The synthesis, molecular structure and chemical behavior of two chloride-dimethyl sulfoxide-ruthenium(III) derivatives, namely [(DMSO)2H] [irarts-Ru(DMSO)2Cl4] (1) and mer-Ru(DMSO)3Cl3 (2), are reported. They represent the first examples of fully characterized halogen-dimethyl sulfoxide-ruthenium(III) complexes. Further relevance in their synthesis comes from the known antitumor properties of isostructural Ru(IIl) complexes with heterocyclic nitrogen ligands and of halogen-dimethyl sulfoxideruthcnium(ll) complexes as well. The crystal structures of 1 and 2 have been determined by three-dimensional X-ray analyses.Crystal data are as follows: [(DMSO)2H] [r/-ans-Ru(DMSO)2Cl4], monoclinic, space group Pl/n, a = 9.273 (1) Á, b = 16.509 (3) Á, c = 14.023 (3) Á, ß = 100.79 (2)°, Z = 4, R = 0.041; for mer-Ru(DMSO)3Cl3, monoclinic, space group /'2,/c, a = 10.105 (2) Á, b = 13.832 (3) Á, c = 11.115 (2) Á, ß = 94.39 (2)°, Z = 4, R = 0.028. In 1 there are two crystallographically independent [Ru(DMSO)2C14]" anions lying on crystallographic 2-fold axes, passing through Ru and two trans Cl atoms, so that the other two Cl atoms and the two S-bonded DMSO molecules are also trans to each other. Cations are provided by protonated DMSO molecules, [Me2SO-H-OSMe2]+. In 2 the three chlorine atoms are in the mer configuration, and the two trans DMSO molecules arc S-bondcd to Ru, while the third one is O-bonded. Both complexes are intermediates in the synthesis of cis-RuCl2(DMSO)4 front hydrated RuC13. Cyclic voltammetric evidence shows that, in dimethyl sulfoxide and dichloromethane solution, 2 is in equilibrium with an isomer that very likely differs in the coordination mode of one DMSO (S-to O-bonded isomerization). The chemical behavior of 1 and 2 in aqueous solution has been studied at low pH (<3), where the formation of polymeric species is prevented. When dissolved in water, both complexes rapidly release one of the two trans S-bonded DMSO's and, in about 24 h at room temperature, produce the same neutral species: mer,m-[RuCl3(H20)2(DMS0)]. A completely similar behavior is
Novel cobalt( 111) complexes of tetradentate chelating agents (chel) and monodentate tertiary phosphines of the type [ColIJ(chel) PR3]+CIO4and [ColI1(chel) PR,( H20)]+CIO4-are reported. A five-co-ordinate square pyramidal structure is suggested for both types of compound in non-complexing solvents. The thermodynamic rrans-effect of PR, is indicated by the stoicheiometric formation constants of [CoIII(chel) (PR,) (NO,)]O which can be correlated with u" Taft constants of the phosphines. The trend of the trans-effect of L in [CoIII(chel)- Trieste, Trieste, ItalyA FIVE-CO-ORDINATE cobalt ( 111) complex [CH3CorIr(chel)]0 [chel = the tetradentate NN'-ethylenebis(acety1acet-0neiminato)dianion (bae) (I) and a methyl group in the axial position] has been reported previously.1,2 A square pyramidal crystal structure was assigned to the compound on the basis of an X-ray diffraction study., On the basis of physicochemical properties, five-coordinate structure was also assumed for other cobalt (111) complexes of general formula RCo(che1) l p 2 p 4 * (R is an organic group and chel = NN'-ethylenebis (salicylideneiminato) (salen) (11) ; NN'-ethylenebis-(7,7'-dimethylsalicylideneiminato) (7 ,7'-Me,-salen) (111) ; o-phenylenebis(salicylideneiminat0) (saloph) (IV) . Reversible changes in optical spectrum of organocobinamides were also explained by the equilibrium, R-CoIII corrin (H,O) R-CoIII corrin + H20 implying a five-co-ordinate approximately square pyramidal species or a very weak CoI11-OH2 bond in ~o l u t i o n . ~ Five-co-ordinate species are thought to be intermediates in S x l substitution reactions 8-10 and can be relevant in the biochemical function of vitamin B,, complexes.Here we report some novel apparently five-co-ordinate complexes with apical tertiary phosphines as ligands [PR,Co(chel)]+ and [PR,Co(chel) (H20)]+. The thennodynamic trans-effect of PR, is correlated with the CT*
In four series of strictly related organocobalt complexes, derived from cobaloximes by replacement of the 0 . . H . ' 0 with 0 . . . BF2. . ' 0 and/or (CH2)3 groups, the trends of 59Co-NMR shielding and electrochemical data are discussed. A largely parallel behaviour of the plots of El12(I) values for the first Co(III)/Co(II) electron transfer us. the 59C0 chemical shifts reflects the similar sensitivity of the two parameters to a change in electron affinity of the central metal ion due to a variation of the organic group R. E,,,(II) values for the second Co(II)/CO(I) electron transfer are less sensitive to the change of R, but the trend of the plot us. S(59C0) is still parallel in the four series. Consistent deviations from a roughly linear dependence of E1,,(I) on pK, of the hydrocarbon acid corresponding to R, on Tuft constant u* and on 59C0 shielding are noticed for the isopropyl derivatives and attributed to a steric effect. This was confirmed in a series of R-Co(DMG)pyridine complexes in which 59C0 shielding decreases steadily with increasing steric parameter E, (Taft) of the alkyl group. There is experimental evidence from X-ray data that S(59C0) decreases with an increase of the Co-C bond length, illustrating steric hindrance in alkyl coordination to be responsible for the decreased shielding of the 59C0 nucleus. The relative displacements of the graphic displays for the different series reflect the effect of changes in electron affinity of the redox center, due to the equatorial ligand, which, in turn, is caused by variations in the electron-withdrawing power due to the introduction of the BF, group and by the change from -2 to -1 valence of the (CH,),-capped ligands.1. Introduction. -The unique features of coenzyme B,, as a naturally occurring organometallic compound containing a Co-C a-bond have attracted the interest of chemists over three decades and stimulated numerous structure and reactivity studies on the coenzyme, the vitamin, and several model systems containing the four-nitrogen equatorial template and the axial Co-C and Co-L bonds in an octahedral ligand sphere of the Co(II1) ion [24]. In this context, a correlation of different features of the solution chemistry of vitamin-B,, model compounds constitutes a main entry to the evaluation of the factors influencing the chemistry of the coenzyme. Of special relevance is a knowledge of the effects caused by the structure of the equatorial ligand and by substitution of the axial ligands R and L which may relate with the essential Co-C bond homolysis step in vitamin-B,,-dependent, enzyme-catalyzed reactions. Thus, relationships between structure, kinetics of axial ligand exchange, and redox properties were examined by many research groups and reviewed [5].Surprisingly, there is only limited information on the above question based upon NMR studies, although several attempts were made to correlate 'H-[6] [7], 13C- [6] [8], and
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