Reactivity Studies on an Intramolecularly Coordinated Organotin(IV

The reactivity of the intramolecularly coordinated organotin(IV) carbonate L(Ph)Sn(CO3) (1), where L stands for an N,C,N-chelating ligand, ...
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Reactivity Studies on an Intramolecularly Coordinated Organotin(IV) Carbonate Barbora Mairychová,† Petr Štěpnička,‡ Aleš Ru̇zǐ čka,† Libor Dostál,† and Roman Jambor*,† †

Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, Pardubice CZ-53210, Czech Republic ‡ Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030, CZ-12840 Prague, Czech Republic S Supporting Information *

ABSTRACT: The reactivity of the intramolecularly coordinated organotin(IV) carbonate L(Ph)Sn(CO3) (1), where L stands for an N,C,N-chelating ligand, 2,6-(Me2NCH2)2C6H3, was studied. The treatment of 1 with ferrocene-based carboxylic acids RCOOH afforded the organotin(IV) dicarboxylates LPhSn(O2CR)2, where R is ferrocenyl (2), 2-ferrocenylethyl (3), and [(1E)-2-ferrocenyl]ethenyl (4). Surprisingly, compounds 2−4 are sensitive to moisture and easily hydrolyze with condensation into the corresponding hexameric organotin oxo clusters (PhSnO)6(O2CR)6 (R = ferrocenyl (5), 2-ferrocenylethyl (6), and [(1E)-2-ferrocenyl]ethenyl (7)) possessing a Sn6O6 drumlike core. On the other hand, treatment of 1 with non-carboxylic acids such as HOTf, H3BO3, H3PO3, and t-BuPO3H2 afforded the triflate salt of a cationic organotin(IV) hydroxide {[LPh(H2O)Sn(μ-OH)]2}(OTf)2 (8), stannaboroxine LPhSnB2O3(OH)2 (9), and organotin(IV) phosphite [L(Ph)Sn(HPO3)]2 (10) and phosphonate {[L(Ph)Sn]2(μ-OH2)(μ-t-BuPO3)2} (11), respectively. Compounds 2−11 were characterized by elemental analysis and multinuclear NMR spectroscopy, and the molecular structures of compounds 6 and 9−11 were determined by single-crystal Xray diffraction analysis. In addition, compounds 2−7 bearing redox-active ferrocenyl groups were studied by cyclic voltammetry.

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INTRODUCTION Organotin compounds with Sn−O bonds have attracted considerable attention in recent years, mostly owing to their structural diversity1 ranging from simple mononuclear compounds to complex clusters and multidimensional networks that are useful for the construction of supramolecular frameworks.2 Organooxotin compounds proved to be efficient catalysts for various organic reactions3 such as the Mukaiyama aldol reaction,4 Robinson annulation,5 acetylation of alcohols,6 and transesterification.7 Furthermore, it has been shown that organotin(IV) compounds can promote the direct carbonation of alcohols8 and several mechanistic studies reported the facile CO2 insertion into Sn−O bonds,9 which makes organooxotin compounds attractive targets for the use of CO2 as a renewable C1 feedstock. Reactivity studies with organotin carbonates showed that the inorganic CO32− moiety can be replaced by organic spacers to provide organooxotin clusters with large cavities.10 In contrast to the numerous organooxotin clusters reported to date,1,2 those bridged by inorganic spacers are still rare. For instance, a number of organostannoxanes containing phosphonates11 and sulfonates12 have been prepared and characterized, but only very few organotin compounds based on arsonate, borate, or other inorganic spacers are known.13 In this context, we have reported the synthesis of the intramolecularly coordinated © XXXX American Chemical Society

organotin carbonate L(Ph)Sn(CO3) (1), where L denotes a N,C,N-chelating organyl ligand, 2,6-(Me2NCH2)2C6H3, and demonstrated that the terminal group carbonate moiety in this compound can be easily substituted by SeO2 to provide welldefined organotin selenites, in which the tin atoms are connected by an inorganic spacer.14 In order to explore the reactivity of 1 in more detail, we started to study the reactions of 1 with various acids. The treatment of 1 with ferrocenecarboxylic acids RCOOH afforded the organotin(IV) dicarboxylates LPhSn(O2CR)2, where R is ferrocenyl (2), 2-ferrocenylethyl (3), and [(1E)-2-ferrocenyl]ethenyl (4), as redox-active species. Surprisingly, compounds 2−4 are sensitive to moisture and easily hydrolyze with condensation into the corresponding hexameric organotin oxoclusters (PhSnO)6(O2CR)6 (R = ferrocenyl (5), 2ferrocenylethyl (6), [(1E)-2-ferrocenyl]ethenyl (7)) possessing a drumlike core structure. On the other hand, treatment of 1 with TfOH gave rise to a dimeric stannoxane dication, {[LPh(H2O)Sn(μ-OH)]2}(OTf)2 (8), while reaction with boric acid (H3BO3) provided LPhSnB2O3(OH)2 (9), containing a six-membered stannaboroxine ring. Analogous reactions of 1 with phosphorous acid (H3PO3) and tert-butylphosphonic Received: March 17, 2014

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signals of the ligand precursor LH appeared upon the addition of water and their intensity increased in time. However, no interaction between LH and liberated ferrocenecarboxylic acid was detected. The 1H NMR spectra of 5−7 not only confirmed the absence of ligand L in the structures but also showed characteristic resonances due to the ferrocene cyclopentadienyls (δH 4.17, 4.32, and 4.76 for 5, δH 4.04 and 4.11 for 6, and δH 4.33 and 4.49 for 7). 13C and 119Sn NMR spectra of 5−7 could not be obtained because of the low solubility of these hexatin(IV) clusters. The molecular structure of 6 is depicted in Figure 1 along with the selected geometric parameters. The structure reveals a

acid (t-BuPO3H2) afforded [L(Ph)Sn(HPO3)]2 (10) and {[L(Ph)Sn]2(μ-OH2)(μ-t-BuPO3)2} (11), respectively, featuring eight-membered rings. The results of these investigations are presented here.

