- Email: [email protected]
Synthesis and characterization of new dinuclear complexes of molybdenum(V) with β′-hydroxy-β-enaminones
www.elsevier.com/locate/ica Inorganica Chimica Acta 328 (2002) 23 – 32
Synthesis and characterization of new dinuclear complexes of molybdenum(V) with b%-hydroxy-b-enaminones Marina Cindric´ a,*, Visˇnja Vrdoljak a, Tanja Kajfezˇ a, Predrag Novak b,1, Ana Brbot-S& aranovic´ c, Neven Strukan a, Boris Kamenar a a
Laboratory of General and Inorganic Chemistry, Chemistry Department, Faculty of Science, Uni6ersity of Zagreb, Ulica kralja Z6onimira 8, POB 153, 10000 Zagreb, Croatia b Laboratory of Analytical Chemistry, Chemistry Department, Faculty of Science, Uni6ersity of Zagreb, Strossmayero6 trg 14, 10000 Zagreb, Croatia c Department of Chemistry, Veterinary Faculty, Uni6ersity of Zagreb, Heinzelo6a 55, 10000 Zagreb, Croatia Received 18 June 2001; accepted 28 August 2001
Abstract New dinuclear molybdenum(V) complexes have been obtained by the reaction of [Mo2O3(acac)4] (acac=acetilacetonate ion) with the polydentate ligands, b%-hydroxy-b-enaminones. All prepared complexes consist of Mo2O42 + core coordinated by two ligands as in the b-diketonates only through two donor oxygen atoms. Such bonding gives the opportunity for the sixth coordination place around molybdenum to be completed by the monodentate solvent molecule D. All compounds have been characterized by means of elemental analyses, one- and two-dimensional NMR spectroscopy, IR spectroscopy as well as by thermal analyses. The molecular and crystal structures of the molybdenum(V) complexes 1a and 1b coordinated by two different isomeric ligands as well as of the isomer a itself have been determined by a single crystal X-ray diffraction method. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Molybdenum(V) complexes; p-Anisidine; Enaminone; 4-Hydroxy-2-pyrone; NMR; Crystal structures
1. Introduction The metal complexes with 2-pyrone derivatives are topic of increasing interest in the coordination and bioinorganic chemistry [1 – 5]. The interest in these complexes derives from the possibility that they can couple to biological substrates, such as proteins, enzymes, nucleic acids etc. giving fluorescent stains suitable for immunoassay procedures and cytological investigations. A series of 4-hydroxy-2-pyrone templates has received also a considerable attention as potential HIV protease
* Corresponding author. Tel.: +385-1-460 6653; fax: +385-1-461 1191. E-mail address: [email protected] (M. Cindric´). 1 Present address: PLIVA Pharm. Inc., Research and Development, Prilaz Baruna Filipovic´a 25, 10000 Zagreb, Croatia.
inhibitors owing to the interaction of the pyrone ring and enzyme active site [6]. Similarly, the heteroconjugated systems such as b%-hydroxy-b-enaminones are of interest when studying the correlation of their steric, electronic and hydrogen bonding effects with their possible relevance in biological processes [7,8]. The enaminone derivatives of 4-hydroxy-2-pyrones are also known as good complexing agents used, for example, as very sensitive and selective reagents for spectrofluorometric determination of beryllium [9]. Furthermore, while such complexes of copper(II) are investigated as models for better understanding of the biological interaction between flavonoides and copper ions [10], the chiral manganese(III) complexes with enaminones are used as catalysts for aerobic enantioselective epoxidation of prochiral non-functionalized olefins [11]. As an extension to our previous work on the structural chemistry of molybdenum complexes with nitro-
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 6 6 6 - 1
24
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
gen, oxygen and sulfur donor ligands, we report here novel complexes obtained by the reaction of [Mo2O3(acac)4] with ligands derived from different enaminones containing 4-hydroxy-2-pyrone ring (Scheme 1) [12–14]. The reactions with such polydentate ligands are also of our interest in establishing which of the donor atoms (oxygen or nitrogen) will be preferred and therefore coordinated to molybdenum. It appears that all prepared complexes are of the general formula [Mo2O4L2D2], where ligand L is coordinated through two oxygen atoms (as in the case b-diketonates), and D is a neutral monodentate ligand (in our case solvent molecule). Although a large number of molybdenum(V) complexes containing didentate ligands have been known, relatively few complexes with b-diketonate (or b-diketonate like) ligands have been synthesized and structurally characterized so far. The structures in these molybdenum complexes are built up from dinuclear complexes such as in: (i) [Mo2O4(dbm)2(morph)2]· morph [15]; (ii) [Mo2O3(acac)3(Sacac)] [16]; (iii) [Mo2O3(acac)2(Sacac)2] [16]; (iv) [Mo2Cl4O2(hfa)2] [17], (v) [Mo2O3(acac)2(fta)2] [18]; and (vi) [Mo2O3(fta)4] [19]; from tetranuclear complexes as in (i) [Mo4O6S2(acac)2(OSCR)2]; and (ii) [Mo4O6S2(ba)2(OSCR)2] [20] and finally from hexanuclear complex molecules as found in R[Mo6O12(OCH3)4(acac)3] [21]. The molecular structures of molybdenum(V) complexes (1a and 1b) with two different isomers: ethyl 4 - hydroxy - 3 - [3 - (4 - methoxyanilino) - 2 - butenoyl] - 2Hpyran-2-on-6-carboxylate (a) and ethyl 4-(4-hydroxy-6methyl-2H-pyran-2-on-3-yl)-2-(4-methoxyanilino)-4oxo-2-butenoate (b) as well as of one isomer a itself have been determined by a single crystal X-ray diffraction method. The complexes have also been characterized by means of chemical analyses, high-resolution NMR spectroscopy, and IR spectroscopy as well as by thermal analyses.
2. Experimental All chemicals and solvents were of reagent grade and used as purchased. The starting acetylacetonato complex [Mo2O3(acac)4] was prepared as described in the literature [15,22]. Ethyl 2-hydroxy-4-(4-hydroxy-6methyl-2H-pyran-2-on-3-yl)-4-oxo-2-butenoate (ehmpb) and two isomeric enaminones a and b (Scheme 2) were prepared according to the literature procedures [12–14]. C, H and N analyses were provided by the Analytical Services Laboratory of Rudjer Bosˇkovic´ Institute, Zagreb. Molybdenum was determined according to the method described in literature [23]. Infrared spectra were recorded in KBr with an FTIR 1600 Fourier transform spectrophotometer in the 4500–450 cm − 1 region. Thermogravimetric (TG) analyses were measured on a Mettler TG 50 thermobalance using aluminum crucibles under oxygen atmosphere with a heating rate of 5 °C min − 1. For all experiments the temperature ranged from 30 to 600 °C. The results were developed by applying the GRAFVARE 2.1. program.
2.1. General procedures for the synthesis of complexes [Mo2O3(acac)4] (0.25 g, 0.4 mmol) was suspended in dry dichloromethane (25 mL) and appropriate ligand (0.4 mmol) was added. The mixture was gently warmed for 0.5 h, the solution was filtered and alcohol (30 mL) added to the filtrate. Upon standing at room temperature (r.t.) for 5–10 days the obtained orange–red crystalline product was filtered off, washed with cold alcohol and dried. All prepared complexes are of the general formula [Mo2O4L2D2], where ligand L is deprotonated isomer a (complexes 1a, 2a and 3a) or b (complexes 1b, 2b and 3b) and ligand D is methanol (1a and 1b), ethanol (2a and 2b) or i-propanol (3a and 3b). Elemental analysis, yields (based on [Mo2O3(acac)4]) and selected IR data are given in Table 1. Thermal analysis data are given in Table 2.
Scheme 1.
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
25
Scheme 2. Table 1 Analytical and IR data for ligands and [Mo2O4L2D2] complexes Formula Mr
Compound
Analysis found (calc.) %C
C19H19O7N 373.56 C40H44Mo2N2O20 1064.658 C42H48Mo2N2O20 1092.712 C44H52Mo2N2O20 1120.765
a b 1a 1b 2a 2b 3a 3b
61.12 61.19 44.91 45.16 45.84 45.98 46.92 46.95
%H (61.12) (61.12) (45.13) (45.13) (46.16) (46.16) (47.15) (47.15)
5.36 5.37 4.10 4.11 4.21 4.32 4.57 4.47
%N (5.13) (5.13) (4.17) (4.17) (4.43) (4.43) (4.68) (4.68)
3.73 3.65 2.70 2.74 2.60 2.67 2.75 2.55
Yield (%)
Selected IR data (cm−1)
55 25 42 59 52 71 65 50
1724, 1655, 1578, 1508 1728, 1646, 1574, 1512 1724, 1654, 1570, 1506, 963, 719 1721, 1645, 1578, 1507, 960, 736 1725, 1655, 1572, 1508, 959, 717 1725, 1641, 1577, 1510, 957, 736 1722, 1655, 1570, 1509, 951, 720 1710, 1650, 1578, 1506, 960, 736
%Mo (3.75) (3.75) (2.63) (2.63) (2.56) (2.56) (2.50) (2.50)
17.75 17.83 17.33 17.23 16.95 17.31
(18.02) (18.02) (17.56) (17.56) (17.12) (17.12)
Table 2 Thermoanalytical data for [Mo2O4L2D2] complexes Formula
[Mo2O4(C19H18O7N)2(CH3OH)2] [Mo2O4(C19H18O7N)2(CH3CH2OH)2] [Mo2O4(C19H18O7N)2{(CH3)2CHOH}2]
Complex
1a 1b 2a 2b 3a 3b
Solvent loss
Decomposition
Temperature range (°C)
Dm (%) found (calc.)
