High-resolution EPR spectroscopic investigations of a homologous set of d9-cobalt(0), d9-rhodium(0), and d9-iridium(0) complexes

The 17-electron complexes [M(tropp(ph))2] (M=Co0, Rh0, Ir0) were prepared and isolated (tropp = tropylidene phosphane). A structural analysis of [Co(tropp(ph))2] revealed this complex to be almost tetrahedral, while the heavier homologues have more planar structures. Partially deuterated tropp complexes [D6][M(tropp(ph))2] were synthesised for M = Rh and Ir in order to enhance the resolution in the EPR spectra. This synthesis involves a four-fold intramolecular C-H activation reaction, whereby alkyl groups are transformed into olefins. Dihydrides were observed as intermediates for M = Ir. The electronic and geometric structures of all complexes [M(tropp(ph))2] (M = Co, Rh, Ir) and [D6][M(tropp(ph))2] (M = Rh, Ir) were investigated by continuous wave (CW) and echo-detected EPR in combination with pulse ENDOR and ESEEM techniques. In accord with their planar structures, cis and trans isomers were detected for [M(tropp(ph))2] (M = Rh0, Ir0) for which a dynamic equilibrium was established. The thermodynamic data show that the cis isomer is slightly preferred by deltaH(o) = -4.7 +/- 0.3 kJ mol(-1) (M = Rh) and delta H(o) = -5.1 +/- 0.5 kJ mol(-1); (M = Ir). The entropies for the process trans-[M(tropp(ph))2] <==> cis-[M(tropp(ph))2] are also negative [deltaS(o) = -5 +/- 1.5 J mol(-1) (M = Rh); deltaS(o) = -17 +/- 3.7 J mol(-1) (M = Rh)], indicating higher steric congestion in the cis isomers. The cobalt(0) and irdium(0) complexes show rather large g anisotropies, while that of the rhodium(0) complex is small (Co: g(parallel) = 2.320, g(perpendicular) = 2.080; cis-Rh: g(parallel) = 2.030, g(perpendicular) = 2.0135; trans-Rh: g(parallel) = 2.050, g(perpendicular) = 2.030; cis-Ir: g(parallel) = 2.030, g(perpendicular) = 2.060; trans-Ir: g(parallel) = 1.980, g(perpendicular) = 2.150). The g matrices of [M(tropp(ph))2] (M = Co, Rh) are axially symmetric with g(parallel) > g(perpendicular), indicating either a distorted square planar structure (SOMO essentially d(x2 - y2) or a compressed tetrahedron (SOMO essentially d(xy)). Interestingly, for [Ir(tropp(ph))2] the inverse ordering, g(perpendicular) > g(parallel) is found; this cannot be explained by simple ligand field arguments and must await a more sophisticated analysis. The hyperfine interactions of the unpaired electron with the metal nuclei, phosphorus nuclei, protons, deuterons and carbon nuclei were determined. By comparison with atomic constants, the spin densities on these centres were estimated and found to be small. However, the good agreement of the distance between the olefinic protons and the metal centres determined from the dipolar coupling parameter indicates that the unpaired electron is primarily located at the metal centre.     

Synthesis and characterization of iron(II) and ruthenium(II) hydrido hydrazine complexes

Treatment of trans-[MHCl(dmpe)(2)] (M = Fe, Ru) with hydrazine afforded the hydrido hydrazine complexes cis- and trans-[MH(N(2)H(4))(dmpe)(2)](+) which have been characterized by NMR spectroscopy ((1)H, (31)P, and (15)N). Both cis and trans isomers of the Fe complex and the trans isomer of the Ru complex were characterized by X-ray crystallography. Reactions with acid and base afforded a range of N(2)H(x) complexes, including several unstable hydrido hydrazido complexes.     

Studies of the isomerization and photophysical properties of a novel 2,2':6',2'-terpyridine-based ligand and its complexes

A novel 2,2':6',2'-terpyridine-based ligand L and its complexes [ML(2)](ClO(4))(2)·CH(2)Cl(2) (M = Cd 1, Zn 2, Cu 4, Mn 5), [CoL(2)](ClO(4))(2)3, CdLI(2)6 and CdL(SCN)(2)7 were synthesized and fully characterized. The crystal structures of 1-6 were solved by single crystal X-ray diffraction analysis. The linear absorption and emission properties, and third-order nonlinear optical (NLO) properties of all the complexes were systematically investigated. The equilibrium of the trans- and cis- isomers of L was studied both experimentally and theoretically. The configurations and photophysical properties of the complexes display a large dependence on the choice of metal ions and anions.     

Study of ruthenium(II) complexes with anticancer drugs as ligands. Design of metal-based phototherapeutic agents

