The chemistry of binuclear palladium(II) and platinum(II) complexes

Oligomeric allyl-palladium(II) complexes of β-substituted ethylselenolates: syntheses, structures and thermal decomposition

Tri-nuclear allyl-palladium complexes, [Pd(μ-SeCH(2)CH(2)COOR)(η(3)-C(3)H(4)R')](3) (R = H, Me, Et and R' = H, Me), have been synthesized by the reaction of [Pd(2)(μ-Cl)(2)(η(3)-C(3)H(4)R')(2)] with NaSeCH(2)CH(2)COOR. These complexes exist in a dynamic equilibrium with a dimeric form in solution and are fluxional at room temperature as shown by variable temperature (1)H NMR spectroscopy. The DFT calculations indicate that there is a negligible energy difference between the dimer and the trimer, and suggest that the delicate balance between the steric factors and angular strain decides the reaction products. These complexes (with R' = H) on treatment with [Pd(2)(μ-Cl)(2)(η(3)-C(3)H(5))(2)] afforded hetero-bridged complexes [Pd(2)(μ-Cl)(μ-SeCH(2)CH(2)COOR)(η(3)-C(3)H(5))(2)] (R = Me, Et). All the complexes have been characterized by NMR ((1)H, (13)C, (77)Se) spectroscopy. The molecular structure of [Pd(μ-SeCH(2)CH(2)COOEt)(η(3)-C(3)H(5))](3) revealed a chair conformation of the six-membered Pd(3)Se(3) ring, in which all the allyl groups lie at one side of the ring (similar to three axial 1,3,5-hydrogens of cyclohexane). Thermolysis of [Pd(μ-SeCH(2)CH(2)COOEt)(η(3)-C(3)H(5))](n) in diphenyl ether or hexadecylamine (HDA) yielded Pd(7)Se(4) as characterized by powder XRD.

Bent dinuclear platinum(II) halo-bridged carbonyl complexes

Crystals of trans-Pt₂(μ-X)₂X₂(CO)₂ (X = Br, I) have been grown and their molecular and crystalline structures have been solved by X-ray diffraction methods. In both cases the dinuclear molecules are bent, with a bending angle of 164.6° and 156.5° for the bromide and the iodide, respectively. While the structure of the bromo-derivative is reported here for the first time, a modification of trans-Pt₂(μ-I)₂I₂(CO)₂ with planar centrosymmetric molecules is known. This appears to be a rare case of a platinum(II) halo-bridged derivative structurally characterized in both bent and planar forms.

Transition metal complexes of an isatinic quinolyl hydrazone

Background

The importance of the isatinic quinolyl hydrazones arises from incorporating the quinoline ring with the indole ring in the same compound. Quinoline ring has therapeutic and biological activities. On the other hand, isatin (1H-indole-2,3-dione) and its derivatives exhibit a wide range of biological activities. Also, the indole ring occurs in Jasmine flowers and Orange blossoms. Recently, the physiological and biological activities of quinolyl hydrazones arise from their tendency to form metal chelates with transition metal ions. In this context, we have reported to isolate, characterize and study the biological activity of some transition metal complexes of an isatinic quinolyl hydrazone; 3-[2-(4-methyl quinolin-2-yl)hydrazono] indolin-2-one.

Results

Mono- and binuclear as well as dimeric chelates were obtained from the reaction of a new isatinic quinolyl hydrazone with Fe(III), Co(II), Ni(II), Cu(II), VO(II) and Pd(II) ions. The ligand showed a variety of modes of bonding viz. (NNO)^2-, (NO)^- and (NO) per each metal ion supporting its ambidentate and flexidentate characters. The mode of bonding and basicity of the ligand depend mainly on the type of the metal cation and its counter anion. All the obtained Pd(II)- complexes have the preferable square planar geometry (D_4h- symmetry) and depend mainly on the mole ratio (M:L).

Conclusion

The effect of the type of the metal ion for the same anion (Cl^-) is obvious from either structural diversity of the isolated complexes (O_h, T_d and D_4h) or the various modes of bonding. The isatinic hydrazone uses its lactim form in all complexes (Cl^-) except complex 5 (SO₄^2-) in which it uses its lactam form. The obtained Pd(II)- complexes (dimeric, mono- and binuclear) are affected by the mole ratio (M:L) and have the square planar (D_4h) geometry. Also, the antimicrobial activity is highly influenced by the nature of the metal ion and the order for S. aureus bacteria is as follows: Nickel(II) > Vanadyl(II) > Cobalt(II) > Copper(II) ≈ Palladium(II) >> Iron(III).