95–158 83–157 92–144 112–160 86–144 116–164
5.79 5.85 7.96 7.85 10.52 10.40
2.2. NMR spectra NMR spectra were recorded on a Bruker Avance DRX500 spectrometer operating at 500.13 MHz for 1H, equipped with a 5 mm diameter inverse detection probe and z-gradient accessory. 1H NMR experiments were acquired with spectral width of 11 000 Hz, 65 K data points and 16 scans. Chemical shifts were determined with respect to TMS as an internal standard. A 30 mg amount of samples was dissolved in 1.0 ml of acetoned6. The digital resolution was 0.1 Hz per point. In 13C APT NMR spectra the spectral width was 31 500 Hz, number of data points 65 K and number of scans 2500– 7000 per spectrum. The digital resolution was 0.5 Hz per point.
(6.02) (8.43) (10.72)
Temperature range (°C)
Dm (%) found (calc.)
189–518 170–533 190–520 170–531 188–519 174–530
67.15 67.24 65.48 65.02 63.25 63.78
(66.94) (65.23) (63.60)
Two-dimensional DQF COSY spectra were obtained using 11 000 Hz spectral windows in both domains, 2 K data points in the time domain and 512 increments for each data set with linear prediction and zero filling to 2 K. A relaxation delay was 1.5 s. Spectra were processed with sine weighting functions. The digital resolution was 3.3 Hz per point in both f1 and f2 domains and the number of scans was four. HSQC and HMBC spectra were recorded with a relaxation delay of 1.5 s and eight scans per increment. The spectral width was 31 000 Hz in acquisition domain f2 and 11 000 Hz in time domain f1. Data were collected into 2048×256 acquisition matrix and processed using a 2×1 K transformed matrix with zero filling in f1 domain. Sine multiplication was performed prior to
26
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
Fourier transformations. In HMBC spectra the delay for long range couplings was set to 60 ms.
2.3. X-ray crystallography Single crystal of isomer a suitable for X-ray structure analysis was obtained by slow evaporation from CH3CN solution. The crystals of the complexes 1a and 1b were grown by slow evaporation of the solutions obtained from the above-described preparations. Intensity data for structures a and 1a were collected at 200 K on a Nonius Kappa CCD diffractometer and data for structure 1b were collected at r.t. on Philips PW1100 diffractometer updated by STOE, in both cases with graphite-monochromatized Mo Ka radiation (u= 0.7107 A, ). Intensity data for a and 1a were reduced using DENZO programme [24], for 1b using X-RED [25]. The structures of all compounds were solved by Patterson and Fourier methods using SHELXS-97 [26] and refined by full matrix least squares method assuming anisotropic temperature factors for all non-H atoms using SHELXL-97 [27] programs. Hydrogen atoms attached to carbon atoms in all structures were generated on geometrical grounds. Hydrogen atoms H1 (bonded to N1) and H34 (between O3 and O4) in structure a were found in a difference Fourier map and their positions were refined, while hydrogen atoms H1 (bonded to N1) and H8 (bonded to O8) in structures 1a and 1b were also found in a difference Fourier map but their coordinates were not refined.
Crystal parameters, data collection details and the results of refinements are summarized in Table 3. Selected bond lengths and angles are listed in Table 4, while the values for hydrogen bonds are given in Table 5. All calculations were performed on an IBM THINKPAD microcomputer (Pentium II processor, 300 MHz). The molecular structure drawings were prepared using ORTEP [28] and PLATON [29].
3. Results and discussion
3.1. Synthesis and characterization of complexes We have recently published syntheses and structures of several isomeric enaminones obtained by the reaction of ethyl 2-hydroxy-4-(4-hydroxy-6-methyl-2H-pyran-2on-3-yl)-4-oxo-2-butenoate (ehmpb) and corresponding amines [12–14]. Analogously, the reaction of ehmpb with p-anisidine results in the formation of two isomers (Scheme 2): a, (2-pyrone ring with ethoxycarbonyl group at position 6) and b, (2-pyrone ring with methyl group at position 6). The reaction of [Mo2O3(acac)4] with polydentate b%-hydroxy-b-enaminones containing 4-hydroxy-2-pyrone ring (in CH2Cl2 and alcohol) yields new molybdenum(V) complexes of the general formula [Mo2O4L2D2] with ligands coordinated to molybdenum through two oxygen atoms and not through nitrogen atom (Scheme 1). These results are in agreement with previous studies of molybdenum complexes with nitrogen and oxygen
Table 3 Crystallographic data for a, 1a and 1b
Empirical formula Formula weight Temperature (K) Crystal system Color Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) i (°) V (A, 3) Z Dcalc (g cm−3) v (cm−1) Crystal size (mm) Data measured Unique data Observed data [I\2|(I)] Number of variables R(Fo) wR(F o2) Max/min Zz (e A, −3)
a
1a
1b
C19H19NO7 373.35 200 monoclinic yellow P21/n
Mo2O4(C20H22NO8)2 1064.65 200 monoclinic red I2/a
Mo2O4(C20H22NO8)2 1064.65 293 monoclinic dark red C2/c
18.223(4) 5.1930(10) 19.388(4) 104.12(3) 1779.3(6) 4 1.394 1.07 0.25×0.27×0.43 5772 3119 2278 256 0.0526 0.1344 0.334 and −0.291
15.115(3) 14.530(3) 18.922(4) 95.16(3) 4138.83 4 1.709 6.94 0.30×0.35×0.52 7156 3660 3017 296 0.0285 0.0627 0.358 and −0.442
17.563(3) 15.955(2) 17.211(3) 116.641(11) 4347.1(10) 8 1.631 6.66 0.28×0.33×0.40 4895 4895 3430 294 0.0427 0.1207 1.029 and −0.623
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32 Table 4 (Continued)
Table 4 Selected bond lengths and angles for a, 1a and 1b a Bond lengths (A, ) Mo(1)Mo(1) a Mo(1)O(11) Mo(1)O(12) Mo(1)O(12) a Mo(1)O(3) Mo(1)O(4) Mo(1)O(8) O(1)C(6) O(1)C(2) O(2)C(2) O(3)C(4) O(3)H(34) O(4)C(7) O(4)H(34) O(5)C(10) O(5)C(11) O(6)C(10) O(7)C(16) O(7)C(19) N(1)C(9) N(1)C(13) N(1)H(1) C(1)C(9) C(1)C(6) C(2)C(3) C(3)C(4) C(3)C(7) C(4)C(5) C(5)C(6) C(6)C(10) C(9)C(10) C(7)C(8) C(8)C(9) Bond angles (°) Mo(1)O(12)Mo(1) a O(11)Mo(1)O(12) O(11)Mo(1)O(12) a O(12)Mo(1)O(12) a O(11)Mo(1)O(3) O(11)Mo(1)O(4) O(12)Mo(1)O(3) O(12)Mo(1)O(4) O(3)Mo(1)O(4) O(12) aMo(1)O(3) O(12) aMo(1)O(4) C(7)O(4)Mo(1) C(4)O(3)Mo(1) C(4)O(3)H(34) C(7)O(4)H(34) C(9)N(1)C(13) C(9)N(1)H(1) C(13)N(1)H(1) C(4)C(3)C(7) O(3)C(4)C(3) O(3)C(4)C(5) O(4)C(7)C(8) O(4)C(7)C(3) C(8)C(7)C(3) C(9)C(8)C(7)
1a
1b
2.549(1) 1.678(2) 1.925(2) 1.931(2) 2.089(2) 2.164(2) 2.212(2)
2.556(1) 1.691(2) 1.923(3) 1.948(2) 2.088(2) 2.152(2) 2.241(3)
1.358(3) 1.398(3) 1.209(3) 1.306(3) 1.25(4) 1.297(3) 1.20(4) 1.315(3) 1.469(4) 1.197(3) 1.370(3) 1.436(3) 1.333(3) 1.432(3) 0.87(3) 1.501(3)
1.355(3) 1.402(3) 1.215(3) 1.288(3)
1.366(4) 1.381(4) 1.222(4) 1.288(4)
1.295(3)
1.279(4)
1.319(3) 1.470(3) 1.201(3) 1.373(3) 1.435(3) 1.340(3) 1.423(3) 0.980 1.498(4)
1.304(5) 1.484(5) 1.199(6) 1.377(6) 1.411(7) 1.344(5) 1.422(5) 0.851
1.437(3) 1.395(3) 1.464(3) 1.430(3) 1.325(3) 1.493(3)
1.440(4) 1.411(4) 1.471(4) 1.436(4) 1.326(4) 1.496(4)
1.400(3) 1.384(3)
1.402(4) 1.397(4)
1.529(4) 1.432(4) 1.364(5)
82.8(1) 105.2(1) 107.0(1) 93.9(1) 93.0(1) 161.3(1) 88.0(1) 89.5(1) 75.8(1) 158.6(1) 82.9(1) 142.1(2) 136.9(2)
82.7(1) 106.3(1) 106.6(1) 94.8(1) 94.8(1) 157.2(1) 85.9(1) 94.6(1) 77.3(1) 157.4(1) 80.1(1) 137.5(2) 134.1(2)
131.8(2) 112.3 115.7 120.3(2) 127.3(2) 114.6(2) 118.0(2) 117.4(2) 124.6(2) 125.0(2)
130.7(3) 115.1 113.3 121.2(3) 124.5(3) 116.5(3) 116.5(3) 120.1(3) 123.5(3) 124.8(3)
100.3(15) 105.0(16) 125.2(2) 115.1(19) 119.2(2) 121.6(2) 118.2(2) 119.9(2) 116.3(2) 123.8(2) 125.9(2) 124.1(2)
27
1.477(5) 1.448(4) 1.427(4) 1.445(5) 1.433(5) 1.335(5)
N(1)C(9)C(8) N(1)C(9)C(1) N(1)C(9)C(10) a
117.8(2) 126.2(2)
121.3(2) 120.6(2)
125.6(3) 121.2(3)
−x+1/2, y, −z+1 for 1a and −x+1, y, −z+1/2 for 1b.
