Well-Defined Dinuclear Gold Complexes for Preorganization-Induced Selective Dual Gold Catalysis

The synthesis, reactivity, and potential of well-defined dinuclear gold complexes as precursors for dual gold catalysis are explored. Using the preorganizing abilities of the ditopic (PNPiPr)-P-H (L-H) ligand, dinuclear Au-I-Au-I complex 1 and mixed-valent Au-I-Au-III complex 2 provide access to structurally characterized chlorido-bridged cationic species 3 and 4 upon halide abstraction. For 2, this transformation involves unprecedented two-electron oxidation of the redox-active ligand, generating a highly rigidified environment for the Au-2 core. Facile reaction with phenylacetylene affords the sigma,pi-activated phenylacetylide complex 5. When applied in the dual gold heterocycloaddition of a urea-functionalized alkyne, well-defined precatalyst 3 provides high regioselectivities for the anti-Markovnikov product, even at low catalyst loadings, and outperforms common mononuclear Au-I systems. This proof-of-concept demonstrates the benefit of preorganization of two gold centers to enforce selective non-classical sigma,pi-activation with bifunctional substrates.