Molybdenum, allyl complex

Molybdenum allyl complexes react with surface OH groups to produce catalysts active for olefin metathesis.34 35 Using silica as a support for the heterog-enization of Ti and Zr complexes for the polymerization of ethylene did not give clear results.36 In these cases, HY zeolite appeared to be a more suitable support. The comparable productivity of the zeolite-supported catalyst with... 

As well as organic chiral auxiliaries, organometallic fragments have found some application as chiral auxiliaries in conjugate addition reactions. Particularly noteworthy are chiral molybdenum allyl complexes [69], chiral iron complexes [70], and planar chiral arene chromium species [71]. 

A wide range of transition metal-allyl complexes are known to react with many types of nucleophiles. In most cases, these reactions occur between cationic allyl complexes and amines or stabilized, anionic carbon nucleophiles. The reaction typically occurs between the nucleophile and the form of the allyl complex, and attack usually occurs at the face of the allyl ligand opposite the metal. However, there are exceptions to these trends. For example, several experiments suggest that unstabilized carbon nucleophiles react first at the metal center, and C-C bond formation occurs between the alkyl and the allyl group by reductive elimination. In addition, a recent study has shown through deuterium labeling that attack of malonate anion on a molybdenum-allyl complex occurs with retention of configuration. ... 

Several recent studies have revealed the dichotomous relationship between the regioselectivity of reactions of unsymmetrical allyl complexes of palladium and that of reactions of unsjmmetrical allyl complexes of other metals. An isolated molybdenum-allyl complex containing an allyl group derived from methyl cinnamyl carbonate (PhCH=CHCH2C)COjMe) reacts with the sodium salt of dimethyl malonate in the presence of a source of CO to generate the branched substitution product (Equation 11.41). The addition of nucleophile to this allyl complex has been shown to occur by retention of configuration, perhaps by initial attack at the metal, rather than the more common external attack at Are allyl group. ... 

In a similar manner, Jt-allyl complexes of manganese, iron, and molybdenum carbonyls have been obtained from the corresponding metal carbonyl halides [5], In the case of the reaction of dicarbonyl(r 5-cyclopentadienyl)molybdenum bromide with allyl bromide, the c-allyl derivative is obtained in 75% yield in dichloromethane, but the Jt-allyl complex is the sole product (95%), when the reaction is conducted in a watenbenzene two-phase system. Similar solvent effects are observed in the corresponding reaction of the iron compound. As with the cobalt tetracarbonyl anion, it is... 

Krylov (62) studied the adsorption of oxygen and propylene on vanadium oxide/MgO and molybdenum oxide/MgO catalysts by ESR and IR at 25°C. He observed the formation of Qr radicals and ir-allyl complexes during the simultaneous adsorption of 02 and C3H . The data indicated that an electron transfer took place from the olefin to the oxygen through the transition metal ion forming the following complex ... 

These observations suggest a reaction scheme for bismuth molybdate catalysts where the allylic species is formed initially at a bismuth center and then reacts further at a molybdenum site to produce acrolein. Thus, once the allylic complex is formed, the MoO polyhedra are highly active and selective for acrolein formation. This hypothesis was tested by investigating the oxidation of bromoallyl (C3HjsBr) over molybdenum oxide 116). Since the C—Br bond in bromoallyl is much weaker than the C—H bond in propylene, the ease of formation of the allylic species should be significantly enhanced with bromoallyl compared with propylene. If the initial propylene activation occurs on bismuth, then the reaction of bromoallyl over molybdenum oxide should approach the activity and selectivity of propylene over bismuth molybdate. This was the observed result, and the authors concluded that the bismuth site was responsible for the formation of the allylic intermediate. 

Phthalic acid, with trinuclear Os clusters, 6, 743 n-acceptor carbon ligands, in molybdenum carbonyls, 5, 455 Ti-allyl complexes, with molybdenum with cyclopentadienyl-supporting ligands, 5, 544 monomeric complexes, 5, 546 oxide surface binding, 5, 546... 

Polymers of 1,4-dienes are obtained in the presence of titanium, and also with Co, Ni, and Rh, where allyl complexes can be isolated. 1,2-Polybutadiene can be produced in the presence of Pd, which is not generally regarded as a Ziegler catalyst. Chromium and molybdenum systems have also been used. Whereas structural isomerism is controlled by the metal in the catalyst center, the geometric isomerism is determined by the ligands and counterions. 

These complexes can also be used to prepare optically pure cis-2,5-disubstituted 5,6-dihydro-2tf-pyrans such as 3 by using a molybdenum nitrosyl allyl complex as an intermediate. 

Sharpless et al. and Muccigrosso et al. were probably the first to perform the direct allylic amination of nonfunctionalized alkenes in the presence of a metal complex [60]. The complex used for the allylic amination was the molibdooscaziridine 109 prepared by reaction of the molybdenum dioxo complex 107 and phenyl hydroxy-lamine 108 (Eq. (25)). 

Sharpless et al. found that heating a solution of 109 with 2-methyl-2-hexene 110 afforded an allylic amination reaction leading to the formation of 111 in 57 % yield together with high yields of the parent molybdenum dioxo complex 107 (Eq. (26)). 

A variety of different metal complexes have been screened as catalysts for allylic amination using phenyl hydroxylamine 108 as the nitrogen fragment donor, and it was found that iron-complexes have better redox capacity compared to molybdenum [64]. With the iron compounds, higher yields and a lower amount of hydroxylamine-derived byproducts are obtained. These byproducts constitute one of the problems in this type of allylic amination reactions in general, as their formation is difficult to suppress. The allylic amination reaction of a-methyl styrene 112 with 108 can, e.g., be catalyzed by the molybdenum dioxo complex 107, iron phthalocyanine 114, or by the combination of the iron chlorides 115 [64,65]. It appears from the results in... 

The (IsQ-coordinated species [Mo(CO)3(py)3] prepared from [Mo(CO)6] and pyridine is useful for the synthesis of various jr-allyl molybdenum compounds (68JOM(13)Pl, 970M5365). The 3-allyl complexes [( 3-allyl)Mo(CO)2Br(py)2] form [( 3-allyl)Mo(CO)2(S,S)(py)] with the anionic S,S-donors, dithiocarbamates and xanthates of sodium and potassium, M (S,S) (81JOM(218)185). [( 3-C3H5)Mo(CO)2(py)2Br] (68JO M(14)375) with thallium hexafluorophosphate in acetonitrile gives... 

Keywords Allylic substitution, Allylation, Allylic alkylation, Jt-Allyl complexes, Palladium, Molybdenum, Ruthenium, Iridium... 

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