The reaction of trans-[RuCl(2)(PPh(3))(3)] (Ph = C(6)H(5)) with 2-thio-1,3-pyrimidine (HTPYM) and 6-thiopurines (TPs) produced mainly crystalline solids that consist of cis,cis,trans-[Ru(PPh(3))(2)(N,S-TPYM)(2)] (1) and cis,cis,trans-[Ru(PPh(3))(2)(N(7),S-TPs)(2)]X(2) (X = Cl(-), CF(3)SO(3)(-)). In the case of TPs, other coordination isomers have never been isolated and reported. Instead, the mother liquor obtained after filtration of 1 produced red single crystals of trans,cis,cis-[Ru(PPh(3))(2)(N,S-TPYM)(2)].2H(3)O(+).2Cl(-) (2.2H(3)O(+).2Cl(-)). Selected ruthenium(II)-thiobase complexes were studied for their structural, reactivity, spectroscopic, redox, and cytotoxic properties. Single crystals of 1 contain thiopyrimidinato anions chelated to the metal center via N and S. The Ru[bond]N bonds are significantly elongated for 1 [2.122(2) and 2.167(2) A] with respect to 2 [2.063(3) A] because of the trans influence from PPh(3). The coordination pseudo-octahedron for 2 is significantly elongated at the apical sites (PPh(3) ligands). Solutions of cis,cis,trans isomers in air are stable for weeks, whereas those of 2 turn green within 24 h, in agreement with the respective redox potentials. cis,cis,trans- and trans,cis,cis-[Ru(PH(3))(2)(N,S-TPYM)(2)], as optimized through the DFT methods at the Becke3LYP level are in good agreement with experimental geometrical parameters (1 and 2), with cis,cis,trans being more stable than trans,cis,cis by 3.88 kcal. The trend is confirmed by molecular modeling based on semiempirical (ZINDO/1) and molecular mechanics (MM) methods. Cytotoxic activity measurements for cis,cis,trans-[Ru(PPh(3))(N-THZ)(N(7),S -H(2)TP)(2)]Cl(2) (4) (THZ = thiazole, H(2)TP = 6-thiopurine) and cis,cis,trans-[Ru(PPh(3))(2)(N(7),S-HTPR)2]Cl(2) (5) (HTPR = 6-thiopurine riboside) against ovarian cancer cells A2780/S gave IC(50) values of 17 +/- 1 and 29 +/- 9 microM, respectively. Furthermore, the spectral analysis of HTPYM, TPs, and their Ru(II) complexes in solution shows that intense absorptions occur in the UVA/vis region of light, whereas standard nucleobases absorb in the UVB region.     

Synthesis and characterization of cyclotetraphosphato complexes of Rh(I), Ir(I), Ru(II), and Pd(II)

The cyclotetraphosphate ion (P(4)O(12)(4)(-)) as a PPN (PPN = (PPh(3))(2)N(+)) salt reacts with [MCl(cod)](2) (M = Rh, Ir; cod = 1,5-cyclooctadiene) to give the dinuclear complexes (PPN)(2)[[M(cod)](2)(P(4)O(12))], in which the two metal moieties are situated trans to each other with respect to the P(4)O(4) ring in the solid state. In solution, however, these complexes exist as mixtures of trans and cis isomers. On the other hand, the P(4)O(12)(4)(-) ion reacts with 4 equiv of [Rh(cod)(MeCN)(x)](+) cation to give the tetranuclear complex [[Rh(cod)](4)(P(4)O(12))], where the four Rh(cod) fragments are bound to the P(4)O(12) platform alternately on both sides of the P(4)O(4) ring. Dinuclear P(4)O(12) complexes of ruthenium and palladium are also synthesized.     

Regulation of geometry around the ruthenium center of bis(2-pyridinecarboxylato) complexes by the nitrosyl moiety: syntheses, structures, and theoretical studies

cis-[Ru(NO)Cl(pyca)(2)] (pyca = 2-pyridinecarboxylato), in which the two pyridyl nitrogen atoms of the two pyca ligands coordinate at the trans position to each other and the two carboxylic oxygen atoms at the trans position to the nitrosyl ligand and the chloro ligand, respectively (type I shown as in Chart 1), reacted with NaOCH(3) to generate cis-[Ru(NO)(OCH(3))(pyca)(2)] (type I). The geometry of this complex was confirmed to be the same as the starting complex by X-ray crystallography: C(13.5)H(13)N(3)O(6.5)Ru; monoclinic, P2(1)/n; a = 8.120(1), b = 16.650(1), c = 11.510(1) A; beta = 99.07(1) degrees; V = 1536.7(2) A(3); Z = 4. The cis-trans geometrical change reaction occurred in the reactions of cis-[Ru(NO)(OCH(3))(pyca)(2)] (type I) in water and alcohol (ROH, R = CH(3), C(2)H(5)) to form [[trans-Ru(NO)(pyca)(2)](2)(H(3)O(2))](+) (type V) and trans-[Ru(NO)(OR)(pyca)(2)] (type V). The reactions of the trans-form complexes, trans-[Ru(NO)(H(2)O)(pyca)(2)](+) (type V) and trans-[Ru(NO)(OCH(3))(pyca)(2)] (type V), with Cl(-) in hydrochloric acid solution afforded the cis-form complex, cis-[Ru(NO)Cl(pyca)(2)] (type I). The favorable geometry of [Ru(NO)X(pyca)(2)](n)(+) depended on the nature of the coexisting ligand X. This conclusion was confirmed by theoretical, synthetic, and structural studies. The mono-pyca-containing nitrosylruthenium complex (C(2)H(5))(4)N[Ru(NO)Cl(3)(pyca)] was synthesized by the reaction of [Ru(NO)Cl(5)](2)(-) with Hpyca and characterized by X-ray structural analysis: C(14)H(24)N(3)O(3)Cl(3)Ru; triclinic, Ponemacr;, a = 7.631(1), b = 9.669(1), c = 13.627(1) A; alpha = 83.05(2), beta = 82.23(1), gamma = 81.94(1) degrees; V = 981.1(1) A(3); Z = 2. The type II complex of cis-[Ru(NO)Cl(pyca)(2)] was synthesized by the reaction of [Ru(NO)Cl(3)(pyca)](-) or [Ru(NO)Cl(5)](2)(-) with Hpyca and isolated by column chromatography. The structure was determined by X-ray structural analysis: C(12)H(8)N(3)O(5)ClRu; monoclinic, P2(1)/n; a = 10.010(1), b = 13.280(1), c = 11.335(1) A; beta = 113.45(1) degrees; V = 1382.4(2) A(3); Z = 4.     

