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.     

Fine tuning of the electronic coupling between metal centers in cyano-bridged mixed-valent trinuclear complexes

We report the synthesis, characterization, and spectroscopic properties of a family of trinuclear cyano-bridged mixed-valent compounds, trans-[Ru(II)L(4)[NCFe(III)(CN)(5)](2)](4-), trans-[Ru(II)L(4)[CNFe(III)(CN)(5)](2)](4-), and cis-[Ru(II)(bpy)(2)[NCFe(III)(CN)(5)](2)](4-) (L = pyridine, 4-tert-butylpyridine, and 4-methoxypyridine). Tetraphenylphosphonium salts of complexes trans-[Ru(II)L(4)[NCFe(III)(CN)(5)](2)](4-) (L = pyridine and 4-tert-butylpyridine) crystallize in the space groups C2 and P2(1)/c, respectively, and show a linear arrangement of the metal units and an almost completely eclipsed configuration of the equatorial ligands. An intense band (epsilon approximately 2000-9000 M(-1) cm(-1)) is observed for all of the compounds in the NIR region of the spectrum, not present in the separated building blocks, and strongly solvent dependent. We assign it as a metal-to-metal charge transfer (MMCT) from the Ru(II) to the terminal Fe(III) moieties in the context of a simplified three-center model. The electrochemistry measurements reveal a splitting of the redox waves for the reduction of the iron centers for some of the complexes with a trans configuration between the metal units, ranging from 100 to 260 mV, depending on the substituting pyridine ligand and the solvent, suggesting long-range metal-metal interactions. These interactions are rationalized in terms of the energy matching between the pi-symmetry orbitals of the metals and the cyanide bridge. The one- and two-electron reduced species derived from compounds trans-[Ru(II)L(4)[NCFe(III)(CN)(5)](2)](4-,5-,6-) were characterized in methanolic solution. The mixed-valent Fe(II)-Ru(II)-Fe(III) system exhibits an intense red shifted band in the NIR region of the spectrum, arising from the superposition of MMCT bands from the central Ru(II) to the terminal Fe(III) fragments and from the 1 nm distant Fe(II) to Fe(III) centers.     

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.     

Kinetics and mechanism of the oxidation of hydroquinones by a trans-dioxoruthenium(VI) complex

The kinetics of the oxidation of hydroquinone (H(2)Q) and its derivatives (H(2)Q-X) by trans-[Ru(VI)(tmc)(O)(2)](2+) (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) have been studied in aqueous acidic solutions and in acetonitrile. In H(2)O, the oxidation of H(2)Q has the following stoichiometry: trans-[Ru(VI)(tmc)(O)(2)](2+) + H(2)Q --> trans-[Ru(IV)(tmc)(O)(OH(2))](2+) + Q. The reaction is first order in both Ru(VI) and H(2)Q, and parallel pathways involving the oxidation of H(2)Q and HQ(-) are involved. The kinetic isotope effects are k(H(2)O)/k(D(2)O) = 4.9 and 1.2 at pH = 1.79 and 4.60, respectively. In CH(3)CN, the reaction occurs in two steps, the reduction of trans-[Ru(VI)(tmc)(O)(2)](2+) by 1 equiv of H(2)Q to trans-[Ru(IV)(tmc)(O)(CH(3)CN)](2+), followed by further reduction by another 1 equiv of H(2)Q to trans-[Ru(II)(tmc)(CH(3)CN)(2)](2+). Linear correlations between log(rate constant) at 298.0 K and the O-H bond dissociation energy of H(2)Q-X were obtained for reactions in both H(2)O and CH(3)CN, consistent with a H-atom transfer (HAT) mechanism. Plots of log(rate constant) against log(equilibrium constant) were also linear for these HAT reactions.     

