Reactivity of Elemental Tin and Zinc toward Organophosphonic Acid

Communication pubs.acs.org/IC

Reactivity of Elemental Tin and Zinc toward Organophosphonic Acid Dialkyl Esters: A New One-Pot Recipe for the Synthesis of Coordination Assemblies Derived from O‑Alkylorganophosphonate Ligands Ravi Shankar,*,† Swati Mendiratta,† Nisha Singla,† Gabriele Kociok-Köhn,‡ Michael Lutter,§ and Klaus Jurkschat§ †

Department of Chemistry, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India Department of Chemistry, University of Bath, Bath BA2 7AY, U.K. § Lehrstuhl für Anorganische Chemie II, Technische Universität, 44221 Dortmund, Germany ‡

S Supporting Information *

has followed subsequently.12 It has been shown that oxidative dissolution of zinc metal in the presence of tert-butyl peracetate and 1,1,1,5,5,5-hexafluoroacetylacetone affords the isolation of trans-Zn(hfac)2(H2O)(CH3COOH).13 Organophosphonic acid dialkyl esters, RP(O)(OR)2, represent an important family of organophosphorus compounds,14 and their relevance in synthetic coordination chemistry has attracted considerable attention in the past.15−18 The inclusion of phosphonate monoester ligands in metal−organic frameworks is a useful strategy to enhancing their hydrolytic stability, a feature essential for their practical application. In the domain of organotin chemistry, several molecular compounds derived from phosphonate ester based pincer ligands have been synthesized and structurally characterized.19 Zuckerman et al. have reported the synthesis of cyclohexameric triphenyltin Omethylmethylphosphonate, [Ph3SnOP(O)(OCH3)CH3]6, by a series of complex steps involving the Arbuzov rearrangement of a Ph3SnOP(OCH3)2 intermediate.20 Our contribution in this area relates to the synthesis of diorganotin bis(Oalkylorganophosphonate)s, R2Sn{O(P)(O)(OR)R}2, and their H-phosphonate analogues from the direct reaction between diorganotin dichloride and the corresponding organophosphonic acid dialkyl ester/H-phosphonic acid dialkyl ester.21,22 The reaction proceeds via the selective cleavage of the (P)O−C bond and the elimination of alkyl halide as the byproduct. During the course of this work, our attention was drawn to several reports related to the decomposition of organophosphonic acid dialkyl esters on metal/metal oxide surfaces. The subject remains an attractive area of research to find remedial steps for phosphorus-based chemical warfare agents and biocides.23−26 These results have provided an impetus to direct our efforts to understand the reactivity of elemental tin toward phosphonic acid dialkyl esters. As a case study, the reaction of tin (powder) with MeP(O)(OMe)2 was investigated under inert conditions in a solvent-free medium (eq 1). A slow dissolution of the metal is observed within 18−20 h, and the resulting viscous liquid upon slow cooling gave Me2Sn{O(P)-

ABSTRACT: A new recipe for the synthesis of diorganotin bis(O-alkylorganophosphonate)s, R12Sn{O(P)(O)(OR1)R}2 [R = R1 = methyl (1); R1 = ethyl and R = methyl (2), allyl (3), 2-thienyl (4), benzyl (5)], has been developed from the direct reaction of elemental tin (powder) with organophosphonic acid dialkyl esters, RP(O)(OR1)2, in the presence of a catalytic amount of potassium iodide under ambient conditions (130 °C, 18− 20 h). The key steps in the proposed catalytic cycle involve the monodealkylation of phosphonate diester and in situ generation of a R1SnI or R12SnI2 intermediate via the oxidative addition of alkyl iodide on tin. Evidence in support of the formation of organotin species comes from the isolation of Me2Sn{O(P)(O)(OiPr)Me}2 (6) from the direct reaction of tin metal with MeP(O)(OiPr)2 in the presence of methyl iodide. The method has also been extended to isolate Zn{OP(O)(OMe)Me}2 (7) using metallic zinc as the precursor. All of the compounds have been characterized by IR and NMR studies as well as X-ray crystallography for 2, 4, 6, and 7.

