A. Peloso

Kinetics of nickel, palladium and platinum complexes

Much work has been reported in recent years dealing with the kinetic behavior of nickel, palladium and platinum complexes, mainly as a consequence of the introduction of new techniques for studying fast reactions’s * . The purpose of the present review is to present an up-to-date outline of what has been achieved in this area. The great amount of information now available-in the literature is such that some restriction of the material to be reported was necessary. For this reason several kinds of process, such as intramolecular rearrangements, rotation and inversion reactions, catalytic and intramolecular oxidationreduction reactions3 -’ 2, will not be considered here. The review is divided in two parts. The first (Sect. B) will consider reactions in which the central metal atom of the complex retains its oxidation state; the second @ct. C) will

Redox reaction mechanisms of platinum (IV) complexes

Abstract Kinetic investigations on redox reactions of platinum-(IV) complexes trans -[Pt(PEt 3 ) 2 Br 4 ], and trans - [Pt(PPr 3 ) 2 Br 4 ]] with SCN - ,I - , SeCN - and S 2 O 3 2- , and of trans -[Pt(PEt 3 )bb]2 Cl 4 ], trans -[Pt(AsEt 3 ) 2 Cl 4 ]and trans - [Pt(AsEt 3 )Br 4 ] with SCN - and SeCN - in methanol are reported. The following reaction scheme has been proposed: The reaction rates of the redox process are first order with respect to both the platinum(IV) complex and the reagent,Y n- . Representing with k 2 the second order rate constants, it was found that the log k 2 for the reactions of the various substrates with different anions are linearly related to log k 2 for the corresponding reactions of the complex trans -[Pt(PPr 3 ) 2 Cl 4 ], (termed as r(X)). according to the linear free energy relationship: log k 2 = r(x)+r s (where the constant r s depends upon the nature of the substrate). This relationship is discussed in terms of a reaction mechanism involoving a weak bond formation between the platinum(IV) complex and Y n- in the activated complex, probably a two electron bridged- transfer of the type:

MgCl2‐supported catalysts for the propylene polymerization: effects of triethers as internal donors on the activity and stereoselectivity

The effects of triethers as internal donors on the activity and stereoselectivity of MgCl 2 -supported Ziegler-Natta type catalysts in the propylene polymerization were studied. In particular, we prepared and fully characterized some procatalysts of the type δ-MgCl 2 /ID/TiCl 4 , where ID are internal donors such as di(ethyleneglycol) diethyl ether (DEGDEE) and di(ethyleneglycol) dimethyl ether (DEGDME). By aging these procatalysts with AlEt 3 (cocatalyst) we obtained δ-MgCl 2 /ID/TiCl 4 /AlEt 3 catalytic systems, which were tested in the propylene polymerization in order to evaluate their catalytic performance. All polymerizations were carried out in the absence of both external donors (ED) and hydrogen. The productivity and the properties (M w , M n , M w /M n , and isotacticity index (I.I.)) of the polymers obtained were determined and the results compared with those obtained by using catalysts either lacking an internal donor or with ethyl benzoate as internal donor. The comparison pointed out that the presence of triethers lowers the productivity of the catalysts and increases their stereoselectivity. Polydispersity is also remarkably enhanced suggesting that a multiplicity of active catalytic sites characterized by different environments is present.

Reduction reactions of trans-PtL2X4 complexes. Influence of the uncharged ligands L on the reduction reaction rates

Abstract Kinetic investigations on redox reactions of platinum(IV) complexes of the type trans-[PtL 2 X 4 (where L = pyridine, piperidine, methyl- and ethylamine, dimethyl- and diethylsulphide; X = Cl or Br) with SCN−, I−, SeCN− and S 2 O 3 2− in methanol are reported. All of the substrates studied are reduced by these anions to platinum(II) complexes; the reaction rates are first order with respect to both the platinum(IV) complex and the reducing anion. The reduction rates of the complexes trans-[PtL 2 X 4 ] increase in the order arsine

Role of steric hindrance of methyl groups on the rates of reduction of N-methyl substituted ethylenediamine complexes of platinum(IV)