Diruthenium dithiolato cyanides: basic reactivity studies and a post hoc examination of nature's choice of Fe versus Ru for hydrogenogenesis

The reaction of Ru2(S2C3H6)(CO)6 (1) with 2 equiv of Et4NCN yielded (Et4N)2[Ru2(S2C3H6)(CN)2(CO)4], (Et4N)2[3], which was shown crystallographically to consist of a face-sharing bioctahedron with the cyanide ligands in the axial positions, trans to the Ru-Ru bond. Competition experiments showed that 1 underwent cyanation >100x more rapidly than the analogous Fe2(S2C3H6)(CO)6. Furthermore, Ru2(S2C3H6)(CO)6 underwent dicyanation faster than [Ru2(S2C3H6)(CN)(CO)5]-, implicating a highly electrophilic intermediate [Ru2(S2C3H6)(mu-CO)(CN)(CO)5]-. Ru2(S2C3H6)(CO)6 (1) is noticeably more basic than the diiron compound, as demonstrated by the generation of [Ru2(S2C3H6)(mu-H)(CO)6]+, [1H]+. In contrast to 1, the complex [1H]+ is unstable in MeCN solution and converts to [Ru2(S2C3H6)(mu-H)(CO)5(MeCN)]+. (Et4N)2[3] was shown to protonate with HOAc (pKa = 22.3, MeCN) and, slowly, with MeOH and H2O. Dicyanide [3]2- is stable toward excess acid, unlike the diiron complex; it slowly forms the coordination polymer [Ru2(S2C3H6)(mu-H)(CN)(CNH)(CO)4]n, which can be deprotonated with Et3N to regenerate [H3]-. Electrochemical experiments demonstrate that [3H]- catalyzes proton reduction at -1.8 V vs Ag/AgCl. In contrast to [3]2-, the CO ligands in [3H]- undergo displacement. For example, PMe3 and [3H]- react to produce [Ru2(S2C3H6)(mu-H)(CN)2(CO)3(PMe3)]-. Oxidation of (Et4N)2[3] with 1 equiv of Cp2Fe+ gave a mixture of [Ru2(S2C3H6)(mu-CO)(CN)3(CO)3]- and [Ru2(S2C3H6)(CN)(CO)5]-, via a proposed [Ru2]2(mu-CN) intermediate. Overall, the ruthenium analogues of the diiron dithiolates exhibit reactivity highly reminiscent of the diiron species, but the products are more robust and the catalytic properties appear to be less promising.     

Isolation and molecular structure of hexacyanoruthenate(III)

The [Ru(CN)(6)](3-) ion is synthesized in aqueous solution and isolated as [Ph(4)As](3)[Ru(CN)(6)].2H(2)O (1). Compound 1 crystallizes as orange needles in the monoclinic space group P2(1)/n with cell parameters a = 11.346(2) A, b = 23.107(5) A, c = 25.015(5) A, beta = 99.55(3) degrees, V = 6467.1(22) A(3), Z = 4. The octahedral anion has Ru-C bond lengths in the range 2.023(6)-2.066(6) A. DFT calculations reproduce experimental geometries for [M(CN)(6)](3-) (M = Fe, Ru) equally well and yield significantly higher spin densities on the cyanide ligands in [M(CN)(6)](3-) (M = Ru, Os) than in [Fe(CN)(6)](3-).     

From one-dimensional chain to pentanuclear molecule. Magnetism of cyano-bridged Fe(III)-Ni(II) complexes

Two cyano-bridged Ni(II)-Fe(III) complexes [(H(3)O)[Ni(H(2)L)](2)[Fe(CN)(6)](2).[Fe(CN)(6)].6H(2)O](n) (1) and [K(18-C-6)(H(2)O)(2)][Ni(H(2)L)](2)[Fe(CN)(6)](3).4(18-C-6).20H(2)O (2) (L = 3,10-bis(2-aminoethyl)-1,3,6,8,10,12-hexaazacyclotetradecane, 18-C-6 = 18-crown-6-ether) have been synthesized and characterized structurally and magnetically. Complex 1 has a zigzag one-dimensional structure, in which two trans-CN(-) ligands of each [Fe(CN)(6)](3)(-) link two trans-[Ni(H(2)L)](4+) groups, and in turn, each trans-[Ni(H(2)L)](4+) links two [Fe(CN)(6)](3)(-) in a trans fashion. Complex 2 is composed of cyano-bridged pentanuclear molecules with moieties connected by the trans-CN(-) ligands of [Fe(CN)(6)](3)(-). Magnetic studies show the existence of ferromagnetic Ni(II)-Fe(III) interactions in both complexes. The intermetallic magnetic coupling constant of both complexes was analyzed by using an approximate model on the basis of the structural features.     