cis-[Ru(2,2':6',2' '-terpyridine)(DMSO)Cl(2)]: useful precursor for the synthesis of heteroleptic terpyridine complexes under mild conditions

[Ru(II)(terpy)(DMSO)Cl(2)] complexes were synthesized as a 5/1 mixture of cis and trans isomers, and their reactivities with CO and with substituted 2,2':6',2' '-terpyridine (terpy) moieties have been investigated. The structure of a trans isomer and its CO adduct have been unambiguously assigned by spectroscopy and X-ray diffraction. The [Ru(terpy)(terpy-Br)](2+) complex prepared either from the cis-[Ru(II)(terpy)(DMSO)Cl(2)] or from the cis-[Ru(II)(terpy-Br)(DMSO)Cl(2)] precursor appeared to be reactive in cross-coupling reactions promoted by low-valent palladium(0) and is an attractive target for the stepwise synthesis of polynuclear complexes bearing vacant coordination sites (terpy-Br for 4'-bromo-2,2':6',2' '-terpyridine). Several bipyridine, phenanthroline, and bipyrimidine complexes were prepared this way and their optical and redox properties determined and discussed.     

Univalent gallium and indium phosphane complexes: from pyramidal M(PPh3)3(+) to carbene-analogous bent M(PtBu3)2(+) (M=Ga, In) complexes

In a new oxidative route, Ag(+)[Al(OR(F))(4)](-) (R(F)=C(CF(3))(3)) and metallic indium were sonicated in aromatic solvents, such as fluorobenzene (PhF), to give a precipitate of silver metal and highly soluble [In(PhF)(n)](+) salts (n=2, 3) with the weakly coordinating [Al(OR(F))(4)](-) anion in quantitative yield. The In(+) salt and the known analogous Ga(+)[Al(OR(F))(4)](-) were used to synthesize a series of homoleptic PR(3) phosphane complexes [M(PR(3))(n)](+), that is, the weakly PPh(3)-bridged [(Ph(3)P)(3)In-(PPh(3))-In(PPh(3))(3)](2+) that essentially contains two independent [In(PPh(3))(3)](+) cations or, with increasing bulk of the phosphane, the carbene-analogous [M(PtBu(3))(2)](+) (M=Ga, In) cations. The M(I)-P distances are 27 to 29 pm longer for indium, and thus considerably longer than the difference between their tabulated radii (18 pm). The structure, formation, and frontier orbitals of these complexes were investigated by calculations at the BP86/SV(P), B3LYP/def2-TZVPP, MP2/def2-TZVPP, and SCS-MP2/def2-TZVPP levels.     

Electronic structures of ruthenium and osmium complexes of 9,10-phenanthrenequinone

The reaction of 9,10-phenanthrenequinone (PQ) with [M(II)(H)(CO)(X)(PPh(3))(3)] in boiling toluene leads to the homolytic cleavage of the M(II)-H bond, affording the paramagnetic trans-[M(PQ)(PPh(3))(2)(CO)X] (M = Ru, X = Cl, 1; M = Os, X = Br, 3) and cis-[M(PQ)(PPh(3))(2)(CO)X] (M = Ru, X = Cl, 2; M = Os, X = Br, 4) complexes. Single-crystal X-ray structure determinations of 1, 2·toluene, and 4·CH(2)Cl(2), EPR spectra, and density functional theory (DFT) calculations have substantiated that 1-4 are 9,10-phenanthrenesemiquinone radical (PQ(?-)) complexes of ruthenium(II) and osmium(II) and are defined as trans-[Ru(II)(PQ(?-))(PPh(3))(2)(CO)Cl] (1), cis-[Ru(II)(PQ(?-))(PPh(3))(2)(CO)Cl] (2), trans-[Os(II)(PQ(?-))(PPh(3))(2)(CO) Br] (3), and cis-[Os(II)(PQ(?-))(PPh(3))(2)(CO)Br] (4). Two comparatively longer C-O [average lengths: 1, 1.291(3) ?; 2·toluene, 1.281(5) ?; 4·CH(2)Cl(2), 1.300(8) ?] and shorter C-C lengths [1, 1.418(5) ?; 2·toluene, 1.439(6) ?; 4·CH(2)Cl(2), 1.434(9) ?] of the OO chelates are consistent with the presence of a reduced PQ(?-) ligand in 1-4. A minor contribution of the alternate resonance form, trans- or cis-[M(I)(PQ)(PPh(3))(2)(CO)X], of 1-4 has been predicted by the anisotropic X- and Q-band electron paramagnetic resonance spectra of the frozen glasses of the complexes at 25 K and unrestricted DFT calculations on 1, trans-[Ru(PQ)(PMe(3))(2)(CO)Cl] (5), cis-[Ru(PQ)(PMe(3))(2)(CO)Cl] (6), and cis-[Os(PQ)(PMe(3))(2)(CO)Br] (7). However, no thermodynamic equilibria between [M(II)(PQ(?-))(PPh(3))(2)(CO)X] and [M(I)(PQ)(PPh(3))(2)(CO)X] tautomers have been detected. 1-4 undergo one-electron oxidation at -0.06, -0.05, 0.03, and -0.03 V versus a ferrocenium/ferrocene, Fc(+)/Fc, couple because of the formation of PQ complexes as trans-[Ru(II)(PQ)(PPh(3))(2)(CO)Cl](+) (1(+)), cis-[Ru(II)(PQ)(PPh(3))(2)(CO)Cl](+) (2(+)), trans-[Os(II)(PQ)(PPh(3))(2)(CO)Br](+) (3(+)), and cis-[Os(II)(PQ)(PPh(3))(2)(CO)Br](+) (4(+)). The trans isomers 1 and 3 also undergo one-electron reduction at -1.11 and -0.96 V, forming PQ(2-) complexes trans-[Ru(II)(PQ(2-))(PPh(3))(2)(CO)Cl](-) (1(-)) and trans-[Os(II)(PQ(2-))(PPh(3))(2)(CO)Br](-) (3(-)). Oxidation of 1 by I(2) affords diamagnetic 1(+)I(3)(-) in low yields. Bond parameters of 1(+)I(3)(-) [C-O, 1.256(3) and 1.258(3) ?; C-C, 1.482(3) ?] are consistent with ligand oxidation, yielding a coordinated PQ ligand. Origins of UV-vis/near-IR absorption features of 1-4 and the electrogenerated species have been investigated by spectroelectrochemical measurements and time-dependent DFT calculations on 5, 6, 5(+), and 5(-).     

