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A preconstrained tricyclic biimidazoline ligand adaptable to diverse coordination modes
Inorganic Chemistry Communications 3 Ž2000. 648–652 www.elsevier.nlrlocaterinoche
A preconstrained tricyclic biimidazoline ligand adaptable to diverse coordination modes Daniel W. Widlicka a , Edward H. Wong a,) , Gary R. Weisman a , Kim-Chung Lam b, Roger D. Sommer b, Christopher D. Incarvito b, Arnold L. Rheingold b a
b
Department of Chemistry, UniÕersity of New Hampshire, Durham, NH 03824, USA Crystallography Laboratory, Department of Chemistry and Biochemistry, UniÕersity of Delaware, Newark, DE 19716, USA Received 19 July 2000
Abstract The tricyclic biimidazoline ligand L possesses a preconstrained synperiplanar bisamidine N s C–C s N and has been shown to have a versatile coordination chemistry. In its manganeseŽII. tris-chelate complex wMnL 3 xŽClO4 . 2 , a distorted trigonal prismatic coordination geometry is adopted. By contrast, a square–planar copperŽII. complex, wCuL 3 xŽClO4 . 2 features one chelating as well as two monodentate L’s. In a third variation, an exclusively a-diimine-bridged dicopper unit is found in both the copperŽI. wCu 2 L 3 xŽBF4 . 2 and copperŽII. wCu 2 L 4 xŽClO4 .4 dimeric complexes. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Biimidazoline ligand; Dicopper complexes; Bridging mode; ManganeseŽII. complex
1. Introduction Diimine and bicyclic a-diimine ligands like 2,2’-bipyridine, 2,2’-bisimidazole, and 2,2’-bisoxazoline ligands are of great importance in coordination, biomimetic, and catalytic chemistry as well as photophysics w1–4x. Bicyclic bisamidines such as 2,2’-biimidazoline ŽBiim. are reported to have an interesting variety of coordination modes in both neutral and anionic forms w5,6x. We report here syntheses and structural studies of the first coordination complexes of a tricyclic biimidazoline, L, Ž2,3,5,6,8,9hexahydrodiimidazow1,2-a:2’,1’-cxpyrazine. which presage an extensive metal complexation chemistry for this family of ligands.
) Corresponding author. Tel.: q1-603-862-1788; fax: q1-603-8624278. E-mail addresses: [email protected] ŽE.H. Wong., [email protected] ŽG.R. Weisman..
Ligand L, readily prepared by condensation of triethylenetetraamine and dithiooxamide, is the immediate precursor in an efficient synthesis of 1,4,7,10 tetraazacyclododecane ŽCyclen. previously reported by one of us w7x. Presence of the six-membered ring preconstrains the a-diimine unit of the bisamidine linkage to a synperiplanar arrangement, free L Ž C2 . having a N s C`C s N torsion angle of 138 by DFT calculation ŽpBPrDN ) ) rrpBPr DN ) ) .1. However, constrained DFT calculations at the same level of theory show that this torsion angle can be
1
Density functional theory ŽDFT. calculations on L were carried out by the perturbative Becke-Perdew method w8,9x using the DN ) ) numerical basis set as implemented in Spartan V5.1.3, Wavefunction, Inc., 18401 Von Karman, Suite 370, Irvine, CA 92612, USA.
1387-7003r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 Ž 0 0 . 0 0 1 5 3 - 2
D.W. Widlicka et al.r Inorganic Chemistry Communications 3 (2000) 648–652
649
varied over the whole synperiplanar range Ž0 " 308. with an energetic cost of - 2 kcalrmol. This flexibility within a preconstrained range endows L with both metal chelating and syn-bridging coordination ability. Absence of readilydeprotonated amidine NH groups in L also avoids complications from amidinate complex formation.
under reduced pressure to give 75.8 mg of a brown powder Ž35.3% yield.. A volume of 5 ml of MeCN was added to give a brown solution. After three days of ether diffusion, brown crystals grew from this solution. IR ŽKBr pellet.: 1617Žm., 1535Žm., 1285Žm., 1092Žs. cmy1 . Anal. Calcd. for Cu 2 ŽC 8 H 12 N4 .4ŽClO4 .4 : C, 32.52; H, 4.09; N, 18.96%. Found: C, 32.55 H, 4.04; N, 18.91%.
2. Experimental
2.4. Synthesis of [Cu 2 L 3 ](BF4 )2
The biimidazoline ligand L was prepared as described in reference w7x. All other reagents and NMR solvents were obtained commercially and used without further purification. Reactions were performed in standard Schlenk apparatus under nitrogen atmosphere. Recrystallizations were performed in closed containers without special precautions to exclude air or moisture.
An amount of CuŽMeCN.4 BF4 Ž54 mg, 0.228 mmol. and ligand L Ž61.3 mg, 0.374 mmol. were combined in a Schlenk flask under nitrogen. A volume of 15 mL of absolute MeOH was added upon which the reactants dissolved to form a yellow solution. The solution was evaporated to dryness under reduced pressure to give a bright yellow powder. X-ray crystals were grown by ether diffusion into a MeOH solution of this product. IR ŽKBr pellet.: 1614Žs., 1525Žs., 1367Žs., 1284Žs., and 1051Žs. cmy1 . Anal. Calcd for Cu 2 ŽC 8 H 12 N4 . 3 ŽBF4 . 2 : C, 36.34; H, 4.57; N, 21.29. Found: C, 36.21; H, 4.50; N, 21.06%.