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RESULT AND DISCUSSION Reactivity of 1 toward Ferrocenecarboxylic Acids. Treatment of carbonate 1 with ferrocenecarboxylic acids RCOOH in a 1:2 molar ratio afforded the corresponding organotin(IV) dicarboxylates LPhSn(O2CR)2, where R = ferrocenyl (2), 2-ferrocenylethyl (3), [(1E)-2-ferrocenyl]ethenyl (4) (Scheme 1). Notably, the reaction at the 1:1 Scheme 1. Synthesis of Diorganotin(IV) Carboxylates 2−4 and Their Hydrolytic Products 5−7

molar ratio provided only mixtures of the starting 1 and the respective organotin(IV) dicarboxylate LPhSn(O2CR)2. Compounds 2−4 were characterized by NMR spectroscopy. The 1H NMR spectra of 2−4 revealed broad signals due to CH2N (δH 3.99 for 2, 3.82 for 3, and 3.92 for 4) and NMe2 protons (δH 2.46 for 2, 2.29 for 3, and 2.32 for 4) of the chelating ligand L. The 119Sn NMR spectra showed single resonances at δSn −459.4 for 2, −432.8 for 3, and at −456.5 for 4, suggesting the presence of six-coordinated tin(IV) centers.15 Rather surprisingly, compounds 2−4 easily hydrolyzed to g i v e t h e h e x a m e r i c o r g a n o t in ( I V ) o x o c l u s t e r s [(PhSnO)6(O2CR)6] (R = ferrocenyl (5), 2-ferrocenylethyl (6), [(1E)-2-ferrocenyl]ethenyl (7)) (see Scheme 1). These clusters were isolated as crystalline materials suitable for X-ray diffraction analysis in moderate yields (around 20%) when the starting organotin(IV) dicarboxylates 2−4 were dissolved in THF/CH2Cl2 and allowed to stand in the air. Similarly, reactions of 2−4 with stoichiometric amounts of water provided crystalline solids of 5−7 in good yields (around 80%). The formation of 5−7 is remarkable in that the related drumlike structures are usually obtained upon treatment of monooganotin(IV) oxides with carboxylic acids16 and that it proceeds readily under ambient conditions despite the fact that Sn−C bond cleavage reactions usually occur at elevated temperatures.17 We suppose that the interaction of the leaving carboxylic acids RCOOH with the dimethylamino group NMe2 of ligand L is the driving force for the Sn−C bond rupture. The ligand L is hydrolytically cleaved off and eliminated in the form of the free ligand precursor LH, which was indeed confirmed by NMR measurements. For instance, when the hydrolysis of 2 was monitored in situ by 1H NMR spectroscopy (in CDCl3),

Figure 1. Molecular structure of 6. Selected bond distances (Å): Sn1− O1 2.165(3), Sn1−O7 2.079(3), Sn1−O8 2.095(3), Sn2−O7 2.084(3), Sn2−O3 2.147(3), Sn3−O7 2.096(3), Sn3−O2 2.149(3), Sn3−O4 2.152(3), Sn3−O8 2.081(3).

drumlike arrangement1,17 in which the central stannoxane unit (Sn6O6) is coordinated by six bidentate ferrocenecarboxylate units. The stannoxane core adopts the usual distortedhexagonal columnar shape with two Sn3O3 units in the bases and six Sn2O2 rhomboidal faces whose tin atoms lying across the diagonal are bridged by the bidentate carboxylate donors. The carboxylate units are delocalized and coordinate the tin atoms in a symmetrical fashion (the Sn−O and C−O bond distances range 2.147(3)−2.165(3) Å) and 1.255(6)−1.268(5) Å, respectively). In addition to the structural characterization, compounds containing the redox-active ferrocene moieties were studied by cyclic voltammetry. The measurements were performed in the anodic region on a glassy-carbon-disk electrode using 1,2dichloroethane solutions containing 0.1 M Bu4NPF6 as the supporting electrolyte. The redox potentials are given relative to the ferrocene/ferrocenium reference. The redox response of 2, as the most simple representative, was rather complex (Figure 2). The compound underwent an oxidation, which was composite in nature, presumably as a result of the convolution of two narrow-spaced redox waves attributable to weakly interacting ferrocene units. The peak potentials were 0.20 and 0.08 V for the anodic and cathodic branches, respectively. During the second scan, the anodic wave B

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somewhat tilted), all at positions virtually identical with those of the respective dicarboxylates (peak potentials E°′ ca. 0.20/ 0.06 V for 5, −0.04 for 6, and 0.10 V for 7). Reactivity of 1 toward Non-Carboxylic Acids. The courses of reactions of 1 with HOTf, H3BO3, H3PO3, and tBuPO3H2 differ substantially (Scheme 2). Thus, the treatment Scheme 2. Synthesis of Organostannoxanes 8−11

Figure 2. Full (solid line) and partial (dashed line) cyclic voltammograms of 2 as recorded in 1,2-dichloroethane at a glassycarbon-disk electrode (first scan in red, second scan in blue).