Reactions of acetonitrile coordinated to a nitrosylruthenium complex with H2O or CH(3)OH under mild conditions: structural characterization of imido-type complexes

The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) (bpy = 2,2'-bipyridine) in H(2)O at room temperature proceeded to afford two new nitrosylruthenium complexes. These complexes have been identified as nitrosylruthenium complexes containing the N-bound methylcarboxyimidato ligand, cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+), and methylcarboxyimido acid ligand, cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+), formed by an electrophilic reaction at the nitrile carbon of the acetonitrile coordinated to the ruthenium ion. The X-ray structure analysis on a single crystal obtained from CH(3)CN-H(2)O solution of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](PF(6))(3) has been performed: C(22)H(20.5)N(6)O(2)P(2.5)F(15)Ru, orthorhombic, Pccn, a = 15.966(1) A, b = 31.839(1) A, c = 11.707(1) A, V = 5950.8(4) A(3), and Z = 8. The structural results revealed that the single crystal consisted of 1:1 mixture of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+) and cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+) and the structural formula of this single crystal was thus [Ru(NO)(NH=C(OH(0.5))CH(3))(bpy)(2)](PF(6))(2.5). The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) in dry CH(3)OH-CH(3)CN at room temperature afforded a nitrosylruthenium complex containing the methyl methylcarboxyimidate ligand, cis-[Ru(NO)(NH=C(OCH(3))CH(3))(bpy)(2)](3+). The structure has been determined by X-ray structure analysis: C(25)H(29)N(8)O(18)Cl(3)Ru, monoclinic, P2(1)/c, a = 13.129(1) A, b = 17.053(1) A, c = 15.711(1) A, beta = 90.876(5) degrees, V = 3517.3(4) A(3), and Z = 4.     

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(-).     

Cyclodiphosphazanes with hemilabile ponytails: synthesis, transition metal chemistry (Ru(II), Rh(I), Pd(II), Pt(II)), and crystal and molecular structures of mononuclear (Pd(II), Rh(I)) and bi- and tetranuclear rhodium(I) complexes

Cyclodiphosphazanes having hemilabile ponytails such as cis-[(t)()BuNP(OC(6)H(4)OMe-o)](2) (2), cis-[(t)()BuNP(OCH(2)CH(2)OMe)](2) (3), cis-[(t)BuNP(OCH(2)CH(2)SMe)](2) (4), and cis-[(t)BuNP(OCH(2)CH(2)NMe(2))](2) (5) were synthesized by reacting cis-[(t)()BuNPCl](2) (1) with corresponding nucleophiles. The reaction of 2 with [M(COD)Cl(2)] afforded cis-[MCl(2)(2)(2)] derivatives (M = Pd (6), Pt (7)), whereas, with [Pd(NCPh)(2)Cl(2)], trans-[MCl(2)(2)(2)] (8) was obtained. The reaction of 2 with [Pd(PEt(3))Cl(2)](2), [{Ru(eta(6)-p-cymene)Cl(2)](2), and [M(COD)Cl](2) (M = Rh, Ir) afforded mononuclear complexes of Pd(II) (9), Ru(II) (11), Rh(I) (12), and Ir(I) (13) irrespective of the stoichiometry of the reactants and the reaction condition. In the above complexes the cyclodiphosphazane acts as a monodentate ligand. The reaction of 2 with [PdCl(eta(3)-C(3)H(5))](2) afforded binuclear complex [(PdCl(eta(3)-C(3)H(5)))(2){((t)BuNP(OC(6)H(4)OMe-o))(2)-kappaP}] (10). The reaction of ligand 3 with [Rh(CO)(2)Cl](2) in 1:1 ratio in CH(3)CN under reflux condition afforded tetranuclear rhodium(I) metallamacrocycle (14), whereas the ligands 4 and 5 afforded bischelated binuclear complexes 15 and 16, respectively. The crystal structures of 8, 9, 12, 14, and 16 are reported.     

