Inactive ruthenium(II)-xantphos complexes from attempted catalyzed lignin reactions

Tests on the use of Ru(H)2(CO)(PPh3)(xantphos) (1) as a hydrogenolysis catalyst for a lignin model compound in bromobenzene at 135 °C under Ar lead to formation of the corresponding, catalytically inactive, but fully characterized complexes, Ru(H)Br(CO)(xantphos) (2) and RuBr2(CO)(xantphos) (3). In 1, the xantphos [xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene] is bidentate with cis-coordinated P-atoms, whereas in 2 and 3 the xantphos is mer-P,O,P-coordinated with the P-atoms trans.

Graphical abstractThe hydridobromo and dibromo complexes, 2 and 3, are formed during attempted hydrogenolysis reactions of a lignin model compound and lignin samples catalyzed by complex 1. Complexes 2 and 3 contain mer-P,O,P-xantphos ligand, in contrast to the cis-P,P-xantphos of 1.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Catalyzed hydrogenolysis of a lignin model compound is impeded in bromobenzene. ► Hydride(s) of a Ru-xantphos catalyst in bromobenzene is(are) replaced by bromide. ► Two, new hydridobromo and dibromo Ru-xantphos complexes are synthesized. ► Both complexes contain a mer-P,O,P-xantphos ligand.