Simplicity Meets Beauty. Trapping Molecular Dimethyltin Oxide in the

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Simplicity Meets Beauty. Trapping Molecular Dimethyltin Oxide in the Novel Organotinoxo Cluster [MeN(CH2CH2O)2SnMe2·Me2SnO]3 Michael Gock, Bianca Wiedemann, Christina Dietz, Chenyu Bai, Michael Lutter, Vinusuya Abeyawarathan, and Klaus Jurkschat* Lehrstuhl für Anorganische Chemie II, Technische Universität Dortmund, 44221 Dortmund, Germany S Supporting Information *

ABSTRACT: The syntheses are reported of the 1,1,5trimethyl-2,8-dioxa-5-aza-1-stannabicyclo[3.3.0]octane MeN(CH2CH2O)2SnMe2 (1), its monosodium aminoalcoholate adduct [MeN(CH 2 CH 2 O) 2 SnMe 2 ·MeN(CH 2 CH 2 ONa)(CH2CH2OH)]2 (2), and the hexanuclear organotin oxo cluster [MeN(CH2CH2O)2SnMe2·Me2SnO]3 (3). The compounds were characterized by 1H, 13C, and 119Sn NMR spectroscopy, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction analysis. In the solid state, compound 1 is a tetramer that is brought about by intermolecular O→Sn interactions. In solution, however, it shows a monomer ⇌ dimer equilibrium that is fast on the 1H, 13C, and 119Sn NMR time scales at room temperature. All compounds show intramolecular N→Sn interactions at Sn−N distances ranging between 2.378(3) Å (2) and 3.026(3) Å (3·0.25H2O). Compound 3 can formally be regarded as a molecular dimethyltin oxide being trapped by head-to-tail complexation with a stannabicyclooctane. In solution, it slowly falls apart into 1 and Me2SnO.

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INTRODUCTION Alkanolamines, R3−nN(CH2CRR′OH)n (R, R′, R″ = H, alkyl, aryl; n = 1−3), are a rather interesting class of chelate ligands that are accessible by simple reactions among cheap industrial commodities such as ammonia, amines, and epoxides.1 A great variety of metal complexes containing such ligands in their deprotonated forms has been reported.2 Among these, the tri-, bi-, and monocyclic derivatives N(CH2CR′R″O)3M, RN(CH2CR′R″O)2M, and R2NCH2CR′R″OM (R, R′, R″ = H, alkyl, aryl; M = main-group elements or transition metals with or without substituents) have been intensely studied.2c,3 Prominent representatives of main-group-element compounds containing N-organoaminoalcoholate ligands are the 2,8-dioxa5-aza-1-stannabicyclo[3.3.0]octane derivatives RN(CH2CH2O)2SnR2 (R = alkyl, aryl) and RN(CH2CR′2O)2Sn (R, R′ = Me, H), containing tin atoms in the oxidation states +IV and +II.4 A characteristic feature of these compounds is the intramolecular N→Sn interaction, the strength of which depends on the substituent pattern at the nitrogen and tin as well at the OC atoms. Notably, although the diorganotin(IV) compounds mentioned above are among the first representatives of metal derivatives of alkanolamines, to the best of our knowledge, only the molecular structure in the solid state of MeN(CH2CH2O)2Sn-t-Bu2,4d as determined by single-crystal X-ray diffraction analysis, has been reported. In this compound, the tin atom is pentacoordinated with a distorted-trigonalbipyramidal environment in which the oxygen atoms occupy the axial positions and the nitrogen atom and the tert-butyl substituents occupy the equatorial positions. Also reported has been the molecular structure of the monoorganotin compound MeN(CH2CH2O)2Sn(S2CNMe2)(CH2)2C(O)OEt,4e in which © XXXX American Chemical Society

the tin atom is six-coordinate. Even more surprising, there are no reports in the literature concerning the synthesis and characterization of the parent compound MeN(CH2CH2O)2SnMe2. Our renewed interest in alkanolamine derivatives of tin especially stems from a recent discovery, according to which such inorganic nontoxic compounds lacking any tin−carbon bond are excellent delayed-action catalysts for polyurethane formation.4k Within the studies related to these compounds we recently reported the unprecedented trinuclear tin aminoalcoholate species [MeN(CH2CMe2O)2SnBr2]2·SnBr2(OH)2, in which molecular tin dibromide dihydroxide, SnBr2(OH)2, is stabilized by two stannabicyclooctane moieties.4i In context with our comprehensive study on the class of compounds mentioned above, we report here our attempts at obtaining MeN(CH2CH2O)2SnMe2 and show that, depending on the reaction conditions employed, the latter compound, its adduct with sodium aminoalcoholate, and an unprecedented hexanuclear tinoxo cluster were obtained. In the last case, the stannabicyclooctane moieties formally stabilize molecular dimethyltin oxide, Me2SnO.

