Heterobimetallics

The nitrogen atom in ri -pyrrolylmanganesetricarbonyl forms a donor-acceptor bond with transition metals. Complexes in which the pyrrolyl ring behaves as a tt ligand for the manganese atom and n-donor for the other metal were synthesized 12 (M = Mn, Re) [78JOM(157)431]. The binuclear heterobimetallic complexes... 

Shibasald et al. reported that lithium-containing, multifunctional, heterobimetallic catalysts such as LaLi3tris((l )-6,6 -dibromobinaphthoxide) 35, with moderate Lewis acidity in non-polar solvents, promote the asymmetric Diels-Alder reaction to give cycloadducts in high optical purity (86% ee) [53] (Scheme 1.67). The lithium... 

These heterobimetallic M -M -binol complexes consdnite a new class of v/idely applicable chiral catidysts as shown in Scheme 3.16. The new catidysts consist of a centtidmetid ion fe.g.. La" , AT , Sin , Ga , three alkali inetid ions fe.g., LT, Na , K l, and three chirid tliphenol... 

Without question, the most significant advance in the use of sulfur-centered nucleophiles was made by Shibasaki, who discovered that 10 mol% of a novel gallium-lithium-bis(binaphthoxide) complex 5 could catalyze the addition of tert-butylthiol to various cyclic and acyclic meso-epoxides with excellent enantioselectiv-ities and in good yields (Scheme 7.11) [21], This work builds on Shibasaki s broader studies of heterobimetallic complexes, in which dual activation of both the electrophile and the nucleophile is invoked [22]. This method has been applied to an efficient asymmetric synthesis of the prostaglandin core through an oxidation/ elimination sequence (Scheme 7.12). 

Scheme 37 shows a reaction sequence leading to a mono(amidinato) indium bia(arylimido) complex. Subsequent treatment of the latter with Ti(NMe2)4 resulted in formation of the heterobimetallic In/Ti complex [But(NPr )2]In /t-NCgH3Pri-2,6 2Ti(NMe2)2 (cf. Sections 111.B.2 and V.A.l)." ... 

The palladium(ll) and heterobimetallic palladium(ll)/zinc oxalamidinate complexes depicted in Scheme 197 have been prepared analogously from the free ligands and Pd(acac)2 or ZnEt2/Pd(acac)2, respectively ... 

In accordance with the electropositive nature of the bridgehead atoms, all di(pyridyl) substituted anions behave like amides with the electron density accumulated at the ring nitrogen atoms rather than carbanions, phosphides or arsenides. The divalent bridging atoms (N, P, As) in the related complexes should in principle be able to coordinate either one or even two further Lewis acidic metals to form heterobimetallic derivatives. According to the mesomeric structures, (Scheme 7), it can act as a 2e- or even a 4e-donor. However, theoretical calculations, supported by experiments, have shown that while in the amides (E = N) the amido nitrogen does function as... 

Magnetism of Heterobimetallics Toward Molecular-Based Magnets Olivier Kahn... 

Shibasaki M, Grdger H (1999) Chiral Heterobimetallic Lanthanoid Complexes Highly Efficient Multifunctional Catalysts for the Asymmetric Formation of C-C, C-O and C-P Bonds. 2 199-232... 

These trinuclear complexes can act as metalloligands to afford a whole series of heterobimetallic M3M Q4 cubane-type complexes and several review articles on the topic have been published in the last decade [31, 32]. 

Structures of the Heterobimetallic Complex AgAu(MTP)2. Inorganica Chimica Acta, 334, 376. 

Blackie, M.A.L., Beagley, P., Chibale, K., Clarkson, C., Moss, J.R. and Smith, P.J. (2003) Synthesis and antimalarial activity in vitro of new heterobimetallic complexes Rh and Au derivatives of chloroquine and a series of ferrocenyl-4-amino-7-chloroquinolines. Journal of Organometallic Chemistry, 688(1-2), 144-152. 

Scheme 5-28 Asymmetric hydrophosphonylation of arylaldehy-des catalyzed by a heterobimetallic La/Li/BINOL catalyst (LLB)...

In the proposed mechanism (Scheme 5-33), both the phosphite and the aldehyde are coordinated to the catalyst before nucleophilic attack forms the P-C bond. Slow addition of the aldehyde was found to improve ees it was suggested that this minimizes unselective attack of the activated phosphite on free aldehyde instead of the desired selective attack on complexed aldehyde [26]. In related chemistry with para-anisaldehyde, Shibuya found that ees also depended on the rare earth (La, Eu, Sm) in the heterobimetallic catalyst [24]. 

Scheme 5-39 Asymmetric addition of methyl phosphinate to aldehydes using heterobimetallic BINOLcatalysts LLB = La/Li/BINOL, LPB = La/K/BINOL, ALB = AI/Li/BINOL...

Shibasaki reported the first catalytic asymmetric hydrophosphonylation of imines in 1995 (Scheme 5-45) using heterobimetallic LLB-type catalysts. 

Scheme 5-45 Asymmetric hydrophosphonyla- nomenclature first letter = rare earth (L=La) tion ofimines catalyzed by heterobimetallic rare second letter = alkali (L = lithium, S = sodium, earth/alkali metal/BINOLcomplexes. Catalyst P = potassium)...

The same group extended this work to a cyclic imine (Scheme 5-47) better results were obtained with heterobimetallic lanthanide catalysts than with chiral titanium alkoxides. 

Scheme 5-47 Asymmetric hydrophosphonylation of a cyclic imine catalyzed by heterobimetallic rare earth/alkali metal/BI-NOL complexes or by chiral titanium alkoxide complexes...

In comparison to related P(III) chemistry, metal-catalyzed additions of P-H bonds in P(V) compounds to unsaturated substrates have been studied in more detail, and several synthetically useful processes have been developed. In particular, the use of heterobimetallic BINOL-based catalysts allows asymmetric hydrophosphonylation of aldehydes and imines in high yield and enantiomeric excess. 

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