Synthesis, solution structure, and reactivity of oxygen-bound amides on cobalt(III)

Abstract

A series of pentaamminecobalt(II1) amide complexes containing oxygen-bonded amides are reported. The electronic structure of the amide ligand remains delocalized on coordination to the metal ion, and there is evidence for increased polarization of the amide upon coordination. There is restricted rotation about the carbon-nitrogen bond as shown by separate NMR signals for the amide nitrogen substituents. Also the unsymmetrically substituted formamides (HCONHCH3 and HCONHC~HS) are in both the 2 and E configurations for both the free and oxygen-coordinated species. In aqueous acid solution and in M e 8 0 the complexes slowly producing free amide; the rates of solvolysis have been measured. Complexes of formamides (HCONR1R2) solvolyze more slowly than thoseof carbon-substituted amides (R3CONRlR2); e.g., 1O6kH = 5.25 s-l and 118 s-I for formamide-0 and acetamide-0. In both categories electron-releasing substituents (-CH3, -C2H5) on the amide nitrogen retard solvolysis compared with the primary amide complexes, while electron-withdrawing substituents on the amide nitrogen accelerate it. Complexes with an electron-withdrawing substituent on the amide carbon solvolyze fastest; e.g. for fluoroacetamide-0, 106kH = 1300 s-1. In basic solution at 22 OC (0.1 M NaOH, 1 .O M NaC104) all formamide complexes undergo ligand hydrolysis (N,N-diethylformamide-0, 46%; N,N-diphenylformamide-0, 90%) producing (format0)pentaamminecobalt and free amine; the balance is hydroxopentaamminecobalt(II1) complex. Rates of reaction have been measured and are correlated with the nature of the substituent on the formamide nitrogen; koH = 24.2 M-I s-I for formamide-0 and 0.32 M-I s-I for N,N-diethylformamide-0, I = 1.1 M (NaC104), 25 OC. The pKa of the formamide-Ocomplex is 11.9, and that for the formanilide-0 complex, 12.0. In contrast the carbon-substituted amide complexes are less reactive toward ligand hydrolysis, the major product being the hydroxopentaamminecobalt(II1) ion. The acetamide4 complex yields only 1% (acetato)pentaamminecobalt(III), and the chloroacetamide-and fluoroacetamide-Ocomplexes yield 7% and 8% of the relevant carboxylato ions, respectively. However complexes of benzamide, acrylamide, acetanilide, and N-methyl-, N,N-dimethyl-, and N,N-diethylacetamide yield only the hydroxopentaamminecobalt-(111) complex under the same conditions. The rates of these reactions have been measured and acidity constants for some primary and secondary amide complexes have been determined: koH = 30.2 M-I s-I, pKa 1 1.6, acetamide42 koH = 33 M-I s-I, pKa 10.6, benzamide-O; koH = 70 M-I s-], pKa 9.7, acetanilide4 koH = 150 M-I s-I, pKa 9.4, chloroacetamide-O; koH = 55 M-1 s-I, pKa 9.7, fluoroacetamide-0 [ I = 1 .OO M, NaC104,25 "C]. The base hydrolysis of the dimer [(NH3)5CoOCHNHCo(NH3)5l5+ has been investigated. The reaction is slow and proceeds largely by cobalt-xygen cleavage but with detectable Co-N cleavage. No amide 0-to N-bonded linkage isomerizationwas detected for any of these complexes, and the reactivity of coordinated amides is compared ...

Fluorescent Metal–Organic Frameworks for Selective Sensing of Toxic Cations (Tl3+, Hg2+) and Highly Oxidizing Anions ((CrO4)2−, (Cr2O7)2−, (MnO4)−)

“…The formate ion in I resulted from the hydrolysis of N , N ′‐diethylformamide employed as the solvent in the synthesis. Similar hydrolysis of N , N ′‐dimethylformamide molecules forming formic acid has been reported earlier . The Mn−O bond lengths are in the range of 2.075(3)–2.306(3) Å, (average=2.188 Å) and the O‐Mn‐O bond angles are in the range 71.90(10) to 175.56(11)° (Table S1 in the Supporting Information).…”

Pentaaqua(dimethylformamide)cobalt(II) sulfate dimethylformamide monosolvate

“…For background to the use of DMF, see: Kolthoff et al (1970); Pastoriza-Santos & Liz-Marzan (1999); Kimmerle & Eben (1975); Gescher (1993); Zhou et al (1996); Matwiyoff (1966). For amide complexes, see: Rao et al (1984); Angus et al (1993); Khum & Maclntyre (1965).…”

“…Due to the model properties for peptides, the amide complexes is of continuing interest. Crystallographic studies have shown that in complexes, the amides are bonded to the metal atom by using their carbonyl oxygen (Rao et al, 1984;Angus et al, 1993;Khum & Maclntyre, 1965).…”

3,5,5-Trisubstituted Hydantoins from Activated (Benzyloxycarbonyl­amino)­malonic Acids

“…10,13 In the case of formanilides, the preference for the Z-isomer was less pronounced. 9,12 In contrast to the hydantoins 11, the methylene protons of the achiral malonic acid diamides 12f-j are not diastereotopic, and their signals appear as quartets. A single-crystal X-ray analysis was carried out on the 2formamidomalonic acid diamide 12f, as an example, confirming its structure and the Z-configuration ( Figure 1).…”

“…This clearly indicates that the N-substituted formamides 12 are present as Z-isomers, because for E-iso-mers much larger coupling constants ( 3 J > 10 Hz) have been detected. [9][10][11][12] The E/Z ratio, as determined on the basis of 1 H NMR assignments, was reported for several Nmonoalkylated formamides, including those with tert-alkyl groups. The proportion of the Z-isomer was generally higher (≥70%).…”