Phosphinines versus mesoionic carbenes: a comparison of structurally related ligands in Au(i)-catalysisElectronic supplementary information (ESI) available: Experimental details for the preparation of all compounds as well as X-ray crystallographic information of 6. CCDC 1503378 and 1015504. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6dt03766f

Gold( i ) complexes based on a 2,4,6-triarylphosphinine and a mesoionic carbene derivative have been prepared and characterized crystallographically. Although structurally related, both heterocycles differ significantly in their donor/acceptor properties. These opposed electronic characteristics have been exploited in Au( i )-catalyzed cycloisomerization reactions. For the conversion of the standard substrate dimethyl 2-(3-methylbut-2-enyl)-2-(prop-2-ynyl)malonate the results obtained for both Au-catalysts were found to be very similar and comparable to the ones reported in the literature for other carbene- or phosphorus( iii )-based Au( i )-complexes. In contrast, a clear difference between the catalytic systems was found for the cycloisomerization of the more challenging substrate N -2-propyn-1-ylbenzamide. A combination of the phosphinine-based complex and [AgSbF 6 ] or [Cu(OTf) 2 ] leads to a catalytic species, which is more active than the mesoionic carbene-based coordination compound. We attribute these differences to the stronger π-accepting ability of phosphinines in comparison to mesoionic carbenes. The here presented results show for the first time that phosphinines can be used efficiently as π-accepting ligands in Au( i )-catalyzed cycloisomerization reactions. Gold( i ) complexes based on a 2,4,6-triarylphosphinine and a mesoionic carbene derivative have been prepared and applied in catalytic reactions.