Abstract The reduction of platinum(IV) complexes of the type [PtCl 4 (N-N)] by FeCp 2 I − ,[Pt(NH 2 Et) 4 ] 2+ or [Pt(en)(NH 2 Et) 2 ] 2+ in the presence of chloride ions in methanol have been investigated (N-N = en, meen, s -dmen, a -dmen, trimen, tmen). The reactions obey second- or third-order rate laws: rate = k FeCp 2 [PtCl 4 (N-N)][FeCp 2 , k I -[PtCl 4 (N-N)][I − ] or k Pt II [PtCl 4 (N-N)][PtL 2+ 4 ][Cl − ]. The rate constants increase by increasing the steric hindrance at the amine ends of the N-N ligand, even if in a measure which is quantitatively dependent on the reducing agent I − > FeCp 2 > [Pt(NH 2 Et) 4 ] 2+ ≈ [Pt(en)(NH 2 Et) 2 ] 2+ . The steric hindrance of the terminal amine groups appears to behave as an additive parameter and linear relationships are found which correlate the reactivities (log k Reductant ) of platinum(IV) complexes to a proposed parameter of relative overall steric hindrance of the N-N ligand. The observed reactivity trend of [PtCl 4 (N-N)] complexes is thought to have basically a thermodynamic origin. Driving forces should also be responsible for the higher reactivity ( ca 20 times) of [Pt(en)(NH 2 Et) 2 ] 2+ with respect to that of [Pt(NH 2 Et) 4 ] 2+ .

Role of the ligands in affecting the stoichiometry and the rate of reactions between platinum(IV) and platinum(II) complexes

Abstract The stoichiometries and the rates of the reactions between trans -[Pt(en)(N-N)Cl 2 ] 2+ and [Pt(en)(N′-N′)] 2+ in the presence of bromide ions have been studied in aqueous solutions (N-N and N′-N′ = en, 1,3-pn, 1,2-pn, meen, dmen, tmen). The platinum(IV) reaction product is either trans -[Pt(en)(N-N)Br 2 ] 2+ or trans -[Pt(en)(N′-N′)Br 2 ] 2+ , depending on the bulkiness of N-N and N′-N′. The reaction rates obey a pseudo-first-order rate law with k obs ≈ { k c [Br − ]+ k d [Br − ] 2 }[Pt(en)(N′-N′) 2+ ]. The ligands significantly affect the rates, mainly via their steric hindrance. An increase of the steric hindrance near the platinum(IV) centre only moderately enhances its reactivity towards reduction, whereas a strong lowering of the reactivity of platinum(II) towards oxidation is caused by an increase of the steric hindrance of the ligands coordinated to this atom centre. The quantitative kinetic effect displayed by changes of such ligands either on platinum(IV) or on platinum(II) complexes is also dependent on the particular platinum(II) or platinum(IV) complex used as the standard reducing or oxidizing reagent. An explanation of the observed behaviour is suggested in terms of an atom-transfer redox mechanism.

Preparation and thermal behaviour of diethylenetriamine complexes of platinum(II)

Abstract Platinum(II) compounds of the type [Pt(dien)(L)]- X 2 (dien = diethylenetriamine; L = aliphatic amine, pyridine or substituted pyridine; X − = Cl − , Br − , I − or ClO 4 − ) have been prepared and their thermal behaviour studied by TG, DSC and FAB-MS techniques. Transformations of the title compounds into [Pt(dien)X]X + L are found to begin at temperatures which are in the order I − − − , perchlorate being not able to replace L before the related compounds explode. The starting temperature of this transformation is also dependent on L, being lower for bulkier amines. At higher tempetures [Pt(dien)-X]X compounds decompose with evolution of HX and other fragments, which leads to a black residue which on further heating decomposes into volatile products and elemental platinum.

Effect of acidity on chelate ring closure occurring by chloro, nitro or azido group displacement in rhodium(III) complexes

Abstract The effect of CH3COOH, ClCH2COOH, Cl2CHCOOH, Cl3CCOOH and of ClCH2COOH-ClCH2COO− buffers on the rates of the conversion of mer-[Rh(L)(L′)Cl2X] into trans-[Rh(L)2Cl2]+ + X− has been investigated in methanol [L and L′ = (o-dimethylaminophenyl)dimethylarsine-NAs and -As, respectively; X− = Cl−, NO2−, N3−. The rates have been found to depend only on the hydrogen ion concentration and not on the particular concentration or strength of the acid used. The observed rate constant of mer-[Rh(L)(L′)Cl3] is decreased by increasing the hydrogen ion concentration. Conversely, kobs for mer-[Rh(L)(L′)Cl2N3] increases smoothly up to a maximum limiting value by increasing the hydrogen ion concentration. A similar behaviour is shown by mer-[Rh(L)(L′)Cl2NO2], but in this case the rate constant achieves a maximum value and then it decreases towards a limiting value as the hydrogen ion concentration is increased further. The dependence of kobs on [H+] for the acid-dependent reaction path of the mer → trans conversion of mer-[Rh(L)(L′)Cl3] and mer-[Rh(L)(L′)Cl2N3] is explained in terms of protonation at the - NMe2 free end of L′, whereas also diprotonation of the complex is tentatively invoked to explain the kinetic effect of acidity on the reactions of mer-[Rh(L)(L′)Cl2NO2].