donor ligands [30,31]. Such bonding gives the opportunity for the sixth coordination place around molybdenum to be completed by the monodentate solvent molecule D. The presence of methanol, ethanol and i-propanol in all complexes is in accordance with the analytical and spectral data (Table 1) as well as with the thermogravimetric analyses (Table 2). As shown in Table 2, all complexes showed similar thermal behavior. While heated the first weight loss could be attributed to the loss of a coordinated alcohol molecule and conversion into a stable species [Mo2O4L2] with five coordinated molybdenum. Further heating resulted in the solid residues identified as MoO3. The agreement between calculated and experimental mass losses are within experimental errors. The complexes were also characterized by IR spectroscopy (selected spectral data are given in Table 1). Two bands at 1725–1710 cm − 1 and 1650–1655 cm − 1 are attributed to the stretching vibrations of the carbonyl group from the ester COOC2H5 and 2-pyrone, respectively. The stretching frequencies at about 1570 and 1510 cm − 1 attributed to the coordinated C···O groups and to w(C···C) are observed at lower values comparing to those found in a free ligand. The single strong absorption maximum at about 960 cm − 1 belongs to MoO (terminal), while the band at 730–720 cm − 1 to the MoO (bridging) stretching frequencies. The remaining frequencies in the IR spectra are due to the vibrations within ligands. All complexes were orange–red crystalline solids and very soluble in coordinating solvents (e.g. dmf, dmso, picoline and py) in which they undergo substitution reactions. They are soluble in dichloromethane and acetone, slightly soluble in methanol and ethanol.
3.2. NMR spectroscopy 3.2.1. Isomers a and b The chemical shifts observed in the 1H and 13C spectra of both isomers a and b (Scheme 2) are assigned by the combined use of one and two dimensional NMR sequences described in the experimental part. The values listed in Table 6 are comparable to those for the analogous compounds already known in the literature [13,14]. The NMR spectroscopic data confirm the existence of an enamine rather than an imine form, which is also in agreement with the crystal structure determination. Large downfield shifts corresponding to the hydroxyl and amine protons (protons of OH found at
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
28
18.82 and 17.56 ppm and those of NH group at 11.97 and 11.58 ppm, in a and b, respectively) imply the strong intramolecular hydrogen bonding in solution. Furthermore, the observed difference in chemical shifts between signals of OH and NH protons suggests that the hydrogen bond OH···O is stronger than that of NH···O. The signals belonging to protons of OH and NH are significantly broadened which might be indicative for some displacements of protons involved in a tautomeric equilibrium. Attention has been turned also to the endo- and exo-enol enamine tautomeric equilibrium, since both tautomers were found in the crystals of compounds with similar structures [13]. However, the NMR spectroscopic data did not show any doubling of NMR resonances
indicating that the predominant form is most likely the endo-enol form with the hydroxy group at position 4. Additionally, the chemical shifts observed for C-4 and C-7 atoms in 13C NMR spectra of both isomers a and b (C-7 more down-field), confirm the existence of endoenol enamine, but in a fast tautomeric equilibrium, most probably present in this case, the existence of small amounts of an exo-form cannot be excluded. However, this equilibrium is too fast on the NMR time scale for the tautomers to be detected separately so that averaged NMR signals were observed for both forms.
3.2.2. Complexes 1a and 1b Both 1H and 13C NMR spectra (Table 6) confirm the formation of complexes 1a and 1b as proved by the
Table 5 Hydrogen bonding geometry in structures a, 1a and 1b DH···A
d(DH)
d(H···A)
ÚDHA
d(DA)
Symmetry codes
a O4H34···O3 N1H1···O4 N1H1···O3i
1.20(4) 0.87(3) 0.87(3)
1.25(4) 2.03(3) 2.35(3)
158(3) 134(3) 140(3)
2.401(2) 2.711(3) 3.070(3)
(i) −x+1, −y, −z+1
1a N1H1···O4 O8H8···O2ii O8H8···O1ii
0.980 0.959 0.959
1.774 1.744 2.623
138.1 173.8 130.2
2.587(3) 2.699(3) 3.323(3)
(ii) −x+1/2, −y+1/2, −z+1/2
1b N1H1···O4 O8H8···O2iii
0.851 0.876
1.997 1.795
132.3 170.4
2.646(4) 2.663(3)
(iii) −x+1, −y+1, −z+1
Table 6 1 H and 13C chemical shifts (ppm) for the compounds a, 1a, b, 1b in acetone-d6 Compound
a
atom
1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 OH NH
1a
H
13
2.18
21.32 159.80 100.53 180.81 110.87 151.84 185.92 95.42 169.36 159.86 63.22 14.30 131.19 127.72 115.39 159.89 115.39 127.72 55.89
6.81
6.72
4.39 1.37 7.04 7.32 7.32 7.04 3.85 18.82 11.97
C
1
b
H
13
2.07
21.38 160.60 101.96 179.51 113.84 148.39 180.30 97.42 166.31 161.52 62.76 14.46 131.35 126.67 114.38 158.10 114.38 126.67 55.61
6.79
6.49
4.43 1.44 7.09 6.67 6.67 7.09 3.71 11.59
C
1
1b
H
13
2.27
20.31 161.19 98.38 181.79 102.38 168.95 192.23 96.27 154.27 164.58 62.98 13.96 132.96 125.00 115.30 159.19 115.30 125.00 55.86
6.08
7.04
4.18 1.09 7.13 6.97 6.97 7.13 3.81 17.56 11.30
C
1
H
13
2.19
19.76 162.73 99.65 182.52 107.46 163.98 185.56 96.81 152.56 165.03 62.72 14.03 132.58 123.54 114.57 157.81 114.57 123.54 55.52
6.02
6.61
4.18 1.14 6.84 6.67 6.67 6.84 3.78 10.74
C
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
Fig. 1. An
ORTEP
29
drawing of the isomer a showing the intramolecular hydrogen bonds of the type OH···O and NH···O.
crystal structure determination. The upfield shifts of 5.62 and 6.67 ppm observed for C-7 atom in the 13C NMR spectra of both compexes 1a and 1b, respectively, suggest that the ligands are coordinated to molybdenum through the enolic oxygen atom. The coordination induced shift is less pronounced for other neighboring carbon atoms in the complexes and alternates with their deshielding, as a consequence of electron density redistribution after the complexation to molybdenum. The change of chemical shift of the carbon atom at position 4, i.e. the second possible interacting site, is only negligible. However, the absence of signal belonging to proton of OH for both 1a and 1b is in accordance with deprotonation of hydroxyl group as a result of complex formation.