shifted slightly to more positive potentials, while the cathodic wave remained practically invariant. Furthermore, the primary redox change became associated with another, much weaker redox wave at more positive potentials. Introduction of a spacer between the ferrocene moiety and the tin-bound carboxylate group obviously reduces the possible interaction between the redox-active terminal groups (Figure 3). Consequently, compounds 3 and 4 undergo single of 1 with HOTf in a 1:1 molar ratio afforded {[LPh(H2O)Sn(μ-OH)]2}(OTf)2, the triflate salt of a cationic organotin(IV) hydroxide (8). In contrast, the reaction of 1 with boric acid provided stannaboroxine LPhSnB2O3(OH)2 (9), whereas addition of phosphorous acid or tert-butylphosphonic acid to 1 resulted in the formation of the dimeric organotin(IV) phosphite [L(Ph)Sn(HPO3)]2 (10) and phosphonate {[L(Ph)Sn]2(μ-OH2)(μ-t-BuPO3)2} (11), respectively. The molecular structure of 8 and selected bond lengths and angles are presented in Figure 4. The crystal structure determination for 8 revealed a dimeric organotin(IV) dication, {[LPh(H2O)Sn(μ-OH)]2}2+, compensated by two OTf− anions. The cationic organotin(IV) hydroxide consists of two identical [(L)Ph(H2O)Sn] moieties connected through hydroxyl bridges into an unsymmetric Sn2O2 central ring. The ligand L is coordinated in a C,Nchelating manner (Sn1−C1 2.189(9) Å, Sn1−N1 2.506(7) Å), making use of only one of its two CH2NMe2 donor pendants. Because of coordination of an additional water molecule, the tin atoms are six-coordinated, possessing a C2NO3 donor set constituted by oxygen atoms O1/O1a and O2 atoms from the hydroxyl groups and the water molecule, respectively, by carbon C1 and nitrogen N1 atoms from ligand L, and finally by the pivotal carbon atom C13 from the tin-bound phenyl group. The OH groups further act as hydrogen bond donors for the adjacent triflate anions (O32···O33 2.847(9) Å). Similarly, the coordinated water molecule acts as a hydrogen bond donor for the triflate anion (O31···O34 2.898(12) Å) and uncoordinated nitrogen atom of ligand L (O31···N2 2.614(11) Å). It should be noted that similar ionic motives were found in the related structures of [R2(H2O)Sn-(μ-OH)2-Sn(H2O)R2]Y2 (Y = CF3SO3, C8F17SO3) bearing bulky substituents at the tin atoms.18 Very likely, the structure of 8 is retained even in CDCl3 solution. Thus, the presence of intramolecular N→Sn

Figure 3. Representative cyclic voltammograms of compounds 3 (red) and 4 (blue). Note that compound 4 is poorly soluble; hence, its saturated solution was used for the analysis.

reversible redox transitions at E°′ −0.04 and 0.10 V, respectively, corresponding to a simultaneous oxidation of both ferrocene units. The position of the waves reflects the influence of the substituents at the ferrocene unit, namely the overall donating effect of the 2-carboxyethyl group that renders the ferrocene oxidation more easy, and the electron-withdrawing nature of the conjugated 2-carboxyvinyl group. Measurements on the hexatin clusters 5−7 were complicated by their poor solubility (particularly for 5). Nonetheless, the analysis of saturated solutions revealed a behavior roughly parallel to that of the corresponding dicarboxylates 2−4. Thus, compound 5 gave rise to a convoluted wave, while its spaced analogues 6 and 7 showed single reversible waves (albeit C

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Figure 4. Molecular structure of 8. Hydrogen atoms residing on carbon atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Sn1−C1 2.189(9), Sn1−C13 2.127(10), Sn1−O31 2.060(6), Sn1−O32 2.090(5), Sn1−O32a 2.206(6), Sn1−N1 2.506(7), O31−H31 0.93; O32−Sn1−O32a 71.5(2), O31−Sn1− O32 92.6(3), O31−Sn1−O32a 163.9(2), C13−Sn1−C1 154.4(4), O31−Sn1−N1 106.5(3), O32−Sn1−N1 158.7(2).

Figure 5. Molecular structure of 9. Selected bond lengths (Å) and angles (deg): Sn1−O5 2.021(4), Sn1−O3 2.026(4), Sn1−C13 2.119(6), Sn1−C1 2.122(5), Sn1−N2 2.583(5), O1−B1 1.392(9), O2−B2 1.349(8), O3−B1 1.323(8), O4−B1 1.385(9), O4−B2 1.395(8), O5−B2 1.341(8); O5−Sn1−O3 88.88(17), O5−Sn1−C1 105.50(19), O3−Sn1−C1 105.69(19), B1−O3−Sn1 127.4(4), B1− O4−B2 125.9(5), B2−O5−Sn1 127.8(4), O3−B1−O4 125.6(7), O3−B1−O1 118.4(6), O4−B1−O1 116.0(6), O5−B2−O2 118.4(6), O5−B2−O4 123.7(6), O2−B2−O4 117.9(6).

coordination was manifested in the 1H NMR spectrum via an AB spin pattern (δH 3.65 and 4.00) for the diastereotopic CH2N protons in the pendant arm coordinated to the tin atom, while a signal at δH 4.29 was observed for the free CH2N group. The 119Sn NMR spectrum of 8 exhibited a singlet at δSn −126.1 ppm, which suggests the presence of [4 + 2] coordinated organotin(IV) cations.19,9 This signal appears shifted downfield in comparison to the starting carbonate 1 (δSn −379.15 ppm)20 and also diorganotin(IV) dichloride Ph(L)SnCl2 (δSn −204.2 ppm).21 The presence of OTf− moieties in 8 was confirmed by 13 C and 19F NMR spectroscopy. The 13C NMR spectrum showed a quartet at δC 120.3 ppm with a 1J(13C,19F) value of 317 Hz, and the 19F NMR spectrum displayed a singlet at δF −78.4 ppm, both attributable to the triflate CF3 group. The molecular structure of 9 and relevant geometric data are presented in Figure 5. The molecule of 9 comprises a central SnB2O3 ring, in which the B−OB bonds are slightly longer (1.395(8) and 1.385(9) Å) than the remaining B−OSn bonds (1.323(8) and 1.341(8) Å), the latter being shorter than the sum of the covalent radii ∑cov(B,O) = 1.48 Å.22 On the other hand, the lengths of the intracyclic B−O bonds are similar to those of the terminal B− OH bonds (1.392(9) and 1.349(8) Å). The SnB2O3 ring is slightly angularly distorted and nonplanar due to the presence of the tin atom, which is displaced from the mean plane of the B2O3 moiety by 0.103 Å. This distortion can be demonstrated also by the interatomic angles O−B−O (123.7(6) and 125.6(7)°) and B1−O4−B2 (125.9(5)°), which are significantly wider than the ideal value of 120° found in symmetrical boroxines R3B3O3 (R = Ph,23 Fc24). The opening of these angles is compensated by a closure of the O5−Sn1−O3 angle, which is only 88.88(17)°. The ligand L is oriented nearly perpendicularly to the SnB2O3 ring, and its nitrogen atoms are coordinated to the tin (Sn−N distances 2.583(5) and 2.720(5) Å) in mutually cis positions (cf. the N1−Sn1−N2 angle of 119.66(15)°). The coordination environment of the tin atom can thus be described as distorted octahedral with the nitrogen

