Molybdenum carbonyl insertion complex

Although bis(phosphite) carbyne complex Cp[P(OMe)3]2Mo=C(c-Pr) is incapable of undergoing carbonyl insertion reactions, it adds 1 equivalent of HCl in ether forming the ring-opened f/ -butadiene complex Cp[P(OMe)3](Cl)Mo( / -butadiene) in 15% yield, and P(OMe)3 in equal amounts (equation 108) . Careful analysis of the reaction using two equivalents of HCl reveals the presence of the metal hydride complex Cp[P(OMe)3]2Cl2MoH as the main products (70%), and free butadiene. It was furthermore shown that the two molybdenum complexes are not interconvertible under the reaction conditions and both the yields and products ratio are invariant with temperature in the range of -40 °C to room temperature and the amount of added HCl (1 or 2 equivalents). 

The anti addition of amines to the double bond of cationic (alkene)(cyclopentadienyl)di-carbonyliron complexes and to the analogous molybdenum and tungsten complexes has been reported31 33. The adducts underwent carbonyl insertion-cyclization to give chelate complexes, which were then oxidized to /8-lactams. For example, from the Fp complexes of ( )- and (Z)-2-butene the corresponding /8-lactams were obtained diastereoselectively in 10-15% yield by the direct oxidation of the benzylamine adducts with chlorine at low temperature33. The stereochemistry was determined by H-NMR spectroscopy. 

Other mechanistic studies on carbonyl insertions of molybdenum(II) complexes, RMo(f7 -C5H5)(CO)3, postulated formation of an acyl intermediate stabilized by interaction of the hydrocarbon portion of the acyl group with the metal, similar to the well-established agostic interaction). 

As part of a study of the reactions of metallacyclic y-ketovinyl complexes of molybdenum and tungsten with acetylenes, directed toward the synthesis of complexed -/-lactones, Stone has reported92 the isolation of several vinyl-ketene complexes. When complex 72 was heated with 2-butyne, one molecule of the alkyne was incorporated into the complex with concomitant carbonylation. X-ray analysis of the product (73) has shown unequivocally that the C-l to C-4 vinylketene fragment is bonded in a planar, rj4-configu-ration. In contrast to the thermal reaction, ultraviolet irradiation of 72 or 74 in the presence of 2-butyne affords the complexes 75 and 76, respectively, where the lone carbonyl remaining after alkyne insertion had been replaced by a third molecule of the alkyne. 

Vinylcyclopropanerearrangements catalyzed by metal carbonyl complexes usually lead to products resulting from the insertion of a carbonyl group.In the case of a recently reported [4 -b 2 +1 - 2] annulation, a metallavinylcyclopropane A, or a (cyclopropylvinyl)ketene metal complex B, has been proposed as a possible intermediate. Similar reactions have been noted during cyclizations using molybdenum and chromium carbene complexes. ... 

Lappert and Poland (1969) were the first authors who reported on the discovery and characterization of mononuclear alkyldiazenido complexes by reaction of (tri-methylsilyl)diazomethane with tricarbonyl(cyclopentadienyl)molybdenum hydride and the analogous tungsten hydride. Scheme (10-18) demonstrates that these reactions are not simple substitutions of a carbonyl by a diazenido ligand, but that they are insertions of the diazoalkane into the M-H bond (see also Lappert and Lorberth, 1967). 

Relative susceptibility of isocyanide and carbonyl ligands to insertion depends on reaction systems. The greater thermodynamic stability of the iminoacyl complexes than the acyl complexes was demonstrated by thermal isomerization of acyl(isocyanide)molybdenum to iminoacyl(carbonyl)molybdenum complexes (Eq. 7.13) [94]. 

The insertion of metallacarbynes of molybdenum into the palladium-methyl bond (non-cyclopalladated) has also been carried out, similarly giving /x-alkylidene, p-carbonyl dimers. The resultant complexes seem to display similar bonding characteristics to the cyclopalladated complexes, although are less stable in solution. 

Hevia E, Perez J, Riera L, et al. Insertion of imsaturated organic electrophiles into molybdenum-akoxide and rhenium-alkoxide bonds of neutral, stable carbonyl complexes. Chem Eur J. 2002 8 4510-4521. 

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