2.1. Synthesis of [MnL 3 ](ClO4 )2 An amount of MnŽClO4 . 2 Ø 6H 2 O Ž43.9 mg, 0.121 mmol. and ligand L Ž61.6 mg, 0.375 mmol. were combined in a Schlenk flask. A volume of 10 mL of abs EtOH was then injected into the reaction flask. The reactants dissolved upon stirring and a yellow precipitate soon formed. After 1 h, the supernatant was decanted off and the remaining solid washed with additional EtOH. The precipitate was dried under reduced pressure to give 39.5 mg Ž0.0539 mmol, 43.4% yield. of the product MnŽC 8 H 12 N4 . 3 ŽClO4 . 2 . This was recrystallized from acetonitrile by slow ether diffusion. Light yellow prismatic crystals were harvested. IR ŽKBr pellet.: 1644Žs., 1565Žs., 1364Žs., 1280Žs. and 1091Žs. cmy1 . Anal. Calcd. for MnŽC 8 H 12 N4 . 3 ŽClO4 . 2 : C, 38.62; H, 4.86; N, 22.52 %. Found: C, 38.50; H, 4.81; N, 22.31%.
2.5. Structure determination Details of the crystals, data collection, structural determination for the four X-ray structures are deposited with the Cambridge Crystallographic Data Centre Žsee Supplementary material section..
3. Results and discussion Reaction of MnŽClO4 . 2Ø6H 2 O with three equivalents of L in absolute ethanol gave a yellow precipitate which can
2.2. Synthesis of [CuL 3 ](ClO4 )2 An amount of CuŽClO4 . 2 Ø 6H 2 O Ž45.2 mg, 0.122 mmol. and slightly more than three equivalents of ligand L Ž66.5 mg, 0.405 mmol. were combined in a Schlenk flask. A volume of 5 mL of MeCN was added whereupon there was an immediate color change to forest green as the starting materials dissolved. The product CuŽC 8 H 12 N4 . 3ŽClO4 . 2 crystallized from solution after slow diethylether diffusion as dark green needles. IR ŽKBr pellet.: 1677Žm., 1649Žm., 1611Žm., 1527Žm., 1365Žm., 1280Žs., 1097Žs. cmy1 . Anal. Calcd. for CuŽC 8 H 12 N4 . 3 ŽClO4 . 2 : C, 38.18; H, 4.81; N, 22..26%. Found: C, 38.05; H, 5.01; N, 22.15%. 2.3. Synthesis of [Cu 2 L 4 ](ClO4 )4 An amount of CuŽClO4 . 2 Ø 6H 2 O Ž57.3 mg, 0.182 mmol. and ligand L Ž51.1 mg, 0..311 mmol. were combined in a Schlenk flask. A volume of 5mL of MeOH was injected with immediate formation of a brown precipitate. The supernatant was decanted off and the residue dried
Fig. 1. Molecular structure of wMnL 3 xŽClO4 . 2 showing atomic labeling scheme. Hydrogens and perchlorates are omitted for clarity. Selected ˚ . and angles Ž8.: MnŽ1. ` NŽ1. 2.289Ž2., MnŽ1. ` NŽ3. bond distances ŽA 2.266Ž2., MnŽ1. ` NŽ5. 2.292Ž2., NŽ1. ` CŽ1. 1.278Ž3., NŽ2. ` CŽ1. 1.347Ž3., NŽ3. ` CŽ6. 1.287Ž3., NŽ4. ` CŽ6. 1.326Ž3., NŽ5. ` CŽ9. 1.281 Ž3 ., N Ž6 . ` C Ž 9 . 1.332 Ž 3 . , N Ž 3 . ` Mn Ž1 . ` N Ž1 . 75.66 Ž 8 . , NŽ5. ` MnŽ1. ` NŽ5A. 75.24Ž11., NŽ1A. ` MnŽ1. ` NŽ3A. 75.66Ž8..
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D.W. Widlicka et al.r Inorganic Chemistry Communications 3 (2000) 648–652
Fig. 2. Molecular structure of wCuL 3 xŽClO4 . 2 showing atomic labeling scheme. Hydrogens and perchlorates have been omitted for clarity. Selected bond ˚ . and angles Ž8.: CuŽ1.`NŽ9. 1.966Ž3., CuŽ1.`NŽ5. 1.967Ž3., CuŽ1.`NŽ1. 2.040Ž3., CuŽ1.`NŽ2. 2.068Ž3., NŽ1.`CŽ7. 1.291Ž5., NŽ3.`CŽ7. distances ŽA 1.317Ž5., NŽ2.`CŽ8. 1.286Ž5., NŽ4.`CŽ8. 1.339Ž5., NŽ5.`CŽ15. 1.283Ž5., NŽ7.`CŽ15. 1.366Ž5., NŽ6.`CŽ16. 1.287Ž5., NŽ8.`CŽ16. 1.357Ž5., NŽ9.`CŽ23. 1.292Ž5., NŽ11.`CŽ23. 1.352Ž5., NŽ10.`CŽ24. 1.277Ž5., NŽ12.`CŽ24. 1.377Ž5., NŽ1.`CuŽ1.`NŽ2. 82.18Ž12., NŽ1.`CuŽ1.`NŽ5. 89.26Ž13., NŽ2.`CuŽ1.`NŽ9. 93.22Ž13., NŽ5.`CuŽ1.`NŽ9. 96.18Ž13..
