N‐Heterocyclic Carbene Self‐assembled Monolayers on Copper and Gold: Dramatic Effect of Wingtip Groups on Binding, Orientation and Assembly

• Published in: Chemphyschem Vol. 18; no. 24; pp. 3536 - 3539
• Main Authors: Larrea, Christian R., Baddeley, Christopher J., Narouz, Mina R., Mosey, Nicholas J., Horton, J. Hugh, Crudden, Cathleen M.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 15.12.2017; John Wiley and Sons Inc
• Subjects: Carbenes; Communication; Communications; Copper; Desorption; Dimers; Gold; Monolayers; N-heterocyclic carbenes; orientation; Self-assembled monolayers; Self-assembly; wingtip; wingtip; copper; orientation; self-assembled monolayers; N-heterocyclic carbenes
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201701045

Self‐assembled monolayers of N‐heterocyclic carbenes (NHCs) on copper are reported. The monolayer structure is highly dependent on the N,N‐substituents on the NHC. On both Cu(111) and Au(111), bulky isopropyl substituents force the NHC to bind perpendicular to the metal surface while methyl‐ or ethyl‐substituted NHCs lie flat. Temperature‐programmed desorption studies show that the NHC binds to Cu(111) with a desorption energy of Edes=152±10 kJ mol−1. NHCs that bind upright desorb cleanly, while flat‐lying NHCs decompose leaving adsorbed organic residues. Scanning tunneling microscopy of methylated NHCs reveals arrays of covalently linked dimers which transform into adsorbed (NHC)2Cu species by extraction of a copper atom from the surface after annealing. Self‐assembled monolayers of N‐heterocyclic carbenes (NHCs) on Cu(111) are reported. NHCs bearing bulky isopropyl substituents bind perpendicular to the metal surface while methyl‐ or ethyl‐substituted NHCs lie flat. The NHC binds to Cu(111) with a desorption energy of Edes=152±10 kJ mol−1. Methylated NHCs reveal arrays of covalently linked dimers which transform into surface‐bound (NHC)2Cu species after annealing.