119Sn Mössbauer spectroscopic studies of the products of the reaction of triorganotin(IV) derivatives with 6-thiopurine

A structural study of the products of the reaction of R₃Sn^IV derivatives (R = Me, Buⁿ, Ph) with 6-thiopurine, 6-TPH₂, and its sodium salt, 6-TPHNa, has been undertaken using Mössbauer spectroscopy and the point-charge model rationalization of the Mössbauer parameter nuclear quadrupole splitting. The synthetic reactions have been carried out at ca. 0 °C, 20 °C and 50 °C. The Mössbauer spectra of the complexes AlK₃Sn(6-TPH) are consistent with the occurrence of two distinct tin(IV) sites in samples prepared at the lower temperature, while one only site appears by increasing the temperature of the reaction. Two tin sites constantly occur in the products of the reactions involving the Ph₃Sn^IV moiety; the stoichiometry is assumed to be (Ph₃Sn)₃(6-TPH)(6-TP) for the uniquely-formed complex. Solid state polymeric structures with trigonal bipyramidal environments of the tin atoms and planar SnC₃ skeletons have been proposed. The apical ligand atoms have been assumed to be N, S and N, N in the samples showing two individual tin(IV) sites, and N, N when a single site was present.     

Organometallic coordination polymers: Sn(IV) derivatives with the bis(triazolyl)methane ligand

Several alkyl- or aryl-tin(IV) halides of general formula SnR_nX_4−n (n = 0-2; R = Me, Et, ⁿBu, ^tBu, Ph; X = Cl, Br), possessing Lewis acidic character, have been reacted with the polydentate N-donor ligand bis(1,2,4-triazolyl)methane (Btm), affording Btm(SnR_nCl_4−n) complexes. (Btm)₂SnⁿBu₂Br₂ and (Btm)SnⁿBu₂(NO₃)₂ are also reported. These materials were characterized by elemental analyses, IR and ¹H (and, in selected cases, ¹¹⁹Sn) NMR spectroscopy, and, were possible, ab initio X-ray powder diffraction methods. The crystal structures determined by the latter method showed that Btm ligands, in the exobidentate mode, link Sn(IV) fragments which lie 9.5-11.2 Å apart (depending on the Btm conformation and on the local metal stereochemistry), in one-dimensional chains packed in parallel bundles. The main geometrical features of these 1D polymers are compared with those of the bis(imidazolyl)methane complexes and of the known Btm derivative, Btm(Ph₂SnBr₂). Interestingly, the expected isomorphous structures for selected couples was not found, as if very subtle energetic differences were driving the crystallization of these species into different structure types.     

Syntheses and characterization of diorganotin(IV) derivatives with areneseleninic acid: X-ray crystal structures of 1D infinite chains containing eight-membered ring

Three new diorganotin(IV) complexes, [Bu₂Sn(O₂SeC₆H₅)₂]_n (1), [Bu₂Sn(O₂SeC₆H₄Me)₂]_n (2), [Me₂Sn(O₂SeC₆H₄Bu)₂]_n (3) have been synthesized by the reaction of benzeneseleninic acid, p-tolueneseleninic acid, and 4-tert-butylbenzeneseleninic acid with Me₂SnCl₂ or Bu₂SnCl₂ in the presence of sodium ethoxide in methanol at 50 °C. All of the complexes were characterized by elemental analysis, FT-IR, NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy and X-ray crystallography. X-ray diffraction studies of 1, 2, 3 show that the areneseleninate groups behave as double bridges between the tin atoms leading to polymeric chain structure with Sn₂O₄Se₂ eight-membered ring. The organic groups bonded to the tin atoms are in trans-position in the resulting octahedral arrangement.     

