 4-bromoanilines can also be used in this hydroamination reaction.     

Trifluoroacetylacetonate rhodium(III) methyl complexes, cis-[Rh(TFA)(PPh3)2(CH3)(L)][BPh4] and cis-[Rh(TFA)(PPh3)2(CH3)(I)] (L = CH3CN, NH3, pyridine), in comparison with their acetylacetonate analogs

The oxidative addition of CH₃I to planar rhodium(I) complex [Rh(TFA)(PPh₃)₂] in acetonitrile (TFA is trifluoroacetylacetonate) leads to the formation of cationic, cis-[Rh(TFA)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (1), or neutral, cis-[Rh(TFA)(PPh₃)₂(CH₃)(I)] (4), rhodium(III) methyl complexes depending on the reaction conditions. 1 reacts readily with NH₃ and pyridine to form cationic complexes, cis-[Rh(TFA)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (2) and cis-[Rh(TFA)(PPh₃)₂(CH₃)(Py)][BPh₄] (3), respectively. Acetylacetonate methyl complex of rhodium(III), cis-[Rh(Acac)(PPh₃)₂(CH₃)(I)] (5), was obtained by the action of NaI on cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] in acetone at −15 °C. Complexes 1-5 were characterized by elemental analysis, ³¹P{¹H}, ¹H and ¹⁹F NMR. For complexes 2, 3, 4 conductivity data in acetone solutions are reported. The crystal structures of 2 and 3 were determined. NMR parameters of 1-5 and related complexes are discussed from the viewpoint of their isomerism.     

Novel rhenium(III) complexes with the picolinate ligand: Synthesis,spectroscopic investigations,X-ray structures and DFT calculations for [ReX2(pic)(PPh3)2] complexes

The paper presents a combined experimental and computational study of novel rhenium(III) complexes with the picolinate ligand – [ReCl₂(pic)(PPh₃)₂] (1) and [ReBr₂(pic)(PPh₃)₂] (2). Both complexes 1 and 2 have been characterised spectroscopically and structurally (by single-crystal X-ray diffraction). Complex 1 has been additionally studied by magnetic measurement. The magnetic behavior is characteristic of a mononuclear d⁴ low-spin octahedral Re(III) complex (³T_1g ground state) and arises because of the large spin–orbit coupling (ζ = 2500 cm⁻¹), which gives a diamagnetic ground state. DFT and time-dependent (TD)DFT calculations have been carried out for complex 1, and UV–vis spectra of the [ReX₂(pic)(PPh₃)₂] compounds have been discussed on this basis.     

New oxorhenium complexes with 2-(2′-hydroxyphenyl)-2-benzoxazolinato ligand. X-ray structure and DFT calculations for [ReOX2(hbo)(AsPh3)] and [ReOX2(hbo)(PPh3)] complexes

The reactions of [ReOX₃(AsPh₃)₂] and [ReOX₃(PPh₃)₂] with 2-(2′-hydroxyphenyl)-2-benzoxazoline (Hhbo) have been examined and [ReOX₂(hbo)(AsPh₃)] and [ReOX₂(hbo)(PPh₃)] (X = Cl, Br) complexes have been obtained. The crystal and molecular structures of [ReOCl₂(hbo)(AsPh₃)] (1) and [ReOBr₂(hbo)(PPh₃)] (4) have been determined. The electronic structures of 1 and 4 have been calculated with the density functional theory (DFT) method. The spin-allowed electronic transitions of 1 and 4 have been calculated with the time-dependent DFT method, and the UV–Vis spectra of these complexes have been discussed.     

Synthesis and crystal structure of the heteroleptic lanthanum(III) bis-diphosphinomethanide complex [La{CH(PPh2)2}2(I)(THF)2]

Treatment of CH₂(PPh₂)₂ with n-BuLi/t-BuOK in diethyl ether affords the potassium diphosphinomethanide complex [K{CH(PPh₂)₂}(OEt₂)_0.5] (1) in high yield. Metathesis of two equivalents of 1 with LaI₃(THF)₄ yields the heteroleptic bis-diphosphinomethanide complex [La{CH(PPh₂)₂}₂(I)(THF)₂] (2). X-ray crystallography shows the diphosphinomethanide ligands in 2 adopt different coordination modes in the solid state; one adopts a κ²-PP mode with no La-C contact, and the other adopts an η³-PCP mode, thus giving an eight-coordinate lanthanum centre.     

