Preparation and structure elucidation of novel organoruthenium amidinates bearing η⁴-diene ligands

A series of novel ruthenium amidinate complexes bearing η⁴-cyclooctadiene (COD) or η⁴-norbornadiene (NBD) ligand was prepared, and their structures were elucidated by spectroscopy and crystallography. A disilver amidinate, Ag₂{μ₂,η-PhNC(H)=NPh}₂, was treated with either (η⁴-COD)Ru(MeCN)₂Cl₂ or (η⁴-NBD)Ru(pyridine)₂Cl₂ to form the corresponding bisamidinate complex, (η⁴-COD)Ru{η²-PhNC(H)=NPh}₂ (5a) or (η⁴-NBD)Ru{η²-PhNC(H)=NPh}₂ (5a′), respectively, in moderate to good yield. Alternatively, (η⁴-COD)Ru{η²-ⁱPrNC(Me)=N ⁱPr}₂ (5b) or (η⁴-NBD)Ru{η²-ⁱPrNC(Me)=N ⁱPr}₂ (5b′) was synthesized by reaction of [(η⁴-COD)RuCl₂]_n or (η⁴-NBD)Ru(pyridine)₂Cl₂ with Li{ⁱPrNC(Me)=NⁱPr}. Careful treatment of (η⁴-NBD)Ru(pyridine)₂Cl₂ with one equivalent of Li{ⁱPrNC(Me)=NⁱPr} resulted in the formation of a monoamidinate complex, (η⁴-NBD)Ru{η²-ⁱPrNC(Me)=N ⁱPr}(pyridine)Br (6) as a good precursor for a mixed amidinate complex, (η⁴-NBD)Ru{η²-ⁱPrNC(Me)=N ⁱPr}{η²-PhNC(H)=NPh} (5c′), which was obtained by the reaction of 6 with Ag₂{μ₂,η-PhNC(H)=NPh}₂. Crystal structures of these complexes revealed the octahedral arrangement of the ligands.