be recrystallized from acetonitrile and ether to give lightyellow rhombic crystals 2 . Analytical data are consistent with formation of the expected wMnL 3 xŽClO4 . 2 complex. This product’s IR spectrum contains coordinated C s N stretches at 1644 and 1565 cmy1 compared with the free ligand value of 1620 cmy1 . The X-ray structure of the complex is shown in Fig. 13. With a twist angle of 248 down the pseudo C3 axis, the coordination geometry around the manganese center is almost midway between trigonal, prismatic Žtwist angle 08. and octahedral Žtwist angle 608. with an average chelate bite angle of 768. An average N s C`C s N torsion angle at the coordinated a-diimines of only 1.68 indicates nearly planar chelate rings. No tris-biim complex of MnŽII. has been characterized structurally, though wFeŽbiim. 3 xŽClO4 . 2 is reported to have a distorted octahedral coordination geometry w6x. In addition,
2
Caution! Perchlorate salts of metal complexes are potentally explosive. Although no detonations of the described salts have occurred in our laboratories, cautious handling of only small quantities is recommended. 3 Crystal data for wMnL 3 xŽClO4 . 2 : C 24 H 36 Cl 2 MnN12 O 8 , M s 746.49, space group monoclinic C2r c, as18.138Ž2., bs10.0709Ž9., cs ˚ b s93.602Ž2.8, V s 3078.8Ž5. A˚ 3, Z s 4, T s173Ž2.K, 16.888Ž2. A, Dc s1.610 g cm -3 , m ŽMoK a . s6.72 cm -1 , final Rs 5.12% for 2965 observed independent reflections.
Fig. 3. Molecular structure of wCu 2 L 4 xŽClO4 .4 showing atomic labeling scheme. Hydrogens and non-coordinating perchlorates have been omitted ˚ . and angles Ž8.: CuŽ1. ` NŽ1. for clarity. Selected bond distances ŽA 1.977Ž3., CuŽ1. ` NŽ3. 1.996Ž3., CuŽ1. ` NŽ5. 1.989Ž3., CuŽ1. ` NŽ7. 1.985Ž3., CuŽ1. Ø Ø Ø CuŽ1A. 2.7746Ž9., NŽ1. ` CŽ1. 1.290Ž5., NŽ2. ` CŽ1. 1.341Ž4., NŽ3. ` CŽ5. 1.300Ž5., NŽ4. ` CŽ5. 1.336Ž5., NŽ5. ` CŽ9. 1.301Ž4., NŽ6. ` CŽ9. 1.337Ž5., NŽ7. ` CŽ13. 1.302Ž4., NŽ8. ` CŽ13. 1.333Ž4., NŽ1. ` CuŽ1. ` NŽ7. 89.08Ž12., NŽ1. ` CuŽ1. ` NŽ5. 177.84Ž12., N Ž 1 . ` Cu Ž 1 . ` N Ž 3 . 90.07 Ž 13 . , N Ž 3 . ` Cu Ž 1 . ` N Ž 5 . 91.21 Ž 12 . , NŽ3. ` CuŽ1. ` NŽ7. 178.67Ž13., NŽ5. ` CuŽ1. ` NŽ7. 89.61Ž12..
D.W. Widlicka et al.r Inorganic Chemistry Communications 3 (2000) 648–652
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Fig. 4. Views down the copper-copper axes in the dimeric structures of: Ža. wCu 2 L 4 xŽClO4 .4 , and Žb. wCu 2 L 3 xŽBF4 . 2 showing the diimine ligand twist angles.
˚ substanthe average Mn`N bond length here is 2.29 A, ˚ even ` tially longer than the Fe N distance of 2.18 A, ˚ Ž . Ž allowing for the larger ionic radius of Mn II 0.97 A ˚ Ž . . compared to Fe II ’s 0.92 A . For comparison, the six Mn–N distances in wMnŽbipyridyl. 3 xŽClO4 . 2 average to ˚ w10x. 2.24 A When CuŽClO4 . 2Ø6H 2 O was reacted with three equivalents of L in acetonitrile, a green solution was obtained from which dark-green crystals of wCuII L 3 xŽClO4 . 2 were obtained after ether diffusion2 . Its IR spectrum contains C s N stretches at 1677, 1649, 1611, and 1527 cmy1 , suggesting multiple coordination modes. Indeed, the X-ray structure of this complex reveals its copperŽII. center in a severely Jahn–Teller distorted tetragonal geometry featuring one chelating and two monodentate ligands in the equatorial plane ŽFig. 2. 4 . The sum of equatorial cis N`Cu`N bond angles around CuŽII. is 3618. Two imino nitrogens, NŽ6. and NŽ10., are positioned at elongated ˚ and 2.807Ž3. A˚ from the metal apical sites 2.844Ž3. A center respectively. The chelate bite angle is 82.2Ž1.8 and ˚ slightly longer than its Cu`N distances average 2.05 A, ˚ the average monodentate Cu`N bond length of 1.97 A. In a 2:1 stoichiometry, L and CuŽClO4 . 2Ø6H 2 O gave brown crystals from acetonitrile after ether diffusion2 . An
X-ray study revealed the dimeric wCu 2 L 4 xŽClO4 .4 complex shown in Fig. 3 5. The four bridging ligands adopt a pseudo-C4 propeller arrangement down the Cu`Cu axis. Each copperŽII. is square pyramidal with four imine N’s forming the basal plane Ž cis N`Cu`N angles sum to ˚ The 3608. and an axial perchlorate oxygen at 2.400Ž3. A. ˚ Ž . metal–metal separation is 2.775 1 A. The twist angles, as defined by the orientation of the two Cu square planes around the Cu`Cu axis, average to 428 in an almost perfectly staggered conformation Ž08 for eclipsed and 458 for staggered. ŽFig. 4a.. This twisting is also mirrored within each bridging ligand. The average diimine N s C`C s N torsion angle is 22.48. A search of the Cambridge Structural Database yielded few precedents of metal dimers bridged exclusively by a-diimines. A binucleating octaaza-cryptand engulfing a copper dimer at several oxidation states within its cavity has been characterized and studied w11–13x. One polymeric dicopper bisoxazoline complex has been reported though bromides also bridge within and between these dimeric units w14x. Treatment of CuŽMeCN.4 BF4 with 1.5 equivalents of L in acetonitrile gave a yellow solution. Recrystallization of the product from acetonitrilerether yielded yellow crystals
4 Crystal data for wCuL 3 xŽClO4 . 2 : C 24 H 36 Cl 2 CuN12 O 8 , M s 755.09, space group monoclinic P21 21 21 , as9.1556Ž9., bs17.116Ž2., cs ˚ V s 3154.1Ž6. A˚ 3, Z s 4, T s173Ž2.K, Dc s1.590 g cm -3, 20.128Ž2. A, m?ŽMoK a . s 0.930 mm -1 , final Rs 4.98% for 7060 observed independent reflections.
