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 Tmp2Sm (Tmp = 2,3,4,5-tetramethyl-1H-phosphol-1-yl) and Cp*2Sm­(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 π-ligands are similar in size. With Tmp2Sm, a simple adduct, Tmp2Sm­(pyridine)2 is isolated, while with Cp*2Sm­(THF)2 pyridine is dimerized with concomitant oxidation of samarium to form [Cp*2Sm­(C5H5N)]2[μ-(NC5H5–C5H5N)]. However, reaction of Tmp2Sm with acridine, a better π-acceptor than pyridine, did result in acridine dimerization and the isolation of [Tmp2Sm]2[μ-(NC13H9–C13H9N)]. DFT calculations on the model structures of Tmp2Sm and Cp*2Sm, and on the single electron transfer step from Sm to pyridine and acridine in these ligand environments, confirmed that, even though the Sm−π-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 Tmp2Sm and Cp*2Sm.