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Title: A Well-Defined Isocyano Analogue of HCo(CO)4. 2: Relative Brønsted Acidity as a Function of Isocyanide Ligation

The m-terphenyl isocyanide complex, HCo(CNArMes2)4 (ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H3), serves as a unique example of a well-defined isocyano analogue to HCo(CO)4. Given the well documented Brønsted acidity of HCo(CO)4 in both protic and nonprotic media, the Brønsted acidity of HCo(CNArMes2)4 was assessed for a quantitative comparison. Acid bracketing experiments in THF solution revealed that HCo(CNArMes2)4 has a Morris relative pKα THF value of 38.5-40.7, which is considerably higher than that of HCo(CO)4 (pKα THF (calc) = 11.4) and thereby indicates insignificant Brønsted acidity. Furthermore, the relative acidity of HCo(CNArMes2)4 rivals that of tetra-phosphine cobalt hydrides (i.e., HCo(PR3)4; pKα THF (calc) ≥ 48), despite the good π-acidity properties of the isocyano unit. To systematically determine the effect of substituting an isocyanide for a CO ligand on the acidity of the Co-H unit in HCoL4 complexes, the full series of HCo(CO)n(CNArMes2)4-n monohydrides and [Co(CO)n(CNArMes2)4-n]- (n = 1-4) metalates were prepared and characterized. Acid bracketing studies on the [Co(CO)n(CNArMes2)4-n]- metalates in THF solution revealed a regular progression of increasing pKα THF values as isocyanides are added to the Co center. However, the monoisocyanide tricarbonyl hydride, HCo(CO)3(CNArMes2), possesses a pKα THF value of 28.6-32.5, which is also significantly higher than that of HCo(CO)4 and themore » monophosphine complex HCo(CO)3(PPh3). Accordingly, the unconventional ability of isocyanide ligands to function as stronger σ-donors than organophosphines is discussed within the context of both the Brønsted acidity and spectroscopic features of the HCo(CO)n(CNArMes2)4-n monohydrides.« less
 [1] ;  [1] ;  [1] ;  [1]
  1. Univ. of California, San Diego, CA (United States). Dept. of Chemistry and Biochemistry
Publication Date:
OSTI Identifier:
Grant/Contract Number:
SC0008058; CHE-1464978
Published Article
Journal Name:
Additional Journal Information:
Journal Volume: 35; Journal Issue: 14; Journal ID: ISSN 0276-7333
American Chemical Society
Research Org:
Univ. of California, San Diego, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States