T

he chemistry of elemental tin is quite ubiquitous in the development of organotin chemistry and offers practical routes to construct Sn−C and/or Sn−X (X = halogen) bonds.1−5 The scope of tin as a catalyst in synthetic organic chemistry has been actively pursued in the past.6 An illustrative example is tinmediated Barbier-type reactions between aldehyde and allyl bromide substrates in an aqueous medium for the synthesis of homoallylic alcohols.7−9 The study provides a mechanistic rationale that involves allyltin bromide/diallyltin dibromide as the reactive intermediates in these reactions. A recent report by Jurkschat et al. has shown that elemental tin (powder) exhibits unusual reactivity with weakly acidic monofunctional alcohols such as N-methyldiethanolamine or triethanolamine to yield tin(II) alkoxides.10 Parallel to these developments, the role of elemental zinc as a reactive metal has also been recognized since the early work of Frankland describing the synthesis of diethylzinc from a direct reaction of the metal with ethyl iodide.11 A renaissance in the chemistry of organozinc reagents © XXXX American Chemical Society

Received: November 21, 2016

A

DOI: 10.1021/acs.inorgchem.6b02789 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

Figure 1. 1D structures of (a) 2 and (b) 6. Selected bond lengths (Å) and bond angles (deg) for 2: Sn1−C1 = 2.131(2), Sn1−O1 = 2.2235(15); C1− Sn1−C1 = 180.0, O2−Sn1−O2 = 180.0, O2−Sn1−O1 = 91.36(5), O2−Sn1−O1 = 88.64(5). Selected bond lengths (Å) and bond angles (deg) for 6: Sn−C1 = 2.110(2), Sn−O4 = 2.1832(15), Sn−O1 = 2.1907(15), Sn−O2 = 2.1950(16), Sn−O5 = 2.2309(16); C1−Sn−C2 = 178.27(10), O4−Sn−O1 = 177.78(6), O4−Sn−O2 = 88.38(6), O1−Sn−O2 = 89.45(6), O4−Sn−O5 = 91.32(6), O1−Sn−O5 = 90.86(6), O2−Sn−O5 = 178.82(6).

The identity of 2−5 is established by IR and 1H, 13C, 31P, and Sn NMR spectroscopy as well as electrospray ionization mass spectrometry. The mass spectra of 2 and 3 identify distinct cluster patterns associated with [M + Na]+ ions at m/z 447.0137 (calcd: m/z 447.0121) and m/z 499.0383 (calcd: m/z 499.0434), respectively. As expected, distinct 1H NMR resonances due to the Et2Sn and RP(O)(OEt)O− groups appear in a 1:2 integral ratio and conform with the composition of each compound. The 31 1 P{ H} NMR spectrum exhibits a single resonance in each case at δ 23.6 and 17.5, and these are upfield shifted with respect to the parent organophosphonic acid diethyl ester. The extreme insolubility of 4 and 5 in common organic solvents precludes their spectroscopic characterization in solution. However, solidstate cross-polarization magic-angle-spinning (CP-MAS) 119Sn NMR spectra exhibit chemical shifts at δ −432 and −458, respectively, and show a significant downfield shift compared to that of analogous diethyltin(IV) phosphonate (2) in solution (δ −364; see the Supporting Information, Figure S2). The large variation in the chemical shifts along with the absence of 1 JSn−C/2JSn−O−P couplings suggests that the structure of these compounds in the solid state is not retained in solution. Single crystals of 2 suitable for X-ray crystallography were grown by the slow evaporation of a solution in a dichloromethane/ethanol mixture. Compound 2 crystallizes in the triclinic P1̅ space group. As shown in Figure 1, the structure adopts a one-dimensional (1D) motif featuring an infinite array of puckered eight-membered [−Sn−O−P−O−]2 cyclic rings due to a bidentate coordination mode of the phosphonate ligand [O1−Sn1 = 2.2235(15) Å and O2−Sn1 = 2.1912(14) Å]. The geometry about the phosphorus atom (P1) is that of a distorted tetrahedron, with O−P−O angles lying in the range of 116.29(9)−106.21(9)°. Each tin atom in the polymeric chain adopts a distorted octahedral geometry with an equatorial SnO4 core (∑360° ± 0.0) and trans-ethyl groups (∠C−Sn−C = 180.0°). For 4, refinement of the crystal data could not proceed well because of severe twinning and strong disorder in the 2thienyl and ethoxy groups. Nevertheless, the structure solution provides atom connectivity to elucidate the structural attributes, similar to that of 2 (see the Supporting Information, Figure S3). The formation 2−5 from phosphonate esters as a singlesource precursor provides a basis to put forth a putative mechanism, as shown in Scheme 1. The role of KI as a catalyst in

