Ligands bicyclic

Nickel(II) complexes of various heteroanalogues of the tridentate tacn ligand ([9]aneN3) have been reported, where one, two, or all three N-donor atoms of the macrocycle are replaced by S, O, or combinations thereof. Such moieties have also been incorporated in bicyclic ligand systems that form complexes with Ni11.1440... 

Compound (39) reacts with Pt(II) and Pd(II) chlorides at room temperature in CH3CN and CHC13, respectively. But in both cases coordination of two ligands with the metal atom was accompanied by nucleophilic substitution at the exocyclic carbon atom. Complexes (210) and (211) having a novel chelate bicyclic ligand with Pt(II) and Pd(II) have been formed in the course of template processes [Eq. (149)] (92IZV335,92MI1). 

Bicyclic-ligand complexes incorporating a void adjacent to the... 

Bicyclic-ligand complexes with a metal-ion void... 

Mg has been studied in a polyelectrolyte system where the counterion is a phosphazene-bound sulphonate group. In this case the finite but low conductivity is due to Mg migration. A large increase in conductivity is noted when a bicyclic ligand, crypt [2.1.1.], is introduced (Hancock and Martell, 1988). Apparently, the cation-anion and cation-polymer interactions are reduced by complex formation, resulting in a more mobile cation, despite its larger effective radius. 

Fig. 8. From left to right Exo-exo, endo-endo and exo-endo conformations of macro-bicyclic ligands of type G, e. g. ligand 30, [2.2.2]...

Lehn and Sauvage (34) suggest that bicyclic ligands should be better suited than non-cyclic polyethers to selectively complex cations. Their data (Table 8) show this to be valid for the series of bicyclic amines represented by the structures in Fig. 3. 

Nickclocene. on the tuber hantl. is more slowly oxidized and undergoes addition ot suitable activated olefins to one ring convening it to a bicyclic ligand. Sumc ligand replacement reactions arc also known for nickclnccne. 

Even with the sterically demanding coumarin derivative as nucleophile, the secondary ether could be formed in excellent regio- (92 8) and enantioselectivity (98% ee) by using the bicyclic ligand 135 (Scheme 8E.36). The alkylation product has efficiently served as a key intermediate in the synthesis of (-)-calanolides A and B, which have the most potent HIV-1-specific reverse-transcriptase inhibitory activity among the chromanol family. 

The structure of 19 was established by X-ray crystallography. It shows a short Fe-C(phenyl) a-bond (2.04 ) when compared to that found in (p5-Cp)Fe(C0)(PPh3>(n -C6H5) (2.14A) (10) and the shortest P-Fe bond observed so far (2.105/1) which may arise from a high Tr-accepting capability and/or a small cone-angle of the constrained bicyclic ligand (11). 

In order to gain more direct access to these bicyclic ligands, methods have been developed which allow the formation of the macrobicycle in one step. The tripod-tripod coupling is an example of this method (Fig. 5.2) which may be performed without the need for high-dilution conditions. The synthesis of the bis-tren macrobicycle, 17, illustrates this approach.3... 

Fig. 3. Side on ORTEP representation of [7 -2,3-bis(methylene)bicyclo [2.2, l]heptane]-zirconocene (5s). Zirconium is bonded to the exo side of the bicyclic ligand. Zr—C bonds to C2 and C3 are noticeably longer than those to Cl and C4.

It has been depicted before in Scheme 29 that complex 78 may add the 14-electron fragment [Pt(PEt3)Cl2] to give complex 79 whereby the structural integrity of the bicyclic ligand was retained. 

A different situation was encountered in the reaction of the free bicyclic ligand 19 with [PtCl2(PEt3)]2 which led to compound 148 (Equation 16). 

The complexes (CgHg)M(CO)3 represent a class in which the olefin has more tt electrons than required by the metal atom. Consequently, (i) part or all of the excess n electrons may become involved in carbon-carbon ff-bond formation resulting in bicyclic ligands (ii) the metal atom may coordinate with three olefinic double bonds leaving the other geometrically isolated or (in) the metal may be simultaneously linked to all the sp carbon atoms with a fraction of each n electron involved in the bonding. 

Fig. 68. Structures of macro-bicyclic ligands and their Ba++/K+ selectivities 1,...

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