Synthesis, structures, and properties of ruthenium(II) complexes of N-(1,10-phenanthrolin-2-yl)imidazolylidenes

Mononuclear ruthenium complexes [RuCl(L1)(CH(3)CN)(2)](PF(6)) (2a), [RuCl(L2)(CH(3)CN)(2)](PF(6)) (2b), [Ru(L1)(CH(3)CN)(3)](PF(6))(2) (4a), [Ru(L2)(CH(3)CN)(3)](PF(6))(2) (4b), [Ru(L2)(2)](PF(6))(2) (5), [RuCl(L1)(CH(3)CN)(PPh(3))](PF(6)) (6), [RuCl(L1)(CO)(2)](PF(6)) (7), and [RuCl(L1)(CO)(PPh(3))](PF(6)) (8), and a tetranuclear complex [Ru(2)Ag(2)Cl(2)(L1)(2)(CH(3)CN)(6)](PF(6))(4) (3) containing 3-(1,10-phenanthrolin-2-yl)-1-(pyridin-2-ylmethyl)imidazolylidene (L1) and 3-butyl-1-(1,10-phenanthrolin-2-yl)imidazolylidene (L2) have been prepared and fully characterized by NMR, ESI-MS, UV-vis spectroscopy, and X-ray crystallography. Both L1 and L2 act as pincer NNC donors coordinated to ruthenium (II) ion. In 3, the Ru(II) and Ag(I) ions are linked by two bridging Cl(-) through a rhomboid Ag(2)Cl(2) ring with two Ru(II) extending to above and down the plane. Complexes 2-8 show absorption maximum over the 354-428 nm blueshifted compared to Ru(bpy)(3)(2+) due to strong σ-donating and weak π-acceptor properties of NHC ligands. Electrochemical studies show Ru(II)/Ru(III) couples over 0.578-1.274 V.     

Trans ruthenium(II) complexes with NH-bridged tetradentate symmetric and asymmetric polypyridyl ligands

NH-Bridged tetradentate ligands were synthesized to achieve stable trans Ru(II) bis(polypyridyl) complexes. The polypyridyl part of the ligand was either symmetric, as in N,N-bis(1,10-phenanthroline-2-yl)amine (phen-NH-phen), or asymmetric, as in N-(1,10-phenanthroline-2-yl)-N-(6-yl-dipyridyl[2,3-a:2',3'-c]phenazine)amine (dppz-NH-phen). Protonation of phen-NH-phen with trifluoroacetic acid and the subsequent reaction with RuCl3 yield trans-[Ru(phen-NH-phen)Cl2]. The chloro ligands in this compound can easily be replaced by stronger ligands, such as CH3CN and DMSO. In this way, complexes trans-[Ru(phen-NH-phen)(CH3CN)(DMSO)](PF6)2 (1), trans-[Ru(phen-NH-phen)(DMSO)2](PF6)2 (2), and trans-[Ru(phen-NH-phen)(CH3CN)2](PF6)2 (3) were obtained. X-ray structures were determined for 1 and 3. Following a procedure similar to that used with phen-NH-phen, the complex trans-[Ru(dppz-NH-phen)(CH3CN)2](PF6)2 (4) was obtained. To our knowledge, this is the first reported trans ruthenium(II) bis(polypyridyl) complex with two different polypyridyl ligands in the equatorial plane.     

Protonation studies of the new iron carbonyl cyanide trans-[Fe(CO)3(CN)2]2-: implications with respect to hydrogenases

The new iron carbonyl cyanide trans-[Fe(CN)(2)(CO)(3)](2)(-), [2](2)(-), forms in high yield via photosubstitution of Fe(CO)(5) with 2 equiv of Et(4)NCN. Protonation of [2](2)(-) generated [HFe(CN)(2)(CO)(3)](-), [2H](-), the first H-Fe-CN-CO species. Further protonation gives dihydrogen. This simple system provides insights into hydrogen evolution by the hydrogenase enzymes, which also feature H-Fe-CN-CO centers.     

