Molybdenum complexes chromium derivatives

The reaction of a series of trifluoromethylphosphorus derivatives with tetracarbonylnorbornadiene-molybdenum or -chromium allows the preparation of the corresponding complexes [9] which give well resolved... 

The carbene complexes M(CO)5 =C(OMe)C6H4feCPh (M = Cr, W) undergo photodecarbonylation and alkyne coordination to form complex 56. The corresponding molybdenum complex undergoes the same reaction in the dark. The chromium species rearranges thermally to form an organic chrysene derivative. s... 

In attempting to extend this reaction to derivatives of chromium and molybdenum, completely different results were obtained under comparable reaction conditions. Reaction of 3-hexyne with (CH CN) Mo(CO) did not appear to give a compound corresponding to the tungsten acetylenic complex, Hexaethylbenzene isolated from the reaction mixture indicates that the molybdenum complex causes cyclotrimerization of the acetylenic molecule. 

Aryl and alkenyl chromium carbene complexes react with HCaC(CH2)3CH=CHCH=CHR (R = C02Et, CH=CHC02Et) by insertion of carbon monoxide to give hydroquinones. Aryl molybdenum carbene complexes give hexahydroazulenes while alkenyl substituted molybdenum complexes generate hydroquinones or cyclopentadiene derivatives. ... 

The high-chromium irons undoubtedly owe their corrosion-resistant properties to the development on the surface of the alloys of an impervious and highly tenacious film, probably consisting of a complex mixture of chromium and iron oxides. Since the chromium oxide will be derived from the chromium present in the matrix and not from that combined with the carbide, it follows that a stainless iron will be produced only when an adequate excess (probably not less than 12% of chromium over the amount required to form carbides is present. It is commonly held, and with some theoretical backing, that carbon combines with ten times its own weight of chromium to produce carbides. It has been said that an increase in the silicon content increases the corrosion resistance of the iron this result is probably achieved because the silicon refines the carbides and so aids the development of a more continuous oxide film over the metal surface. It seems likely that the addition of molybdenum has a similar effect, although it is possible that the molybdenum displaces some chromium from combination with the carbon and therefore increases the chromium content of the ferrite. 

Chromium cyclopropylcarbene complexes react with alkynes to provide cyclopentenone derivatives in a formal [2c+2s+lCo] cycloaddition process (see Sect. 3.2). However, tungsten and molybdenum cyclopropylcarbene complexes... 

Indirect electroreduction with Ni, Co, and Fe complexes has been well studied, and will be discussed first. Furthermore, the synthetic use of palladium, rhodium, and ruthenium complexes as mediators in the electroreduction of organic compounds are finding increasing apphcations. Metallic complexes derived from chromium, manganese, molybdenum, tungsten, and rhenium have also been used as mediators for special conversions. Recently, tin, zinc, and mercury... 

Chromium(IV) and chromium(V), previously encountered as the oxides and halides and as unstable intermediates in solution, are now represented by complexes of ligands stabilized by heavy substitution against oxidation by the metal ion, and oxo and nitrido derivatives. These remain unimportant oxidation states compared with molybdenum and tungsten. 

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