3.3. X-ray analysis 3.3.1. Crystal structure of isomer a The molecular structure of isomer a (Fig. 1) can be described as consisting of three structural fragments: (i) 2-pyrone ring at position 6 substituted by ethoxycarbonyl group; (ii) central enaminone part of molecule; and (iii) N-substituent consisting of phenyl ring with methoxy group at position 4. In crystalline state isomer is in an enamine form (CCNH) with the C8C9 bond length of 1.384(3) A, and C9N1 of 1.333(3) A, . The C9N1C13C14 torsion angle of 60.0(3)° is indicative of a torsion flexibility of N-substituents induced by twisting around single Nsp2Csp3 bond. The bond lengths and angles of the phenyl ring, the ethoxycarbonyl group, as well as of the pyran ring are within expected values [32].
All available OH and NH protons participate in hydrogen bonding (Fig. 2). The difference Fourier map exhibits only one possible position of H34 atom at almost the same distance from O3 and O4 (O3···H34 1.25(4) A, and O4···H34 1.20(4) A, ). Thus, six-membered ring formed in b-diketone fragment is stabilized by the resonance assisted with OH···O hydrogen bond of very short distance O3···O4 of 2.401(2) A, . Consequently, the O3C4 and O4C7 bond distances of 1.306(3) and 1.297(3) A, are longer than keto CO (1.21 A, ) and shorter than Csp2OH (1.33 A, ) bond distances [32]. The other six-membered ring (enamine fragment), is formed through the NH···O intramolecular hydrogen bond of d(N1···O4) =2.711(3) A, ). Two molecules, related by inversion center, are connected through moderately strong intermolecular NH···O hydrogen bond, d(N1···O3i)= 3.070(3) A, . In such a way discrete dimers, lying in a ac plane, form an eight-membered ring containing three-center hydrogen bonds.
3.3.2. Crystal structures of complexes 1a and 1b The structures of complexes 1a and 1b are shown in Figs. 3 and 4, respectively. Both structures of complex molecules with [Mo2O4]2 + cores have crystallographically imposed twofold symmetry axes. Six oxygen atoms in the form of a distorted octahedron coordinate each molybdenum atom with the angles at molybdenum atom ranging from 82.7(1) to 107.0(1)° in 1a and 82.7(1) to 106.6(1)° in 1b. The MoO bond lengths of 1.678(2) A, in 1a and 1.691(2) A, in 1b are of usual values for molybdenum to terminal oxygen bond lengths. The two bridging MoO bond lengths are 1.925(2) and 1.931(2) A, in 1a and 1.923(3) and 1.948(2)
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
30
A, in 1b. Two MoO bonds with the oxygen atoms from the didentate ligand amount to 2.089(2) and 2.164(2) A, in 1a and 2.088(2) and 2.152(2) A, in 1b depending upon their positions in the structure, i.e. either cis or trans to
the terminal oxo oxygen atoms. Two MoO bonds with the oxygen atoms from the methanol molecules are 2.211(2) A, in 1a and 2.241(3) A, in 1b. The MoMo distances of 2.549(1) A, in 1a and 2.556(1) A, in 1b
Fig. 2. Packing diagram of the isomer a showing also the intermolecular hydrogen bonds NH···O within pairs of symmetrically related molecules.
Fig. 3. An
ORTEP
view of the dinuclear complex 1a (hydrogen atoms are omitted for clarity).
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
Fig. 4. An
ORTEP
31
view of the dinuclear complex 1b (hydrogen atoms are omitted for clarity).
correspond to a single bond between two molybdenum atoms [33]. In crystalline state ligand is in an enamine form (CCNH) with the C8C9 bond length of 1.397(4) A, in 1a and 1.364(5) A, in 1b. The C9N1C13C14 torsion angles of 25.84(2)° in 1a and 35.2(7)° in 1b are of considerably smaller values compared to that found in the free ligand a. Analogously as in the structure of isomer a, in structures of 1a and 1b the six membered rings are formed in enamine fragments by NH···O hydrogen bonds amounting to 2.587(3) in 1a and 2.646(4) A, and 1b.
References [1] [2] [3] [4] [5] [6]
[7] [8]
4. Supplementary material A full list of crystal data and refinement has been deposited with the Cambridge Crystallographic Data Centre, CCDC nos. 164781– 164783 for compounds 1a, 1b and a, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: + 441223-336-033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
[9] [10] [11] [12] [13] [14] [15]
[16]
Acknowledgements This research was supported by the Ministry of Science and Technology of the Republic of Croatia (Grant No. 119407). We are indebted to BsC Predrag Tepesˇ for performing some NMR experiments. We thank Gerald Giester (Institut fu¨ r Mineralogie und Kristallographie, Geozentrum, Universita¨ t Wien, Althanstraße 14, A1090 Wien, Austria) for data collection.
[17] [18] [19] [20] [21]
J.-C.G. Bu¨ nzli, Inorg. Chim. Acta 139 (1987) 219. W. Horrocks, M. Albin, Prog. Inorg. Chem. 31 (1984) 1. F.S. Richardson, Chem. Rev. 82 (1982) 541. C. Bisi Castellani, O. Carugo, Inorg. Chim. Acta 159 (1989) 157. C. Bisi Castellani, O. Carugo, C. Tomba, A. Invernizzi Gamba, Inorg. Chem. 27 (1988) 3965. S. Thaisrivongs, D.L. Romero, R.A. Tommasi, M.N. Janakiraman, J.W. Strohbach, S.R. Turner, C. Biles, R.R. Morge, P.D. Johnson, P.A. Aristoff, P.K. Tomich, J.C. Lynn, M.M. Horng, K.T. Chong, R.R. Hinshaw, W.J. Howe, B.C. Finzel, K.D. Watenpaugh, J. Med. Chem. 39 (1996) 4630. G. Gilli, V. Bertolasi, V. Ferretti, P. Gilli, Acta Crystallogr., Sect. B 49 (1993) 564. P. Gilli, V. Bertolasi, V. Ferretti, G. Gilli, J. Am. Chem. Soc. 122 (2000) 10405. V. Drevenkar, Z. S& tefanac, A. Brbot, Microchem. J. 21 (1976) 402. O. Carugo, C. Bisi Castellani, M. Rizzi, Polyhedron 9 (1990) 2061. R.I. Kureshy, N.H. Khan, S.H.R. Abdi, P. Iyer, S.T. Patel, Polyhedron 18 (1999) 1773. A. Brbot-S& aranovic´ , B. Katusˇin-Razˇ em, I. Susˇnik, Heterocycles 29 (1989) 1559. A. Brbot-S& aranovic´ , G. Pavlovic´ , M. Cindric´ , Struct. Chem. 11 (2000) 65. A. Brbot-S& aranovic, G. Pavlovic´ , V. Vrdoljak, M. Cindric´ , Croat. Chem. Acta 74 (2001) 441. B. Kamenar, B. Korpar-C& olig, M. Cindric´ , D. Matkovic´ C& alogovic´ , M. Penavic´ , Bull. Chem. Technol. Macedonia 16 (1997) 33. B. Kamenar, B. Korpar-C& olig, M. Penavic´ , M. Cindric´ , J. Crystallogr. Spectrosc. Res. 22 (1992) 391. M.G.B. Drew, K.J. Shanton, Acta Crystallogr., Sect. B 34 (1978) 276. B. Kamenar, B. Korpar-C& olig, M. Penavic´ , Cryst. Struct. Commun. 11 (1982) 1583. E.L. Akhmedov, A.S. Kotel’nikova, P.A. Koz’min, M.D. Surazhskaya, T.B. Larina, Koord. Khim. 13 (1987) 698. M. Cindric´ , D. Matkovic´ -C& alogovic´ , V. Vrdoljak, B. Kamenar, Inorg. Chim. Acta 284 (1999) 223. M. Cindric´ , G. Pavlovic´ , V. Vrdoljak, B. Kamenar, Polyhedron 19 (2000) 1471.
32
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
[22] F.W. Moore, R.E. Rice, Inorg. Chem. 7 (1968) 2510. [23] G.A. Parker, Analytical Chemistry of Molybdenum, SpringerVerlag, New York, 1983. [24] Z. Otwinowski, Proceedings of the CCP4 Study Weekend: Data Collection, Warington, Daresbury Laboratory, UK, 1993. [25] Stoe & Cie, X-RED, Data Reduction Program for Windows, Darmstadt, Germany, 1995. [26] G.M. Sheldrick, SHELXS-97, Program for the Solution of Crystal Structures, University of Go¨ ttingen, Germany, 1997. [27] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures, University of Go¨ ttingen, Germany, 1997.
[28] C.K. Johnson, ORTEP-II, Rep. ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. [29] A.L. Spek, The EUCLID package, in: D. Sayre (Ed.), Computational Crystallography, Clarendon Press, Oxford, 1982, p. 528. [30] B. Kamenar, B. Korpar C& olig, M. Penavic´ , M. Cindric´ , J. Chem. Soc., Dalton Trans. (1990) 1125. [31] E. McCarron III, J.F. Whitney, D.B. Chase, Inorg. Chem. 23 (1984) 3275. [32] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G. Orpen, R.J. Taylor, J. Chem. Soc., Perkin Trans. 2 (1987) S1. [33] F.A. Cotton, Inorg. Chem. 4 (1965) 334.
