Synthesis and structure of rhodium(I) silyl carbonyl complexes: photochemical C-F and C-H bond activation of fluorinated aromatic compounds

The rhodium(I) silyl carbonyl complexes [Rh{Si(OEt)(3)}(CO)(dippp)] (1) and [Rh{Si(OEt)(3)}(CO)(dippe)] (2) (dippp = 1,3-bis(diisopropylphosphino) propane, dippe = 1,2-bis-(diisopropylphosphino) ethane) were synthesized on treatment of the methyl compounds [Rh(CH3)(CO)(dippp)] (3) or [Rh(CH3)(CO)(dippe)] (4) with HSi(OEt)(3) at low temperature. The methyl complexes 3 and 4 were prepared starting from the binuclear complexes [{Rh(mu-Cl)(dippp)}(2)] (5) and [{Rh(mu-Cl)(dippe)}(2)] (8), respectively. The silyl complexes 1 and 2 as well as the precursors [{Rh(mu-I)(dippp)}(2)] (6), [Rh(X)(CO)(dippp)] (3: X = CH3, 7: X = I) and [Rh(X)(CO)(dippe)] (4: X = CH3, 9: X = Cl) were characterized by NMR and IR spectroscopy and the structures in the solid state were determined by X-ray crystallography. The silyl complex 1 converts into the carbonyl-bridged complex [{Rh(mu-CO)(dippp)} 2] (10) above temperatures of -30 degrees C by loss of the silyl ligand, whereas 2 is more thermally stable and a reaction to the binuclear complex [{Rh(mu-CO)(dippe)}(2)] (11) was observed at 50 degrees C. The silyl complex 2 reacted under irradiation with hexafluorobenzene and pentafluoropyridine to give the C-F activation products [Rh(C6F5)(CO)(dippe)] (12) and [Rh(2-C5F4N)(CO)(dippe)] (17), respectively. As additional products the silyl dicarbonyl complex [Rh{Si(OEt) 3}(CO) 2(dippe)] (13) and the cationic complex [Rh-2(mu-H)(mu-CO)(2)(dippe)(2)](+)[SiF5](-)(14) were identified. Compound 13 was synthesized independently by treatment of 2 with gaseous CO. In a similar manner, the dippp analogue [Rh{Si(OEt) 3}(CO)(2)(dippp)] (15) was also prepared starting from 1. Photochemical reaction of 2 with pentafluoro-benzene and 2,3,5,6-tetrafluoropyridine resulted selectively in C-H bond activation to afford 12 and [Rh(4-C5F4N)(CO)(dippe)] (18), respectively.