(O)(OMe)Me}2 (1) as a white crystalline solid in nearly 68% isolable yield.

119

Sn + 2MeP(O)(OMe)2 N2

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ Me2Sn{OP(O)(OMe)Me}2 130 ° C, 18 − 20 h

(1)

It is believed that the concurrent formation of the Sn−C and Sn− O(P) bonds in 1 occurs via oxidative addition of the ligand on the zerovalent tin. The result finds an analogy with an earlier report on the oxidative addition of phosphate esters on metallic zinc.27 The IR and NMR spectroscopic data of 1 (see the Supporting Information, SI) are identical with those of an authentic sample obtained from the reaction of dimethyltin dichloride with methylphosphonic acid dimethyl ester.22 To expand the substrate scope, the reaction of MeP(O)(OEt)2 with tin powder under conditions similar to those described for 1 has been studied. Nevertheless, no dissolution of the metal was observed, and the starting precursor was recovered even after prolonged heating for 72 h. However, the addition of a catalytic amount (0.2 equiv with respect to tin) of KI into the reaction mixture accelerated dissolution of the metal within 18−20 h and resulted in the precipitation of a white solid, which was characterized as diethyltin bis(O-ethylmethylphosphonate) (2; eq 2). The method is found to be quite general and tolerant to the functional groups on the phosphorus atom, as is evident from the isolation of analogous diorganotin(IV) phosphonate esters, 3−5. Using this approach, we have been able to synthesize 1 with an isolable yield, which is comparable to that obtained from the direct reaction of tin metal with phosphonate diester in the absence of KI (vide supra). Sn + 2RP(O)(OEt)2 N2,KI

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→

Et 2Sn{OP(O)(OEt)R}2 130 ° C, 18 − 20 h R = methyl (2), allyl (3), 2‐thienyl (4), benzyl (5)

(2)

The slow reactivity of methylphosphonic acid diethyl ester with respect to dealkylation, as observed herein, finds an analogy with earlier reports.28,29 It has been shown that the reactivity of phosphonate esters, RP(O)(OR1)2, toward Me3SiCl/NaI decreases with an increase in the bulk of the alkyl (R1) groups and follows the order Me > Et > iPr. B

DOI: 10.1021/acs.inorgchem.6b02789 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry Scheme 1. Catalytic Cycle for the Formation of 2−5

Figure 2. Structure of 7. All hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and bond angles (deg): Zn1−O1 = 1.928(2), Zn1−O3 = 1.931(2), Zn1−O2 = 1.937(3), Zn1−O11 = 1.929(2), Zn2−O7 = 1.923(2), Zn2−O5 = 1.926(2), Zn2−O9 = 1.931(2), Zn2− O6 = 1.940(2); O1−Zn1−O2 = 112.47(11), O1−Zn1−O3 = 106.89(10), O11−Zn1−O3 = 115.66(10), O3−Zn1−O2 = 104.28(10).

