Synthesis, Structural Characterization, and Catalytic Activity of Indenyl Tris(N-pyrrolyl)phosphine Complexes of Ruthenium

The synthesis, characterization, and catalytic activity of new ruthenium complexes of the tris(N‐pyrrolyl)phosphine ligand [P(pyr)3] are described. The new ruthenium complexes [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] (ind = indenyl, η5‐C9H7–) were synthesized in 73 and 63 % isolated yields, respectively, by thermal ligand exchange of [RuCl(ind)(PPh3)2] with P(pyr)3. The electronic and steric properties of the new complexes were studied through analysis of the X‐ray structures and cyclic voltammetry. The new complexes [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] and the known complex [RuCl(ind){(PPh3)2}] differed only slightly in their steric properties, as seen from the comparable bond lengths and angles around the ruthenium centers. The oxidation potentials of [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] of +0.34 and +0.71 V versus Cp2Fe0/+ (Cp = cyclopentadienyl) are substantially higher than that of [RuCl(ind)(PPh3)2] (–0.023 V), in accordance with the enhanced π‐acidity of the P(pyr)3 ligand. The new complexes are catalytically active in the etherification of propargylic alcohols and in the first ruthenium‐catalyzed formation of known and new xanthenones from propargylic alcohols and diketones (18 to 72 h at 90 °C in ClCH2CH2Cl or toluene, 1–2 mol‐% catalyst, 69–22 % isolated yields). The ruthenium tris(N‐pyrrolyl)phosphine [P(pyr)3] complexes [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] exhibit increased oxidation potentials owing to the π‐acidic P(pyr)3 ligands. The complexes are catalytically active in the etherification of propargylic alcohols and in the formation of known and new xanthenones from propargylic alcohols and diketones.