Inorg. Chem. 1991, 30, 1396-1402
1396
Conclusions Norbornene adducts of the S3N3+cation are readily obtained by the reaction of (NSC1)3 with an excess of norbornene in 1,4dioxane followed by treatment of C7HIo.S3N3C1so formed with a chloride ion acceptor or silver salt. Although the structural data for one of these adducts indicate localized *-bonding a t opposite ends of the S,N3 ring, it is likely that the structure of the unattached S,N3+ cation will be significantly different from that of the a d d ~ c t . ~The ' structural weakness implied by the variations (3 I ) The structure of the norbornadiene adduct of the 8-r-electron system Ph2PN3S2 shows substantial differences in ring conformation, bond lengths, and bond angles compared to that of Ph,PN,S,.6
in S-N bond lengths in the adduct is reflected in the facile loss of the -NSN- bridge. Acknowledgment. W e a r e grateful to Dr. R. Yamdagni for assistance with the measurement of the I3C and I4N NMR spectra and Dr. M. J. Schriver (Dalhousie University) for providing the unpublished I3C NMR data for (C7Hlo)2-NS2+.W e thank the N S E R C (Canada), the National Science Foundation, and the State of Arkansas for financial support. Supplementary Material Available: Listings of crystallographic parameters, thermal parameters, hydrogen atom parameters, and leastsquares planes (5 pages); a table of observed and calculated structure factors (18 pages). Ordering information is given on any current masthead page.
Contribution from the Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
Dioxygen Adducts of Nickel(I1) and Cobalt(11) Dioxopentaazamacrocyclic Complexes: Kinetics, Stabilities, and Hydroxylation of the Ligands in the Nickel Dioxygen Complexes Dian Chen, Ramunas J. Motekaitis, and Arthur E. Martell* Received August 2, 1990
The macrocyclic ligands 1,4,7,IO,13-pentaazacyclohexadecane-14,16-dione, 15-ethyl-I ,4,7,IO,i3-pentaazacyclohexadecane14.16-dione. and 15-benzyl-I,4,7,10,13-pentaazacyclohexadecane-14,16-dione have been prepared, and the stability constants of their Cu(lI), Ni(ll), and Co(l1) complexes have been determined potentiometrically. The dioxygen affinities of the Ni(1I) and Co(ll) complexes have been measured as a function of partial pressure of dioxygen and temperature. The nickel(I1) macrocycles form 1: I , superoxo-type dioxygen complexes, while the Co(l1) complexes of the same ligands form 2:l peroxo-bridged binuclear AH', and AS' of dioxygenation are reported. All dioxygen complex formation dioxygen adducts. Equilibrium constants (KO>), reactions are strongly exothermic with strongly negative entropy changes. Both nickel and cobalt dioxygen complexes undergo facilc degradation in aqueous solution but have significant lifetime for determination of oxygenation constants by dioxygen sorption mcasurcmcnts. The cobalt(l1) complexes have higher dioxygen affinities than the nickel(I1) complexes with the same ligands. The rates of dioxygen complex formation and degradation have been measured qualitatively and semiquantitatively by UV-visible absorbance studies. The result of this investigation confirms the previous discovery of the formation of dioxygen adducts from nickel( I I ) complexes, but they are found to undergo irreversible degradation too rapidly to be employed for dioxygen separation or transport. All three Ni(ll) dioxygen complexes studied hydroxylate the macrocyclic ligand at the electron-rich 15-carbon position, thus providing new examples of oxygen insertion (monooxygenase-like activity) by the activation of coordinated dioxygen.
