Synthesis and solution behavior of mononuclear palladium(II) and platinum(II) complexes containing pyridine-2-thiolate as a ligand. Crystal structure of chloro(pyridine-2-thiolato)- (triphenylphosphine)palladium(II)

Compounds of the types Pn(pyS)3 (Pn = P, As, Bi; pyS: pyridine-2-thiolate) and Sb(pyS) x Ph3–x (x = 3–1); molecular structures and electronic situations of the Pn atoms

The compounds Pn(pyS)3 (Pn = P, As, Sb, Bi) were synthesized from the respective chloride (Pn = P, As, Sb) or nitrate (Bi), pyridine-2-thiol (pySH) and triethylamine (NEt3) as a supporting base in THF (P, Sb), CHCl3 (As) or methanol (Bi). Sb(pyS)3 was also obtained from the reaction of SbCl3 with LipyS (prepared in situ) in methanol. The compounds Sb(pyS)2Ph and Sb(pyS)Ph2 were prepared in a one-pot reaction starting from SbCl3 and SbPh3 (1:1 ratio). Upon Cl/pyS substitution, the resulting reaction mixture allows for a facile separation of the products in hot hexane. P(pyS)3 and As(pyS)3 crystallize isostructurally to the reported structure of Sb(pyS)3 with κ-S-bound pyS ligands. These crystal structures feature close Pn···Pn contacts which are most pronounced for the arsenic derivative. Bi(pyS)3 adopts a different molecular structure in the solid state, which features two chelating (κ 2-S,N-pyS) ligands and a κ-S-bound ligand. The presence of N→Bi interactions between the nitrogen atom of the κ-S-pyS ligand and the Bi atom of another molecule renders this structure a polymer chain along the crystallographic b axis with Bi⋅⋅⋅Bi van-der-Waals contacts. The structures of this set of Pn(pyS)3 compounds were also studied in solution using 1H NMR spectroscopy, revealing equivalent pyS ligands in discrete Pn(pyS)3 molecules. The molecular structure of Sb(pyS)Ph2 was optimized by quantum chemical methods, and a comparison with the structures reported for the other Sb/pyS/Ph combinations reveals Sb(pyS)2Ph to feature the strongest Sb···N interactions with the κ-S-pyS ligand. The results of 1H NMR spectroscopic investigations of the compounds Sb(pyS) x Ph3–x (x = 3–0) suggest the Ph protons in ortho position to be incorporated into intramolecular C–H···S contacts for x = 2 and 1. Natural localized molecular orbital (NLMO) calculations were employed in order to gain insights into the electronic situations of the Pn atoms and Pn–R bonds (R = S, C), especially for the effects caused by formal substitution of Pn in the compounds Pn(pyS)3 and the ligand patterns in the compounds Sb(pyS) x Ph3–x (x = 3–0). For the latter series of compounds, the electronic situation of the Sb atom was further studied by 121Sb Mössbauer spectroscopy, providing a correlation between the calculated electron density at Sb [ρ(0)] and the experimentally observed isomer shift δ. The missing link between group 15 and group 13 metal compounds of the type M(pyS)3, compound Al(pyS)3, was synthesized in this work. In the solid state (confirmed crystallographically), the mer isomer of this tris-chelate complex with distorted octahedral Al coordination sphere was found. This coordination mode was confirmed for the solution state (CDCl3) by 1H and 13C NMR spectroscopy at T = −40 °C.

Trivalent Antimony as L-, X-, and Z-Type Ligand: The Full Set of Possible Coordination Modes in Pt-Sb Bonds