Preparation and characterization of mixed-ligand cobalt(III) complexes containing (3-aminopropyl)dimethylphosphine (pdmp). Conformation of the six-membered pdmp chelate ring

Several new cobalt(III) complexes containing (3-aminopropyl)dimethylphosphine (pdmp) have been prepared, and their molecular structures have been determined. A dichloro complex of trans(Cl,Cl)-cis(P,P)-[CoCl(2)(pdmp)(2)]PF(6) (1) was prepared from trans-[CoCl(2)(py)(4)]Cl.6H(2)O and pdmp. X-Ray crystallography confirmed the (C(2))-chair(2) conformation of two six-membered pdmp chelate rings in 1, while the analogous 1,3-bis(dimethylphosphino)propane (dmpp) complex trans-[CoCl(2)(dmpp)(2)]ClO(4) (3) exhibited the (D(2d))-twist(2) conformation. Substitution reactions of 1 for ethane-1,2-diamine (en), pentane-2,4-dionate (acac), and N,N-dimethyldithiocarbamate (dtc) gave the mixed-ligand tris(chelate)-type complexes of [Co(en)(2)(pdmp)]Cl(2)(PF(6)) (5), [Co(acac)(pdmp)(2)](PF(6))(2) (7), and [Co(dtc)(3-n)(pdmp)(n)](PF(6))(n) [n = 1 (9) or 2 (10)], respectively. The conformer of the complex cation in 5 was assigned as lel.ob.chair by X-ray analysis. In the case of the acac complex 7, both trans(P,N) (7a) and trans(N,N) (7b) isomers were isolated, and the complex cations were characterized as syn-chair(2) and anti-chair(2) conformers, respectively, with respect to the six-membered pdmp chelate rings. These conformers coincide with the most stable ones anticipated by the DFT optimum geometry calculations. In the crystal structure of trans(P,N)-[Co(dtc)(pdmp)(2)](BPh(4))(2) (10') one of the pdmp chelate rings adopted a skew-boat (twist) conformation, which reduced the intramolecular steric ring-ring interaction effectively. The DFT optimized geometries for several isomers and/or conformers of [CoCl(2)(pdmp)(2)](+) were compared.     

Six-coordinate and five-coordinate Fe(II)(CN)(2)(CO)(x) thiolate complexes (x = 1, 2): synthetic advances for iron sites of [NiFe] hydrogenases

The dicyanodicarbonyliron(II) thiolate complexes trans,cis-[(CN)(2)(CO)(2)Fe(S,S-C-R)](-) (R = OEt (2), N(Et)(2) (3)) were prepared by the reaction of [Na][S-C(S)-R] and [Fe(CN)(2)(CO)(3)(Br)](-) (1). Complex 1 was obtained from oxidative addition of cyanogen bromide to [Fe(CN)(CO)(4)](-). In a similar fashion, reaction of complex 1 with [Na][S,O-C(5)H(4)N], and [Na][S,N-C(5)H(4)] produced the six-coordinate trans,cis-[(CN)(2)(CO)(2)Fe(S,O-C(5)H(4)N)](-) (6) and trans,cis-[(CN)(2)(CO)(2)Fe(S,N-C(5)H(4))](-) (7) individually. Photolysis of tetrahydrofuran (THF) solution of complexes 2, 3, and 7 under CO led to formation of the coordinatively unsaturated iron(II) dicyanocarbonyl thiolate compounds [(CN)(2)(CO)Fe(S,S-C-R)](-) (R = OEt (4), N(Et)(2) (5)) and [(CN)(2)(CO)Fe(S,N-C(5)H(4))](-) (8), respectively. The IR v(CN) stretching frequencies and patterns of complexes 4, 5, and 8 have unambiguously identified two CN(-) ligands occupying cis positions. In addition, density functional theory calculations suggest that the architecture of five-coordinate complexes 4, 5, and 8 with a vacant site trans to the CO ligand and two CN(-) ligands occupying cis positions serves as a conformational preference. Complexes 2, 3, and 7 were reobtained when the THF solution of complexes 4, 5, and 8 were exposed to CO atmosphere at 25 degrees C individually. Obviously, CO ligand can be reversibly bound to the Fe(II) site in these model compounds. Isotopic shift experiments demonstrated the lability of carbonyl ligands of complexes 2, 3, 4, 5, 7, and 8. Complexes [(CN)(2)(CO)Fe(S,S-C-R)](-) and NiA/NiC states [NiFe] hydrogenases from D. gigas exhibit a similar one-band pattern in the v(CO) region and two-band pattern in the v(CN) region individually, but in different positions, which may be accounted for by the distinct electronic effects between [S,S-C-R](-) and cysteine ligands. Also, the facile formations of five-coordinate complexes 4, 5, and 8 imply that the strong sigma-donor, weak pi-acceptor CN(-) ligands play a key role in creating/stabilizing five-coordinate iron(II) [(CN)(2)(CO)Fe(S,S-C-R)](-) complexes with a vacant coordination site trans to the CO ligand.     

