Seventeen-electron chromium(i)tricarbonyltris(phosphine) complexes supported by tris(phosphinomethyl)phenylborates

Paul J. Fischer, Shuruthi Senthil, Jeremy T. Stephan, McKinley L. Swift, Victor G. Young

Research output: Contribution to journalArticlepeer-review

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)36-(PhBPPh3)Cr(CO)3}, Cr(CO)36-(((3,5-CH3)C6H3)BPPh3)Cr(CO)3}) and W(0)/Cr(i) (W(CO)36-(((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 languageEnglish (US)
Pages (from-to)16705-16712
Number of pages8
JournalDalton Transactions
Volume48
Issue number44
DOIs
StatePublished - Jan 1 2019

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