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High barrier to rotation about the Pd-N bond in trans-dichloro-dihydrazone-palladium(II) complexes
No full textNewly synthesized trans-[PdCl2(R1R2C[double bond, length half m-dash]N1–N2R3R4)2] complexes have a high Pd–N1 rotational barrier which, in solution, gives rise to two isomers depending on the relative orientations of the hydrazone molecules with respect to each other (symmetrical in one isomer and asymmetrical in the other)
On the dynamic behaviour of trans-dihalide-bishydrazone-palladium(II) complexes
No full textThe intensity ratio of the 2 sets of signals present in the 1H NMR spectrum of trans-PdX2(Me2C=N-NMePh)2 changes going from chloro to bromo analogs. Similar changes occur in trans-PdCl2(R1R2C=N-NR3R4)2 varying the bulkiness of R1 (R1 = Me, Et, or iso-Pr), which is cis to the metal atom. All these facts prove the presence in soln. of 2 rotational isomers differing by mutual orientation of coordinated ligands rather than unequivalence of the 2 hydrazones within the same mol. In trans-PdCl2(Me2C=N-NMePh)(Me2C=N-NMe2) the sepn. of the 2 sets of signals relative to the -NMePh hydrazone is similar to that showed by the -NMe2 hydrazone in the sym. trans-PdCl2(Me2C=N-NMe2)2. In an analogous way the sepn. of signals relative to the -NMe2 hydrazone is similar to that showed by the -NMePh one in trans-PdCl2(Me2C=N-NMePh)2. Therefore the splitting is detd. by reciprocal influence of trans ligands in the 2 isomers.
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Palladium(II) complex of azocyclohexene derivatives
No full textNew complexes of palladium(II) containing as ligands R-azo-cyclohexene derivatives have been prepared. Their characterisation by way of various physical-chemical techniques, including 1H n.m.r. and i.r. spectra, indicate that they are all neutral complexes of the type trans-PdL2Cl2 and that the co-ordination occurs through a nitrogen–palladium σ-bond.
Some aspects of their chemical properties are also reported and discussed
Preparation of a five-co-ordinate Platinum pi-ethylene complex: (biacetyl bis-methylphenyl hydrazone)dichloro-pi-ethylene Platinum(II)
No full textReaction of K[PtCl3(C2H4)] with biacetyl bis-methylphenylhydrazone leads to (biacetyl bismethylphenylhydrazone)dichloro-π-ethyleneplatinum(II), a trigonal bipyramidal complex with two chlorine atoms in the apical positions
The bonding of thiazoles to platinum(II) complexes. X-ray crystal structure of cis- and trans-[Pt(dimethyl sulfoxide)(thiazole)Cl-2]
No full textThe crystal structures of neutral cis- and trans-[Pt(dimethylsulfoxide)(thiazole)Cl2] have been determined by X-ray diffraction. The longer C4-C5 bond distance of the N-coordinated thiazole in both the square planar complexes, as compared to the free ligand, is interpreted in terms of a negative charge density transfer toward the antibonding orbital system of the thiazolic ring
Reduction of gold(III) to gold(I) by dialkyl sulphides. Evidence for an atom-transfer redox process
No full textA kinetic study of the reduction of gold(III) to gold(I) by dialkyl sulphides, in aqueous mathanol, is reported. The reaction takes place in two steps. In the first step, substitution equilibria which are strongly dependent on the bulkiness of the entering sulphide are set up. In the second step, the gold(III) complexes react with an extra molecule of sulphide to give gold(I) species and sulphoxide; very likely the reductant attacks the substrate at a chlorine and not at the metal centre, the halogen is then transferred from gold to sulphur leaving an electron pair on the metal. The reactivity of the gold(III) substrates increases with increasing substitution {[AuCl4]–[double less-than, compressed][AuCl3(SR2)] < [AuCl2(SR2)2]+} paralleling the increasing positive charge on the complex; on the other hand that of the sulphides parallels their basicity (SMe2 < SEt2 < SPri2) indicating that in the redox step polar effects are more important than steric ones. The reaction rate also exhibits a marked solvent dependence, and increases with increasing percentage of water in the reaction medium, the relationship of log k1,2 to solvent polarity being linear
Complexes of hydrazones with dichloro (η-ethylene)platinum(II): stereochemical and conformational analysis of the co-ordinated ligands
No full textBy reaction of the hydrazones (Me2C:N·NMePh, L1; MeHC:N·NMe2, L2; MeHC:N·NMePh, L3; EtHC:N·NMe2, L4; EtHC:N·NMePh, L5: and Me2C:N·NHPh, L6) with Zeise's salt, complexes of formula trans-[Pt(C2H4)Cl2-(hydrazone)] have been prepared in which the imino-nitrogen acts as donor atom. Of the hydrazones derived from aldehydes, which in the free state are present as pure syn isomers, L2 and L4 retain their configuration on co-ordination to the metal, while L3 and L5 give two isomeric complexes, in one of which the ligand keeps the syn configuration, whereas in the other isomerization to the anti form occurs (with respect to the C:N double bond). Evidence of rotational isomerism about the N·N bond has been found in the case of L6. The coupling of the ligand protons with the 195Pt nucleus has been measured and correlated with their relative cis or trans position about the C:N double bond. A coupling of ca. 74 and 27 Hz has been found for the aldehydic proton, trans and cis to platinum respectively. For the methyl substituents at the carbonylic carbon, a higher coupling constant (11-13 Hz) is observed when the methyl group is cis to platinum and a lower one (6-8 Hz) when it is trans. This result is discussed in connection with other literature data
Equilibrium and Kinetic.Studies on the Displacement of Pyridine by Chloride Ion in 2,6-Bis(methylthiomethyl)pyridine Palladium (II) Perchlorate
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The reactivity of neutral nitrogen donors on planar d8 metal complexes. Part 3.The system chloro(2,2':6',2''-terpyridine)platinum(II) cation with pyridines and ammonia in methanol.Effect of basicity π-acceptor capacity and steric hindrance
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