Mono-, bi- and polynuclear complexes of diphenylmethane with Cr, Co and Ru. Synthesis and investigation by 1H, 13C and 17O NMR

Abstract 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 1 H and 13 C-and 17 O-NMR spectroscopy. Strong shielding effects are caused by the metal valence electrons on the 1 H- and 13 C-NMR chemical shifts of aromatic protons and carbons in π-coordinated ring(s) diphenylmethane. Generally, the order of these shielding effects on the nuclei of the aromatic rings in 1 H-NMR was Co 4 (CO) 9 6 C(CO) 14 3 and in 13 C-NMR Co 4 (CO) 9 3 6 C(CO) 14 . In addition, aromatic solvent exhibits an enhanced shielding effect on the 1 H-NMR chemical shifts of the π-coordinated ring induced probably by aromatic solvent induced shifts (ASIS). The 1 H-NMR chemical shifts of the exocyclic methylene protons are shielded or deshielded depending on the solvent, the metal and the degree of π-coordination. These findings can be explained by the varying conformational states adopted by the flexible ligand. The 13 C-NMR chemical shifts of the methylene carbon are generally 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 heterobimetallic chromium cobalt derivatives 1, 2 and 5 , 17 O-NMR spectroscopy proved to have excellent sensitivity comparable with that of 13 C-NMR. In cobalt clusters 3 and 4 no 17 O-NMR lines were observed, which is probably because of strongly broadened 17 O-NMR signals of carbonyls undergoing dynamic exchange. In the ruthenium cluster 6 only one broad 17 O-NMR line at 30°C was observed. An inverse relation between the 13 C- and 17 O-NMR chemical shifts of the carbonyl groups can be explained by the effect of π-backbonding.