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Facile One-Pot Synthesis of Triphenylbismuth(V) Bis(carboxylate) Complexes Ish Kumar,† Prateek Bhattacharya,† and Kenton H. Whitmire* Department of Chemistry, MS60, Rice University, 6100 Main Street, Houston, Texas 77005-1892, United States S Supporting Information *
ABSTRACT: Triphenylbismuth(V) bis(carboxylates), Ph3Bi(O2CR)2 (R = 5-Br-2-OH-C6H3 (1), 2-OH-C6H4 (2), 2,6(OH)2-C6H3 (3), 3-Me-2-NH2-C6H3 (4), Ph (5), Me (6)), were obtained from the reaction of triphenylbismuth with hydrogen peroxide and excess carboxylic acid in wet 2-propanol. The synthesis avoids the use of halogens as oxidants, and the products crystallize directly from the solution as pure compounds. They crystallize from solution without further need for purification. The structures of 1−5 were confirmed by single-crystal X-ray diffraction. Compounds 2 and 5 exhibit a polymorph different from that previously reported in the literature. While all of the Bi(V) compounds adopt a trans-axial trigonal-bipyramidal configuration with the carboxylates in axial positions, there is considerable variation in the coordination of the carboxylate that ranges from simple η1 to a mixture of mono- and bidentate chelating bonding modes.
O
or to detect it spectroscopically in solution were not successful. In the absence of the carboxylic acid we observed decomposition and side products rather than the formation of a stable complex. Further study of this reaction proved it to be general and applicable to a diverse set of carboxylic acids, as illustrated in Figure 1. Salicylic acid and its derivatives were targeted because (i) they display wide variety of chemotherapeutic properties such as antibacterial and antiparasitic activity27,28 and (ii) they possess a wide variety of coordination modes29,30 which can be useful in the construction of organic frameworks. Our group has previously reported the structure of Bi(Hsal)3 adducts with nitrogen-containing chelating ligands and monophenylbismuth
rganobismuth compounds, particularly bismuth carboxylates, have antimicrobial properties and are commonly used as pharmaceutical agents in chemotherapy and in the treatment of Helicobacter pylori infections.1 The versatility of these bismuth compounds in organometallic reactions also enables them to be extensively used in the synthesis of heterobimetallic complexes2 and as catalysts.3,4 Triphenylbismuth undergoes reactions with 3 equiv of carboxylic acids in the presence of polar and nonpolar solvents to yield complete replacement of the aryl groups, but these compounds are often sensitive to hydrolysis and oxo-cluster compounds result.5−7 Nuclearities up to 38 bismuth atoms have been reported.5,8,9 It is possible to obtain monophenyl bismuth(III) dicarboxylato compounds by careful addition of stoichiometric amounts of the carboxylic acid. 10,11 Interestingly, conducting these reactions in reagent-grade 2-propanol led to isolation of triphenylbismuth(V) bis(carboxylates), whose formation we were ultimately able to trace to the presence of peroxides in the solvent, which was confirmed by qualitative analysis. Normally, these compounds are prepared in a two-step process, first by reacting BiPh3 with chlorine or bromine to produce Ph3BiX2 followed by reaction with an alkali-metal salt of an appropriate anionic ligand.12 Several examples of BiPh3(O2CR)2 have been reported previously (R = Me,13,14 Et,14 Ph,13,14 Bu,13 CHCH 2 , 13 Me(CH 2 ) 8 , 13 Me(CH 2 ) 10 , 13 oxalate, 13 pOHC6H4CH2CH2,15 Cl3C,16 ClCH2,16 BrCH2,16 F3C,17 3MeC 6H 4 ,18 4-MeC6 H 4,18 2-AcOC 6H 4,18 F 5 C6 ,19 3,4,5-F C6H2,20 C3H521). Bi(V) compounds have been studied extensively as aryl transfer reagents in organic synthesis.22−26 We have presumed that the reaction proceeds through the intermediacy of Ph3BiO, but attempts to isolate that compound © XXXX American Chemical Society
Figure 1. Acids used in the present study: (A) 5-bromosalicylic acid; (B) salicylic acid; (C) 2,6-dihydroxybenzoic acid; (D) 3-methylanthranilic acid; (E) benzoic acid; (F) acetic acid. Received: March 28, 2014
A
dx.doi.org/10.1021/om500337z | Organometallics XXXX, XXX, XXX−XXX
Organometallics
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carboxylate complexes, [PhBi(O2CR)] (where R = 2-OHC6H4, 4-Me-2-OH-C6H3).7,10 Recently we also reported the structure of the simplest oxo cluster, [Bi4(μ3-O)2(Hsal)8], containing a salicylate ligand.9 The yield and physical properties of all complexes prepared are provided in the Supporting Information. A detailed comparison of the bismuth(V) carboxylato complexes is presented here and shows systematic variation in the structural parameters of the compounds as a function of the carboxylate used. The complexes are stable in the solid state and are soluble in acetone and DMSO. All of the complexes were characterized by NMR spectroscopy, IR spectroscopy, elemental analyses, and melting points. Molecular structures were confirmed using single-crystal X-ray diffraction. The structures of 231 and 520 have been previously determined, although those reported here are new polymorphs. Pictures of the new compounds 1 and 4 are presented in Figures 2 and 3, respectively. Figures of the other molecules are given in the Supporting Information. The selected Bi−O(carboxylate), O−Bi−O, and Bi−O−C angles of 1−5 are reported in Table 1.
