MONONUCLEAR, BINUCLEAR AND POLYNUCLEAR COMPLEXES OF DIPHENYLMETHANE WITH CR, CO AND RU - SYNTHESIS AND INVESTIGATION BY H-1, C-13 AND O-17 NMR

Complexes of diphenylmethane (Ph(2)CH(2)): Ph(2)CH(2)Cr(CO)(3) (1), Ph (2)CH(2)[Cr(CO)(3)](2) (2), Ph(2)CH(2)Co(4)CO)(9) (3), Ph(2)CH(2)[Co-4 (CO)(9)](2) (4), Ph(2)CH(2)Cr(CO)(3)Co-4(CO)(9) (5) and Ph(2)CH(2)Ru( 6)C(CO)(14) (6) have been prepared and characterized by H-1 and C-13- O-17-NMR spectroscopy. Strong shielding effects are caused by the meta l valence electrons on the H-1- and C-13-NMR chemical shifts of aromat ic protons and carbons in pi-coordinated ring(s) of diphenylmethane. G enerally, the order of these shielding effects on the nuclei of the ar omatic rings in H-1-NMR was Co-4(CO)(9) < Ru6C(CO)(14) < Cr(CO)(3) and in C-13-NMR Co-4(CO)(9) < Cr(CO)(3) < Ru6C(CO)(14). In addition, arom atic solvent exhibits an enhanced shielding effect on the H-1-NMR chem ical shifts of the rr-coordinated ring induced probably by aromatic so lvent induced shifts (ASIS). The 1H-NMR chemical shifts of the exocycl ic methylene protons are shielded or deshielded depending on the solve nt, the metal and the degree of rr-coordination. These findings can be explained by the varying conformational states adopted by the flexibl e ligand. The C-13-NMR chemical shifts of the methylene carbon are gen erally shielded supporting the above explanation. This conformational flexibility can be of extreme importance in controlling the catalytic activity of these organometallic compounds. In chromium and heterobime tallic chromium cobalt derivatives 1, 2 and 5, O-17-NMR spectroscopy p roved to have excellent sensitivity comparable with that of C-13-NMR. In cobalt clusters 3 and 4 no O-17-NMR lines were observed, which is p robably because of strongly broadened O-17-NMR signals of carbonyls un dergoing dynamic exchange. In the ruthenium cluster 6 only one broad O -17-NMR line at 30 degrees C was observed. An inverse relation between the C-13- and O-17-NMR chemical shifts of the carbonyl groups can be explained by the effect of pi-backbonding.