Direct Lanthanide-Transition Metal Interactions: Synthesis of (NH(3))(2)YbFe(CO)(4) and Crystal Structures of {[(CH(3)CN)(3)YbFe(CO)(4)](2).CH(3)CN}(infinity) and [(CH(3)CN)(3)YbFe(CO)(4)](infinity)

The heterometallic complex (NH(3))(2)YbFe(CO)(4) was prepared from the reduction of Fe(3)(CO)(12) by Yb in liquid ammonia. Ammonia was displaced from (NH(3))(2)YbFe(CO)(4) by acetonitrile in acetonitrile solution, and the crystalline compounds {[(CH(3)CN)(3)YbFe(CO)(4))](2).CH(3)CN}(infinity) and [(CH(3)CN)(3)YbFe(CO)(4)](infinity) were obtained. An earlier X-ray study of {[(CH(3)CN)(3)YbFe(CO)(4)](2).CH(3)CN}(infinity) showed that it is a ladder polymer with direct Yb-Fe bonds. In the present study, an X-ray crystal structure analysis also showed that [(CH(3)CN)(3)YbFe(CO)(4)](infinity) is a sheetlike array with direct Yb-Fe bonds. Crystal data for {[(CH(3)CN)(3)YbFe(CO)(4)](2).CH(3)CN}(infinity): monoclinic space group P2(1)/c, a = 21.515(8) ?, b = 7.838(2) ?, c = 19.866(6) ?, beta = 105.47(2) degrees, Z = 4. Crystal data for [(CH(3)CN)(3)YbFe(CO)(4)](infinity): monoclinic space group P2(1)/n, a = 8.364(3) ?, b = 9.605(5) ?, c = 17.240(6) ?, beta = 92.22(3) degrees, Z = 4. Electrical conductivity measurements in acetonitrile show that these acetonitrile complexes are partially dissociated into ionic species. IR and NMR spectra of the solutions reveal the presence of [HFe(CO)(4)](-). However, upon recrystallization, the acetonitrile complexes show no evidence for the presence of [HFe(CO)(4)](-) on the basis of their IR spectra. The solid state MAS (2)H NMR spectra of deuterated acetonitrile complexes give no evidence for [(2)HFe(CO)(4)](-). It appears that rupture of the Yb-Fe bond could occur in solution to generate the ion pair [L(n)Yb](2+)[Fe(CO)(4)](2-), but then the highly basic [Fe(CO)(4)](2-) anion could abstract a proton from a coordinated acetonitrile ligand to form [HFe(CO)(4)](-). However, upon crystallization, the proton could be transferred back to the ligand, which results in the neutral polymeric species.     

Metal Cyanide Ions Mx(CN)y]+,- in the gas phase: M = Fe,Co, Ni,Zn, Cd,Hg, Fe + Ag,Co + Ag