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RESULTS AND DISCUSSION Reaction of Dimethyltin Dichloride, Me2SnCl2, with Disodium N -M et hy la m inod i et ha nola t e, MeN(CH2CH2ONa)2. The reaction of the sodium salt of Nmethyldiethanolamine, MeN(CH2CH2ONa)2, with dimethyltin dichloride, Me2SnCl2, provided the 1,1,5-trimethyl-2,8-dioxa-5Received: May 16, 2013

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dx.doi.org/10.1021/om400432k | Organometallics XXXX, XXX, XXX−XXX

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doublet of doublets resonance at δ 2.74 (J(1H−1H) = 4 Hz, 5 Hz). The OCH2 protons are split in two signals, which show an AB system, at δ 3.73 (2J(1H−1H) 11 Hz, 3J(1H−1H) = 4 Hz, J(1H−117/119Sn) = 120 Hz) and δ 3.95 (2J(1H−1H) = 11 Hz, 3 1 J( H−1H) = 5 Hz, J(1H−117/119Sn) = 60 Hz), respectively. A 13 C{ 1 H} NMR spectrum showed two equally intense resonances at δ −1.2 and 0.3 (SnCH3) and three signals at δ 41.7 (NCH3), δ 58.2 (J(1H−117/119Sn) = 30 Hz, NCH2), and δ 61.1 (J(1H−117/119Sn) = 36 Hz, OCH2). A 119Sn{1H} NMR spectrum in CDCl3 showed a single resonance at δ −59 ppm without 117Sn satellites. The chemical shift is between those reported for Me2Sn(O-t-Bu)2 (δ −1, tetracoordinated tin atom) and Me2Sn(O-s-Bu)2 (δ −93, pentacoordinated tin atom by dimerization via an O→Sn interaction).5b The NMR data reveal that (i) the tetramer observed in the solid state is not retained in solution, (ii) the existence of a monomer ⇌ dimer equilibrium is fast on the 1H, 13C, and 119Sn NMR time scales at room temperature, and (iii) the tin atom in the monomer is pentacoordinated with the Sn−methyl groups and the nitrogen atom located in the equatorial positions of a trigonal-bipyramidal environment (Chart 1, A). For the alternative structure B (Chart 1), the 2J(1H−117/119Sn) coupling constants should be rather different, as was indeed demonstrated a long time ago for the sulfur-containing compound MeN(CH2CH2S)2SnMe2.5c A 119Sn NMR spectrum of a clear solution of compound 1 in toluene that had been heated at reflux for 3 h under noninert conditions and the volume of which had been reduced in vacuo showed three resonances at δ −61 (1, integral 76), −137 (integral 12), and −376 (integral 12). The last two signals belong to the unusual organotinoxo cluster 3 (see below). Further heating caused the integral ratios of the signals to change in favor of compound 3 and the appearance of a resonance at δ −450 (integral 2) that is assigned to the spirocyclic compound spiro-[MeN(CH2CH2O)2]2Sn.4h Along this process, formation of a colorless solid, (Me2SnO)n, was observed. An electrospray ionization mass spectrum (positive mode), hereafter referred to as ESI MS, of compound 1 in acetonitrile showed mass clusters centered at m/z 268.0 ([1 + H]+), m/z 430.1 ([1 + Me2SnO − H]+) and 533.1 ([2·1 + H]+). In an independent experiment, the reaction according to eq 1 was performed with a 5% excess of MeN(CH2CH2ONa)2. It

aza-1-stannabicyclo[3.3.0]octane (1) in moderate yield as a colorless crystalline material that is soluble in CH2Cl2, toluene, and THF (eq 1). The structure in the solid state of compound 1 (as the tetramer) is shown in Figure 1, and selected bond distances and angles are given in Table 1.

In the solid state compound 1 is a centrosymmetric tetramer with two crystallographically independent tin atoms. The Sn(1) atom is hexacoordinated by one nitrogen, two carbon, and three oxygen atoms and exhibits a distorted-octahedral environment with the methyl substituents being cis. The distortion from the ideal octahedral geometry is expressed by the O(11)−Sn(1)−O(37), O(17)−Sn(1)−C(1), and N(14)− Sn(1)−C(2) angles of 160.41(13), 158.00(16), and 164.63(18)°, respectively, deviating from 180°. The Sn(2) atom is heptacoordinated by one nitrogen, two carbon, and four oxygen atoms and adopts a distorted-pentagonalbipyramidal environment in which the methyl substituents occupy the axial positions and the O(37), N(34), O(31), O(31A), and O(17) atoms occupy the equatorial positions. The Sn(1)−N(14) and Sn(2)−N(34) distances of 2.437(4) and 2.510(4) Å are longer than the corresponding distances of 2.30(2)−2.34(2) Å reported for the three crystallographically independent molecules of MeN(CH2CH2O)2Sn-t-Bu24d and for MeN(CH 2 CH 2 O) 2 Sn(S 2 CNMe 2 )(CH 2 ) 2 C(O)OEt (2.322(7) Å).4e The Sn−O distances range from 2.069(4) to 2.345(3) Å. A concentration-independent 1H NMR spectrum displayed two equally intense sharp resonances at δ 0.26 (J(1H−117/119Sn) = 65 Hz) and 0.45 (J(1H−117/119Sn) = 63 Hz), respectively, that are assigned to the Sn−methyl protons. Employing Lockhart’s equation (θ = 0.0161(2J)2 − 1.32(2J) + 133.4)5a for the estimation of Me−Sn−Me angles from 2J(1H−119Sn) coupling constants gives values of 115.6 and 114.1°, respectively. The sharp resonance at δ 2.38 (J(1H−117/119Sn) = 12 Hz) is assigned to the N-methyl protons. The NCH2 protons show a

