No abstract

Complexes of the type cis-[PtL(2)Me(2)] (1-14) (L = an extended series of phosphines of widely different steric and electronic properties) were synthesized, characterized, and used as precursors for the formation of cis-monoalkylplatinum(II) solvento species in methanol. The cleavage of the first platinum-alkyl bond by protonolysis is a fast process, but the subsequent cis to trans isomerization of the cationic solvento species [PtL(2)(Me)(MeOH)](+) is relatively slow and it can be( )()monitored using (31)P NMR or conventional spectrophotometry. A large collection of (1)H and (31)P NMR data for cis-[PtL(2)Me(2)], cis-[PtL(2)Me(MeOH)](+), and trans-[PtL(2)Me(MeOH)](+) complexes showed interesting dependencies upon the size, the sigma-donor capacity, and the mutual position of the phosphines in the coordination sphere of the metal. The rate constants for isomerization of cis-[PtL(2)Me(MeOH)](+) were resolved quantitatively into steric and electronic contributions of the phosphine ligands, by means of correlations with parameters which reflect their sigma-donor ability (chi values) and steric requirements (Tolman's cone angles, theta). The electronic and steric profiles obtained for these reactions are discussed within the framework of a mechanism which involves dissociative loss of the solvent molecule and interconversion of two geometrically distinct 3-coordinate T-shaped 14-electron intermediates. The factors controlling the stability of these coordinatively unsaturated species are discussed. The electronic and steric influences of phosphines as "spectator" ligands in a dissociative process are compared with those shown by these ligands when used as nucleophiles in associative substitution processes. The activation parameters DeltaH() and DeltaS() were measured using both conventional isothermal and non-isothermal spectrophotometric kinetics.

No abstract

Bistren cryptands can be easily synthesised through the Schiff base condensation of two molecules of tren and three molecules of a dialdehyde, followed by hydrogenation of the six C=N double bonds to give octamine cages, whose ellipsoidal cavity can be varied at will, by choosing the appropriate dialdehyde, in order to include substrates of varying sizes and shapes. Bistrens can operate as effective anion receptors in two ways: (i) in their protonated form, providing six secondary ammonium groups capable of establishing hydrogen bonding interactions with the anion; (ii) as dicopper(II) cryptates, in which the two coordinatively unsaturated metal centres can be bridged by an ambidentate anion. Representative examples of the two approaches, as well as the design of an anion molecular dispenser, in which a dicopper(II) bistren cryptate acts as a bottle will be illustrated.

The thioethers 2-pyridylmethyl p-tolyl sulfide (a) and p-chlorophenyl 2-pyridylmethyl sulfide (b) react with the precursors cis-[RuCl 2 (N,N-diimine) 2 ] [diimine = di-2-pyridyl sulfide (dps), 1; 2,2Ј-bis(4-methylpyridyl) sulfide (4mdps), 2; 2,2Ј-bis(5-methylpyridyl) sulfide (5mdps), 3; di-2-pyrimidyl sulfide (dprs), 4; and 2,2Ј-bis(5-ethylpyrimidyl) sulfide (5edprs), 5] in the presence of NH 4 PF 6 to give the complexes [Ru(N,Ndiimine) respectively. As a consequence of the N,S chelation all the complexes contain a five-membered RuSCCN(Ru−N) ring, the sulfur and ruthenium atoms of which are stereogenic centres, with (R) and (S) and ∆ and Λ configurations, respectively. Furthermore, the coordinated thioethers contain anisochronous methylene protons and phenyl protons which are sensor nuclei for pyramidal sulfur inversion and rotation of the pendant phenyl ring, respectively. In the low-temperature 1 H NMR spectra of the complexes a single AB system for the methylene protons, in agreement with a fast sulfur inversion, is observed. Well-separated signals of the two ortho-as well as the meta-phenyl protons, indicating restricted phenyl rotation, are also observed. At higher temperatures