Successive OH and sp 3 CH bond activation of ortho-substituted phenols by a ruthenium(0) complex

Abstract

Successive OH and sp 3 CH bond activation of ortho-substituted phenols has been achieved by the reactions of Ru(1,5-cyclooctadiene)(1,3,5-cyclooctatriene) ( 1) with 2,6-xylenol and 2-allylphenol in the presence of PMe 3 giving oxaruthenacycle complexes such as cis- Ru[OC 6H 3 ( 2-C H 2)(6-Me)](PMe 3) 4 ( 4) or Ru[OC 6H 4(2-η 3-C 3H 4)](PMe 3) 3 ( 5), respectively. They are formed by the initial protonation of Ru(1-2-η 2:5-6-η 2-cycloocta-1,5-diene)(1-4-η 4-cycloocta-1,3,5-triene)(PMe 3) by phenols giving cationic (η 5-cyclooctadienyl)ruthenium(II) complexes [Ru(η 5-C 8H 11)(PMe 3) 3] +[OAr] −·(HOAr) n [Ar=C 6H 3Me 2-2,6 ( 2a), C 6H 4(2-CH 2CHCH 2) ( 2b), C 6H 4{2-( E)-CHCHMe} ( 2c), Ph ( 2d); C 6H 4Me-2 ( 2e); C 6H 4(2-CHMe 2) ( 2f), and C 6H 4(2-CMe 3) ( 2g)] followed by sp 3 CH bond cleavage reaction. The molecular structure of 2c reveals that the cyclooctadienyl group coordinates to the ruthenium center by an η 5-fashion, where one equivalent of ( E)-2-propenylphenol is associated with aryloxo anion. Further treatment of 2a and 2c with PMe 3 results in the formation of oxaruthenacycle complexes to give 4 and 5, respectively. These facts clearly demonstrate that this sp 3 CH bond cleavage reaction occurs at a divalent ruthenium center. On the other hand, reactions of 2d– g afford (hydrido)(aryloxo)ruthenium(II) complexes, cis-Ru(H)(OAr)(PMe 3) 4 [Ar=Ph ( 6a), C 6H 4Me-2 ( 6b), C 6H 4(2-CHMe 2) (6c), C 6H 4(2-CMe 3) ( 6d)].