Palladium(II) complexes of imidazolin-2-ylidene N-heterocyclic carbene ligands with redox-active dimethoxyphenyl or (hydro)quinonyl substituents

Four novel imidazolium salts, precursors to N-heterocyclic carbene (NHC) ligands, with 2,5-dimethoxybenzyl or 2,5-dihydroxybenzyl (i.e., p-hydroquinone) substituents have been prepared. The crystal structure of the hydroquinone-substituted imidazolium salt H₃L³Br reveals Br⁻?H-O bridged chiral chains of alternating [H₃L³]⁺ cations and Br⁻ counter-ions parallel to the x-axis. Palladium(II) complexes were accessible from reactions of the dimethoxyphenyl-substituted imidazolium precursors with palladium(II) acetate, but not from reactions of imidazolium cations with hydroquinonyl substituents. The crystal structure of the bis(dimethoxybenzyl)-substituted bis(NHC)Pd complex, cis-[PdBr₂(L²)] (2), is described. Puckering of the bis(NHC) ligand leads to a cleft in which an included molecule of dimethylformamide is situated. The cleft is closed by one of the dimethoxybenzyl groups which π-stacks with the dimethylformamide; the other dimethoxybenzyl group points away from the cleft and Pd(II) centre. Reaction of complex 2 with BBr₃ afforded the targeted bis(hydroquinone)-substituted bis(NHC)Pd(II) complex 3 (97% yield) which, in turn, was oxidised by 2,3-dichloro-5,6-dicyano-benzoquinone to the corresponding p-benzoquinone-substituted bis(NHC)Pd(II) complex 4 (98% yield). The cyclic voltammograms of the Pd(II) complexes 2-4 reveal waves that are attributed to an admix of the anticipated ligand-centred and [Pd(C-NHC)₂Br₂]-centred processes.     

Synthesis, characterization and antimicrobial activity of new silver complexes with N-heterocyclic carbene ligands

Synthesis, structure, and antimicrobial studies of silver complexes of N-heterocyclic carbene (NHC) are reported. All the silver-NHC complexes (1a-f) were prepared from the benzimidazolium salts by the reactions with Ag₂O in dichloromethane as a solvent at room temperature. The new compounds characterized by ¹H NMR, ¹³ C NMR, IR and elemental analysis techniques which support the proposed structures. Chloro[1-(2,4,6-trimethylbenzyl)-3-(methoxyethyl)benzimidazol-2-ylidene]silver(I) complex was structurally characterized by single-crystal X-ray diffraction. A series of new Ag-NHC complexes were screened for their in vitro antimicrobial activity against a variety of Gram-positive and Gram-negative bacteria as well as for their antifungal activity against a Candida albicans and Candida tropicalis.     

Tetrazole and triazole carbene complexes of group 6 metal carbonyls

In order to study the relative stability of cis- and trans-isomers of bis(NHC)tetracarbonyl complexes of group 6 metals, we synthesized the corresponding complexes with triazolin- and tetrazolinylidene ligands. By reaction of the free carbene (L = 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazolin-5-ylidene) - first synthesized by Enders - with the hexacarbonyls of Cr, Mo and W the corresponding M(L)(CO)₅ complexes are generated. Depending on an excess of carbene also the cis-(L)₂Mo(CO)₄ complex was obtained. The latter can be photolytically converted to the trans-(L)₂Mo(CO)₄ complex. The corresponding complexes with the 1,4-dimethyltetrazolin-5-ylidene ligand (L′), Cr(L′)(CO)₅, cis-(L′)₂Cr(CO)₄ and trans-(L′)₂Cr(CO)₄ can be obtained by reaction of hexacarbonyl-μ-trihydroxy-dichromate with dimethyltetrazolium salt. In the cis-(L′)₂Cr(CO)₄ complex, one carbonyl ligand can be replaced by donor ligands such as pyridine or phenylisocyanide to form sym-mer-tricarbonyl complexes. All new complexes are fully characterized by spectroscopy and most by single-crystal X-ray analysis.     

Novel benzimidazol-2-ylidene carbene precursors and their silver(I) complexes: Potential antimicrobial agents

Novel benzimidazolium salts were synthesized as N-heterocyclic carbene (NHC) precursors, these NHC precursors were metallated with Ag₂O in dichloromethane at room temperature to give novel silver(I)–NHC complexes. Structures of these benzimidazolium salts and silver(I)–NHC complexes were characterized on the basis of elemental analysis, ¹H NMR, ¹³C NMR, IR and LC–MS spectroscopic techniques. A series of benzimidazolium salts and silver(I)–NHC complexes were tested against standard bacterial strains: Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and the fungal strains: Candida albicans and Candida tropicalis. The results showed that benzimidazolium salts inhibited the growth of all bacteria and fungi strains and all silver(I)–NHC complexes performed good activities against different microorganisms.     

