Dinuclear iron(II)-cyanocarbonyl complexes linked by two/three bridging ethylthiolates: relevance to the active site of [Fe] hydrogenases

Dinuclear iron(II)-cyanocarbonyl complex [PPN](2)[Fe(CN)(2)(CO)(2)(mu-SEt)](2) (1) was prepared by the reaction of [PPN][FeBr(CN)(2)(CO)(3)] and [Na][SEt] in THF at ambient temperature. Reaction of complex 1 with [PPN][SEt] produced the triply thiolate-bridged dinuclear Fe(II) complex [PPN][(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)] (2) with the torsion angle of two CN(-) groups (C(5)N(2) and C(3)N(1)) being 126.9 degrees. The extrusion of two sigma-donor CN(-) ligands from Fe(II)Fe(II) centers of complex 1 as a result of the reaction of complex 1 and [PPN][SEt] reflects the electron-rich character of the dinuclear iron(II) when ligated by the third bridging ethylthiolate. The Fe-S distances (2.338(2) and 2.320(3) A for complexes 1 and 2, respectively) do not change significantly, but the Fe(II)-Fe(II) distance contracts from 3.505 A in complex 1 to 3.073 A in complex 2. The considerably longer Fe(II)-Fe(II) distance of 3.073 A in complex 2, compared to the reported Fe-Fe distances of 2.6/2.62 A in DdHase and CpHase, was attributed to the presence of the third bridging ethylthiolate, instead of pi-accepting CO-bridged ligand as observed in [Fe] hydrogenases. Additionally, in a compound of unusual composition ([Na.(5)/(2)H(2)O][(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)])(n)((1)/(2)O(Et)(2))(n) (3), the Na(+) cations and H(2)O molecules combining with dinuclear [(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)](-) anions create a polymeric framework wherein two CN(-) ligands are coordinated via CN(-)-Na(+)/CN(-)-(Na(+))(2) linkages, respectively.     

A new series of pyrimidine-containing linear molecules: their elegant crystal structures and intriguing photophysical properties

A new series of aza-substituted analogues 3-5 based on the 1,4-bis(phenylethynyl)benzene moiety have been synthesized by the selective Pd-catalyzed Sonogashira coupling reaction from 5-bromo-2-iodopyrimidine (1). In these linear molecules, the dipolar pyrimidine moiety is introduced as a probe to investigate factors that control the intermolecular interactions over the crystal engineering. The results reveal that the manner of packing changes both dipolar interactions between linear pyrimidine-containing molecules and transition moments simultaneously, resulting in remarkably different photophysical properties. Due to their versatile dipole-dipole and face-to-face pi-piinteractions in a crystal motif, further applications on the design of ordered crystalline materials for the field effect transistors are promising.     

Dimeric iron n-confused porphyrin complexes

A dimeric iron N-confused porphyrin, [Fe(NCTPP)]2 was obtained from the anaerobic reaction of Fe(NCTPP)Br with NaSePh while under aerobic conditions a hydroxo bridged iron dimer with Na bridging the outer-N atoms was obtained and oxygenation occurred on the inner core pyrrolic carbon to form a novel ONCTPP porphyrinic ring.     

Syntheses of double- and triple-decker clusters of osmium and cobalt metals linked by cyclotetradeca-1,8-diyne ligands

Photoirradiation of Os₃(CO)₁₀(C₁₄H₂₀) (1) in n-hexane produces the double-decker cluster [Os₃(CO)₉(C₂₈H₄₀)] [Os₃(CO)₁₀] (7), which can also be prepared from the reaction of Os₃(CO)₉(C₂₈H₄₀) (2) and Os₃(CO)₁₀(NCMe)₂. Further reaction of 7 with Os₃(CO)₁₀(NCMe)₂ affords the triple-decker cluster [Os₃(CO)₉(C₂₈H₄₀)][Os₃(CO)₁₀]₂ (8). The bis(diyne) complex Os₃(CO)₈(C₁₄H₂₀)₂ (3) reacts with Os₃(CO)₁₀(NCMe)₂ sequentially to yield the double-decker cluster [Os₃(CO)₈(C₁₄H₂₀)₂][Os₃(CO)₁₀] (4) and the triple-decker cluster [Os₃(CO)₈(C₁₄H₂₀)₂][Os₃(CO)₁₀]₂ (5). Treatment of 3 with Co₂(CO)₈ at room temperature leads to the mixed-metal triple-decker cluster [Os₃(CO)₈(C₁₄H₂₀)₂][Co₂(CO)₆]₂ (6), while the reaction of 2 and Co₂(CO)₈ produces [Os₃(CO)₉(C₂₈H₄₀)][Co₂(CO)₆]₂ (9) and [Os₂(CO)₆(C₂₈H₄₀)][Co₂(CO)₆]₂ (10). Compound 10, which involves cluster degradation from Os₃ to Os₂, has been structurally characterized by an X-ray diffraction study.     

One-Pot Formation of Carbonates from the Reactions of Carbonyl Compounds with Samarium Diiodide and Methyl Chloroformate

Treatment of carbonyl compounds with SmI₂ and methyl chloroformate in the presence of molecular sieves provides the cyclic carbonates or biscarbonates of pinacols. This one-pot reaction proceeds rapidly even with aliphatic ketones. The stereochemistry obtained by this procedure is different from that of conventional pinacolic couplings.     