the formation of RP(O)(OR1)O−K+ (A) parallels earlier reports on the monodealkylation of phosphonate diesters with alkalimetal halides.30 The in situ generated ethyl iodide likely undergoes oxidative addition on tin metal2,31 to form EtSnI or Et2SnI2. Although we have not been able to isolate or detect the formation of these species under the prescribed conditions, the isolation of R2Sn{OP(O)(OR)R}2 from a direct reaction between diorganotin dihalide and phosphonate diester has been reported earlier by us.22 The formation of 2−5 is effected by either salt elimination and/or oxidative addition steps with the elimination of KI. The role of in situ generated ethyl iodide in the catalytic cycle is further substantiated by reacting tin metal with methylphosphonic acid diisopropyl ester in the presence of 2 equiv of methyl iodide (eq 3). The reaction affords Me2Sn{O(P)(O)(OiPr)Me}2 (6) exclusively, suggesting the involvement of MeSnI or Me2SnI2 as reactive intermediates that subsequently react with phosphonate diester to give the desired product. It is likely that isopropyl iodide formed during this reaction does not participate in the oxidative addition because of its low reactivity. Compound 6 crystallizes in the monoclinic P21/n space group. The structure (Figure 1) consists of an infinite array of puckered eight-membered [−Sn−O−P−O−]2 cyclic rings [Sn−O = 2.2309(16)−2.1832(15) Å and ∠O−P−O = 116.72(9)− 106.04(9)°] similar to those observed for 2. The 1H NMR spectrum in a CDCl3 solution reveals distinct resonances due to Sn−Me, P−Me, and P−OPri groups at their routine positions with observed heteronuclear couplings (2JSn−H = 108.6 and 2JP−H = 17.4 Hz), while a single 31P NMR resonance appears at δ 23.6.

while the methoxy groups of the ester moiety remain appended to the 1D chain. The average Zn−O bond lengths [1.923(2)− 1.940(2) Å] and O−Zn−O bond angles [104.28(10)− 115.66(10)°] (see the Supporting Information, Table S4) lie in the normal range found in known zinc phosphonates.32 In summary, we have demonstrated that the reactivity of tin with organophosphonic acid dialkyl esters in the presence of KI as a catalyst has offered an attractive synthetic route to diorganotin phosphonate esters 1−6. The method allows the concurrent formation of Sn−C and Sn−O(P) bonds in a one-pot reaction without taking recourse to diorganotin dihalides/oxides as the substrates. The isolation of 7 from zinc dust suggests a wide applicability of this approach in the coordination chemistry of metal phosphonates. Further studies are in progress in this direction.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02789. Synthetic procedures and spectroscopic data for 1−7 (PDF) X-ray crystallographic data in CIF format for 2 (CCDC 1447622) (CIF) X-ray crystallographic data in CIF format for 6 (CCDC 1517303) (CIF) X-ray crystallographic data in CIF format for 7 (CCDC 1485870) (CIF)

Sn + 2MeP(O)(Oi Pr)2 + MeI N2

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ Me2Sn{O(P)(O)(Oi Pr)Me}2 + 2iPrI 130 ° C, 18 − 20 h

(3)

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We were also interested in understanding the behavior of other reactive metals toward phosphonate diesters. To this end, we investigated the reaction of zinc dust with methylphosphonic acid dimethyl ester under the conditions described for 1. Interestingly, complete dissolution of metal occurs within 18−20 h, yielding Zn{OP(O)(OMe)Me}2 (7) and suggesting chemoselective reactivity of the (P)O−C ester bond (see the Supporting Information). Compound 7 crystallizes in the monoclinic P21/n space group. A perspective view, as shown in Figure 2, reveals that the structure is built from the corner sharing of ZnO4 and [MeP(O)(OMe)O]− tetrahedra, with the anionic phosphonate monoester groups bridging the adjacent zinc atoms. The phosphorus atoms P2 and P4 show disorder over two positions with 40:60 and 70:30 occupancies, respectively, and only one of these sites is shown in Figure 2. The structure is reminiscent of an infinite array of vertex-shared eight-membered Zn2O4P2 rings,

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Ravi Shankar: 0000-0002-4991-7018 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by CSIR Grant 01(2651)/12/EMR-II. S.M. is grateful to the UGC-CSIR for providing a Senior Research Fellowship. The authors gratefully acknowledge Prof. Pavletta Shestakova (Laboratory of Nuclear Magnetic Resonance, Institute of Organic Chemistry, Bulgarian Academy of Sciences) for solid-state CP-MAS 119Sn NMR studies. C

