SYNTHESIS AND CHARACTERIZATION OF A SERIES OF LIPOPHILIC CISPLATIN ANALOGS WITH CIS-1,4-DIAMINOCYCLOHEXANE AS NONLEAVING AMINE LIGAND

Abstract

A series of lipophilic platinum(II) complexes of the type [Pt(cis-1,4-DACH)L₂] (where cis-1,4-DACH = cis-1,4-diaminocyclohexane and L = acetate, propionate, butyrate, valerate, hexanoate, heptanoate, octanoate, 2,2′-dimethyloctanoate, nonanoate, decanoate, undecanoate, laureate, tridecanoate, myristate, pentadecanoate, palmitate, heptadecanoate, stearate, nonadecanoate, or eicosanoate) has been synthesized and characterized by elemental analysis and by infrared, ¹³C, and ¹⁹⁵Pt nuclear magnetic resonance spectroscopic techniques.     

Synthesis and Characterization of New 1-Methyl-4-(Methylamino)Piperidine and Decahydroquinoline Platinum(II) Complexes Containing Disubstituted Sulfide as a Leaving Group

A series of cationic platinum(II) complexes of the type [Pt(mmap)R'R"S)Cl](NO₃) and [Pt(dhq)₂(R'R"S)Cl]-(NO₃) (where mmap=1-methyl-4-(methylamino)piperidine; dhq=decahydroquinoline; and R'R"S=dimethylsulfide, diethylsulfide, diisopropylsulfide, diphenylsulfide, dibenzylsulfide, methylphenylsulfide or methyl-p-tolylsulfide) has been synthesized and characterized by elemental analysis, infrared, ¹H and ¹⁹⁵Pt nuclear magnetic resonance spectroscopic techniques.     

Synthesis characterization and X-ray crystal structures of cis-1,4-diaminocyclohexane-platinum(II) nucleobase adducts

Platinum complexes of the type [Pt(cis-1,4-DACH)(L)₂]X, where cis-1,4-DACH = cis-1,4-diaminocyclohexane; L = adenine (ade) (1), hypoxanthine (hyp) (2), 9-methylguanine (9-megua) (3), cytosine (cyt) (4), or 1-methylcytosine (1-mecyt) (5); and X = SO₄ or Cl₂ groups, were synthesized and characterized by elemental analysis and by ¹H, ¹³C, and ¹⁹⁵Pt nuclear magnetic resonance spectroscopy. The crystals of [Pt(cis-1,4-DACH)(9-megua)₂]SO₄[9-megua-H]₂SO₄ (3) and [Pt(cis-1,4-DACH)(1-mecyt)₂]Cl₂ · 6H₂O (5) were also subjected to single-crystal X-ray diffraction. The base/PtN4 coordination plane dihedral angles were 74.55° and 85.61° in complex 3 and 78.12° and 81.80° in complex 5. The platinum had distorted square planar geometry in both complexes; the two adjacent corners were occupied by the two nitrogen atoms of cis-1,4-DACH, and the other two corners were occupied by the two N7 atoms of 9-megua in complex 3 and the two N3 atoms of 1-mecyt in complex 5. The cis-1,4-DACH, which has a unique twist-boat configuration, formed a seven-member chelating ring with platinum, which led to considerable strain during bidentate cis-1,4-DACH binding. Cations of both complexes 3 and 5 adopted C₂ molecular symmetry. These adducts were the models for the intrastand cross-links that were relevant to the binding of the Pt(II) antitumor drugs to DNA.     

Platinum(II) Mixed Ligand Complexes with Thiourea Derivatives,Dimethyl Sulphoxide and Chloride: Syntheses,Molecular Structures,and ESCA Data

