Ligands heterobidentate

Additional combinatorial variation sites allow the heterocyclic self-assembly units. Thus, it has been shown that heterocycles 11 and 14-17 can serve as A-analogous donor-acceptor ligands self-assembling with the T-analogous acceptor-donor ligands isoquinolone 12 and 7-azaindole 18 (Scheme 30) [92]. All combinations form the heterobidentate ligands exclusively upon simple mixing in the presence of a transition metal salt (proven by X-ray, NMR). 

Scheme 8.7 Selective formation of heterobidentate ligands on a template with identical binding sites.

Template-induced formation of heterobidentate ligands and their application in the asymmetric hydroformylation of styrene. Chem. Commun., 4679 681. (b) Kuil, M., Goudriaan, P.E.. Kleij, A.W., Tooke, D.M., Spek, A.L.. van Leeuwen, P.W.N.M. and Reek, J.N.H. (2007) Rigid bis-zinc([[) salphen building blocks for the formation of template-assisted bidentate ligands and their application in catalysis. Dalton Trans., 2311-2320. 

It occurred to us that ionic interactions might be a highly suitable binding motif to enforce the formation of heterobidentate ligand combinations [48[. The assembly ligand 14 /IS has been formed from the well-known TPPMS (14, monosulfonated triphenylphosphine sodium salt) and 3-(diphcnylphosphinyl)aniline hydrochloride (IS) by a simple ion-exchange reaction (Scheme 10.6). The coordination behavior ofthe ion-pair 14 /I S has been tested with various transition metal complexes. Other... 

Although amino acids and related compounds frequently react in a monodentate fashion with bisperoxovanadate, they can react in a bidentate manner, but the products are often not bisperoxo complexes rather, one peroxide is eliminated in the condensation reaction. This is not necessarily true for all conditions, and bisperoxo-heterobidentate-ligand complexes are known, although in the solid state where a number of x-ray structures have been reported. In this case, one coordination site is an apical position, and a pentagonal bipyramidal product is formed, in the fashion of the oxalato [15] and picolinato (pyridine-2-carboxylato) [16] complexes, as represented diagrammatically in Scheme 6.3. There seems to be no detailed study of these and similar complexes in aqueous solution. Preliminary studies [17,18] of the... 

COMPLEXES OF LIGANDS WITH MIXED DONOR SETS 3.7.8.1 Complexes of Heterobidentate Ligands... 

In this chapter, we focus on a more recent direction in asymmetric hydrogenation, the development of Ir catalysts based on heterobidentate ligands, which have considerably enhanced the substrate scope for this transformation. In particular, the major ligand classes and the underlying design principles as well as the special features and selected applications of these catalysts are discussed. We also dwell on recent mechanistic... 

With Rh(I) salts heterobidentate ligands such as 3 form catalysts of greater activities than homobidentate ligands 4, for enantioselective hydrogenation of acrylate and cinnamate esters. The findings are rationalized in terms of conformational and allosteric effects of the substrates. ... 

The similar N,0 heterobidentate ligands include -aminoalcohols such as -amino-a-phenylethanol (APE) (77) and its N-substituted derivatives (Fig. 9). The terdentate 0,N,0 ligand, bis(2-hydroxy-2-phenylethyl)benzylamine (HPBA) (78) proved to be efficient in samarium-catalyzed enantioselective transfer hydrogenation of acetophenone derivatives, providing excellent enantioselection. 

The ferrocenyl-monophosphane, PPFA (82), and modified PPFA ligands also represent also the class of P,N heterobidentate ligands. 

There have been a few reports of heterobidentate ligands containing oxygen donor ligands in combination with nitrogen, sulfur, or phosphorus donor groups.t For example, cyclic acetals have been used, as represented by ligands 68, 69, and 70 in Scheme 13. 

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