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Ainooson, Michael K.

Darkwa, James

Guzei, Ilia A.

Spencer, Lara C.

English

University of Johannesburg Institutional Repository

Intramolecular hydrogen bonding indichloridobis(3,5-di-tert-butyl-1H-pyrazole-jN2)cobalt(II) as aconsequence of ligand steric bulkIlia A. Guzei,a,b* Lara C. Spencer,a Michael K. Ainoosonband James DarkwabaDepartment of Chemistry, University of Wisconsin–Madison, 1101 UniversityAvenue, Madison, WI 53706, USA, and bDepartment of Chemistry, University ofJohannesburg, Auckland Park Kingsway Campus, Auckland Park 2006, South AfricaCorrespondence e-mail: iguzei@chem.wisc.eduReceived 17 August 2010Accepted 8 October 2010Online 21 October 2010The title compound, [CoCl2(C11H20ClN2)2], forms two intra-molecular hydrogen bonds [graph set S(5)] between the Natoms of the pyrazole ligands and the chloride ligands. Thishydrogen-bonding motif is uncommon among relatedcompounds but occurs here because of the bulk of tert-butylsubstituents on the pyrazole ligands which shield the centralmetal atom to a significantly larger extent than pyrazoleligands with smaller 3,5-substituents.CommentPyrazole and pyrazolyl transition metal complexes continue tobe investigated as catalysts in ethylene oligomerization andpolymerization reactions (Ojwach et al., 2010). The ability ofsuch metal complexes to catalyze the formation ofpolyethylene depends on the electrophilicity and steric bulk ofthe catalysts. Both of these factors are usually dictated by thenature and size of substituents on the pyrazolyl unit. However,in the polymer catalysts bis(pyrazole) nickel (Nelana et al.,2004), pyrazole palladium (Li et al., 2002) and pyrazolylpalladium complexes (Guzei et al., 2003; Mohlala et al., 2005)the high electrophilic metal centers ensure rapid insertionregardless of the steric bulk of these catalysts. In an extensionof this study, we prepared the title compound, (I), which hadappreciably lower catalytic activity than its nickel and palla-dium analogues.The coordination geometry of the Co atom in (I) isdistorted tetrahedral (Fig. 1). The metric parameters for bonddistances and angles about the cobalt center are similar tothose in six related compounds where a Co atom binds to twomonodentate chloride ligands and two monodentate substi-tuted pyrazole ligands (Table 1) [Cambridge StructuralDatabase (CSD), Version 1.12, August 2010 update; Allen,2002; the actual compounds are specified below]. However theN1—Co1—N3 angle in (I) is significantly larger and fallsoutside of the range of measurements for the relatedcompounds in the CSD. This larger than expected angle can beattributed to the two intramolecular hydrogen bonds in (I)absent in similar compounds.In complex (I), there are two intramolecular hydrogenbonds of the type N—H  Cl formed between the pyrazoleand chloride ligands. It has been shown that Cl atoms coor-dinated to transition metals may act as moderately stronghydrogen-bond acceptors (Aullo´n et al., 1998). But in the caseof (I), the hydrogen bonds are considered weak because of thesuboptimal N—H  Cl angles averaging 130.0 (13) (Table 2).These intramolecular hydrogen-bonding interactions aredescribed with the graph set S(5) (Bernstein et al., 1995).Compared to the six related compounds in the CSD, (I) isthe only compound that forms exactly two intramolecularS(5) N(pz)—H  Cl hydrogen bonds. Three compoundsincluding dichlorobis(3,5-dimethylpyrazole)cobalt(II) (CSDrefcode