Coordination Chemistry of Low-Valent Rhenium Polypyridyl Complexes: Synthesis, Reactivity, and Electrochemistry

The complex Re(III)(benzil)(PPh(3))Cl(3) (2) is used to synthesize a variety of Re(III) and Re(II) polypyridyl complexes of the type cis-[Re(III)(L(2))(2)Cl(2)](+), [Re(II)(L(2))(3)](2+), Re(III)(L(3))Cl(3), [Re(III)(L(3))(2)Cl](2+), and [Re(III)(L(4))Cl(2)](+), where L(2) = bpy (3and 6), tbpy (4 and 7), phen (5 and 8); L(3) = terpy (9and 10); L(4) = TMPA (11). The complex cis-[Re(III)(bpy)(2)Cl(2)](+) (3) is a useful synthon in the formation of complexes of the type [Re(bpy)(2)L(x)()](n)()(+) that are six- or seven-coordinate Re(III) complexes (13, 16, and 18) or octahedral Re(II) or Re(I) complexes (12 and 17). The [Re(III)(terpy)(2)Cl](2+) (10) complex can be reduced to form the Re(I) complex, [Re(I)(terpy)(2)](+) (21) and then electrochemically reoxidized to form new complexes of the type [Re(III)(terpy)(2)L](n)()(+). Similar behavior is observed for the [Re(II)(bpy)(3)](2+) (6) complex where [Re(III)(bpy)(3)((t)BuNC)](3+) (20) and [Re(I)(bpy)(3)](+) (19) may be formed. The electrochemistry of these complexes is discussed in relation to their reactivity and the observed pi-acidity of the polypyridyl ligands. In addition, X-ray crystal structures for cis-[Re(III)(bpy)(2)Cl(2)]PF(6) (3) and [Re(I)(bpy)(3)]PF(6) (19) are reported. cis-[Re(III)(bpy)(2)Cl(2)]PF(6) (3, ReC(20)H(16)N(4)Cl(2)F(6)P) crystallizes in the monoclinic space group C2/c with Z = 4 and lattice parameters a = 15.043(5) ?, b = 13.261(4) ?, c = 12.440(4) ?, and beta = 108.86(2) degrees at -100 degrees C. [Re(I)(bpy)(3)]PF(6) (19, ReC(30)H(24)N(6)F(6)P) crystallizes in the rhombohedral space group R&thremacr;c(h) (No. 167) with Z = 12 and lattice parameters a = 13.793(3) ? and c = 51.44(3) ? at -100 degrees C.     

The role of the atomic charges on the ligands and platinum(II) in affecting the cis and trans influences in [PtXL(PPh3)2]+ complexes (X = NO3, Cl, Br, I; L = 4-substituted pyridines, amines, PPh3). A 31P NMR and DFT investigation

One bond Pt-P coupling constants (1)J(PtP) of a series of cationic complexes [PtXL(PPh(3))(2)](+) (X = NO(3), Cl, Br, I; L = 4-Z-pyridines, Z = electron withdrawing or releasing groups, 4a-k; or X = Cl, L = NH(3), PhCH(2)NH(2) and (i)PrNH(2), 5a-c) have been used to establish the trans and cis influence sequences of X and pyridines. The crystal structure of compound 4f(BF(4)) with Z = (t)Bu has been resolved. In the pyridine complexes 4a-d (Z = H, variable X), both the trans and cis influence series of the anionic ligands X decrease along the same sequence I > Br > Cl > NO(3), as previously found for [PtX(PPh(3))(3)](+) (X = NO(3), Cl, Br, I, 3a-d), however in 4a-d the cis influence turns out to be more important than the trans. On the contrary, in [PtCl(4-Z-py)(PPh(3))(2)](+) (4b,e-k) the sequence of the trans influence of the 4-Z-pyridines is opposite to that of the cis, the latter being Z = CN > CHO > Br > PhCO > H > Me > (t)Bu > NH(2), i.e. the most basic pyridine gives rise to the lowest cis influence. This correlation was found to hold also for complexes 5a-c (L = amines). All the observed trends have been fully reproduced by B3LYP/def2-SVP DFT calculations, by looking at the relevant optimized bond lengths of selected complexes of type 3, 4 and 5. Subsequent evaluation of the atomic charges, by resorting to two independent methods, i.e., the Natural Bond Order analysis of the wavefunction and the Bader's Quantum Theory of Atoms in Molecules, allowed for rationalization of the origin of the cis and trans influences. The negative charge on the nitrogen atoms of free pyridines becomes more negative upon protonation and even more so when coordinated to the [PtCl(PPh(3))(2)](+) moiety. The least negatively charged nitrogen atom of coordinated pyridines is that of 4-CN-py (the highest cis influencing pyridine derivative), which gives rise to the lowest positive charge on Pt, confirming the relationship between the lowering of the charge on the metal ion and a high cis influence. The trans influence can be described in terms of competition between the charges on the two trans donor atoms. In contrast with the behaviour of pyridines, the positive charge on the phosphorous atom of free PPh(3) increases upon coordination to Pt(II), moreover the PPh(3) ligands acquire a substantial positive charge, thus efficiently delocalising the charge of the cationic complex.     