The platinum(II) mixed ligand complexes [PtCl(L^1‐6)(dmso)] with six differently substituted thiourea derivatives HL, R₂NC(S)NHC(O)R′ (R = Et, R′ = p‐O₂N‐Ph: HL¹; R = Ph, R′ = p‐O₂N‐Ph: HL²; R = R′ = Ph: HL³; R = Et, R′ = o‐Cl‐Ph: HL⁴; R₂N = EtOC(O)N(CH₂CH₂)₂N, R′ = Ph: HL⁵) and Et₂NC(S)N=CNH‐1‐Naph (HL⁶), as well as the bis(benzoylthioureato‐κO, κS)‐platinum(II) complexes [Pt(L^{1, 2})₂] have been synthesized and characterized by elemental analysis, IR, FAB(+)‐MS, ¹H‐NMR, ¹³C‐NMR, as well as X‐ray structure analysis ([PtCl(L¹)(dmso)] and [PtCl(L^{3, 4})(dmso)]) and ESCA ([PtCl(L^{1, 2})(dmso)] and [Pt(L^{1, 2})₂]). The mixed ligand complexes [PtCl(L)(dmso)] have a nearly square‐planar coordination at the platinum atoms. After deprotonation, the thiourea derivatives coordinate bidentately via O and S, DMSO bonds monodentately to the Pt^II atom via S atom in a cis arrangement with respect to the thiocarbonyl sulphur atom. The Pt—S‐bonds to the DMSO are significant shorter than those to the thiocarbonyl‐S atom. In comparison with the unsubstituted case, electron withdrawing substituents at the phenyl group of the benzoyl moiety of the thioureate (p‐NO₂, o‐Cl) cause a significant elongation of the Pt—S(dmso)‐bond trans arranged to the benzoyl‐O—Pt‐bond. The ESCA data confirm the found coordination and bonding conditions. The Pt 4f_7/2 electron binding energies of the complexes [PtCl(L^{1, 2})(dmso)] are higher than those of the bis(benzoylthioureato)‐complexes [Pt(L^{1, 2})₂]. This may indicate a withdrawal of electron density from platinum(II) caused by the DMSO ligands.     

DNA-binding and cleavage activity of polypyridyl ruthenium(II) complexes

Polypyridyl ruthenium(II) complexes [Ru^II(3-bptpy)(dmphen)Cl]ClO₄ (1), [Ru^II(3-cptpy)(dmphen)Cl]ClO₄ (2), [Ru^II(2-tptpy)(dmphen)Cl]ClO₄ (3), and [Ru^II(9-atpy)(dmphen)Cl]ClO₄ (4) {where 3-bptpy?=?4′-(3-bromophenyl)-2,2′:6′,2″-terpyridine, 3-cptpy?=?4′-(3-chlorophenyl)-2,2′:6′,2″-terpyridine, 2-tptpy?=?4′-(2-thiophenyl)-2,2′:6′,2″-terpyridine, 9-atpy?=?4′-(9-anthryl)-2,2′:6′,2″-terpyridine, dmphen?=?2,9-dimethyl-1,10-phenanthroline} have been synthesized and characterized. The DNA-binding properties of the complexes with Herring Sperm DNA have been investigated by absorption titration and viscosity measurements. The ability of complexes to break the pUC19 DNA has been checked by gel electrophoresis. The experimental results suggest that all the complexes bind DNA via partial intercalation. The results also show that the order of DNA-binding affinities of the complexes is 4?<?3?<?2?<?1, confirming that planarity of the ligand in a complex is very important for DNA-binding.     

NMR and kinetic studies of the interactions of [Au(cis-DACH)Cl2]Cl and [Au(cis-DACH)2]Cl3 with potassium cyanide in aqueous solution

The interactions of [Au(cis-DACH)Cl₂]Cl and [Au(cis-DACH)₂]Cl₃ [where cis-DACH is cis-1,2-diaminocyclohexane] with enriched KCN were carried out in CD₃OD and D₂O, respectively. The reaction pathways of these complexes were studied by ¹H, ¹³C, ¹⁵N NMR, UV spectrophotometry, and electrochemistry. The kinetic data for the reaction of cyanide with [Au(cis-DACH)₂]Cl₃ are k = 18 M^?1s^?1, ?H^≠ = 11 kJ M^?1, ?S^≠ = ?185 JK^?1 M^?1, and E_a = 13 kJ M^?1 with square wave voltammetric (SWV) peak +1.35 V, whereas the kinetic data for the reaction of cyanide ion with [Au(cis-DACH)Cl₂]Cl are k = 148 M^?1s^?1, ?H^≠ = 39 kJM^?1, ?S^≠ = ?80 JK^-1 M^?1, and E_a = 42 kJM^?1 along with SWV peak +0.82 V, indicating much higher reactivity of [Au(cis-DACH)Cl₂]Cl toward cyanide than [Au(cis-DACH)₂]Cl₃. The interaction of these complexes with potassium cyanide resulted in an unstable [Au(¹³CN)₄]^? species which readily underwent reductive elimination reaction to generate [Au(¹³CN)₂]^? and cyanogen.     

