Assessing the influence of phosphine substituents on the catalytic properties of self-stabilised digold(I) complexes with supporting ferrocene phosphinonitrile ligands

Gold(I) phosphine complexes are often used in catalysis, but the role of their auxiliary ligands still remains poorly understood. Thus, building on our previous research, we prepared a series of Au(I) complexes [Au2(µ-R2PfcCN)2][SbF6]2 (fc = ferrocene-1,1’-diyl) to assess the effect of phosphine groups PR2 on the catalytic properties of these highly catalytically active, dimeric Au(I)-phosphine complexes. Catalytic testing in Au-mediated cyclisation of N-propargyl amides to 2-substituted 5-methyleneoxazolines showed that weaker donating phosphines gave rise to more active, albeit partly destabilised, catalysts. Nevertheless, thanks to their self-stabilisation by reversible nitrile coordination, [Au2(µ-R2PfcCN)2]+ cations readily converted into catalytically active species (by dissociation) and, in addition, remained catalytically active even at very low metal loadings. The experimental results were supported by the trends in 1JPSe coupling constants for R2P(Se)fcCN (as a measure of ligand basicity), and by DFT calculations.