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.