5 Crystal data for wCu 2 L 4 xŽClO4 .4 : C 32 H 48 Cl 4 Cu 2 N16 O16 , M s 1181.74, space group monoclinic C2r c, as19.948Ž2., bs14.014Ž1., ˚ b s109.078Ž2.8, V s 4589.7Ž13. A˚ 3, Z s 4, T s cs17.373Ž2. A, 173Ž2.K, Dcs 1.710 g cm -3 , m ŽMoK a ?s1.247 mm -1 , final Rs 4.01% for 4164 observed independent reflections.
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D.W. Widlicka et al.r Inorganic Chemistry Communications 3 (2000) 648–652
In addition to the four complexes described here, we also have preliminary data for the CoŽII., NiŽII., ZnŽII., CrŽCO.4 , MoŽCO.4 , and WŽCO.4 complexes of L w18x. Further explorations into the scope of the coordination and reaction chemistry of this promising class of ligands are in progress.
4. Supplementary material
Fig. 5. Molecular structure of wCu 2 L 3 xŽBF4 . 2 showing atomic labeling scheme. Hydrogens and tetrafluoroborates have been omitted for clarity. ˚ . and angles Ž8.: CuŽ1. ` NŽ1. 1.957Ž4., Selected bond distances ŽA Cu Ž1 . ` N Ž3 . 1.967 Ž3 ., Cu Ž1 . ` N Ž5 . 1.973 Ž4 ., Cu Ž1 . Ø Ø Ø Cu Ž1A . 2.5264Ž10., NŽ1. ` CŽ3. 1.301Ž5., NŽ2. ` CŽ3. 1.363Ž6., NŽ3. ` CŽ7. 1.290Ž6., NŽ4. ` CŽ7. 1.353Ž6., NŽ5. ` CŽ11. 1.302Ž6., NŽ6. ` CŽ11. 1.343Ž6., NŽ1. ` CuŽ1. ` NŽ3. 120.05Ž16., NŽ1. ` CuŽ1. ` NŽ5. 120.58Ž15., N Ž3. ` CuŽ1. ` N Ž5. 116.02Ž16., N Ž1. ` CuŽ1. ` CuŽ1A . 94.80Ž10., NŽ3. ` CuŽ1. ` CuŽ1A. 97.13Ž11., NŽ5. ` CuŽ1. ` CuŽ1A. 96.42Ž10..
analyzing as wCuI2 L 3 xŽBF4 . 2 . Its dimeric structure is shown in Fig. 5 6 . The two nearly trigonal planar copper centers are spanned by three ligand bridges with these two coordination planes at an average twist angle of 168 Ž08 for eclipsed and 608 for staggered. about the Cu Ø Ø Ø Cu axis ˚ ŽFig. 4b.. A copper–copper separation of only 2.526Ž1. A is found, which is shorter than that in metallic copper Ž2.56 ˚ ., though the existence of CuŽI.`CuŽI. bonding interacA tion remains controversial w15–17x. Within each chelate, the a-diimine torsion angle is only 7.78, substantiating the ability of L to adapt to different metal Ø Ø Ø metal separations through this conformational pliancy.
6 Crystal data for wCu 2 L 3 xŽBF4 . 2 : C 24 H 36 B 2 Cu 2 F8 N12 , M s 793.34, space group monoclinic C2r c, as18.23812., bs10.0477Ž7., cs ˚ b s92.659Ž1.8, V s 3092.3Ž4. A˚ 3, Z s 4, T s173Ž2.K, 16.892Ž1. A, Dc s1.704 g cm -3 , m ŽMoK a . s1.466 mm -1 , final Rs6.33% for 3473 observed independent reflections.
Additional details of the crystal structural determinations and data tables have been deposited at the Cambridge Crystallographic Data Centre ŽCCDC Nos. 148389, 148390, 148387, and 149388.. Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK ŽFax: q441223-336-033; e-mail: [email protected] or www: http: rrwww.ccdc.cam.ac.uk..
