Ligand structural effects on Cu2S2 bonding and reactivity in side-on disulfido-bridged dicopper complexes.
To assess supporting ligand effects on S-S bond activation, a series of [Cu2(mu-eta2:eta2-S2)]2+ complexes supported by various beta-diketiminate or anilido-imine ligands (L) were synthesized via the reaction of Cu(I) precursors LCu(CH(3)CN) with S8. For the cases where L = beta-diketiminate, the syntheses were complicated by formation of clusters [Cu(SR)]4, where SR represents the ligand functionalized by sulfur at the central methine position. The [Cu2(mu-eta2:eta2-S2)]2+ products were characterized by X-ray crystallography and electronic absorption and resonance Raman spectroscopy. Correlations among the Cu-S, Cu-Cu, and S-S distances and the nu(S-S) values were observed and interpreted within the framework of a previously described bonding picture (Chen, P.; Fujisawa, K.; Helton, M. E.; Karlin, K. D.; Solomon, E. I. J. Am. Chem. Soc. 2003, 125, 6394). Comparison of these data to those for other relevant species revealed a remarkable degree of S-S bond activation in the compounds supported by the beta-diketiminate and anilido-imine ligands, which through strong electron donation increase backbonding from the copper ions into the S-S sigma* orbital and cause S-S bond weakening. Reactions of one of the complexes supported by an anilido-imine ligand with PPh(3) and xylyl isocyanide were explored, revealing facile transfer of sulfur to PPh(3) but only displacement of sulfur to yield a LCu(I)-CNAr (Ar = xylyl) complex with the isocyanide.
Brown
Eric C
EC
Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, USA.
Bar-Nahum
Itsik
I
York
John T
JT
Aboelella
Nermeen W
NW
Tolman
William B
WB
D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman
D008024:Ligands; D003300:Copper; C017846:cupric sulfide