Ligand Influence on the Redox Chemistry of Organosamarium Complexes: Experimental and Theoretical Studies of the Reactions of (C5Me5)2Sm(THF)2 and (C4Me4P)2Sm with Pyridine and Acridine

The reactions of the samarium(II) complexes Tmp(2)Sm (Tmp = 2,3,4,5-tetramethyl-1H-phosphol-1-yl) and Cp-2*Sm(THF)(2) (Cp* = 1,2,3,4,5-tetramethyl-2,4-cyclopentadien-1-yl) with pyridine were found to be different, despite the fact that the Cp* and Tmp pi-ligands are similar in size. With Tmp(2)Sm, a simple adduct, Tmp(2)Sm(pyridine)(2) is isolated, while with Cp-2*Sm(THF)(2) pyridine is dimerized with concomitant oxidation of samarium to form [Cp-2*Sm(C5H5N)](2)[mu-(NC5H5-C5H5N)]. However, reaction of Tmp(2)Sm with acridine, a better pi-acceptor than pyridine, did result in acridine dimerization and the isolation of [Tmp(2)Sm](2)[mu-(NC13H9-C13H9N)]. DFT calculations on the model structures of Tmp(2)Sm and Cp-2*Sm, and on the single electron transfer step from Sm to pyridine and acridine in these ligand environments, confirmed that, even though the Sm-pi-ligand bonds are mostly ionic, the different electronic properties of the Tmp ligand versus that of Cp are responsible for the difference in reactivity of Tmp(2)Sm and Cp-2*Sm.