Heteropolymetallic complexes

LLB, KHMDS (0.9 equiv to LLB) and H20 (1 equiv to LLB), which presumably forms a heteropolymetallic complex (LLB-ID, was found to be a superior catalyst for the direct catalytic asymmetric aldol reaction giving 49 in 89 % yield and 79 % ee (using 8 mol% of LLB). We employed this method to generate KOH in situ because of its insolubility in THE The use of KO-t-Bu instead of KHMDS gave a similar result, indicating that HMDS dose not play a key role. Interestingly, further addition of H20 (1 equiv with respect to LLB) resulted in the formation of 49 in 83 % yield and higher ee. The powder obtained from the cata-... 

Scarcia V, Furlani A, Longato B, Corain B, Pilloni G (1988) Heteropolymetallic complexes of 1, l -bis(diphenylphosphino)ferrocene (dppf). IV. Solvolytic behavior and cytostatic properties towards the KB cell-line of dppf and 1, 2-bis(diphenylphosphino)ethane cis complexes of platinum(II) and palladium(II). Inorg Chim Acta 153 67-70... 

We thus believe that the BINOL core of the active complex is essentially LLB. Therefore, the heteropolymetallic complex of LLB and KOH, with KOH axially coordinated to La, among other possible complexes, would be the most effective catalyst for this reaction. To clarify the reaction mechanism, we conducted kinetic studies. As a result, significant isotope effects 5) were observed, and the reaction rate... 

Another spectacular series of heteropolymetallic complexes containing bis(diphenyl-phosphino)ferrocene as a ligand is shown in Scheme 7-47 [49],... 

Scheme 25 Enol ester synthesis catalyzed by Ti/Ru heteropolymetallic complexes...

Trost et al. [11] reported another impressive example of bimetallic catalysts in which a Zn-Zn homobimetallic complex (17, Scheme 7) serves as an effective catalyst for direct aldol reactions [11-13]. The proposed structure of the catalyst was verified by mass spectrometry and the best ratio of Et2Zn and the ligand. The chemical yield was moderate in the reaction of methyl ketones (1) (Scheme 7, top) [11,12], but a highly atom-economic system was achieved when a-hydroxylated ketones (10) were used as a substrate (Scheme 7, bottom) [13]. Excellent diastereo- and enantioselectivity were obtained under mild conditions. In contrast to the case of Shibasaki s heteropolymetallic catalyst, syn-1,2-diols (syn-11) were obtained as the major diastereomers. 

The synthesis of heteropolymetallic d-f complexes is well documented and understood because the two metal ions display highly different stereochemical preferences. Valence... 

We have prepared a variety of new Schiff base bis crown ether ligands (98-100) that contain alkali and transition metal coordinating sites via the condensation of two or three equivalents of 4-formyl-benzo-15-crown-5 with an appropriate di- or triamine (Scheme 18). Homometallic copper(I), silver(I), and heteropolymetallic copper(I)-sodium, silver-(I)-sodium, and potassium complexes have been isolated. The singlecrystal X-ray structure of the [Cu(57)K](PF6)2 complex (100) is shown... 

Examples of other interesting additions (225) across the Rh=Rh bond include complexes of S02 (96 ) (225,230,231), selenium (97 ) (225,232), tellurium (225), sulfur (225,233), and AuCl [from AuCl(CO)] (225,230). The latter reaction results in a Rh2Au triangle and is just one of a large number of heteropolymetallic cluster complexes built up from 4 and 5 (see below). 

SO that eventually the formation of metal clusters of metallic layers can influence the catalytic performance of the MOE Remarkably, however, the voltammetric profile is maintained upon repetitive cycling the potential scan. This suggests that eventually, zerovalent copper can be formed under these conditions, with no formation of metal deposits, as described in recent literature for heteropolymetallic transition metal complexes (Packheiser et al., 2008). 

The best practical HDS catalysts are those composed of sulfides of two different metals (e.g. Co-Mo, Ni-W, see Chapter 1) and therefore heterobimetallic complexes are to be considered as better model complexes for HDS-related reactions. Despite this obvious consideration, such chemistry is still rather underdeveloped, possibly due to the increased difficulty that is generally encountered when dealing with heterobimetallic or heteropolymetallic systems as compared to mononuclear complexes nevertheless, a few interesting examples of this type of cooperative chemistry have indeed appeared in tire literature. 

Hess law, 30, 85, J46 heteropolar bond, 23 heteropolymetallate, 223 high-spin complex, 213 HOMO, 75, 90 homopolar bond, 23 H ckel theory, 82 Hund s first rule, KL, 11, 70 hybridization, 73, 77 hydrazine, 162 hydride, 26,129,150 hydroformylation, 268 hydrogen bond, 79, 91, 151 hydrogen electrode, 140, 143 hydrogen peroxide, 171, 266 hydrogenation, 268 hydrothermal reaction, 41, 114, 257 hydroxide, 130,132,138,119,110 hypervalence, see octet expansion... 

The field of the heteropolymetallic magnetic systems is still rather new. As a matter of fact, the first EPR spectrum of an heteropair appeared in 1967 and the first preliminary magnetic data dealing with compounds of this type in 1968. This article is, to our knowledge, the first review on the subject. It largely concerns heterobinuclear complexes and covers the field up to the first attempts to obtain molecular ferromagnets. One may anticipate that, in a few years, another review will be necessary and that its main emphasis will be the systems of higher nuclearity and the extended systems with subtle spin orders. 

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