Synthesis and Characterization of an <i>N</i> -Trifluoromethyl 1,4-Azaborine-Based Phosphine Ligand and Its Transition Metal Complexes

The synthesis of <i>N</i>-trifluoromethyl 1,4-azaborine-based phosphine ligands (FinnPhos) is described. X-ray diffraction analysis of FinnPhos <b>L1-CF3</b> and its <i>N</i>-methyl analogue reveals a stronger contribution of the neutral resonance form to the structure of the 1,4-azaborine ring. Density functional theory (DFT) calculations predict the FinnPhos to exhibit a unique η³-C,C,B coordination mode to Pd(0). We demonstrate that the <i>N</i>-trifluoromethyl ligand provides superior reactivity to its <i>N</i>-methyl and carbonaceous analogues in the Au-catalyzed cycloisomerization of 1,6-enynes.