Complexes 1−5 have distorted-trigonal-bipyramidal geometry with the carboxylate oxygen atoms in the axial positions and the carbon atoms of the phenyl groups in equatorial positions. One of the phenyl groups in 3 is disordered over two positions, and three carbons of another aryl group are slightly disordered; this could not be resolved. Both carboxylate ligands in 1−3 bind in an η1(O) fashion, whereas for 4 both bind in a symmetrical η2(O,O′) fashion. In 5, there are two molecules in the asymmetric unit; in one of the molecules both carboxylate ligands bind in a η1(O) fashion, whereas for the other molecule the carboxylate ligands bind in both η2(O,O′) and η1(O) modes. The bonding modes of the oxygen atom of the carboxylate ligands vary from monodentate to a mixture of both monodentate and bidentate modes (Figure 4). The IR spectra
Figure 4. Variation in the bonding modes of the carboxylate oxygen.
of all the complexes show asymmetrical and symmetrical stretching carboxylate modes. Complexes 1−3 display a Δν value (Δν = νasymm − νsymm) greater than 200 cm−1, indicating a monodentate bonding mode as observed in the solid-state structure, whereas complexes 4 and 5 exhibit Δν values less than 200 cm−1, consistent with the bidentate bonding mode observed in their solid-state structures. The Bi−O(carboxylate) bond lengths and O−Bi−O and Bi− O−C bond angles of complexes 1−5 are consistent with the corresponding distances and angles of other triphenylbismuth(V) bis(carboxylate) complexes reported in the literature.15−17 The structural data show a correlation between the pKa values of the carboxylate ligands and Bi−O bond lengths, with the weaker acids having shorter Bi−O distances. Interestingly, the average Bi−O distance is the same for both independent molecules in spite of the variation in Bi−carboxylate binding. The Bi−O−C bond angles, where the O atom is that in the axial position which always has the shorter Bi−O distance, were also considered, as this value should correlate with a tilt of the carboxylate group; a smaller angle corresponds to a greater tilt. The less acidic carboxylates exhibit a greater angle (see the Supporting Information Table S2), which corresponds to an
Figure 2. Molecular structure of 1. Phenyl hydrogens have been omitted for clarity.
Figure 3. Molecular structure of [BiPh3(3-CH3-2-NH2-C6H3CO2)2] (4). Phenyl hydrogens have been omitted for clarity.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 1−5
Bi(X)−O(X11) Bi(X)−O(X12) Bi(X)−O(X21) Bi(X)−O(X22) O(X11)−Bi(1)−O(X21) Bi(X)−O(X11)−C(X17) Bi(X)−O(X21)−C(X27)
1 (X = 1)
2 (X = 1)
3 (X = 1)
4 (X = 1)
5 (X = 1)
5 (X = 2)
2.292(3) 3.016(4) 2.278(3) 2.997(3) 172.6(1) 112.0(3) 111.4(3)
2.290(3) 2.859(3) 2.247(3) 2.869(3) 170.6(1) 108.2(3) 109.2(3)
2.291(3) 2.916(3) 2.329(3) 2.862(3) 170.7(1) 110.2(2) 107.1(3)
2.263(6) 2.755(7) 2.283(6) 2.699(7) 170.7(2) 105.9(5) 103.5(5)
2.254(4) 2.886(5) 2.270(4) 2.795(4) 170.3(1) 108.9(3) 104.9(3)
2.290(4) 2.752(4) 2.272(4) 2.893(4) 172.2(1) 103.9(3) 107.7(3)
B
dx.doi.org/10.1021/om500337z | Organometallics XXXX, XXX, XXX−XXX
Organometallics
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were referenced to tetramethylsilane (TMS). Melting points were obtained in sealed capillaries on an Electrothermal melting point instrument. Elemental analyses (C, H, N) were performed at Galbraith Laboratories. IR spectra were recorded on a Perkin-Elmer FTIR spectrometer. General Synthetic Procedure. BiPh3 (0.33 mmol) and the appropriate carboxylic acid (1.00 mmol) were combined and dissolved in 8.0 mL of reagent grade 2-propanol (used as received from Fisher Scientific) by stirring on low heat for 2 min. The homogeneous solutions were stored at room temperature for 2−3 days while crystals formed. The crystals were isolated, dried, and identified as Bi(V) complexes. The composition of these complexes is given in Table 1. The analytical data have been provided in the Supporting Information. The experiment was repeated by performing the reaction in distilled 2propanol with the addition of 30% H2O2 solution (5 μL). The results obtained were the same, but the yield obtained through this synthetic method was generally higher than that in the absence of added peroxide. There was a trace amount of 2-propanol (
