Giovanni Natile

Five-coordinate ethylene complexes of platinum(II) containing different types of n-donor bidentate ligands

Abstract Diimines, aliphatic and aromatic diamines react with Zeises salt to give stable five-coordinate complexes of general formula [Pt(C 2 H 4 )Cl 2 (NN)], which have trigonal bipyramidal structure with the chlorine atoms in the apical positions and the bidentate ligand in the equatorial plane. The five-coordinate species decompose releasing ethylene and giving square-planar complexes of formula [PtCl 2 (NN)].

The organothio-bridged derivatives of iron carbonyl. II. The dynamic nuclear magnetic resonance study of the anti-syn isomerism in bis(μ-tertiarybutylsulphido)hexacarbonyldiiron and its monosubstituted products with some phosphines and phosphites: an unusually fast interconversion rate☆

Abstract The anti-syn interconversion rate of (μ-Bu t S) 2 Fe 2 (CO) 6 is about one thousand times faster than that of the other alkyl and aryl derivatives and becomes fast in the NMR time scale at temperatures above 90 °C. The coalescence temperature of the Bu t signals is lowered by substitution of a carbonyl group with a phosphorus ligand and a single sharp resonance is observed at room temperature with the more basic phosphines The mechanism of inversion at sulphur is discussed in connection with related systems. Not all monosubstituted products are stable in solution and their tendency to release the coordinated phosphine increases with the bulkiness of the ligand.

Decomposition of [Pt(C2H4)Cl2(bipyridyl)] to [PtCl2(bipyridyl)] and ethylene in different solvents

Abstract The decomposition of the 5-coordinate complex [Pt(C2H4)Cl2(bipy)] to the 4-coordinate [PtCl2(bipy)] and ethylene has been studied in 1,2-dichloroethane and in aqueous methanol (95% v/v). The reaction proceeds with different mechanisms in the two solvents. In 1,2-dichloroethane the 5-coordinate substrate decomposes in a single step with ΔH‡ = 18.6 ± 0.6 Kcal mol−1 and ΔS‡ = −8 ± 2 cal K−1 mol−1. In aqueous methanol [Pt(C2H4)Cl2(bipy)] gives the cationic ethylene complex [Pt(C2H4)Cl(bipy)]+ which then reacts with chloride ion in a slow bimolecular process to form [PtCl2(bipy)] and ethylene.

The bonding of hydrazones in transition metal complexes. Crystal and molecular structure of trans-dichloro-ethylene-acetonemethylphenylhydrazone- and trans-dichloro-ethylene-acetaldehydedimethylhydrazone-platinum(II) complexes

Abstract The X-ray structures of trans-[Pt(C2H4)Cl2(Me2C = NNMePh)], I, and trans-[Pt(C2H4Cl2(MeHC = NNMe2)], II, have been determined. They were solved by conventional Patterson and Fourier methods giving conventional discrepancy factors of R = 0.066 for 1476 reflections in compound I and R = 0.065 for 866 reflections in compound II. Compound I crystallizes in the space group P21/c with four formula weights in a cell Measuring a = 9.488(8), b = 11.315(8), c = 14.726 (9) A; β = 105.2°; compound II crystallizes in the space group P21, with two formula weights per unit cell having a 6.652(7), b = 11.961(8), c = 7.143(7) A; β = 98.8°. Crystal densities are 1.987 g/cm3 and 2.31 g/cm3 for compound I and II respectively. The structures consist of individual monomeric molecules with the platinum atom in a four coordinate arrangement. The hydrazone molecule coordinates through the iminic nitrogen; the two nitrogen atoms and the skeleton of the carbonylic residue lie essentially in a plane which 70.3° in compound I and of 87.7° in compound II. The geometry around the aminic nitrogen, N(2), is pyramidal and in both cases its methyl substituent is directed towards the metal. The structural data are compared with those of the palladium complex trans-[PdCl2(Me2C = NNmePh)2].

Hindered rotation about the metal-nitrogen bond in trans-dichlorodihydrazonepalladium(II) complexes and X-ray crystal structure of trans-bis(acetone methylphenylhydrazone)dichloropalladium(II)

The complexes trans-[PdCl2L2][L = Me2CN–NMePh (L1); Et2CN–NMePh (L2); PrnMeCN–NMePh (L3); MeHCN–NMePh (L4); Me2CN–NMe2(L5); or MeHCN–NMe2(L6)] have been prepared by reaction of the hydrazone ligands with [PdCl2(NCPh)2]. The crystal and molecular structure of trans-[PdCl2(Me2CN–NMePh)2] has been determined from three-dimensional X-ray data. The complex crystallizes in the monoclinic space group P21/n with two molecules in a cell of dimensions a= 18.83(3), b= 7.53(2), and c= 7.76(2)A, β= 89.1(5)°. The palladium atom lies at a centre of symmetry; consequently the four ligating atoms, i.e. the two chloride ions and the two imino-nitrogens of the hydrazones, are located rigorously in a plane passing through the central metal. The co-ordination plane is nearly perpendicular to the plane containing the non-hydrogen atoms of the hydrazone skeleton Me2CN–N. Significant bond distances are Pd–Cl 2.298(4) and Pd–N 2.047(2)A. Another isomeric structure of this complex can be obtained by 180° rotation about the Pd–N bond of one of the two hydrazone ligands. This isomer is not centrosymmetric but contains a plane of symmetry which is perpendicular to the co-ordination plane and passes through the Cl–Pd–Cl axis. Both these isomers exist in equilibrium in solution for all the prepared complexes. Values of free energies of activation for the interconversion process have been obtained from temperatures of coalescence of the n.m.r. signals; they vary from 58 to 89 kJ mol–1 with the nature of the ligand substituents. In particular, complexes of hydrazones derived from aldehydes (L4 and L6) have ΔG‡ 10–14 kJ mol–1 lower than those of analogous hydrazones derived from ketones (L1–L3 and L5); complexes of hydrazones derived from methylphenylhydrazine (L1–L4) have ΔG‡ 17–21 kJ mol–1 lower than those of analogous hydrazones derived from dimethylhydrazine (L5 and L6).

Reactivity of amines towards dichloro[biacetylbis(N-methyl, N-phenyl)osazone]platinum(II)

Abstract We have investigated the kinetics of substitution with amines of one of the coordinated chlorides in the complex Pt(Oz)Cl2, where Oz = Biacetylbis(N-methyl,N-phenyl)osazone. The results obtained are compared with those relative to the complex Pt(bipy) Cl2 and indicate that the greater reactivity of Pt(Oz) Cl2 can be attributed to a labilizing effect due to an interaction in the transition state between one of the ortho hydrogens of one of the phenyl rings of the ligand and the developping chloride.

Preparation of a five-co-ordinate platinum–π-ethylene complex: (biacetyl bismethylphenylhydrazone)dichloro-π-ethyleneplatinum(II)

Reaction 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.

Complexes of hydrazones with dichloro(η-ethylene)platinum(II): stereo-chemical and conformational analysis of the co-ordinated ligand

By 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 Zeises 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.

The behaviour of trans-dihalogenobis(hydrazone)palladium(II) complexes: rotational isomerism or non-equivalence of the two ligands within the same molecule?

A detailed 1H n.m.r. analysis of a series of trans-dihalogenobis(hydrazone)palladium(II) complexes has been made in order to demonstrate unequivocally the presence of two rotational isomers differing in the mutual orientation of the co-ordinated ligands.

High barrier to rotation about the Pd-N bond in trans-dichloro- dihydrazonepalladium(II) complexes

Newly synthesized trans-[PdCl2(R1R2CN1–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).