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Synthesis and Characterization of Functionalized N,N-Diphenylformamidinate Silver(I) Dimers:  Solid-State Structures and Solution Properties

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posted on 29.11.1999, 00:00 by Stephen J. Archibald, Nathaniel W. Alcock, Daryle H. Busch, David R. Whitcomb
Functionalized N,N-diphenylformamidines and their deprotonated silver(I) complexes have been synthesized:  silver(I) N,N-di(4-alkyl)phenylformamidinate (alkyl = methyl, ethyl, n-butyl, and n-hexadecyl) 14; silver(I) N,N-di(4-trifluoromethyl)phenylformamidinate 5, silver(I) N,N-di(3-methoxy)phenylformamidinate 6, silver(I) N,N-di(3-methylmercapto)phenylformamidinate 7, silver(I) N,N-di(2-methoxy)phenylformamidinate 8, silver(I) N,N-di(2-methylmercapto)phenylformamidinate 9. The effects of increasing the coordination number of the silver(I) centers by donor substituents on the phenyl groups have been investigated by solution and solid-state studies. Variable-temperature proton NMR (223−303 K) for 14 shows coupling between the proton attached to the amidinate carbon and the 107/109Ag centers at room temperature which is unaffected by cooling (2). For the four-coordinate complexes, 8 and 9, such coupling is only observed on cooling. Molecular weight measurements recorded in solution by vapor pressure osmometry at 310 K show some aggregation to higher molecular weight species than simple dimers for 14 and 6, but 8 and 9 exist as discrete dimeric species. Measurement of thermal stability shows the expected increase in stability with increasing coordination number. Compounds 8 and 9 were structurally characterized by X-ray methods. Both show four-coordinate silver dimers bridged by two amidinate ligands with additional longer interactions with the ether oxygens or thioether sulfurs.