FUFVUX02; Guzei & Spencer, 2006), bis{di-chloro[2-bis(3,5-dimethyl-4-pyrazolyl)methane]cobalt(II)}ethanol solvate (CAFXIQ; Foces-Foces et al., 1983) and di-chlorobis(3,5-diethyl-4-methyl-1H-pyrazole)cobalt(II) (DEM-PCO10; Agre et al., 1978) form two intermolecular N(pz)—H  Cl hydrogen bonds with the graph set R22(10). Anotherrelated compound, dichlorobis(3-methyl-5-phenylpyrazol-2-yl)cobalt(II) (SEHTUU; Verweij et al., 1989), forms only oneintramolecular N(pz)—H  Cl S(5) hydrogen bond but cannotform a second intramolecular hydrogen bond with the otherpyrazole N-atom donor. The other N(pz)—Cl distance is toolong and the N(pz)—H  Cl angle too acute for SEHTUU toform two S(5) intramolecular bonds as in (I). The protonatedpyrazole N atom on the two remaining related compoundsforms inter- and intramolecular hydrogen bonds with O and Natoms in side chains of the pyrazole rings, respectively [CSDrefcodes FOYWEW (Leovac et al., 2007) and YOCYAR (Caiet al., 2008)].The fact that (I) forms two intramolecular N(pz)—H  Clhydrogen bonds is likely responsible for the larger thanaverage N—Co—N angle as the Cl—Co—N angles involved inthe five-membered hydrogen-bonded rings are significantlysmaller [99.93 (10) and 100.78 (11); ignoring the minordisordered position for Cl2] than the ideal tetrahedral angle.Compound (I) is believed to form the intramolecular ratherthan intermolecular N(pz)—H  Cl hydrogen bonds, seem-metal-organic compoundsm336 # 2010 International Union of Crystallography doi:10.1107/S0108270110040412 Acta Cryst. (2010). C66, m336–m338Acta Crystallographica Section CCrystal StructureCommunicationsISSN 0108-2701ingly more popular among related compounds, because thebulky tert-butyl pyrazole substituents in the 3,5-positionsprevent molecules of (I) from approaching each other closeenough to form intermolecular bonds. To substantiate this lineof reasoning, we calculated the G-parameters and sizes of thepyrazole ligands in (I) and the six aforementioned complexes.The G-parameter (computed with the program Solid-G;Guzei, 2006) is the percentage of the coordination sphere ofthe central metal shielded by the ligand (Guzei & Wendt,2006). This methodology is based on solid angles and is illu-strated in Fig. 2. Each ligand ‘casts a shadow’ on a sphere of anarbitrary radius centered at the Co atom, and the percentageof the sphere shielded by each ligand is its G-parameter. It hasbeen shown that even small (2–3%) changes in the G-para-meters can lead to substantial changes in the mutual ligandarrangement (Fukin et al., 2007). The ligand size is representedby the volume of the smallest parallelepiped circumscribingthe free ligand as computed with the WBOX routine in theprogram OLEX2 (Dolomanov et al., 2009). This approach hasbeen previously applied to alkali metal complexes of nonactin(Guzei et al., 2009). Table 3 summarizes the geometriccomputations. The average G-parameter of the pyrazoleligands in (I) is significantly larger at 25.0 (5)% than that inany of the related compounds. Thus, the approach of adjacentcomplex molecules to the Cl ligands and formation of inter-molecular bonds are hampered. The average pyrazole ligandvolume in (I) is substantially larger than that for all relatedcompounds, except for 3,5-dimethyl-4-pyrazolylmethane(Table 3). However, whereas the volume of 3,5-dimethyl-4-pyrazolylmethane is larger than that for (I), this ligand formsan elongated chain directed away from