The cyclometalated complex 2 is easily obtained in high yield from the 14-electron complex [RuCl2{(2,6-Me2C6H3)PPh2}2] (1) by reaction with formaldehyde in the presence of triethylamine. The molecular structure of 2 has been determined by an X-ray investigation and reveals a five-coordinate complex with a δ-agostic interaction of one ortho-methyl group. By displacement of one phosphane from 2, a series of new cyclometalated complexes can be obtained. The derivative 4 bearing 2-(aminomethyl)pyridine is a highly active catalyst for hydrogen transfer reactions. Thus, a large number of ketones can be quantitatively converted to alcohols with very high TOF values (up to 63000 h-1)

The five-coordinate complex RuCl{(2-CH 2 -6-MeC 6 H 3 )PPh 2 }(CO)(L*) (2; L* ) (2,6-Me 2 C 6 H 3 )-PPh 2 ) was prepared in high yield by reaction of the 14-electron complex RuCl 2 (L*) 2 (1) with formaldehyde in the presence of NEt 3 via cyclometalation of an ortho methyl group and aldehyde decarbonylation. Alternatively, 2 can be obtained from RuCl 3 hydrate, L*, H 2 CO, and amine in a one-pot reaction. Treatment of 2 with CO affords the cis-dicarbonyl derivative RuCl{(2-CH 2 -6-MeC 6 H 3 )PPh 2 }(CO) 2 (L*) (3), whereas reaction with phosphines leads to the five-and six-coordinate complexes RuCl{( 2 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-CH 2 -6-MeC 6 H 3 )PPh 2 }(CO)(L) (L ) 2-(aminomethyl)pyridine ( 7), ethylenediamine ( 8)) in high yield. The related iodide derivative RuI{(2-CH 2 -6-MeC 6 H 3 )PPh 2 }-(CO)(L*) (9) has been prepared from 2 and NaI by chloride displacement. Treatment of 2 with Na[BAr f 4 ] in the presence of 2,2′-bipyridine or 2-(aminomethyl)pyridine gives the cationic complexes 11)), while with 3 equiv of pyridine the derivative [Ru{(2-CH 2 -6-MeC 6 H 3 )-PPh 2 }(CO)(Py) 3 ][BAr f 4 ] ( 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 .

Complexes of platinum group metals with PCP pincer ligands are currently being investigated in both stoichiometric and catalytic reactions.

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