Synthesis and characterization of functionalized N,N '-diphenylformamidinate silver(I) dimers: Solid-state structures and solution properties

Functionalized N,N'-diphenylformamidines and their deprotonated silver(I) c omplexes have been synthesized: silver(I) N,N'-di(4-alkyl)phenylformamidina te (alkyl = methyl, ethyl, n-butyl, and n-hexadecyl) 1-4; silver(I) N,N'-di (4-trifluoromethyl)phenylformamidinate 5, silver(I) N,N'-di(3-methoxy)pheny lformamidinate 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-m ethylmercapto)phenylformamidinate 9. The effects of increasing the coordina tion number of the silver(I) centers by donor substituents on the phenyl gr oups have been investigated by solution and solid-state studies. Variable-t emperature proton NMR (223-303 K) for 1-4 shows coupling between the proton attached to the amidinate carbon and the Ag-107/109 centers at room temper ature which is unaffected by cooling (2). For the four-coordinate complexes , 8 and 9, such coupling is only observed on cooling. Molecular weight meas urements recorded in solution by vapor pressure osmometry at 310 K show som e aggregation to higher molecular weight species than simple dimers for 1-4 and 6, but 8 and 9 exist as discrete dimeric species. Measurement of therm al stability shows the expected increase in stability with increasing coord ination number. Compounds 8 and 9 were structurally characterized by X-ray methods. Both show four-coordinate silver dimers bridged by two amidinate l igands with additional longer interactions with the ether oxygens or thioet her sulfurs.