Title: Relativistic Effects on a Metal–Metal Bond: Osmium Corrole Dimers

Abstract

A series of metal–metal bonded osmium corrole dimers, {Os[TpXPC]}₂, were synthesized in reasonably good yields (35–46%) via the interaction of the corresponding free-base meso-tris(p-X-phenyl)corroles (H₃[TpXPC], X = CF₃, H, CH₃, and OCH₃), Os₃(CO)₁₂, and potassium carbonate in 1,2,4-trichlorobenzene under an inert atmosphere at 180 °C over several hours. The complexes are only the second class of Os corroles reported to date (the first being Os^VIN corroles) and also the second class of metal–metal bonded metallocorrole dimers (the other being Ru corrole dimers). Comparison of the X-ray structures, redox potentials, and optical spectra of analogous Ru and Os corrole dimers, along with scalar-relativistic DFT calculations, has provided an experimentally calibrated account of relativistic effects in these complexes. Three of the Os corrole dimers (X = CF₃, H, and OCH₃) were analyzed with single-crystal X-ray diffraction analysis, revealing inversion-related corrole rings with eclipsed Os–N bonds and Os–Os distances of ~2.24 Å that are ~0.06 Å longer than the Ru–Ru distances in the analogous Ru corrole dimers. Interestingly, a comparison of scalar-relativistic and nonrelativistic DFT calculations indicates that this difference in metal–metal bond distance does not, in fact, reflect a differential relativistic effect. Additionally, for a given corrole ligand, the Ru and Osmore » corrole dimers exhibit nearly identical oxidation potentials but dramatically different reduction potentials, with the Os values ~0.5 V lower relative to Ru, suggesting that whereas oxidation occurs in a ligand-centered manner, reduction is substantially metal-centered, which indeed was confirmed by scalar-relativistic calculations. The calculations further indicate that approximately a third of the ~0.5 V difference in reduction potentials can be ascribed to relativity. The somewhat muted value of this relativistic effect appears to be related to the finding that reduction of an Os corrole dimer is not exclusively metal-based but that a significant amount of spin density is delocalized over to the corrole ligand; in contrast, reduction of an Ru corrole dimer occurs exclusively on the Ru–Ru linkage. For isoelectronic complexes, the Ru and Os corrole dimers exhibit substantially different UV–vis spectra. Furthermore, a key difference is a strong near-UV feature of the Os series, which in energy terms is blue-shifted by ~0.55 V relative to the analogous feature of the Ru series. TDDFT calculations suggest that this difference may be related to higher-energy Os(5d)-based LUMOs in the Os case relative to analogous MOs for Ru.« less

Authors:

Alemayehu, Abraham B. ^[1]; MCormick, Laura J. ^[2]; Vazquez-Lima, Hugo ^[1]; Ghosh, Abhik ^[1]

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+ Show Author Affiliations

1. The Arctic Univ. of Norway, Tromsø (Norway)
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Publication Date:

Thu Feb 07 00:00:00 EST 2019

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES), Scientific User Facilities Division; Research Council of Norway (AG)

OSTI Identifier:

1656500

Grant/Contract Number:  

AC02-05CH11231; 262229

Resource Type:

Accepted Manuscript

Journal Name:

Inorganic Chemistry

Additional Journal Information:

Journal Volume: 58; Journal Issue: 4; Journal ID: ISSN 0020-1669

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Potassium; redox reactions; oligomers; aromatic compounds; quantum mechanics