Grubbs and Hoveyda-type ruthenium complexes bearing a cyclic bent-allene

Stable cyclic bent-allene 1 displaces the chelating ether linkage of the Hoveyda–Grubbs-type ruthenium complex 2 bearing triphenylphosphine. The resulting complex 3 features an unusual cis-arrangement of the phosphine and the cyclic bent-allene, while retaining a distorted square pyramidal geometry around the ruthenium center. Monitoring by 31P NMR spectroscopy the reaction of cyclic bent-allene 1 with the indenylidene bis(triphenylphosphine)ruthenium dichloride complex 4 allowed for the observation of dissociated triphenylphosphine, and the formation of a ruthenium complex featuring 1 and triphenylphosphine in the desired trans-configuration. However, continued reaction times saw the disappearance of this complex, and after workup complex 5 featuring a cis-arrangement was isolated.

The first ruthenium complexes featuring a cyclic bent-allene, which is a strong σ-donor and weak π-acceptor ligand, have been isolated; they feature an unusual cis-arrangement of the phosphine and bent-allene.Figure optionsDownload as PowerPoint slideHighlights
► The first cyclic bent-allene Hoveyda Grubbs-style ruthenium complexes are described.
► The reported complexes feature an unusual cis-conformation of donor ligands around the metal center.
► Trans-arrangement around the metal appears as requirement for catalytic activity.