Synthesis, Reactions, and ⁷⁷Se NMR Studies of η⁵-Selenophene Complexes of Chromium, Manganese, Ruthenium, and Iridium

The series of η⁵-selenophene transition metal complexes (η⁵-Seln)Cr(CO)₃ (1-3), [(η⁵-Seln)Mn(CO)₃]SO₃CF₃(4–6), [(η⁵-Seln)RuCp*]SO₃CF₃(7–9), and [(η⁵-Seln)IrCp*](BF₄)₂ (10-12), where Seln = selenophene (Sel), 2-methylselenophene (2-MeSel), or 2,5-dimethylselenophene (2,5-Me₂Sel), were synthesized and characterized by ¹H, ¹³C, and ⁷⁷Se NMR and IR spectroscopy. The molecular structure of (η⁵-2,5-Me₂Sel)Cr(CO)₃ (3) was determined. Reactions of [(η⁵-Sel)Mn(CO)₃]SO₃CF₃(4) with nucleophiles (Nuc = H^-, CN^-) give the neutral addition products [(Sel-Nuc)Mn(CO)₃] [Nuc = H^-(4a), Nuc = CN^-(4b)] in which three carbon atoms and the Se are bonded to the Mn. The reaction of [(η⁵-Sel)RuCp*]SO₃CF₃(7) with H^-, however, results in cleavage of the C-Se bond to form a butadiene selenide complex ((η⁵-SeCH═CHCH═CH₂)RuCp*) (7a). Still another type of product results from the reaction of [(η⁵-2,5-Me₂Sel)IrCp*](BF₄)₂ (12) with 2 equiv of H^-; in this case, the H^- acts as a reducing agent to give the ring-opened complex (C, Se-2,5-Me₂Sel)IrCp* (12a). All of these reactions are similar to those of the analogous η⁵-thiophene complexes. The ⁷⁷Se NMR chemical shift values for the η⁵-Seln ligands in complexes 1–12 fall within a range of 225 ppm; they are influenced by the metal and its ligands, the charge on the complex, and the number of methyl groups in the selenophene.