Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen

Abstract

Experimental and Synthetic Details General Considerations All reactions were performed at room temperature in a nitrogen filled M. Braun glovebox or using standard Schlenk techniques unless otherwise specified. Glassware was oven dried at 140 o C for at least two hours prior to use, and allowed to cool under vacuum. Bis(odiisopropylphosphinophenyl)-chlorophosphine (P2P Cl) was prepared as described elsewhere. 1 All other reagents were obtained commercially unless otherwise noted and typically stored over activated 4 Å molecular sieves. Tetrahydrofuran, toluene-d8 and benzene-d6 were dried using sodium/benzophenone ketyl, degassed with three freeze-pump-thaw cycles, vacuum transferred, and stored over 3 Å molecular sieves prior to use. Diethyl ether, benzene, toluene, acetonitrile, hexanes, and pentane were dried by sparging with nitrogen for at least 15 minutes, then passing through a column of activated A2 alumina under positive nitrogen pressure. 1 H and 31 P NMR spectra were recorded on a Varian 300 or 400 MHz spectrometer. All chemical shifts (δ) are reported in ppm, and coupling constants (J) are in hertz. The 1 H-NMR spectra were referenced using residual H impurity in the deuterated solvent. UV-Vis spectra were recorded on a Varian Cary Bio 50 spectrophotometer. Infrared (ATR-IR) spectra were recorded on a Bruker ALPHA ATR-IR spectrometer. Elemental analyses were performed at Caltech. Physical Methods Mössbauer Measurements. Zero field 57 Fe Mössbauer spectra were recorded in constant acceleration on a spectrometer from See Co (Edina, MN) equipped with an SVT-400 cryostat (Janis, Wilmington, WA). The quoted isomer shifts are relative to the centroid of the spectrum of α-Fe foil at room temperature. Unless otherwise noted, samples were prepared by grinding polycrystalline (20-50 mg) into a fine powder and pressed into a homogenous pellet with boron nitride in a cup fitted with a screw cap. The data were fitted to Lorentzian lineshapes using the program WMOSS (www.wmoss.org). Magnetic Measurements. Magnetic measurements for 5 were conducted with a Quantum Design MPMS3 SQUID Magnetometer at the University of California, Los Angeles. A polycrystalline sample of 5 was wrapped in plastic film and placed in a gelatin capsule. The capsule was then inserted into a plastic straw. Magnetization data at 100 K from 0 to 4 T were collected to confirm the absence of ferromagnetic impurities. Direct current variable temperature magnetic susceptibility measurements were collected between 1.8 and 300 K with a 0.1 T field. Magnetic susceptibility data was corrected for diamagnetism of the sample, estimated using Pascal's constants. Magnetic susceptibility data was simulated with PHI. 2 X-ray Crystallography. For compounds 4-8, low-temperature (100 K) diffraction data (φand ω-scans) were collected on a Bruker AXS D8 VENTURE KAPPA diffractometer coupled to a PHOTON 100 CMOS detector with Mo Kα radiation (λ = 0.71073 Å) or with Cu Kα (λ = 1.54178 Å). All diffractometer manipulations, including data collection, integration, and ...

The influences of carbon donor ligands on biomimetic multi-iron complexes for N2reduction

“…However, a recent article by Agapie and co-workers described a diiron m-alkylidyne m-hydride complex with a Fe/ Fe/H/C core, which undergoes Fe-C bond cleavage and C-H bond formation to give various products including iron(II) alkyl and alkylidene species with N 2 bound. 17 These may bear resemblance to the intermediates during N 2 reduction by 1. This gains signicance because the Fe/Fe/H/C diamond core in the alkylidyne complex is in a more reduced state (closer to the level of N 2 -binding FeMoco intermediates) than the diiron alkylidene sulde 2.…”

“…3,16 This could be accompanied by C-H bond formation, an idea that is supported by recent work on a synthetic diiron complex containing a bridging carbyne. 17 Other proposals involve direct interactions between the carbide and N 2 . [18][19][20] The wide variety of these proposals underscores the limited understanding of the structural and electronic contributions of bridging carbon ligands to reactivity in iron-sulfur clusters.…”

“…In functional synthetic models, mononuclear iron complexes have been used to gauge the N 2 -coordinating ability of compounds with Fe-C bonds. 16,17,[23][24][25][26][27][28] 16,27,29 Studies of iron species with bridging carbon and sulfur ligands that are high-spin with greater electronic and structural delity to the Fe2/Fe6 site are needed to improve the understanding of how biological S-and C-based donors impact N 2 reactivity.…”

Cluster Models of FeMoco with Sulfide and Carbyne Ligands: Effect of Interstitial Atom in Nitrogenase Active Site

“…Figure 1: Top: Structure of FeMoco in Mo-dependent nitrogenase from PDB structure 3U7Q with blue circle emphasizing the cubane subsite and its schematic representation highlighting in color the subsite of focus in this study; bottom: carbyne and carbide containing model complexes. [9][10][11]…”

“…Bi-and multimetallic model systems focused on interrogating the role of the interstitial atom and multimetallic effects have been targeted 7,[9][10][11][12][13][14][15][16][17][18][19][20][21][22] , but complexes that display bridging carbide 11,[23][24][25][26] or even carbyne 9,10,27 ligands are rare. Carbide-containing Fe clusters display four to six metal centers, but invariably are rich in CO ligands.…”