Platinum(II) Mono-N1-(2"-Tetrahydrofuranyl)-5-Fluorouracilate Complexes with Ammonia

The reaction between cis-[Pt(NH₃)₂Cl₂], N¹-(2"-tetrahydrofuranyl)-5-fluorouracil (HL), and NaOH (taken in a molar ratio of 1 : 1 : 1) or between cis-[Pt(NH₃)₂Cl₂], HL, and Ag₂O (taken in the molar ratio of 1 : 1 : 0.5) was used to synthesize complexes Ia (in the case of NaOH) or Ib (in the case of Ag₂O) with composition Pt(NH₃)₂LCl. The model complex [Pt(NH₃)₃L]NO₃ (II) was synthesized by the reaction between [Pt(NH₃)₃Cl]Cl, HL, AgNO₃, and Ag₂O (1 : 1 : 1 : 0.5). The obtained compounds were characterized by chemical analysis, chromatography, thermogravimetry, conductometry, potentiometry, IR, electronic, and NMR spectroscopies. Complexes Ia and Ib were found to have both similar and different properties. The structures of the compounds and the type of L^– coordination to platinum(II) were suggested. Cytotoxic properties of Iaand Ib were studied.     

Charge-Transfer Salts of Ferrocene Derivatives with Bis(maleonitriledithiolato)metallate(III) Complexes ([M(mnt)2]−, M=Ni,Pt): A Ground-State High-Spin [(Ni(mnt)2)2]2− Dimer

New hexamethylated ferrocene derivatives containing thioether moieties (1,1′-bis[(tert-butyl)thio]-2,2′,3,3′,4,4′-hexamethylferrocene ( 3a , b )) or fused S-heteropolycyclic substituents (rac-1-[(1,3-benzodithiol- 2-yliden)methyl]-2,2′,3,3′,4,4′-hexamethylferrocene ( 5 ) and rac-1-[1,2-bis(1,3-benzodithiol-2-yliden)ethyl]-2,2′,3,3′,4,4′-hexamethylferrocene ( 14 )), as well as a series of ferrocene-substituted vinylogous tetrathiafulvalenes (1,1′-bis[1,2-bis(1,3-benzodithiol-2-yliden)ethyl]ferrocene ( 6a ), 1,1′-bis[1-(1,3-benzodithiol-2-yliden)-2-(5,6-dihydro-1,3-dithiolo[4,5-b] [1,4]dithiin-2-yliden)ethyl]ferrocene ( 6b ), [1,2-bis(1,3-benzodithiol-2-yliden)ethyl]ferrocene ( 21a ), [1-(1,3-benzodithiol-2-yliden)-2-(5,6-dihydro-1,3-dithiolo[4,5-b] [1,4]dithiin-2-yliden)ethyl]ferrocene ( 21b ), [1,2-bis(5,6-dihydro-1,3-dithiolo[4,5-b] [1,4]dithiin-2-yliden)ethyl]ferrocene ( 21c ), [1-(5,6-dihydro-1,3-dithiolo[4,5-b] [1,4]dithiin-2-yliden)-2-(1,3-benzodithiol-2-yliden)ethyl]ferrocene ( 21d )) were prepared and fully characterized. Their redox properties show that some of them are easily oxidized and undergo transformation to paramagnetic salts containing bis(maleonitriledithiolato)-metallate(III) anions [M(mnt)₂]⁻ (M=Ni, Pt; bis[2,3-dimercapto-κS)but-2-enedinitrilato(2⁻)]nickelate (1⁻) or -platinate (1⁻). The derivatives [ 3a ] [Ni(mnt)₂] ( 26 ), [ 3a ] [Pt(mnt)₂] ( 27 ), [Fe{(η⁵-C₅Me₄S)₂S}] [Ni(Mnt)₂] ( 28 ), [Fe{(η⁵-C₅Me₄S)₂S}] [Pt(mnt)₂] ( 29 ), [ 5 ] [Ni(mnt)₂]⋅ClCH₂CH₂Cl ( 30 ), [ 6a ] [Ni(mnt)₂] ( 31 ), [ 6a ] [Ni(mnt)₂]⋅ClCH₂CH₂Cl ( 31a ), [ 6a ] [Pt(mnt)₂] [ 32 ), and [ 6b ] [Ni(mnt)₂] ( 33 ) were prepared and fully characterized, including by SQUID (superconducting quantum interference device) susceptibility measurements. X-Ray crystal-structural studies of the neutral ferrocene derivatives 6a , b , 21c , d , and 1,1′-bis[1-(1,3-benzodithiol-2-yliden)-2-oxoethyl]ferrocene ( 23 ), as well as of the charge-transfer salts 26 – 28 , 30 , and 31a , are reported. The salts 28 and 30 display both a D⁺A⁻A⁻D⁺ structural motif, however, with a different relative arrangement of the [{Ni(mnt)₂}₂]²⁻ dimers, thus giving rise to different but strong antiferromagnetic couplings. Salt 26 exhibits isolated ferromagnetically coupled [{Ni(mnt)₂}₂]²⁻ dimers. Salt 27 displays a D⁺A⁻D⁺A⁻ structural motif in all three space dimensions, and a week ferromagnetic ordering at low temperature. Salt 31a , on the contrary, shows segregated stacks of cations and anions. The cations are connected with each other in two dimensions, and the anions are separated by a 1,2-dichloroethane molecule.     