References w1x G. Van Koten, K. Vrieze, Adv. Organomet. Chem. 21 Ž1982. 151. w2x J. Reedjik, in: G. Wilkins, R.D. Gillard, J.A McCleverty ŽEds.., Comprehensive Coordination Chemistry, Pergamon, Oxford, 1986, p. 73, vol. 2. w3x E.C Constable, Adv. Inorg. Chem 34 Ž1989. 1. w4x E.C Constable, P.J. Steel, Coord. Chem. Rev. 93 Ž1989. 205. w5x J. Barker, M. Kilner, Coord. Chem. Rev. 133 Ž1994. 219. w6x J.P. Roth, S. Lovell, J.M. Mayer, J. Am. Chem. Soc. 122 Ž2000. 5486. w7x G.R. Weisman, D.P. Reed, J. Org. Chem. 61 Ž1996. 5186, Correction: J. Org. Chem. 62 Ž14. Ž1997. 4548. w8x A.D. Becke, Phys. Rev. A: At. Mol. Opt. Phys. 38 Ž1988. 3089. w9x J.P. Perdew, Phys. Rev. B: Condens. Matter 33 Ž1986. 8822. w10x X.-M. Chen, R.-Q. Wang, Z.-T. Xu, Acta Cryst. C 51 Ž1995. 820. w11x C. Harding, V. McKee, J. Nelson, J. Am. Chem. Soc. 133 Ž1991. 9684. w12x J.A Farrar, V. McKee, A.H.R. Al-Obaidi, J.J. McGravey, Nelson, A.J. Thompson, Inorg. Chem. 34 Ž1995. 1302. w13x A. Al-Obaidi, G. Baranovic, J. Coyle, C.G. Coates, J.J. McGarvey, V. McKee, J. Nelson, Inorg. Chem. 37 Ž1998. 3567. w14x D.M. Haddleton, D.J. Duncalf, A.J. Clark, M.C. Crossman, D. Kukulj, New J. Chem. 1 Ž1998. 315. w15x P.K. Mehrota, R. Hoffmann, Inorg. Chem. 17 Ž1978. 2187. w16x F.A. Cotton, X. Feng, M. Matsuz, R. Poli, J. Am. Chem. Soc. 110 Ž1988. 7077. w17x K.M. Merz, R. Hoffmann, Inorg. Chem. 27 Ž1988. 2120. w18x D.W. Widlicka, University of New Hampshire, unpublished results.
A preconstrained tricyclic biimidazoline ligand adaptable to diverse coordination modes Daniel W. Widlicka a , Edward H. Wong a,) , Gary R. Weisman a , Kim-Chung Lam b, Roger D. Sommer b, Christopher D. Incarvito b, Arnold L. Rheingold b a
b
Department of Chemistry, UniÕersity of New Hampshire, Durham, NH 03824, USA Crystallography Laboratory, Department of Chemistry and Biochemistry, UniÕersity of Delaware, Newark, DE 19716, USA Received 19 July 2000
Abstract The tricyclic biimidazoline ligand L possesses a preconstrained synperiplanar bisamidine N s C–C s N and has been shown to have a versatile coordination chemistry. In its manganeseŽII. tris-chelate complex wMnL 3 xŽClO4 . 2 , a distorted trigonal prismatic coordination geometry is adopted. By contrast, a square–planar copperŽII. complex, wCuL 3 xŽClO4 . 2 features one chelating as well as two monodentate L’s. In a third variation, an exclusively a-diimine-bridged dicopper unit is found in both the copperŽI. wCu 2 L 3 xŽBF4 . 2 and copperŽII. wCu 2 L 4 xŽClO4 .4 dimeric complexes. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Biimidazoline ligand; Dicopper complexes; Bridging mode; ManganeseŽII. complex
1. Introduction Diimine and bicyclic a-diimine ligands like 2,2’-bipyridine, 2,2’-bisimidazole, and 2,2’-bisoxazoline ligands are of great importance in coordination, biomimetic, and catalytic chemistry as well as photophysics w1–4x. Bicyclic bisamidines such as 2,2’-biimidazoline ŽBiim. are reported to have an interesting variety of coordination modes in both neutral and anionic forms w5,6x. We report here syntheses and structural studies of the first coordination complexes of a tricyclic biimidazoline, L, Ž2,3,5,6,8,9hexahydrodiimidazow1,2-a:2’,1’-cxpyrazine. which presage an extensive metal complexation chemistry for this family of ligands.
) Corresponding author. Tel.: q1-603-862-1788; fax: q1-603-8624278. E-mail addresses: [email protected] ŽE.H. Wong., [email protected] ŽG.R. Weisman..
Ligand L, readily prepared by condensation of triethylenetetraamine and dithiooxamide, is the immediate precursor in an efficient synthesis of 1,4,7,10 tetraazacyclododecane ŽCyclen. previously reported by one of us w7x. Presence of the six-membered ring preconstrains the a-diimine unit of the bisamidine linkage to a synperiplanar arrangement, free L Ž C2 . having a N s C`C s N torsion angle of 138 by DFT calculation ŽpBPrDN ) ) rrpBPr DN ) ) .1. However, constrained DFT calculations at the same level of theory show that this torsion angle can be
1
Density functional theory ŽDFT. calculations on L were carried out by the perturbative Becke-Perdew method w8,9x using the DN ) ) numerical basis set as implemented in Spartan V5.1.3, Wavefunction, Inc., 18401 Von Karman, Suite 370, Irvine, CA 92612, USA.
1387-7003r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 Ž 0 0 . 0 0 1 5 3 - 2
D.W. Widlicka et al.r Inorganic Chemistry Communications 3 (2000) 648–652
649
varied over the whole synperiplanar range Ž0 " 308. with an energetic cost of - 2 kcalrmol. This flexibility within a preconstrained range endows L with both metal chelating and syn-bridging coordination ability. Absence of readilydeprotonated amidine NH groups in L also avoids complications from amidinate complex formation.
under reduced pressure to give 75.8 mg of a brown powder Ž35.3% yield.. A volume of 5 ml of MeCN was added to give a brown solution. After three days of ether diffusion, brown crystals grew from this solution. IR ŽKBr pellet.: 1617Žm., 1535Žm., 1285Žm., 1092Žs. cmy1 . Anal. Calcd. for Cu 2 ŽC 8 H 12 N4 .4ŽClO4 .4 : C, 32.52; H, 4.09; N, 18.96%. Found: C, 32.55 H, 4.04; N, 18.91%.
2. Experimental
2.4. Synthesis of [Cu 2 L 3 ](BF4 )2
The biimidazoline ligand L was prepared as described in reference w7x. All other reagents and NMR solvents were obtained commercially and used without further purification. Reactions were performed in standard Schlenk apparatus under nitrogen atmosphere. Recrystallizations were performed in closed containers without special precautions to exclude air or moisture.