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.     

Unsymmetrical linear pentanuclear nickel string complexes: [Ni(5)(tpda)(4)(H(2)O)(BF(4))](BF(4))(2) and [Ni(5)(tpda)(4)(SO(3)CF(3))(2)](SO(3)CF(3))

The one-electron oxidized linear pentanuclear nickel complexes [Ni(5)(tpda)(4)(H(2)O)(BF(4))](BF(4))(2) (1) and [Ni(5)(tpda)(4)(SO(3)CF(3))(2)](SO(3)CF(3)) (2) have been synthesized by reacting the neutral compound [Ni(5)(tpda)(4)Cl(2)] with the corresponding silver salts. These compounds have been characterized by various spectroscopic techniques. Compound 1 crystallizes in the monoclinic space group P2(1)/n with a = 15.3022(1) A, b = 31.0705(3) A, c = 15.8109(2) A, beta = 92.2425(4) degrees, V = 7511.49(13) A(3), Z = 4, and compound 2 crystallizes in the monoclinic space group C2/c with a = 42.1894(7) A, b = 17.0770(3) A, c = 21.2117(4) A, beta = 102.5688(8) degrees, V = 14916.1(5) A(3), Z = 8. X-ray structural studies reveal an unsymmetrical Ni(5) unit for both compounds 1 and 2. Compounds 1 and 2 show stronger Ni-Ni interactions as compared to those of the neutral compounds.     

Ruthenium complexes of 2-[(4-(arylamino)phenyl)azo]pyridine formed via regioselective phenyl ring amination of coordinated 2-(phenylazo)pyridine: isolation of products,X-ray structure,and redox and optical properties

Aromatic ring amination reactions in the ruthenium complex of 2-(phenylazo)pyridine is described. The substitutionally inert cationic brown complex [Ru(pap)(3)](ClO(4))(2) (1) (pap = 2-(phenylazo)pyridine) reacts smoothly with aromatic amines neat and in the presence of air to produce cationic and intense blue complexes [Ru(HL(2))(3)](ClO(4))(2) (2) (HL(2) = 2-[(4-(arylamino)phenyl)azo]pyridine). These were purified on a preparative TLC plate. The X-ray structure of the new and representative complex 2c has been solved to characterize them. The results are compared with those of the starting complex, [Ru(pap)(3)](ClO(4))(2) (1). The transformation 1 --> 2 involves aromatic ring amination at the para carbon (with respect to the diazo function) of the pendant phenyl rings of all three coordinated pap ligands in 1. The transformation is stereoretentive, and the amination reaction is regioselective. The extended ligand HL(2) coordinates as a bidentate ligand and chelates to ruthenium(II) through the pyridine and one of the azo nitrogens. The amine nitrogen of this bears a hydrogen atom and remains uncoordinated. Similarly, the amination reaction on the mixed-ligand complex [Ru(pap)(bpy)(2)](ClO(4))(2) produces the blue complex [Ru(HL(2))(bpy)(2)](ClO(4))(2) (3) as anticipated. The reactions of [RuCl(2)(dmso)(4)] and [Ru(S)(2)(L)(2)](2+) (dmso = dimethyl sulfoxide, S = labile coordinated solvent, L = 2,2'-bipyridine (bpy) and pap) with the preformed HL(2) ligand have been explored. The structure of the representative complex [RuCl(2)(HL(2a))(2)] (5a) is reported. It has the chlorides in trans configuration while the pyridine as well as azo nitrogens are in cis geometry. Optical spectra and redox properties of the newly synthesized complexes are reported. All the ruthenium complexes of HL(2) are characterized by their intense blue solution colors. The lowest energy transitions in these complexes appear near 600 nm, which have been attributed to intraligand charge-transfer transitions. For example, the lowest energy visible range transition in [Ru(HL(2b))(3)](2+) appears at 602 nm and its intensity is 65 510 M(-1) cm(-1). All the tris chelates show multiple-step electron-transfer processes. In [Ru(HL(2))(3)](2+), six reductions waves constitute the complete electron-transfer series. The electrons are believed to be added successively to the three azo functions. In the mixed-ligand chelates [Ru(HL(2))(pap)(2)](2+) and [Ru(HL(2))(bpy)(2)](2+) the reductions due to HL(2), pap, and bpy are observed.     

Complexation and C-H bond activation of 1,5-cyclooctadiene on triosmium carbonyl clusters

Reaction of Os₃(CO)₁₀(NCMe)₂ and 1,5-cyclooctadiene (C₈H₁₂) affords the diene complex Os₃(CO)₁₀(η⁴-C₈H₁₂) (1) with the two alkene moieties coordinated to an equatorial and an axial positions of one osmium atom. Thermolysis of 1 in refluxing n-hexane results in a vinylic C-H bond activation to form (μ-H)Os₃(CO)₉(μ,η⁴-C₈H₁₁) (2) in good isolated yield. The crystal structures of 1 and 2 have been established by an X-ray diffraction study.