Phosphines iron compounds

Aside from the thermal and photochemical activation of Fe(CO)5 and related iron carbonyl compounds, the field of iron catalyzed hydrogenation lay mostly dormant for decades. As outhned in the previous section, comprehensive follow-up papers on Fe(CO)5 chemistry had appeared but few new metal-ligand platforms for cata- 

R = CHj, CH2Ph, CHjCMea Ph pR-j = PMea, PEta, PMePhj Flydrogenation of [PhBPf jFe-R in the presence of phosphines. 

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Despite the ubiquity of iron phosphine complexes, few aside from the Bianchini compounds have been shown to be active for hydrogenation catalysis. In 2004, Daida and Peters [72] reported a series of pseudo-tetrahedral iton(II) alkyl complexes, [PhBP3 "]Fe-R (PhBPi = [PhB(CH2P Pr2)3], R=CH3, CHjPh, CHjCMej), that are readily hydrogenated in the presence of various phosphines to yield the corresponding Fe(lV) trihydride phosphine complexes (Scheme 4.4). 

Besides apparently from tab.l, small concentration phosphororganic compounds render appreciable improving effect at their sharing with Polygard. The highest parameter of mechanical properties from all investigated compositions with phosphororganic compounds has bivalent iron phosphinate at his use in quantity of 0,1 %. 

Although trialkyl- and triarylbismuthines are much weaker donors than the corresponding phosphoms, arsenic, and antimony compounds, they have nevertheless been employed to a considerable extent as ligands in transition metal complexes. The metals coordinated to the bismuth in these complexes include chromium (72—77), cobalt (78,79), iridium (80), iron (77,81,82), manganese (83,84), molybdenum (72,75—77,85—89), nickel (75,79,90,91), niobium (92), rhodium (93,94), silver (95—97), tungsten (72,75—77,87,89), uranium (98), and vanadium (99). The coordination compounds formed from tertiary bismuthines are less stable than those formed from tertiary phosphines, arsines, or stibines. 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

The coordinated silylenes in both the iron and the chromium compounds can be photolytically activated Photolysis of the complexes in the presence of triphenylphosphine gives the trans-silylene-phosphine complex, which in a second step is transformed into the trnns-bisphosphine compound by excess phosphine. If the silylenes are not trapped, polysilanes are isolated in almost quantitative... 

Second, as a logical development of the first approach, polyphosphazenes have been synthesized that bear phosphine units connected to aryloxy side groups (37). The phosphine units bind organometallic compounds, such as those of iron, cobalt, osmium, or ruthenium (38). In several cases, the catalytic activity of the metal is retained in the macromolecular system (39). A similar binding of transition metals has been accomplished through nido carboranyl units linked to a polyphosphazene chain (40). 

One mole of isoprene reacted with one mole of acetoacetate by using a bidentate phosphine as ligand (56). Reaction of 2,3-dimethylbutadiene with acetoacetate was carried out by using PdCl2 in the presence of sodium phenoxide. When PPh3 was used, a 1 2 adduct was obtained. On the other hand, use of P-phenyl-l-phospha-3-methyl-3-cyclopentene (105) at 100°C caused the 1 1 addition to give 3-carbomethoxy-5,6-dimethyl-5-hepten-2-one (106), from which 5,6-dimethyl-5-hepten-2-one (107) was formed. This compound is the useful intermediate for a-irone synthesis (96). 

Ru3(CO)10(Ph2C2)2, and Ru3(CO)9(C2(Ph)2)3 (128). The dinuclear complex Ru2(CO)6(C2Ph2)2, containing a metallocyclopentadiene ring similar to that observed for both iron and osmium, is a further product in the reaction this does imply very similar structures for the trinuclear adducts to those observed for iron and osmium. The carbonyl reacts with tetracyclone to yield the complex Ru3(CO)i0(C2Ph2)2, which may be related to the osmium compounds discussed later. Phosphine substitution of the carbonyls in some of these compounds has been established. 

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). 

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