Synthesis, crystal structures, cytotoxicity and qualitative structure-activity relationship (QSAR) of cis-bis{5-[(E)-2-(aryl)-1-diazenyl]quinolinolato}di-n-butyltin(IV) complexes, (n)Bu2Sn(L)2

A series of cis-bis{5-[(E)-2-(aryl)-1-diazenyl]quinolinolato}di-n-butyltin(IV) complexes has been synthesized and characterized by ¹H-, ¹³C-, ¹¹⁹Sn NMR, ESI-MS (electrospray ionization mass spectrometry), IR and ^119mSn Mössbauer spectroscopic techniques in combination with elemental analyses. The structures of four di-n-butyltin(IV) complexes, viz., ⁿBu₂Sn(L³)₂ (3), ⁿBu₂Sn(L⁴)₂ (4), ⁿBu₂Sn(L⁵)₂ (5) and ⁿBu₂Sn(L⁷)₂ · 0.5C₆H₆ (7) (LH = 5-[(E)-2-(aryl)-1-diazenyl)quinolin-8-ol) were determined by single crystal X-ray diffraction. In general, the complexes were found to adopt a distorted cis-octahedral arrangement around the tin atom. These complexes retain their solid-state structure in non-coordinating solvent as evidenced by ¹¹⁹Sn and ¹³C NMR spectroscopic results. The in vitro cytotoxicity of di-n-butyltin(IV) complexes (3-8) is reported against seven well characterized human tumour cell lines. The basicity of the two quinolinolato donor N and O atoms of the ligands are discussed in relation to the cytotoxicity data.     

Organotin(IV) 4-methoxyphenylethanoates: Synthesis, spectroscopic characterization, X-ray structures and in vitro anticancer activity against human prostate cell lines (PC-3)

A series of organotin(IV) carboxylates, [Bu₂SnL₂] (1), [Et₂SnL₂] (2), [Me₂SnL₂] (3), [Bu₃SnL]_n(4), [Me₆Sn₂L₂]_n(5), [Ph₃SnL]_n(6) and [Oct₂SnL₂] (7), where L = O₂CCH₂C₆H₄OCH₃-4, have been synthesized. These complexes have been characterized by elemental analysis, FT-IR and multinuclear NMR (¹H, ¹³C and ¹¹⁹Sn). Based on spectroscopic results, the ligand appeared to coordinate to the Sn atom through COO moiety. Single crystal analysis has shown a bridging behavior of ligand in tributyl- and trimethyltin(IV) derivatives, and a chelating bidentate mode in diethyltin(IV) complex. Bioassay results have shown that these compounds have good antibacterial, antifungal and antitumor activity. The activity against prostate cancer cell lines (PC-3) decreased in the order 1 > 5 > 2 > 3 > 7.     

Diorganotin(IV) complexes of dipeptides containing the alpha-aminoisobutyryl residue (Aib): preparation, structural characterization, antibacterial and antiproliferative activities of [(n-Bu)2 Sn(H(-1)L)] (LH=H-Aib-L-Leu-OH, H-Aib-L-Ala-OH)

Two new organotin(IV) complexes with dianionic dipeptides containing the α-aminoisobutyryl residue (Aib) as ligands are described. The solid complexes [(n-Bu)₂Sn(H₋₁L_A)] · 2MeOH (1 · 2MeOH) (L_AH = H-Aib-L-Leu-OH) and [(n-Bu)₂Sn(H₋₁L_B)] · MeOH (2 · MeOH) (L_BH = H-Aib-L-Ala-OH) have been isolated and characterized by single-crystal X-ray crystallography and spectroscopic techniques (H₋₁L²⁻ is the dianionic form of the corresponding dipeptide). Complexes 1 · 2MeOH and 2 · MeOH are monomeric with similar molecular structures. The doubly deprotonated dipeptide behaves as a N(amino), N(peptide), O(carboxylate) ligand and binds to the Sn^IV atom. The five-coordinate metal ion has a distorted trigonal bipyramidal geometry. A different network of intermolecular hydrogen bonds in each compound results in very dissimilar supramolecular features. The IR, far-IR, Raman and ¹¹⁹Sn NMR data are discussed in terms of the nature of bonding and known structures. The antibacterial and antiproliferative activities as well as the effect of the new compounds on pDNA were examined. Complexes 1 and 2 are active against the gram-positive bacteria Bacillus subtilis and Bacillus cereus. The IC₅₀ values reveal that the two compounds express promising cytotoxic activity in vitro against a series of cell lines.     