Figure 1. Structure of compound 1 in the solid state (ORTEP presentation at 30% probability of the depicted atoms and atom numbering scheme). Symmetry code: (A) −x, −y, −z + 2. The hydrogen atoms are omitted for clarity. B


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Table 1. Selected Bond Lengths (Å) and Angles (deg) for Compound 1a Sn(1)−O(11) Sn(1)−O(17) Sn(1)−O(37) Sn(1)−N(14) Sn(1)−C(1) Sn(1)−C(2) Sn(2)−O(17) O(11)−Sn(1)−O(37) O(17)−Sn(1)−C(1) O(31)−Sn(2)−O(31A) O(31)−Sn(2)−O(37) N(14)−Sn(1)−C(2) a

2.069(4) 2.134(3) 2.147(3) 2.437(4) 2.153(6) 2.141(5) 2.345(3) 160.41(13) 158.00(16) 70.17(13) 138.48(12) 164.63(18)

Sn(2)−O(31) Sn(2)−O(31A) Sn(2)−O(37) Sn(2)−N(34) Sn(2)−C(21) Sn(2)−C(22) O(17) −Sn(2)−O(31) O(17)−Sn(2)−N(34) O(31A)−Sn(2)−N(34) O(37)−Sn(2)−O(31A) C(21)−Sn(2)−C(22)

2.274(3) 2.208(3) 2.314(3) 2.510(4) 2.123(4) 2.115(4) 156.39(11) 134.74(13) 138.98(13) 151.30(12) 178.1(2)

Symmetry code: (A) −x, −y, −z + 2.

centrosymmetric head-to-tail dimer via an unsymmetric O(17)···H(27A)−O(27A) hydrogen bridge at a O(17)···O(27A) distance of 2.629(4) Å. In addition, there is an electrostatic Na(1)···O(11A) interaction at a distance of 2.345(3) Å supporting the dimerization. As in compound 1, the Sn(1) atom is hexacoordinated and shows a distortedoctahedral environment, with the methyl substituents being cis. The O(11)−Sn(1)−C(31), O(17)−Sn(1)−O(21), and N(14)−Sn(1)−C(32) angles are 166.21(14), 161.76(11), and 162.84(15)°, respectively, and express the distortion from the ideal octahedral geometry. The Sn(1)−N(14) distance of 2.378(3) Å is shorter than the corresponding distance in compound 1. The Na(1) cation is five-coordinated by four oxygen atoms and one nitrogen atoms at Na−O distances ranging between 2.305(3) (Na(1)−O(21)) and 2.427(3) Å (Na(1)−O(11)). These distances compare well with the values reported for {Ph 2 (I)SnCH 2 Sn(Ph)(I)CH 2 -[16]-crown-5}·NaF·CH 3 OH (2.363(3)−2.479(3) Å)5c and for the sodium iodide complex of [15]-crown-5 (2.398(4)−2.444(4) Å).6 The Na(1)−N(24) distance of 2.560(17) Å is comparable with Na−N distances (2.550(4)−2.797(4) Å) found in the cyclene-based tert-butyl triester derivative7 and in [CH2N(Me)CH2CMe2OH]2·NaOMe (2.509(3), 2.515(3) Å).8 An ESI MS of compound 2 in acetonitrile showed mass clusters centered at m/z 268.0 ([1 + H]+), m/z 409.1 ([0.5·2 + H]+) and m/z 533.1 ([2·1 + H]+). Reaction of Dimethyltin Oxide, (Me2SnO)n, with NMethyldiethanolamine, MeN(CH2CH2OH)2. The reaction of 1 molar equiv of dimethyltin oxide, (Me2SnO)n, 1 molar equiv of freshly distilled N-methyldiethanolamine, MeN(CH 2 CH 2 OH) 2 , and a catalytic amount of potassium hydroxide, KOH, in boiling toluene in a Dean−Stark apparatus gave a reaction mixture, the 119Sn{1H} NMR spectrum of which, after some of the solvent had been evaporated in vacuo (Figures S1 and S2, Supporting Information), showed a major resonance at δ −65 (integral 59, 1) and four pairs of equally intense resonances at δ −137/−376 (J(119Sn−117/119Sn) = 59 Hz, integral 4, 3), −386/−515 (J(119Sn−117/119Sn) = 224 Hz, integral 8, signals a/a′), −400/−521 (J(119Sn−117/119Sn) = 234 H z , i n t e g r a l 5 , s i g n a l s b / b ′ ) , a n d −3 9 8 / −5 2 5 (J(119Sn−117/119Sn) = 208 Hz, integral 3, signals c/c′), respectively (Scheme 1). In addition, there are resonances of very low intensity at δ −451 (integral 0.5, spiro-[MeN(CH2CH2O)2]2Sn) and δ −2 (integral 1, SnMe4). The identity of the species belonging to the high-field pairs of resonances a/ a′, b/b′, and c/c′ has not yet been unveiled. One possibility is