Mass spectra of some (Z)-α-Phenyl-β-(2-thienyl)acrylonitriles

The mass spectra of some (Z)α-(4-R′-phenyl)-β-(2-thienyl-5-R)acrylonitriles (R = H, CH₃, Br; R′ = H, CH₃O, CH₃, Cl, NO₂) at 70 eV are reported. Mass spectra exhibit pronounced molecular ions. The compound's where R = H, and CH₃ are characterized by the occurrence of a strong [M - H]⁺ peak. Moreover, in all the compounds a m/z 177 peak occurs. In the compounds where R = H, [M - HS]* and [M - CHS]* ions are present except the nitroderivatives. Where R = CH₃, [M - HS]⁺ ion occurs.     

Tin(II) Halide Insertion or Halogen Exchange in the Reactions of Dihaloplatinum(II) Complexes with Tin(II) Halide

Reactions of SnCl₂ with the complexes cis‐[PtCl₂(P₂)] (P₂=dppf (1,1′‐bis(diphenylphosphino)ferrocene), dppp (1,3‐bis(diphenylphosphino)propane=1,1′‐(propane‐1,3‐diyl)bis[1,1‐diphenylphosphine]), dppb (1,4‐bis(diphenylphosphino)butane=1,1′‐(butane‐1,4‐diyl)bis[1,1‐diphenylphosphine]), and dpppe (1,5‐bis(diphenylphosphino)pentane=1,1′‐(pentane‐1,5‐diyl)bis[1,1‐diphenylphosphine])) resulted in the insertion of SnCl₂ into the Pt? Cl bond to afford the cis‐[PtCl(SnCl₃)(P₂)] complexes. However, the reaction of the complexes cis‐[PtCl₂(P₂)] (P₂=dppf, dppm (bis(diphenylphosphino)methane=1,1′‐methylenebis[1,1‐diphenylphosphine]), dppe (1,2‐bis(diphenylphosphino)ethane=1,1′‐(ethane‐1,2‐diyl)bis[1,1‐diphenylphosphine]), dppp, dppb, and dpppe; P=Ph₃P and (MeO)₃P) with SnX₂ (X=Br or I) resulted in the halogen exchange to yield the complexes [PtX₂(P₂)]. In contrast, treatment of cis‐[PtBr₂(dppm)] with SnBr₂ resulted in the insertion of SnBr₂ into the Pt? Br bond to form cis‐[Pt(SnBr₃)₂(dppm)], and this product was in equilibrium with the starting complex cis‐[PtBr₂(dppm)]. Moreover, the reaction of cis‐[PtCl₂(dppb)] with a mixture SnCl₂/SnI₂ in a 2 : 1 mol ratio resulted in the formation of cis‐[PtI₂(dppb)] as a consequence of the selective halogen‐exchange reaction. ³¹P‐NMR Data for all complexes are reported, and a correlation between the chemical shifts and the coupling constants was established for mono‐ and bis(trichlorostannyl)platinum complexes. The effect of the alkane chain length of the ligand and Sn^II halide is described.     