Synthesis of diorganotin(IV) complexes with nucleosides and their Characterization by Mössbauer and infrared spectroscopy

A number of new complexes of R₂Sn^IV with adenosine, guanosine, inosine, cytidine and uridine were synthesized by reaction of ribonucleosides with diorganotin oxide in hot methanol. The complexes were characterized by infrared and ¹¹⁹Sn Mössbauer spectroscopy as O(2′), O(3′) (diorganostannylene) nucleosides; the occurence of dimers with three-co-ordinate oxygen atoms is inferred on the basis of spectroscopic data.     

Insertion reactions of CO2, OCS, and CS2 into the Sn-N bonds of (Me2N)2Sn: NMR and X-ray structural characterization of the products

The interactions of the heteroallenes CO₂, OCS, and CS₂ with (Me₂N)₂Sn have been investigated. These CX₂ species insert into the Sn-N bonds under mild conditions to provide products bis-(N,N-dimethylcarbamato)tin(II), [(Me₂NCO₂)₂Sn]₂, bis-(N,N-dimethylthiocarbamato)tin(II), [Me₂NC(O)S]₂Sn and bis-(N,N-dimethyldithiocarbamato)tin(II), (Me₂NCS₂)₂Sn. These molecules have been fully characterized by traditional spectroscopic methods as well as by X-ray crystallography. The [Me₂NC(O)S]₂Sn product is the first example of a structurally characterized Sn(II) thiocarbamate. The solid-state structures of the final products vary depending on the heteroallene inserted. The CO₂-inserted product is dimeric in the solid-state, with both bridging and chelating carbamate ligands. These dimers form a chain-like network via intermolecular Sn?O interactions. The monomeric thiocarbamate also shows a chain-like extended structure, through both Sn?O and Sn?S interactions, while the dithiocarbamate product has no significant intermolecular contacts.     

Organotin(IV) derivatives containing bis(diphenylphosphine)- and bis(diphenylphosphineoxo)alkanes

Di-organotin(IV)halides R₂SnCl₂ (R=Me or Ph) react with bis(diphenylphosphine)methane (DPPM) and bis(diphenylphosphine)ethane (DPPE) in ethanol in aerobic conditions yielding 1:1 adducts [R₂SnCl₂(DPPM–O₂)] and [R₂SnCl₂(DPPE–O₂)], respectively, containing the bis(diphenylphosphine) in oxidized form. The 1:1 adduct [SnMe₂Cl₂(DPPM–O₂)] is composed of separate molecules containing six-coordinate tin, with the ligands coordinated in the bidentate O₂-fashion, whereas [SnMe₂Cl₂(DPPE–O₂)] is polymeric, with octahedral and centrosymmetric (all trans) tin atoms. In inert atmosphere, the interaction between R₂SnCl₂ and DPPM or DPPE does not take place. Mono-organotin halides RSnCl₃ (R=Me, Buⁿ or Ph) react with DPPM and DPPE yielding 1:1 adducts [RSnCl₃(DPPM)] (R=Me, Buⁿ or Ph) and [RSnCl₃(DPPE)] (R=Buⁿ or Ph).     

Syntheses and spectroscopic and structural characterization of silver(I) complexes containing tris(isobutyl)phosphine and poly(azol-1-yl)borates