Synthesis and characterization of new dinuclear complexes of molybdenum(V) with b%-hydroxy-b-enaminones Marina Cindric´ a,*, Visˇnja Vrdoljak a, Tanja Kajfezˇ a, Predrag Novak b,1, Ana Brbot-S& aranovic´ c, Neven Strukan a, Boris Kamenar a a
Laboratory of General and Inorganic Chemistry, Chemistry Department, Faculty of Science, Uni6ersity of Zagreb, Ulica kralja Z6onimira 8, POB 153, 10000 Zagreb, Croatia b Laboratory of Analytical Chemistry, Chemistry Department, Faculty of Science, Uni6ersity of Zagreb, Strossmayero6 trg 14, 10000 Zagreb, Croatia c Department of Chemistry, Veterinary Faculty, Uni6ersity of Zagreb, Heinzelo6a 55, 10000 Zagreb, Croatia Received 18 June 2001; accepted 28 August 2001
Abstract New dinuclear molybdenum(V) complexes have been obtained by the reaction of [Mo2O3(acac)4] (acac=acetilacetonate ion) with the polydentate ligands, b%-hydroxy-b-enaminones. All prepared complexes consist of Mo2O42 + core coordinated by two ligands as in the b-diketonates only through two donor oxygen atoms. Such bonding gives the opportunity for the sixth coordination place around molybdenum to be completed by the monodentate solvent molecule D. All compounds have been characterized by means of elemental analyses, one- and two-dimensional NMR spectroscopy, IR spectroscopy as well as by thermal analyses. The molecular and crystal structures of the molybdenum(V) complexes 1a and 1b coordinated by two different isomeric ligands as well as of the isomer a itself have been determined by a single crystal X-ray diffraction method. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Molybdenum(V) complexes; p-Anisidine; Enaminone; 4-Hydroxy-2-pyrone; NMR; Crystal structures
1. Introduction The metal complexes with 2-pyrone derivatives are topic of increasing interest in the coordination and bioinorganic chemistry [1 – 5]. The interest in these complexes derives from the possibility that they can couple to biological substrates, such as proteins, enzymes, nucleic acids etc. giving fluorescent stains suitable for immunoassay procedures and cytological investigations. A series of 4-hydroxy-2-pyrone templates has received also a considerable attention as potential HIV protease
* Corresponding author. Tel.: +385-1-460 6653; fax: +385-1-461 1191. E-mail address: [email protected] (M. Cindric´). 1 Present address: PLIVA Pharm. Inc., Research and Development, Prilaz Baruna Filipovic´a 25, 10000 Zagreb, Croatia.
inhibitors owing to the interaction of the pyrone ring and enzyme active site [6]. Similarly, the heteroconjugated systems such as b%-hydroxy-b-enaminones are of interest when studying the correlation of their steric, electronic and hydrogen bonding effects with their possible relevance in biological processes [7,8]. The enaminone derivatives of 4-hydroxy-2-pyrones are also known as good complexing agents used, for example, as very sensitive and selective reagents for spectrofluorometric determination of beryllium [9]. Furthermore, while such complexes of copper(II) are investigated as models for better understanding of the biological interaction between flavonoides and copper ions [10], the chiral manganese(III) complexes with enaminones are used as catalysts for aerobic enantioselective epoxidation of prochiral non-functionalized olefins [11]. As an extension to our previous work on the structural chemistry of molybdenum complexes with nitro-
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 6 6 6 - 1
24
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
gen, oxygen and sulfur donor ligands, we report here novel complexes obtained by the reaction of [Mo2O3(acac)4] with ligands derived from different enaminones containing 4-hydroxy-2-pyrone ring (Scheme 1) [12–14]. The reactions with such polydentate ligands are also of our interest in establishing which of the donor atoms (oxygen or nitrogen) will be preferred and therefore coordinated to molybdenum. It appears that all prepared complexes are of the general formula [Mo2O4L2D2], where ligand L is coordinated through two oxygen atoms (as in the case b-diketonates), and D is a neutral monodentate ligand (in our case solvent molecule). Although a large number of molybdenum(V) complexes containing didentate ligands have been known, relatively few complexes with b-diketonate (or b-diketonate like) ligands have been synthesized and structurally characterized so far. The structures in these molybdenum complexes are built up from dinuclear complexes such as in: (i) [Mo2O4(dbm)2(morph)2]· morph [15]; (ii) [Mo2O3(acac)3(Sacac)] [16]; (iii) [Mo2O3(acac)2(Sacac)2] [16]; (iv) [Mo2Cl4O2(hfa)2] [17], (v) [Mo2O3(acac)2(fta)2] [18]; and (vi) [Mo2O3(fta)4] [19]; from tetranuclear complexes as in (i) [Mo4O6S2(acac)2(OSCR)2]; and (ii) [Mo4O6S2(ba)2(OSCR)2] [20] and finally from hexanuclear complex molecules as found in R[Mo6O12(OCH3)4(acac)3] [21]. The molecular structures of molybdenum(V) complexes (1a and 1b) with two different isomers: ethyl 4 - hydroxy - 3 - [3 - (4 - methoxyanilino) - 2 - butenoyl] - 2Hpyran-2-on-6-carboxylate (a) and ethyl 4-(4-hydroxy-6methyl-2H-pyran-2-on-3-yl)-2-(4-methoxyanilino)-4oxo-2-butenoate (b) as well as of one isomer a itself have been determined by a single crystal X-ray diffraction method. The complexes have also been characterized by means of chemical analyses, high-resolution NMR spectroscopy, and IR spectroscopy as well as by thermal analyses.
2. Experimental All chemicals and solvents were of reagent grade and used as purchased. The starting acetylacetonato complex [Mo2O3(acac)4] was prepared as described in the literature [15,22]. Ethyl 2-hydroxy-4-(4-hydroxy-6methyl-2H-pyran-2-on-3-yl)-4-oxo-2-butenoate (ehmpb) and two isomeric enaminones a and b (Scheme 2) were prepared according to the literature procedures [12–14]. C, H and N analyses were provided by the Analytical Services Laboratory of Rudjer Bosˇkovic´ Institute, Zagreb. Molybdenum was determined according to the method described in literature [23]. Infrared spectra were recorded in KBr with an FTIR 1600 Fourier transform spectrophotometer in the 4500–450 cm − 1 region. Thermogravimetric (TG) analyses were measured on a Mettler TG 50 thermobalance using aluminum crucibles under oxygen atmosphere with a heating rate of 5 °C min − 1. For all experiments the temperature ranged from 30 to 600 °C. The results were developed by applying the GRAFVARE 2.1. program.
2.1. General procedures for the synthesis of complexes [Mo2O3(acac)4] (0.25 g, 0.4 mmol) was suspended in dry dichloromethane (25 mL) and appropriate ligand (0.4 mmol) was added. The mixture was gently warmed for 0.5 h, the solution was filtered and alcohol (30 mL) added to the filtrate. Upon standing at room temperature (r.t.) for 5–10 days the obtained orange–red crystalline product was filtered off, washed with cold alcohol and dried. All prepared complexes are of the general formula [Mo2O4L2D2], where ligand L is deprotonated isomer a (complexes 1a, 2a and 3a) or b (complexes 1b, 2b and 3b) and ligand D is methanol (1a and 1b), ethanol (2a and 2b) or i-propanol (3a and 3b). Elemental analysis, yields (based on [Mo2O3(acac)4]) and selected IR data are given in Table 1. Thermal analysis data are given in Table 2.
Scheme 1.
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
25
Scheme 2. Table 1 Analytical and IR data for ligands and [Mo2O4L2D2] complexes Formula Mr
Compound
Analysis found (calc.) %C
C19H19O7N 373.56 C40H44Mo2N2O20 1064.658 C42H48Mo2N2O20 1092.712 C44H52Mo2N2O20 1120.765
a b 1a 1b 2a 2b 3a 3b
61.12 61.19 44.91 45.16 45.84 45.98 46.92 46.95
%H (61.12) (61.12) (45.13) (45.13) (46.16) (46.16) (47.15) (47.15)
5.36 5.37 4.10 4.11 4.21 4.32 4.57 4.47
%N (5.13) (5.13) (4.17) (4.17) (4.43) (4.43) (4.68) (4.68)
3.73 3.65 2.70 2.74 2.60 2.67 2.75 2.55
Yield (%)
Selected IR data (cm−1)
55 25 42 59 52 71 65 50
1724, 1655, 1578, 1508 1728, 1646, 1574, 1512 1724, 1654, 1570, 1506, 963, 719 1721, 1645, 1578, 1507, 960, 736 1725, 1655, 1572, 1508, 959, 717 1725, 1641, 1577, 1510, 957, 736 1722, 1655, 1570, 1509, 951, 720 1710, 1650, 1578, 1506, 960, 736
%Mo (3.75) (3.75) (2.63) (2.63) (2.56) (2.56) (2.50) (2.50)
17.75 17.83 17.33 17.23 16.95 17.31
(18.02) (18.02) (17.56) (17.56) (17.12) (17.12)
Table 2 Thermoanalytical data for [Mo2O4L2D2] complexes Formula
[Mo2O4(C19H18O7N)2(CH3OH)2] [Mo2O4(C19H18O7N)2(CH3CH2OH)2] [Mo2O4(C19H18O7N)2{(CH3)2CHOH}2]
Complex
1a 1b 2a 2b 3a 3b
Solvent loss
Decomposition
Temperature range (°C)
Dm (%) found (calc.)
