CLUSTERS amidinates

The reaction of diisopropylcarbodiimide with ZnMe2 (90 °C, 60 h) was recently reported to yield a product mixture, from which three unusual compounds could be isolated and structurally characterized, including two tetranuclear zinc amidinate clusters (Scheme 162). ... 

Tetranudear gold(I) amidinate complexes are synthesized by the reaction of Au(THT)Cl with the potassium or sodium salt of the amidinate ligand in THF, Figure 1.4. Syntheses involving various substituted amidinates resulted in tetra-nuclear gold(I) clusters, [Au4(ArNC(H)NAr)4]. The C-functionalized substituted amidine ligands, ArNC(Ph)NHAr and ArNC(Me)NHAr, Ar=-QH5, were synthesized and reacted with Au(THT)Cl after deprotonation. Only tetranudear clusters were isolated. 

Table 1.2 Average Au Au distances (A) and Au Au Au angles (°) of tetranuclear gold(l) amidinate and related clusters.

Density functional theory (D FT) modeling calculations show that a dinuclear gold(I) amidinate complex is less stable than the tetranuclear gold(I) amidinate cluster, [Au4(HNC(H)NH)4]. However, replacing C by Si in the backbone reduces ring strain and makes the energies similar. Figures 1.21 and 1.22 [39]. 

Amidines have been known to coordinate with metals in a variety of monomeric,81,82 dimeric83 and cluster84 systems, but it was only in 1983 that amidine clusters were structurally characterized.83... 

These amidine clusters have been thermally decarbonylated to the corresponding nonacarbonyl compounds of which [Os3(/i-H)(CO)9(MeCN2H2)] alone exists as two tautomeric forms (36) and (37) ... 

Further reactions of the imido cluster complexes with nitriles are possible. Depending on the nature of the organonitriles, either mixed imido clusters are formed or amidinate complexes are produced as a result of nucleophilic addition of the R-N (R = Lu, Y) imido unit to a C-N triple bond, as shown in Figure 56 (Cui et al., 2005b). 

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