the central Co atom.Consequently, it does not crowd the central Co atom as muchas 3,5-bis-tert-butylpyrazole does in (I), as evidenced by thelargerG-parameter of the latter. It appears that the type of thehydrogen bonds in dipyrazole–dichloride complexes of CoII isdictated by the ligand steric parameters.ExperimentalA solution of CoCl2 (0.58 g, 4.45 mmol) and tert-butylpyrazole(1.60 g, 4.44 mmol) in CH2Cl2 (20 ml) was stirred at room tempera-ture for 18 h. The resultant blue solution was reduced to about 10 ml,followed by the addition of about 5 ml of hexane. The solution waskept at 269 K for a day to produce blue crystals suitable for X-raycrystallography (yield 1.40 g, 64%). Analysis calculated for C22H40-Cl2CoN4: C 62.99, H 9.61, N 13.36%; found: C 62.60, H 9.70, N13.55%.Crystal data[CoCl2(C11H20ClN2)2]Mr = 490.41Monoclinic, P21=na = 12.483 (4) A˚b = 17.516 (7) A˚c = 12.604 (4) A˚ = 90.22 (2)V = 2755.9 (17) A˚3Z = 4Cu K radiation = 6.76 mm1T = 296 K0.45  0.30  0.30 mmData collectionBruker SMART APEXIIarea-detector diffractometerAbsorption correction: analytical(SADABS; Bruker, 2007)Tmin = 0.151, Tmax = 0.23644217 measured reflections5156 independent reflections4195 reflections with I > 2(I)Rint = 0.030RefinementR[F 2 > 2(F 2)] = 0.068wR(F 2) = 0.205S = 1.065156 reflections271 parameters65 restraintsH-atom parameters constrainedmax = 0.72 e A˚3min = 0.41 e A˚3metal-organic compoundsActa Cryst. (2010). C66, m336–m338 Guzei et al.  [CoCl2(C11H20ClN2)2] m337Figure 2A diagram of the solid angles of (I), which shows the shielding of the Coatom by the various ligands. (Color key for the electronic version of thepaper: pyrazole ligands are shown as red and green, and chloride ligandsare yellow.)Figure 1The molecular structure of (I) drawn with 50% probability displacementellipsoids. All H atoms attached to C atoms and the minor components ofdisordered atoms have been omitted for clarity. Atoms C9–C14 andC20–C22 were refined isotropically. The two intramolecular hydrogenbonds are shown with dashed lines.The crystals of (I) do not survive thermal shock and shatter whenimmersed in a cold stream of nitrogen at either 100, 150, 200 or 250 K;thus, the crystal structure was determined at room temperature.There is positional disorder in the structure of (I). Atom Cl2 isdisordered over two positions with a 79 (2)% major componentcontribution. The tert-butyl groups at atoms C8 and C15 are disor-dered over two positions with 60.8 (7) and 59.7 (13)% majorcomponent contributions. The tert-butyl group at atom C19 is disor-dered over three positions in a 40.9 (6):34.1 (7):25.0 (7)% ratio. In thedisordered tert-butyl groups, all 1–2 distances were restrained to1.538 (2) A˚ and 1–3 distances to 2.512 (2) A˚. The isotropic displace-ment parameters of the methyl C atoms of each disordered tert-butylgroup were constrained to be the same. The distances between the Coatom and both positions of the disordered Cl2 atom were restrainedto be the same within 0.002 A˚ and the anisotropic displacementparameters of atoms Cl2 and Cl2A were constrained to be the same.All H atoms were placed in idealized positions, with N—H distancesof 0.86 A˚, Csp2—H distances of 0.93 A˚ and Csp3—H distances of0.96 A˚. All H atoms were refined as riding with displacement para-meters of Uiso(H) = 1.2Ueq(parent atoms) for all N—H and Csp2—Hgroups and 1.5Ueq(parent atoms) for all Csp3—H groups.Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT(Bruker, 2007); data reduction: SAINT; program(s) used to solvestructure: SHELXTL (Sheldrick, 2008); program(s) used to refinestructure: SHELXTL and FCF_filter (Guzei, 2007); moleculargraphics: SHELXTL, DIAMOND (Brandenburg, 1999) and OLEX2(Dolomanov et al., 2009); software used to prepare material forpublication: SHELXTL, publCIF (Westrip, 2010) and modiCIFer(Guzei, 2007).Supplementary data for this paper are available from the IUCr electronicarchives (Reference: KU3032). Services for accessing these data aredescribed at the back of the journal.ReferencesAgre, V. M., Krol, I. A., Trunov, V. K., Ivanov, O. V. & Dziomko, V. M. (1978).Koord. Khim. 4, 1603–1607.Allen, F. H. (2002). Acta Cryst. B58, 380–388.Aullo´n, G., Brammer, L., Bruton, E. 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Molecular StructureLaboratory, University of Wisconsin–Madison, Madison, Wisconsin, USA.Guzei, I. A., Li, K., Bhikzanova, G., Darkwa, J. & Mapolie, S. F. (2003).DaltonTrans. pp. 715–722.Guzei, I. A. & Spencer, L. C. (2006). Private communication.Guzei, I. A., Wang, C., Zhan, Y., Dolomanov, O. V. & Cheng, Y.-Q. (2009).Acta Cryst. C65, o521–o524.Guzei, I. A. & Wendt, M. (2006). Dalton Trans. pp. 3991–3999.Leovac, V. M., Tomic, Z. D., Szecsenyi, K. M., Jovanovic, L. S. & Joksovic, M.D. (2007). J. Serb. Chem. Soc. 72, 1281–1293.Li, K., Darkwa, J., Guzei, I. A. & Mapolie, S. F. (2002). J. Organomet. Chem.660, 108–115.Mohlala, S. M., Guzei, I. A., Darkwa, J. &Mapolie, S. F. (2005). J. Mol. Catal. AChem. 241, 93–100.Nelana, S. M., Darkwa, J., Guzei, I. A. & Mapolie, S. F. (2004). J. Organomet.Chem. 689, 1835–1842.Ojwach, S. O. & Darkwa, J. (2010). Inorg. Chim. Acta, 363, 1947–1964.Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.Verweij, P. D., Rietmeijer, F. J., De Graaff, R. A. 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C66, m336–m338Table 1Comparison of bond lengths (A˚) and angles () of (I) with six related compounds in the CSD.Co—Cl Co—N Cl—Co—Cl N—Co—N Cl—Co—N Angle between pyrazolering planesCompound (I) average (including disordered atoms) 2.269 (2) 2.036 (15) 109 (9) 121.93 (13) 107 (8) 89.93 (13)Six related compounds in CSD average 2.243 (14) 2.011 (14) 116 (4) 106 (5) 109 (7) 77 (11)Six related compounds in CSD range 2.222–2.283 1.992–2.049 108.32–122.82 97.40–116.07 98.61–119.93 59.34–89.83Table 2Hydrogen-bond geometry (A˚, ).D—H  A D—H H  A D  A D—H  AN2—H2  Cl2 0.86 2.52 3.131 (4) 129N2—H2  Cl2A 0.86 2.46 3.099 (13) 131N4—H4  Cl1 0.86 2.48 3.103 (4) 130Table 3Solid angle and WBOX volume measurements for the pyrazole ligands of(I) and related compounds.See Comment for CSD refcode references.Compound G-parameteraverage (%)WBOX volumeaverage (A˚3)3,5-Di-tert-butylpyrazole, (I) 25.0 (5) 487 (2)3,5-Dimethylpyrazole, FUFVUX02 21.11 (18) 205 (6)2-Bis(3,5-dimethylpyrazol-4-yl)-methane, CAFXIQ21.5 (7) 600 (40)3,5-Diethyl-4-methyl-1H-pyrazole,DEMPCO1022.35 (16) 400 (30)3-Methyl-5-phenylpyrazol-2-yl,SEHTUU20.7 (6) 317 (18)1-(3-Amino-5-methyl-1H-pyrazol-4-yl)ethanone, FOYWEW20.60 289.1223,5-Dimethyl-1H-pyrazol-4-amine-N2, YOCYAR20.69 (8) 241 (8)

Intramolecular hydrogen bonding in dichloridobis(3,5-di-tert-butyl-1Hpyrazole-kN²)cobalt(II) as a consequence of ligand steric bulk

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Intramolecular hydrogen bonding in dichloridobis(3,5-di-tert-butyl-1Hpyrazole-kN²)cobalt(II) as a consequence of ligand steric bulk

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