Chart 1

provided the heterobimetallic compound [MeN(CH 2 CH 2 O) 2 SnMe 2 ·MeN(CH 2 CH 2 ONa)(CH 2 CH 2 OH)] 2 (2) as a colorless crystalline material. The molecular structure of 2 is shown in Figure 2, and selected interatomic distances and angles are given in Table 2. Compound 2 contains an adduct consisting of the stannabicyclooctane 1 and the monosodium aminoalcoholate MeN(CH2CH2ONa)(CH2CH2OH). This adduct forms a

Figure 2. Molecular structure of compound 2 (ORTEP presentation at 30% probability of the depicted atoms and atom numbering scheme). Symmetry code: (A) −x + 1, −y + 1, −z + 1. The hydrogen atoms, except H(27), are omitted for clarity. C


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Table 2. Selected Bond Lengths (Å) and Angles (deg) for Compound 2a Sn(1)−O(11) Sn(1)−O(17) Sn(1)−O(21) Sn(1)−N(14) Sn(1)−C(31) Sn(1)−C(32) O(17)−Sn(1)−O(21) O(11)−Sn(1)−C(31) N(14)−Sn(1)−C(32) O(11A)−Na(1)−N(24) a

2.127(3) 2.112(3) 2.089(3) 2.378(3) 2.174(4) 2.165(4) 161.76(11) 166.21(14) 162.84(15) 118.6(2)

Na(1)−O(11) Na(1)−O(11A) Na(1)−O(21) Na(1)−O(27) Na(1)−N(24) O(17)···O(27A) O(11)−Na(1)−N(24) O(11)−Na(1)−O(27) O(21)−Na(1)−O(11A) O(21)−Na(1)−O(27)

2.427(3) 2.345(3) 2.305(3) 2.396(4) 2.560(17) 2.629(4) 138.8(2) 149.44(13) 137.42(12) 129.29(12)

Symmetry code: (A) −x + 1, −y + 1, −z + 1.

Scheme 1. Reaction of Dimethyltin Oxide with NMethyldiethanolamine

The molecular structure of compound 3·0.25H2O is shown in Figure 3. Selected bond lengths and angles are given in Table 3.

Figure 3. Molecular structure of compound 3·0.25H2O (ORTEP presentation at 30% probability of the depicted atoms and atom numbering scheme). The water solvate molecule and the hydrogen atoms are omitted for clarity. Symmetry code: (A) 1 − x + y, 1 − x, z; (B) 1 − y, x − y, z; (C) x, y, 1.5 − z; (D) 1 − x + y, 1 − x, 1.5 − z; (E) 1 − y, x − y, 1.5 − z.

the formation of polynuclear tin oxo clusters containing tin atoms that carry only one or even no methyl substituent. This idea gets support from the observation of volatile SnMe4 and spiro-[MeN(CH2CH2O)2]2Sn in the crude reaction mixture. This can be seen in analogy to the phenyl group migration observed upon heating of MeN(CH2CH2O)2SnPh2 to give [MeN(CH2CH2O)2]2Sn and SnPh4.4f In support of that, a 1Hcoupled 119Sn NMR spectrum gave septet resonances for the signals at δ −137/−376 while the signal pairs a/a′, b/b′, and c/ c′ gave only broad resonances. Interestingly, the composition of the reaction mixture according to Scheme 1 did not change significantly upon variation of the tin oxide to ethanolamine ratio between 1:1 and 1:5. The compound 3, as its aqua solvate 3·0.25H2O, was isolated as either colorless blocks or needles by crystallization from a CH2Cl2/hexanes mixture at 4 °C. The unit cell parameters, as determined by X-ray diffraction analysis, proved to be identical. Only the data obtained from the block-shaped crystals were refined.

The molecular structure contains the two crystallographically independent tin atoms Sn(1) and Sn(2). The Sn(1) atom is [6 + 1]-coordinate. It adopts a strongly distorted monocapped octahedral environment with the two methyl substituents occupying the axial positions (C(1)−Sn(1)−C(1C) = 170.92(17)°), the O(1), O(1A), O(11), and O(17) atoms occupying the equatorial positions, and N(14) being the capping atom at a N−Sn distance of 3.026(3) Å (edge attack). This distance is much longer than the N−Sn distances in 1 and 2. Nevertheless, the N→Sn interaction causes the O(11)− Sn(1)−O(17) angle to increase to 119.39(9)° and the O(1)− Sn(1)−O(11) angle to decrease to 71.59(9)°. The Sn(2) atom is five-coordinate and adopts a distorted trigonal-bipyramidal environment in which the O(1) and O(17B) atoms are located in the axial positions and the C(2), C(2C), and O(1) atoms occupy the equatorial positions. The distortion from the ideal geometry is expressed by a O(11)−Sn(2)−O(17B) angle of 155.53(12)° that deviates from 180°. D


