Inorg. Chem. 1993, 32, 988-994
988
Rhenium(V)-Oxo Complexes of Neutral and Monoanionic Tetraazamacrocycles. X-ray Structures of trans-Oxohydroxo( 1,4,8,1l-tetraazacyclotetradecan-2-one)rhenium(V) Perrhenate and trans-Oxohydroxo(1,4,8,1l-tetraazacyclotetradecane)rhenium(V) Bis(perch1orate) Brenda Winckler Tsang, Joseph Reibenspies, and Arthur E. Martell' Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255
Received September 12, 1991 The complexes of Reo2+ and ReO(OH)2+ with 1,4,8,1l-tetraazacyclotetradecane (cyclam) and 1,4,8,11tetraazacyclotetradean-2-one (Olcyclam)have been synthesized and characterized. The complexes were prepared by ligand exchange reactions of the macrocycles with a variety of starting compounds including ReOC13(PPhs)2 and Re02(en)2C1. The ReO(OH)2+complexes have been structurally characterized. Re0(OH)(H..,O1cyclam)ReO4 crystallizes in the monoclinic P21/n space group with a = 10.308(3) A, b = 9.527(2) A, c = 17.808(3) A, and p = 106.57(2)'. ReO(OH)(cyclam)(Cl04)2 crystallizes in the monoclinic C 2 / c space group with a = 9.734(4) A, b = 16.999(5) A, c = 12.187(5) A, and 0 = 106.36'. The complex Re0(OH)(H-IOlcyclam)Re04 has a distorted octahedral structure with one short ReO(oxo) bond and one long ReO(hydrox0) bond (1.685(8) vs 1.970(8) A). The deprotonated amide ReN(sp2) bond is shorter than the other three ReN(sp3) bond lengths (1.98(1) vs 2.13(3) A (average)). The structure of the ReO(OH)(~yclam)(ClO~)~ complex shows no distinction between the lengths of the two ReO(oxo and hydroxo) bonds (1.766(5) A) due to disorder of the oxo and hydroxo groups. Spectroscopic evidence is reported to confirm the presence of both oxo and hydroxo groups coordinated to rhenium.
Introduction
charged donor groups can remove the need for two multiply bound oxogroups as in the case of monooxo square pyramidal complexes While research on Tc(V) macrocyclic complexes has been such as ReO(ethanedithi~lato)~-.~~ The present study was pursued because of the potential development of useful radioundertaken to synthesize and characterize Re(V) complexes with pharmaceuticals, the work on similar Re complexes has been cyclam and the cyclam derivatives shown in Figure 1. The somewhat neglected. However, some Re isotopes have been additional thermodynamic stability provided by macrocyclic suggested for the development of diagnostic and therapeutic ligands over open-chain ligands warrants the development of radiopharmaceuticals.1-3Most rhenium studies have concenefficient ways of synthesizing these types of complexes. In this trated on complexes with multidentate open-chain ligands, study, we report the syntheses by ligand exchange reactions and primarily simple bidentate ligand^.^ The syntheses of complexes characterizations of the Re02(cyclam)+, ReO(OH)(cyclam)2+, of technetium with tetraaza macrocycles such as cyclam and its Re02(H-IOlcyclam), ReO(OH)( H-IOIcyclam)+, and ReOderivatives and biodistributions of some of these complexes have (H-202cyclam)C1,and structural determinations of the two oxobeen reported in the literat~re.~-*Structural studies of both hydroxo complexes. Re02(cyclam)+ and Tc02(cyclam)+ have been p ~ b l i s h e d . ~ ~ ~ ~ Other examples of macrocyclic complexes on which structural Experimental Section studies have been reported include the Tc02+complex with 14Materials. KRe04 was purchased from Strem Chemical Co. ane-N& containing two thioether donor groups in place of two Re02(en)2Cl, ReOCI3(PPh&, ReOJ(PPh&, and ReOC14N(n-Bu4) were amino groups and the (octaethylporphyrinato)oxorhenium(V) synthesized by the use of literature method^.'