Synthesis and chiroptical properties of organometallic complexes of helicenic N‐heterocyclic carbenes

Novel [4, 6]helicenes ( 4a,b ) bearing a fused imidazolium unit have been prepared from [4, 6]helicene‐2,3‐di‐n‐propyl‐amines 3a,b . The in situ formation of N‐heterocyclic carbene (NHC) derivatives followed by their complexation to iridium(I) or rhodium(I) gave access to complexes 1a , 1′a , and 1b , containing mono‐coordinated helicene‐NHC, chloro and COD (COD = 1,5‐cyclooctadiene) ligands. Ir and Rh complexes 1a and 1′a were characterized by X‐ray crystallography. HPLC and NMR analyses showed that Ir(I) complex 1b existed as a mixture of two diastereomeric complexes corresponding to enantiomeric pairs M‐(?)/P‐(+)‐ 1b ¹ and M‐(?)/P‐(+)‐ 1b ² which differ by the position of COD through space. The chiroptical properties (electronic circular dichroism and optical rotation) of the four stereoisomers were measured. These complexes were also tested as catalysts in a transfer hydrogenation reaction.     

Comparison of structural features of three new cis-dioxomolybdenum(VI) complexes with 2-hydroxy-1-naphthaldehyde-S-methylisothiosemicarbazone: Possible role of intermolecular interactions on the geometry of the cis-MoO2 unit

Three closely related [MoO₂(L)(ML)] complexes, where L is the 2-hydroxy-1-naphthaldehyde-S-methylisothiosemicarbazone ligand, and ML is EtOH (I), Py (II) and DMSO (III), were synthesized, characterized by NMR and IR spectra, and their X-ray crystal structures were determined. The crystal structure properties of these three closely related complexes were compared. Two cis-Mo-O bond lengths were almost the same in the crystal structure of complexes II and III, while in complex I a significant difference between the two cis-Mo-O bond lengths was observed. At the same time, the geometry of L ligand in complex I is different, compared to II and III. DFT calculations on the isolated molecule I, as well as geometrical analysis of the complexes indicate that intramolecular interactions are not responsible for these structural differences. On the other hand, the pattern of intermolecular contacts in the crystal structure of I differs from those observed in II and III. Analyses indicate that differences in cis-Mo-O bond lengths and in the geometry of ligand L could be related to intermolecular interactions. These results suggest the possibility that in enzymes oxotransferases or in their model systems, the Mo-O bond length could be designed by the interactions of chelate ligands with the surroundings.     

Synthesis,characterization and antimicrobial activities of novel silver(I) complexes with coumarin substituted N-heterocyclic carbene ligands

Eight new coumarin substituted silver(I) N-heterocyclic carbene (NHC) complexes were synthesized by the interaction of the corresponding imidazolium or benzimidazolium chlorides and Ag₂O in dichloromethane at room temperature. Structures of these complexes were established on the basis of elemental analysis, ¹H NMR, ¹³C NMR, IR and mass spectroscopic techniques. The antimicrobial activities of carbene precursors and silver NHC complexes were tested against standard strains: Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and the fungi Candida albicans and Candida tropicalis. Results showed that all the compounds inhibited the growth of the all bacteria and fungi strains and some complexes performed good activities against different microorganisms. Among all the compounds, the most lipophilic complex bis[1-(4-methylene-6,8-dimethyl-2H-chromen-2-one)-3-(naphthalene-2-ylmethyl)benzimidazol-2-ylidene]silver(I) dichloro argentate (5e) was found out as the most active one.     