Silver(I) derivatives [Ag(L)(PⁱBu₃)] (L = H₂B(tz)₂ (dihydrobis(1H-1,2,4-triazol-1-yl)borate), HB(tz)₃ (hydrotris(1H-1,2,4-triazol-1-yl)borate), Tp (hydrotris(1H-pyrazol-1-yl)borate), Tp∗ (hydrotris(3,5-dimethyl-1H-pyrazol-1-yl)borate), Tp^Me (hydrotris(3-methyl-1H-pyrazol-1-yl)borate), Tp^CF3 (hydrotris(3-trifluoromethyl-1H-pyrazol-1-yl)borate), Tp^4Br (hydrotris(4-bromo-1H-pyrazol-1-yl)borate), HB(btz)₃ (hydrotris(1H-1,2,4-benzotriazol-1-yl)borate), Tm (hydrotris(3-methy-1-imidazolyl-2-thione)borate), pzTp (tetrakis(1H-pyrazol-1-yl)borate), pz⁰Tp^Me (tetrakis(3-methyl-1H-pyrazol-1-yl)borate) have been synthesized from the reaction of [Ag(NO₃)(PⁱBu₃)₂] with ML (M = Na or K) and characterized both in solution (¹H- and ³¹P{¹H} NMR, ESI MS spectroscopy, conductivity) and in the solid state (IR, single crystal X-ray structure analysis). These complexes are air-stable and light-sensitive and non-electrolytes in CH₂Cl₂ and acetone in which they slowly decompose, even with the strict exclusion of oxygen and light, yielding metallic silver and/or azolate (Az) species of formula [Ag(Az)(PⁱBu₃)_x] upon breaking of the bridging B-N_(azole) bond. The solid state structures of [Ag(Tp)(PⁱBu₃)], [Ag(Tp^Me)(PⁱBu₃)], [Ag(Tp^CF3)(PⁱBu₃)], [Ag{HB(btz)₃}(PⁱBu₃)], and [Ag(Tm)(PⁱBu₃)] show that the silver atom adopts a distorted tetrahedral coordination geometry. [Ag(L)(PPh₃)] can be easily obtained from the reaction of [Ag(L)(PⁱBu₃)] with excess PPh₃, whereas from the reverse reaction of [Ag(L)(PPh₃)] with PⁱBu₃a mixture of [Ag(L)(PⁱBu₃)] and [Ag(L)]₂ and [Ag(L)(PPh₃)] was recovered. ³¹P{¹H} NMR variable temperature NMR studies showed that in the pz⁰Tp^x derivatives the scorpionate ligand acts as a bidentate donor, whereas tridentate coordination is found for all tris(azolyl)borate derivatives, both in solution and in the solid state. ESI MS data suggest the existence in solution of species such as [Ag(PⁱBu₃)₂]⁺ upon dissociation of the L ligand, and also the formation of dimeric species of the form [Ag₂(L)(PⁱBu₃)₂]⁺.     

Self-assembled diorganotin(IV) moieties with 2,3,4,5-tetrafluorobenzoic acid: Syntheses, characterizations and crystal structures

A series of new organotin(IV) derivatives with 2,3,4,5-tetrafluorobenzoic acid: {[(2,3,4,5-F₄C₆HCO₂)R₂Sn]₂O}₂ (R = Et 1, n-Bu 2, Ph 3), [R₂Sn(O₂CC₆F₄H)₂]_n (R = n-Bu 4, Et 5, Ph 6), and Sn₂R₄(O₂CC₆F₄H)₃(OH) (R = Et 7, n-Bu 8, Ph 9), were synthesized by the reaction of diorganotin oxide and 2,3,4,5-tetrafluorobenzoic acid. All the complexes 1-9 have been characterized by elemental analysis, IR, ¹H, ¹³C, ¹¹⁹Sn NMR spectra. Among them complexes 2, 4, 8 were also characterized by X-ray crystallography diffraction analyses. The crystal structure of complex 2 exhibited a tetra-nuclear geometry with the Sn₂O₂ symmetry core. Complex 4 formed a 1D helical double-chain structure through intermolecular O→Sn coordinating and completed a DNA-like assembly. Complex 8 revealed that the both Sn atoms were held together by hydroxide and acetate bridges, forming a chair-like six-membered ring. Moreover, the supramolecular structures of dimer, 1D chain or 2D network have been found in complexes 4 and 8 by intermolecular C-H?F weak hydrogen bond and non-bonded F?F or F?Sn interaction, which were highly effective in the assembly of supramolecular structures and could lead to the formation of complexes with fascinating topologies properties.     

