Snapshot of a Chelation-Assisted C−H/Alkyne Coupling: A Ruthenium Complex Caught in the Act of C−C Bond Formation

The complex Ru(CO)2(PPh3)3 (1) reacts with o-(diphenylphosphanyl)benzaldehyde within 2 min at 20 °C to give the hydrido acyl complex Ru(H){P(C6H5)2(C6H4)C(O)}(CO)2(PPh3) (2) via selective activation of the C−H bond of the aldehyde function. Further addition of diphenylacetylene (110 °C, 3 h) affords the novel complex Ru{P(C6H5)2(C6H4)C(O)(C6H5)CCH(C6H5)}(CO){P(C6H5)3} (3), incorporating the newly assembled o-(diphenylphosphanyl)phenyl (E)-stilbenyl ketone ligand. The α,β-unsaturated ketone moiety of the latter is bound to the metal in an η4 coordination mode involving both a side-on coordination of the carbonyl group and a more classical η2 linkage of the olefinic bond. Both complexes were fully characterized by spectroscopic methods and by X-ray diffraction. The whole reaction sequence provides a valuable experimental model for the chelation-assisted hydroacylation of an alkyne with a tethered aldehyde.