The generation of metal cyanide ions in the gas phase by laser ablation of M(CN)(2) (M = Co, Ni, Zn, Cd, Hg), Fe(III)[Fe(III)(CN)(6)] x xH(2)O, Ag(3)[M(CN)(6)] (M = Fe, Co), and Ag(2)[Fe(CN)(5)(NO)] has been investigated using Fourier transform ion cyclotron resonance mass spectrometry. Irradiation of Zn(CN)(2) and Cd(CN)(2) produced extensive series of anions, [Zn(n)(CN)(2n+1)](-) (1 < or = n < or = 27) and [Cd(n)(CN)(2n+1)](-) (n = 1, 2, 8-27, and possibly 29, 30). Cations Hg(CN)(+) and [Hg(2)(CN)(x)](+) (x = 1-3), and anions [Hg(CN)(x)](-) (x = 2, 3), are produced from Hg(CN)(2). Irradiation of Fe(III)[Fe(III)(CN)(6)] x xH(2)O gives the anions [Fe(CN)(2)](-), [Fe(CN)(3)](-), [Fe(2)(CN)(3)](-), [Fe(2)(CN)(4)](-), and [Fe(2)(CN)(5)](-). When Ag(3)[Fe(CN)(6)] is ablated, [AgFe(CN)(4)](-) and [Ag(2)Fe(CN)(5)](-) are observed together with homoleptic anions of Fe and Ag. The additional heterometallic complexes [AgFe(2)(CN)(6)](-), [AgFe(3)(CN)(8)](-), [Ag(2)Fe(2)(CN)(7)](-), and [Ag(3)Fe(CN)(6)](-) are observed on ablation of Ag(2)[Fe(CN)(5)(NO)]. Homoleptic anions [Co(n)(CN)(n+1)](-) (n = 1-3), [Co(n)(CN)(n+2)](-) (n = 1-3), [Co(2)(CN)(4)](-), and [Co(3)(CN)(5)](-) are formed when anhydrous Co(CN)(2) is the target. Ablation of Ag(3)[Co(CN)(6)] yields cations [Ag(n)(CN)(n-1)](+) (n = 1-4) and [Ag(n)Co(CN)(n)](+) (n = 1, 2) and anions [Ag(n)(CN)(n+1)](-) (n = 1-3), [Co(n)(CN)(n-1)](-) (n = 1, 2), [Ag(n)Co(CN)(n+2)](-) (n = 1, 2), and [Ag(n)Co(CN)(n+3)](-) (n = 0-2). The Ni(I) species [Ni(n)(CN)(n-1)](+) (n = 1-4) and [Ni(n)(CN)(n+1)](-) (n = 1-3) are produced when anhydrous Ni(CN)(2) is irradiated. In all cases, CN(-) and polyatomic carbon nitride ions C(x)N(y)(-) are formed concurrently. On the basis of density functional calculations, probable structures are proposed for most of the newly observed species. General structural features are low coordination numbers, regular trigonal coordination stereochemistry for d(10) metals but distorted trigonal stereochemistry for transition metals, the occurrence of M-CN-M and M(-CN-)(2)M bridges, addition of AgCN to terminal CN ligands, and the occurrence of high spin ground states for linear [M(n)(CN)(n+1)](-) complexes of Co and Ni.     

Synthesis of acetimino complexes of Pt(II) and Pt(IV) and the first heteronuclear mu-acetimido complexes

The reactions of [Ag(NH=CMe2)2]ClO4 with cis-[PtCl2L2] in a 1:1 molar ratio give cis-[PtCl(NH=CMe2)(PPh3)2]ClO4 (1cis) or cis-[PtCl(NH=CMe2)2(dmso)]ClO4 (2), and in 2:1 molar ratio, they produce [Pt(NH=CMe2)2L2](ClO4)2 [L = PPh3 (3), L2= tbbpy = 4,4'-di-tert-butyl-2,2'-dipyridyl (4)]. Complex 2 reacts with PPh3 (1:2) to give trans-[PtCl(NH=CMe2)(PPh3)2]ClO(4) (1trans). The two-step reaction of cis-[PtCl2(dmso)2], [Au(NH=CMe2)(PPh3)]ClO4, and PPh3 (1:1:1) gives [SP-4-3]-[PtCl(NH=CMe2)(dmso)(PPh3)]ClO4 (5). The reactions of complexes 2 and 4 with PhICl2 give the Pt(IV) derivatives [OC-6-13]-[PtCl3(NH=CMe2)(2)(dmso)]ClO4 (6) and [OC-6-13]-[PtCl2(NH=CMe2)2(dtbbpy)](ClO4)2 (7), respectively. Complexes 1cis and 1trans react with NaH and [AuCl(PPh3)] (1:10:1.2) to give cis- and trans-[PtCl{mu-N(AuPPh3)=CMe2}(PPh3)2]ClO4 (8cis and 8trans), respectively. The crystal structures of 4.0.5Et2O.0.5Me2CO and 6 have been determined; both exhibit pseudosymmetry.     