Mononuclear platinum(II) complexes incorporating kappa2-carboxylate ligands: synthesis, structure, and reactivity

The chloro-bridged dimer [(PC)Pt(mu-Cl)](2) (PC = [((t)Bu(2)P-o-C(6)H(4))-CMe(2)](-)) reacts with silver(I) acetate to yield the monomeric kappa(2)-acetate complex [(PC)Pt(kappa(2)-OOCMe)]. Its trifluoroacetate analogue exists in solution as a mixture of the monomer and two isomeric dimers, and crystallizes as the approximately C(2)-symmetrical dimer [(PC)Pt(mu-OOCCF(3))](2). NMR experiments and density functional theory calculations show that the monomeric species are favored by bulky ligands and electron-rich carboxylates. [(PC)Pt(OOCCF(3))] undergoes a ligand-dehydrogenation reaction in hot trifluoroacetic acid to yield [(PCC)Pt(OOCCF(3))(2)] (PCC = ((t)Bu(2)P-o-C(6)H(4))-C(Me)=CH(2)).

Synthesis and C-C coupling reactivity of a dinuclear Ni(i)-Ni(i) complex supported by a terphenyl diphosphine

Mono- and bimetallic complexes of nickel supported by a terphenyl diphosphine have been synthesized. The reported complexes show diverse metal-arene interactions in the solid state. Reactions of an o,o'-biphenyldiyl dinickel complex with CO and dichloroalkanes lead to fluorene derivatives, indicating the formation of carbon-carbon bonds at a bimetallic moiety.

Unusual metal-coordinated zwitterionic P-C-N-C-N-C phosphido adducts

Rare examples of homodinuclear zwitterionic Pd(II) and Pt(II) complexes with bridging, two-coordinate P{cyclo-CH(2)N(R)CHN(R)CH(2)} ligands (R = 4-FC(6)H(4)CH(2), C(6)H(5)CH(2)) have been characterized by single-crystal X-ray diffraction using synchrotron radiation. Short N-C distances and enlarged N-C-N bond angles support electron delocalization in the central N-C-N backbone.

2-Mercapto-1-t-butylimidazolyl as a Bridging Ligand: Synthesis and Structural Characterization of Nickel and Palladium Paddlewheel Complexes

Nickel and palladium paddlewheel complexes that feature 2-mercapto-1-t-butylimidazolyl (mim(Bu(t) )) bridging ligands, namely Ni(2)[mim (Bu(t) )](4) and Pd(2)[mim (Bu(t) )](4), have been synthesized and structurally characterized by X-ray diffraction. Since the mim (Bu(t) ) ligand bridges in an asymmetric manner via a sulfur and nitrogen donor, paddlewheel compounds of the type M(2)[mim (Bu(t) )](4) may exist as isomers that are distinguished by the relative orientations of the ligands. In this regard, the (4,0)-Ni(2)[mim (Bu(t) )](4) and trans-(2,2)-Ni(2)[mim (Bu(t) )](4) isomers have been isolated for the nickel system, while the (4,0)-Pd(2)[mim (Bu(t) )](4) and (3,1)-Pd(2)[mim (Bu(t) )](4) isomers have been isolated for the palladium system.

Pd/X group interchange in the [Pd(Br)(PH3)(C6H5)(C6H5X)] system — Theoretical insights from the isolobal analogy perspective

DFT-B3LYP calculations have been carried out to assess the fate of the Pd/X group intermolecular exchange in the [PdBr(PH3)(C6H5)(C6H5X)] system, where X is either H, an electropositive atom, or a group such as Li, Na, BH2, AlH2, BeH or BeCH3, and an electronegative atom, or a group such as F, Cl, Br, CH3, OH, and SH. The transfer of H is best viewed as involving the migration of a proton between the two phenyls. At variance with this result, the transfer of the more electropositive entities such as X = Li, Na, BH2, AlH2, BeH, or BeCH3 is not complete. It stops halfway to yield a stable structure in which X can experience interactions with the two phenyl groups that are quite ionic. These stable structures are rationalized through isolobal analogy arguments. In the case of beryllium, the correspondence has been made also with the experimentally known cyclopentadienylberyllium borohydride system, CpBeH4. The results of the DFT geometry optimization call for a re-examination of the gas-phase electron-diffraction structure determination, especially for the bond distances and angles that pertain to the two bridging hydrogens. For the halogen series X = F, Cl, or Br and for the electronegative groups CH3, OH, or SH, the transfer between the two phenyls takes place via a two-step Pd(II)/Pd(IV) oxidative addition/reductive elimination mechanism. The associated energy barriers are nevertheless quite high, except for Br and SH for which the process might be feasible. The dimerization of the PdBr(PH3)(C6H5) system is also analyzed within the isolobal analogy framework.

Chlorine photoelimination from a diplatinum core: circumventing the back reaction

The d(9)...d(9) Pt(2)(I,I)(tfepma)(2)Cl(2) (1) compound (tfepma = ((CF(3)CH(2)O)(2)P)(2)NCH(3)), d(7)-d(9) Pt(2)(I,III)(tfepma)(2)Cl(4) (2) and d(7)-d(7) Pt(2)(III,III)(tfepma)(2)Cl(6) (3), homologous suite of compounds have been prepared. Irradiation of 3 with visible light generates 2 in solution in the presence of 2,3-dimethyl-1,3-butadiene with a quantum efficiency of approximately 38%. The evolution of Cl(2) upon solid-state photolysis of 3 represents the first example of the thermodynamically unfavorable halogen elimination without the use of a chemical trap.