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The pure anti and syn forms of the compounds (μ-RS) 2 Fe 2 (CO) 6 (R = CH 3 , C 2 H 5 ) isomerize to equilibrium mixtures having the K = [anti]/[syn] values of 3.2 and 3.6, respectively. If R = C 6 H 5 or C 6 F 5 no evidence for “pure” isomers has been found, but anomalies of the IR spectra point to differences in the ring orientations. The new derivative R = C 6 Cl 5 has been prepared by photochemical reaction. The two isomers of the R = alkyl derivatives react with different rates (k syn >k anti ) with phosphines to give the monosubstituted derivatives (μ-RS) 2 Fe 2 (CO) 5 PR′ 3 (R′ = n-Bu, Ph) which have also two distinct isomers. The K = [ anti ]/[ syn ] value changes in favour of the syn isomers in the substituted compounds.

The evolution in basic medium ([RO-] = 1 M in methanol, R = H or Me) of five-coordinate platinum(II) compounds, [PtCl2(eta2-C2H4)(N-N)], 2a-c, (N-N = N,N,N',N'-tetramethyl-1,2-ethanediamine, a; 2,2'-bipyridyl, b; 1,10-phenanthroline, c) leads to the formation of [PtCl(eta1-CH2CH2-OCH3)(N-N)], 5a-c. The analogous compound 5d (N-N = 2,9-dimethyl-1,10-phenanthroline, d) can also be prepared, but not via transformation of the five-coordinate species 2d in basic medium where it is quite stable. 5d can instead be prepared by reaction of d with a strongly basic methanol solution of Zeise's anion [PtCl3(eta2-C2H4)](-), 1. In such a medium the di-anionic trans-[PtCl2(OR)(eta1-CH2CH2-OCH3)](2-) species (1") reacts with to form exclusively 5d. Hydrolysis of with acids bearing weakly coordinating anions leads to [PtCl(eta2-C2H4)(N-N)]+, 3a-c, as stable cations; upon the same treatment 5d does not generate 3d, but it reacts with HCl to give 2d in almost quantitative yield. Cationic complexes 3b, 3c, here reported for the first time, were reacted with some nucleophiles and their behaviour compared with that of the already known 3a. In 3b, 3c the metal centre competes with the coordinated ethene for binding to nucleophiles; therefore the acetylacetonate anion can either add to the olefin (affording compounds 6b, 6c ) or to the metal ion replacing the ethene ligand (yielding compounds 7b, 7c). Under similar conditions, 3a gives exclusively 6a. Secondary amines readily add to ethene in 3b, 3c, affording the addition products 8b, 8c, which undergo a ready cyclization to an azaplatinacyclobutane ring (9b, 9c). The remarkable ease of the four-membered ring formation has been related to the high electrophilic character of the metal core in 3b, 3c.

Zeise's anion in strongly basic hydroxylated solvents undergoes unprecedented nucleophilic addition of OR- (R = H, Me, Et) to the eta2-ethene giving trans-[PtCl2(eta1-C2H4OR)(OR)]2- which readily reacts with bidentate nitrogen donors N-N to give Cl- and OR- substitution and formation of [PtCl(CH2CH2OR)(N-N)]. Protonolysis of this stable organometallic species offers a versatile route to cationic [PtCl(eta2-C2H4)(N-N)]+ complexes.

To get further insight in the reaction of nucleophilic substitution upon changing the ligand trans to a η(2)-olefin, the reactivity of some monoanionic platinum(II) complexes (trans-[PtCl(2)X(η(2)-C(2)H(4))](-), X = Cl(-), 1, OH(-), 2, and CH(2)NO(2)(-), 3) towards pyridines with different steric hindrance (py, 4-Mepy, and 2,6-Me(2)py) has been tested. All crystallographic (2 and 3 reported for the first time) and spectroscopic data are in accord with a platinum-olefin interaction decreasing in the order 2 > 1 > 3, paralleling the decreasing electronegativity of the donor atom (O > Cl > C). Not only the platinum-olefin bond but also the bond between platinum and the ligand trans to the olefin appear to be strongest in 2 (Pt-O distance at the lower limit for this type of bond). In the reaction with py, the ligand trans to the olefin is displaced in 1 and 2. Moreover the reaction is in equilibrium in the case of sterically hindered 2,6-Me(2)py, the equilibrium being shifted moderately or prevalently toward the reagents in the case of 1 and 2, respectively. In the case of 3, the reaction with pyridines leads to substitution of the olefin instead of the carbanion. This is in accord with the observation that carbanions strongly weaken the trans Pt-olefin bond.

