Reactions of the bis(bidentate) Schiff-bases N,N'-bis(6-alkyl-2-pyridylmethylene)ethane-1,2-diamine (where alkyl = H, Me, iPr) (L) with tetrakis(acetonitrile)copper(I) hexafluorophosphate and silver(I) hexafluorophosphate afforded, respectively, the double-stranded, dinuclear metal helicates [T-4-(R,R)]-(+/-)-[M2L2](PF6)2 (M = Cu, Ag). The helicates were characterized by 1H and 13C NMR spectroscopy, conductivity, microanalysis, and single-crystal X-ray structure determinations on selected compounds. Intermolecular ligand exchange and intramolecular inversion rates for the complexes were investigated by 1H NMR spectroscopy. Reversible intermolecular ligand exchange between two differently substituted helicates followed first-order kinetics. The rate constants (k) and corresponding half-lives (t(1/2)) for ligand exchange for the dicopper(I) helicates were k = (1.6-1.8) x 10(-6) s(-1) (t(1/2) = 110-120 h) in acetone-d6, k = 4.9 x 10(-6) s(-1) (t(1/2) = 40 h) in dichloromethane-d2, and k> 2 x 10(-3) s(-1) (t(1/2) < 5 min) in acetonitrile-d3. Ligand exchange for the disilver(I) helicates occurred with k > 2 x 10(-3) s(-1) (t(1/2) < 5 min). Racemization of the dicopper(I) helicate by an intramolecular mechanism was investigated by determination of the coalescence temperature for the diastereotopic isopropyl-Me groups in the appropriate complex, and DeltaG() >> 76 kJ mol(-1) was calculated for the process in acetone-d6, nitromethane-d3, and dichloromethane-d2 with DeltaG() = 75 kJ mol(-1) in acetonitrile-d3. Complete anion exchange of the hexafluorophosphate salt of a dicopper(I) helicate with the enantiomerically pure Delta-(-)-tris(catecholato)arsenate(V) ([As(cat)3]-) in the presence of Dabco gave the two diastereomers (R,R)-[Cu2L2][Delta-(-)-[As(cat)3]]2 and (S,S)-[Cu2L2][Delta-(-)-[As(cat)3]]2 in up to 54% diastereomeric excess, as determined by (1)H NMR spectroscopy. The diastereomerically and enantiomerically pure salt (R,R)-[Cu(2)L2][Delta-(-)-[As(cat)3]]2 crystallized from the solution in a typical second-order asymmetric transformation. The asymmetric transformation of the dicopper(I) helicate is the first synthesis of a diastereomerically and enantiomerically pure dicopper(I) helicate containing achiral ligands.

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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 ...

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