Stereolability of Chiral Ruthenium Catalysts With Frozen NHC Ligand Conformations Investigated by Dynamic‐HPLC

The stereolability of chiral Hoveyda–Grubbs II type ruthenium complexes bearing N‐heterocyclic carbene (NHC) ligands with Syn‐phenyl groups on the backbone and Syn‐ or Anti‐oriented o‐tolyl N‐substituents was studied by resorting to dynamic high‐performance liquid chromatography (D‐HPLC). A complete chromatographic picture of the involved stereoisomers (four for Anti‐ and two for Syn‐complexes) was achieved at very low temperatures (?53°C and ?40°C respectively), at which the NHC‐Ru bond rotations were frozen out. Inspection of the chromatographic profiles recorded at higher temperatures revealed the presence of plateau zones between the couples of either Syn or Anti stereoisomers, attesting to the active interconversion between the eluted species. Such dynamic chromatograms were successfully simulated through procedures based on both theoretical plate and classical stochastic models. The good superimposition achieved between experimental and simulated chromatographic profiles allowed determination of the related isomerization energy barriers (ΔG_isom^#), all derived by rotation around the NHC‐Ru bond. The obtained diastereomerization barriers between the Anti isomers were found in very good agreement with those previously measured by experimental nuclear magnetic resonance (NMR) and assessed through Density Functional Theory (DFT) calculations. With the same approach, for the first time we also determined the enantiomerization barrier of the Syn isomer. Focused changes to the structure of complex Syn, studied by a molecular modeling approach, were found suitable to strongly reduce the stereolability arising from rotation around the NHC‐Ru bond. Chirality 27:685–692, 2015. © 2015 Wiley Periodicals, Inc.     

On the complex formation of iron(III) bromide in the space-demanding solvent N,N′-dimethylpropyleneurea and the structure of the trisbromoiron(III) complex in solution and crystalline state

The complex formation between iron(III) and bromide has been studied calorimetrically in N,N′-dimethylpropyleneurea (DMPU), and the structure of the DMPU solvated tribromoiron(III) complex has been studied in solution by extended X-ray absorption fine structure (EXAFS) and large angle X-ray scattering (LAXS), and in solid state by EXAFS and single crystal X-ray diffraction. The calorimetric study showed that iron(III) forms three medium strong bromide complexes in DMPU, and the thermodynamic pattern strongly indicates that all complexes are formed in entropy driven substitution reactions. In DMPU solution, the tribromoiron(III) complex has a regular trigonal planar configuration with a mean Fe-Br bond distance of 2.36 Å, and without any solvent molecules strongly bound to iron(III). In the solid state, however, the structure is a slightly distorted trigonal bipyramid, with one short and two slightly longer Fe-Br bonds, 2.37 and 2.44 Å, respectively, in a somewhat distorted trigonal plane, and two DMPU solvent molecules (mean Fe-O bond distance 1.98 Å) in the apical positions. The DMPU solution of iron(III) bromide and the [FeBr₃(dmpu)₂] crystals are both blackish red.     

Reactivity of the N-heterocyclic carbene complexes [Ru(IMes)2(CO)HX] (X = OH, Cl) with alkynes

Treatment of the 16-electron hydroxy hydride complex [Ru(IMes)₂(CO)H(OH)] (1, IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene) with HCCR affords the alkynyl species [Ru(IMes)₂(CO)H(CCR)] (R = Ph 3, SiMe₃, 4) and [Ru(IMes)₂(CO)(CCR)₂] (R = Ph, 5). Deuterium labelling studies show that the mono-alkynyl complexes are formed via hydrogen transfer from a coordinated alkyne ligand to Ru-OH, while bis-alkynyl formation is proposed to take place through hydrogen transfer to Ru-H. Both 3 and 5 readily coordinate CO to give the corresponding dicarbonyl species 6 and 7. Addition of HCCPh to the hydride chloride precursor [Ru(IMes)₂(CO)HCl] (2) results in a different reaction pathway involving alkyne insertion into the Ru-H bond to yield the alkenyl chloride complex [Ru(IMes)₂(CO)(CHCHPh)Cl] 8. Complexes 3-8 have been structurally characterised by X-ray crystallography.     

Methyl-substituted 4-nitropyridine N-oxides as ligands: structural, spectroscopic, magnetic and cytotoxic characteristics of copper(II) complexes

Seven new mono- and dinuclear Cu(II) complexes containing various methyl substituted 4-nitropyridine N-oxides as ligands were isolated and characterized physicochemically and biologically. The characterization included elemental analysis, magnetic and spectroscopic methods (diffuse reflectance and UV-visible absorption, IR, FIR). A single crystal X-ray diffraction analysis was performed for the complex with 2,5-dimethyl-4-nitropyridine N-oxide. Trans- and cis-square planar configuration around Cu ion was established for mono- and dinuclear species, respectively. In methanolic solutions the dinuclear species decompose into mononuclear ones with increasing 4 → 6 coordination number with attachment of two solvent molecules.The IR spectra showed that the strength of the Cu-ligand bond gauged by the degree of N-O elongation changed irregularly with position and number of methyl groups. Cytotoxic studies on the MCF-7 human breast cancer line revealed a structure-activity relationship: double blocking of the NO₂ group with two CH₃ groups rendered the complex completely inactive.     

