RuCl₂[(2,6-Me₂C₆H₃)PPh₂]₂:  A New Precursor for Cyclometalated Ruthenium(II) Complexes

Abstract

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 .

Osmium Pyme Complexes for Fast Hydrogenation and Asymmetric Transfer Hydrogenation of Ketones

“…[3,4] Interestingly, we have observed that a dramatic increase of activity in TH with ruthenium-based catalysts is achieved by using the ligand 1-(pyridin-2-yl)methanamine (Pyme). [5] By employment of 1-substituted Pyme ligands (RPyme; R = Me, tBu, Ph), we have recently isolated the complexes cis-[RuCl 2 A C H T U N G T R E N N U N G (Josiphos)A C H T U N G T R E N N U N G (RPyme)] which are among the most active catalysts for the asymmetric TH of a variety of aryl ketones. [6] It is worth noting that few compounds, namely [RuCl 2 (PP)(NN)] (PP = diphosphane; NN = Pyme, [5d, 7] diamine [3,8] ), [RuCl(NN)A C H T U N G T R E N N U N G (arene)], [4b, 9] [RuCl 2 -A C H T U N G T R E N N U N G (PPh 3 )(oxazoline)], [10] Ru-Binap, [11] and (cyclopentadienone)Ru carbonyl complexes, [12] catalyze both the asymmetric TH and HY of carbonyl compounds.…”

“…This rate is surprisingly high and can be compared with that of the most active catalysts for TH-based on ruthenium. [5,17] Actually, the activity of 3/4 appears higher than that of the analogue cis-[RuCl 2 -…”

Ruthenium and osmium complexes containing 2-(aminomethyl)pyridine (Ampy)-based ligands in catalysis

“…The use of the related ligand 2-(aminomethyl)pyridine (with a CH 2 CH 2 spacer instead of CH 2 between the pyridine ring and the amino group) resulted in a much less active system (TOF of about 4 × 10 3 h −1 ), indicating that the chain length is crucial for the catalyst activity. Thus, the complex 3 was isolated by reaction of 2 with an equimolar amount of Ampy, and its structure was established in solution through a Roesy NMR experiment (Scheme 3) [15]. Compound 3 displayed the same activity of 2/Ampy, catalyzing the quantitative TH of a large number of aliphatic (linear and cyclic) and aromatic ketones within few minutes with TOF up to 6.3 × 10 4 h −1 .…”

Transfer Hydrogenation Reactions Catalyzed by Free or Silica‐Immobilized [RuCl2(ampy){RN(CH2PPh2)2}] Complexes

“…[17] Accordingly, all catalytic tests were run in the presence of sodium 2-propoxide generated by dissolution of metallic sodium into the alcohol. (5) As complexes 1 and 2 showed only partial solubility in 2-propanol, even when heated at reflux and in catalytic conditions, we turned our attention to in situ prepared catalytic systems. Thus, the catalytic reactions were carried out with the use of a 0.1  solution of acetophenone in 2-propanol in the presence of 0.05 mol-% of the cis,cis-[RuCl 2 (PPh 3 ) 2 -(ampy)] complex, 0.06 mol-% of the appropriate R 1 N-(CH 2 PPh 2 ) 2 ligand, and 2 mol-% of (CH 3 ) 2 2 ] system, for which the exclusive formation of 1 was observed.…”

“…Recently, we reported the synthesis of a series of phosphanyl-Ru II complexes bearing the (2-aminomethyl)pyridine (ampy) [5][6][7][8] ligand or the related 6-(4Ј-methylphenyl)-2-pyridylmethylamine ligand, [9,10] and examined their ability to catalyze the reduction of ketones. Among complexes with the ampy ligand, exceptionally high catalytic activity was observed for complexes also bearing diphosphane ligands ( Figure 1) with the cis isomer showing higher efficiency.…”