Synthesis, crystal structures and in vitro antibacterial activity of two novel organotin(IV) complexes

Two triorganotin(IV) carboxylates [nBu₃SnOL]_n (KK1) and [Ph₃SnOL]_n (KK2) have been prepared by the reactions of (E)-3-(4-(diphenylamino)phenyl)acrylic acid (HL) with n(Bu₃Sn)₂O and Ph₃Sn(OH), respectively. Complexes KK1 and KK2 have been structurally characterized by IR, elemental analysis and X-ray crystallography, confirming that both complexes possess infinite 1D chain structures. It’s exciting to discover that KK1 and KK2 exhibit strong solid-state luminescence emission while the HL almost quenches. Furthermore, both complexes were assayed for in vitro antibacterial activity against two Gram-positive bacterial strains (Bacillus subtilis ATCC 6633 and Staphylococcus aureus ATCC 6538) and two Gram-negative bacterial strains (Pseudomonas aeruginosa ATCC 13525 and Escherichia coli ATCC 35218) by MTT method. Complex KK2 exhibited powerful antibacterial activities against S. aureus with MIC value of 0.78 μg/mL, which was superior to the positive controls penicillin G. On the basis of the biological results, structure-activity relationships were discussed.     

Linkage isomerism in the metal complex hexa(thiocyanato)rhenate(IV): Synthesis and crystal structure of (NBu4)2[Re(NCS)6] and [Zn(NO3)(Me2phen)2]2[Re(NCS)5(SCN)]

The linkage isomers [Re(NCS)₆]^2? and [Re(NCS)₅(SCN)]^2? are obtained by the reaction of [ReBr₆]^2? with NCS^? in dimethylformamide. Some differences in the chemical behavior allowed their separation and structural characterization in the form of (NBu₄)₂[Re(NCS)₆] (1) and [Zn(NO₃)(Me₂phen)₂]₂[Re(NCS)₅(SCN)] (2), respectively (Bu = n-C₄H₉ and Me₂phen = 2,9-dimethyl-1,10-phenanthroline).     

Syntheses and crystal structures of di- and trimethyltin (IV) derivatives with phenylphosphonic acid

Three types of methyltin phosphonates, {[(CH₃)₃Sn]₄(O₃PPh)₂}_n (1), {[(CH₃)₃Sn]₂(O₃PPh) · CH₃OH}_n (2) and {[(CH₃)₂SnO₃PPh]₄}_n (3) were synthesized by the reaction of phenylphonic acid with trimethyltin (IV) chloride and dimethyltin (IV) dichloride, respectively. Complexes 1, 2 and 3 were characterized by elemental analysis, IR, NMR (¹H, ¹³C, ³¹P and ¹¹⁹Sn) spectroscopy, TGA and X-ray crystallography diffraction analysis. The X-ray analysis of complex 1 shows that the structure is a polymeric infinite 1D zigzag chain. In complex 2, the oxygen atom of methanol molecule is coordinated to the tin atoms, and a 2D network is generated via O–H?O hydrogen bonds. In complex 3, a novel 2D network containing 12-membered (Sn₃O₆P₃) rings is formed.     

Syntheses and crystal structures of trimethyltin(IV) coordination polymers based on mixed ligands of 5-nitroisophthalate and 2,2′(4,4′)-bipy or phen

The trimethyltin(IV) polymer [(Me₃Sn)₂(nip) · EtOH]_n (1) of 5-nitroisophthalic acid (H₂nip) and its three derivatives with mixed organic N-donor ligands 2,2′-bipy [(Me₃Sn)₂(nip) · 2H₂O] · [(Me₃Sn)₂(nip) · H₂O] · 2(2,2′-bipy) (2) 4,4′-bipy {[(Me₃Sn)₂(nip)]₂(4,4′-bipy)}_n (3) or phen [(Me₃Sn)₂(nip) · H₂O] · (phen) (4) have been synthesized by the reaction of trimethyltin(IV) chloride and H₂nip when sodium ethoxide was added in the presence of 2,2′-bipy 4,4′-bipy or phen. All complexes 1–4 were characterized by elemental, IR, ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy and X-ray crystallography analyses. Crystal, data collection and structure refinement parameters for complexes 1, 2, 3 and 4 are shown in Table 1, Table 2, respectively. The X-ray data showed the geometries of all the tin atoms in complexes 1–4 are trigonal bipyramidal. The X-ray analysis of 1 showed that the structure was a polymeric infinite chain with neighboring triorganotin centers being linked by dicarboxylate ligands and hydrogen bonds were found between adjacent chains. For 2, two different monomers were found, in one monomer, Me₃Sn were coordinated to both carboxyl groups of the ligand and water molecules were coordinated to the two Sn(IV) centers. In the other monomer, water molecules were coordinated to only one Sn center. Co-crystallized2,2′-bipy was found in 2 and a 2D supermolecular structure was formed via O–H⋯O and O–H⋯N (N atoms derived from 2,2′-bipy) hydrogen bonds. In 3 however, a 2D polymeric block was formed due to the inversion center of the 4,4′-bipy. For 4, due to the O–H⋯O and O–H⋯N (N atoms derived from phen) hydrogen bonds and intermolecular Sn⋯O bonds, a 2D polymeric structure was formed.     