Syntheses and properties of Re(III) complexes derived from hydrotris(1-pyrazolyl)methanes: molecular structure of [ReCl2(HCpz3)(PPh3)][BF4]

The complexes [ReCl₂{N₂C(O)Ph}(Hpz)(PPh₃)₂] (1) (Hpz = pyrazole), [ReCl₂{N₂C(O)Ph}(Hpz)₂(PPh₃)] (2), [ReCl₂(HCpz₃)(PPh₃)][BF₄] (3) and [ReCl₂(3,5-Me₂Hpz)₃(PPh₃)]Cl (4) were obtained by treatment of the chelate [ReCl₂{η²-N,O-N₂C(O)Ph}(PPh₃)₂] (0) with hydrotris(1-pyrazolyl)methane HCpz₃ (1,3), pyrazole Hpz (1,2), hydrotris(3,5-dimethyl-1-pyrazolyl)methane HC(3,5-Me₂pz)₃ (4) or dimethylpyrazole 3,5-Me₂Hpz (4). Rupture of a C(sp³)-N bond in HCpz₃ or HC(3,5-Me₂pz)₃, promoted by the Re centre, has occurred in the formation of 1 or 4, respectively. All compounds have been characterized by elemental analyses, IR and NMR spectroscopy, FAB-MS spectrometry, cyclic voltammetry and, for 1 · CH₂Cl₂ and 3, also by single crystal X-ray analysis. The electrochemical E_L Lever parameter has been estimated, for the first time, for the HCpz₃ and the benzoyldiazenide NNC(O)Ph ligands.     

Four isomers from the oxidative addition of Me3SnH to Os(CO)2(PPh3)3 and the crystal structure of Os(SnMeI2)I(CO)2(PPh3)2, in which the pairs of CO and PPh3 ligands are mutually trans

Reaction between Os(CO)₂(PPh₃)₃ and Me₃SnH produces Os(SnMe₃)H(CO)₂(PPh₃)₂ (1). Multinuclear NMR studies of solutions of 1 reveal the presence of four geometrical isomers, the major one being that with mutually cis triphenylphosphine ligands and mutually trans CO ligands. Os(SnMe₃)H(CO)₂(PPh₃)₂ undergoes a redistribution reaction, at the trimethylstannyl ligand, when treated with Me₂SnCl₂ giving Os(SnMe₂Cl)H(CO)₂(PPh₃)₂ (2). Solutions of 2 again show the presence of four isomers but now the major isomer is that with mutually trans triphenylphosphine ligands and mutually cis CO ligands. The redistribution reaction of 1 with SnI₄ produces Os(SnMeI₂)H(CO)₂(PPh₃)₂ (3) which exists in solution as only one isomer, that with mutually trans triphenylphosphine ligands and mutually trans CO ligands. Treatment of 3 with I₂ cleaves the Os-H bond with retention of geometry giving Os(SnMeI₂)I(CO)₂(PPh₃)₂ (4). The crystal structure of 4 has been determined. No isomerization of the trans dicarbonyl complex 4 occurs when 4 is heated, instead there is a formal loss of “MeSnI” and formation of OsI₂(CO)₂(PPh₃)₂ (5).     

