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.

The reaction of nitrosothiol, Ph3CSNO, with a divalent iron N-confused porphyrin complex, Fe(HCTPPH)Br, yields a {Fe(NO)}6 iron nitrosyl complex with a sulfur atom inserted in the Fe-C bond. The crystal structure reveals a bent Fe-N-O geometry and an eta2-(C,S) bonding mode between iron and the C-S bond. A reaction mechanism involving a transnitrosation and a nitrosothiol C-S bond cleavage is proposed.

Conformation control of a flexible tetratopic ligand by modulation of the length of the rigid bridging ligand is achieved during the self-assembly of metallacycles. The ability to control the conformation of the flexible ligand using an ancillary rigid ligand provides a new method for the preparation of novel metallacycles that contain both flexible and rigid modules with highly accurate prediction of the final structures.Precise control of supramolecular metallacycles requires a rational design of molecular components, because the information that determines the specific assembly should be encoded in the molelcular architecture. 1 Recently, the use of flexible motifs to construct metallacycles has increased because of the advantages associated with their use, such as adaptive recognition properties and breathing ability in the solid state. [2][3][4][5] Flexible organic components are generally less predictable during self-assembly and have a tendency to generate [2]catenanes 2 or oligomers upon reaction with metal ions. Prior research in this area has focused on the use of di-and tritopic flexible N-donors to construct both ionic and neutral metallacycles. [2][3][4][5][6] The synthesis and use of semirigid tetratopic N-donors as structural components for metallacycles is rare because of their higher conformational flexibility, which must be restricted to obtain well-preorganized subunits. 7 Herein, we report an effective rigiditymodulated approach for the design of neutral metallacycles. The rigid anionic linker responsible for determination of M 3 3 3 M separation allows for conformational control of the flexible motif with simultaneous use of a rigid bis(chelator), tetratopic flexible N-donors, and fac-Re(CO) 3 cores during self-assembly (Scheme 1).In this study, the flexible ligand 1,2,4,5-tetrakis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene (TXyBim) and two rigid moieties, 2,2 0 -bis(benzimidazolyl) (H 2 -Bim) 8 and chloranilic acid (H 2 -CA), were explored as basic building units. In the case of TXyBim, four benzimidazoles are connected via flexible methylene groups to an arene core. This flexibility permits TXyBim to adopt several possible conformations because of the orientation of the four benzimidazolyl arms (Chart S1 in the Supporting Information). 9 Compound 1 was assembled from Re 2 (CO) 10 , TXyBim, and H 2 -Bim in toluene in 68% yield under solvothermal conditions (Scheme 2). 10 The resulting yellow product is airand moisture-stable and slightly soluble in polar solvents. The IR spectrum of 1 exhibited strong bands at 2018, 1914, and 1900 cm -1 , characteristic of fac-Re(CO) 3 . The structure of compound 1 was determined by X-ray crystallographic analysis, which revealed that metallacycle 1 contains four fac-Re(CO) 3 cores, two Bim groups, and one TXyBim moiety, as shown in Figure 1. 10 The coordination geometry around the Re centers is a distorted octahedron with a C 3 N 3donor environment. The dianionic Bim is coordinated in a

Five‐coordinate gallium and indium complexes stabilized by tridentate, substituted pyrrole ligands have been synthesized and characterized. The reaction of MCl3 with 1 equiv. of Li[NC4H2(CH2NMe2)2‐2,5] in diethyl ether affords [{NC4H2(CH2NMe2)2‐2,5}MCl2] [M = Ga (1), In (2)] in high yield. Reaction of 1 with 2 equiv. of MeLi in diethyl ether at −78 °C followed by heating to reflux for 30 min affords the alkylated product [{NC4H2(CH2NMe2)2‐2,5}GaMe2] (3). Similarly, the reaction of 2 with 2 equiv. of MeLi or nBuLi affords the dialkylated complexes 4 and 5, respectively. Complex 2 is a strong Lewis acid which readily absorbs H2O forming [{[C4H2N(CH2NMe2)2‐2,5]InCl2}2(μ‐OH2)] (6). Complexes 3, 4, and 6 have been characterized by X‐ray crystallography. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)