Syntheses, structures and properties of a series of non-heme alkoxide-Fe(III) complexes of a benzimidazolyl-rich ligand as models for lipoxygenase

The treatment of Fe(ClO(4))(2)·6H(2)O or Fe(ClO(4))(3)·9H(2)O with a benzimidazolyl-rich ligand, N,N,N',N'-tetrakis[(1-methyl-2-benzimidazolyl)methyl]-1,2-ethanediamine (medtb) in alcohol/MeCN gives a mononuclear ferrous complex, [Fe(II)(medtb)](ClO(4))(2)·?CH(3)CN·?CH(3)OH (1), and four non-heme alkoxide-iron(III) complexes, [Fe(III)(OMe)(medtb)](ClO(4))(2)·H(2)O (2, alcohol = MeOH), [Fe(III)(OEt)(Hmedtb)](ClO(4))(3)·CH(3)CN (3, alcohol = EtOH), [Fe(III)(O(n)Pr)(Hmedtb)](ClO(4))(3)·(n)PrOH·2CH(3)CN (4, alcohol = n-PrOH), and [Fe(III)(O(n)Bu)(Hmedtb)](ClO(4))(3)·3CH(3)CN·H(2)O (5, alcohol = n-BuOH), respectively. The alkoxide-iron(III) complexes all show 1) a Fe(III)-OR center (R = Me, 2; Et, 3; (n)Pr, 4; (n)Bu, 5) with the Fe-O bond distances in the range of 1.781-1.816 ?, and 2) a yellow color and an intense electronic transition around 370 nm. The alkoxide-iron(III) complexes can be reduced by organic compounds with a cis,cis-1,4-diene moiety via the hydrogen atom abstraction reaction.     

Discrete Rh(III)/Fe(II) and Rh(III)/Fe(II)/Co(III) cyanide-bridged mixed valence compounds

The heterotrinuclear complexes trans- and cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) are unprecedented examples of mixed valence complexes based on ferrocyanide bearing three different metal centers. These complexes have been assembled in a stepwise manner from their {trans-III-L(14S)Co(III)}, {cis-VI-L(15)Rh(III)}, and {Fe(II)(CN)(6)} building blocks. The preparative procedure follows that found for other known discrete assemblies of mixed valence dinuclear Cr(III)/Fe(II) and polynuclear Co(III)/Fe(II) complexes of the same family. A simple slow substitution process of [Fe(II)(CN)(6)](4-) on inert cis-VI-[Rh(III)L(15)(OH)](2+) leads to the preparation of the new dinuclear mixed valence complex [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) with a redox reactivity that parallels that found for dinuclear complexes from the same family. The combination of this dinuclear precursor with mononuclear trans-III-[Co(III)L(14S)Cl](2+) enables a redox-assisted substitution on the transient {L(14S)Co(II)} unit to form [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+). The structure of the final cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) complex has been established via X-ray diffraction and fully agrees with its solution spectroscopy and electrochemistry data. The new species [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) and [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) show the expected electronic spectra and electrochemical features typical of Class II mixed valence complexes. Interestingly, in the trinuclear complex, these features appear to be a simple addition of those for the Rh(III)/Fe(II) and Co(III)/Fe(II) moieties, despite the vast differences existent in the electronic spectra and electrochemical properties of the two isolated units.     

Cluster carbonyls of the [Re(6)(mu(3)-Se)(8)](2+) core: synthesis, structural characterization, and computational analysis