^-'^ 1,4,8,1l-Tetraazacyand technetium(V) comp1exes.l I-13 clotetradecane (cyclam) was purchased from Aldrich Chemical Co. In most cases, with Re and Tc in the oxidation state +5, the 1,4,8,1l-Tetrazacyclotetradecan-2-one(Olcyclam) and 1,4,8,1 I-tetmacrocycle forms a stable and readily characterized complex raazacyclotetradecane-2,4-dione(02cyclam) were synthesized by modwith the M-02+ core (M = Tc, Re). However, adding negatively ifications of known method^.^^,^^ ( I ) Mathieu, L.; Chevalier, P.; Galy, G.; Berger, M. Int. J. Appl. Radiat. Isot.. B 1979, 30, 725. (2) Weininger, J.; Ketring, A. R.; Deutsch, E.; Maxon, H. R. J. Nucl. Med. 1983, 24, P125. (3) Quadri, S. M.; Wessels, B. W. Int. J. Appl. Radiat. Isot., B, 1986. 13, 447. (4) Wilkinson, G., Ed. Comprehensioe Coordination Chemistry: The Synthesis. Reactions. Properties and Applications of Coordination Compounds; Pergamon Press: Oxford, England, 1987;Vol. 4, p 184. (5) Franz, J.; Volkert, W. A.; Barefield, E. K.,;Holmes, R. A. Nucl. Med. Biol. 1987, 14, 569. ( 6 ) Ketring,A. R.;Troutner, D. E.; Hoffman,T. J.;Stanton, D. K.; Volkert. W. A.; Holmes, R. A . Int. J. Nucl. Med. Biol. 1984, 11, 113. (7) Volkert, W. A,; Troutner, D. E.; Holmes, R. A . Int. J. Appl. Radial. .. Isot. 1982, 33, 941. Zuckman, S.A,; Freeman, G. W.; Trounter, D. E.; Volkert, E. K. Inorg. Chem. 1981, 20, 2386. Marchi, A.; Rossi, R.; Magon, L.; Duatti, A.; Casellato, U.; Graziani, R.; Vidal, M.; Riche, F. J. Chem. Soc.. Dalton Trans. 1990, 1935. Blake, A . J.; Greig, J. A.; Schroder, M. J. Chem. Soc., Dalton Trans. 1988, 2645. lanoz, E.; Mantegazzi, D.; Lerch, P.; Nicolo, F.; Chapuis, P. Inorg. Chim. Acta 1989, 156. 235. Lawrence, A. J.; Thornback, J. R.; Zanelli, G. D.; Lawson, A. Inorg. Chim. Acta 1988, 141, 165.
Buchler, J. W., Robbock, K. Inorg. Nucl. Chem. Lett. 1972. 8, 1073.
Methods. IR spectra were measured with an IBM FTIR 40s spectrophotometer in KBr pellets. UV-vis spectra were measured with a Perkin-Elmer fast scan UV-vis spectrophotometer with 1.000 f 0.001 cm matched quartz cells. All 'H-NMR spectra were measured with an XL200 N M R spectrometer. Mass spectra were obtained by fast atom bombardment on a VG Analytical 70s high-resolution double-focusing magnetic sector spectrometer attached to a VG Analytical 11/250J data system, with nitrobenzyl alcohol as the matrix solvent, by Tom Sharp at the Mass Spectrometry Applications Laboratory, Center for Chemical Characterization and Analysis, Texas A & M University. Re02(cyclam)C104-H20.Method 1. To a solution of 0.16 g of cyclam (0.79mmol) in 2 mL of H2O and 2 m L of MeOH was added a solution of 0. IO g of ReO~(en)zCl(0.262mmol). The solution color immediately ~~
Davison, A.; Orvig, C.; Trop, H. S.;John, M.; De Pamphilis. B. V.; Jones, A. G.Inorg. Chem. 1980, 19, 1988. ( I 5 ) Murmann. K. Inorg. Synth. 1966, 8, 173. (16) Chatt, J.; Garaforth, J. D.; Johnson, N. P.; Rowe, G. A J. Chem. SOC 1964, 1012. (17) Ciani, G. F.;D'Alfonso, G.;Romiti, P. F.; Sironi, A,; Freni, M. Inorg. Chim. Acta 1983, 72, 29. (18) Cotton, F. A.; Lippard, S.J. Inorg. Chem. 1966, 5. 9. (19) Machida, R.;Kimura, E.; Kodama, M., Inorg. Chem. 1983,22, 2055. ( 2 0 ) Tabushi, 1.; Taniguchi. Y.; Kato, H. Tetrahedron Lett. 1977, 1049. (14)
0020-166919311332-0988%04.00/0 0 1993 American Chemical Society
Inorganic Chemistry, Vol. 32, No. 6, 1993 989
Rhenium(V)-Oxo Complexes
Table 1. Crystal Data, Data Collection, and Solution Refinement Parameters ~~~
ReO(OH)(cyclam)(c104)2 (1) empirical formula color and habit cryst size
cyclam:
R1
01-cyClam: R1
- - R2
CH2
CH2, R2
O ~ - C Y C ~ R1 O ~ : R2
C-0
Figure 1. Macrocyclic ligands to be studied.
