Substituent effects in formally quintuple-bonded ArCrCrAr compounds (Ar = terphenyl) and related species.

Robert Wolf, Chengbao Ni, Tailuan Nguyen, Marcin Brynda, Gary J. Long, Andrew D. Sutton, Roland C. Fischer, J. C. Fettinger, Matthew Hellman, Lihung Pu, Philip P. Power

Research output: Contribution to journalArticle

Abstract

Redn. of Cr(I) dimeric chlorides gave substituted bis-terphenylyl dichromium complexes bound by formally quintuple Cr-Cr bond; the effects of terphenyl ligand substituents on the quintuple Cr-Cr bonding in arylchromium(I) dimers were investigated. Redn. of chloro-bridged Cr(II) dimers [(4'-X-Ar1)Cr(μ-Cl)]2 by KC8 gave metal-metal-bonded complexes [(4'-X-Ar1)CrCr(4'-X-Ar1)] (1-4; 4'-X-Ar1 = 4'-X-2,2'',6,6''-tetraisopropyl-1,1':3',1''-terphenyl-2'-yl, X = H, SiMe3, OMe, F), whereas similar redn. of [(4'-CF3-Ar1)Cr(μ-Cl)]2 gave [(4'-CF3-Ar1)Cr(μ-F)(THF)]2 (5) as a result of activation of the CF3 moiety. Redn. of monomeric Cr(II) chloride of the larger Ar* ligand, which prevents Cr-Cr bond formation, Ar*CrCl (Ar* = 2,2'',4,4',4'',6,6',6''-hexaisopropyl-1,1':3',1''-terphenyl-2'-yl) gave monomeric complexes [Ar*Cr(L)] (6, 7; L = THF, PMe3) and unusual dinuclear benzyl Cr(II)-Cr(0)-triple-decker [Ar*Cr(η3:η6-CH2C6H5)Cr(Ar*H)] (8). The x-ray crystal structures of the complexes display similar trans-bent C(ipso)CrCrC(ipso) cores with short Cr-Cr distances that range from 1.8077(7) to 1.8351(4) Å. Weaker Cr-C interactions [2.294(1)-2.322(2) Å] involving an C(ipso) of one of the flanking aryl rings are also present. The data show that the changes induced in the Cr-Cr bond length by the different substituents X in the para positions of the central aryl ring of the terphenyl ligand are probably a result of packing rather than electronic effects. This is in agreement with d. functional theory (DFT) calcns., which predict that the model compds. (4-XC6H4)CrCr(C6H4-4-X) (X = H, SiMe3, OMe, and F) have similar geometries in the gas phase. Magnetic measurements in the temp. range of 2-300 K revealed temp.-independent paramagnetism in 1-4. UV-visible and NMR spectroscopic data indicated that the metal-metal-bonded solid-state structures of 1-4 are retained in soln. The structures of monomers 6 and 7 contain almost linearly coordinated Cr(I) atoms, with high-spin 3d5 configurations. The electronic structures of 5-8 were analyzed with the aid of DFT calcns. [on SciFinder(R)]
Original languageEnglish
Pages (from-to)11277-11290
Number of pages14
JournalInorganic chemistry
Volume46
Issue number26
DOIs
Publication statusPublished - 2007

Cite this

Wolf, R., Ni, C., Nguyen, T., Brynda, M., Long, G. J., Sutton, A. D., ... Power, P. P. (2007). Substituent effects in formally quintuple-bonded ArCrCrAr compounds (Ar = terphenyl) and related species. Inorganic chemistry, 46(26), 11277-11290. https://doi.org/10.1021/ic702112e