and oxygen atoms in cis positions and the carbon atoms occupying mutually trans positions. The terminal B−OH bonds in the structure of 9 are involved in intermolecular hydrogen-bonding interactions that give rise to infinite chains (Figure 6). The B1−O1−H1 fragment

Figure 6. Intermolecular hydrogen-bonding interactions in 9 resulting in the formation of infinite chains. The organic ligands and all hydrogens are omitted for clarity.

interconnects two adjacent molecules through hydrogen bonds toward O2a and O7a (O1···O2a 3.018(5) Å, O1···O7a 2.936(5) Å). The other fragment B2−O2−H2 forms three hydrogen bonds: two to proximal B−OH moieties (O2···O1b 3.018(6) Å and O2···O6b 2.831(6) Å) and one to O10 in another stannaboroxine ring (O2···O10 2.885(6) Å). The 1H NMR spectra of compound 9 showed signals due to the ligand L and B−OH groups in a 1:2 mutual ratio. Furthermore, the 1H NMR spectrum revealed an AB spin system pattern for the methylene (CH2N: δH 2.88 and 4.32) and one signal for the NMe2 group (δH 2.10 ppm), indicating the presence of a N→Sn interaction with a pseudofacial coordination of the CH2NMe2 arms from the ligand L to the central tin atom. A broad signal at δH 3.07 was assigned to the D

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B−OH groups. Finally, the 119Sn NMR spectrum displayed a single resonance at δSn −346.6 ppm, consistent with the presence of six-coordinated tin centers.15 The molecular structure of 10 depicted in Figure 7 corroborates the dimeric nature of this organotin(IV) phosphite.

The molecular structure of organotin(IV) phosphonate 11 (Figure 8) indicated the compound to be a dimer in which two

Figure 7. Molecular structure of 10. Selected bond lengths (Å) and angles (deg): Sn1−O1 2.0518(19), Sn1−O2a 2.048(2), Sn1−C13 2.116(3), Sn1−C1 2.117(3), Sn1−N1 2.764(2), Sn1−N2 2.514(2), P1−O3 1.483(2), P1−O1 1.539(2), P1−O2 1.543(2), P1−H1 1.29; O2a−Sn1−O1 86.72(7), C13−Sn1−C1 141.79(10), O1−P1−O2 108.50(11), N1−Sn1−N2 121.06(7).

Figure 8. Molecular structure of 11. Selected bond lengths (Å) and angles (deg): Sn1−O3 2.065(2), Sn1−O1 2.124(2), Sn1−O6 2.163(2), Sn1−C1 2.175(3), Sn1−C13 2.188(4), Sn1−N1 2.323(3), Sn2−O7 2.094(2), Sn2−O4 2.111(3), Sn2−O1 2.125(2), Sn2−C31 2.166(4), Sn2−C19 2.192(3), Sn2−N3 2.384(4), P1−O2 1.523(3), P1−O4 1.523(3), P1−O3 1.537(3), P2−O6 1.524(3), P2−O7 1.534(3), P2−O5 1.536(3); O3−Sn1−O1 91.01(10), O3−Sn1−O6 84.41(9), O1−Sn1−O6 83.99(9), O7−Sn2−O4 83.87(9), O7−Sn2− O1 88.13(9), O4−Sn2−O1 88.19(9).

In the structure of 10, two identical organotin fragments L(Ph)SnIV are linked via μ-O,O′ phosphito groups into the dimer [L(Ph)Sn(HPO3)]2 with an eight-membered Sn2P2O4 central ring. The bridging phosphite moiety shows distinct bond lengths for the terminal (P1−O3 = 1.483(2) Å) and tinbonded P−O bonds (P1−O1 = 1.539(2) Å, P1−O2 = 1.543(2) Å). However, all P−O bond lengths are substantially shorter than the typical covalent single bond (∑cov(P,O) = 1.79 Å).22 In contrast, the Sn−O bonds within the eight-membered ring (2.0518(19) and 2.048(2) Å) are close to the value expected for a covalent single bond (∑cov(Sn,O) = 2.03 Å).22 The intracyclic P−O−Sn angles vary between 132.89(11) and 135.28(11)°, and the O−Sn−O angle is 86.72(7)°. According to a classification scheme recently introduced for eightmembered rings, phosphite 10 adopts a G-type structure.25 The Sn−N bond distances (2.514(2) and 2.764(2) Å) suggest the presence of medium-strong Sn−N interactions, and therefore, the coordination environment of the tin atom can be described as strongly distorted octahedral. The intramolecular N→Sn coordination in 10 is apparently preserved in CDCl3 solution, being manifested through an ABtype pattern for the diastereotopic CH2N protons (δH 2.75 and 4.30) and two signals for the NMe2 protons (δH 1.91 and 2.36) in the 1H NMR spectrum. Moreover, the 1H NMR spectrum exhibits a doublet at δH 7.20 with 1J(1H,31P) = 631 Hz, typical for the PH moiety. The presence of a phosphito moiety in 10 was further confirmed by the 31P NMR spectrum, showing a doublet at δP −4.1 ppm with the same coupling constant. Finally, the 119Sn NMR spectrum of 10 displayed a signal at δSn −395.7, which is in accordance with the values characteristic for hexacoordinated tin(IV) atoms.15