DOI: 10.1021/acs.inorgchem.6b02789 Inorg. Chem. XXXX, XXX, XXX−XXX

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methylmethylphosphato triphenyltin(IV). J. Organomet. Chem. 1983, 244, 17−33. (21) Shankar, R.; Asija, M.; Singla, N.; Basu, S.; Kociok-Köhn, G.; Molloy, K. C. Synthesis, characterization and selective de-esterification of diorganotin bis(O-methylphosphite)s. Dalton Trans. 2013, 42, 15591−15598. (22) Shankar, R.; Asija, M.; Singla, N.; Kociok-Köhn, G.; Molloy, K. C. Synthesis, characterization and hydrolytic stability of diorganotin(IV) bis(O-alkyl alkylphosphonate)s. Can. J. Chem. 2014, 92, 549−555. (23) Ekerdt, J. G.; Klabunde, K. J.; Shapley, J. R.; White, J. M.; Yates, J. T., Jr. Surface chemistry of organophosphorus compounds. J. Phys. Chem. 1988, 92, 6182−6188. (24) Ratliff, J. S.; Tenney, S. A.; Hu, X.; Conner, S. F.; Ma, S.; Chen, D. A. Decomposition of dimethyl methylphosphonate on Pt, Au, and Au-Pt clusters supported on TiO2 (110). Langmuir 2009, 25, 216−225. (25) Henderson, M. A.; White, J. M. Adsorption and decomposition of dimethyl methylphosphonate on platinum (111). J. Am. Chem. Soc. 1988, 110, 6939−6947. (26) Jang, Y. J.; Kim, K.; Tsay, O. G.; Atwood, D. A.; Churchill, D. G. Destruction and detection of chemical warfare agents. Chem. Rev. 2015, 115, PR1−PR76. (27) Jubert, C.; Knochel, P. Preparation of new classes of aliphatic, allylic, and benzylic zinc and copper reagents by the insertion of zinc dust into organic halides, phosphates, and sulfonates. J. Org. Chem. 1992, 57, 5425−5431. (28) Morita, T.; Okamoto, Y.; Sakurai, H. Dealkylation reactions of acetals, phosphonate, and phosphate esters with chlorotrimethylsilane/ metal halide reagent in acetonitrile, and its application to the synthesis of phosphonic acids and vinyl phosphates. Bull. Chem. Soc. Jpn. 1981, 54, 267−273. (29) Gray, M. D. M.; Smith, D. J. H. Selective demethylation of phosphorous esters. Tetrahedron Lett. 1980, 21, 859−860. (30) Krawczyk, H. A convenient route for monodealkylation of diethyl phosphonates. Synth. Commun. 1997, 27, 3151−3161. (31) Wakeshima, I.; Kijima, I. Preparation of monoalkyltin(IV) compounds by the reaction of organic tin(II) compounds with n-alkyl halides. J. Organomet. Chem. 1974, 76, 37−41. (32) Hix, G. B.; Kariuki, B. M.; Kitchin, S.; Tremayne, M. Synthesis and structural characterization of Zn(O3PCH2OH), a new microporous zinc phosphonate. Inorg. Chem. 2001, 40, 1477−1481.

