Reduction of aldehydes and ketones by transition-metal hydrides. 1. Reaction of trans,trans-WH(CO)2(NO)(PMe3)2 with simple and phenoxy-functionalized aldehydes and ketones

Article abstract of DOI:10.1021/om00042a020

The reaction of trans,trans-WH(CO)₂(NO)(PMe₃)₂ (1) with propanal and benzaldehyde yields unstable insertion products. The C=O double bond of salicylaldehyde rapidly inserts into the W-H bond of 1, affording the alkoxide 3a. This compound readily isomerizes to the more stable phenolate 3b. In the presence of excess salicylaldehyde 3a and 3b react further to the isolable tungsten salicylates 3c and 3d, respectively, with liberation of the organic reduction product α,2-dihydroxytoluene. Compound 3d crystallizes in the monoclinic space group P2₁/c with a = 8.863 (3) A?, b = 10.849 (3) A?, c = 19.939 (6) A?, β = 96.31 (2)°, V = 1905.7 (10) A?³, Z = 4, and R = 0.0558 for 3402 observed reflections. In the solid-state structure of 3d the salicylate moiety, acting as an O,O′-bidentate ligand to tungsten, shows some quinoid character. Similarly, 1 reacts with 2 equiv of 2-hydroxyacetophenone, producing 4 and 1-(2-hydroxyphenyl)ethanol. Treating 1 with methyl salicylate affords 5, albeit via a simple acid-base reaction with evolution of H₂. Reaction of 1 with 4-hydroxybenzaldehyde initially yields the insertion product 6a, after which an equilibrium reaction between different tungsten phenolates sets in.