Versatility and adaptative behaviour of the P^N chelating ligand MeDalphos within gold() π complexes

• Published in: Chemical science (Cambridge) Vol. 11; no. 1; pp. 275 - 2758
• Main Authors: Navarro, Miquel, Toledo, Alberto, Mallet-Ladeira, Sonia, Sosa Carrizo, E. Daiann, Miqueu, Karinne, Bourissou, Didier
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 11.03.2020; The Royal Society of Chemistry
• Subjects: Alkenes; Alkylation; Alkynes; Catalysis; Charge transfer; Chelation; Chemical bonds; Chemical Sciences; Chemistry; Coordination; Coordination chemistry; Crystallography; Electrons; Gold; Indoles; Ligands; NMR spectroscopy; Spectrum analysis
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c9sc06398f

The hemilabile P^N ligand MeDalphos enables access to a wide range of stable gold( i ) π-complexes with unbiased alkenes and alkynes, as well as electron-rich alkenes and for the first time electron-poor ones. All complexes have been characterized by multi-nuclear NMR spectroscopy and whenever possible, by X-ray diffraction analyses. They all adopt a rare tricoordinate environment around gold( i ), with chelation of the P^N ligand and side-on coordination of the alkene, including the electron-rich one, 3,4-dihydro-2 H -pyrane. The strength of the N → Au coordination varies significantly in the series. It is the way the P^N ligand accommodates the electronic demand at gold, depending on the alkene. Comparatively, when the chelating P^P ligand ( ortho -carboranyl)(PPh 2 ) 2 is used, gold( i ) π-complexes are only isolable with unbiased alkenes. The bonding situation within the gold( i ) P^N π-complexes has been thoroughly analyzed by DFT calculations supplemented by Charge Decomposition Analyses (CDA), Natural Bond Orbital (NBO) and Atoms-in-Molecules (AIM) analyses. Noticeable variations in the donation/back-donation ratio, C&z.dbd;C weakening, alkene to gold charge transfer and magnitude of the N → Au coordination were observed. Detailed examination of the descriptors for the Au/alkene interaction and the N → Au coordination actually revealed intimate correlation between the two, with linear response of the MeDalphos ligand to the alkene electronics. The P^N ligand displays non-innocent and adaptative character. The isolated P^N gold( i ) π-complexes are reactive and catalytically relevant, as substantiated by the chemo and regio-selective alkylation of indoles. The hemilabile P^N ligand MeDalphos enables access to a wide range of stable gold( i ) π-complexes with unbiased alkenes and alkynes, as well as electron-rich alkenes and for the first time electron-poor ones.