Multimetallic Arrays: Bi-, Tri-, Tetra-, and Hexametallic Complexes Based on Gold(I) and Gold(III) and the Surface Functionalization of Gold Nanoparticles with Transition Metals

Reaction of [AuCl(PPh₃)] with the zwitterion S₂CNC₄H₈NH₂ yields [(Ph₃P)Au(S₂CNC₄H₈NH₂)]BF₄. Treatment of this species with NEt₃ and CS₂ followed by [AuCl(PPh₃)] leads to [{(Ph₃P)Au}₂(S₂CNC₄H₈NCS₂)], which can also be obtained directly from [AuCl(PPh₃)] and KS₂CNC₄H₈NCS₂K. A heterobimetallic variant, [(dppm)₂Ru(S₂CNC₄H₈NCS₂)Au(PPh₃)]⁺, can be prepared by the sequential reaction of [(dppm)₂Ru(S₂CNC₄H₈NH₂)]²⁺ with NEt₃ and CS₂ followed by [AuCl(PPh₃)]. Reaction of the same ruthenium precursor with [(dppm)(AuCl)₂] under similar conditions yields the trimetallic complex [(dppm)₂Ru(S₂CNC₄H₈NCS₂)Au₂(dppm)]²⁺. Attempts to prepare the compound [(dppm)Au₂(S₂CNC₄H₈NH₂)]²⁺ from [(dppm)(AuCl)₂] led to isolation of the known complex [{(dppm)Au₂}₂(S₂CNC₄H₈NCS₂)]²⁺ via a symmetrization pathway. [{(dppf)Au₂}₂(S₂CNC₄H₈NCS₂)]²⁺ was successfully prepared from [(dppf)(AuCl)₂] and crystallographically characterized. In addition, a gold(III) trimetallic compound, [{(dppm)₂Ru(S₂CNC₄H₈NCS₂)}₂Au]³⁺, and a tetrametallic gold(I) species, [{(dppm)₂Ru(S₂CNC₄H₈NCS₂)Au}₂]²⁺, were also synthesized. This methodology was further exploited to attach the zwitterionic (dppm)₂Ru(S₂CNC₄H₈NCS₂) unit to the surface of gold nanoparticles, which were generated in situ and found to be 3.4 (±0.3) and 14.4 (±2.5) nm in diameter depending on the method employed. Nanoparticles with a mixed surface topography were also explored.