Synthesis and Characterization of an N‑Trifluoromethyl 1,4-Azaborine-Based Phosphine Ligand and Its Transition Metal Complexes

The synthesis of N-trifluoromethyl 1,4-azaborine-based phosphine ligands (FinnPhos) is described. X-ray diffraction analysis of FinnPhos L1-CF3 and its N-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 N-trifluoromethyl ligand provides superior reactivity to its N-methyl and carbonaceous analogues in the Au-catalyzed cycloisomerization of 1,6-enynes.