Large effects of ion pairing and protonic-hydridic bonding on the stereochemistry and basicity of crown-, azacrown-, and cryptand-222-potassium salts of anionic tetrahydride complexes of iridium(III)

The compounds [K(Q)][IrH(4)(PR(3))(2)] (Q = 18-crown-6, R = Ph, (i)Pr, Cy; Q = aza-18-crown-6, R = (i)Pr; Q = 1,10-diaza-18-crown-6, R = Ph, (i)Pr, Cy; Q = cryptand-222, R = (i)Pr, Cy) were formed in the reactions of IrH(5)(PR(3))(2) with KH and Q. In solution, the stereochemistry of the salts of [IrH(4)(PR(3))(2)](-) is surprisingly sensitive to the countercation: either trans as the potassium cryptand-222 salts (R = Cy, (i)Pr) or exclusively cis (R = Cy, Ph) as the crown- and azacrown-potassium salts or a mixture of cis and trans (R = (i)Pr). There is IR evidence for protonic-hydridic bonding between the NH of the aza salts and the iridium hydride in solution. In single crystals of [K(18-crown-6)][cis-IrH(4)(PR(3))(2)] (R = Ph, (i)Pr) and [K(aza-18-crown-6)][cis-IrH(4)(P(i)Pr(3))(2)], the potassium bonds to three hydrides on a face of the iridium octahedron according to X-ray diffraction studies. Significantly, [K(1,10-diaza-18-crown-6)][trans-IrH(4)(P(i)Pr(3))(2)] crystallizes in a chain structure held together by protonic-hydridic bonds. In [K(1,10-diaza-18-crown-6)][cis-IrH(4)(PPh(3))(2)], the potassium bonds to two hydrides so that one NH can form an intra-ion-pair protonic-hydridic hydrogen bond while the other forms an inter-ion-pair NH.HIr hydrogen bond to form chains through the lattice. Thus, there is a competition between the potassium and NH groups in forming bonds with the hydrides on iridium. The more basic P(i)R(3) complex has the lower N-H stretch in the IR spectrum because of stronger N[bond]H...HIr hydrogen bonding. The trans complexes have very low Ir-H wavenumbers (1670-1680) due to the trans hydride ligands. The [K(cryptand)](+) salt of [trans-IrH(4)(P(i)Pr(3))(2)](-) reacts with WH(6)(PMe(2)Ph)(3) (pK(alpha)(THF) 42) to give an equilibrium (K(eq) = 1.6) with IrH(5)(P(i)Pr(3))(2) and [WH(5)(PMe(2)Ph)(3)](-) while the same reaction of WH(6)(PMe(2)Ph)(3) with the [K(18-crown-6)](+) salt of [cis-IrH(4)(P(i)Pr(3))(2)](-) has a much larger equilibrium constant (K(eq) = 150) to give IrH(5)(P(i)Pr(3))(2) and [WH(5)(PMe(2)Ph)(3)](-); therefore, the tetrahydride anion displays an unprecedented increase (about 100-fold) in basicity with a change from [K(crypt)](+) to [K(crown)](+) countercation and a change from trans to cis stereochemistry. The acidity of the pentahydrides decrease in THF as IrH(5)(P(i)Pr(3))(2)/[K(crypt)][trans-IrH(4)(P(i)Pr(3))(2)] (pK(alpha)(THF) = 42) > IrH(5)(PCy(3))(2)/[K(crypt)][trans-IrH(4)(PCy(3))(2)] (pK(alpha)(THF) = 43) > IrH(5)(P(i)Pr(3))(2)/[K(crown)][cis-IrH(4)(P(i)Pr(3))(2)] (pK(alpha)(THF) = 44) > IrH(5)(PCy(3))(2)/[K(crown)][cis-IrH(4)(PCy(3))(2)]. The loss of PCy(3) from IrH(5)(PCy(3))(2) can result in mixed ligand complexes and H/D exchange with deuterated solvents. Reductive cleavage of P-Ph bonds is observed in some preparations of the PPh(3) complexes.     

Multinuclear platinum(II)-amine complexes containing bis(aminopropyl)dicarba-closo-dodecaborane(12) ligands

