Phosphine complexes of molybdenum

The discovery that dimtrogen was capable of forming stable complexes with transition metals (Chapter 5) led to extensive investigation of the possibility of fixation via such complexes. An imporiant development was the discovery that certain phosphine complexes of molybdenum and tungsten containing dinitrogen readily yield ammonia... 

Mo Phosphine complexes of molybdenum(O) show satellites which are attributed (408) to coupling to both Mo and Mo. P- H is,., Mo decoupling experiments have shown (409) that the satellites arise solely from Mo. The much larger quadrupole moment of Mo compared with Mo broadens the Mo satellites to such an extent that they are not observed. 

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 ... 

ABSTRACT. Dicarbonyl(t 5-cyclopentadienyl)carbyne complexes of molybdenum and tungsten prove to be a valuable synthetic tool Reaction with phosphines provides substituted carbyne complexes and leads via an intramolecular CC-coupling to t 1- or Tj -ketenyl complexes respectively. Electrophiles attack the metal carbyne triple bond forming hetero- and acyclic carbene complexes, r 2-acyl compounds, T -ketene complexes and metalla-dithia-bicyclobutane cations. Dithio-carboxylates are formed in reaction of these dicarbonyl(Ti5 cyclo-pentadienyl)carbyne complexes with sulfur or cyclohexene sulfide. 

Dinitrogen complexes of molybdenum and tungsten with mono-, di - and tii - tertiary phosphine co -ligands are electrosynthesised from molecular nitrogen andMo or precursors vw cleavage of halide or thiolate bonds and from Mo or oxide, imide or hydrazide complexes by... 

Electrochemical oxidation of closed - shell, teitiary phosphine dinitrogen complexes of molybdenum and tungsten give successively 17- and 16 - electron species. The stability of the electron - deficient species is determined by the rate of loss of dinitrogen removal of electrons... 

Baker PK, Armstrong EM (1990) Mono- and dinuclear phosphine coordinated 1,4-bis (diphenylphosphino)ethyne seven-coordinate complexes of molybdenum(ll) and tungsten(II). Polyhedron 9 801-804... 

Edwards PG, Fleming JS, Liyanage SS et al (1996) Primary alkenyl phosphine complexes of chromium and molybdenum synthesis and characterisation of tricaibonyl(l,5,9-triphosphacyclododecane)chromium(O). J Chem Soc Dalton Trans 1801-1807... 

The formation of rings that contain a thioether linkage does not appear to be catalyzed efficiently by Ru, even when terminal olefins are present. On the other hand, molybdenum appears to work relatively well, as shown in Eqs. 30 [207] and 31 [208]. Under some conditions polymerization (ADMET) to give poly-thioethers is a possible alternative [26]. Aryloxide tungsten catalysts have also been employed successfully to prepare thioether derivatives [107,166,169]. Apparently the mismatch between a hard earlier metal center and a soft sulfur donor is what allows thioethers to be tolerated by molybdenum and tungsten. Similar arguments could be used to explain why cyclometalated aryloxycarbene complexes of tungsten have been successfully employed to prepare a variety of cyclic olefins such as the phosphine shown in Eq. 32 [107,193]. 

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