Improved Efficiency of the Ruthenium-Catalyzed Redox Isomerization of Allyl Alcohols

Abstract

The new complexes [RuCp(PR 3 )(CH 3 CN) 2 ]PF 6 (R ) Ph, Me, Cy) are highly active catalysts for the redox isomerization of allyl alcohols to give the corresponding carbonyl compounds in high yields and high efficiency. All reactions proceed under mild reaction conditions. In some cases, allylations of the carbonyl compounds could be achieved in a tandem catalytic process.

Scope, mechanism and diene inhibition of isomerization of allylic alcohols to saturated ketones catalyzed by ruthenium(II)-cyclopentadienyl complexes

“…In the presence of 1 and two equivalents of triphenylphosphine, a fast isomerization of 3-buten-2-ol to MEK takes place, after a negligible induction period (Fig. 1) [15]. As can be seen from Fig.…”

“…In the publications of Trost on the isomerization of allylic alcohols, catalyzed by [RuClCp(PPh 3 ) 2 ], a low substrate-to-catalyst ratio of 100 was employed [13,14]. The catalytic efficiency of the RuCp-moiety can be increased considerably by using [RuCp(MeCN) 2 (PPh 3 )] + as catalyst precursor [15,16]. This complex has been prepared quantitatively from [RuCp(MeCN) 3 ](PF 6 ) (1) and triphenylphosphine by Slugovc et al [15,16].…”

“…The catalytic efficiency of the RuCp-moiety can be increased considerably by using [RuCp(MeCN) 2 (PPh 3 )] + as catalyst precursor [15,16]. This complex has been prepared quantitatively from [RuCp(MeCN) 3 ](PF 6 ) (1) and triphenylphosphine by Slugovc et al [15,16]. To avoid tedious synthetic procedures and allow for faster screening of catalytic activity of various ligands in combination with the RuCp-moiety, an in situ strategy is adopted here.…”

“…This prompted us to investigate alternative catalyst precursors with higher intrinsic isomerization activities. Ruthenium-cyclopentadienyl complexes with phosphine ligands have been shown by Trost and co-workers [13,14] and Slugovc et al [15,16] to be active isomerization catalysts. Indeed, [RuClCp(PPh 3 ) 2 ] in the presence of silver(I) salts with non-coordinating anions proved to be extremely active in the isomerization of 3-buten-2-ol [17].…”

“…Next to phosphine ligands, which have been discussed in the literature previously [14,15,17], for the first time ligands containing nitrogen-donor atoms are included in this study intending to explore the scope of this catalytic system. Furthermore, the mechanism of the isomerization is investigated by 31 P NMR spectroscopy both in the absence and the presence of dienes in an attempt to shed light on the intriguing effect of dienes on the isomerization reaction.…”