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Table 3. Selected Bond Lengths (Å) and Angles (deg) for Compound 3·0.25H2Oa Sn(1)−O(1) Sn(1)−O(11) Sn(1)−O(17) Sn(1)−N(14) Sn(1)−C(1) C(1)−Sn(1)−C(1C) O(1)−Sn(1)−O(17) O(1A)−Sn(1)−O(11) O(1)−Sn(1)−O(11) O(11)−Sn(1)−O(17) C(2)−Sn(2)−C(2C) a

2.146(3) 2.314(2) 2.323(3) 3.026(3) 2.110(3) 170.92(17) 165.81(12) 169.29(9) 71.59(9) 119.39(9) 120.7(2)

Sn(2)−O(1) Sn(2)−O(11) Sn(2)−O(17B) Sn(2)−C(2) O(1)−Sn(2)−C(2) O(11)−Sn(2)−O(17B) Sn(1)−O(1)−Sn(2) Sn(1)−O(11)−Sn(2) O(1)−Sn(2)−O(11)

2.020(2) 2.077(2) 2.104(3) 2.119(4) 119.63(11) 155.53(12) 108.54(10) 100.65(10) 79.21(10)

Symmetry code: (A) 1 − x + y, 1 − x, z; (B) 1 − y, x − y, z; (C) x, y, 1.5 − z.

Chart 2

benzannulated lutidine-bridged bis-stannylene.9 The Sn−O distance in this compound is 2.079(2) Å. In the related cluster [{MeN(CH 2 CH 2 O) 2 Sn(Cl)R} 2 ·{R(Cl)SnO} 2 ] (R = Me3SiCH2), the molecular organotin oxide cyclo-[R(Cl)SnO]2 is stabilized by two stannabicyclooctane derivatives.10 A further interesting analogy can be seen between 3 and the nonsymmetric substituted tetraorganodistannoxane [t-Bu2(Cl)SnOSn(Cl)Me2]211 and [E(OSn-t-Bu2)2O·t-Bu2SnX2] (E = Ph2Si, Me2Si, CO, MesB, Ph2P+; X = OH, F),12 in which the μ3oxygen atom is bound to the tin atoms at distances between 2.0204(2) and 2.152(2) Å (Chart 2).

In the hexanuclear cluster [MeN(CH2CH2O)2SnMe2·Me2SnO]3 (3), the Sn(1) and O(1) atoms form a central, planar Sn3O3 ring, to which the symmetry-related Sn(2) atoms are connected via the O(1) atoms. Notably, the Sn(1)−O distances ranging between 2.146(3) (Sn1−O1) and 2.323(3) Å (Sn1−O17) are longer than the Sn(2)−O distances (2.020(2)−2.104(3) Å), with the shortest distance being Sn(2)−O(1). Formally, the cluster 3 can be interpreted as composed of “molecular” dimethyltin oxide, Me2SnO, that is stabilized by head-to-tail complexation with MeN(CH2CH2O)2SnMe2 (1). The situation resembles that reported for “molecular” SnO being stabilized by a E


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to which intermediate oligomers molecular Me2SnO assembles to finally give the polymeric bulk dimethyltin oxide, (Me2SnO)n. Such investigations are of general interest for an understanding of processes forming nanosized tinoxo clusters.14,15 Although the tin atoms in compounds 1−3 all show the same Me2SnO2 substituent pattern and are supposed to have rather similar Lewis acidity, the intramolecular N→Sn interactions differ considerably, with distances ranging between 2.378(3) (2) and 3.026(3) Å (3). This indicates the influence of the intermolecular O→Sn interactions on these distances and suggests that the N→Sn interactions have considerable electrostatic character.

