Heterobimetallic lanthanide-alkali metal complexes

Lanthanide amides Ln[N(SiMe3)2]3()tt-Cl)Li(THF)3 or Ln[N(SiMe3)2]3 have been reported to be efficient catalysts for amidation of aldehydes with amines under mild conditions without the use of peroxide and base. But this kind of catalyst is not suitable for the amidation of aldehydes with secondary cycUc amines. Heterobimetallic lanthanide/alkali metal complexes stabilized by phenolate ligand are new classes of bimetallic catalysts for amidation of... 

The lanthanide-alkali metal heterobimetallic complexes have also been shown to promote other reactions, such as nitro-Mannich (aza-Henry) reaction [154],... 

Metallotropic rearrangement, in mercury tri-azenide complexes, 30 41 Metals, see also Heterobimetallics specific element Transition metal complex alkoxides, 15 159-297 of actinides, 15 290-293 of alkali metals, 15 260-263 of alkaline earths, 15 264-266 of aluminium, 15 266-272 of beryllium, 15 264-266 double type, 15 293-294 of gallium, 15 266-272 of lanthanides, 15 290-293 of magnesium, 15 264-266 properties of, 15 260 of transition metals, 15 272-290 trialkylsilyloxides, 15 295-297 of zinc, 15 264-266... 

Shibasaki has developed a family of heterobimetallic complexes 274 to 279 derived from the alkali metal diaryloxy salt of chiral binaphthols and lanthanide alkoxides these complexes function as catalysts in a variety of useful enantiose-lective addition reactions [127,128,13j]. 

One of the more reactive and selective catalysts of this type involves a bifunctional catalyst containing an alkali metal cation and an anionic lanthanide complex resulting from addition of excess binolate with lanthanide halides. Such catalysts have been used in asymmetric nitroaidol (Henry) reactions of ketones. Heterobimetallic Li-La alkoxo complexes (Figure 4.15) catalyzed these reactions with particularly high enantioselectivity. ... 

In 1995, Shibasaki s group disclosed the first example of multifunctional heterobimetallic complex-catalyzed Michael reaction of malonate to enone. The chiral catalyst, lanthanum-sodium-BINOL complex (/ )-LSB, was prepared from La(Of-Pr)3, (/ )-BINOL, and NaOt-Bu. Two different metals indeed play their unique roles to enhance the reactivity of both substrate partners by locating them in designated positions. The Lewis acidic metal (lanthanides or group 13 elements) has been found capable to activate the acceptor, whereas the second metal center (alkali metals bound to a Brpnsted base) assists the coordination of enolate. The proposed catalytic cycle is shown in Scheme 9.5. 

Shibasald s concept of a cooperative effect exhibited by two different metals (usually an alkali with a group 3 metal or a lanthanide) in heterobimetallic BINOL-derived complexes was also fruitful in consecutive Michael-aldol additions. Thus, Al-Li-bis[binaphthoxide] complex R,R)-449, readily accessible from lithium aluminum hydride and 2 equiv. of (S)-BINOL, functions as a highly... 

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