chemically identical but crystallographically nonequivalent L(Ph)Sn moieties are bridged by two phosphonate anions and one water molecule into a bicyclic cage. As a result, the two chemically equivalent tin atoms are six-coordinated, having an octahedral C2NO3 donor set with facially organized oxygen donors. Interestingly, the mutually similar P−O bonds within the phosphate groups (1.523(3)−1.536(3) Å) are substantially shorter than a covalent single bond (∑cov(P,O) = 1.79 Å).22 All Sn−O (2.065(2)−2.163(2) Å) distances compare well with the sum of the covalent radii (∑cov(Sn,O) = 2.03 Å).22 On the other hand, the unlike Sn−N separations (Sn1−N1 2.323(3) Å, Sn2−N3 2.384(4) Å, Sn1−N2 3.813(3) Å, and Sn2−N4 4.910(4) Å) clearly suggest a bidentate, C,N-chelating coordination of the N,C,N ligand L. It is also noteworthy that one hydrogen from the water molecule forms hydrogen bridges toward the terminal P1−O2 and P2−O5 bonds (O2··· O5 2.449(3) Å), whereas the second hydrogen is involved in hydrogen bonding toward the noncoordinated nitrogen atom N2 in ligand L (O1···N2 2.786(4) Å). The dimeric nature of 11 contrasts with the polymeric or oligomeric structures usually found for organotin(IV) phophonates.26 Like the compounds mentioned above, the molecules of organotin(IV) phosphonate 11 do not disintegrate upon dissolution. For instance, in the 1H NMR spectrum recorded in THF-d8, the intramolecular N→Sn coordination gave rise to an AB pattern for the CH2N hydrogens (δH 3.00 and 4.59) in the coordinated arm while the protons of the dangling CH2N moiety resonated at δH 3.48. The 119Sn and 31P NMR spectra of 11 exhibited singlets at δSn −344.8 and δP 26.6, respectively, thereby proving the presence of hexacoordinated tin(IV) centers and the phosphonate units, respectively. E

