EPR studies of 1:1 complexes of rhodium (II) and cobalt (II) porphyrinswith {sigma} donor and {pi} acceptor ligands. Origins of rhodium (II) metalloradical reactivity

Journal Article · Wed Aug 25 04:00:00 EDT 1993 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja00070a011· OSTI ID:41658

Wayland, B B; Sherry, A E; Bunn, A G ^[1]

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1. Univ. of Pennsylvania,Philadelphia, PA (United States)

Tetrakis ((2,4,6-trimethylphenyl)porphyrinato)rhodium(II) ((TMP)Rh) and tetrakis((2,4,6-trilsopropylphenyl)-porphyrinato)rhodium(II) ((TTiPP)Rh) occur as low-spin d{sup 7} complexes with EPR parameters associated with a(d{sub xy}){sup 2}-(d{sub xz,yz}){sup 4}(d,2){sup 1} ground configuration. (por)Rh{sup II} species typically react as metalloradicals with a wide variety of substrates to give diamagnetic products; however, the use of increased porphyrin or substrate steric demands has permitted observation of paramagnetic 1:1 adducts. EPR spectra were used in examining features related to the electronic structure for a series of 1:1 five-coordinate complexes with nitrogen, phosphorus, arsenic, and carbon donor ligands. Each of the five-coordinate species is a low-spin d{sup 7} complex with the unpaired electron occupying a d{sub z}2 MO (d{sub xy}d{sub xz}d{sub yz}){sup 6}-(d{sub z}{sup 2}){sup 1} ground configuration. The ligands form 1:1 adducts that have effective axial symmetry with the exceptions of CO, which has as a bent Rh-CO unit, and ethene, which has a symmetrical {pi} complex structure. Donor atom spin densities are estimated from ligand hyperfine coupling. Rhodium-103 hyperfine coupling is used in evaluating the rhodium 4d{sub x}2 (0.67) and Ss (0.02) spin density in the ethene {pi} complex, which combined with the total ethene C{sub 2p} (0.278) and C{sub 2s} (0.008) spin densities, determined from the ligand hyperfine coupling, accounts for most of the unpaired electron. Estimates of the d{sub z}2 to d{sub xz} and d{sub yz} energy separations for the series of 1:1 complexes illustrate the elevation of d{sub z}2 by {sigma} donor ligands and the combined lowering of d{sub xz}, d{sub yz}, and d{sub z}2 elevation by ligands with {pi} acceptor ability. 26 refs., 2 figs., 2 tabs.

• Sponsoring Organization: USDOE
• DOE Contract Number: FG02-86ER13615
• OSTI ID: 41658
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 17 Vol. 115; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
COBALT COMPLEXES
ELECTRON SPIN RESONANCE
ETHYLENE
EXPERIMENTAL DATA
LIGANDS
ORGANOMETALLIC COMPOUNDS
PORPHYRINS
RADICALS
RHODIUM COMPLEXES