Reaction network governing diphosphine-protected gold nanocluster formation from nascent cationic platforms

We identify the reaction network governing gold monolayer protected cluster (MPC) formation during the reduction of Au(PPh₃)Cl and L⁵ (L⁵ = 1,5-bis(diphenylphosphino)pentane) in solutions. UV-vis spectroscopy and electrospray ionization mass spectrometry (ESI-MS) monitored the formation of ligated Au_x: 6 ≤ x ≤ 12 clusters, which comprise the reaction intermediates and final products. Initially, predominantly [Au₂L⁵₂]²⁺ complexes form through dissolution of Au(PPh₃)Cl. These complexes control the reduction and nucleation reactions that form nascent phosphine-ligated Au₈ and Au₁₀ ionic clusters. [Au₁₀L⁵₄]²⁺ is an observed growth platform for ligated Au₁₁ and Au₁₂ clusters. The data for syntheses of Au : L⁵ systems evidence that the nascent reaction products (t < 3 days) are less dependent on the chosen reducing agent (borane tert-butylamine complex or NaBH₄); instead, after reduction ceases, subsequent solution phase processing provides greater control for tuning cluster nuclearity.