The reactions of the previously reported cluster complexes [Re(6)(mu(3)-Se)(8)(PEt(3))(5)I]I, trans-[Re(6)(mu(3)-Se)(8)(PEt(3))(4)I(2)], and cis-[Re(6)(mu(3)-Se)(8)(PEt(3))(4)I(2)] with the [Re(6)(mu(3)-Se)(8)](2+) core with CO in the presence of AgSbF(6) afforded the corresponding cluster carbonyls [Re(6)(mu(3)-Se)(8)(PEt(3))(5)(CO)][SbF(6)](2) (), trans-[Re(6)(mu(3)-Se)(8)(PEt(3))(4)(CO)(2)][SbF(6)](2) (), and cis-[Re(6)(mu(3)-Se)(8)(PEt(3))(4)(CO)(2)][SbF(6)](2) (). Infrared spectroscopy indicated weakening of the bond in CO, suggesting the existence of backbonding between the cluster core and the CO ligand(s). Electrochemical studies focusing on the reversible, one-electron oxidation of the cluster core revealed a large increase in the oxidation potential upon going from the acetonitrile derivatives to their carbonyl analogs, consistent with the depleted electron density of the cluster core upon CO ligation. Disparities between the IR spectra and oxidation potential between and indicate that electronic differences exist between sites trans and cis to the location of a ligand of interest. The active role played by the Se atoms in influencing the cluster-to-CO bonding interactions is suggested through this result and density functional (DF) computational analysis. The computations indicate that molecular orbitals near the HOMO account for backbonding interactions with a high percentage of participation of Se orbitals.     

An Approach to Heterometallic Complexes with Selenolate and Tellurolate Ligands: Crystal Structures of cis-[Mn(CO)(4)(SePh)(2)](-), [(CO)(3)Mn(&mgr;-SeMe)(3)Mn(CO)(3)](-), (CO)(4)Mn(&mgr;-TePh)(2)Co(CO)(&mgr;-SePh)(3)Mn(CO)(3), and (CO)(3)Mn(&mgr;-SePh)(3)Fe(CO)(3)

Oxidative addition of diorganyl diselenides to the coordinatively unsaturated, low-valent transition-metal-carbonyl fragment [Mn(CO)(5)](-) produced cis-[Mn(CO)(4)(SeR)(2)](-). The complex cis-[PPN][Mn(CO)(4)(SePh)(2)] crystallized in triclinic space group P&onemacr; with a = 10.892(8) ?, b = 10.992(7) ?, c = 27.021(4) ?, alpha = 101.93(4) degrees, beta = 89.79(5) degrees, gamma = 116.94(5) degrees, V = 2807(3) ?(3), and Z = 2; final R = 0.085 and R(w) = 0.094. Thermolytic transformation of cis-[Mn(CO)(4)(SeMe)(2)](-) to [(CO)(3)Mn(&mgr;-SeMe)(3)Mn(CO)(3)](-) was accomplished in high yield in THF at room temperature. Crystal data for [Na-18-crown-6-ether][(CO)(3)Mn(&mgr;-SeMe)(3)Mn(CO)(3)]: trigonal space group R&thremacr;, a = 13.533(3) ?, c = 32.292(8) ?, V = 5122(2) ?(3), Z = 6, R = 0.042, R(w) = 0.041. Oxidation of Co(2+) to Co(3+) by diphenyl diselenide in the presence of chelating metallo ligands cis-[Mn(CO)(4)(SePh)(2)](-) and cis-[Mn(CO)(4)(TePh)(2)](-), followed by a bezenselenolate ligand rearranging to bridge two metals and a labile carbonyl shift from Mn to Co, led directly to [(CO)(4)Mn(&mgr;-TePh)(2)Co(CO)(&mgr;-SePh)(3)Mn(CO)(3)]. Crystal data: triclinic space group P&onemacr;, a = 11.712(3) ?, b = 12.197(3) ?, c = 15.754(3) ?, alpha = 83.56(2) degrees, beta = 76.13(2) degrees, gamma = 72.69(2) degrees, V = 2083.8(7) ?(3), Z = 2, R = 0.040, R(w) = 0.040. Addition of fac-[Fe(CO)(3)(SePh)(3)](-) to fac-[Mn(CO)(3)(CH(3)CN)(3)](+) resulted in formation of (CO)(3)Mn(&mgr;-SePh)(3)Fe(CO)(3). This neutral heterometallic complex crystallized in monoclinic space group P2(1)/n with a = 8.707(2) ?, b = 17.413(4) ?, c = 17.541(4) ?, beta = 99.72(2) degrees, V = 2621(1) ?(3), and Z = 4; final R = 0.033 and R(w) = 0.030.