Compound 3 is not stable in solution and slowly falls apart to give the stannabicyclooctane 1 and (Me2SnO)n. Thus, a 119 Sn{1H} NMR spectrum of single crystals of compound 3 dissolved in CDCl3 showed a resonance at δ −59 (integral 74, 1) and a pair of equally intense resonances at δ −136/−377 (J(119Sn−O117/119Sn) = 60 Hz, integral 14, 3). After 5 days, only the signal assigned to compound 1 was observed and (Me2SnO)n had completely precipitated. The identity of the latter was verified by elemental analysis. The degradation of compound 3 in solution is also visible in the 1H NMR spectrum (CDCl3). The spectrum of a sample that had been stored for 4 h showed in addition to the resonances assigned to compound 1 (see above) two resonances for the Sn−methyl protons of 3 at δ 0.27 (J(1H−117/119Sn) = 70 Hz, Me2SnO moiety)) and 0.57 (J(1H−117/119Sn) = 116 Hz, MeN(CH2CH2O)2SnMe2 moiety). Again employing Lockhart’s equation5a gives a Me−Sn−Me angle of 119.9° for the MeSnO moiety and 163.4° for the MeN(CH2CH2O)2SnMe2 moiety. The first value fits well with the data obtained for the solid-state structure (120.7(2)°), while the second value is 7.5° smaller than the 170.92(17)° observed in the crystal. The observation of only one instead of two resonances for each pair of Sn−methyl protons indicates the intramolecular N→Sn interaction to be kinetically labile on the 1H NMR time scale at room temperature. This gets support from the NCH3 protons showing a singlet resonance at δ 2.07 that, in contrast to the signal observed for 1, lacks 117/119Sn satellites. The NCH2 and OCH2 protons showed triplet resonances at δ 2.43 and 3.42, respectively. The ESI MS (positive mode) of a solution of single crystals of 3 in acetonitrile showed mass clusters centered at m/z 236.0 ([1 − 2 CH3 − H]+), 268.1 ([1 + H]+), 400.0 ([1 + Me2SnO − 2 CH3 − H]+), 432.0 ([1 + Me2SnO + H]+), 533.1 ([2·1 + H]+), 596.0 ([1 + 2 Me2SnO + H]+), and 697.1 ([2·1 + Me2SnO + H]+). The attempt to replace one or more Me2SnO moieties in 3 by, for instance, a t-Bu2SnO moiety failed. Thus, the 119Sn NMR spectrum of a solution of compound 3 to which had been added (t-Bu2SnO)3 showed, in addition to the intensitylowered resonances of 1, a sharp resonance at δ −210 unambiguously indicating formation of MeN(CH2CH2O)2Sn-tBu2.4c In addition, precipitation of (Me2SnO)n was observed.

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EXPERIMENTAL SECTION

General Considerations. All solvents were dried and purified by standard procedures. All reactions were carried out under an atmosphere of dry argon. Bruker DRX 500, Bruker DPX-300, and Bruker DRX400 spectrometers were used to obtain 1H and 13C NMR spectra; the Bruker DPX-300 instrument was used to obtain the 119Sn NMR spectra. 1H, 13C, and 119Sn NMR chemical shifts are given in ppm and were referenced to Me4Si (1H, 13C) and Me4Sn (119Sn). Melting points are uncorrected and were measured on a Büchi SMP20 instrument. The electrospray mass spectra were recorded on a Thermoquest-Finnigan instrument using MeOH or CH3CN as the mobile phase. The samples were introduced as solutions via a syringe pump operating at a rate of 0.5 μL/min. The capillary voltage was 4.5 kV, while the cone skimmer voltage varied between 50 and 250 kV. Identification of the expected ions was assisted by comparison of experimental and calculated isotope distribution patterns. The m/z values reported correspond to those of the most intense peak in the corresponding isotope pattern. Elemental analyses were performed on a LECO-CHNS-932 analyzer. Synthesis of MeN(CH2CH2O)2SnMe2 (1). N-Methyldiethanolamine (0.8 g, 7.2 mmol) was added to a solution of NaOMe, made from Na (0.40 g, 17.4 mmol) in excess MeOH. After heating at reflux for 1 h, reducing the volume of MeOH in vacuo to one-fourth, adding THF (20 mL), and stirring overnight, the resultant solution was transferred via cannula to Me2SnCl2 (1.60 g, 7.2 mmol) in THF (20 mL). The suspension was filtered over Celite, and the solvent was removed in vacuo to give compound 1 (1.30 g, 4.8 mmol, 67%) as a yellow oil, which crystallized on prolonged standing; mp 124 °C. 1 H NMR (400.13 MHz, CDCl3): δ (ppm) 0.26 (s, 2J(1H − 117/119 Sn) = 64 Hz, 3 H, SnCH3), 0.45 (s, 2J(1H−117/119Sn) = 63 Hz, 3 H, SnCH3), 2.38 (s, 3J(1H−117/119Sn) = 12 Hz, 3 H, NCH3), 2.74 (dd, 3 1 J( H−1H) = 4 Hz, 3J(1H−1H) = 5 Hz, 4 H, NCH2), 3.73 (dt, 2 1 J( H−1H) = 11 Hz, 3J(1H−1H) = 4 Hz, 3J(1H−117/119Sn) = 120 Hz, 2 H, CH2O), 3.95 (dt, 2J(1H−1H) = 11 Hz, 3J(1H−1H) = 5 Hz, 3 1 J( H−117/119Sn) = 60 Hz, 2 H, CH2O). 13C{1H} NMR (100.63 MHz, CDCl3): δ (ppm) −1.2 (s, SnCH3), 0.3 (s, SnCH3), 41.7 (s, NCH3), 58.2 (s, 3J(13C−117/119Sn) = 30 Hz, CH2N), 61.1 (s, 3J(13C−117/119Sn) = 36 Hz, CH2O). 119Sn{1H} NMR (CDCl3, 111.92 MHz): δ (ppm) −59 (s). ESIMS (MeCN, m/z): positive mode, 268.0 (1 + H)+. Anal. Calcd for C7H17NO2Sn (265.93): C, 31.6; H, 6.4; N, 5.3. Found: C, 31.3; H, 6.4; N, 5.3. Synthesis of [MeN(CH 2 CH 2 O) 2 SnMe 2 ·MeN(CH 2 CH 2 OH)(CH2CH2ONa)]2 (2). N-Methyldiethanolamine (1.7 mL, 14.8 mmol) was added to NaOMe that had been freshly prepared from Na (0.68 g, 29.6 mmol) in 10 mL of methanol. After heating at reflux for 1 h and diluting with THF (20 mL), the resultant solution was transferred via cannula to Me2SnCl2 (3.10 g, 14.1 mmol) in THF (20 mL) and heated at reflux for 1 h. The reaction mixture was filtered over Celite, and the remaining solvent was removed in vacuo. The colorless solid was dissolved in CH2Cl2 (10 mL) and filtered over Celite before hexanes (10 mL) was added. After concentration of the solution to half of its original volume, compound 2 (0.257 g, 0.6 mmol, 4%) crystallized as colorless cubes with mp 180 °C.

