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

摘要

Mercapto (-SH) and isocyano (-N C) terminated conducting pi-linkers are often employed in the ever-growing 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 pi-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)(5)Cr(eta(1)-2-isocyano-1,3-diethoxycarbonyl-6-mercaptoazulene)] (7) with Ph3PAuCl, under basic conditions, afforded X-ray structurally characterized heterobimetallic Cr-0/Au-I ensemble [(OC)(5)Cr(mu-eta(1): eta(1)-2-isocyano-1,3-diethoxycarbonyl-6-azulenylthiolate) AuPPh3] (8). Analysis of the C-13 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 = -N C, Br, H, SH, SCH2CH2CO2CH2CH3, SAuPPh3) unveiled remarkably consistent inverse-linear correlations delta((COtrans)-C-13) vs. delta((CN)-C-13) and delta((COcis)-C-13) vs. delta((CN)-C-13) that appear to hold well beyond the above 2-isocyanoazulenic series to include complexes [(OC)(5)Cr(CNR)] containing strongly electron-withdrawing substituents R, such as CF3, CFClCF2Cl, C2F3, and C6F5. In addition to functioning as a sensitive C-13 NMR handle, the essentially C-4v-symmetric [(-NC)Cr(CO)(5)] moiety proved to be an informative, remote, nu(N=C)u(C=O) infrared reporter in probing chemisorption of 7 on the Au(111) surface.