Q
Introduction The recent reports by Kimura et al.'a-f that the Ni(I1) complexes of dioxopentaazamacrocyclic ligands form stable dioxygen adducts is of considerable interest in view of the fact that such complexes are the first nickel(l1) dioxygen carriers to be described. The possibility that these Ni(l1) macrocyclic complexes may be employed for the separation of dioxygen from air deserves further investigation, especially in view of the reportla that they may undergo several oxygenation and deoxygenation cycles. An even more unique characteristic is the reported endothermic nature of the formation of these nickel dioxygen complexes, which was suggestedfa as the possible reason for their unusual properties. In view of the novelty of these nickel(l1) dioxygen complexes, it was considered worthwhile to carry out equilibrium and kinetic studies on their formation and to compare their properties with those of the corresponding cobalt dioxygen complexes involving the same ligands. The three ligands selected for this study seem particularly effective in forming stable nickel(I1) dioxygen complexes: 1,4,7,10,13-pentaazacyclohexadecane-14,16-dione, P N O H ( I ) , and its derivatives with ethyl and benzyl groups a t the 15position, to give 15-ethyl-I ,4,7, IO,13-pentaazacyclohexadecane14,16-dione, P N O E T (2), and 15-benzyI-l,4,7,10,13-pentaazaKimura, E.; Machida, R.; Kodama, M. J . Am. Chem. SOC.1984, 106,5497. (b) Kimura, E.; Machida, R. J . Chem. SOC.,Chem. Commun. 1984. 499. (c) Kushi, Y.; Machida, R.; Kimura, E. J . Chem. SOC., Chem. Commun. 1985, 216. (d) Kimura, E.; Anan, H.; Toike, T.; Shiro, M. J. Org. Chem. 1989, 54, 3998. (e) Kimura, E.; Sakonaka, A,; Machida, R. J. Am. Chem. SOC.1982, 104, 4255. (f) Machida, R.; Kimura, E.; Kushi, Y.Inorg. Chem. 1986,25, 3461
(1) (a)
FH2
1 PNOH,L
2 PN0ET.L'
3 PNOBZ. L"
cyclohexadecane- 14,16-dione, P N O B Z (3), respectively.
Experimental Section Materials. The malonic acid and substituted malonic acid esters employed in the following syntheses, diethyl malonate, diethyl ethylmalonate, and diethyl benzylmalonate, were obtained as pure substances from Aldrich Chemical Co. Tetraethylenepentamine was purified as described in the literature.2 1,4,7,10,13-Pentaazacyclohexadecane-14,16-dione,PNOH (l), was prepared by a modification of the method of Kimura et al.' 'H NMR (CDCI,-Me,Si): 6 1.83 (s, 3 H, CH2NHCH2),2.71-2.91 (m, 12 H. (2) Jonassen, H. B.; Frey, F. W.; Schaafsma, A. J . Phys. Chem. 1957,61, 504.
0020~1669/91/1330-1396$02.50/00 1991 American Chemical Society
O2Adducts of Ni(I1) and Co(I1) Complexes
Inorganic Chemistry, Vol. 30, No. 6, 1991 1397
CH2NHCH2), 3.23 (s, 2 H, COCH2CO), 3.39-3.44 (m, 4 H, OCNHCH,), 8.09 (t, 2 H, CNHCO). Mp 170 "C (lit.' 179 "C). 15-Ethyl-1,4,7,10,13-pentaazacyclohexadecane-14,16-dione, PNOET (2). was synthesized by a modification of the method of Kimura et a1.l IH NMR (CDC13-Me4Si): 6 0.96 (t, 3 H, CH3), 1.91 (M, 2 H, CH,), 2.13 (s, 3 H, CH2NHCH2).2.65-2.80 (m, 12 H, CH2NHCH2),3.01 (t. I H. COCHCO), 3.24-3.61 (m, 4 H, CONHCH,), 7.72 (t, 2 H, CNHCO). Mp 203 "C (1it.I 203 "C). IS-Benzyl-1,4,7,10,13-pentaazacyclohexadecane-14,Iddione, PNOBZ (3), was synthesi~edby a modification of the method of Kimura et aLIa 'H NMR (CDC13-Me4Si): 6 1.91 (s, 3 H, CH2NHCH2),2.51-2.71 (m, I2 H, CHzNHCHz),3.14 (m, 4 H, CONHCH,), 3.25 (m. 1 H, COCHCO), 3.49 (m. 2 H. phenyl-CH,), 7.17-7.25 (m, 5 H, phenyl), 7.45 (t, 2 H. CNHCO). Mp 204 "C (1it.I 202 "C). The inorganic salts were reagent grade and were used without