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CONCLUSION In an attempt to complete the family of 2,8-dioxa-5-aza-1stannabicyclo[3.3.0]octanes by its simplest representative, MeN(CH2CH2O)2SnMe2 (1), we learned that the latter is accessible via a salt metathesis reaction between the sodium aminoalcoholate MeN(CH2CH2ONa)2 and dimethyltin dichloride. In the solid state, it is a tetramer via intermolecular O→Sn coordination, while it shows a monomer−dimer equilibrium in solution. Most surprisingly, the reaction of dimethyltin oxide, (Me2SnO)n, with MeN(CH2CH2OH)2 gave the unprecedented hexanuclear organotin oxo cluster [MeN(CH2CH2O)2SnMe2·Me2SnO]3 (3), which can formally be interpreted as molecular dimethyltin oxide being trapped by stannabicyclooctane complexation. It appears that the combined Lewis base (via the oxygen donor)−Lewis acid (via the tin atom) capacity of the latter or related compounds provides ideal conditions for trapping molecular Me 2 SnO, SnBr2(OH)2,4i cyclo-[R(Cl)SnO]2,10 ClSnOSnCl,13 and even SnO.9 The observation of a “controlled release” in solution of Me2SnO from compound 3 might offer the chance of learning F


Organometallics

Article

1 H NMR (499.79 MHz, CDCl3): δ (ppm) 0.25 (s, 2J(1H−119Sn) = 65 Hz, 6 H, SnCH3), 0.44 (s, 2J(1H−119Sn) = 63 Hz, 6 H, SnCH3), 2.29 (bs, 3 H, NCH3), 2.37 (s, 6 H, NCH3), 2.55 (bs, 4 H, NCH2), 2.73 (pt, 3J(1H−1H) = 5 Hz, 8 H, NCH2), 3.60 (bs, 4 H, OCH2), 3.72 (bs, 4 H, OCH2), 3.92 (bs, 4 H, OCH2). 13C{1H} NMR (125.68 MHz, CDCl3): δ (ppm) −1.2 (s, SnCH3), 0.3 (s, SnCH3), 41.6 (s, NCH3), 42.2 (s, NCH3), 58.2 (s, 3J(13C−117/119Sn) = 28 Hz, CH2N), 59.0 (s, OCH2), 59.2 (s, NCH2), 61.0 (s, 3J(13C−117/119Sn) = 35 Hz, CH2O), 61.3 (s, CH2N). 119Sn{1H} NMR (111.92 Hz, CDCl3): δ (ppm) = −57 (s, 1). ESIMS (MeCN, m/z): positive mode, 268.0 [1 + H]+, 409.1 [2 + H]+, 533.1 [2·1 + H]+. Anal. Calcd for C12H29N2NaO4Sn (814.10): C, 35.4; H, 7.2; N, 6.9. Found: C, 34.9; H, 7.1; N, 6.8. Synthesis of [MeN(CH2CH2O)2SnMe2·Me2SnO]3 (3). A suspension of Me2SnO (2.50 g, 15.2 mmol), KOH (0.03 g, 0.5 mmol), and N-methyldiethanolamine (1.80 mL, 1.84 g, 15.7 mmol) in toluene (50 mL) was heated at reflux in a Dean−Stark apparatus for 6 h. After filtration of the solution, the solvent and excess N-methyldiethanolamine were removed in vacuo and the remaining solid was recrystallized from a mixture of CH2Cl2 and n-hexane at 4 °C to give [MeN(CH2CH2O)2SnMe2·Me2SnO]3 (3; 1.24 g, 8.65 mmol, 57%) as colorless crystals with mp 190 °C. 119 Sn{1H} NMR of the crude reaction mixture (C6D6, 111.92 MHz): δ (ppm) −2 (s, 1%, Me4Sn), −65 (s, 59%, 1), −137 (s, 2 119 J( Sn−119Sn) = 59 Hz, 4%, Me2SnO in 3), −376 (s, 2J(119Sn−119Sn) = 59 Hz, 4%, MeN(CH 2 CH 2 O) 2 SnMe 2 in 3), −386 (s, 2 119 J( Sn−119Sn) = 224 Hz, 9%), −398 (s, 2J(119Sn−119Sn) = 208 Hz, 3%), −400 (s, 2 J( 119 Sn− 119 Sn) = 234 Hz, 5%), −515 (s, 2 119 J( Sn−119Sn) = 224 Hz, 8%), −521 (s, 2J(119Sn−119Sn) = 234 Hz, 5%), −525 (s, 2J(119Sn−119Sn) = 208 Hz, 3%). NMR Spectra of 3 (Isolated Crystals of 3). 