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glassy-carbon-disk working electrode (2 mm diameter), a platinumsheet auxiliary electrode, and a double-junction Ag/AgCl (3 M KCl) reference electrode. The compounds were dissolved in anhydrous 1,2dichloroethane (Sigma-Aldrich) to give a solution containing ca. 1 mM of the analyte (saturated solutions were used for the less soluble compounds) and 0.1 M Bu4N[PF6] (Fluka, p.a. for electrochemistry). The solutions were deaerated by bubbling with argon and kept under an argon blanket during the measurement. The redox potentials are given relative to ferrocene/ferrocenium reference (E°′ = 0.46 V under the experimental conditions). Synthesis of Compound 2. Solid ferrocenecarboxylic acid (0.11 g, 0.47 mmol) was added to a solution of 1 (0.11 g, 0.24 mmol) in CH2Cl2 (15 mL) at room temperature. The resulting mixture was stirred for 2 h at room temperature and evaporated in vacuo. The solid residue was washed with n-hexane to give 2 as an orange powder (yield 0.33 g, 86%). Mp: 228 °C dec. Anal. Calcd for C38H42N2O4Fe2Sn (820.40): C, 57.99; H, 6.64. Found: C, 57.93; H, 6.61. 1H NMR (CDCl3, 400.13 MHz): δ 2.46 (s, 12H, NCH3), 3.99 (s, 4H, CH2N), 4.07 (s, 10H, C5H5), 4.84 (s, 4H, C5H4), 5.35 (s, 4H, C5H4), 7.35 (d, 2H, ArH), 7.46 (t, 1H, ArH), 7.98 (m, 3H, ArH). 13C NMR (CDCl3, 100.62 MHz): δ 46.0 (NCH3), 64.0 (NCH2), 128.5 (CPh(3,5)), 129.4 (C(3,5)), 130.3 (C(4)), 134.1 (CPh(2,6); 1J(119Sn−31C) = 90.6 Hz), 138.2 (CPh(4)), 141.8 (C(2,6)), 144.0 (CPh(1)), 148.2 (C(1)), 181.3 (CO2). 119Sn NMR (CDCl3, 149.21 MHz): δ −459.4. Synthesis of Compound 3. 3-Ferrocenylpropanoic acid (0.12 g, 0.47 mmol) was added to a solution of 1 (0.11 g, 0.24 mmol) in CH2Cl2 (15 mL) at room temperature. The resulting mixture was stirred for 2 h at room temperature and evaporated. The residue was washed with n-hexane to give 3 as an orange powder (yield 0.10 g, 50%). Mp: 117−119 °C. Anal. Calcd for C44H50N2O4Fe2Sn (872.4): C, 59.59; H, 7.08. Found: C, 59.53; H, 7.04. 1H NMR (CDCl3, 400.13 MHz): δ 2.29 (s, 12H, NCH3), 2.56 (bs, 2H, CH2), 2.65 (bs, 2H, CH2), 3.82 (s, 4H, CH2N), 4.02 (s, 8H, C5H4), 4.10 (s, 10H, C5H5), 7.26 (d, 2H, ArH) 7,39 (t, 1H, ArH), 7.40 (m, 2H, ArH), 7.47 (t, 1H, ArH), 7.81 (d, 2H, ArH). 13C NMR (CDCl3, 100.62 MHz): δ 25.6 (NCH2), 45.5 (CH2CH2), 63.7 (NCH3), 67.2 (Cp), 68.0 (Cp), 68.5 (Cp), 127.8 (C(3,5)), 129.2 (C(4)), 128.9 (CPh(3,5)), 129.6 (CPh(4)), 134.3 (CPh (2,6); 1J( 119Sn−31C) = 70.4 Hz), 136.9 (C(2,6); 1 119 J( Sn−31C) = 40.2 Hz), 143.0 (C(1) 1J(119Sn−31C) = 85.5 Hz), 181.2 (CO2). The signal due to CPh(1) was not found. 119Sn NMR (CDCl3, 149.21 MHz): δ −432.8. Synthesis of Compound 4. (E)-3-Ferrocenyl-2-propenoic acid (0.050 g, 0.18 mmol) was added to a solution of 1 (0.040 g, 0.09 mmol) in CH2Cl2 (15 mL) at room temperature. The resulting mixture was stirred for 2 h at room temperature and then evaporated in vacuo. The solid residue was washed with n-hexane to give 4 as an orange powder (yield 0.70 g, 87%). Mp: 130−132 °C. Anal. Calcd for C44H46N2O4Fe2Sn (896.4): C, 59.97; H, 6.50. Found: C, 59.94; H, 4.47. 1H NMR (CDCl3, 400.13 MHz): δ 2.32 (s, 12H, NCH3), 3.92 (s, 4H, CH2N), 4.05 (s, 10H, C5H5), 4.30 (s, 4H, C5H4), 4.40 (s, 4H, C5H4), 6.03 (d, 3JHH = 7.2 Hz, 2H, CHCH), 7.24 (d, 3JHH = 7.8 Hz, 2H, CHCH), 7.29−7.34 (m, 4H, ArH), 7.53 (d, 2H, ArH), 7.72 (d, 2H, ArH). 13C NMR (CDCl3, 100.62 MHz): 45.8 (NCH3), 53.5 (CHCH), 63.9 (NCH2), 68.5 (Cp), 69.6 (Cp), 70.6 (Cp), 127.6 (C(3,5)), 128.4 (CPh(3,5)), 129.1 (C(4)), 129.3 (CPh(4)), 134.1 (C(1)) 143.4 (C(2,6)), 146.0 (CPh(2,6)), 176.3 (CO2). The signal due to CPh(1) was not found. 119 Sn NMR (CDCl3, 149.21 MHz): δ − 456.5. Synthesis of Compound 5. Compound 2 (0.15 g) was dissolved in 15 mL of THF/CH2Cl2 (1/1). Slow diffusion of the organic solvents in the air provided 5 as an orange crystalline solid (yield 0.144, 30%). The crystals were used directly for X-ray diffraction analysis. Mp: 220 °C dec. Anal. Calcd for C102H84O18Fe6Sn6 (2643.2): C, 48.04; H, 7.08. Found: C, 48.02; H, 7.06. 1H NMR (CDCl3, 400.13 MHz): δ 4.17 (s, 5H, C5H5), 4.32 (s, 2H, C5H4), 4.76 (s, 2H, C5H4), 7.09−17.18 (m, 2H, ArH).

CONCLUSION We have explored the reactivity of carbonate 1 toward various protic acids and isolated several new organotin(IV) compounds with oxo ligands.27 The treatment of 1 with ferrocenecarboxylic acids provided an easy access to organotin(IV) bis-carboxylates of the formula LPhSn(O2CR)2 that readily hydrolyze to give the respective hexameric organotin oxo clusters (PhSnO)6(O2CR)6 possessing Sn6O6 drumlike structures. The formation of stannoxane cages in these compounds represents a rare example of Sn−C bond cleavage occurring under ambient conditions. The electrochemical behavior of these organotin compounds suggests a limited electronic communication between the redox-active ferrocene pendants. The reactions of 1 with HOTf, H3BO3, H3PO3, and t-BuPO3H2 take a different course, affording compounds 8−11. While the treatment of 1 with TfOH gave rise to a dimeric stannoxane dication, {[LPh(H2O)Sn(μ-OH)]2}(OTf)2 (8), the reaction with boric acid H3BO3 provided LPhSnB2O3(OH)2 (9), containing a six-membered stannaboroxine ring. In contrast, the reactions of 1 with phosphorous acid (H3PO3) and tertbutylphosphonic acid (t-BuPO 3H2 ) afforded [L(Ph)Sn(HPO3 )]2 (10) and {[L(Ph)Sn]2(μ-OH2)(μ-t-BuPO3) 2} (11), respectively. The solid-state structure analysis of 8−11 suggested the presence of both typical Sn−O covalent bonds and medium-strong Sn←N interactions and showed that different non-carboxylic acids do not affect the character of the Sn−O bond substantially. It is also noteworthy that compounds 8−11 comprising different stannacycles in their structures form inter- and/or intramolecular hydrogen bonds in the solid state. Thus, the dimeric stanoxane core in 8 was enlarged to a six-membered stannaboroxine ring by using boric acid as an inorganic spacer in stannaboroxine 9. The structure of 9 also revealed the presence of hydrogen bonds providing a 2-D infinite polymeric architecture based on the inorganic Sn2B2O3 core. In contrast, organotin(IV) phosphite 10 represents a rare example of an organotin(IV) compound where tin(IV) fragments are connected via an inorganic phosphite spacer into an eight-membered Sn2P2O4 ring. A change of the inorganic spacer to phosphonate units provided the tin(IV) phosphonate 11, containing a well-defined bicyclic cage with two L(Ph)Sn moieties bridged by two phosphonate anions and one water molecule. It appears likely that compounds 8 and 11 contain more Lewis acidic tin atoms (in comparison to 9 and 10), which consequently coordinate an additional water molecule. These water molecules in turn take part in intramolecular hydrogen interactions in the solid state.