Synthesis and structural investigation of sandwich polyoxotungstates containing cerium (III/IV) and mono-lacunary Keggin tungstophosphate units

The two isostructural anions, [Ce^III(α-PW₁₁O₃₉)₂]¹¹⁻ and [Ce^IV(α-PW₁₁O₃₉)₂]¹⁰⁻, both composed of Ce^III/IV sandwiched by two mono-lacunary Keggin units [α-PW₁₁O₃₉]⁷⁻, were isolated as dimethylammonium salts and structurally characterized by single-crystal X-ray diffraction analysis. The structures of the [Ce^III/IV(α-PW₁₁O₃₉)₂]^11−/10− anions exhibit two enantiomers d- and l-forms due to C₂ (2) symmetry from the square-antiprismatic coordination of the central Ce^III/IVO₈ polyhedron. The Ce^III compound crystallizes in achiral space group P2₁/n, while the Ce^IV analog in chiral space group P2₁ shows spontaneous resolution without any chiral auxiliaries. The correlation between the ionic radius of the central metal (M) and twist angle of the two mono-lacunary units was studied for a series of [M(α-PW₁₁O₃₉)₂]ⁿ⁻ (M = Ce^III/IV, Eu^III, Zr^IV, Hf^IV) anions and explained in terms of steric repulsion between the O atoms in the mono-lacunary units.     

Diorganotin(IV) N-acetyl-l-cysteinate complexes: Synthesis, solid state, solution phase, DFT and biological investigations

Diorganotin(IV) complexes of N-acetyl-l-cysteine (H₂NAC; (R)-2-acetamido-3-sulfanylpropanoic acid) have been synthesized and their solid and solution-phase structural configurations investigated by FTIR, Mössbauer, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. FTIR results suggested that in R₂Sn(IV)NAC (R = Me, Bu, Ph) complexes NAC²⁻ behaves as dianionic tridentate ligand coordinating the tin(IV) atom, through ester-type carboxylate, acetate carbonyl oxygen atom and the deprotonated thiolate group. From ¹¹⁹Sn Mössbauer spectroscopy it could be inferred that the tin atom is pentacoordinated, with equatorial R₂Sn(IV) trigonal bipyramidal configuration. In DMSO-d₆ solution, NMR spectroscopic data showed the coordination of one solvent molecule to tin atom, while the coordination mode of the ligand through the ester-type carboxylate and the deprotonated thiolate group was retained in solution. DFT (Density Functional Theory) study confirmed the proposed structures in solution phase as well as the determination of the most probable stable ring conformation. Biological investigations showed that Bu₂SnCl₂ and NAC2 induce loss of viability in HCC cells and only moderate effects in non-tumor Chang liver cells. NAC2 showed lower cytotoxic activity than Bu₂SnCl₂, suggesting that the binding with NAC²⁻ modulates the marked cytotoxic activity exerted by Bu₂SnCl₂. Therefore, these novel butyl derivatives could represent a new class of anticancer drugs.     

