Intramolecular 1,2 C−H Addition of o‐Methyl Groups to Form Unique Ruthenium Pincer Tuck‐in Complexes

Abstract

AbstractNew RPNHP ligands containing 2,4‐xylyl (4mXPNHP) and mesityl (MesPNHP) groups on the phosphorus atoms were synthesized. 4mXPNHP reacts with [(cymene)RuCl2]2 followed by PMe3 to produce κ3‐4mXPNHPRu(PMe3)Cl2. MesPNHP reacts with [(cymene)RuCl2]2 to produce monomeric κ3‐MesPNHPRuCl2 that reacts with CO forming κ3‐MesPNHPRu(CO)Cl2. Surprisingly, dehydrohalogenation of these complexes results in the activation of ortho methyl groups of the pincer ligands, rather than formation of κ3‐RPNPRuLCl complexes. This results from transient κ3‐RPNPRuLCl formation followed by 1,2‐addition of an ortho C−H bond across the Ru‐amide bond. The transient amide complex of κ4‐4mXPNHPRu(PMe3)Cl was trapped with CO forming κ3‐4mXPNPRu(PMe3)(CO)Cl. In contrast, κ4‐MesPNHPRu(CO)Cl does not react with ligands to trap the expected amide complex of reverse C−H addition. Instead, CO and PMe3 displace the chloride ligand forming cationic complexes. In both cases, hemi‐lability of the pincer ligand was observed spectroscopically. The new complexes serve as precursors to moderately active catalysts for the acceptorless dehydrogenative coupling of n‐butanol.