C-0
C IoH25N4010ChRe violet parallelepiped 0.3 mm X 0.5 mm X 0.6 mm monoclinic, C 2 / c space group (No. 15) unit cell dimens a = 9.734(4) A b = 16.999(5) A c = 12.187(5) A @ = 106.36(3)O 1935.1( 13) AJ volume 4 formula units/cell 618.4 amu fw 2.123 g/cmJ density (calcd) 67.0 cm-1 abs coeff 1208 eF(000) 193 K temp w (Wyckoff) scan mode 4.0- 50.0 28 range -1 1 < h c 11, -20 c index ranges & C 0, -14 < I < 0 no. of reflcns collcd 1859 no. of unique reflcns 1712 1631 1 2 l.Oo(I) no. of obsd reflcns semiempirical abs cor 0.9994666 Tmax-Tmm extinction cor22 x = 0.00013(2) where F* = Fc/[l 0.002xFc2/ (sin 28)]0.25 final residuals" R = 0.066; R , = 0.073 S = 6.85 goodness of fit" 0.044,0.009 largest, mean d/s data-to-param ratio 11.6:l
ReO(OH)(H-,oxocyclam)ReO4 (11) C I oH2 I N407Re2 red sphere 0.05 mm monoclinic, R 1 / n (No. 14) a = 10.303(4) A b = 9.533(3) A c = 17.813(7) A @ = 106.44(2)O 1678(1) A' 4 682.7 amu 2.702 g / c d 147 cm-1 1264 e296 K 8/28 4.0-50.0 -12 c h c 12, -1 1 c & < 0 , 2 1< I C 6 3206 295 1 295 1 semiempirical 0.965-0.806 x = 0.00003(2) where F* = Fc/ [ 1 + O.O02XFc2/ (sin 28)]0.25 R = 0.067; R , = 0.063 S = 1.07 0.05,0.003 14:l
became golden yellow. The reaction mixture was refluxed for 6 h. After the solution was cooled, it was extracted with three 5-mL portions of CHCI, to remove excess ligand. The volume of the aqueous layer was reduced by half and excess NaC104 was added. The solvent was allowed to slowly evaporate on standing, yielding orange-yellow crystals of the product. Thecrystalswerewashed withcoldEtOH (30%). In theabsence of NaC104, the chloride salt was isolated in a 60% yield; mp 195-197 OC. Anal. Calcd for ReO2(cyclam)ClO4~H~0: C, 22.41; H, 4.89; N , 10.45. Found: C, 22.30; H, 4.97; N, 10.30. FAB+ MS: m/z 419 [Re02(cyclam)+] and m/z 403 [ReO(cyclam)2+ - e-]. FTIR (KBr pellet): 772 cm-1 u,,(ReO). Caution! Precaution must be used when working with perchlorate compounds as explosions have been known to occur. Method 2. A 0.15-g sample of n-Bu4NReOC14(0.26 mmol)and 0.16 g of citric acid monohydrate (0.79 mmol) were dissolved in 5 mL of MeOH. To this solution was added 0.16 g of cyclam (0.79 mmol) in 1 mL of MeOH. The solution color changed from blue to yellow upon adjustment of the pH to 11 with 1 M NaOH. The MeOH was removed by evaporation and the aqueous solution was extracted with three 5-mL portions of CHCI3. Excess NaC104 was added to the aqueous layer. Orange-yellow plates of product were isolated and washed with cold EtOH (40%). FAB+ MS: m / z 419 [ReO2(cyclam)+]. FTIR (KBr pellet): 772 cm-' uaS(ReO). ReO(OH)(cyclrm)CIOdPF(,. A 100-mgsample of ReO2(cyclam)PS Crystals suitable for X-ray structure analysis were grown from an was dissolved in a minimal amount of 2 M HCIO4, and the lavender aqueous solution of the violet solid over several weeks and were formulated product was precipitated out with acetone. UV-vis (HC104): 646,482, as the perrhenate salt (structure 11). 