In the course of our investigations of the coordination chemistry of trivalent antimony (Sb) compounds, we studied heteronuclear complexes formed in reactions of the compounds RSb(pyS)₂ (R = pyS, Ph; pyS^- = pyridine-2-thiolate) with [Pt(PPh₃)₄], i.e., complexes [(R)Sb(μ-pyS)₂Pt(PPh₃)] (R = pyS, 1; R = Ph, 2). The reaction of 1 with o-chloranil proceeds cleanly with elimination of 2,2'-dipyridyl disulfide and formation of the salt [(PPh₃)Pt(μ-pyS)₂Sb(μ-pyS)₂Pt(PPh₃)]⁺[Sb(C₆Cl₄O₂)₂]^- (3^III), which features the cation 3⁺. The charge-neutral, unsymmetrically substituted compound [(PPh₃)Pt(μ-pyS)₂Sb(μ-pyS)₂Pt(κS-pyS)] (4) can be accessed by the reaction of 3⁺ with LipyS. The oxidation of 2 with o-chloranil furnishes the complex [(κ-O,O-C₆Cl₄O₂)PhSb(μ-pyS)₂Pt(PPh₃)] (5). The oxidation of 1 with PhICl₂ afforded the paddlewheel-shaped complex [Sb(μ-pyS)₄PtCl] (6). Moreover, compound 6 was obtained by the reaction of Sb(pyS)₃ with [PtCl(pyS)(PPh₃)]. The polarization of Pt-Sb bonds of compounds 1-6 was investigated by natural localized molecular orbital (NLMO) calculations, which suggest X-type ligand character (covalent Pt-Sb bonds) for 1 and 2, whereas the Sb ligand of 6 reflects Z-type character (dative Pt→Sb bonds). In 3⁺, 4, and 5, high contributions of the reverse, i.e., L-type (dative Pt←Sb bonds), were observed. In conjunction with the results of NLMO analyses, ¹²¹Sb Mössbauer spectroscopy proves that complexes 1-6 represent essentially trivalent Sb complexes with either a free lone pair (LP) at the Sb atom (1, 2, and 6) or LP character involved in L-type Pt←Sb coordination (3⁺, 4, and 5).

Reactivity of a half-lantern Pt2(ii,ii) complex with triphenylphosphine: selectivity in a protonation reaction

Reaction of PPh₃ with half-lantern complex [{Pt(ppy)(μ₂-Spy)}₂], 1, gave complex [Pt(ppy)(η¹-S-Spy)(PPh₃)], 2, as a result of platinum–nitrogen bonds dissociation. Complex 2 revealed anionic selectivity upon protonation reaction with acidic species.

C–H reductive elimination during the reaction of cycloplatinated(ii) complexes with pyridine-2-thione: kinetic follow up

Reactions of the cycloplatinated(ii) complexes [PtR(ppy)(SMe₂)], 1, where ppy = deprotonated 2-phenylpyridine and R = Me or p-MeC₆H₄, with pyridine-2-thione, C₅H₅SN, were studied by UV-vis and ¹H NMR spectroscopies and on the basis of the data a mechanism is proposed.

cis-to-trans Isomerization Promoted by Pyridine as a Crucial Step for the Selective Preparation of trans-Pt(SAr)(Cl)(PAr‘3)2

The general strategy for the syntheses of trans-Pt(SAr)(Cl)(PAr'3)2 (1) (Ar = Ph, C6H4-2-Me, C6H4-3-OMe C6H4-2-F, etc.; Ar' = Ph, C6H4-4-OMe, C6H4-4-Me, and C6H4-4-CF3) by the reaction of cis-PtCl2(PAr'3)2 with ArSH has been developed. The mechanistic investigation suggested that isomerization of cis-1 into trans-1 promoted by the combined use of C6H6 as a solvent and pyridine as a base was the key to the successful preparation of 1.

Pyridine-2-thionate as a versatile ligand in Pd(ii) and Pt(ii) chemistry: the presence of three different co-ordination modes in [Pd2(μ2-S,N-C5H4SN)(μ2-κ2S-C5H4SN)(μ2-dppm)(S-C5H4SN)2]

Reactions of [MCl2(L-L)], M = Pt, Pd; L-L = bis(diphenylphosphino)methane (dppm) or bis(diphenylphosphino)ethane (dppe), with NaC5H4SN in a 1 : 2 molar ratio lead to mononuclear species [M(S-C5H4SN)2(P-P)], M = Pt; L-L = dppm (1) or dppe (2) and M = Pd; L-L = dppe (3), as well as to the dinuclear [Pd2(micro2-S,N-C5H4SN)(micro2-kappa2S-C5H4SN)(micro2-dppm)(S-C5H4SN)2] (4). In contrast, reaction of [MCl2(dppm)] with NaC5H4SN in a 1 : 1 molar ratio leads to [Pd2(micro2-S,N-C5H4SN)3(micro2-dppm)]Cl (5) and trans-[Pt(S-C5H4SN)2(PPh2Me)2] (6) respectively. The latter is formed in low yield by cleavage of the dppm ligand. The dinuclear derivatives 4 and 5 present an A-frame and lantern structure, respectively. The former showing three different co-ordination modes in the same molecule with a short Pd-Pd distance of 2.9583 (9) A and the latter with three bridging S,N thionate ligands showing a shorter Pd-Pd distance of 2.7291 (13) A. Both distances could be imposed by the bridging ligands or point to some sort of metal-metal interaction.

