Bimetallic compounds

An improved route to iodomethylzinc iodide has made the iodometh-yltin compounds, R3SnCH2l, more accessible (280). Bimetallic compounds of the types MejSnCBrjMgCl (281), MejSnCClBrLi (282), and MesSnCHIZnI (280, 283), have been prepared in solution at low temperature, and thence, the ditin compounds (MeaSnljCClBr, (MegSnljCBri, (MejSnlaCHI (284). 

This finding is also in agreement with another three-component Michael/aldol addition reaction reported by Shibasaki and coworkers [14]. Here, as a catalyst the chiral AlLibis[(S)-binaphthoxide] complex (ALB) (2-37) was used. Such hetero-bimetallic compounds show both Bronsted basicity and Lewis acidity, and can catalyze aldol [15] and Michael/aldol [14, 16] processes. Reaction of cyclopentenone 2-29b, aldehyde 2-35, and dibenzyl methylmalonate (2-36) at r.t. in the presence of 5 mol% of 2-37 led to 3-hydroxy ketones 2-38 as a mixture of diastereomers in 84% yield. Transformation of 2-38 by a mesylation/elimination sequence afforded 2-39 with 92 % ee recrystallization gave enantiopure 2-39, which was used in the synthesis of ll-deoxy-PGFla (2-40) (Scheme 2.8). The transition states 2-41 and 2-42 illustrate the stereochemical result (Scheme 2.9). The coordination of the enone to the aluminum not only results in its activation, but also fixes its position for the Michael addition, as demonstrated in TS-2-41. It is of importance that the following aldol reaction of 2-42 is faster than a protonation of the enolate moiety. 

This chapter is intended to highlight the synthesis and use of geminal bimetallic compounds such as gem-metallozirconocenes, but we will concentrate on the chemistry of aluminum, boron, lithium, gallium, germanium, tin, zinc, and zirconium. 

The significant increase in catalytic performance is shown by a comparison of the bimetallic compounds 55 and 56, NHC/phosphine complex 54, dicarbene complex 53, and diphosphine complex 52 in ROMP of 1,5-cyclooctadiene (Fig. 2). ... 

Reaction of tri(fert-butyl)sulfurtriimide with one equivalent of MeLi followed by an in situ reaction with one equivalent of Mc2Zn afforded the bimetallic compound 77 (equation 19). The molecular geometry of 77 was unambiguously established by an... 

An alternative complementary olefination procedure involving alkylidene malonates was also developed that produces (Z) olefins as major stereoisomers when the R substituent is aliphatic (equation 93)130. The stereoselectivity depends on the bimetallic compounds and may be improved by bulky ester substituents (such as menthyl groups)131. 

In this mechanism, the catalytically active rhodium(I) derivative is a bimetallic compound thereby providing active sites on two adjacent rhodium atoms. The methods of enzyme kinetics (12) yield the following rate equation for this bimetallic mechanism ... 

This paper consists of three parts. The first part describes the high pressure synthesis of bimetallic compounds of NbN and MN where M is a Group 13 metal such as Al, Ga, or In. The second part discusses crystal structure investigations of a series of alkaline earth and transition metal nitrides, carried out to understand the bonding surrounding the transition metals. The third part describes the preparation of new metastable transition metal nitride and their solid solutions by rf-sputter deposition. 

Metalametallations of alkenes and alkynes are useful methods for the construction of 1,2-dimetala-alkanes and 1,2-dimetala-l-alkenes, which react subsequently with suitable electrophiles to form substituted alkanes and alkenes. Metalametallation is carried out usually with bimetallic reagents of the type R Si-M R, or R Sn-M R in which M = B, Al, Mg, Cu, Zn, Si or Sn. Some metalametallations proceed without catalysts Cu, Ag and Pd compounds are good catalysts. The metalametallation with bimetallic compounds, such as Si-B, Si-Mg, Si-Al, Si-Zn, Si-Sn, Si-Si, Sn-Al or Sn—Sn bonds, catalysed by transition metal complexes, is explained by the oxidative addition of the bimetallic compounds to form 478, and insertion of alkene generates 479. Finally 1,2-dimetallic compounds 480 are formed by reductive elimination. Dimetallation of alkynes proceeds similarly to give 481. Dimetallation is syn addition. 

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. 

Some authors have proposed mechanisms based on bimetallic palladium species. Keim and colleagues, for instance, proposed a reaction mechanism for the telomerization of acetic acid with butadiene (Scheme 10), where the key intermediate is a bispalladium compound such as Pd2([i-1,2,3,6,7,8-r 6-octa-2,7-dien-l, 8-diyl)((j,-OAc)2] [65]. It was shown that these bimetallic compounds are able to catalyse telomerization in the presence of 1,3-butadiene, acetic acid and a phosphine ligand. 

Because of the relatively poor coordinating properties displayed by the P-menthyl-substituted monodentate ligands toward some catalytically useful metals like rhodium and iridium, development of the coordination chemistry of chelating phosphetanes was required. Early studies established that the bidentate ligand P(6 ),C (6 )-43 binds well to rhodium centers. It gives the chelating complex 26 with [Rh(COD)2]PF6 and the bimetallic compound 68 when reacted with [Rh(COD)Cl]2 under an atmosphere of CO (COD = cyclooctadiene Scheme 5) <19950M4983>. 

Finally, some clusters appear to be mixed metal but in truth they are not. The cluster Os3Mo2(CO),5(C5H5)2(PC Bu) is simply a cluster of type Os3(CO)x, (PR3) where the PR3 ligand is the interesting bimetallic compound Mo2(CO)4(C5H5)2(PC Bu) (504). 

The titanium complexes 29 and 30 were found to polymerize ethylene after the addition of the Lewis add AlEtCl2- The reaction of 10 with methyl alumoxane resulted in the m-methyl bridged bimetallic compound 31, Eq. (31), which was able to polymerize ethylene in the absence of a Lewis acid cocatalyst, when dichloromethane was used as solvent... 

The absorption spectra of the bimetallic compounds showed intense 4f-4f bands along with a small nephelauxetic effect. The observed small nephelauxetic effect may be due to lowering of Slater-Condon (Fk) and Racah (Ek) interaction parameters which is in agreement with the ionic nature of the compounds in water and trifluoroacetic acid [234]. 

Bimetallated compound 199, derived from thioanisole, reacts with 2 molar equiv of methyl chlorocarbonate to give the diester 200, which is converted into benzothiophene 201 (Scheme 39) <2002T4529>. 

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