Bimetal complexes

Bilinear chemometrics methods, 6 39-57 Billet products, titanium, 24 858 Bill of Material, 15 460, 470 Bills of lading, 25 330 Bimetal complexes, 16 88 Bimetallic deactivation processes, 16 93-94 Bimetallic fluorides, 15 396 Bimetallic metal nitrides, 17 199 Bimetallic organometallic uranium complexes, 25 442 Bimetallic organometallic thorium complexes, 24 773-774... 

On the contrary, two of three samples containing bimetal Pd(ll)-Fe(lll) complexes with the PW9O34 anion developed appreciable activity after reduction. The Fe(IlI) ions rather than heteropolytungstate are responsible for the promotion effect in this case. Bimetal complexes with heteropolytungstate included Pd(II) and Fe(III) ions in different combinations, some of them were advantageous to create the catalytic activity of palladium. The detailed structure of... 

Formation of Bimetal Complexes from Early and Late Transition Metals... 

A bimetal initiator system was explored by Kuntz (104) involving an aluminum complex similar to the Vandenberg Catalyst and diethylzinc. The bimetal complex could be envisaged as... 

Ferrocen-l,l -diylbismetallacycles are conceptually attractive for the development of bimetal-catalyzed processes for one particular reason the distance between the reactive centers in a coordinated electrophile and a coordinated nucleophile is self-adjustable for specific tasks, because the activation energy for Cp ligand rotation is very low. In 2008, Peters and Jautze reported the application of the bis-palladacycle complex 56a to the enantioselective conjugate addition of a-cyanoacetates to enones (Fig. 31) [74—76] based on the idea that a soft bimetallic complex capable of simultaneously activating both Michael donor and acceptor would not only lead to superior catalytic activity, but also to an enhanced level of stereocontrol due to a highly organized transition state [77]. An a-cyanoacetate should be activated by enolization promoted by coordination of the nitrile moiety to one Pd(II)-center, while the enone should be activated as an electrophile by coordination of the olefinic double bond to the carbophilic Lewis acid [78],... 

As it is seen from the data of Figure 8, all modified materials have poor cycling performance their reversible capacities fade faster than the one of initial non-modified material, and become lower after the first 8-10 charge-discharge cycles. Thus, we can conclude that no positive effect is achieved by means of modification of the Carbon-Type material with bimetal tri-nuclear complex of Co(III)-Ni(II). 

Another route that has been used recently to prepare Ft bimetal-lies (FtRu, i PtNi, and PtCr ) is via metal carbonyl chemistry. In this method, metal carbonyl complexes (either preformed or formed in situ)... 

D) Schematic drawing of the same complex showing positions of the CuA dimetal center, bound Mg2+, heme a, the bimetal heme a3 - CuB center, and bound Zn2+. The location of an 0.48-nm membrane bilayer is marked. From Tsukihara et al 29 (A), (B), and (D) courtesy of Shinya Yoshikawa. 

The hexamethylborazole complex [B3N3(Me)6]Cr(CO)3 exhibits as the main peaks the ions [(B3N3(Me)6]Cr(CO) ]+ (n = 0, 1, 3) and B3N3(Me)6+ (168). The mass spectra of some bimetallic compounds (XIX)-(XXIV) have been measured (135) and the bimetal ions [Cr—Cr]+ and [Cr—Fe]+ observed. The elimination of the carbonyl groups is not predictable and does not usually occur in a stepwise manner, but rather the first three carbonyl groups are lost in one step, and the remaining three CO molecules are eliminated in a stepwise manner. 

When a mixture of tetrachloromethane and benzaldehyde in DMF was treated, at room temperature, with a catalytic amount of lead(ll) bromide and a shght excess of aluminum as a stoichiometric reductant the coupled product was obtained in good yield (Scheme 13.69) [86]. Subsequent reductive 1,2-elimination of trichloromethyl carbinol by means of the Pb/Al bimetal system could be readily achieved by changing the reaction media. The mechanism of the Pb/Al bimetal redox system presumably involves lead(O) reduction of polyhalomethane to provide an organolead complex which then reacts wifh an aldehyde to give the couphng product. Regenerahon of lead(O) by reduchon of lead(ll) with aluminum metal would complete the catalyhc cycle. 

The samples prepared from Pd(II) complexes with another heteropolytungstate PW9034 anion showed poor catalytic activity in oxidation of hydrocarbons. By contrast, bimetal Pd(II)-Fe(IIl) complexes with the same anion gave active catalysts after supporting and H2 treatment. 

We explored the hydroformylation reaction for monometal model complexes that represent one half of the bimetal catalysts 1 or 5. These tests give us an idea about whether each metal centre is functioning as a conventional mononuclear catalyst or whether there is some cooperativity. Thus the catalytic activity and selectivity of the complexes [RuCl(j/ -Ph2PCH2PPh2)Cp], [RuCl -HC(PPh2)3)Cp] and [ RhCl(CO)2 2] were studied under the same conditions as described above. 

The activity and regioselectivity of 1 and 5 therefore contrast to those of monometal rhodium or ruthenium complexes, and the regioselectivity of complex 1 is particularly noteworthy. These results indicate that the active species uses some sort of bimetal cooperativity to effect high regioselectivities. 

We also tested the reactivity and selectivity of mono metalated complexes (Type V). These catalysts, although reactive, were in general less selective than bimetal-ated compounds with head-to-tail configuration. Finally, preliminary studies of reactivity of doubly metalated compounds with the head-to-head configuration (Type Vllb) showed that these compounds are not promising catalysts for C-H insertion reactions. 

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