C,N-chelating ligands

SCHEME 11. Triorganotin hydrides containing one C,N-chelating ligand... 

It should be noted here that Corriu and co-workers have reported on organosilicon compounds containing C,N-chelating ligands in which the silicon atom is penta- or hexacoordinate (55-58). Such organosilicon compounds are models for the intermediates proposed for the activation of enoxysilanes by F leading to cross-aldolizations or Michael reactions (59). 

Fig. S. Divalent organotin compounds stabilized by two C,N-chelating ligands.

Valuable information concerning the structures in solution of organotin compounds containing a C,N-chelating ligand is obtained from H, l3C, and 119Sn NMR spectroscopic studies. Furthermore, these studies provide sometimes detailed information on the fluxional processes that are operative in solutions of these compounds. It appears that the 119Sn chemical... 

A rather unusual series of compounds, which may be regarded as tetra-organotin compounds containing a potentially C,N-chelating ligand, are the triorganotin hydrides 37-39 shown in Fig. 11 (105,106). 

The triorganotin halides containing one monoanionic C,N-chelating ligand that has been studied are depicted in Fig. 12. 

These compounds include the following type of C,N-chelating ligands 2-[(dimethylamino)methyl]phenyl 40a-45 (54.114-117) [2-(dimethyla-mino)phenyl]methyl 46a-c, 47a-c (80) 8-dimethylamino-l-naphthyl 48 -50 (110) 2-[(dimethylamino)methyl]phenyl methyl 51,52 (118), 8-(dimethylamino)methyl-l-naphthyl, 53,54 (118), 2-(4,4-dimethyl-2-oxa-zoline)-5-(methyl)phenyl 55,56 (119) and 2-(phenylazo)phenyl 57a,57b (120,121). For some representative examples, the structure was unambiguously proven by an X-ray crystal structure determination 40c (115), 41b (114), 44b (116), 47b (80), 49 (96), 54 (118), 56 (119), 57a (121), and 57b (122). The last compound was obtained as an unexpected by-product from the reaction of 2,4-dinitrophenyldiazonium cation with (3-methoxy-phenyl)trimethyltin (120) ... 

It has been well established that the configurational stability of the tin centers in trioiganotin halides, which is usually very low, is enhanced to a considerable extent when intramolecularly coordinating substituents are present (123). The presence of a C,N-chelating ligand allows a detailed study concerning the fluxional processes that may be operative in solution. The two basic processes are (i) Sn—N dissociation/association and (ii) inversion of configuration of the tin center see Fig. 13. 

Fio. 13. The two basic fluxional processes operative in solutions of triorganotin halides containing a C,N-chelating ligand. 

Fig. 19. Triorganotin halides containing two C,N-chelating ligands in which the tin atom may be regarded as hexacoordinate.

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