Preparation and structural characterization of [RuCl2(CO)2{Te(CH2SiMe3)2}2] and [RuCl2(CO){Te(CH2SiMe3)2}3]

The objective of the present work was to synthesize mononuclear ruthenium complex [RuCl₂(CO)₂{Te(CH₂SiMe₃)₂}₂] (1) by the reaction of Te(CH₂SiMe₃)₂ and [RuCl₂(CO)₃]₂. However, the stoichiometric reaction affords a mixture of 1 and [RuCl₂(CO){Te(CH₂SiMe₃)₂}₃] (2). The X-ray structures show the formation of the cis(Cl), cis(C), trans(Te) isomer of 1 and the cis(Cl), mer(Te) isomer of 2. The ¹²⁵Te NMR spectra of the complexes are reported. The complex distribution depends on the initial molar ratio of the reactants. With an excess of [RuCl₂(CO)₃]₂ only 1 is formed. In addition to the stoichiometric reaction, a mixture of 1 and 2 is observed even when using an excess of Te(CH₂SiMe₃)₂. Complex 1 is, however, always the main product. In these cases the ¹²⁵Te NMR spectra of the reaction solution also indicates the presence of unreacted ligand.     

Synthesis, characterization and molecular structures of allenylidene, vinylidene-alkylidene complexes containing [CpOs(PPh3)2] fragment

The reaction of [CpOs(PPh₃)₂Br] with diphenylpropargylic alcohol HCCCPh₂(OH) in the presence of ammonium hexafluorophosphate leads to the formation of cationic osmiumallenylidene complex [CpOs(CCCPh₂)(PPh₃)₂][PF₆] (1), but when the dimethylpropargylic alcohol HCCCMe₂(OH) was used as a substrate, a dicationic diosmium vinylidene-alkylidene complex of the formula [(CpOs)₂(μ-C₁₀H₁₂)(PPh₃)₄][PF₆]₂ (2) was obtained. The structures of these complexes have been determined by X-ray diffraction. Complex 1 crystallizes in monoclinic space group P21/c with a=13.4083(6) Å, b=19.5700(9) Å, c=20.3806(9) Å and β=100.3620(10)°. Complex 2 crystallizes in triclinic space group with a=13.0396(11) Å, b=15.2420(13) Å, c=21.6406(19) Å and α=72.5290(10)°, β=75.1960(10)°, γ=85.6360(10)°.     

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 characterisation of six Fe(II or III), Co(II) or Zr(IV) complexes containing the ligand [CH(SiMe2R)P(Ph)2NSiMe3] (R = Me, NEt2) and of [Co{N(SiMe3)C(Ph)C(H)P(Ph)2NSiMe3}2]

The C,N-(trimethylsilyliminodiphenylphosphoranyl)silylmethylmetal complexes [Fe(L)₂] (3), [Co(L)₂] (4), [ZrCl₃(L)]·0.83CH₂Cl₂ (5), [Fe(L)₃] (6), [Fe(L′)₂] (7) and [Co(L′)₂] (8) have been prepared from the lithium compound Li[CH(SiMe₂R)P(Ph)₂NSiMe₃] [1a, (R = Me) {≡ Li(L)}; 1b, (R = NEt₂) {≡ Li(L′)}] and the appropriate metal chloride (or for 7, FeCl₃). From Li[N(SiMe₃)C(Ph)C(H)P(Ph)₂NSiMe₃] [≡ Li(L″)] (2), prepared in situ from Li(L) (1a) and PhCN, and CoCl₂ there was obtained bis(3-trimethylsilylimino- diphenylphosphoranyl-2-phenyl-N-trimethylsilyl-1-azaallyl-N,N′)cobalt(II) (9). These crystalline complexes 3-9 were characterised by their mass spectra, microanalyses, high spin magnetic moments (not 5) and for 5 multinuclear NMR solution spectra. The X-ray structure of 3 showed it to be a pseudotetrahedral bis(chelate), the iron atom at the spiro junction.     

Oxorhenium(V) complexes with quinoline-2-carboxylate ligand. X-ray structure of [ReOCl2(quin-2-c)(PPh3)] and [ReOBr2(quin-2-c)(AsPh3)] complexes: DFT and TD-DFT calculations for [ReOCl2(quin-2-c)(PPh3)]

Novel [ReOX₂(quin-2-c)(EPh₃)] complexes (X = Cl, Br; E = As, P; quin-2-c = quinoline-2-carboxylate ion) have been prepared by treatment of [ReOX₃(EPh₃)₂] with quinoline-2-carboxylic acid in acetone at room temperature. All the complexes were characterised by IR, UV–Vis spectroscopy and elemental analysis. The crystal and molecular structures have been determined for [ReOCl₂(qiun-2c)(PPh₃)] (1) and [ReOBr₂(qiun-2c)(AsPh₃)] (4). The electronic structure of 1 has been calculated with the density functional theory (DFT) method. The spin-allowed electronic transitions of 1 have been calculated with the time-dependent DFT method.     

