TY - JOUR
T1 - Substituent effects in formally quintuple-bonded ArCrCrAr compounds (Ar = terphenyl) and related species
AU - Wolf, Robert
AU - Ni, Chengbao
AU - Nguyen, Tailuan
AU - Brynda, Marcin
AU - Long, Gary J.
AU - Sutton, Andrew D.
AU - Fischer, Roland C.
AU - Fettinger, J. C.
AU - Hellman, Matthew
AU - Pu, Lihung
AU - Power, Philip P.
PY - 2007/12/24
Y1 - 2007/12/24
N2 - The effects of different terphenyl ligand substituents on the quintuple Cr-Cr bonding in arylchromium(I) dimers stabilized by bulky terphenyl ligands (Ar) were investigated. A series of complexes, ArCrCrAr (1-4; Ar = C 6H2-2,6-(C6H3-2,6- iPr2)2-4-X, where X = H, SiMe3, OMe, and F), was synthesized and structurally characterized. Their X-ray crystal structures 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. There also weaker Cr-C interactions [2.294(1)-2.322(2) Å] involving an C(ipso) of one of the flanking aryl rings. 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 density functional theory (DFT) calculations, which predict that the model compounds (4-XC6H 4)CrCr(C6H4-4-X) (X = H, SiMe3, OMe, and F) have similar geometries in the gas phase. Magnetic measurements in the temperature range of 2-300 K revealed temperature-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 solution. Reduction of (4-F 3CAr′)CrCl (4-F3CAr′ = C6H 2-2,6-(C6H3-2,6-iPr 2)2-4-CF3) with KC8 gave non-Cr-Cr-bonded fluorine-bridged dimer {(4-F3CAr′)Cr(μ-F) (THF)}2 (5) as a result of activation of the CF3 moiety. The monomeric, two-coordinate complexes [(3,5-iPr 2Ar*)Cr(L)] (6, L = THF; 7, L = PMe3; 3,5- iPr2Ar* = C6H1-2,6-(C 6H-2,4,6-iPr3)2-3,5- iPr2) were obtained with use of the larger 3,5-Pr i2-Ar* ligand, which prevents Cr-Cr bond formation. Their structures contain almost linearly coordinated Cr1 atoms, with high-spin 3d5 configurations. The addition of toluene to a mixture of (3,5-iPr2Ar*)CrCl and KC8 gave the unusual dinuclear benzyl complex [(3,5-iPr2Ar*) Cr(η3:η6-CH2Ph)Cr(Ar*-1-H-3,5- iPr2)] (8), in which a C-H bond from a toluene methyl group was activated. The electronic structures of 5-8 have been analyzed with the aid of DFT calculations.
AB - The effects of different terphenyl ligand substituents on the quintuple Cr-Cr bonding in arylchromium(I) dimers stabilized by bulky terphenyl ligands (Ar) were investigated. A series of complexes, ArCrCrAr (1-4; Ar = C 6H2-2,6-(C6H3-2,6- iPr2)2-4-X, where X = H, SiMe3, OMe, and F), was synthesized and structurally characterized. Their X-ray crystal structures 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. There also weaker Cr-C interactions [2.294(1)-2.322(2) Å] involving an C(ipso) of one of the flanking aryl rings. 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 density functional theory (DFT) calculations, which predict that the model compounds (4-XC6H 4)CrCr(C6H4-4-X) (X = H, SiMe3, OMe, and F) have similar geometries in the gas phase. Magnetic measurements in the temperature range of 2-300 K revealed temperature-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 solution. Reduction of (4-F 3CAr′)CrCl (4-F3CAr′ = C6H 2-2,6-(C6H3-2,6-iPr 2)2-4-CF3) with KC8 gave non-Cr-Cr-bonded fluorine-bridged dimer {(4-F3CAr′)Cr(μ-F) (THF)}2 (5) as a result of activation of the CF3 moiety. The monomeric, two-coordinate complexes [(3,5-iPr 2Ar*)Cr(L)] (6, L = THF; 7, L = PMe3; 3,5- iPr2Ar* = C6H1-2,6-(C 6H-2,4,6-iPr3)2-3,5- iPr2) were obtained with use of the larger 3,5-Pr i2-Ar* ligand, which prevents Cr-Cr bond formation. Their structures contain almost linearly coordinated Cr1 atoms, with high-spin 3d5 configurations. The addition of toluene to a mixture of (3,5-iPr2Ar*)CrCl and KC8 gave the unusual dinuclear benzyl complex [(3,5-iPr2Ar*) Cr(η3:η6-CH2Ph)Cr(Ar*-1-H-3,5- iPr2)] (8), in which a C-H bond from a toluene methyl group was activated. The electronic structures of 5-8 have been analyzed with the aid of DFT calculations.
UR - https://www.scopus.com/pages/publications/38149082806
U2 - 10.1021/ic702112e
DO - 10.1021/ic702112e
M3 - Article
AN - SCOPUS:38149082806
SN - 0020-1669
VL - 46
SP - 11277
EP - 11290
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 26
ER -