Phosphine complexes molybdenum

Bis(amido) phosphine-donor complexes, with Zr(IV), 4, 816 Bis(amido) pyridines, with Zr(IV) and Hf(IV), 4, 790 Bis(aminoalkylidyne) complexes, diiron carbonyl complexes with cyclopentadienyl ligands, 6, 248-251 Bisaminosilylenes, in molybdenum carbonyls, 5, 406 Bis(tj-arc nc) complexes, as metal vapor synthesis milestone, 1, 236... 

Nitrido molybdenum complexes have been reported for MoVI, Mov, and MoVI. Among these, MoVI nitrides have been the most extensively studied. For the other two classes of nitrido molybdenum complexes, phosphine and thioalkoxide ligands are common, as they are suggested to stabilize the lower oxidation states through n-back bonding. 

The first reaction (346) consists of hydroperoxide formation by a typical autoxidation process, and the second represents selective epoxidation by the hydroperoxide. In the absence of the autoxidation catalyst, no reaction is observed under these conditions due to efficient removal of chain-initiating hydroperoxide molecules by reaction (347). Optimum selectivities obtain when the autoxidation catalyst is of low activity, which implies a low total activity of the catalytic system. The molybdenum complexes related to Mo02(oxine)2 are among the most effective catalysts for epoxidation.496 Although the autoxidation catalysts were limited to two types (phosphine complexes of noble metals and transition metal acetylacetonates), there is no reason, a priori, why other complexes such as naphthenates should not produce similar results. 

S6re6 de Roch and co-workers503 have demonstrated an alternative means of activating molecular oxygen in the liquid phase. The principle depends on the lability of an M=0 bond in oxo-molybdenum complexes. Thus, oxo-dialkyl-thiocarbamate complexes of molybdenum catalyze the oxidation of triphenyl-phosphine via the sequence ... 

Simple chiral phosphines have already been mentioned (Section 3.1.3) and the macrocycle enantiomers are discussed below (Section 4.6). Current research in this area is concentrated on bidentate chiral phosphines, such as the ligands (24)-(27). Although their transition metal complexes are normally used for stereospecific synthesis, Whitmire and coworkers used the molybdenum complexes to resolve their racemic bisphosphines via flash chromatography. The phosphines were decomplexed by reductive cleavage at low temperatures (-78 °C) using sodium naphthalenide (Scheme 1). 

Norbornadiene (NBD) in (NBD)M(CO)4 (353) is readily displaced by CO (274) or (2-allylphenyl)(diphenyl)phosphine (50, 312). Although the latter reaction gives the compound of expected composition, (C2iHi9P)M(CO)4, both the chemical and spectral data indicate that it has the structure (26) in which the C21H19P ligand is the isomeric (2-propenyl)(diphenyl)phosphine. For the molybdenum complex this structure has been confirmed by X-ray diffraction (379). 

The yields were found also to increase in the presence of phosphines, particularly trimethyl or tributyl phosphine. After all the improvements of the catalyst and reaction conditions the system became by far the most active of known non-biological catalytic systems for the reduction of dinitrogen at ambient temperature and pressure. The specific activity (the rate of N2 reduction per mole of the complex) reached and even exceeded that of nitrogenase. Up to 1000 turnovers relative to the molybdenum complex can be observed at atmospheric pressure and more than 10 000 turnovers at elevated N2 pressures. 

The gradual substitution of the phenyl groups in the phosphine ligand for ferro-cenyl subunits affords the diferrocenyl- and triferrocenyl-phosphinepentacarbonyl-molybdenum complexes, respectively. With respect to the redox pathway shown in Fig. 7-11, each added ferrocenyl ligand involves the appearance of a further one-electron oxidation [50]. The relevant redox potentials are given in Table 7-7. 

Like the molybdenum complexes, a series of monoferrocenyl-, diferrocenyl- and triferrocenyl-phosphine pentacarbonyltungsten complexes have been prepared. Each ferrocenyl ligand undergoes reversible one-electron oxidation, whereas the tungsten moiety undergoes irreversible oxidation. The relevant potential values are reported in Table 7-12. 

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