Synthesis, spectroscopy and thermal behavior of new lead(II) complexes derived from S-methyl/benzyldithiocarbazates (SMDTC/SBDTC): X-ray crystal structure of [Pb(SMDTC)(NO3)2]

Lead(II) complexes of S-methyldithiocarbazate (SMDTC), [Pb(SMDTC)(NO₃)₂] (1) and S-benzyldithiocarbazate (SBDTC), [Pb(SBDTC)(NO₃)₂] (2) have been synthesized for the first time and characterized by elemental analysis, IR and TGA techniques. The complexes were obtained by addition of the appropriate ligand to an aqueous ethanolic solution of lead(II) nitrate in 1:1 molar ratio. The X-ray crystal structure of complex 1 has been determined by single crystal X-ray diffractometry. In complex 1, lead(II) is in a nine coordinated sphere with seven oxygen atoms of the nitrate groups and thione sulfur, β-nitrogen of neutral bidentate NS chelating ligand. Three nitrate groups act as bidentate chelating whereas the fourth nitrate group is coordinating to the central lead(II) and at the same time it bridges with neighboring lead(II) atom. Coordination geometry of the central lead(II) atom has a tricapped trigonal prismatic arrangement with streochemically inactive lone pair. The lead atoms are linked into polymeric chains and these chains form twin polymeric ribbons linked through bridging oxygen atoms. The N-H?O hydrogen bond network between N_SMDTC and O_nitrate atom leads to self-assembled molecular conformation and stabilizes the crystal structure. The complex 2 with similar spectral and thermal behavior is expected to have a tricapped trigonal prismatic structure. The thermal behavior studies shows that the complexes start to decompose at relatively low temperature (ca. 110 °C) to give PbS residue.     

Theoretical Study of N‐Heterocyclic Carbenes‐Catalyzed Cascade Annulation of Benzodienones and Enals

Growing attention in developing new N‐heterocyclic carbene (NHC)‐mediated reactions involving homoenolate intermediates has prompted our interest in exploring the mechanistic details of the related reactions. In this work, we carried out a detailed theoretical study for the NHC‐catalyzed annulation reaction of cinnamaldehyde ( A ) and benzodi(enone) ( B ) in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU). By performing density functional theory calculations, we show clearly the detailed reaction mechanism and rationalize the experimental observation. The reaction of A and B falls into two stages: the formation of homoenolate intermediate and the annulation of homoenolate with B . In the homoenolate formation stage, three possible paths are characterized. The pathway involving the DBU‐assisted 1,2‐proton transfer with a stepwise mechanism is kinetically more favorable, and the DBU‐assisted C1 proton departure is the rate‐determining step of the total reaction. The annulation of homoenolate with B involves four elementary steps. The conformational difference of homoenolate (cis and trans) leads to two slightly different reaction processes. In the total reaction, the process involving cis‐conformation of A is kinetically more feasible. This can be clearly understood through the frontier molecular orbital analysis and the electronic inductive effect. The calculated results are expected to offer valuable information for further design and development of NHC‐mediated reactions. Chirality 25:521‐528, 2013. © 2013 Wiley Periodicals, Inc.     

Complexes of oxomethoxovanadium(V) with tridentate thiobenzhydrazide based Schiff bases

A family of complexes containing the {VO(OMe)}²⁺ motif with the O,N,S-donor Schiff bases (H₂tbhsR) derived from thiobenzhydrazide and 5-substituted salicylaldehydes has been reported. Reactions of [VO(acac)₂] with H₂tbhsR in methanol provide the complexes having the general formula [VO(OMe)(tbhsR)] (R = H, OMe, Cl, Br and NO₂) in 40-53% yields. Microanalytical, various spectroscopic (IR, UV-Vis and NMR) and electrochemical measurements have been used for the characterization of the complexes. All the complexes are redox active and display a near reversible metal centred reduction in the potential range 0.20-0.47 V (versus Ag/AgCl). The trend in these potential values reflects the polar effect of the substituent on the salicylidene fragment of tbhsR²⁻. The X-ray crystal structures of all the complexes have been determined. In each of the complexes where R = H, OMe, Cl and Br, the metal ion is in a distorted square-pyramidal O₃NS coordination sphere assembled by the O,N,S-donor tbhsR²⁻, the methoxo and the oxo groups. The complex where R = NO₂, crystallizes as a hexacoordinated species due to coordination of a methanol O-atom at the vacant sixth site. The bond parameters associated with the metal ions and the physical properties of the complexes are consistent with the +5 oxidation state of the metal ion in all the complexes. Scrutiny of crystal packing reveals dimeric, one-dimensional and two-dimensional self-assembled structures via intermolecular C-H?O and O-H?O interactions. The two-dimensional network contains the cyclic tetramer of methanol.     

