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
- 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
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