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EXPERIMENTAL SECTION

G e n e r a l Me t h o d s . T he st a r t i n g c om p ou n d s [2 , 6 (Me2NCH2)2C6H3](Ph)SnCO3 (1),20 (E)-3-ferrocenyl-2-propenoic acid,28 and 3-ferrocenylpropanoic acid29 were prepared according to the literature. Boric acid, phosphonic acid, t-BuPO3H2, and trifluoromethanesulfonic acid were purchased from Sigma-Aldrich. All reactions were carried out under an argon atmosphere using standard Schlenk techniques. Solvents were dried by standard methods and distilled prior to use. 1H, 13C, 31P, and 119Sn NMR spectra were recorded on a Bruker Avance500 spectrometer at 300 K. The 1H, 13C, 31 P, and 119Sn NMR chemical shifts (δ) are given in ppm and referenced to external Me4Sn (119Sn), Me4Si (13C, 1H), and 85% aqueous H3PO4 (31P). Elemental analyses were performed on a LECO CHNS-932 analyzer. Electrochemical measurements were performed with a μAUTOLAB III computer-controlled polarograph (Eco Chemie) at ambient temperature using a Metrohm three-electrode cell equipped with a F

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(s, 12H, NCH3), 3.00 (AX system, 2H, CH2N), δ 3.48 (s, 4H, CH2N), 4.59 (AX system, 2H, CH2N), 7.20−7.40 (m, 6H, ArH), 7.51 (m, 6H, ArH), 7.91 (d, 4H, ArH). 13C NMR (THF-d8, 100.62 MHz): δ 18.7 (C(CH3)3), 42.8 (NCH3), 62.7 (CH2N), 123.2 (C(3,5)), 125.2 (C(4)), 127.1 (CPh(3,5)), 127.5 (CPh(4)), 132.7 (CPh(2,6)), 134.5 (CPh(1)), 141.7 (C(1)), 144.0 (C(2,6)). 31P NMR (THF-d8, 161.97 MHz): δ 26.6. 119Sn NMR (THF-d8, 149.18 MHz): δ −344.8. X-ray Crystallography. Single crystals of compounds 6 and 8−11 were obtained by slow evaporation of their saturated solutions (CHCl3 for 6 and 10 and 11, CH2Cl2 for 8, and toluene for 9). The diffraction data (see the Supporting Information, Table S1) for colorless crystals of 6 and 8−11 were obtained at 150 K using an Oxford Cryostream low-temperature device and a Nonius KappaCCD diffractometer with Mo Kα radiation (λ = 0.71073 Å). Data reductions were performed with DENZO-SMN.30 The absorption was corrected by integration methods.31 Structures were solved by direct methods (SIR92)32 and refined by full-matrix least squares based on F2 (SHELXL97).33 Hydrogen atoms were mostly localized on the difference Fourier maps; however, in order to ensure uniformity of the treatment of the crystal structures, all hydrogen atoms were recalculated into their idealized positions (riding model) and assigned temperature factors Uiso(H) = 1.2[Ueq(pivotal atom)] (1.5Ueq for the methyl groups) with C−H 0.96, 0.97, and 0.93 Å for methyl, methylene, and hydrogen atoms in aromatic rings, respectively. The OH and NH hydrogens in the structures of 8 and 11 were placed on the appropriate atoms according to the best fitting of maxima on the Fourier difference electron density maps. The cyclopentadienyl rings in the structure of 6 are disordered, and their carbon atoms were treated isotropically. Attempts to treat this disorder by standard constraint and restraint procedures implemented in the SHELXL33,34 program were unsuccessful. Crystallographic data associated with this paper have been deposited with the Cambridge Crystallographic Data Centre as CCDC nos. 984390−984395.