An amount of CuŽMeCN.4 BF4 Ž54 mg, 0.228 mmol. and ligand L Ž61.3 mg, 0.374 mmol. were combined in a Schlenk flask under nitrogen. A volume of 15 mL of absolute MeOH was added upon which the reactants dissolved to form a yellow solution. The solution was evaporated to dryness under reduced pressure to give a bright yellow powder. X-ray crystals were grown by ether diffusion into a MeOH solution of this product. IR ŽKBr pellet.: 1614Žs., 1525Žs., 1367Žs., 1284Žs., and 1051Žs. cmy1 . Anal. Calcd for Cu 2 ŽC 8 H 12 N4 . 3 ŽBF4 . 2 : C, 36.34; H, 4.57; N, 21.29. Found: C, 36.21; H, 4.50; N, 21.06%.
2.1. Synthesis of [MnL 3 ](ClO4 )2 An amount of MnŽClO4 . 2 Ø 6H 2 O Ž43.9 mg, 0.121 mmol. and ligand L Ž61.6 mg, 0.375 mmol. were combined in a Schlenk flask. A volume of 10 mL of abs EtOH was then injected into the reaction flask. The reactants dissolved upon stirring and a yellow precipitate soon formed. After 1 h, the supernatant was decanted off and the remaining solid washed with additional EtOH. The precipitate was dried under reduced pressure to give 39.5 mg Ž0.0539 mmol, 43.4% yield. of the product MnŽC 8 H 12 N4 . 3 ŽClO4 . 2 . This was recrystallized from acetonitrile by slow ether diffusion. Light yellow prismatic crystals were harvested. IR ŽKBr pellet.: 1644Žs., 1565Žs., 1364Žs., 1280Žs. and 1091Žs. cmy1 . Anal. Calcd. for MnŽC 8 H 12 N4 . 3 ŽClO4 . 2 : C, 38.62; H, 4.86; N, 22.52 %. Found: C, 38.50; H, 4.81; N, 22.31%.
2.5. Structure determination Details of the crystals, data collection, structural determination for the four X-ray structures are deposited with the Cambridge Crystallographic Data Centre Žsee Supplementary material section..
3. Results and discussion Reaction of MnŽClO4 . 2Ø6H 2 O with three equivalents of L in absolute ethanol gave a yellow precipitate which can
2.2. Synthesis of [CuL 3 ](ClO4 )2 An amount of CuŽClO4 . 2 Ø 6H 2 O Ž45.2 mg, 0.122 mmol. and slightly more than three equivalents of ligand L Ž66.5 mg, 0.405 mmol. were combined in a Schlenk flask. A volume of 5 mL of MeCN was added whereupon there was an immediate color change to forest green as the starting materials dissolved. The product CuŽC 8 H 12 N4 . 3ŽClO4 . 2 crystallized from solution after slow diethylether diffusion as dark green needles. IR ŽKBr pellet.: 1677Žm., 1649Žm., 1611Žm., 1527Žm., 1365Žm., 1280Žs., 1097Žs. cmy1 . Anal. Calcd. for CuŽC 8 H 12 N4 . 3 ŽClO4 . 2 : C, 38.18; H, 4.81; N, 22..26%. Found: C, 38.05; H, 5.01; N, 22.15%. 2.3. Synthesis of [Cu 2 L 4 ](ClO4 )4 An amount of CuŽClO4 . 2 Ø 6H 2 O Ž57.3 mg, 0.182 mmol. and ligand L Ž51.1 mg, 0..311 mmol. were combined in a Schlenk flask. A volume of 5mL of MeOH was injected with immediate formation of a brown precipitate. The supernatant was decanted off and the residue dried
Fig. 1. Molecular structure of wMnL 3 xŽClO4 . 2 showing atomic labeling scheme. Hydrogens and perchlorates are omitted for clarity. Selected ˚ . and angles Ž8.: MnŽ1. ` NŽ1. 2.289Ž2., MnŽ1. ` NŽ3. bond distances ŽA 2.266Ž2., MnŽ1. ` NŽ5. 2.292Ž2., NŽ1. ` CŽ1. 1.278Ž3., NŽ2. ` CŽ1. 1.347Ž3., NŽ3. ` CŽ6. 1.287Ž3., NŽ4. ` CŽ6. 1.326Ž3., NŽ5. ` CŽ9. 1.281 Ž3 ., N Ž6 . ` C Ž 9 . 1.332 Ž 3 . , N Ž 3 . ` Mn Ž1 . ` N Ž1 . 75.66 Ž 8 . , NŽ5. ` MnŽ1. ` NŽ5A. 75.24Ž11., NŽ1A. ` MnŽ1. ` NŽ3A. 75.66Ž8..
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D.W. Widlicka et al.r Inorganic Chemistry Communications 3 (2000) 648–652
Fig. 2. Molecular structure of wCuL 3 xŽClO4 . 2 showing atomic labeling scheme. Hydrogens and perchlorates have been omitted for clarity. Selected bond ˚ . and angles Ž8.: CuŽ1.`NŽ9. 1.966Ž3., CuŽ1.`NŽ5. 1.967Ž3., CuŽ1.`NŽ1. 2.040Ž3., CuŽ1.`NŽ2. 2.068Ž3., NŽ1.`CŽ7. 1.291Ž5., NŽ3.`CŽ7. distances ŽA 1.317Ž5., NŽ2.`CŽ8. 1.286Ž5., NŽ4.`CŽ8. 1.339Ž5., NŽ5.`CŽ15. 1.283Ž5., NŽ7.`CŽ15. 1.366Ž5., NŽ6.`CŽ16. 1.287Ž5., NŽ8.`CŽ16. 1.357Ž5., NŽ9.`CŽ23. 1.292Ž5., NŽ11.`CŽ23. 1.352Ž5., NŽ10.`CŽ24. 1.277Ž5., NŽ12.`CŽ24. 1.377Ž5., NŽ1.`CuŽ1.`NŽ2. 82.18Ž12., NŽ1.`CuŽ1.`NŽ5. 89.26Ž13., NŽ2.`CuŽ1.`NŽ9. 93.22Ž13., NŽ5.`CuŽ1.`NŽ9. 96.18Ž13..