further purification: NiCI2.6H20, CoCI2.6H20, and CuCI2.2H20 from J. T. Baker Chemical Co. and Co(OOCCH3),.4H,O from Fisher Scientific Co. I8O2was obtained from Cambridge Isotope Laboratories, Woburn, MA. in 98% purity. Carbon dioxide free potassium hydroxide solutions were prepared with doubly distilled water and Baker Dilut-It ampules. Oxygenation Constants. The equilibrium constants for the formation of 1 :1 and 2: 1 dioxygen complexes defined by eq 2 and 3 were measured by the volumetric gas uptake method described previously.' [MH_zL][H'l2 M2++ L -+MH_2L+ 2H+ K M L= (1) [LI
w2+1
(3) The corresponding relationships for PI/,, the dioxygen partial pressure corresponding to half-conversion of the oxygen-free complex to the oxygenated form are P1p(I:l)= Ko;l
,
(4)
P1/,(2:1) = [MH-,L(initial)]-'K0;' (5) It is noted that half-oxygen constants for the 1:l dioxygen complexes are independent of concentration, while those of the 2:1 dioxygen complexes are concentration dependent. The oxygenation constants are expressed in terms of partial pressure of dioxygen in equilibrium with the dioxygen-saturated solutions, thus avoiding complications of changing solubilities of dioxygen with changes in temperature, ionic strength, and other solvent conditions. Enthalpies of Dioxygenation, AH", were calculated from the temperature coefficient of the dioxygenation constants through the use of Van't Hoff plots. Entropies of Dioxygenation, AS", were calculated from the standard relationships, -AGO = RT In KO and T U o = AH" - AGO. Equilibrium Measurements. Because of the complications resulting from the fact that some of the dioxygenation reactions are slow and some metal complex formation reactions are even slower and the added problem that some of the dioxygen complexes began to undergo irreversible degradation under the conditions at which equilibrium was measured, special precautions were taken to make certain that equilibrium had been reached when the oxygen uptake equilibrium data were recorded. The first precautions involved making certain that sufficient time had been allowed to reach equilibrium. For the more rapidly degrading solutions, this consideration involved a trade-off between the time required for equilibrium and the time during which an appreciable fraction of the dioxygen complex underwent degradation. For those systems less accuracy was achieved in measuring the oxygenation constants. The second, and most convincing, criterion of equilibrium was to measure at least three equilibrium positions for each temperature investigated. The data would consist of three volumes of dioxygen absorbed corresponding to three different partial pressures of dioxygen at equilibrium. The test for equilibrium was the calculation of the same dioxygenation constant from the three sets of data. Potentiometric Measurements. The potentiometric method employed for the determination of the stability constants of metal complexes of the The macrocyclic ligands 1-3 is the same as that previously de~cribed.~ determinations were carried out on 3.5 X IO-' M ligand and/or metal (3) Chen, D.: Martell, A. E. Inorg. Chem. 1987, 26, 1026. (4) Martell. A . E.; Motekaitis, R. J. Determination and Use ofSrability Constants: VCH Publishers: New York, 1989.
Table I. Protonation Constants
quotient IHL+l/IH+lILl _.. iH2Li']j [H+lW+l
PNOH (1) PNOET (2) PNOBZ (3) this this this work" lit.b work" lit.* work' lit! DIE" 9.40 9.01 9.31 9.17 9.01 9.23 9.84 8.00 7.43 7.91 9.02 8.22 8.69 7.98
IH,L~+~/
2.29
Ulil
0.015