On the reactivity of [IrCl(N2)(PPh3)2] with alkynylsilanes - A new route to vinylidene iridium(I) complexes

The iridium dinitrogen complex [IrCl(N₂)(PPh₃)₂] (1) was found to react with alkynylsilanes to form the vinylidene iridium(I) complexes trans- (R/R′ = Ph/Me, 2; Me/Me, 3; Bn/Me, 4; SiMe₃/Me, 5; SiEt₃/Et, 6; ⁱPr/Me, 7) and with Me₃SiCCC(O)R to yield the iridium η²-alkyne complexes trans-[IrCl{η²-Me₃SiCCC(O)R}(PPh₃)₂] (R = OEt, 9; Me, 11). Complex 9 was found to isomerize upon heating or upon UV irradiation yielding the vinylidene complex trans-[IrCl{CC(SiMe₃)CO₂Et}(PPh₃)₂] (10). The reaction of 1 with Me₃SiCCCCSiMe₃ yielded the complex trans-[IrCl{CC(SiMe₃)CCSiMe₃}(PPh₃)₂] (8), whereas with MeO₂CCCCO₂Me the iridacyclopentadiene complex [Ir{C₄(CO₂Me)₄}Cl(PPh₃)₂] (13) was formed. The complexes were characterized by means of ¹H, ¹³C and ³¹P NMR spectroscopy as well as by IR spectroscopy and microanalysis.     

Syntheses and X-ray crystallographic studies of {[Ni(en)2(pot)2]0.5CHCl3} and [Ni(en)2](3-pytol)2

Two novel Ni(II) complexes {[Ni(en)₂(pot)₂]0.5CHCl₃} (3) {pot = 5-phenyl-1,3,4-oxadiazole-2-thione} (1) and [Ni(en)₂](3-pytol)₂ (4) {3-pytol = 5-(3-pyridyl)-1,3,4-oxadiazole-2-thiol} (2) have been synthesized using en as coligand. The metal complexes have been characterized by physical and analytical techniques and also by single crystal X-ray studies. The complexes 3 and 4 crystallize in monoclinic system with space group P21/a and P121/c, respectively. The complex 3 has a slightly distorted octahedral geometry with trans (pot)⁻ ligands while 4 has a square planar geometry around the centrosymmetric Ni(II) center with ionically linked trans (3-pytol)⁻ ligands. The π?π (face to face) interaction plays an important role along with hydrogen bondings to form supramolecular architecture in both complexes.     

Oxorhenium complexes with the 8-quinolinolato ligand. X-ray structure and DFT calculations for [ReOX2(hqn)(AsPh3)] and [ReOX2(hqn)(PPh3)] complexes

The reactions of [ReOX₃(AsPh₃)₂] and [ReOX₃(PPh₃)₂] with 8-hydroxyquinoline (Hhqn) have been examined and the complexes [ReOX₂(hqn)(AsPh₃)] and [ReOX₂(hqn)(PPh₃)] (X = Cl, Br) have been obtained, respectively. The crystal and molecular structures of [ReOCl₂(hqn)(AsPh₃)] (1) and [ReOBr₂(hqn)(PPh₃)] (4) have been determined. The electronic structure of 1 has been calculated with the density functional theory (DFT) method. The spin-allowed electronic transitions of 1 have been calculated with the time-dependent DFT method, and the UV–Vis spectrum of [ReOCl₂(hqn)(AsPh₃)] has been discussed on this basis.     

