Successive OH and sp3 CH bond activation of ortho-substituted phenols by a ruthenium(0) complex

Successive OH and sp3 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 PMe3 giving oxaruthenacycle complexes such as cis-(H2)(6-Me)](PMe3)4 (4) or 3H4)](PMe3)3 (5), respectively. They are formed by the initial protonation of Ru(1-2-η2:5-6-η2-cycloocta-1,5-diene)(1-4-η4-cycloocta-1,3,5-triene)(PMe3) by phenols giving cationic (η5-cyclooctadienyl)ruthenium(II) complexes [Ru(η5-C8H11)(PMe3)3]+[OAr]−·(HOAr)n [Ar=C6H3Me2-2,6 (2a), C6H4(2-CH2CHCH2) (2b), C6H4{2-(E)-CHCHMe} (2c), Ph (2d); C6H4Me-2 (2e); C6H4(2-CHMe2) (2f), and C6H4(2-CMe3) (2g)] followed by sp3 CH bond cleavage reaction. The molecular structure of 2c reveals that the cyclooctadienyl group coordinates to the ruthenium center by an η5-fashion, where one equivalent of (E)-2-propenylphenol is associated with aryloxo anion. Further treatment of 2a and 2c with PMe3 results in the formation of oxaruthenacycle complexes to give 4 and 5, respectively. These facts clearly demonstrate that this sp3 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)(PMe3)4 [Ar=Ph (6a), C6H4Me-2 (6b), C6H4(2-CHMe2) (6c), C6H4(2-CMe3) (6d)].