The cationic complex [Pt(η2-C2H4)Cl(tmen)]+1(tmen =N,N,N′,N′-tetramethylethylenediamine) reacts with carbon nucleophiles [an acidic carbon substrate (HL) in the presence of a base (Na2CO3); HL = acetylacetone, HL1; ethyl acetoacetate, HL2; or diethyl malonate, HL3] to give the corresponding addition products [Pt(CH2CH2L)Cl(tmen)](L = L1, 3; L2, 4; or L3, 5) and [{(tmen)ClPtCH2CH2}2(L1– H)]6. Compound 3 exhibits a keto–enol tautomerism. The keto tautomer is kinetically and thermodynamically favoured and in solution it represents about 90% of the equilibrium mixture; on the contrary, the enol tautomer is the favoured form in the solid. In compound 4 the carbon atom of the nucleophile which has bound to ethylene is chiral and, as a consequence, the methylene protons exhibit a diastereotopic splitting which is greater for the methylene group next to platinum than for that next to the asymmetric carbon. Treatment of compounds 3–6 with acids (HCl or HClO4) does not reverse the carbon to carbon coupling but cleaves the platinum–carbon bond, forming the ethylated nucleophile and [PtCl2(tmen)] or [{PtCl(tmen)}2][ClO4]2 depending on the acid used. The cationic complex [Pt(η2-C2H4)(NO2)(tmen)]+2 reacts with carbon nucleophiles in a similar way to 1. Treatment of the addition products with HClO4 under an ethylene atmosphere gives the ethylated nucleophile and the starting complex 2.

Proton sponge [1,8-bis(dimethylamino)naphthalene] acts as a carbon nucleophile towards co-ordinated alkenes in [Pt(η2-alkene)Cl(Me2NCH2CH2NMe2)]+(alkene = ethylene, propene or styrene), the resulting Pt–C σ bond being cleaved by acids to afford the 4-alkyl-substituted base.

The bis(acetonitrile)dichloroplatinum(II) obtained by the standard procedure has been shown to be a mixture of the cis and trans isomers the composition of which depends upon the experimental conditions used. The pure isomers have been characterized by i.r. and 1H n.m.r. spectroscopy and the conditions for the preferential obtainment of each isomer have been explored. Kinetic measurements have shown that the formation of the cis isomer is kinetically favoured in the reaction of [PtCl3(NCMe)]– with a second molecule of acetonitrile, indicating that the chlorine ligand exerts a trans-labilizing effect greater than that of acetonitrile.

In order to find correlations between chemical reactivity and biological activity, we have started an investigation on the mutagenic activity of different platinum‐chloroamine complexes towards different strains of Salmonella Typhimurium. The first class of compounds examined includes complexes of general formula cis‐[PtCl2(amine)(L)] in which L represents a strong trans‐labilizing ligand. Using dimethylsulphoxide as solvent these compounds were not toxic or mutagenic, on the contrary in acetone they were toxic towards all strains of bacteria independently from their excision‐repair ability. An entirely different behaviour was exhibited by a second class of compounds having general formula cis‐[PtCl2(amine)2] which includes also cis‐dichlorodi‐ammoniaplatinum(II) (cis‐DDP). These compounds were much less toxic than the previous ones in acetone and were mutagenic; moreover they were able to discriminate between different bacteria strains. Therefore some complexes were active only towards hisG46/pKM101 stra...

The effect of bridging with an ethylene chain the two aminic nitrogens cis -coordinated to the metal in a platinum-dichloro-diamine complex has been examined by studying forward mutagenesis in strains of Salmonella typhimurium carrying hisG46 and hisD3052 mutations and differing at the uvrB locus. While the complexes with the monodentate amines NH 3 and α-methylbenzylamine (mba) exhibit strong mutagenic activity, the corresponding species with chelating diamines, 1,2-diaminoethane (en) and N,N ′-bis(α-methylbenzyl)1,2-diaminoethane (mben), show much weaker activity. Moreover, the latter complexes appear to be more active via ‘frame shift’ than ‘base substitution’ mechanisms and do not differentiate appreciably between cells differing in the rfa locus. Complexes with amines bearing alkyl substituents of opposite chirality ( R -mba and S -mba, R,R -mben and S,S -mben) were tested separately and appeared to have comparable activity.

Preparation de [PtCl 2 (N,N'-R 2 en)] et [Pt(η 2 -C 2 H 4 )Cl 2 (N,N'-R 2 en)]. Spectres RMN et structure cristalline

Platinum complexes with different chirality either at the coordinated nitrogens themselves or at the carbon atoms of the organic chain bridging the two nitrogens of a diamine have been tested for their mutagenic activity towards different strains of Salmonella typhimurium. In the case of [PtCl2(i-Pr2-en)] the isomer with different absolute configuration at the two nitrogens (R,S) appears to be more active towards TA92, TA2410 and TA100 strains while those with equal configuration at the nitrogens (R,R or S,S) are more active towards the TA98 strain. In the case of [PtCl2(1,2-diaminocyclohexane)], [PtCl2(2,3-diaminobutane)] and [PtCl2(1,2-diaminopropane)] the isomers with S configuration at the asymmetric carbons are by far the most active towards all strains of bacteria.

The complex [PtCl(dms)(en)]Cl (dms = dimethyl sulphide and en = 1,2-diaminoethane) reacts with concentrated hydrochloric acid displacing one end of en and substituting dms by Cl–, to form [PtCl3(Hen)](Hen = monoprotonated en). The structure of this compound has been solved by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.030 for 1 326 observed reflections. The structure consists of zwitterionic molecules in which the co-ordination around the metal is square planar with three chlorine and one nitrogen atom from the mono-protonated en ligand. The conformation of the organic ligand is gauche with a hydrogen bond between the ammonium group and a cis chlorine atom; the same ligand in [PtCl5(Hen)] had a perfectly trans conformation.