Endogenous U2·U5·U6 snRNA complexes in S. pombe are intron lariat spliceosomes

Excision of introns from pre-mRNAs is mediated by the spliceosome, a multi-megadalton complex consisting of U1, U2, U4/U6, and U5 snRNPs plus scores of associated proteins. Spliceosome assembly and disassembly are highly dynamic processes involving multiple stable intermediates. In this study, we utilized a split TAP-tag approach for large-scale purification of an abundant endogenous U2·U5·U6 complex from Schizosaccharomyces pombe. RNAseq revealed this complex to largely contain excised introns, indicating that it is primarily ILS (intron lariat spliceosome) complexes. These endogenous ILS complexes are remarkably resistant to both high-salt and nuclease digestion. Mass spectrometry analysis identified 68, 45, and 43 proteins in low-salt-, high-salt-, and micrococcal nuclease-treated preps, respectively. The protein content of a S. pombe ILS complex strongly resembles that previously reported for human spliced product (P) and Saccharomyces cerevisiae ILS complexes assembled on single pre-mRNAs in vitro. However, the ATP-dependent RNA helicase Brr2 was either substoichiometric in low-salt preps or completely absent from high-salt and MNase preps. Because Brr2 facilitates spliceosome disassembly, its relative absence may explain why the ILS complex accumulates logarithmically growing cultures and the inability of S. pombe extracts to support in vitro splicing.     

Synthesis and structural analysis of palladium biscarbene complexes derived from bisimidazolium ligand precursors

The palladation of potentially chelating bisimidazolium ligand precursors with palladium acetate gives bridging bimetallic, chelating monometallic, and homoleptic tetracarbene complexes. The coordination mode of the biscarbene ligand has been identified by spectroscopic analysis and crystallographic characterization of representative complexes, including the first example of a biscarbene A-frame structure. Substantial concentrations of free acetate favor the formation of tetracarbene over biscarbene palladium complexes, while in the absence of a base, the concentration of reactants influences the selectivity for bridging bimetallic versus chelating monometallic species. Preliminary kinetic and mechanistic studies indicate that chelating biscarbene palladium acetate complexes are intermediates in the formation of the homoleptic tetracarbene complexes. Probably due to the high trans effect of the biscarbene ligand, such complexes are more efficient palladating agents for bisimidazolium salts than palladium acetate.     

Low-dimensional compounds containing cyano groups. XIX. Crystal structure, spectroscopic, thermal and magnetic properties of {[Cu(tn)2]3[Pt(CN)4]2}[Pt(CN)4] (tn = 1,3-diaminopropane) complex

Violet prismatic crystals of {[Cu(tn)₂]₃[Pt(CN)₄]₂}[Pt(CN)₄] (tn = 1,3-diaminopropane) were crystallized from the water-methanol solution containing CuCl₂·2H₂O, tn and K₂[Pt(CN)₄]·3H₂O. Prepared complex was characterized using elemental analysis, infrared and UV-Vis spectroscopy, magnetic measurement and thermal analysis. X-ray analysis revealed an ionic character of the complex containing mononuclear square planar [Pt(CN)₄]²⁻ complex anions and penta-nuclear [Cu(tn)₂-Pt(CN)₄-Cu(tn)₂-Pt(CN)₄-Cu(tn)₂]²⁺ complex cations. The inner Cu(II) atom of the complex cation is hexa-coordinated, whereas two crystallographically equivalent peripheral Cu(II) atoms are penta-coordinated in the shape of a deformed square pyramid. Four v(CN) absorption bands observed in the IR spectrum are in agreement with the higher number of crystallographically different cyano groups and a broad highly asymmetric band observed in the reflectance UV-Vis spectrum is consistent with the presence of both hexa- and penta-coordinated Cu(II) atoms in the structure. The temperature dependence of the inverse susceptibility suggests the presence of a weak antiferromagnetic exchange coupling between Cu(II) ions. The complex is stable up to 210 °C when its two-stage thermal decomposition starts.     

