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

Abstract

The gold(I) complexes [Au{S2CN(CH2CH═CH2)2}(L)] [L = PPh3, PCy3, PMe3, CN(t)Bu, IDip] are prepared from KS2CN(CH2CH═CH2)2 and [(L)AuCl]. The compounds [L2(AuCl)2] (L2 = dppa, dppf) yield [(L2){AuS2CN(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 [Au2{S2CN(CH2CH═CH2)2}2] is prepared from [(tht)AuCl] (tht = tetrahydrothiophene) and the diallyldithiocarbamate ligand. This product ring-closes with [Ru(═CHPh)Cl2(SIMes)(PCy3)] to yield [Au2(S2CNC4H6)2], whereas ring-closing of [Au{S2CN(CH2CH═CH2)2}(PR3)] fails. Warming [Au2{S2CN(CH2CH═CH2)2}2] results in formation of gold nanoparticles with diallydithiocarbamate surface units, while heating [Au2(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(═CHC6H4O(i)Pr-2)Cl2(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 [Au2{S2CN(CH2CH═CH2)2}2]. In the latter, exceptionally short intermolecular aurophilic interactions are observed.