Abstract
The inaugural crystallographic characterization of chromium(i)tricarbonyltris(phosphine) radicals has been achieved. Oxidation of [PPN][Cr(CO)3(PhBPPh3)] (PhBPPh3 = [PhB(CH2PPh2)3]-) and analogous Cr(0) complexes featuring 3,5-dimethylphenyl and 3,5-bis(trifluoromethyl)phenyl borate substituents affords charge-neutral Cr(CO)3(PhBPPh3) zwitterions, containing the first fully characterized [Cr(CO)3P3]+ units. The stabilization affected by the intramolecular charge separation established by PhBPPh3 ligands dramatically increases the robustness of these seventeen-electron Cr(i) complexes. Previous attempts to isolate salts of mer/fac-[Cr(CO)3P3]+ were frustrated by the thermal instability of these cations. The EPR spectroscopic data of Cr(CO)3(PhBPPh3) supports Rieger's hypothesized low temperature preparation of fac-[Cr(CO)3{CH3C(CH2PPh2)3}]+. The robust [Cr(CO)3P3]+ unit of Cr(CO)3(PhBPPh3) motivated the preparation of structurally characterized Cr(0)/Cr(i) (Cr(CO)3{η6-(PhBPPh3)Cr(CO)3}, Cr(CO)3{η6-(((3,5-CH3)C6H3)BPPh3)Cr(CO)3}) and W(0)/Cr(i) (W(CO)3{η6-(((3,5-CH3)C6H3)BPPh3)Cr(CO)3}) complexes. While these bimetallics feature classical κ3-phosphine and η6-arene metal-binding, they are noteworthy since all other reported mixed-valent Cr(0)/Cr(i) complexes exhibit (a) significant thermal instability that has precluded their isolation and (b) greater uncertainty regarding the presence of distinct Cr(i) and Cr(0) centers. This work illustrates the utility of tris(phosphino)borates for the stabilization of cationic metal fragments within zwitterions that are inaccessible or difficult to characterize independently.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 16705-16712 |
| Number of pages | 8 |
| Journal | Dalton Transactions |
| Volume | 48 |
| Issue number | 44 |
| DOIs | |
| State | Published - 2019 |
| Externally published | Yes |
Bibliographical note
Funding Information:The National Science Foundation (CHE-1464515) and the Henry Dreyfus Teacher-Scholar Awards Program supported this research. The Bruker-AXS D8 Venture Photon-II diffractometer was purchased from an NSF-MRI grant (CHE-1229400) and the University of Minnesota. The authors are grateful to Dr. Mark Nilges and Michael Drummond (University of Illinois) for their EPR contributions, and Prof. Graham Sazama (Lawrence University) for a helpful discussion. P. J. F. dedicates this manuscript to Prof. Rebecca C. Hoye on her retirement from Macalester College, and in gratitude for her sharing of insight and experience of organic laboratory techniques.
Publisher Copyright:
© 2019 The Royal Society of Chemistry.