be recrystallized from acetonitrile and ether to give lightyellow rhombic crystals 2 . Analytical data are consistent with formation of the expected wMnL 3 xŽClO4 . 2 complex. This product’s IR spectrum contains coordinated C s N stretches at 1644 and 1565 cmy1 compared with the free ligand value of 1620 cmy1 . The X-ray structure of the complex is shown in Fig. 13. With a twist angle of 248 down the pseudo C3 axis, the coordination geometry around the manganese center is almost midway between trigonal, prismatic Žtwist angle 08. and octahedral Žtwist angle 608. with an average chelate bite angle of 768. An average N s C`C s N torsion angle at the coordinated a-diimines of only 1.68 indicates nearly planar chelate rings. No tris-biim complex of MnŽII. has been characterized structurally, though wFeŽbiim. 3 xŽClO4 . 2 is reported to have a distorted octahedral coordination geometry w6x. In addition,
2
Caution! Perchlorate salts of metal complexes are potentally explosive. Although no detonations of the described salts have occurred in our laboratories, cautious handling of only small quantities is recommended. 3 Crystal data for wMnL 3 xŽClO4 . 2 : C 24 H 36 Cl 2 MnN12 O 8 , M s 746.49, space group monoclinic C2r c, as18.138Ž2., bs10.0709Ž9., cs ˚ b s93.602Ž2.8, V s 3078.8Ž5. A˚ 3, Z s 4, T s173Ž2.K, 16.888Ž2. A, Dc s1.610 g cm -3 , m ŽMoK a . s6.72 cm -1 , final Rs 5.12% for 2965 observed independent reflections.
Fig. 3. Molecular structure of wCu 2 L 4 xŽClO4 .4 showing atomic labeling scheme. Hydrogens and non-coordinating perchlorates have been omitted ˚ . and angles Ž8.: CuŽ1. ` NŽ1. for clarity. Selected bond distances ŽA 1.977Ž3., CuŽ1. ` NŽ3. 1.996Ž3., CuŽ1. ` NŽ5. 1.989Ž3., CuŽ1. ` NŽ7. 1.985Ž3., CuŽ1. Ø Ø Ø CuŽ1A. 2.7746Ž9., NŽ1. ` CŽ1. 1.290Ž5., NŽ2. ` CŽ1. 1.341Ž4., NŽ3. ` CŽ5. 1.300Ž5., NŽ4. ` CŽ5. 1.336Ž5., NŽ5. ` CŽ9. 1.301Ž4., NŽ6. ` CŽ9. 1.337Ž5., NŽ7. ` CŽ13. 1.302Ž4., NŽ8. ` CŽ13. 1.333Ž4., NŽ1. ` CuŽ1. ` NŽ7. 89.08Ž12., NŽ1. ` CuŽ1. ` NŽ5. 177.84Ž12., N Ž 1 . ` Cu Ž 1 . ` N Ž 3 . 90.07 Ž 13 . , N Ž 3 . ` Cu Ž 1 . ` N Ž 5 . 91.21 Ž 12 . , NŽ3. ` CuŽ1. ` NŽ7. 178.67Ž13., NŽ5. ` CuŽ1. ` NŽ7. 89.61Ž12..
D.W. Widlicka et al.r Inorganic Chemistry Communications 3 (2000) 648–652
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Fig. 4. Views down the copper-copper axes in the dimeric structures of: Ža. wCu 2 L 4 xŽClO4 .4 , and Žb. wCu 2 L 3 xŽBF4 . 2 showing the diimine ligand twist angles.
