RuCl<sub>2</sub>[(2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)PPh<sub>2</sub>]<sub>2</sub>: A New Precursor for Cyclometalated Ruthenium(II) Complexes
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The five-coordinate complex RuCl{(2-CH2-6-MeC6H3)PPh2}(CO)(L*) (2; L* = (2,6-Me2C6H3)PPh2) was prepared in high yield by reaction of the 14-electron complex RuCl2(L*)2 (1) with formaldehyde in the presence of NEt3 via cyclometalation of an ortho methyl group and aldehyde decarbonylation. Alternatively, 2 can be obtained from RuCl3 hydrate, L*, H2CO, and amine in a one-pot reaction. Treatment of 2 with CO affords the cis-dicarbonyl derivative RuCl{(2-CH2-6-MeC6H3)PPh2}(CO)2(L*) (3), whereas reaction with phosphines leads to the five- and six-coordinate complexes RuCl{(2-CH2-6-MeC6H3)PPh2}(CO)(L)n (n = 1, L = PCy3 (4), Ph2P(CH2)3PPh2 (6); n = 2, L = PMePh2 (5)) by displacement of L*, according to the steric requirement of the incoming ligand. Similarly, complex 2 reacts with the bidentate nitrogen ligands 2-(aminomethyl)pyridine and ethylenediamine, affording the six-coordinate derivatives RuCl{(2-CH2-6-MeC6H3)PPh2}(CO)(L) (L = 2-(aminomethyl)pyridine (7), ethylenediamine (8)) in high yield. The related iodide derivative RuI{(2-CH2-6-MeC6H3)PPh2}(CO)(L*) (9) has been prepared from 2 and NaI by chloride displacement. Treatment of 2 with Na[BArf4] in the presence of 2,2‘-bipyridine or 2-(aminomethyl)pyridine gives the cationic complexes [Ru{(2-CH2-6-MeC6H3)PPh2}(CO)(L*)(L)][BArf4] (L = 2,2‘-bipyridine (10), 2-(aminomethyl)pyridine (11)), while with 3 equiv of pyridine the derivative [Ru{(2-CH2-6-MeC6H3)PPh2}(CO)(Py)3][BArf4] (12) is obtained. The structure of the δ-agostic complex 2 has been established through an X-ray crystal study, whereas the structure for 7 is supported by 2D NMR experiments in solution. Complexes 7 and 8 are active catalysts for transfer hydrogenation of ketones in 2-propanol, displaying TOF values up to 63 000 h-1.
