Synthesis and Characterization of Phosphido-Monolayer-Protected Gold Nanoclusters

Gold−phosphido-monolayer-protected clusters (MPCs) of 1−2-nm diameter, Au_x(PR₂)_y, analogues of the well-known thiolate materials Au_x(SR)_y, were prepared by NaBH₄ reduction of a mixture of HAuCl₄·3H₂O and a secondary phosphine PHR₂ in tetrahydrofuran/water. In comparison to the Au−thiolate MPCs, fewer of the larger phosphido groups are required to cover the surface, and the Au−P bond is not cleaved as readily in reactions with small molecules as is its Au−S counterpart. ³¹P NMR spectroscopy provides a direct method to study cluster formation and the interaction of the phosphido ligand with the gold surface.