New routes toward metallated methanofullerene terdentate bisaminoaryl ligands

The preparation of a series of new ligands, comprising a NCN ligand (C₆H₂(CH₂NMe₂)₂-2,6-X-4, X=H, Br, I) substituted on the para position with a [1,2]-methanofullerene group is described. Metallation of these ligands is achieved via an oxidative addition reaction of nickel(0) or palladium(0) complexes. The first step of this reaction comprises the formation of a π-complex between the metal center and the fullerene moiety of the ligand, which upon heating in a subsequent step is followed by oxidative addition of the NCN-halide bond to the metal center. The nickel(II) complex C₆₀C(Me)NCN·NiBr (9) was isolated in pure form. Low temperature NMR spectroscopy and theoretical calculations showed that the NCN moiety in 9 rotates about the (Me)CNCN bond at room temperature. UV-Vis spectroscopic measurements of 9 suggest that binding a metal center via a covalent metal-carbon bond to the NCN moiety does not lead to a substantial change in the electronic structure of the fullerene moiety. The cyclo voltammograms of 9 showed the absence of a Ni(II)/Ni(III) oxidation/reduction process, while the second and fourth C₆₀ reduction potentials were anodically shifted.     

Preparation, crystal structures and spectroscopic properties of novel [MCl3 − n(P)3 + n] (M = Co, Rh; n = 0, 1, 2 or 3) series of complexes containing tripodal tridentate phosphine, 1,1,1-tris(dimethylphosphinomethyl)ethane

Cobalt(III) and rhodium(III) complexes of the series of [M^IIICl_3 − n(P)_3 + n]ⁿ⁺ (M = Co or Rh; n = 0, 1, 2 or 3) have been prepared with the use of 1,1,1-tris(dimethylphosphinomethyl)ethane (tdmme) and mono- or didentate phosphines. The single-crystal X-ray analyses of both series of complexes revealed that the M-P and M-Cl bond lengths were dependent primarily on the strong trans influence of the phosphines, and secondarily on the steric congestion around the metal center resulting from the coordination of several phosphine groups. In fact, the M-P(tdmme) bonds became longer in the order of [MCl₃(tdmme)] < [MCl₂(tdmme)(PMe₃)]⁺ < [MCl(tdmme)(dmpe)]²⁺ (dmpe = 1,2-bis(dimethylphosphino)ethane) < [M(tdmme)₂]³⁺ for both Co^III and Rh^III series of complexes, while the M-Cl bond lengths were shortened in this order (except for [M(tdmme)₂]³⁺). Such a steric congestion around the metal center can also account for the structural and spectroscopic characteristics of the series of complexes, [MCl(tdmme)(dmpm, dmpe or dmpp)]²⁺ (dmpm = bis(dimethylphosphino)methane, dmpp = 1,3-bis(dimethylphosphino)propane). The X-ray analysis for [CoCl(tdmme)(dmpm or dmpe)](BF₄)₂ showed that all Co-P bonds in the dmpm complex were shorter by 0.03-0.04 Å than those in the dmpe complex. Furthermore, the first d-d transition energy of the Co^III complexes and the ¹J_Rh-P(tdmme) coupling constants observed for the Rh^III complexes indicated an unusual order in the coordination bond strengths of the didentate diphosphines, i.e., dmpm > dmpe > dmpp.     

Synthesis, structures and in vitro cytotoxicity of some cationic cis-platinum(II) complexes containing chelating thiocarbamates

The thiocarbamates 4-RC₆H₄NHC(S)NR₂′ (R = H, Cl; R′ = Me, Et), 4-ClC₆H₄NHC(S)NR (NR = 2-pyridylpiperazine) react with cis-[PtCl₂(PTA)₂] (PTA = 1,3,5-triaza-7-phosphaadamantane) in the presence of base to afford the monocationic platinum(II) complexes cis-[Pt{SC(NR₂′) = NC₆H₄R}(PTA)₂]⁺ (R = H, Cl; R′ = Me, Et), cis-[Pt{SC(NR) = NC₆H₄Cl}(PTA)₂]⁺ (NR = 2-pyridylpiperazine), which were isolated as their PF₆ salts in high yields. The complexes were fully characterised spectroscopically and also by X-ray crystallography. Cytotoxicity of these complexes was studied in vitro in three human cancer cell lines (CH1, A549 and SW480) using the MTT assay.