Patricia M. Angus

Synthesis and rearrangements of the pentaamminecobalt(III) linkage isomers of some amidic acids

Abstract The unidentate pentaamminecobalt(III) linkage isomers of phthalamic and malonamic acids bonded through the deprotonated amide nitrogen or the carboxylate group have been synthesized and characterized. The carboxylate-bonded complexes were synthesized directly from their amidic acids; they, as well as carboxylate-bonded succinamic acid, solvolyzed very slowly in aqueous acid ( 1 M , t 1 2 days) and at pH 10 they decomposed very slowly; the amide group was not hydrolyzed while the amidic acid ligand was bonded to the metal. The malonamato- N complex was prepared by base hydrolysis at pH 7 of the corresponding cyanoacetate- N complex. Pentaammine (phthalamato- N )cobalt(III) was synthesized by base catalyzed hydration of the corresponding phthalimido- N complex; the latter was prepared directly from free ligand and pentaammine (dimethyl sulfoxide) cobalt(III). The rate law for the base catalyzed hydration (10 −7 M ≤ [OH − ] ≤ 0.05 M) of the phthalimido- N complex is: k ohs = k OH [OH − ] where K OH = 0.40 M −1 s 1 (25°C, I = 1.0 M (NaCl). In acid the amido- N linkage isomers are protonated on both the amide oxygen and on the carboxylate group. In water they undergo the usual solvolysis and amide- N to O rearrangement, but, concurrently, amide- N to carboxylate-bonded rearrangement. This first-formed amide- O complexes aquate relatively rapidly so that the observed products were the pentaammineaquacobalt(III) complex and the carboxylate-bonded complexes of malonamic acid (73%), phthalamic acid (36%) and succinamic acid (24%), respectively. In Me 2 SO-d 6 amide- N to O and amide- N to carboxylate-bonded rearrangements were observed directly, with the ultimate products being pentaammine (dimethyl sulfoxide) cobalt(III) and the carboxylate-bonded complexes of malonamic acid (10%), phthalamic (33%) and succinamic acid (5%), respectively. The effects of a one-versus two-C length organic backbone, flexible (−CH 2 CH 2 −) versus rigid ( o -phenylene) geometry, and solvent (H 2 O versus Me 2 SO) in influencing the competitive rearrangements are considered.

CARBON-OXYGEN BOND CLEAVAGE : A NEW REACTION MODE FOR AMIDES BONDED THROUGH OXYGEN TO COBALT(III)

Abstract Azide ion competition experiments and oxygen-17 and -18 studies have been used to determine the extent of cleavage of the coordinated oxygen–carbon bond when (amide- O )pentaamminecobalt(III) complexes were reacted in aqueous base. Base hydrolysis in the presence of azide ion at 22°C (0.10 M NaOH, 1.0 M NaN 3 ) of [(NH 3 ) 5 CoOC(CH 3 )NH 2 ] 2 (S 2 O 6 ) 3 ·3H 2 O and [(NH 3 ) 5 CoOC(CH 3 )N(CH 3 ) 2 ](CF 3 SO 3 ) 3 ·H 2 O produced 12.5 and 13.0% azido complex respectively, as expected for tripositive complexes reacting solely by cobalt–ligand bond cleavage. However reaction of [(NH 3 ) 5 CoOC(C 6 H 5 )NH 2 ] 2 (S 2 O 6 ) 3 ·3H 2 O produced only 10.5% azido complex and this implied that 17% of the complex was reacting by carbon–oxygen bond cleavage. 17 O NMR spectroscopy of the products of base hydrolysis of [(NH 3 ) 5 CoOC(CH 3 )N(CH 3 ) 2 ](CF 3 SO 3 ) 3 ·H 2 O in 22 atom% H 2 17 O confirmed that it reacted largely by ligand substitution but the same experiment using [(NH 3 ) 5 CoOC(CH 2 F)NH 2 ] 2 (S 2 O 6 ) 3 ·3H 2 O was inconclusive because of secondary hydrolysis of the liberated amide. Oxygen-18 analysis of coordinated water has demonstrated conclusively that for complexes of primary or secondary amides with electron-withdrawing substituents carbon–oxygen bond cleavage in aqueous base is a significant reaction: [(NH 3 ) 5 CoOC(C 6 H 5 )NH 2 ] 2 (S 2 O 6 ) 3 ·3H 2 O, 19%; [(NH 3 ) 5 CoOC(CH 2 F)NH 2 ] 2 (S 2 O 6 ) 3 ·3H 2 O, 10%; and [(NH 3 ) 5 Co(succinimido- O )](CF 3 SO 3 ) 2 ·H 2 O, 9%. The reaction was not detected when [(NH 3 ) 5 CoOC(CH 3 )NH 2 ] 2 (S 2 O 6 ) 3 ·3H 2 O and [(NH 3 ) 5 CoOC(CH 3 )N(CH 3 ) 2 ](CF 3 SO 3 ) 3 ·H 2 O were dissolved in aqueous base as these amides are not electronically activated, nor was it detected for reaction of [(NH 3 ) 5 CoOC(H)N(CH 3 ) 2 ](CF 3 SO 3 ) 3 ·H 2 O; this complex is activated towards addition by hydroxide ion (84% C–N cleavage) but lacks an ionisable proton on the amide nitrogen to facilitate proton transfer in the intermediate in the C–O bond rupture process.

A simple synthesis of the ripening agent 1-aminocyclopropane-1-carboxylic acid

Conversion of chelated homoserine to 2-amino-4-bromobutyrate and treatment with aqueous base leads directly to chelated 1-aminocyclopropane-1-carboxylate.

Nitrogen and oxygen bonded (2-pyrrolidinone)-pentaamminecobalt(III): the first monodentate linkage isomers of a secondary amide

Abstract The cyclic secondary amide 2-pyrrolidinone has been coordinated to the pentaamminecobalt(III) moiety to afford both O- and N-bonded linkage isomers. A deprotonated N-bonded form has also been isolated. In non-coordinating solvents the N-form rearranges to its O-bonded isomer, and in coordinating solvents some solvolysis competes with this, but much less so than for the primary amide ligand systems investigated previously. The O-bonded product ultimately loses the amide ligand completely in water, DMSO or aqueous base; there is no detectable CN cleavage.

An unusual pendant-arm macrocycle formed by condensation of a cobalt(III) tripodal complex with methanal

The reaction of [Co(ten)]3+ {ten = 4,4′,4″-ethylidynetris(3-thiabutan-1-amine)} with methanal and base in acetonitrile or water led to the synthesis of an unusual pendant-arm macrocyclic complex, 8-(4′-ammonio-2′-thiabutyl)-8-methyl-1-oxa-6,10-dithia-3,13-diazacyclo-tetradecane(chloro)cobalt(III) triperchlorate trihydrate. The structure of the complex has been established by X-ray crystallographic analysis and such molecules can readily be tied to polymers and proteins. The synthesis, chemical reactions, spectroscopy and electrochemical properties of the macrocyclic complex are described.

An amidine-functionalized cobalt(III) cage complex: synthesis, structure and properties

The template synthesis, structure and properties of an unusual tricyclic amidine-functionalized triaza-trithia cobalt(III) cage complex are described.