First p-linker featuring mercapto and isocyano anchoring groups within the same molecule: synthesis, heterobimetallic complexation and selfassembly on Au(111)

Abstract

Mercapto (–SH) and isocyano (–N^C) terminated conducting p-linkers are often employed in the evergrowing quest for organoelectronic materials. While such systems typically involve symmetric dimercapto or diisocyano anchoring of the organic bridge, this article introduces the chemistry of a linear azulenic p-linker equipped with one mercapto and one isocyano terminus. The 2-isocyano-6-mercaptoazulene platform was efficiently accessed from 2-amino-6-bromo-1,3-diethoxycarbonylazulene in four steps. The 2-N^C end of this 2,6-azulenic motif was anchrored to the [Cr(CO)5] fragment prior to formation of its 6-SH terminus. Metalation of the 6-SH end of [(OC)5Cr(h1-2-isocyano-1,3-diethoxycarbonyl-6-mercaptoazulene)] (7) with Ph3PAuCl, under basic conditions, afforded X-ray structurally characterized heterobimetallic Cr0/AuI ensemble [(OC)5Cr(m-h1:h1-2-isocyano-1,3-diethoxycarbonyl-6-azulenylthiolate)AuPPh3] (8). Analysis of the 13C NMR chemical shifts for the [(NC) Cr(CO)5] core in a series of the related complexes [(OC)5Cr(2-isocyano-6-X-1,3-diethoxycarbonylazulene)] (X ¼ –N^C, Br, H, SH, SCH2CH2CO2CH2CH3, SAuPPh3) unveiled remarkably consistent inverse-linear correlations d(13COtrans) vs. d(13CN) and d(13COcis) vs. d(13CN) that appear to hold well beyond the above 2-isocyanoazulenic series to include complexes [(OC)5Cr(CNR)] containing strongly electron-withdrawing substituents R, such as CF3, CFClCF2Cl, C2F3, and C6F5. In addition to functioning as a sensitive 13C NMR handle, the essentially C4v-symmetric [(–NC)Cr(CO)5] moiety proved to be an informative, remote, nN^C/nC^O infrared reporter in probing chemisorption of 7 on the Au(111) surface.