Reliable and Economical Preparation of Macrocyclic Complexes Synthesis and Reactivity of a Tetraazaligand for an Advanced Inorganic Laboratory John R. Chipperfield and Simon Woodward School of Chemistry, University of Hull, Cottingham Road, Hull HU6 7RX, UK Spontaneous self-assembly reactions hold a fascination for chemists a s we attempt to mimic anabolic reactions without enzymes ( I ) , and synthesize new tailored poly(2). The ability of mers with special electrical properties . . certain transition metals, especially nickel, to coerce intranlolecular Sch~lrs-basereactions into mncmcvcle formation is well known ( 3 , 4 ) .Undergraduates seldom have the chance to carry out experimental work in this important area of inorganic chemistry because published procedures can give low yields of products with poor solubilites (51,in-
Nitemplate
volve difficult product separations, long reaction times (61, or require the use of hazardous perchlorate counteranions (7). We sought a preparation to overcome these difficulties and yield a variety of macrocyclic complexes.
and Of the many "macrocycle template" reactions available, the preparation of Geodken's macrocycle 1' (the figure) is particularly attractive (61, for the low-cost of the starting materials, and the good solubilitylcrystallinity of most of its complexes. The original inorganic Synthesis preparation (6) calls for a 48-hour MeOH reflux for the initial nickel-templating reaction, well beyond the time-span of most undergraduate laboratory classes. We found that changing the reaction solvent to n-BuOH reduces the reaction time to only three hours. Even shorter reaction times are possible, but they give somewhat lower yields of a n inferior-quality product. Use of n-BuOH reduces reaction time because its higher boiling point of (118 "C) compared to MeOH (65 "C) causes both a faster rate and preferential evaporation of water from the reaction medium. Initially all the reactants do not dissolve so stirring the reaction mixture gives the best results. Comparable vields are obtained with simple refluxing using a heiting mantle and occasional manual shaking.' Stirred reaction mixtures have the advantage that number of color changes are detected-the initial pale green color of the [Nilo-(H2N)C6H4I3l2+ complex, the formation of the purple-coloured organic 2, and the final dark green macrocyclic complex 3 are readily seen. Spectroscopic data are obtained readily on the complex 3 and easily assimed by students. I n particular a clear molecular ion with the u~rrectisotope pattern at 40U mass units is observcd in thc El mass spectrum. As the nickel complex is diamagnetic, the r&ulting 'H NMR spectrum affords good teaching opportunities to demonstrate the reduction in the number of signals presented by a high symmetry species. The macrocyclic complex is stripped easily of i t s nickel template by the published procedure (6). Addition of HC1 gas results in turquoise [Hylacl[NiClJ, and then the nickelate anion is replaced by two PFs moieties.3 The presence of a base yields the yellow free
aNH2 No template
I NHz 7
a
(i) HCI (ii) 2NHaPF6 (iii) NEt3
/
'Because the full name of this compound, S,l4-dihydro6,8,15,17-tetramethyldibenzo[b.il-[l,4,8,111 tetraazacyciotetra-
Synthesis and reactions of Geodken's macrocycle.
decahexene, is torturously long, we call it 'the macrocycle' here and write it as (H,Mac). 2Some slight contamination with unreacted 1.2-diarninobenzene often is encountered , but this is removed when the free macrocycle is isolated. 3The ditetrafluoroboratesalt is water-soluble so no economies may be effectedhere by use of NaBF,. Volume 71
Number 1 January 1994
75
macrocycle [HzMacl 1,with nickel contamination directly orooortional to the ereenness of the samole. Because ~ H ~ M ~is C quite ] ~ reactive + it is best to these species and final macrowcle in one laboratory session. The isolated macrocycle gives excellent spectr~scopicresults for most techniques, offering many possible teaching exercises. The ready supply of 1 allows a range of complexation studies to be undertaken in the laboratory. Reaction of 1 with C U ( O ~ C M ~ ) ~ allows . H ~ O easy preparation of the copper complex CuIMacl, 4, isostructural with the nickel complex (8).More interestingly, the thermal reaction of 1with MO(CO)~ yields the unusual species 5, the product of a hyThe oresence of a remaining drogen mieration reaction (9). ~ ~ ~ f u n c t is r odetected n i n t h e IR spectrum, VNH (KBrj 3420 ern-'. and bv 'H NMR soectroscoov where a high fre12.54. The quency amine is observed, ~"'(cDc~) lower svmmetrv of the comolex 5 is also aovarent by the greatei number of signals bbserved in t h e proton spectrum, Srr (270 MHz. CDCl4 1.93 (s. 6 H. Me), 2.05 (s. 6 H, Me), 3.87 (apparent s, 2 H, CH,), 4.53 (s, 1H, CHI, 6.937.20 (m, 8 H, aromatics), and 12.54 (s, 1H, NH). In ameement with its C, symmetry, four carbonyl stretches a& observed by vibrational spectroscopy, vco (KBr) 2005, 1897, 1875, and 1835 em-'. A tungsten analogue of 5, prepared similarly, is structurally characterized (10). Experimental
All reagents were used a s supplied except 1,2diaminobenzene (phenylenediamine) that was purified by a single recrystallization from EtOH in the presence of decolorizing charcoal. The solvents "BuOH and EkO were dried over 4Amolecular sieves. Preparation times and isolated yields represent typical student values. Experienced workers will complete the experiments in less time and higher yield. Preparation of the Nickel Macroc clic Complex (4-6 h depending on experience{
A 100-mL short-necked round-bottomed flask was charged with a spinbar, Ni(OzCMe)z.4Hz0(2.00 g, 8.03 mmol), 1,2-diaminobenzene (phenylenediamine) (1.73 g, 16.01 mmol), dry butan-1-01 (30 mL), and acetylacetone (2.4-oentanedione)(1.7 mL. -16.6 mmol) added bv svrinae. The flask was set up in an oil bath on a hot pl&esti
