Mixed donors

Related to the crown ethers are compounds, such as hexamethyl-[14]-4,ll-diene (6), which differ by the replacement of one or more of the oxygen atoms by other kinds of donor atoms, particularly N or S. MacrocycHc amine and thioether compounds have been synthesized. Compounds having more than one kind of heteroatom in the ring are called mixed-donor macrocycles. The naturally occurring metaboUtes nonactin [6833-84-7] and monactin [7182-54-9] have both ether and ester groups incorporated in the macrocyclic stmcture. 

Hydrogen and Hydrides as Ligands Mixed Donor Atom Ligands... 

West and colleagues206 have reported the initial examples involving a N -> O/S -> O mixed donor ligand such as 2-(ethylsulphinyl)pyridine A-oxide for transition metal ion and lanthanide metal ion as shown in Scheme 22. Crystal field parameters based on... 

A detailed comparative study of the allylic substitution in allylacetates by amines has been carried ont for the two related mixed donor ligand systems 113 and 114 shown in Fig. 2.19. The P-C system shows dramatically lower activity than N-P, which has been atlribnted to the decreased electrophiUcity of the coordinated aUyl gronp, originating from the strongly o-donating NHC and P donors, compared to N and P donors. 

Fig. 2.19 Allylic substitutions with mixed donor Pd complexes...

It is appropriate to identify our approach to developing the present review in the context of the Co chapter in CCC(1987). The first-edition chapter on Co featured a focused discussion and tabulation of synthetic methods, and many of these basic methods are still employed in synthesis today. Consequently, to avoid repetition, there will be diminished description here where prior appropriate methods have been provided, and only newer developments featured. The last two decades feature the development of many mixed-donor and sophisticated multidentate and macrocyclic ligands, which found limited coverage in the previous edition, and these will be discussed in more detail herein. Reaction kinetics and mechanism were also described thoroughly in the previous edition. We shall not reiterate this material, since the core mechanisms of many reactions involving Co compounds are now adequately defined. 

Polyimines of low-valent Co are now well represented, particularly with macrocyclic or mixed-donor ligands. The monovalent Co complex (5) of the 14-membered macrocyclic hexamethyl diimine (hmd), may be generated electrochemically from its divalent precursor. Furthermore,... 

Trivalent Co complexes of the mixed donor amino arsine emda (2-aminoethyl)dimethylarsine) have been synthesized.936 Examples include trans(X,X), cA(As,As)-[CoX2(edma)2]+ (X = C1, Br, and I), trans( As,As)- and trara(As,N)-[Co(acac)(edma)2]2+, trara(As,N)-[Co(C03)(edma)2]+, [Co(acac)2(edma)]+, and /ao[Co(edma)3]3+. The /ao[Co(edma)3]3+ complex was resolved and the absolute configuration of the (+)49o CD isomer was assigned as A on the basis of the CD spectrum. Racemization of this complex was first order in both complex and hydroxide ions. The crystal structure of [Co(acac)2(emda)]C104 has been reported.937... 

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