Synthesis of Compound 6. In a manner similar to that for 5, compound 3 (0.15 mg) provided complex 6 (yield 0.13, 27%). Mp: 202 °C dec. Anal. Calcd for C114H108O18Fe6Sn6 (2811.3). C, 50.67; H, 7.91. Found: C, 50.64; H, 7.88. 1H NMR (CDCl3, 400.13 MHz): δ 2.57 (t, 3JHH = 8.2 Hz, 2H, CH2), 2.66 (t, 3JHH = 7.6 Hz, 2H, CH2), 4.04 (s, 4H, C5H4), 4.11 (s, 5H, C5H5), 7.20−17.48 (m, 5H, ArH). Synthesis of Compound 7. Analogously to the preparation of 5, compound 4 (0.10 mg) afforded complex 7 (yield 0.05g, 17%). Mp: 143−144 °C. Anal. Calcd for C114H96O18Fe6Sn6 (2799.3): C, 50.74; H, 7.48. Found: C, 50.72; H, 7.46. 1H NMR (CDCl3, 400.13 MHz): δ 4.15 (s, 5H, C5H5), 4.33 (s, 2H, C5H4), 4.49 (s, 2H, C5H4), 6.02 (d, 3 JHH = 8.3 Hz, 2H, CHCH), 6.92 (d, 3JHH = 7.6 Hz, CHCH), 7.24−7.69 (m, 5H, ArH). Synthesis of Compound 8. Neat trifluoromethanesulfonic acid (0.054 mL, 0.59 mmol) was introduced to a solution of 1 (0.27 g, 0.59 mmol) in CH2Cl2 (10 mL) at room temperature, and the resulting mixture was stirred for 2 h. The volatiles were removed in vacuo, and the solid residue was washed with n-hexane to give 8 as a white powder (yield 0.32 g, 77%). Mp: 158−160 °C. Anal. Calcd for C38H56F6N4O10S2Sn2 (1143.4): C, 42.09; H, 5.21. Found: C, 42.06; H, 5.19. 1H NMR (CDCl3, 500.13 MHz): δ 2.20 (s, 12H, NCH3), 2.52 (s, 12H, NCH3), 3.87 (AB system, 4H, CH2N), 4.29 (bs, 4H, CH2N), 7.22−7.28 (m, 10H, ArH), 7.44 (d, 4H, ArH), 7.60 (d, 2H, ArH), 9.37 (bs, 4H, H2O). 13C NMR (CDCl3, 100.62 MHz): δ 46.1 (NCH2), 63.1 (NCH3), 120.3 (CF3, 1 19 J( F−31C) = 317 Hz), 126.6 (C(3,5)), 129.2 (C(4)), 129.9 (CPh(3,5)), 131.8 (C(1)), 132.9 (CPh(1)), 134.2 (CPh(4)), 135.6 (CPh(2,6)), 142.0 (C(2,6)). 19F NMR (CDCl3, 376.46 MHz): δ −78.4; 119Sn NMR (CDCl3, 149.15 MHz): δ −126.1. Synthesis of Compound 9. Solid H3BO3 (0.07 g, 1.14 mmol) was added to a solution of 1 (0.26 g, 0.07 mmol) in CH2Cl2 (15 mL) at room temperature, and the resulting mixture was stirred for 24 h. Then, the solvent was evaporated in vacuo to afford a solid, which was washed with n-hexane to give 9 as a white powder (yield 0.25 g, 88%). Mp: 190−192 °C. Anal. Calcd for C18H26B2N2O5Sn (490.73): C, 44.06; H, 5.34. Found: C, 44.01; H, 5.29. 1H NMR (CDCl3, 500.13 MHz): δ 2.10 (s, 12H, NMe2), δ 2.88 (AX system, 2H, CH2N), 3.07 (bs, 2H, OH), 4.32 (AX system, 2H, CH2N), 7.00 (d, 2H, ArH), 7.21 (s, 1H, ArH), 7.35 (m, 3H, ArH), 7.55 (d, 2H, ArH). 13C NMR (CDCl3, 125.77 MHz): δ 44.8 (NCH3), 63.0 (NCH2), 127.1 (C(3,5)), 128.6 (CPh(3,5)), 129.6 (C(4)), 130.2 (CPh(4)), 134.5 (CPh(2,6), 1 119 J( Sn−31C) = 60.4 Hz)), 138.6 (CPh(1)), 141.5 (C(1)), 145.2 (C(2,6), 1J(119Sn−31C) = 45.3 Hz)). 119Sn NMR (CDCl3, 186.49 MHz): δ −346.6. Synthesis of Compound 10. Phosphonic acid (0.020 g, 0.24 mmol) was added to a solution of 1 (0.050 g, 0.12 mmol) in CH2Cl2 (15 mL) at room temperature. The resulting mixture was stirred for 24 h at room temperature and then evaporated in vacuo. The resulting solid residue was washed with n-hexane to give 10 as a white powder (yield 0.080 g, 77%). Mp: 297−298 °C. Anal. Calcd for C36H50N4P2O6Sn2 (934.15): C, 46.29; H, 5.40. Found: C, 46.23; H, 5.36. 1H NMR (CDCl3, 400.13 MHz): δ 1.91 (s, 12H, NCH3), δ 2.36 (s, 12H, NCH3), 2.75 (AX system, 4H, CH2N), 4.30 (AX system, 4H, CH2N), 6.90 (d, 4H, ArH), 7.20 (d, 2H, PH, 1J(1H−31P) = 631 Hz), 7.29−7.40 (s, 8H, ArH), 7.71 (d, 4H, ArH). 13C{1H} NMR (CDCl3, 100.62 MHz): δ 43.8 (NCH3), 46.0(NCH3), 62.7 (NCH2), 127.3 (C(3,5)), 128.5 (C(4)), 128.8 (CPh (3,5)), 130.0 (CPh (4)), 134.8 (CPh (2,6); 1J(119Sn−31C) = 60.9 Hz), 137.7 (CPh (1)), 140.1 (C(1)), 145.0 (C(2,6); 1J(119Sn−31C) = 50.7 Hz). 31P{1H} NMR (CDCl3, 161.97 MHz): δ −4.1 (1J(1H,31P) = 631 Hz). 119Sn{1H} NMR (CDCl3, 149.21 MHz): δ −395.7. Synthesis of Compound 11. Solid tert-butylphosphonic acid (0.030 g, 0.24 mmol) was added to a solution of 1 (0.11 g, 0.24 mmol) in CH2Cl2 (15 mL) at room temperature, and the resultant mixture was stirred for 24 h at room temperature. The solvent was evaporated in vacuo, leaving a solid residue that was washed with n-hexane to afford 11 as a white powder (yield 0.10 g, 50%). Mp: 219−221 °C. Anal. Calcd for C44H69N4O7P2Sn2 (1065.39): C, 49.61; H, 6.53. Found: C, 49.57; H, 6.49. 1H NMR (THF-d8, 400.13 MHz): δ 0.9−1.3 (bs, 18H, C(CH3)3), δ 2.29 (bs, 12H, NCH3), δ 2.43

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ASSOCIATED CONTENT

S Supporting Information *

Tabular summary of relevant crystallographic data (Table S1) and CIF files giving crystallographic data for 6 and 8−11. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail for R.J.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the Czech Science Foundation (project nos. 13-00289S and P207/11/0705) and by the Ministry of Education, Youth and Sports of the Czech Republic (project no. MSM0021620857).

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REFERENCES

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dx.doi.org/10.1021/om5002759 | Organometallics XXXX, XXX, XXX−XXX