Synthesis of N-[chloro(diorganyl)silyl]anilines

A series of N-[chloro(diorganyl)silyl]anilines RR′Si(NR″Ph)Cl (R, R′ = Me, Ph, CH₂=CH, ClCH₂, Cl(CH₂)₃; R″ = H, Me) was prepared via the reaction of diorganyldichlorosilanes with aniline or N-ethylaniline in the presence of triethylamine.     

SYNTHESIS AND CHARACTERIZATION OF A SERIES OF LIPOPHILIC CISPLATIN ANALOGS WITH PIPERIDINE AS NONLEAVING AMINE LIGAND

Abstract

A series of lipophilic platinum(II) complexes of the type cis-[Pt(PIP)₂ L ₂] where PIP = piperidine and L = acetate, propionate, butanoate, pentanoate, hexanoate, heptanoate, octanoate, nonanoate, decanoate, undecanoate, laurate, tridecanoate, myristate, pentadecanoate, palmitate, heptadecanoate, stearate, nonadecanoate and eicosanoate has been synthesized and characterized by elemental analysis, and by infrared, ¹³C and ¹⁹⁵Pt nuclear magnetic resonance spectroscopic techniques. The complexes have been prepared as potential antitumor agents for liposome entrapment.     

The infrared spectra of imidazole complexes of platinum(II) halides and nitrite

Summary The i.r. spectra (4000-90 cm^–1) of the [Pt(Him)₄]X₂ complexes (Him = imidazole, X = Cl, Br or I) andcis- andtrans-[Pt(Him)₂X₂] (X = Cl, Br, I or NO₂) and their D₃-labelled analogues have been determined. The distinction between the ring and C-H (or N-H) modes of imidazole is based on the relative shifts which these bands undergo on D₃-labelling. Assignments, based on the effects of imidazole deuteriation and halide substitution, are provided for the v(Pt-Him) and v(Pt-X) modes.     

Synthesis and DNA-binding properties of binuclear platinum complexes with two <Emphasis Type="Italic">trans</Emphasis>-[Pt(NH<Subscript>3</Subscript>)<Subscript>2</Subscript>Cl]<Superscript>+</Superscript> units bridged by 4,4′-dipyridyl sulfide or selenide

Two novel dinuclear platinum complexes, {trans-[Pt(NH₃)₂Cl]₂(dpsu)}(NO₃)₂ (1) and {trans-[Pt(NH₃)₂Cl]₂ (dpse)}(NO₃)₂ (2) (dpsu = 4,4-dipyridyl sulfide and dpsu = 4,4-dipyridyl selenide) have been prepared for use as potential antitumor drugs. Compared to the known monofunctional complex, [cis-Pt(NH₃)₂Cl(4-methylpyridine)]NO₃, (1) exhibits an almost two-fold stronger DNA-binding ability, a result suggesting that (1) may bind bifunctionally to DNA. Kinetic studies show that (1) significantly impedes intercalation of ethidium bromide (EtdBr) into DNA in 0.3 mol dm^–3 KNO₃ but not in 0.3 mol dm^–3 KCl, indicating that the hydrolysis is the first step upon addition of the complex to DNA. Also, the complex may interact with DNA by non-intercalation. Unlike its dinuclear analogs linked by aliphatic diamines, complex (1) does not induce a transition of poly(dG–dC) · poly(dG–dC) from the B form to the Z form. Moreover, complex (1) significantly inhibits the cleavage activity of BamHI endonuclease, but has no effect on that of EcoRI endonuclease. In contrast, its cis analog containing two [cis-Pt(NH₃)₂Cl]⁺ units greatly inhibits those of both BamHI and EcoRI, a result suggesting that the two isomers with the same aromatic ligand probably have different properties of DNA binding, and that (1) possibly shows higher DNA-binding selectivity than its cisanalog.     

