Phosphine ligands iron complexes with

As already mentioned earlier, the ruthenium complex [Ru(bdmpza) Cl(PPh3)2l (24) easily releases one of the two phosphine ligands and allows the substitution not only of a chlorido but also of a triphenylphosphine ligand for K -coordinating carboxylato or 2-oxocarboxylato ligands (58). The purpose of these studies was to find structural ruthenium models for the active site of 2-OG dependent iron enzymes, since ruthenium(II) complexes are low spin and thus suitable for NMR characterization, whereas ferrous iron complexes with NJV,0-ligands are often difficult to investigate, due to their... 

Some iron and nickel cyanide and carbonyl complexes have been reported as models of the [FeNi]-hydrogenase enzymes. The preparation and structures of the trigonal bipyramidal nickel and iron complexes with the tetradentate ligands tris(2-phenylthiol)phosphine (PS3) and tris(3-phenyl-2-thiophenyl)phosphine (PS3 ) have been reported [70, 71]. The nickel carbonyl complex [Ni(PS3 )(CO)] exhibits vco at 2029 cm compared with the value of 1940 em" for the iron earbonyl complex [Fe(PS3 )(CO)]. Both of these complexes lose CO upon oxidation. The use of cyanide in place of carbon monoxide allows for the preparation of both [Fe (PS3)(CN)] and [Fe (PS3 )(CN)] eomplexes. The IR properties of... 

Although a number of iron complexes having phosphine ligands have been prepared, of particular interest are a series of iron diphosphine complexes. They have been extensively studied because the iron(O) complexes generated from them are capable of activating C—H bonds or small molecules (Scheme 10.13). In this section, iron complexes with phosphines are briefly reviewed from the viewpoint of the chemistry of zero-valent iron complexes. Other recommended reading is given in ref 5. 

Fig. 5. Dependence of the antitumour activity (P388 leukaemia in mice) of R3PAUX complexes on the phosphine R3P and the trans ligand X. Complexes with the more strongly bound Irons Ugands TATG (tetraacetyl-P-D-thioglucose), CN or CH3 tend to be most active. Data from Ref. 55...

Sketch (a) the transition state for a concerted metal atom-assisted 3,9 hydride shift (b) two PNP ligands (c) the ligand used for selective dimerization of butadiene (d) a general structure for molybdenum- and tungsten-based metathesis precatalyst (e) a six-coordinate rathenium precatalyst for metathesis (f) a solid isolated from the reaction between Pd(OAc)j plus PRj (R = o-tolyl) (g) a T-shaped palladium complex and a two-coordinate palladium complex with a monodentate phosphine (h) an iron complex with a seven-membered metallacycle (i) the transition state for metal-catalyzed cyclopropanation (j) a rhodium and a copper precatalyst used in cyclopropanation reactions. 

We do not know exactly where the hydrogen binds at the active site. We would not expect it to be detectable by X-ray diffraction, even at 0.1 nm resolution. EPR (Van der Zwaan et al. 1985), ENDOR (Fan et al. 1991b) and electron spin-echo envelope modulation (ESEEM) (Chapman et al. 1988) spectroscopy have detected hyperfine interactions with exchangeable hydrous in the NiC state of the [NiFe] hydrogenase, but have not so far located the hydron. It could bind to one or both metal ions, either as a hydride or H2 complex. Transition-metal chemistry provides many examples of hydrides and H2 complexes (see, for example. Bender et al. 1997). These are mostly with higher-mass elements such as osmium or ruthenium, but iron can form them too. In order to stabilize the compounds, carbonyl and phosphine ligands are commonly used (Section 6). 

The iron compound readily sublimes and yields well-formed, black lustrous crystals. The cobalt complex will also readily sublime, but dependent upon the temperature at which the crystals are formed, they can be either black or brown in color. The crystal structures of both the cobalt and iron complexes have been determined.3 The nickel complex sublimes only in small amounts with difficulty. All three complexes are unstable to air and water, and the nickel complex readily undergoes thermal decomposition above 100°C. All three compounds will also readily form complexes with a variety of donor ligands such as tertiary arsines or phosphines. The nickel compound usually forms 2 1 adducts such as [(C6HS )3P]2Ni(NO)I, while the iron and cobalt complexes often undergo disproportionation.5... 

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