Intra- and intermolecular hydrogen bonds in [Ag(PPh3)3(HL)] complexes [H2L: H2xspa = 3(aryl)-2-sulfanylpropenoic acids; H2cpa = 2-cyclopentylidene-2-sulfanylacetic acid]

Compounds of the type [Ag(PPh₃)₃(HL)] {H₂xspa=3(aryl)-2-sulfanylpropenoic acids: x = Clp [3-(2-chlorophenyl)-], -o-mp [3-(2-methoxyphenyl)-], -p-mp [3-(4-methoxyphenyl)-], -o-hp [3-(2-hydroxyphenyl)-], -p-hp [3-(4-hydroxyphenyl-); H₂cpa = 2-cyclopentylidene-2-sulfanylacetic acid} were synthesized and characterised by IR and NMR (¹H ¹³C and ³¹P) spectroscopy and by FAB mass spectrometry. The crystal structures of [Ag(PPh₃)₃(HClpspa)], [Ag(PPh₃)₃(H-o-mpspa)], [Ag(PPh₃)₃(H-p-mpspa)] and [Ag(PPh₃)₃(Hcpa)] reveal the presence of discrete molecular units containing an intramolecular O-H···S hydrogen bond between the S atom and one of the O atoms of the COOH group. This intramolecular hydrogen bond remains in [Ag(PPh₃)₃(H-o-hpspa)]·EtOH and [Ag(PPh₃)₃(H-p-hpspa)] but in both cases polymeric structures are built on the basis of O-H···O interactions that involve the -OH substituent of the phenyl group of the sulfanylpropenoate fragment.     

Monomeric and dimeric ruthenium thiooxalate complexes: Structures of CpRu(PPh3)2SCOCO2Me and CpRu(dppe)SCOCO2Et

The hydrosulfido complexes CpRu(L)(L′)SH react with one equivalent of O-alkyl oxalyl chlorides (ROCOCOCl) to form the corresponding O-alkylthiooxalate complexes CpRu(L)(L′)SCOCO₂R (L = L′ = PPh₃ (1), (2); L = PPh₃, L′ = CO (3); R = Me (a), Et (b)). The reactions of the hydrosulfido complexes with half equivalent of oxalyl chloride produce the bimetallic complexes [CpRu(L)(L′)SCO]₂ (L = L′ = PPh₃ (4), (5); L = PPh₃, L′ = CO (6)). The crystal structures of CpRu(PPh₃)₂SCOCO₂Me (1a) and CpRu(dppe)SCOCO₂Et (2b) are reported.     

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.     

Reactivity of 2,3-bis(2-pyridyl)pyrazine with [Re2(CO)8(CH3CN)2]: Molecular structures of [Re2(CO)8(C14H10N4)] and [Re2(CO)8(C14H10N4)Re2(CO)8]

The reaction of the labile compound [Re₂(CO)₈(CH₃CN)₂] with 2,3-bis(2-pyridyl)pyrazine in dichloromethane solution at reflux temperature afforded the structural dirhenium isomers [Re₂(CO)₈(C₁₄H₁₀N₄)] (1 and 2), and the complex [Re₂(CO)₈(C₁₄H₁₀N₄)Re₂(CO)₈] (3). In 1, the ligand is σ,σ′-N,N′-coordinated to a Re(CO)₃ fragment through pyridine and pyrazine to form a five-membered chelate ring. A seven-membered ring is obtained for isomer 2 by N-coordination of the 2-pyridyl groups while the pyrazine ring remains uncoordinated. For 2, isomers 2a and 2b are found in a dynamic equilibrium ratio [2a]/[2b]  =  7 in solution, detected by ¹H NMR (−50 °C, CD₃COCD₃), coalescence being observed above room temperature. The ligand in 3 behaves as an 8e-donor bridge bonding two Re(CO)₃ fragments through two (σ,σ′-N,N′) interactions. When the reaction was carried out in refluxing tetrahydrofuran, complex [Re₂(CO)₆(C₁₄H₁₀N₄)₂] (4) was obtained in addition to compounds 1-3. The dinuclear rhenium derivative 4 contains two units of the organic ligand σ,σ′-N,N′-coordinated in a chelate form to each rhenium core. The X-ray crystal structures for 1 and 3 are reported.