Mixed dimethyl sulfoxide-thiocarbamic ester complexes of platinum(II) halides

Summary The platinum(II) halidecis-[Pt(DMTC)(DMSO)X₂] andcis-[Pt(DETC)(DMSO)X₂](X=Cl or Br; DMSO=dimethyl sulfoxide; DMTC=EtOSCN-Me₂; DETC=EtOSCNEt₂) adducts and the platinum(II) and palladium(II) halide adducts,trans-[M(DETC)₂X₂] (M=Pt or Pd; X=Cl or Br), have been prepared. The complexes were characterized by i.r., and¹H and¹³Cn.m.r. spectroscopy. Both DMTC and DETC coordinate through the sulphur atoms. The 1:2 DETC complexes present the usualtrans configuration, whereas the presence of DMSO favourscis geometry in the mixed species.     

INTERACTION OF 2,4,6-TRINITROTOLUENE AND ITS ANALOGUES WITH ALDEHYDES. SYNTHESIS OF BENZOANNELATED HETEROCYCLES FROM THE PRODUCTS OF CONDENSATION

ABSTRACT

2,4,6-Trinitrotoluene (TNT) and its sulfonyl analogue 2-isobutylsulphonyl-4,6-dinitrotoluene undergo smooth condensation with chloral and fluoral to give 2-R-4,6-dinitrophenyl-1-(trihalomethyl)ethanols which easily cyclize to give 4-R-6-nitro-2-trihalomethyl-2,3-dihydrobenzo[b]furans (R=NO₂, i-Bu; halogen = F or Cl) in the presence of K₂CO₃. 2-R′-sulphonyl-4,6-dinitrotoluenes, prepared from TNT, condense with aromatic aldehydes to form 1-(2-R′-sulphonyl-4,6-dinitro)-2-arylethenes in which the ortho-nitro group, upon interaction with NaN₃ was selectively substituted by the azido group. Thermolysis of the obtained azides gave 2-aryl-4-R′-sulphonyl-6-nitroindoles (R′ = Ph, i-Bu, PhCH₂). Such N-methylated indole (R′ = i-Bu) was regioselectively aminated.     

Preparation and Properties of trans-[CoCl2(tmd>)2]Cl,and trans- and cis-[Co(NCS)2(tmd)2]NO3 (tmd: Tetramethylenediamine)

The cobalt(III) complexes [CoX₂(tmd)₂]⁺ (X: Cl^? or NCS^?, tmd: tetramethylenediamine), in which tmd forms a seven-membered chelate ring, have been prepared. Trans-[CoCl₂(tmd)₂]Cl was derived from [Co(NO₂)₂(tmd)₂]NO₃ in a fairly good yield. Two geometrical isomers, trans and cis, of [Co(NCS)₂-(tmd)₂]NO₃ were independently synthesized from trans-[CoCl₂(tmd)₂]Cl by different methods. The geometrical configurations of the isomeric pair of the NCS complex have been determined based on chromatographic behavior, electronic absorption spectra, and vibrational spectra. The d-d and CT absorption maxima of the NCS complex (18.7 x 10³cm^?1 (ε = 275) and 30.9 x 10³cm^?1 (ε = 3630) for the trans isomer, 19.3 x 10³cm^?1 (ε = 302) and 31.0 x 10³cm^?1 (ε = 4070) for the cis isomer) and the Co-N(amine) stretching frequency of trans-[CoCl₂(tmd)₂]Cl (418 cm^?1) have been compared with those of the corresponding ethylenediamine and trimethylenediamine complexes.     

