Phosphinine-Based Ligands in Gold-Catalyzed Reactions.

A series of substituted phosphinines, 1-phosphabarrelenes and 5-phosphasemibullvalenes were synthesized and evaluated for their potential application as ligands in homogeneous catalytic reactions. While their buried volume %Vbur was calculated to get insight into the steric properties, [LNi(CO)3] complexes were prepared in order to determine the corresponding Tolman electronic parameter. ETS-NOCV calculations on [LAuCl] complexes further allowed an estimation of the σ- and π-contributions to the L-M interaction. Au(I) coordination compounds of selected examples were prepared and characterized by means of single crystal X-ray diffraction. Finally, the three classes of P(III) compounds were successfully employed in the Au(I) catalyzed homogeneous cycloisomerization of N-2-propyn-1-ylbenzamide towards its oxazoline constitutional isomer. The here presented catalysts show very good activities and selectivities, which are comparable with the reported data of state-of-the-art cationic phosphorus-based homogeneous gold catalysts.