210, 195 nm. FTIR (KBr pellet): 969 cm-I u,,(ReO). Anal. Calcd for Re02(H_IOlcyclam). A 1.1-g sample of Re02(en)2CI (0.47 mmol) R ~ C I O H ~ S N ~ O ~ C IC, P F18.09; , , : H, 3.79; Re, 28.04. Found: C, 18.03; was dissolved in 2 mL of H20. To this solution was added 0.20 g of H, 3.76; Re, 29.77 Olcyclam (0.93 mmol) in 1 mL of 1 M NaOH. The reaction solution Crystalssuitablefor X-ray structureanalysis weregrown froma solution was refluxed for 2 h, and the hot solution was extracted with CHCI3 to of the lavender precipitate in 2 M HC104 over 1 week and formulated remove the excess ligand. The solvent was removed from the aqueous as the diperchlorate salt (structure I). layer, and the remaining yellow residue was extracted with CH3CN. Upon removal of the solvent, an orange-yellow solid remained. FTIR ReO(OH)(H_lOlcyclnm)+. Method 1. A 0.26-g sample of R ~ O C I J (KBr pellet): 771 cm-' n,$(ReO). FAB+ MS: cluster of peaks at m/z (PPh3)2 (0.31 mmol) was suspended in 17 mL of dry CH2C12, and the 43 1 corresponding to [ReO~(H_~O~-cyclam)-]+. solution was purged with N2. To this suspension were added 0.13 g of Olcyclam (0.62 mmol) and 100 pL of triethylamine in 3 mL of CH2C12. ReO(H-202cyclam)CI.DMF. Method 1. To a degassed solution of The reaction mixture was stirred at room temperature for 8 h, the solvent J ) ~ mmol) in 10 mL of CH2C12 was added 0.10 g of R ~ O C L J ( P P ~(0.120 was then removed, and the brown residue was taken up in 5 mL of HzO. 30 mg of Ozcyclam in 1 mL of EtOH. The solution was stirred under The insoluble P P ~ was J removed by filtration and the aqueous solution argon for 24 h. Immediately upon addition of the ligand solution, the was extracted with CHCIJ to remove excess ligand. The solution was set green solution of the starting compound turned dark brown. A light gray aside for slow evaporation, and after several days violet microcrystals of precipitate was filtered off and washed with EtOH, reprecipitated in the CI salt were formed (57%). Anal. Calcd for R ~ O J C I O H ~ ~ N ~ CDMF/EtOH, I and dried in vacuo; yield 83%. FTIR (KBr pellet): 912 (ReO(OH)(H.IOlcyclam)CI): C, 25.67; H, 4.74; N, 11.97; CI, 7.57. u,,(ReO); 1540, 1644 u ( C 0 ) ; 3245 u(NH). Anal. Calcd. for Found: C, 25.52; H, 4.85; N, 11.92; CI, 7.29. Diamagnetism was R ~ C I J H ~ ~ H ~ C, O ~29.07; C I : H, 4.69; N, 13.04. Found: C, 29.69; H, determined with the Evan's NMR methodz1in DzO with CHJCN as the 5.45; N, 13.66. reference. FTIR (KBr pellet): 952 cm u,,(ReO). FAB+M S: m / z Crystal Data Collection, Solution, and Refinement. The crystal data 415. and details of data collection and refinement are summarized for both Methad 2. A 0.12-g sample of ReO2I(PPh,)z (0.14 mmol) was crystal structures in Table I, while the X-ray experimental methods are suspended in 2 mL of MeOH. A solution of 0.07 g of Olcyclam (0.33 described below. For both crystals, preliminary examination and data mmol)and 46 p L of triethylamine (0.33 mmol) in 3 mL of CH?C12 was collection were performed on a Nicolet R3m/V X-ray diffractometer added to the suspension. The reaction mixture was refluxed for 1 h, and (M0Ka.X =0.710 73Aradiation,withorientedgraphitemonchromator). the orange-brown solution was set aside for evaporation, yielding a violet The solution and refinement of the structures were performed with microcrystalline solid of the I salt. FAB+ MS: m / z 415. FTIR (KBr SHELXTL PLUS (MicroVax 11).z2 Background measurement by pellet): 952 cm v,,(ReO). stationary crystal and counter technique was done at the beginning and end of each scan for half of the total scan time. Three control reflections, collected every 97 reflections, showed no significant trends. A semiem(21) Evans, D.F. J . Chem. SOC.1959, 2003.
+
Tsang et al.