REFERENCES

(1) Thoonen, S. H. L.; Deelman, B.-J.; van Koten, G. Synthetic aspects of tetraorganotins and organotin(IV) halides. J. Organomet. Chem. 2004, 689, 2145−2157. (2) Smith, A. C.; Rochow, E. G. Direct synthesis of organotin halides Preparation of dimethyltin dichloride. J. Am. Chem. Soc. 1953, 75, 4103− 4105. (3) Sisido, K.; Takeda, Y.; Kinugawa, Z. Direct synthesis of organotin compounds - Di- and tribenzyltin chlorides. J. Am. Chem. Soc. 1961, 83, 538−541. (4) Vargas-Pineda, D. G.; Guardado, T.; Cervantes-Lee, F.; MettaMagana, A. J.; Pannell, K. H. Intramolecular chalcogen-tin interactions in [(o-MeEC6H4)CH2]2SnPh2‑nCln (E = S, O, CH2; n = 0, 1, 2) and intermolecular chlorine-tin interactions in the meta- and para-methoxy isomers. Inorg. Chem. 2010, 49, 960−968. (5) Evans, C. J. In Chemistry of tin; Smith, P. J., Ed.; Blackie Academic and Professionals: London, 1998; p 442. (6) Pereyre, M.; Quintard, J.-P.; Rahm, A. Tin in organic synthesis; Butterworth: London, 1987. (7) Chan, T. H.; Yang, Y.; Li, C. J. Organometallic reactions in aqueous media. The nature of the organotin intermediate in the tin-mediated allylation of carbonyl compounds. J. Org. Chem. 1999, 64, 4452−4455. (8) Lin, M.-H.; Hung, S.-F.; Lin, L.-Z.; Tsai, W.-S.; Chuang, T.-H. Tin mediated allylation reactions of enol ethers in water. Org. Lett. 2011, 13, 332−335. (9) Dam, J. H.; Fristrup, P.; Madsen, R. Combined experimental and theoretical mechanistic investigation of the Barbier allylation in aqueous media. J. Org. Chem. 2008, 73, 3228−3235. (10) Zöller, T.; Iovkova-Berends, L.; Dietz, C.; Berends, T.; Jurkschat, K. On the reaction of elemental tin with alcohols: A straightforward approach to tin(II) and tin(IV) alkoxides and related tin oxo clusters. Chem. - Eur. J. 2011, 17, 2361−2364. (11) Seyferth, D. Zinc alkyls, Edward Frankland, and the beginnings of main-group organometallic chemistry. Organometallics 2001, 20, 2940− 2955. (12) Knochel, P.; Singer, R. D. Preparation and reactions of polyfunctional organozinc reagents in organic synthesis. Chem. Rev. 1993, 93, 2117−2188. (13) Visintin, P. M.; Bessel, C. A.; White, P. S.; Schauer, C. K.; DeSimone, J. M. Oxidative dissolution of copper and zinc metal in carbon dioxide with tert-butyl peracetate and a β-diketone chelating agent. Inorg. Chem. 2005, 44, 316−324. (14) Queffélec, C.; Petit, M.; Janvier, P.; Knight, D. A.; Bujoli, B. Surface modification using phosphonic acids and esters. Chem. Rev. 2012, 112, 3777−3807. (15) Gelfand, B. S.; Lin, J.-B.; Shimizu, G. K. H. Design of a humiditystable metal−organic framework using a phosphonate monoester ligand. Inorg. Chem. 2015, 54, 1185−1187. (16) Zhang, J. W.; Zhao, C. C.; Zhao, Y. P.; Xu, H. Q.; Du, Z. Y.; Jiang, H. L. Metal-organic frameworks with improved moisture stability based on a phosphonate monoester: Effect of auxiliary N-donor ligands on framework dimensionality. CrystEngComm 2014, 16, 6635−6644. (17) Yamada, T.; Kitagawa, H. Syntheses of metal−organic frameworks with protected phosphonate ligands. CrystEngComm 2012, 14, 4148−4152. (18) Richards, A. F.; Beavers, C. M. Synthesis and structures of a pentanuclear Al(III) phosphonate cage, an In(III) phosphonate polymer, and coordination compounds of the corresponding phosphonate ester with GaI3 and InCl3. Dalton Trans. 2012, 41, 11305−11310. (19) Peveling, K.; Henn, M.; Löw, C.; Mehring, M.; Schürmann, M.; Costisella, B.; Jurkschat, K. Mechanistic studies on the cyclization of organosilicon and organotin compounds containing the O,C,Ocoordinating pincer-type ligand {4-t-Bu-2,6-[P(O)(OR)2]2C6H2}− (R = i-Pr, Et): Phosphorus (POC)- versus carbon (POC)-attack. Organometallics 2004, 23, 1501−1508. (20) Masters, J. G.; Nasser, F. A. K.; Hossain, M. B.; Hagen, A. P.; van der Helm, D.; Zuckerman, J. J. Oxy- and thio-phosphorus acid derivatives of tin(IV). The crystal and molecular structure of OD

DOI: 10.1021/acs.inorgchem.6b02789 Inorg. Chem. XXXX, XXX, XXX−XXX