Heterobimetallic homogeneous

Heterobimetallic homogeneous catalysts [e.g. (12)] have been developed26 for the alkylation of a range of aromatic compounds by n-activated alcohols. The superior electrophilicity is attributed to the high-valent T-Sn core in the structures. A review has appeared of reactions involving the hydroxyalkylation and cycloalkylation of arenes by hydrofurans, lactones, and unsaturated acids 27... 

Figure 14.6 A heterobimetallic Ti-Mg silsesquioxane, a homogeneous catalyst for ethylene polymerization after AlEtj activation, a possible model for the heterogeneous catalyst TiCl4/MgCl2/Si02 (one of the proposed surface structures) and a patented route to precatalyst, active after activation with MAO.

Finally, we reported a di-iron(III) catalyst 24 and the corresponding copolymerization activity [147]. This system was able to produce copolymer with CHO/C02 and demonstrated a TOF of 53 h 1, at 80°C, lObar and aCHO/Fe ratio of 10,000 1. The system did not yield copolymer with PO, but addition of one equivalent of [PPN]C1, per Fe centre, allowed the conversion of PO into cyclic propylene carbonate with TOFs around 10 h 1. Previously, some heterobimetallic iron tert-butoxide complexes ( (7-BuO)5FeLa] and [(f-BuO)4FeZn]) had been reported for the copolymerization of PO and C02 [153]. This catalyst was the first use of an iron complex for the homogeneous copolymerization of CHO and C02. Rieger and coworkers recently reported a mononuclear Fe system that showed similar behaviour towards PO [154] and some copolymer formation with CHO/C02 strongly dependent on the co-catalyst system [98]. 

Curtis has provided some homogeneous work that represents without doubt the closest model available for real Co-Mo-S catalysts. Heterobimetallic clusters, which contain the right combination of metals (Co-Mo) linked through sulfur bridges, were used, thereby beautifully mimicking a Co-Mo-S site [68, 69]. Even though this complex could be considered as just another example of a heterobimetallic cluster, its unique relation to real HDS catalysts seemed to justify its description in some detail in a separate section of its own. 

Keywords Heterobimetallic catalysts, Lanthanoid complexes, Asymmetric synthesis, Homogenous catalysis... 

Our work on the electrooxidation of alcohols with homogeneous heterobimetallic catalysts was initially motivated by the advances in DMFC anodes 8,21-23). The strategy initially employed for this project was to utilize the bifunctional oxidation mechanism observed in DMFC anodes to design discrete bimetallic complexes as catalysts for the electrooxidation of renewable fuels. These complexes can be viewed as utilizing all of the metal as opposed to bulk metal anodes, where the reaction occurs only at active surface sites. Although bimetallic complexes are not accurate models of the proposed surface binding site on bulk metal anodes, our investigations address the question of whether it is possible to reproduce the essential functions of the proposed electrooxidation mechanism in discrete heterobinuclear complexes 24-26). 

Derivatives Containing Transition Metals.-This Section can be conveniently divided into species with a direct bond to a transition metal (TM) and heterobimetallic species which lack this interaction. There seems a noticable shift in emphasis away from the latter grouping, for so long driven by the relevance of such species to homogeneous catalysis, towards MOCVD applications and the former class. 

Finally, a homogeneous heterobimetallic Pd(COD)Cl-SnCl3 catalyst for the 5 reactions that form a new C-C bond between primary and secondary allylic alcohols and nucleophiles such as arenes, heteroarenes, active methylene-, and organometallic compounds has been reported. Yields range from 60 to 92%. The Sf 2/Sj 2 ratio is usually high, even up to 100/0, although exceptions occur. The reaction is successful when ben-zylic and propargylic alcohols or symmetric and unsymmetric allyl ethers are used in place of allylic alcohols. 

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