990 Inorganic Chemistry, Vol. 32, No. 6, 1993 pirical absorption correction??was applied to the data for structures I and 11. Neutral atom scattering factors and anomalous scattering correction terms were taken from refs 23,24. Hydrogen atoms were placed in idealized positions with isotropic thermal parameters fixed at 0.08 A?. For structures I and I1 the extinction coefficient x was refined to 0.00013(2) and 0.00021(5), re~pectively.~~ The largest peaks in the final Fourier difference map were 1.47 and 1.69 e A 3 for structures I and 11, respectively. Both peaks were near a rhenium atom, indicating possible errors in the absorption correction methods for both structures. Structure I was seen to crystallize in the space group C2/c or Cc. The structure of I was solved in both space groups; however, attempts to anisotropically refine I in the space group Cc failed, presumably due to high correlation of the parameters of atoms related by a pseudoinversion center. Thespacegroup C2/c waseventuallychosenfor further structural refinement. For structure I only half of the [ReO(OH)(cyclam)]*+was contained in the asymmetric unit, with the rhenium atom located on the crystallographic inversion center. The remaining half of the molecule can be generated by the inherent symmetry. The anisotropic parameters measured for the rheniumatom in structure I were unusual. It is unclear whether these parameters are due to problems in the overall absorption correction or due to disorder of the rhenium atom. It has been suggested that coordination of the rhenium atom to both an oxo and hydroxy ligand would draw the rhenium atom out of the plane of the four ligating nitrogen atoms. For this structure such a displacement would result in an apparent disorder of the rhenium atom. Two choices ofcounter ions (PFs and c104) were possible for structure I, based upon the synthetic pathway. Initial bond distances between the central atom of the counter ion fragment and the terminal atoms (1.331.38 A) were judged too short for P-F bond lengths (1.55-1.60 A), and thus the choice of counter ion was perchlorate. Both perchlorate anions were found to sit on the crystallographic 2-fold axis. One of the two anions was found to be disordered. The disordered anion was modeled by positioning thechlorine atom on thecrystallographic axisand locating the oxygen atoms on general positions, with their site occupation factors fixed at 50%. Bond distance restraints were imposed on the chlorineoxygen and oxygen-oxygen distances. The chlorine atom of the second perchlorate anion was positioned on the crystallographic 2-fold axis, and two oxygen atoms were located on general positions, in such a way as to utilize the apparent 2-fold axis in the perchlorate tetrahedron. The resulting model was refined anisotropically. The anisotropic thermal parameters for the anion were very large, indicating possible disorder. An attempt to model the disorder failed. It is unclear whether the large anisotropic parameters are a result of disorder or thermal motion of the terminal atoms. The anisotropic model was finally chosen, and the structure was refined to convergence.
SolutionStudies. The liganddissociationconstant, K,, wasdetermined M solution of ReO2(cyclam)CI, adjusted by titration of an 8.03 X to an ionic strength of 0.100 M with KCI, with a standard 0.0975 M HCI solution delivered with a Metrohm piston buret, in a jacketed cell to maintain a constant temperature of 25.0 f 0.1 O C sealed under purified Nz as described by Martell and Motekaitis.26 The -log [H+] measurements were taken with a Model 150 Corning p[H] meter using a Corning glass electrode and saturated calomel reference electrode filled with saturated KCI, after calibration of the electrodes using standard aqueous HCI and NaOH solutions at p = 0.100 M to read -log [H+]directly. The All crystallographiccalculations were performed with SH ELXTL-PLUS
Rev 3.4, I988 (G. M. Sheldrick, Institut fur Anorganische Chemie der Universitat, Tammanstrasse 4, D-3400 Gottingen, FRG) supplied by Nicolet Analytical X-ray Instruments, Madison, WI, on a pVaxIl minicomputer. Internafional TablesforX-Ray Crystallography, Hahn,T., Ed; D. Reidel Publishing Co.: Dordrecht, Holland, 1987; VoI. A. pp 39, 101-709. International TablesforX-Ray Crystallography, Ibers, J. A,, Hamilton, W. D., Eds.; Kynoch Press: Birmingham, England, 1974; Vol. IV. p 149. Larson. A. C. Acra Crystallogr. 1967, A23, 604. Martell, A. E.; Motekaitis, R. J. Determination and Use ofSlability Constants, VCH Publishers: New York. 1988.
Table 11. UV-Visible and Infrared Spectral Results UV-vis, nm M-l cm-I)
comulex
(e.
ReO?(cyclam)+ ReO(OH)(cyclam)2+ Re02(01cyclam) ReO(OH)(Olcyclam)+ R e o ( 0zcyclam)Cl KBr pellets.
/I
440 (16), 284 (1049), 258 (466) 646 (12), 482 (16) 446 (17) 648 (12), 490 (37), 280 (1060) not measured
IRO v,,(ReO), cm-I 772 969 77 1 952,908* 912
v,,(ReO) for R e o 4
method of Martell and Motekaitis (program BEST)26was utilized to compute the value of K, for the equilibrium: K,
R e 0 2 L + + H + == ReO(OH)L2+
Results Synthesisand Characterizationof Metal Complexes. The transReo2+and trans-ReO(OH)+ macrocyclic complexes are readily prepared by ligand displacement reactions between the appropriate macrocycle and the starting complexes Re02(en)2Cl, ReOC13(PPh&, R e 0 ~ 1 ( P P h ~and ) ~ ,“Re(V)
