Photochemistry of neutral isonitrile gold(I) complexes:: Modulation of photoreactivity by aurophilicity and π-acceptance ability

This work demonstrates for the first time that aurophilicity and ligand pi-acceptance ability sensitize the photoreactivity of Au(I) complexes. Photolysis of (LAuCI)-C-1 (L = RNC or CO) complexes leads to free L, Au-III, and Au-0 photoproducts. Solutions of (p-tosyl)CH2NCAuCl in clichloromethane undergo significant oligomerization leading to dimers and trimers with formation constants of 1.61 x 10(3) and 6.61 X 10(3) M-1, respectively, representing the highest values reported to date for complexes that exhibit aurophilic association in solution. The photoproduct quantum yield Phi varies with the (LAuCl)-Cl-I concentration in solution. For (ptosyl)CH2NCAuCl, metallic gold forms with Phi = 0.0065 and 0.032 in 4.0 x 10(-5) and 4.0 x 10(-3) M dichloromethane solutions, respectively. Meanwhile, irradiation of t-BuNCAuCl primarily produces t-BuNCAuCl3 with Phi = 0.0045 and 0.013 for 5.0 x 10(-5) and 5.0 x 10(-3) M dichloromethane solutions, respectively. For Au(CO)Cl, metallic gold forms with Phi = 0.013 and 0.065 upon irradiation of 8.0 x 10(-5) and 8.0 x 10(-3) M clichloromethane solutions, respectively. Hence, *[LAuX](n) oligomeric species are more photoreactive than monomeric species. The results also demonstrate intuitive control of Phi via modulation of the pi-acceptance ability of L, as both follow CO > (p-tosyl)CH2NC > (alkyl)NC in LAuCl, a trend that is also commensurate with the relative long-term photosensitivity of the corresponding solids and solutions. A new method for preparing stable small gold nanoparticles is described based on the fundamental findings above. Thus, photolysis of different concentrations of LAuX in solutions containing a primary amineterminated dendrimer leads to clear solutions exhibiting tunable visible plasmon absorptions of gold nanoparticles; these solutions maintain their colors and stability indefinitely. TEM measurements for representative samples prepared by photolysis of (p-tosyl)CH2NCAuCl solutions give rise to spherical nanoparticles as small as 5 nm.