Large Ring Complexes

Large ring systems are now known in which metal-P linkages are involved either internally or externally. These include calixarenes, polysaccharide rings, P-S-N rings and many others (8.373) and (8.374) [22-27] (see also Chapters 5.7 and 6.8). 

Corbridge, The structural chemistry of phosphorus compounds. Topics Phos. Ghent., 3, 57,1966. 

Aronsson, T. Lundsrtom, and S. Rundqvist, Borides, Silicides and Phosphides, Methuen, London, 1966. 

Franzen, Structure and bonding in metal-rich pnictides, chalcides and halides. Prog. Solid St. Chem., 12, 1, 1978. 

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A second important class of complexes contains both thiolate and tertiary phosphine ligands. These are prepared by reactions such as those of equations (28) or (29).187,228,233-236 Bridged complexes (9) and (10) may be prepared either from dithiols or from tertiary phosphine thiol derivatives, respectively.187,237 The structure of the large ring complex (10) has been determined.238... 

Large-ring Complexes. Variable-temperature n.m.r. studies of the l(l f),2-diazepine complex (40 = R = H) reveal the fluxional/tautomeric rearrangement shown... 

This type of alkyne dimerization is also catalyzed by certain nickel complexes, as well as other catalysts and has been carried out internally to convert diynes to large-ring cycloalkynes with an exocyclic double bond. ... 

The formulas of some ARs are given in Figure 11.1, where it can be seen that they have some structural resemblance to both dicoumarol and vitamin K in its quinone form. All possess quinone rings linked to unsubstituted phenyl rings. The phenyl rings of the rodenticides confer hydrophobicity, especially in the relatively large and complex molecules of brodifacoum and flocoumafen. The chemical properties of some ARs are given in Table 11.1... 

Crane, W.S. and Beall, H. (1978) The structure of a large ring gold complex. Inorganica Chimica Acta, 31, L469-L470. 

Another process that is widely used involves reduction by Zn-Cu couple. This reagent is especially reliable when prepared from TiCl3 purified as a DME complex,243 and is capable of forming normal, medium, and large rings with comparable efficiency. 

A feature of the metal-ion chemistry of these large ring macrocycles is thus the structural diversity which may occur from one system to the next. This diversity can result directly from small changes in the structure of the cyclic ligand and is also aided by the inherent flexibility of the large rings involved. It is clearly also influenced by the nature of the other ligands available for complex formation. 

A review of the stabilities and catalytic properties of binuclear metal complexes of large-ring N,0 macrocycles concentrates on the iron(II) and iron(III) complexes of (184) and (185). ... 

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