95–158 83–157 92–144 112–160 86–144 116–164
5.79 5.85 7.96 7.85 10.52 10.40
2.2. NMR spectra NMR spectra were recorded on a Bruker Avance DRX500 spectrometer operating at 500.13 MHz for 1H, equipped with a 5 mm diameter inverse detection probe and z-gradient accessory. 1H NMR experiments were acquired with spectral width of 11 000 Hz, 65 K data points and 16 scans. Chemical shifts were determined with respect to TMS as an internal standard. A 30 mg amount of samples was dissolved in 1.0 ml of acetoned6. The digital resolution was 0.1 Hz per point. In 13C APT NMR spectra the spectral width was 31 500 Hz, number of data points 65 K and number of scans 2500– 7000 per spectrum. The digital resolution was 0.5 Hz per point.
(6.02) (8.43) (10.72)
Temperature range (°C)
Dm (%) found (calc.)
189–518 170–533 190–520 170–531 188–519 174–530
67.15 67.24 65.48 65.02 63.25 63.78
(66.94) (65.23) (63.60)
Two-dimensional DQF COSY spectra were obtained using 11 000 Hz spectral windows in both domains, 2 K data points in the time domain and 512 increments for each data set with linear prediction and zero filling to 2 K. A relaxation delay was 1.5 s. Spectra were processed with sine weighting functions. The digital resolution was 3.3 Hz per point in both f1 and f2 domains and the number of scans was four. HSQC and HMBC spectra were recorded with a relaxation delay of 1.5 s and eight scans per increment. The spectral width was 31 000 Hz in acquisition domain f2 and 11 000 Hz in time domain f1. Data were collected into 2048×256 acquisition matrix and processed using a 2×1 K transformed matrix with zero filling in f1 domain. Sine multiplication was performed prior to
26
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
Fourier transformations. In HMBC spectra the delay for long range couplings was set to 60 ms.
2.3. X-ray crystallography Single crystal of isomer a suitable for X-ray structure analysis was obtained by slow evaporation from CH3CN solution. The crystals of the complexes 1a and 1b were grown by slow evaporation of the solutions obtained from the above-described preparations. Intensity data for structures a and 1a were collected at 200 K on a Nonius Kappa CCD diffractometer and data for structure 1b were collected at r.t. on Philips PW1100 diffractometer updated by STOE, in both cases with graphite-monochromatized Mo Ka radiation (u= 0.7107 A, ). Intensity data for a and 1a were reduced using DENZO programme [24], for 1b using X-RED [25]. The structures of all compounds were solved by Patterson and Fourier methods using SHELXS-97 [26] and refined by full matrix least squares method assuming anisotropic temperature factors for all non-H atoms using SHELXL-97 [27] programs. Hydrogen atoms attached to carbon atoms in all structures were generated on geometrical grounds. Hydrogen atoms H1 (bonded to N1) and H34 (between O3 and O4) in structure a were found in a difference Fourier map and their positions were refined, while hydrogen atoms H1 (bonded to N1) and H8 (bonded to O8) in structures 1a and 1b were also found in a difference Fourier map but their coordinates were not refined.
Crystal parameters, data collection details and the results of refinements are summarized in Table 3. Selected bond lengths and angles are listed in Table 4, while the values for hydrogen bonds are given in Table 5. All calculations were performed on an IBM THINKPAD microcomputer (Pentium II processor, 300 MHz). The molecular structure drawings were prepared using ORTEP [28] and PLATON [29].
3. Results and discussion
3.1. Synthesis and characterization of complexes We have recently published syntheses and structures of several isomeric enaminones obtained by the reaction of ethyl 2-hydroxy-4-(4-hydroxy-6-methyl-2H-pyran-2on-3-yl)-4-oxo-2-butenoate (ehmpb) and corresponding amines [12–14]. Analogously, the reaction of ehmpb with p-anisidine results in the formation of two isomers (Scheme 2): a, (2-pyrone ring with ethoxycarbonyl group at position 6) and b, (2-pyrone ring with methyl group at position 6). The reaction of [Mo2O3(acac)4] with polydentate b%-hydroxy-b-enaminones containing 4-hydroxy-2-pyrone ring (in CH2Cl2 and alcohol) yields new molybdenum(V) complexes of the general formula [Mo2O4L2D2] with ligands coordinated to molybdenum through two oxygen atoms and not through nitrogen atom (Scheme 1). These results are in agreement with previous studies of molybdenum complexes with nitrogen and oxygen
Table 3 Crystallographic data for a, 1a and 1b
Empirical formula Formula weight Temperature (K) Crystal system Color Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) i (°) V (A, 3) Z Dcalc (g cm−3) v (cm−1) Crystal size (mm) Data measured Unique data Observed data [I\2|(I)] Number of variables R(Fo) wR(F o2) Max/min Zz (e A, −3)
a
1a
1b
C19H19NO7 373.35 200 monoclinic yellow P21/n
Mo2O4(C20H22NO8)2 1064.65 200 monoclinic red I2/a
Mo2O4(C20H22NO8)2 1064.65 293 monoclinic dark red C2/c
18.223(4) 5.1930(10) 19.388(4) 104.12(3) 1779.3(6) 4 1.394 1.07 0.25×0.27×0.43 5772 3119 2278 256 0.0526 0.1344 0.334 and −0.291
15.115(3) 14.530(3) 18.922(4) 95.16(3) 4138.83 4 1.709 6.94 0.30×0.35×0.52 7156 3660 3017 296 0.0285 0.0627 0.358 and −0.442
17.563(3) 15.955(2) 17.211(3) 116.641(11) 4347.1(10) 8 1.631 6.66 0.28×0.33×0.40 4895 4895 3430 294 0.0427 0.1207 1.029 and −0.623
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32 Table 4 (Continued)
Table 4 Selected bond lengths and angles for a, 1a and 1b a Bond lengths (A, ) Mo(1)Mo(1) a Mo(1)O(11) Mo(1)O(12) Mo(1)O(12) a Mo(1)O(3) Mo(1)O(4) Mo(1)O(8) O(1)C(6) O(1)C(2) O(2)C(2) O(3)C(4) O(3)H(34) O(4)C(7) O(4)H(34) O(5)C(10) O(5)C(11) O(6)C(10) O(7)C(16) O(7)C(19) N(1)C(9) N(1)C(13) N(1)H(1) C(1)C(9) C(1)C(6) C(2)C(3) C(3)C(4) C(3)C(7) C(4)C(5) C(5)C(6) C(6)C(10) C(9)C(10) C(7)C(8) C(8)C(9) Bond angles (°) Mo(1)O(12)Mo(1) a O(11)Mo(1)O(12) O(11)Mo(1)O(12) a O(12)Mo(1)O(12) a O(11)Mo(1)O(3) O(11)Mo(1)O(4) O(12)Mo(1)O(3) O(12)Mo(1)O(4) O(3)Mo(1)O(4) O(12) aMo(1)O(3) O(12) aMo(1)O(4) C(7)O(4)Mo(1) C(4)O(3)Mo(1) C(4)O(3)H(34) C(7)O(4)H(34) C(9)N(1)C(13) C(9)N(1)H(1) C(13)N(1)H(1) C(4)C(3)C(7) O(3)C(4)C(3) O(3)C(4)C(5) O(4)C(7)C(8) O(4)C(7)C(3) C(8)C(7)C(3) C(9)C(8)C(7)
1a
1b
2.549(1) 1.678(2) 1.925(2) 1.931(2) 2.089(2) 2.164(2) 2.212(2)
2.556(1) 1.691(2) 1.923(3) 1.948(2) 2.088(2) 2.152(2) 2.241(3)
1.358(3) 1.398(3) 1.209(3) 1.306(3) 1.25(4) 1.297(3) 1.20(4) 1.315(3) 1.469(4) 1.197(3) 1.370(3) 1.436(3) 1.333(3) 1.432(3) 0.87(3) 1.501(3)
1.355(3) 1.402(3) 1.215(3) 1.288(3)
1.366(4) 1.381(4) 1.222(4) 1.288(4)
1.295(3)
1.279(4)
1.319(3) 1.470(3) 1.201(3) 1.373(3) 1.435(3) 1.340(3) 1.423(3) 0.980 1.498(4)
1.304(5) 1.484(5) 1.199(6) 1.377(6) 1.411(7) 1.344(5) 1.422(5) 0.851
1.437(3) 1.395(3) 1.464(3) 1.430(3) 1.325(3) 1.493(3)
1.440(4) 1.411(4) 1.471(4) 1.436(4) 1.326(4) 1.496(4)
1.400(3) 1.384(3)
1.402(4) 1.397(4)
1.529(4) 1.432(4) 1.364(5)
82.8(1) 105.2(1) 107.0(1) 93.9(1) 93.0(1) 161.3(1) 88.0(1) 89.5(1) 75.8(1) 158.6(1) 82.9(1) 142.1(2) 136.9(2)
82.7(1) 106.3(1) 106.6(1) 94.8(1) 94.8(1) 157.2(1) 85.9(1) 94.6(1) 77.3(1) 157.4(1) 80.1(1) 137.5(2) 134.1(2)
131.8(2) 112.3 115.7 120.3(2) 127.3(2) 114.6(2) 118.0(2) 117.4(2) 124.6(2) 125.0(2)
130.7(3) 115.1 113.3 121.2(3) 124.5(3) 116.5(3) 116.5(3) 120.1(3) 123.5(3) 124.8(3)
100.3(15) 105.0(16) 125.2(2) 115.1(19) 119.2(2) 121.6(2) 118.2(2) 119.9(2) 116.3(2) 123.8(2) 125.9(2) 124.1(2)
27
1.477(5) 1.448(4) 1.427(4) 1.445(5) 1.433(5) 1.335(5)
N(1)C(9)C(8) N(1)C(9)C(1) N(1)C(9)C(10) a
117.8(2) 126.2(2)
121.3(2) 120.6(2)
125.6(3) 121.2(3)
−x+1/2, y, −z+1 for 1a and −x+1, y, −z+1/2 for 1b.
