| Abstract
| - Mild routes to the first Ru(η3-pincer) derivatives of bis((dicyclohexylphosphino)methyl)benzene are reported. RuCl(η3-PCP)(PPh3) (3·PPh3; PCP = [2,6-(Cy2PCH2)2C6H3]) is formedquantitatively on reaction of the PC(H)P-arene ligand with RuCl2(PPh3)3 at 22 °C in thepresence of base. Treatment of 3·PPh3 with KHBsBu3 under nitrogen atmosphere generatesRuH(η3-PCP)(PPh3)(N2), 4, as a mixture of conformational isomers in which the hydrideand N2 ligands are trans or cis (4a or 4b, respectively). On exposure to H2, 4a/b undergoimmediate, quantitative exchange of bound N2 for η2-H2, affording the corresponding isomersof RuH(η3-PCP)(PPh3)(H2), 5a/b. Complex 3·PPh3 resists displacement of PPh3 by H2 at 22°C, but on exposure to CO, readily yields RuCl(η3-PCP)(CO)2, 6. Transfer hydrogenation ofketones is efficiently catalyzed by 3·PPh3 and 4, in a pathway involving loss of PPh3 and(for 3) exchange of chloride for hydride. The duration of pretreatment of 3·PPh3 with base(KOH, tBuOK) in refluxing 2-propanol is critical to activity, and indirect evidence supportsformation of a catalytically active dihydride species during this process. X-ray crystalstructures are reported for 3, 4a, 5a, and 6.
- Routes are reported to RuX(η3-PCP)(PPh3)(Ln) (n = 0, X = Cl; n = 1, X = H, L = N2, H2; PCP = [2,6-(Cy2PCH2)2C6H3]), the first cyclohexyl-pincer complexes of a group 8 metal. The chloride complex is a convenient and efficient precatalyst for transfer hydrogenation of ketones; indirect evidence is consistent with formation of a Ru dihydride species.
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