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

Journal Article · · Organometallics
 [1];  [1];  [1];  [1]
  1. Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, Mail Code 0358, La Jolla, California 92093-0358, United States
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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 the 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.

Research Organization:
Univ. of California, San Diego, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
Grant/Contract Number:
SC0008058; CHE-1464978
OSTI ID:
1260851
Alternate ID(s):
OSTI ID: 1281963
Journal Information:
Organometallics, Journal Name: Organometallics Vol. 35 Journal Issue: 14; ISSN 0276-7333
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 16 works
Citation information provided by
Web of Science

Cited By (11)

CCDC 1502707: Experimental Crystal Structure Determination: UTOLAS : (carbonyl)-(diethyl ether)-(2,2'',4,4'',6,6''-hexamethyl-1,1':3',1''-terphenyl-2'-isocyano)-bis(μ-2,2'',4,4'',6,6''-hexamethyl-1,1':3',1''-terphenyl-2'-isocyano)-sodium-cobalt dataset September 2016
CCDC 1502708: Experimental Crystal Structure Determination: UTOLEW : bis(2,2'',4,4'',6,6''-hexamethyl-1,1':3',1''-terphenyl-2'-isocyano)-bis(μ-carbonyl)-tris(tetrahydrofuran)-sodium-cobalt dataset September 2016
UTOLIA: bis(triphenylphosphino)iminium dicarbonyl-bis(2,2'',4,4'',6,6''-hexamethyl-1,1':3',1''-terphenyl-2'-isocyano)-cobalt diethyl ether solvate dataset September 2016
CCDC 1502710: Experimental Crystal Structure Determination: UTOLOG : dicarbonyl-bis(2,2'',4,4'',6,6''-hexamethyl-1,1':3',1''-terphenyl-2'-isocyano)-hydrido-cobalt dataset September 2016
CCDC 1502711: Experimental Crystal Structure Determination: UTOLUM : bis(carbonyl)-(μ-carbonyl)-(diethyl ether)-(μ-2,2'',4,4'',6,6''-hexamethyl-1,1':3',1''-terphenyl-2'-isocyano)-sodium-cobalt dataset September 2016
CCDC 1502712: Experimental Crystal Structure Determination: UTONOI : bis(triphenylphosphino)iminium tricarbonyl-(2,2'',4,4'',6,6''-hexamethyl-1,1':3',1''-terphenyl-2'-yl isocyanido)-cobalt fluorobenzene solvate dataset September 2016
Controlled Expansion of a Strong-Field Iron Nitride Cluster: Multi-Site Ligand Substitution as a Strategy for Activating Interstitial Nitride Nucleophilicity journal May 2018
Dianionic Mononuclear Cyclo -P 4 Complexes of Zero-Valent Molybdenum: Coordination of the Cyclo -P 4 Dianion in the Absence of Intramolecular Charge Transfer journal September 2019
Oxidorhenium(V) and Rhenium(III) Complexes with m -Terphenyl Isocyanides: Oxidorhenium(V) and Rhenium(III) Complexes with m -Terphenyl Isocyanides journal May 2020
Controlled Expansion of a Strong‐Field Iron Nitride Cluster: Multi‐Site Ligand Substitution as a Strategy for Activating Interstitial Nitride Nucleophilicity journal May 2018
Dianionic Mononuclear Cyclo ‐P 4 Complexes of Zero‐Valent Molybdenum: Coordination of the Cyclo ‐P 4 Dianion in the Absence of Intramolecular Charge Transfer journal September 2019

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