Synthesis and electrochemical characterization of halide, isocyanide, and alkynyl synthons containing the encumbered triangular cluster unit Pt3(mu-P(t)Bu2)3.

Useful synthons containing the tribridged triangular unit {Pt(3)} = [Pt(3)(mu-P(t)Bu(2))(3)](+) were prepared starting from the known tricarbonyl derivative [{Pt(3)}(CO)(3)]Z, [(1(+))Z, Z = CF(3)SO(3)(-)]. This was easily converted into the monohalides {Pt(3)}(CO)(2)X [2, X = Cl; 3, X = Br; 4, X = I], by reaction with the appropriate halide salt. The coupling reaction between 2 and terminal alkynes in the presence of CuI afforded in good yields the sigma-alkynyl derivatives {Pt(3)}(CO)(2)(CC-R) [6, R = SiMe(3); 7, R = CC-SiMe(3); 8, R = C(6)H(5); 9, R = C(6)H(4)-4-Br; 10, R = C(6)H(4)-4-CCH; 11, R = 2-C(4)H(2)S-5-CCH; 12, R = 9-C(14)H(8)-10-CCH], while desilylation of 6 or 7 with TBAF/THF gave, respectively, the derivatives 13 (R = H) and 14 (R = CCH). The stepwise elongation of the arylalkynyl chain was obtained by the Sonogashira coupling of 10 with an excess of 1,4-diiodobenzene, which produced 15 (R = C(6)H(4)-4-CC-C(6)H(4)-4-I), and by coupling the latter with an excess of 1,4-diethynylbenzene, which formed 16 (R = [C(6)H(4)-4-CC](3)H). Branched synthons were obtained by substitution of the carbonyl ligands with functional isocyanides; the reaction of an excess of CN-C(6)H(4)-4-R (R = I, CCH) with {Pt(3)}(CO)(2)H, 5, or with complex (1(+))Z afforded, respectively, {Pt(3)}(CN-C(6)H(4)-4-I)(2)H, 17, or [{Pt(3)}(CN-C(6)H(4)-4-R)(3)]Z [(18(+))Z, R = I; (19(+))Z, R = CCH]. The crystal structures of complexes 2, 8, and 9 were established by X-ray diffraction studies. The electrochemical characterization of representative examples of the clusters prepared in this work shows that all clusters are characterized by the presence of two oxidations; an analysis of ligands' effects on the redox processes is also included.

The two modes of binding of Ru(phen)(2)dppz(2+) to DNA: thermodynamic evidence and kinetic studies.

The binding of Ru(phen)(2)dppz(2+) (dppz=dipyrido[3,2-a:2',3'-c]phenazine) to DNA was investigated at pH 7.0 and 25 degrees C using stopped-flow and spectrophotometric methods. Equilibrium measurements show that two modes of binding, whose characteristics depend on the polymer to dye ratio (C(P)/C(D)), are operative. The binding mode occurring for values of C(P)/C(D) higher than 3 exhibits positive cooperativity, which is confirmed by kinetic experiments. The reaction parameters are K=2 x 10(3)M(-1), omega=550, n=1, k(r)=(1.9+/-0.5) x 10(7)M(-1)s(-1) and k(d)=(9.5+/-2.5)x10(3)s(-1) at I=0.012 M. The results are discussed in terms of prevailing surface interaction with DNA grooves accompanied by partial intercalation of the dppz residue. The other binding mode becomes operative for C(P)/C(D)<3 and the equilibria analysis shows this is an ordinary intercalation mode (K=1.3 x 10(6) M(-1), n=1.5 at I=0.012 M and K=2 x 10(5) M(-1), n=1.2 at I=0.21 M). Similar behaviour is displayed by double-stranded poly(A).

Aqueous Organometallic Chemistry of Ruthenium(II). Aquo Carbonyl Derivatives and Related Ethene Hydrocarboxylation in Fully Aqueous Solvent.

A series of new water soluble and stable organometallic compounds is reported, and the peculiar role of water in their formation and stabilization is documented together with their catalytic properties in aqueous solution. The complex fac-Ru(OCOCF(3))(2)(CO)(3)(H(2)O) (1) constitutes the entry to a new type of aqueous organometallic chemistry. The substitution of trifluoroacetato ligands by H(2)O yields [fac-Ru(CO)(3)(H(2)O)(3)](2+) (2), isolated as the tetrafluoroborate derivative, the first structurally characterized complex bearing CO and H(2)O ligands only. In water, 2 undergoes nucleophilic attack by the solvent yielding [fac-Ru(COOH)(CO)(2)(H(2)O)(3)](+) (3), followed by CO(2) elimination to give [fac-RuH(CO)(2)(H(2)O)(3)](+) (4), a ruthenium(II) hydride devoid of group-15-donor coligands and stable toward strong acids. 4 inserts ethene in water to give [fac-Ru(C(2)H(5))(CO)(2)(H(2)O)(3)](+) (5), an exceptionally inert alkyl complex which inserts CO yielding [fac-Ru(C(O)C(2)H(5))(CO)(2)(H(2)O)(3)](+) (6). Attempts to isolate the mononuclear cationic acyl complex gave the tetranuclear Ru(4)(C(O)C(2)H(5))(4)(OH)(2)(CF(3)SO(3))(2)(CO)(8) (7). At 140 degrees C the mononuclear organometallic complexes become labile intermediates of a Reppe hydrocarboxylation of ethene in fully aqueous solvent.