Ring-Closing Metathesis and Nanoparticle Formation Based on Diallyldithiocarbamate Complexes of Gold(I): Synthetic, Structural, and Computational Studies

The gold(I) complexes [Au{S2CN(CH2CH=CH2)(2)}(L)] [L = PPh3, PCy3, PMe3, (CNBu)-Bu-t, IDip] are prepared from KS2CN(CH2CH=CH2)(2) and [(L)AuCl]. The compounds [L-2(AuCl)(2)] (L-2 = dppa, dppf) yield [(L-2){AuS2-CN-(CH2CH=CH2)(2)}(2)] while the cyclic complex [(dppm){Au2S2CN(CH2CH=CH2)(2)}]OTf is obtained from [dppm(AuCl)(2)] and AgOTf followed by KS2CN(CH2CH=CH2)(2). The compound [Au-2{S2CN(CH2CH=CH2)(2)}(2)] is prepared from [(tht)AuCl] (tht = tetrahydrothiophene) and the diallyldithiocarbamate ligand. This product ring-closes with [Ru(=CHPh)Cl-2(SIMes)(PCy3)] to yield [Au-2(S2CNC4H6)(2)], whereas ring-closing of [Au{S2CN(CH2CH=CH2)(2)}(PR3)] fails. Warming [Au-2{S2CN(CH2CH=CH2)(2)}(2)] results in formation of gold nanoparticles with diallydithiocarbamate surface units, while heating [Au-2(S2CNC4H6)(2)] with NaBH4 results in nanoparticles with 3-pyrroline dithiocarbamate surface units. Larger nanoparticles with the same surface units are prepared by citrate reduction of HAuCl4, followed by addition of the dithiocarbamate. The diallydithiocarbamate-functionalized nanoparticles undergo ring-closing metathesis using [Ru(= (CHC6H4OPr)-Pr-i-2)Cl-2(SIMes)]. The interaction between the dithiocarbamate units and the gold surface is explored using computational methods to reveal no need for a countercation. Preliminary calculations indicate that the Au S interactions are substantially different from those established in theoretical and experimental studies on thiolate-coated nanoparticles. Structural studies are reported for [Au{S2CN(CH2CH=CH2)(2)}(PPh3)] and [Au-2{S2CN(CH2CH=CH2)(2)}(2)] In the latter, exceptionally short intermolecular aurophilic interactions are observed.