Methyl-palladium(II) complexes of pyridine-bridged bis(nucleophilic heterocyclic carbene) ligands: Substituent effects on structure,stability, and catalytic performance

A series of discrete, mononuclear palladium(II)–methyl complexes, together with several palladium(II)–chloro analogues, of pyridine-functionalised bis-NHC ligands have been prepared via ligand transmetallation from the silver(I)-NHC complexes. The reported complexes comprise examples with both the methylene-bridged 2,6-bis[(3-R-imidazolin-2-yliden-1-yl)methyl]pyridine (_RC^∧N^∧C; R = Mes, dipp, ^tBu) and planar 2,6-bis(3-R-imidazolin-2-yliden-1-yl)pyridine (_RCNC; R = Mes, dipp) ligands and, when combined with the previously reported _MeC^∧N^∧C/_MeCNC examples, cover a broad spectrum of ligand substituent steric and electronic properties, including the bulky Mes and dipp groups frequently used in catalytic applications. The palladium(II) complexes have been characterised by a variety of methods, including single crystal X-ray crystallography, with the shielding of the Pd–Me groups in the proton NMR spectra of some of the N-aryl substituted examples correlated with the proximity of the aryl rings to the methyl group in the solid state structures. The [PdMe(_RC^∧N^∧C/_RCNC)]⁺ complexes undergo thermal degradation via reductive methyl-NHC coupling to give 2-methyl-3-R-imidazolium-1-yl species with relative stabilities in the order of [PdMe(_MesC^∧N^∧C)]BF₄ > [PdMe(_MeC^∧N^∧C)]BF₄ ≈ [PdMe(_MesCNC)]BF₄ > [PdMe(_MeCNC)]BF₄ > [PdMe(_tBuC^∧N^∧C)]BF₄ ≫ [PdMe(_tBuCNC)]BF₄ (not isolable). A comparison of the activity of the complexes as precatalysts in a model Heck coupling reaction shows greatest activity in those species bearing bulkier N-substituents, with complexes bearing _RC^∧N^∧C ligands generally more efficient precatalysts than those bearing _RCNC ligands.     

Synthesis and structure of monoribbed-functionalized disulfide iron(II) clathrochelates and their coordination as the ligands toward platinum(II) and platinum(IV) ions

Disulfide monoribbed-functionalized clathrochelates (i.e., fuctionalization of one of the three α-dioximate fragments) with ribbed thioalkyl, S₃-thioalkyl and hydroxythioalkyl substituents have been synthesized starting from the FeBd₂(Cl₂Gm)(BF)₂ precursor (where Bd²⁻ and Cl₂Gm²⁻ are α-benzyldioxime and dichloroglyoxime dianions) using the corresponding thiol/triethylamine system in dichloromethane solution. Clathrochelate S₆-dithiol in basic media underwent the intramolecular dealkylation to yield the S₃-thiocrown etheric clathrochelate. Clathrochelates obtained have been studied as the ligands toward Pt²⁺ and Pt⁴⁺ ions. The S-demethylation reaction of the methylsulfide complex with [PtCl₄]²⁻ dianion produced the polynuclear complexes of the dianionic clathrochelate dithiolate ligand. The reaction of n-butylsulfide clathrochelate with the trans-Pt^IVCl₄(C₆H₅CH₂CN)₂ afforded the binuclear compound with the disulfide iron(II) clathrochelate as a monodentate ligand. The obtained macrobicycles, their clathrochelate derivatives, and polynuclear complexes have been characterized using elemental analysis, MALDI-TOF and PD mass, IR, UV-Vis, and NMR spectra, and X-ray crystallography. The encapsulated iron(II) ion coordination polyhedra distortion angle φ values and the main distances in the molecules of polynuclear complexes have been deduced (obtained) using ⁵⁷Fe Mössbauer parameters and EXAFS data, respectively.     

The preparation,spectral studies,and the crystal structure of dimethylbis(O-ethylxanthato)tin(IV)

Tin-119 NMR data indicate that the tin atom in (CH₃)₂Sn(S₂COC₂H₅)₂ is four co-ordinated in dichloromethane solution. However, single crystal X-ray analysis shows the tin atom to be six co-ordinated in the solid state in which the bidentate xanthate ligands display gross asymmetry in their mode of co-ordination to the tin. The crystals are molecular and there is no association between neighbouring molecules. The unit cell of Me₂Sn(exa)₂ is orthorhombic, Pnma, a = 14.165(1), b = 7.675(9), c = 13.977(2) Å with Z = 4. The structure was refined by conventional least squares methods with final R 0.041 and R_w 0.043 for 1229 unique reflections with 1 ? 2σ(I).