Reactions of cisplatin hydrolytes, cis-[Pt(15NH3)2(H2O) 2]2+, with N-acetyl-L-cysteine

The reaction of cis-[Pt(¹⁵NH₃)2(H₂O) ₂] ²⁺ (3) with N-acetylcysteine [H₃accys] was investigated in aqueous solution. In this reaction, the ammine in the platinum complex formed was liberated. A mono-dentate sulfur-boundplatinum(II) product cis-[Pt(¹⁵NH₃)₂(H₂O)(H2accys-S)]⁺ (7) and six-membered che-late ring complex cis-[Pt(¹⁵NH₃)₂ (Haccys-S,O)] (8) were formed in solution. The dinuclear sulfur-bridged complex 9, giving a broad peak in ¹⁵N NMR, was also observed, but only present in very tiny amounts. The mass spectrometry (ES-MS) was undertaken from this re action, and the product detected was only the dinuclear sulfur bridged platinum species and species related to it by ammine loss.     

A kinetic investigation into the rate of chloride substitution from chloro terpyridine platinum(II) and analogous complexes by a series of azole nucleophiles

The substitution kinetics of the complexes [Pt(terpy)Cl]Cl·2H₂O (PtL1), [Pt(^tBu₃terpy)Cl]ClO₄ (PtL2), [Pt{4′-(2′′′-CH₃-Ph)terpy}Cl]BF₄ (PtL3), [Pt{4′-(2′′′-CF₃-Ph)terpy}Cl]CF₃SO₃ (PtL4), [Pt{4′-(2′′′-CF₃-Ph)-6-Ph-bipy}Cl] (PtL5) and [Pt{4′-(2′′′-CH₃-Ph)-6-2′′-pyrazinyl-2,2′-bipy}Cl]CF₃SO₃ (PtL6) with the nucleophiles imidazole (Im), 1-methylimidazole (MIm), 1,2-dimethylimidazole (DIm), pyrazole (Pyz) and 1,2,4-triazole (Trz) were investigated in a methanolic solution of constant ionic strength. Substitution of the chloride ligand from the metal complexes by the nucleophiles was investigated as a function of nucleophile concentration and temperature under pseudo first-order conditions using UV/Visible and stopped-flow spectrophotometric techniques. The reactions follow the rate law k_\textobs = k₂ [ \textNu ] + k _{- 2} k_{\text{obs}} = k_{2} \left[ {\text{Nu}} \right] + k_{ - 2} . The results indicate that changing the nature or distance of influence of the substituents on the terpy moiety affects the π-back-donation ability of the chelate. This in turn controls the electrophilicity of the metal centre and hence its reactivity. Electron-donating groups decrease the reactivity of the metal centre, while electron-withdrawing groups increase the reactivity. Placing a strong σ-donor cis to the leaving group greatly decreases the reactivity of the complex, while the addition of a good π-acceptor group significantly enhances the reactivity. The results indicate that the metal is activated differently by changing the surrounding atoms even though they are part of a conjugated system. It is also evident that substituents in the cis position activate the metal centre differently to those in the trans position. The kinetic results are supported by DFT calculations, which show that the metal centre is less electrophilic when a strong σ-donor is cis to the leaving group and more electrophilic when a good π-acceptor group is part of the ring moiety. The temperature dependence studies support an associative mode of activation. An X-ray crystal structure of Pyz bound to PtL3 was obtained and confirmed the results of the DFT calculations as to the preferred N-atom as a binding site.     

Synthesis and spectral studies of diorganotin(IV) dialkyldithiophosphates

Two series of diorganotin(IV) dialkyldithiophosphates, [RR′Sn{SSP(OR″)₂}₂](R = Me or Et; R′= Ph; R″ = Et, Prⁿ, Prⁱ or Buⁿ) and [RR′Sn(Cl){SSP(OR″)₂}] (R = R′= Me, Et or Ph; R″ = Ph; R″ = Et, Prⁱ or Buⁿ) were prepared and characterised by i.r. and NMR (¹H, ¹³C, ³¹P, ¹⁹⁹Sn) spectroscopy. The NMR data indicate five and six coordinate geometries for [RR′Sn(Cl){SSP(OR″)₂}] and [RR′Sn{SSP(OR″)₂}₂] complexes, respectively. The chloro complexes showed ²J (PSn) whereas such couplings were not observed in the spectra of [RR′Sn{SSP(OR″)₂}₂].