1H NMR (500.13 MHz, CDCl3): δ (ppm) 0.27 (s, 2J(1H−117/119Sn) = 70 Hz, 6 H, SnCH3), 0.28 (s, 2J(1H−117/119Sn) = 64 Hz, 3 H, SnCH3), 0.47 (s, 2 1 J( H−117/119Sn) = 60 Hz, 3 H, SnCH3), 0.57 (s, 2J(1H−117/119Sn) = 116 Hz, 6 H, SnCH3), 2.07 (s, 3 H, NCH3), 2.40 (s, 3J(1H−117/119Sn) = 12 Hz, 3 H, NCH3), 2.43 (t, 3J(1H−1H) = 5 Hz, 4 H, NCH2), 2.76 (dd, 3J(1H−1H) = 4 Hz, 3J(1H−1H) = 5 Hz, 4 H, NCH2), 3.42 (t, 3 1 J( H−1H) = 5 Hz, 4 H, CH2O), 3.75 (m, 2 H, CH2O), 3.96 (m, 2 H, CH2O). 119Sn{1H} NMR (CDCl3, 111.92 MHz): δ (ppm) −59 (s, 74%, MeN(CH2CH2O)2SnMe2), −136 (s, 2J(119Sn−119Sn) = 60 Hz, 14%, Me2SnO in 3), −377 (s, 2J(119Sn−119Sn) = 60 Hz, 12%, MeN(CH2CH2O)2SnMe2 in 3). ESIMS (MeCN, m/z): positive mode, 236.0 [1 − 2 CH3 − H]+, 268.1 [1 + H]+, 400.0 [1 + Me2SnO − 2 CH3 − H]+, 432.0 [1 + Me2SnO + H]+, 533.1 [2·1 + H]+, 596.0 [1 + 2 Me2SnO + H]+, 697.1 [2·1 + Me2SnO + H]+. Anal. Calcd for C27H69N3O9Sn6 (1292.11): C, 25.1; H, 5.4; N, 3.3. Found: C, 25.0; H, 5.2; N, 3.1. No spectra of the pure compound could be obtained, since the cluster decomposes in solution to give MeN(CH2CH2O)2SnMe2 (1) and a colorless solid of Me2SnO. After 5 days the cluster completely vanished. The identity of Me2SnO was confirmed by elemental analysis. Anal. Calcd for C2H6OSn (164.78): C, 14.6; H, 3.7. Found: C, 14.5; H, 3.7. Reaction of Compound 3·0.25H2O with t-Bu2SnO. In a NMR tube, compound 3·0.25H2O (0.080 g, 61.7 mmol) and t-Bu2SnO (0.013 g, 52.4 mmol) were dissolved in CDCl3. 119 Sn{1H} NMR (CDCl3, 111.92 MHz): δ (ppm) −59 (s, 16%, 1), −210 (s, 84%, MeN(CH2CH2O)2Sn-t-Bu2). Crystallography. All intensity data were collected with an XcaliburS CCD diffractometer (Oxford Diffraction) using Mo Kα radiation at 110 K. The structures were solved with direct methods using SHELXS-97,16 and refinements were carried out against F2 by using SHELXL-97.16 All non-hydrogen atoms were refined using anisotropic displacement parameters. The C−H hydrogen atoms were positioned with idealized geometry and refined using a riding model. In compound 2 the atoms C(24) to C(26) and N(24) are affected by disorder and were refined with a split model over two positions (occupancy 60:40). Their Uij values were restrained to nearly isotropic behavior and 1,2-distances were restrained using SADI. The H(27) atom involved in the hydrogen bridge was located in the difference

Fourier map. In compound 3·0.25H2O the atoms C(13) to O(17) are also affected by disorder; the second part is generated by the mirror plane through Sn(1), O(11), and C(12) (see Figure S3 in the Supporting Information). The water molecule in compound 3·0.25H2O is located on a 6-fold axis, resulting in 1/24 O(1L) in the asymmetric unit; consequently no hydrogen atoms are located in the difference Fourier map. For decimal rounding of numerical parameters and su values the rules of IUCr have been employed.17 CCDC-939079 (1), CCDC-939080 (2), and CCDC-939081 (3·0.25H2O) contain supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/ cif.

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ASSOCIATED CONTENT

S Supporting Information *

Crystallographic data for compounds 1−3 (CIF files and Table S1), 119Sn NMR spectra of the reaction mixture according to Scheme 1 (Figures S1 and S2), and a figure illustrating the partial disorder in the structure of 3 (Figure S3). 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 K.J.: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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