Communication pubs.acs.org/Organometallics
Synthesis and Structure of a CuI3S Cluster Unsupported by Other Bridging Ligands Junjie Zhai,* Michael D. Hopkins, and Gregory L. Hillhouse† Department of Chemistry, The University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, United States
Downloaded by FLORIDA INTL UNIV on September 7, 2015 | http://pubs.acs.org Publication Date (Web): July 14, 2015 | doi: 10.1021/acs.organomet.5b00421
S Supporting Information *
ABSTRACT: The facile synthesis of a {LCuI}3(μ3-S) cluster supported by monodentate N-heterocyclic carbene ligands has been accomplished through an approach in which twocoordinate (NHC)Cu+ centers are installed sequentially on a sulfido ligand. The reaction between (IPr)CuCl (IPr = 1,3bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and S(SiMe3)2 yields (IPr)Cu(SSiMe3) (2). Treatment of 2 with [(IPr)Cu(NCMe)][BF4] produces the dicopper cluster [{(IPr)Cu}2(μ-SSiMe3)][BF4] (3[BF4]), which undergoes subsequent reaction with (IPr)CuF to afford [{(IPr)Cu}3(μ3-S)][BF4] (1[BF4]) in high yield. The X-ray crystal structure of 1[BF4] establishes it as a rare example of a CuIn(μn-S)Lm cluster, and the first that is not also supported by other bridging ligands.
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clusters would require sterically demanding supporting ligands that would prevent aggregation to higher CunSm clusters. Bulky N-heterocyclic carbene (NHC) ligands are well-known to stabilize low-coordination-number metal complexes.8 Greg Hillhouse made particularly important contributions in this area,9 a highlight of which was the pioneering synthesis of the first two-coordinate metal−imido complex, (NHC)NiNR.9c With these considerations in mind, we targeted the synthesis of the cluster [{(IPr)Cu}3(μ3-S)]+ (1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), which would be a twocoordinate analogue of the smallest CuIn(μn-S)Lm clusters yet prepared. The supporting ligand IPr was chosen because its steric bulk is intermediate among NHCs, thus providing opportunities for steric control through NHC variation. Reported here is a facile synthetic route to 1, as well as its molecular structure. The general strategy envisioned for the synthesis of [{(NHC)CuI}3(μ3-S)]+ clusters, shown in Scheme 1 for the specific example of a [(IPr)Cu]+ building block, is to sequentially install copper centers on a copper−thiolato compound of the form (NHC)Cu(SSiR3) (2), in which the sulfido ligand that will appear in 1 is protected by a silyl group. The second copper center would be added via a reaction between 2 and [(NHC)Cu(NCMe)]+,10 from which displacement of the acetonitrile ligand by the SSiR3 group in 2 would yield [{(NHC)Cu}2(μ-SSiR3)]+ (3). This reaction is analogous to that reported by Warren and co-workers which produced the related ions [{(IPr)Cu}2(μ-SR)]+ (R = tBu, CH2Ph) from the reaction between (IPr)Cu(SR) and [(IPr)Cu(NCMe)]+.11 The reaction between 3 and a suitable (NHC)CuX source would result in XSiR3 elimination and concomitant addition of a third [(NHC)Cu]+ center to the sulfido ligand to provide 1. This last
opper clusters that contain bridging sulfido ligands possess a rich variety of structures and properties, and as a result the development of rational synthetic routes to copper−sulfido clusters of specific size and connectivity has been of considerable interest.1−5 Selected examples of the diversity of these clusters and their properties include the active site of nitrous oxide reductase, which contains a histidinesupported Cu4(μ4-S) or Cu4(μ4-S)(μ2-S) core that catalyzes N−O bond cleavage,6 high-nuclearity clusters ranging in size up to Cu136S56Lm,1 which at this limit structurally resemble solid Cu2S but exhibit quantum-confinement effects,7 and CuI Cu4SLm and Cu12S6Lm clusters that exhibit strong photoluminescence.4b,f,5e Among the plethora of copper−sulfido clusters that have been prepared, however, CuI clusters containing a single bridging sulfido ligand are rare.4 Prior examples of such CuIn(μn-S)Lm clusters are limited to {Cu8[S2P(OiPr)2]6}(μ8-S), which was isolated in low yield (