Treatment of the bridging bidentate 1,Z-bis(aminopropyl)-1,Z-dicarba-closo-dodecaborane(12)(1,Z-bis(aminopropyl)-1,Z-carborane) ligands of the type 1,Z-[H(2)N(CH(2))(3)](2)-1,Z-C(2)B(10)H(10)(L(1), Z= 7, 5) or (L(2), Z= 12, 6) with two equivalents of trans-[PtClI(2)(NH(3))](-), followed by halogen ligand metathesis with AgOTf and HCl((aq)) afforded the novel diplatinum(II)-amine species cis-[[PtCl(2)(NH(3))](2)L(n)](7(n= 1) or 8(n= 2), respectively). Similarly, the reaction of L(1) or L(2) with the labile trans-[PtCl(dmf)(NH(3))(2)](+) afforded trans-[[PtCl(NH(3))(2)](2)L(n)](OTf)(2)(9(n= 1) or 10(n= 2), respectively) in good yield and purity. However, isolation of the analogous 1,2-carborane complexes was not possible owing to decomposition reactions that led to extensive degradation of the carborane cage and reduction of the metal centre. The mixed dinuclear complex [cis-[PtCl(2)(NH(3))]-L(1)-trans-[PtCl(NH(3))(2)]]OTf (19) was prepared by treatment of the Boc-protected amine ligand 1-[(Boc)(2)N(CH(2))(3)]-7-[H(2)N(CH(2))(3)]-1,7-C(2)B(10)H(10)(L(3), 15) with trans-[PtCl(dmf)(NH(3))(2)](+) to yield trans-[PtCl(NH(3))(2)L(3)]OTf (16), followed by acid deprotection of the pendant amine group, complexation with trans-[PtClI(2)(NH(3))](-), and halogen ligand metathesis using AgOTf and HCl((aq)). A novel trinuclear species containing 5 was prepared by the addition of two equivalents of 15 to the labile precursor cis-[Pt(dmf)(2)(NH(3))(2)](2+) followed by acid deprotection of the pendant amine groups. Further complexation with two equivalents of trans-[PtClI(2)(NH(3))](-) followed by halogen ligand metathesis using AgOTf and HCl((aq)) afforded the triplatinum(II)-amine species [cis-[Pt(NH(3))(2)(L(1))(2)]-cis-[PtCl(2)(NH(3))](2)](OTf)(2)(23). Complexes 7-10, 19 and 23 represent the first examples of multinuclear platinum(ii)-amine derivatives containing carborane cages. Preliminary in vitro cytotoxicity studies for selected complexes are also reported.     

New ruthenium(II) complexes with enantiomerically pure bis- and tris(pinene)-fused tridentate ligands. Synthesis, characterization and stereoisomeric analysis

A new set of Ru-Cl complexes containing either the pinene[5,6]bpea ligand (L1) or the C3 symmetric pinene[4,5]tpmOMe (L2) tridentate ligand in combination with the bidentate (B) 2,2'-bipyridine (bpy) or 1,2-diphenylphosphinoethane (dppe) with general formula [RuCl(L1 or L2)(B)](+) have been prepared and thoroughly characterized. In the solid state, X-ray diffraction analysis techniques have been used. In solution, cyclic voltammetry (CV) and 1D and 2D NMR spectroscopy have been employed. DFT calculations have been also performed on these complexes and their achiral analogues previously reported in our group, to interpret and complement experimental results. Whereas isomerically pure complexes ([Ru(II)Cl(L2)(bpy)](BF4), 5 and [Ru(II)Cl(L2)(dppe)](BF4), 6) are obtained when starting from the highly symmetric [Ru(III)Cl3(L2)], 2, isomeric mixtures of cis, fac-[Ru(II)Cl(L1)(bpy)](BF4) (3b/3b'), trans,fac- (3a) and up/down,mer- (3c, 3d) isomers are formed when bpy is added to the less symmetric [Ru(III)Cl3(L1)], 1, in contrast to the case of the bulky dppe ligand that, upon coordination to 1, leads to the trans,fac-[Ru(II)Cl(L1)(dppe)](BF4) (4a) complex as a sole isomer due to steric factors.     

Cobalt(III) complexes of monodentate N9-bound adeninate (ade-), [Co(ade-kappaN9)Cl(en)2]+ (en = 1,2-diaminoethane): syntheses, crystal structures, and protonation behaviors of the geometrical isomers

In acidic aqueous solution, a cobalt(III) complex containing monodentate N(9)-bound adeninate (ade(-)), cis-[Co(ade-kappaN(9))Cl(en)(2)]Cl (cis-[1]Cl), underwent protonation to the adeninate moiety without geometrical isomerization or decomposition of the Co(III) coordination sphere, and complexes of cis-[CoCl(Hade)(en)(2)]Cl(2) (cis-[2]Cl(2)) and cis-[Co(H(2)ade)Cl(en)(2)]Cl(3) (cis-[3]Cl(3)) could be isolated. The pK(a) values of the Hade and H(2)ade(+) complexes are 6.03(1) and 2.53(12), respectively, at 20 degrees C in 0.1 M aqueous NaCl. The single-crystal X-ray analyses of cis-[2]Cl(2).0.5H(2)O and cis-[3]Cl(2)(BF(4)).H(2)O revealed that protonation took place first at the adeninate N(7) and then at the N(1) atoms to form adenine tautomer (7H-Hade-kappaN(9)) and cationic adeninium (1H,7H-H(2)ade(+)-kappaN(9)) complexes, respectively. On the other hand, addition of NaOH to an aqueous solution of cis-[1]Cl afforded a mixture of geometrical isomers of the hydroxo-adeninato complex, cis- and trans-[Co(ade-kappaN(9))(OH)(en)(2)](+). The trans-isomer of chloro-adeninato complex trans-[Co(ade-kappaN(9))Cl(en)(2)]BF(4) (trans-[1]BF(4)) was synthesized by a reaction of cis-[2](BF(4))(2) and sodium methoxide in methanol. This isomer in acidic aqueous solution was also stable toward isomerization, affording the corresponding adenine tautomer and adeninium complexes (pK(a) = 5.21(1) and 2.48(9), respectively, at 20 degrees C in 0.1 M aqueous NaCl). The protonated product of trans-[Co(7H-Hade-kappaN(9))Cl(en)(2)](BF(4))(2).H(2)O (trans-[2](BF(4))(2).H(2)O) could also be characterized by X-ray analysis. Furthermore, the hydrogen-bonding interactions of the adeninate/adenine tautomer complexes cis-[1]BF(4), cis-[2](BF(4))(2), and trans-[2](BF(4))(2) with 1-cyclohexyluracil in acetonitrile-d(3) were investigated by (1)H NMR spectroscopy. The crystal structure of trans-[Co(ade)(H(2)O)(en)(2)]HPO(4).3H(2)O, which was obtained by a reaction of trans-[Co(ade)(OH)(en)(2)]BF(4) and NaH(2)PO(4), was also determined.     