donor ligands [30,31]. Such bonding gives the opportunity for the sixth coordination place around molybdenum to be completed by the monodentate solvent molecule D. The presence of methanol, ethanol and i-propanol in all complexes is in accordance with the analytical and spectral data (Table 1) as well as with the thermogravimetric analyses (Table 2). As shown in Table 2, all complexes showed similar thermal behavior. While heated the first weight loss could be attributed to the loss of a coordinated alcohol molecule and conversion into a stable species [Mo2O4L2] with five coordinated molybdenum. Further heating resulted in the solid residues identified as MoO3. The agreement between calculated and experimental mass losses are within experimental errors. The complexes were also characterized by IR spectroscopy (selected spectral data are given in Table 1). Two bands at 1725–1710 cm − 1 and 1650–1655 cm − 1 are attributed to the stretching vibrations of the carbonyl group from the ester COOC2H5 and 2-pyrone, respectively. The stretching frequencies at about 1570 and 1510 cm − 1 attributed to the coordinated C···O groups and to w(C···C) are observed at lower values comparing to those found in a free ligand. The single strong absorption maximum at about 960 cm − 1 belongs to MoO (terminal), while the band at 730–720 cm − 1 to the MoO (bridging) stretching frequencies. The remaining frequencies in the IR spectra are due to the vibrations within ligands. All complexes were orange–red crystalline solids and very soluble in coordinating solvents (e.g. dmf, dmso, picoline and py) in which they undergo substitution reactions. They are soluble in dichloromethane and acetone, slightly soluble in methanol and ethanol.
3.2. NMR spectroscopy 3.2.1. Isomers a and b The chemical shifts observed in the 1H and 13C spectra of both isomers a and b (Scheme 2) are assigned by the combined use of one and two dimensional NMR sequences described in the experimental part. The values listed in Table 6 are comparable to those for the analogous compounds already known in the literature [13,14]. The NMR spectroscopic data confirm the existence of an enamine rather than an imine form, which is also in agreement with the crystal structure determination. Large downfield shifts corresponding to the hydroxyl and amine protons (protons of OH found at
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
28
18.82 and 17.56 ppm and those of NH group at 11.97 and 11.58 ppm, in a and b, respectively) imply the strong intramolecular hydrogen bonding in solution. Furthermore, the observed difference in chemical shifts between signals of OH and NH protons suggests that the hydrogen bond OH···O is stronger than that of NH···O. The signals belonging to protons of OH and NH are significantly broadened which might be indicative for some displacements of protons involved in a tautomeric equilibrium. Attention has been turned also to the endo- and exo-enol enamine tautomeric equilibrium, since both tautomers were found in the crystals of compounds with similar structures [13]. However, the NMR spectroscopic data did not show any doubling of NMR resonances
indicating that the predominant form is most likely the endo-enol form with the hydroxy group at position 4. Additionally, the chemical shifts observed for C-4 and C-7 atoms in 13C NMR spectra of both isomers a and b (C-7 more down-field), confirm the existence of endoenol enamine, but in a fast tautomeric equilibrium, most probably present in this case, the existence of small amounts of an exo-form cannot be excluded. However, this equilibrium is too fast on the NMR time scale for the tautomers to be detected separately so that averaged NMR signals were observed for both forms.
3.2.2. Complexes 1a and 1b Both 1H and 13C NMR spectra (Table 6) confirm the formation of complexes 1a and 1b as proved by the
Table 5 Hydrogen bonding geometry in structures a, 1a and 1b DH···A
d(DH)
d(H···A)
ÚDHA
d(DA)
Symmetry codes
a O4H34···O3 N1H1···O4 N1H1···O3i
1.20(4) 0.87(3) 0.87(3)
1.25(4) 2.03(3) 2.35(3)
158(3) 134(3) 140(3)
2.401(2) 2.711(3) 3.070(3)
(i) −x+1, −y, −z+1
1a N1H1···O4 O8H8···O2ii O8H8···O1ii
0.980 0.959 0.959
1.774 1.744 2.623
138.1 173.8 130.2
2.587(3) 2.699(3) 3.323(3)
(ii) −x+1/2, −y+1/2, −z+1/2
1b N1H1···O4 O8H8···O2iii
0.851 0.876
1.997 1.795
132.3 170.4
2.646(4) 2.663(3)
(iii) −x+1, −y+1, −z+1
Table 6 1 H and 13C chemical shifts (ppm) for the compounds a, 1a, b, 1b in acetone-d6 Compound
a
atom
1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 OH NH
1a
H
13
2.18
21.32 159.80 100.53 180.81 110.87 151.84 185.92 95.42 169.36 159.86 63.22 14.30 131.19 127.72 115.39 159.89 115.39 127.72 55.89
6.81
6.72
4.39 1.37 7.04 7.32 7.32 7.04 3.85 18.82 11.97
C
1
b
H
13
2.07
21.38 160.60 101.96 179.51 113.84 148.39 180.30 97.42 166.31 161.52 62.76 14.46 131.35 126.67 114.38 158.10 114.38 126.67 55.61
6.79
6.49
4.43 1.44 7.09 6.67 6.67 7.09 3.71 11.59
C
1
1b
H
13
2.27
20.31 161.19 98.38 181.79 102.38 168.95 192.23 96.27 154.27 164.58 62.98 13.96 132.96 125.00 115.30 159.19 115.30 125.00 55.86
6.08
7.04
4.18 1.09 7.13 6.97 6.97 7.13 3.81 17.56 11.30
C
1
H
13
2.19
19.76 162.73 99.65 182.52 107.46 163.98 185.56 96.81 152.56 165.03 62.72 14.03 132.58 123.54 114.57 157.81 114.57 123.54 55.52
6.02
6.61
4.18 1.14 6.84 6.67 6.67 6.84 3.78 10.74
C
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
Fig. 1. An
ORTEP
29
drawing of the isomer a showing the intramolecular hydrogen bonds of the type OH···O and NH···O.
crystal structure determination. The upfield shifts of 5.62 and 6.67 ppm observed for C-7 atom in the 13C NMR spectra of both compexes 1a and 1b, respectively, suggest that the ligands are coordinated to molybdenum through the enolic oxygen atom. The coordination induced shift is less pronounced for other neighboring carbon atoms in the complexes and alternates with their deshielding, as a consequence of electron density redistribution after the complexation to molybdenum. The change of chemical shift of the carbon atom at position 4, i.e. the second possible interacting site, is only negligible. However, the absence of signal belonging to proton of OH for both 1a and 1b is in accordance with deprotonation of hydroxyl group as a result of complex formation.
3.3. X-ray analysis 3.3.1. Crystal structure of isomer a The molecular structure of isomer a (Fig. 1) can be described as consisting of three structural fragments: (i) 2-pyrone ring at position 6 substituted by ethoxycarbonyl group; (ii) central enaminone part of molecule; and (iii) N-substituent consisting of phenyl ring with methoxy group at position 4. In crystalline state isomer is in an enamine form (CCNH) with the C8C9 bond length of 1.384(3) A, and C9N1 of 1.333(3) A, . The C9N1C13C14 torsion angle of 60.0(3)° is indicative of a torsion flexibility of N-substituents induced by twisting around single Nsp2Csp3 bond. The bond lengths and angles of the phenyl ring, the ethoxycarbonyl group, as well as of the pyran ring are within expected values [32].