˚ substanthe average Mn`N bond length here is 2.29 A, ˚ even ` tially longer than the Fe N distance of 2.18 A, ˚ Ž . Ž allowing for the larger ionic radius of Mn II 0.97 A ˚ Ž . . compared to Fe II ’s 0.92 A . For comparison, the six Mn–N distances in wMnŽbipyridyl. 3 xŽClO4 . 2 average to ˚ w10x. 2.24 A When CuŽClO4 . 2Ø6H 2 O was reacted with three equivalents of L in acetonitrile, a green solution was obtained from which dark-green crystals of wCuII L 3 xŽClO4 . 2 were obtained after ether diffusion2 . Its IR spectrum contains C s N stretches at 1677, 1649, 1611, and 1527 cmy1 , suggesting multiple coordination modes. Indeed, the X-ray structure of this complex reveals its copperŽII. center in a severely Jahn–Teller distorted tetragonal geometry featuring one chelating and two monodentate ligands in the equatorial plane ŽFig. 2. 4 . The sum of equatorial cis N`Cu`N bond angles around CuŽII. is 3618. Two imino nitrogens, NŽ6. and NŽ10., are positioned at elongated ˚ and 2.807Ž3. A˚ from the metal apical sites 2.844Ž3. A center respectively. The chelate bite angle is 82.2Ž1.8 and ˚ slightly longer than its Cu`N distances average 2.05 A, ˚ the average monodentate Cu`N bond length of 1.97 A. In a 2:1 stoichiometry, L and CuŽClO4 . 2Ø6H 2 O gave brown crystals from acetonitrile after ether diffusion2 . An
X-ray study revealed the dimeric wCu 2 L 4 xŽClO4 .4 complex shown in Fig. 3 5. The four bridging ligands adopt a pseudo-C4 propeller arrangement down the Cu`Cu axis. Each copperŽII. is square pyramidal with four imine N’s forming the basal plane Ž cis N`Cu`N angles sum to ˚ The 3608. and an axial perchlorate oxygen at 2.400Ž3. A. ˚ Ž . metal–metal separation is 2.775 1 A. The twist angles, as defined by the orientation of the two Cu square planes around the Cu`Cu axis, average to 428 in an almost perfectly staggered conformation Ž08 for eclipsed and 458 for staggered. ŽFig. 4a.. This twisting is also mirrored within each bridging ligand. The average diimine N s C`C s N torsion angle is 22.48. A search of the Cambridge Structural Database yielded few precedents of metal dimers bridged exclusively by a-diimines. A binucleating octaaza-cryptand engulfing a copper dimer at several oxidation states within its cavity has been characterized and studied w11–13x. One polymeric dicopper bisoxazoline complex has been reported though bromides also bridge within and between these dimeric units w14x. Treatment of CuŽMeCN.4 BF4 with 1.5 equivalents of L in acetonitrile gave a yellow solution. Recrystallization of the product from acetonitrilerether yielded yellow crystals
4 Crystal data for wCuL 3 xŽClO4 . 2 : C 24 H 36 Cl 2 CuN12 O 8 , M s 755.09, space group monoclinic P21 21 21 , as9.1556Ž9., bs17.116Ž2., cs ˚ V s 3154.1Ž6. A˚ 3, Z s 4, T s173Ž2.K, Dc s1.590 g cm -3, 20.128Ž2. A, m?ŽMoK a . s 0.930 mm -1 , final Rs 4.98% for 7060 observed independent reflections.
5 Crystal data for wCu 2 L 4 xŽClO4 .4 : C 32 H 48 Cl 4 Cu 2 N16 O16 , M s 1181.74, space group monoclinic C2r c, as19.948Ž2., bs14.014Ž1., ˚ b s109.078Ž2.8, V s 4589.7Ž13. A˚ 3, Z s 4, T s cs17.373Ž2. A, 173Ž2.K, Dcs 1.710 g cm -3 , m ŽMoK a ?s1.247 mm -1 , final Rs 4.01% for 4164 observed independent reflections.
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In addition to the four complexes described here, we also have preliminary data for the CoŽII., NiŽII., ZnŽII., CrŽCO.4 , MoŽCO.4 , and WŽCO.4 complexes of L w18x. Further explorations into the scope of the coordination and reaction chemistry of this promising class of ligands are in progress.
4. Supplementary material
Fig. 5. Molecular structure of wCu 2 L 3 xŽBF4 . 2 showing atomic labeling scheme. Hydrogens and tetrafluoroborates have been omitted for clarity. ˚ . and angles Ž8.: CuŽ1. ` NŽ1. 1.957Ž4., Selected bond distances ŽA Cu Ž1 . ` N Ž3 . 1.967 Ž3 ., Cu Ž1 . ` N Ž5 . 1.973 Ž4 ., Cu Ž1 . Ø Ø Ø Cu Ž1A . 2.5264Ž10., NŽ1. ` CŽ3. 1.301Ž5., NŽ2. ` CŽ3. 1.363Ž6., NŽ3. ` CŽ7. 1.290Ž6., NŽ4. ` CŽ7. 1.353Ž6., NŽ5. ` CŽ11. 1.302Ž6., NŽ6. ` CŽ11. 1.343Ž6., NŽ1. ` CuŽ1. ` NŽ3. 120.05Ž16., NŽ1. ` CuŽ1. ` NŽ5. 120.58Ž15., N Ž3. ` CuŽ1. ` N Ž5. 116.02Ž16., N Ž1. ` CuŽ1. ` CuŽ1A . 94.80Ž10., NŽ3. ` CuŽ1. ` CuŽ1A. 97.13Ž11., NŽ5. ` CuŽ1. ` CuŽ1A. 96.42Ž10..
analyzing as wCuI2 L 3 xŽBF4 . 2 . Its dimeric structure is shown in Fig. 5 6 . The two nearly trigonal planar copper centers are spanned by three ligand bridges with these two coordination planes at an average twist angle of 168 Ž08 for eclipsed and 608 for staggered. about the Cu Ø Ø Ø Cu axis ˚ ŽFig. 4b.. A copper–copper separation of only 2.526Ž1. A is found, which is shorter than that in metallic copper Ž2.56 ˚ ., though the existence of CuŽI.`CuŽI. bonding interacA tion remains controversial w15–17x. Within each chelate, the a-diimine torsion angle is only 7.78, substantiating the ability of L to adapt to different metal Ø Ø Ø metal separations through this conformational pliancy.
6 Crystal data for wCu 2 L 3 xŽBF4 . 2 : C 24 H 36 B 2 Cu 2 F8 N12 , M s 793.34, space group monoclinic C2r c, as18.23812., bs10.0477Ž7., cs ˚ b s92.659Ž1.8, V s 3092.3Ž4. A˚ 3, Z s 4, T s173Ž2.K, 16.892Ž1. A, Dc s1.704 g cm -3 , m ŽMoK a . s1.466 mm -1 , final Rs6.33% for 3473 observed independent reflections.
Additional details of the crystal structural determinations and data tables have been deposited at the Cambridge Crystallographic Data Centre ŽCCDC Nos. 148389, 148390, 148387, and 149388.. Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK ŽFax: q441223-336-033; e-mail: [email protected] or www: http: rrwww.ccdc.cam.ac.uk..
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