Synthesis of Spirocyclic Diphosphite-Supported Gold Metallomacrocycles via a Protodeauration/Cyclization Strategy:...

A spirocylic diphosphite was used to generate P-metalated bimetallic complexes through protodeauration reactions involving LAuC₆H₄^tBu (L = JohnPhos, ^tBuXPhos) and metallomacrocycles through protodeauration/cyclization using ^tBuC₆H₄AuP^PAuC₆H₄^tBu precursors (P^P = flexible diphosphine). While the synthesis of the bimetallic complexes followed a stepwise process, generation of the metallomacrocycles was highly complex because of a series of reversible ligand redistribution reactions. The self-assembly was monitored, and key intermediates were identified by NMR spectroscopy and high-resolution mass spectrometry. The mechanistic investigation showed that using flexible diphosphine linkers was critical to the selective synthesis of metallomacrocycles because rigid diphosphines generated intractable mixtures of linear and cyclic compounds. The X-ray structure of a 32-membered metallomacrocycle revealed that the compound crystallized in an unsymmetrical collapsed form that was held together by two supported aurophilic interactions while the flexible diphosphines were folded along opposite sides of the metallomacrocycle. The solution structure was consistent with a symmetric species, which suggested interconversion between an open and collapsed form and/or rapid twisting of a collapsed form. The 32-membered metallomacrocycle was used to bind estrogen primarily through the formation of AuP-O^-···H-OR hydrogen bonds.