Chelated derivatives

It is clear from the preceding discussion that organometallic photoinitiators (metal carbonyl or chelate derivatives) can provide a convenient route for synthesizing vinyl polymers with a variety of different reactive end group or photoreactive pendant groups or side chains through the polymer chain. 

An excess of Grignard reagent (4 equivalents) or the addition of strong Lewis acids promotes the preference for chelation-controlled. vvn-products (Table 20)22 21 u. In addition, the use of diethyl ether or dichloromethane instead of tetrahydrofuran improves the yield of the chelation-derived syn-product24. 

Chiral nitrogen chelates derived from sugars were prepared by Ruffo [48], introducing diimines and diamines functionalities on inexpensive monoses, a-D-glucose and a-D-mannose. 

Complexes having a tridentate A,A,C chelate derived from 2,9-diphenyl-phen,1944 4-(4-methoxy-phenyl)-6-phenyl-2,2 -bipyridine,1945 6-benzyl-2,2 -bipyridine,1946 or 6-But-2,2 -bipyridine1946 have been prepared from heating solutions of the ligand and [AuCl4] with the assistance of a silver salt. Equation (18) shows one example. 

Ligands for catalytic Mukaiyama aldol addition have primarily included bidentate chelates derived from optically active diols,26 diamines,27 amino acid derivatives,28 and tartrates.29 Enantioselective reactions induced by chiral Ti(IY) complex have proved to be one of the most powerful stereoselective transformations for synthetic chemists. The catalytic asymmetric aldol reaction introduced by Mukaiyama is discussed in Section 3.4.1. 

The purification of chelates derived from the above scheme was tedious because of the trifunctionality of these substances and the corresponding possibility of mixtures of products. Again this problem was solved by studying this series of reactions on the dichlorochromium chelate (XXXVI), which has only one reactive ring. 

The bidentate ligand MeSCH2CH2SMe forms a chelate derivative of gold(III) (71), but the structures of AuCl3-L where L = MeSe(CH2)3SeMe or Se(CH2CH2)2Se are not known.219,540,541... 

Rare earth chelates derived from alkyl- and fiuoroalkyi-substituted jS-diketones are useful, even as mixtures, as anti-knock additives in gasoline.354,355... 

These spectra were routinely obtained for most of the compounds discussed in forthcoming sections. Specific studies were performed on selected compounds such as (i) (+)-(S )-4,5,6,7-tetrahydroimidazo-9-chloro-5-methyl-6-(3-methyl-but-2-enyl)imidazo [4,5,1 -jk [1,4] benzodiazepin-2(l//)-thione (9-chloro-TIBO)187 and (ii) series of metal chelates derived from l,2-dithiol-3-thion-4,5-dithiolate (dmt)188. The equilibria between 2-ethoxycarbonylthiolane-3-thiones and their (Z)-enethiol tautomers were also studied by these techniques189. It was found that the equilibrium is largely shifted in favor of the enethiols. NMR was also used to study the syn-anti conformational equilibria of seven A-(l-methoxycarbonylethyl)-A4-thiazoline-2-thiones with S conformation of the chiral rotor (43)190. A variety of substituents were used. 

Neutral chelates derived from divalent transition-metal ions are prepared readily by metathetical reactions in water or, when the solubility of the ligand in water is low, in DMF-water mixtures. With the exception of some bidentate chelates of Mn(II) and Fe(II), which are air-sensitive, the transition-metal compounds are stable to air, and an inert atmosphere is not required during their synthesis or storage. The following procedures are applicable to the preparation of chelates derived from other transition-metal ions. 

Heterocyclic analogues of benzenedithiolates are also available. 3,4-Thio-phene-dithiolate is generated from the corresponding dibromothiophene (44). The isoelectronic but inorganic l,2,5-thiadiazole-3,4-dithiolate, [SN2C2S2]2 (tdas, see Fig. 2) can be prepared by sulfidation of SN2(CC1)2 the dianion forms bis(chelate) derivatives of Ni(II) and Fe(III) (45). 

Johansson and Davidsson47 have reported on the NMR studies of a mixture of two different chelating lithium amides, one with an ether chelate, derived from (R)-l-methylamino-2-methoxy-l-phenylethane (9), and one with an amine chelate (Li-4). It was found that the Et20 solution contained different dimers, both homo and hetero dimers. Based on NMR data it was concluded that a mixture of the two hetero dimers, both symmetrically ((Li-4/Li-9) 2Et20) and unsymmetrically ((Li-4/Li-9) Et20) solvated, dominated in solution. 

In a subsequent investigation it was observed that the reaction of tetracyanoethylene oxide with 5,10,15,20-tetraphenylporphyrin-zinc chelate produced the corresponding zinc chelated derivative of 5,10,15,20-tetraphenyl-2,3-(3 -dicyano)cyclopropano-2,3-chlorin and is described by the author (4). 

---