Synthesis, characterization, and cytotoxicity of platinum(IV) carbamate complexes

The synthesis, characterization, and cytotoxicity of eight new platinum(IV) complexes having the general formula cis,cis,trans-[Pt(NH(3))(2)Cl(2)(O(2)CNHR)(2)] are reported, where R = tert-butyl (4), cyclopentyl (5), cyclohexyl (6), phenyl (7), p-tolyl (8), p-anisole (9), 4-fluorophenyl (10), or 1-naphthyl (11). These compounds were synthesized by reacting organic isocyanates with the platinum(IV) complex cis,cis,trans-[Pt(NH(3))(2)Cl(2)(OH)(2)]. The electrochemistry of the compounds was investigated by cyclic voltammetry. The aryl carbamate complexes 7-11 exhibit reduction peak potentials near -720 mV vs Ag/AgCl, whereas the alkyl carbamate complexes display reduction peak potentials between -820 and -850 mV vs Ag/AgCl. The cyclic voltammograms of cis,cis,trans-[Pt(NH(3))(2)Cl(2)(O(2)CCH(3))(2)] (1), cis,cis,trans-[Pt(NH(3))(2)Cl(2)(O(2)CCF(3))(2)] (2), and cis-[Pt(NH(3))(2)Cl(4)] (3) were measured for comparison. Density functional theory studies were undertaken to investigate the electronic structures of 1-11 and to determine their adiabatic electron affinities. A linear correlation (R(2) = 0.887) between computed adiabatic electron affinities and measured reduction peak potentials was discovered. The biological activity of 4-11 and, for comparison, cisplatin was evaluated in human lung cancer A549 and normal MRC-5 cells by the MTT assay. The compounds exhibit comparable or slightly better activity than cisplatin against the A549 cells. In MRC-5 cells, all are equally or slightly less cytotoxic than cisplatin, except for 4 and 5, which are more toxic.     

Synthesis and structures of cis- and trans-bis(alkyneselenolato)platinum(II) complexes

The reaction of 2 equiv of LiSeCC-n-C(5)H(11) (1) with cis-PtCl(2)(Ph(3)P)(2) (2) gives a mixture of the cis and trans isomers of Pt(Ph(3)P)(2)(SeCC-n-C(5)H(11))(2) (3), which slowly isomerizes in CH(2)Cl(2) to the preferred trans form trans-3. The closely related cis-[Pt(dppf)(2)(SeCC-n-C(5)H(11))(2)] (4) (dppf = bis(diphenylphosphino)ferrocene) was prepared by a similar metathetical reaction using the platinum chloride complex of the chelating dppf to impose the cis geometry. The structures of the cis and trans complexes have been investigated in solution by heteronuclear NMR ((31)P, (77)Se, and (195)Pt) and, in the cases of trans-3 and 4, characterized in the solid state by single-crystal X-ray diffraction. Changing the coordination geometry from cis to trans induces significant changes in the structural and spectroscopic parameters, which do not comply with the previously anticipated donor-acceptor properties of selenolate ligands.     

Ligand substitution,pH dependent deoxygenation,and linkage isomerization reactions of the 2,2'-bipyridinetetranitroruthenate dianion

The reaction of the [Ru(bpy)(NO(2))(4)](2-) (bpy = 2,2'-bipyridine) ion in aqueous solutions produces two different nitrosyl complexes, depending on the pH of the solution. At acidic pH, complex cis,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) was isolated. At neutral or basic pH, [Ru(bpy)(NO(2))(4)](2-) reacts to give cis,trans-Ru(bpy)(NO(2))(2)(NO)(OH). Both new complexes were fully characterized by elemental analysis and UV-vis, IR, (1)H NMR, and (15)N NMR spectroscopy. A single-crystal X-ray structure of cis,trans-Ru(bpy)(NO(2))(2)(NO)(OH) was also obtained. cis,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) isomerizes in acetone or water solution to give a mixture of the trans,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) and cis,cis-Ru(bpy)(ONO)(2)(NO(2))(NO) linkage isomers as determined by (1)H and (15)N NMR spectroscopy. A single-crystal X-ray structure of a solid solution of cis,cis-Ru(bpy)(ONO)(2)(NO(2))(NO)/trans,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) was also obtained. This pair of isomers is the first crystallographically characterized compound with nitro, nitrito, and nitrosyl ligands. The kinetic studies of the Ru-NO(2) --> Ru-NO conversion reactions of [Ru(bpy)(NO(2))(4)](2)(-) in buffered solutions from pH 3 to pH 9 complement previous studies of the reverse reaction. The reactions are first order in [Ru(bpy)(NO(2))(4)](2-). At high pH, the reaction is independent of the concentration of H(+) while, at low pH, the reaction is first order in the concentration of H(+). The rate determining step of the high pH reaction involves breakage of the Ru-NO(2) bond while, at low pH, the mechanism involves a rapid reversible protonation of a NO(2) ligand followed by the rate determining loss of hydroxide to produce a nitrosyl ligand.