A pyrimidine thiolate Rh(I) complex: structure, bonding and one-dimensional interactions in solid and in solution

The reaction of [Rh(micro-Cl)(COD)]2 with 4,6-dimethyl-pyrimidinethiolate (Me2-pymt) and subsequent substitution of COD by CO yields [Rh(Me2-pymt)(CO)2]. The stacking pattern found in this compound is in contradiction with previously studied comparable square-planar complexes of type d8-[M(chelate)(monodentate)2] in which each ligand has different pi-acidic character. A theoretical study of the intermolecular interactions and conformation of the title compound has been carried out, combining semi-empirical band calculations on the real chains and ab initio(MP2 level) calculations on a model dimer. The combination of electronic and steric effects determines the rotation of the successive monomers and the deviation from linearity of the one-dimensional stacks. Its behaviour in solution is also special, developing a blue colour and forming micelles, when adding water to acetone solutions.

Triphenyl phosphine adducts of platinum(IV) and palladium(II) dithiocarbamates complexes: a spectral and in vitro study

Triphenyl phosphine adducts of dithiocarbamate complexes of platinum(IV) and palladium(II) of the type [Pt(L)2PPh3Cl2] and [Pd(L)2PPh3] [L: morpholine dithiocarbamate (L1), aniline dithiocarbamate (L2) and N-(methyl, cyclohexyl) dithiocarbamate (L3)] were prepared and characterized by elemental analysis, electronic, IR, 1H NMR and 13C NMR spectral studies. Thermal studies of the complexes were carried out. In vitro antitumor activity has been screened towards human adenocarcinoma cell lines and showed significant inhibition even at very low concentration.

cis-dichloro-palladium(II) complexes with diaminosuccinic acid and its diethyl ester: synthesis, molecular structure, and preliminary DNA-binding and antitumor studies

The reactions of K2PdCl4 with meso-diaminosuccinic acid (H2dasa) in 0.1 M HCl or its diethyl ester dihydrochloride Et2dasa.2HCl in neutralized aqueous solution yield cis-[Pd(H2dasa)Cl2](I) and cis-[Pd(Et2dasa)Cl2](II), respectively. These products were characterized by elemental analysis, IR spectroscopy, and TG-DTA thermal analysis. The crystal of II is monoclinic, space group C2/c (a = 14.292(5), b = 14.636(5), c = 13.435(5) A, beta = 98.08(2) degrees, Z = 8, R = 0.041 and wR = 0.06). The Pd(II) atom exhibits a roughly square planar coordination with two Pd-N bonds (Et2dasa) (2.014(2) and 2.049(7) A) and two cis-imposed Pd-Cl bonds (2.294(2) and 2.303(2) A). Compound I reacts with 2,2'-bipyridine in neutral aqueous solution to give [Pd(2,2'-bipy)(dasa)].3H2O(III) in a process of cis-chloride substitution by 2,2'-bipy as a model N-heterocyclic chelating entity. The molecular and crystal structure of III is also reported. It was observed that both cis-dichloro-Pd(II) complexes having Pd(H2dasa) (acidic) and Pd-(Et2dasa)(esterified) chelate entities induce conformational changes in the covalent closed circular (ccc) form of pUC8 plasmid. Both compounds were assayed for antitumor activity in vitro against MDA-MB 468 and HL-60 human cancer cell lines. The results show that compounds I and II have values of ID50 lower than those of K2PdCl4, and also lower than those of diaminoacid ligands (meso-diaminosuccinic acid and meso-diaminosuccinate diethyl ester). Thus it is likely that the imposed cis-coordination of the chelating H2dasa or Et2dasa to the Pd(II) center increases the biological activity of these palladium(II) complexes.