All available OH and NH protons participate in hydrogen bonding (Fig. 2). The difference Fourier map exhibits only one possible position of H34 atom at almost the same distance from O3 and O4 (O3···H34 1.25(4) A, and O4···H34 1.20(4) A, ). Thus, six-membered ring formed in b-diketone fragment is stabilized by the resonance assisted with OH···O hydrogen bond of very short distance O3···O4 of 2.401(2) A, . Consequently, the O3C4 and O4C7 bond distances of 1.306(3) and 1.297(3) A, are longer than keto CO (1.21 A, ) and shorter than Csp2OH (1.33 A, ) bond distances [32]. The other six-membered ring (enamine fragment), is formed through the NH···O intramolecular hydrogen bond of d(N1···O4) =2.711(3) A, ). Two molecules, related by inversion center, are connected through moderately strong intermolecular NH···O hydrogen bond, d(N1···O3i)= 3.070(3) A, . In such a way discrete dimers, lying in a ac plane, form an eight-membered ring containing three-center hydrogen bonds.
3.3.2. Crystal structures of complexes 1a and 1b The structures of complexes 1a and 1b are shown in Figs. 3 and 4, respectively. Both structures of complex molecules with [Mo2O4]2 + cores have crystallographically imposed twofold symmetry axes. Six oxygen atoms in the form of a distorted octahedron coordinate each molybdenum atom with the angles at molybdenum atom ranging from 82.7(1) to 107.0(1)° in 1a and 82.7(1) to 106.6(1)° in 1b. The MoO bond lengths of 1.678(2) A, in 1a and 1.691(2) A, in 1b are of usual values for molybdenum to terminal oxygen bond lengths. The two bridging MoO bond lengths are 1.925(2) and 1.931(2) A, in 1a and 1.923(3) and 1.948(2)
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
30
A, in 1b. Two MoO bonds with the oxygen atoms from the didentate ligand amount to 2.089(2) and 2.164(2) A, in 1a and 2.088(2) and 2.152(2) A, in 1b depending upon their positions in the structure, i.e. either cis or trans to
the terminal oxo oxygen atoms. Two MoO bonds with the oxygen atoms from the methanol molecules are 2.211(2) A, in 1a and 2.241(3) A, in 1b. The MoMo distances of 2.549(1) A, in 1a and 2.556(1) A, in 1b
Fig. 2. Packing diagram of the isomer a showing also the intermolecular hydrogen bonds NH···O within pairs of symmetrically related molecules.
Fig. 3. An
ORTEP
view of the dinuclear complex 1a (hydrogen atoms are omitted for clarity).
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
Fig. 4. An
ORTEP
31
view of the dinuclear complex 1b (hydrogen atoms are omitted for clarity).
correspond to a single bond between two molybdenum atoms [33]. In crystalline state ligand is in an enamine form (CCNH) with the C8C9 bond length of 1.397(4) A, in 1a and 1.364(5) A, in 1b. The C9N1C13C14 torsion angles of 25.84(2)° in 1a and 35.2(7)° in 1b are of considerably smaller values compared to that found in the free ligand a. Analogously as in the structure of isomer a, in structures of 1a and 1b the six membered rings are formed in enamine fragments by NH···O hydrogen bonds amounting to 2.587(3) in 1a and 2.646(4) A, and 1b.
References [1] [2] [3] [4] [5] [6]
[7] [8]
4. Supplementary material A full list of crystal data and refinement has been deposited with the Cambridge Crystallographic Data Centre, CCDC nos. 164781– 164783 for compounds 1a, 1b and a, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: + 441223-336-033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
[9] [10] [11] [12] [13] [14] [15]
[16]
Acknowledgements This research was supported by the Ministry of Science and Technology of the Republic of Croatia (Grant No. 119407). We are indebted to BsC Predrag Tepesˇ for performing some NMR experiments. We thank Gerald Giester (Institut fu¨ r Mineralogie und Kristallographie, Geozentrum, Universita¨ t Wien, Althanstraße 14, A1090 Wien, Austria) for data collection.
[17] [18] [19] [20] [21]
J.-C.G. Bu¨ nzli, Inorg. Chim. Acta 139 (1987) 219. W. Horrocks, M. Albin, Prog. Inorg. Chem. 31 (1984) 1. F.S. Richardson, Chem. Rev. 82 (1982) 541. C. Bisi Castellani, O. Carugo, Inorg. Chim. Acta 159 (1989) 157. C. Bisi Castellani, O. Carugo, C. Tomba, A. Invernizzi Gamba, Inorg. Chem. 27 (1988) 3965. S. Thaisrivongs, D.L. Romero, R.A. Tommasi, M.N. Janakiraman, J.W. Strohbach, S.R. Turner, C. Biles, R.R. Morge, P.D. Johnson, P.A. Aristoff, P.K. Tomich, J.C. Lynn, M.M. Horng, K.T. Chong, R.R. Hinshaw, W.J. Howe, B.C. Finzel, K.D. Watenpaugh, J. Med. Chem. 39 (1996) 4630. G. Gilli, V. Bertolasi, V. Ferretti, P. Gilli, Acta Crystallogr., Sect. B 49 (1993) 564. P. Gilli, V. Bertolasi, V. Ferretti, G. Gilli, J. Am. Chem. Soc. 122 (2000) 10405. V. Drevenkar, Z. S& tefanac, A. Brbot, Microchem. J. 21 (1976) 402. O. Carugo, C. Bisi Castellani, M. Rizzi, Polyhedron 9 (1990) 2061. R.I. Kureshy, N.H. Khan, S.H.R. Abdi, P. Iyer, S.T. Patel, Polyhedron 18 (1999) 1773. A. Brbot-S& aranovic´ , B. Katusˇin-Razˇ em, I. Susˇnik, Heterocycles 29 (1989) 1559. A. Brbot-S& aranovic´ , G. Pavlovic´ , M. Cindric´ , Struct. Chem. 11 (2000) 65. A. Brbot-S& aranovic, G. Pavlovic´ , V. Vrdoljak, M. Cindric´ , Croat. Chem. Acta 74 (2001) 441. B. Kamenar, B. Korpar-C& olig, M. Cindric´ , D. Matkovic´ C& alogovic´ , M. Penavic´ , Bull. Chem. Technol. Macedonia 16 (1997) 33. B. Kamenar, B. Korpar-C& olig, M. Penavic´ , M. Cindric´ , J. Crystallogr. Spectrosc. Res. 22 (1992) 391. M.G.B. Drew, K.J. Shanton, Acta Crystallogr., Sect. B 34 (1978) 276. B. Kamenar, B. Korpar-C& olig, M. Penavic´ , Cryst. Struct. Commun. 11 (1982) 1583. E.L. Akhmedov, A.S. Kotel’nikova, P.A. Koz’min, M.D. Surazhskaya, T.B. Larina, Koord. Khim. 13 (1987) 698. M. Cindric´ , D. Matkovic´ -C& alogovic´ , V. Vrdoljak, B. Kamenar, Inorg. Chim. Acta 284 (1999) 223. M. Cindric´ , G. Pavlovic´ , V. Vrdoljak, B. Kamenar, Polyhedron 19 (2000) 1471.
32
M. Cindric´ et al. / Inorganica Chimica Acta 328 (2002) 23–32
[22] F.W. Moore, R.E. Rice, Inorg. Chem. 7 (1968) 2510. [23] G.A. Parker, Analytical Chemistry of Molybdenum, SpringerVerlag, New York, 1983. [24] Z. Otwinowski, Proceedings of the CCP4 Study Weekend: Data Collection, Warington, Daresbury Laboratory, UK, 1993. [25] Stoe & Cie, X-RED, Data Reduction Program for Windows, Darmstadt, Germany, 1995. [26] G.M. Sheldrick, SHELXS-97, Program for the Solution of Crystal Structures, University of Go¨ ttingen, Germany, 1997. [27] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures, University of Go¨ ttingen, Germany, 1997.
[28] C.K. Johnson, ORTEP-II, Rep. ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. [29] A.L. Spek, The EUCLID package, in: D. Sayre (Ed.), Computational Crystallography, Clarendon Press, Oxford, 1982, p. 528. [30] B. Kamenar, B. Korpar C& olig, M. Penavic´ , M. Cindric´ , J. Chem. Soc., Dalton Trans. (1990) 1125. [31] E. McCarron III, J.F. Whitney, D.B. Chase, Inorg. Chem. 23 (1984) 3275. [32] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G. Orpen, R.J. Taylor, J. Chem. Soc., Perkin Trans. 2 (1987) S1. [33] F.A. Cotton, Inorg. Chem. 4 (1965) 334.