Sulfoxides bidentate

In pyridine- X-C interactions, the C - X moiety is roughly coplanar with the pyridine and the two C-N- X angles are approximately 120° [129,143, 144]. The same holds for other nitrogen heteroaromatics (e.g. pyrazine, quinoline, etc.) [145-147]. A carbonyl group pins the donors after a trigonal planar geometry and works either as a mono- [148,149] or bidentate XB acceptor [150]. Sulfoxides behave similarly [151,152] and imines form XB along the expected axis of the lone pair [153]. 

Nickel(II) complexes of a variety of bidentate sulfoxide ligands have been reported (326,378,413) and [NiL3][C104]2 species reported where L is the unusual bidentate ligand 2-(ethysulfinyl)pyridine-iV-oxide. Bidentate 0,0-coordination via sulfoxide and pyridine-N-oxide donors is assigned from infrared data (63). 

Significant deviations toward decreased stabilities of Li " complexes from a linear relationship between LCB and GB values also appear for several fluorine-substituted compounds while reasonably good correlation is observed for the S=0 (sulfoxides and sulfones) and P=0 bases. Within the class of oxygen bases the ethers give the worst correlation between basicities. This is because the lithium adducts are much more prone to bidentate chelate ethers as is evident by the enhanced stabilities of Li complexes of methoxy- and fluorine-substituted ethers. Their LCBs are therefore significantly higher than predicted from the linear relationship between LCB and GB values for unsubstituted... 

A new enantiopure, bidentate ligand (35, 45 )-2,2,5,5-tetramethyl-3,4-hexanediol [(35, 45)-186] was developed by Yamanoi and Imamoto and investigated as asymmetric inductor in the titanium-catalyzed sulfoxidation reaction with various hydroperoxides as oxygen donors (Scheme 107). The catalytically active species was then prepared in situ from Ti(OPr-/)4 and ligand (35,45)-186. The most efficient hydroperoxide in terms of enantio-selectivity turned out to be cumyl hydroperoxide (95% ee compared to 30% ee in the case of methyl p-tolyl hydroperoxide), and molecular sieves 4 A had a beneficial effect on the... 

The best results were obtained with the bisoxazole class of ligands such as 35, described by Kanemasa and coworkers [64—66] and for the derivative 36 reported by Corey and coworkers [67, 68] and Sibi et al. [69], who applied heterocyclic additives to the iron-catalyzed reaction. The bidentate sulfoxide ligand 37 introduced by Khiar et al. [70] and the phosphorus oxide ligand 38 reported by Imamoto s group [71] were less effective with respect to chiral induction. 

Complexation of lanthanides in dimethyl sulfoxide with nitrate ion studied with Er(III) and Y(III) showed [98] coordination of 1.5 nitrate groups to the metal ion and 6 DMSO molecules. The nitrate is probably in a bidentate disposition with M-O(l) bond length of 2.38 A and M-0(2) length of 2.57 A. The overall coordination number for Er(III) is close to 9, similar to the solid complex of the composition Er(N03)3 -6DMS0. 

A few tris-bidentate di-sulfoxides also are known,310 and a bidentate phosphate ester311 and amide312. 

Bidentate thioether complexes are reasonably stable in neutral and acidic aqueous solutions but readily hydrolyze in alkali, and the process appears to be reversible. Oxidation to the sulfoxide is difficult but once thioether S is dissociated from the metal becomes relatively easy (Scheme 95). 

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