Inorg. Chem. 1982, 21, 1986-1997
1986
Contribution from the Research School of Chemistry, The Australian National University, Canberra, A.C.T., Australia, 2600, the Department of Chemistry, University of Otago, Dunedin, New Zealand, and the Chemistry Division, Department of Scientific and Industrial Research, Private Bag, Petone, New Zealand
Base-Catalyzed Condensation of a Coordinated Amine and a Nitrile To Form a Tridentate Amidine, [Co(en)(NH2CH2CH2NC(NH2)CH2NH2)XI2+ (X = C1, Br), and the Subsequent Hydrolysis of Halide DAVID A. BUCKINGHAM,*' CHARLES R. CLARK, BRUCE M. FOXMAN, GRAEME J. GAINSFORD, ALAN M. SARGESON, MARK WEIN, and ANDREW ZANELLA Received June 25, 1981 The condensation of the deprotonated amine function trans to halide in the C~~-[CO(~~)~(NH~CH~CN)X]~+ ions (X = CI, The rate Br) results in the rapid formation of the tridentate amidine [Co(NH2CH2CH2NC(NH2)CH2NH2)(en)XI2+. law takes the form -d[Co]/dt = kAm[Co][OH-]with kAm = (9.6 i 0.3) X lo3 mol-' dm3 s-' (X = Cl), (1.5 & 0.1) X lo4 mol-I dm3 s-' (X = Br) at 25.0 OC and p = 1.0 (NaC104), and full retention of configuration about the metal center obtains. A crystal structure of h(+)S46-[C~(NH2CH2CH2NC(NH2)CH2NH2)(en)C1]C12.H20 (P212121,28 11 reflections, R = 0.049) demonstrates a "bent" configuration of the amidine. Subsequent hydrolysis of halide follows the rate law -d[Co]/dt = (k,[OH-] + kzK[0H-l2)/(1 + K[OH-])[Co] with k l = 0.88 mol-' dm3 s-', k2 = 0.14 mol-' dm3 s-', and K = 4.5 mol-' dm3 (X = CI) and kl = 4.40 mol-I dm3 s-l, k2 = 0.90 mol-' dm3 s-I, and K = 6.7 mol-! dm3 (X = Br) at 25.0 OC and p = 1.O (NaCIO,), where K is interpreted as the acidity constant of the amidine moiety. Two products result from each of the k , and k2 paths, the first (1) having the same configuration as the starting complex (with full retention of optical properties) and the second (2) having a "planar" configuration of the amidine grouping with inversion of optical configuration about the metal. The k , path produces 51 i 2% 1 and 49 i 3% 2 and the k2 path 70 i 2% 1 and 30 & 2% 2 for both X = CI and X = Br. The structure of 2-CI is established by a crystal structure on [Co(NH2CH2CH2NC(NH2)CH2NH2)C1]ZnCl4(Cc, 2131 reflections, R = 0.049). Strain energy minimization calculations confirm that 2 is more stable than 1 and that the remaining unobserved configurational isomer 3 is least stable. Base hydrolysis of 2-CI follows the rate law -d[Co]/dt = k2[OH-] [Co] with k2 = 26.7 f 0.5 mol-l dm3 s-' at 25.0 OC, p = 1.0 (NaC104); 2-OH is the only product, and full retention of optical configuration obtains.
Introduction
Scheme I3
Previously we described the formation of chelated amides via the intramolecular condensation of cobalt(II1)-coordinated hydroxide ( C o - O H ) with the nitrile function of pendant aminoacetonitrile and aminopropionitrile where the amine is also bound to the metal (Scheme I).2 In this paper we discuss the related rapid formation of a n amidine via the condensation of a deprotonated coordinated amine function of a n ethvlenediamine moietv with Co(I1Ib bound aminoacetonitrile: reaction 1 ( X = 61, Br), a n d t h e
