Stannylene-Based Lewis Pairs - ACS Publications - American

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Stannylene-Based Lewis Pairs Sarah Freitag, Kilian M. Krebs, Jens Henning, Janina Hirdler, Hartmut Schubert, and Lars Wesemann* Institute of Inorganic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany S Supporting Information *

ABSTRACT: Intramolecular stannylene-based Lewis pairs with phosphine Lewis bases were synthesized at the ortho position in benzene or the peri position in acenaphthene. The spectroscopic data of the Lewis pairs are discussed, and the reactivity toward unsaturated hydrocarbons and organic azides is presented.

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INTRODUCTION Research concerning frustrated Lewis pairs (FLPs) is currently of major interest because of their reactivity toward small molecules such as dihydrogen, olefins, aryl azides, carbon dioxide, and alkynes.1−3 Furthermore, FLPs were investigated to act as catalysts in hydrogen transfer reactions or in the metalfree reduction of syngas.1,4 This research was started with phosphines as Lewis bases and boranes as Lewis acids.1 Carbenes as well as amines and imines were also introduced to act as the Lewis bases in FLPs.5,6 In the case of the Lewis acidic part of the FLPs recently the use of alanes and transition metals was published.2,7 Generally FLPs were studied as intermolecular Lewis pairs of two molecules or intramolecular combinations of a Lewis acidic and a Lewis basic fragment in one molecule. Recently we have presented a synthesis for phosphastannirane A (Chart 1), a three-membered cyclic

substitution at acenaphthene together with a discussion of their molecular structures, spectroscopic data, and reactivity toward alkynes and azides.

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RESULTS AND DISCUSSION Synthesis. The benzene-based Sn−P Lewis pair was synthesized straightforwardly following a Br−Li exchange at (2-bromophenyl)diphenylphosphine to give (2(diphenylphosphino)phenyl)lithium (1), which was reacted with isopropyl-substituted m-terphenyltin chloride 2 (Scheme 1). The diarylstannylene 3 was recrystallized from a mixture of Scheme 1. Synthetic Procedure for the Benzene-Based Lewis Pair 3a

Chart 1. Recent Examples of Sn−P Lewis Pairs and Products of the Reactions with Phenylacetylene (B) and Pentene (C)a a

a

benzene and hexamethyldisiloxane to give crystals suitable for X-ray diffraction. Other solvent mixtures did not give crystals of high quality. Following a reaction sequence corresponding to the synthesis of 3, the Lewis pair 5 was synthesized starting with 5-bromo-6(diisopropylphosphino)acenaphthene (4) in moderate yield (Scheme 2). Lewis pairs 3 and 5 are both sensitive toward moisture and air and were characterized by heteronuclear NMR spectroscopy, crystal structure analysis, and elemental analysis. Crystallographic Analysis. Single-crystal X-ray diffraction data were obtained for both stannylenes 3 and 5. The crystals are orange (3) or brown (5) and are soluble in all common

R = C6H3-2,6-Trip2, Trip = C6H2-2,4,6-iPr3.

molecule, showing reactivity in addition reactions with alkynes (B) and reversible addition of 1-pentene (C).8 This stannylenebased Lewis pair A was synthesized straightforwardly by reaction of the lithiated benzyldiphenlyphosphine with isopropyl-substituted m-terphenyltin chloride. In order to study the intramolecular Sn−P interaction more generally, we started to synthesize Lewis pairs with suitable backbones. ortho-Substituted benzene and ortho-substituted naphthalene or acenaphthene are prominent molecules for the investigation of such intramolecular interactions.9−17 In this publication we present the formation of two Sn−P Lewis pairs on the basis of ortho substitution at benzene and 5,6© XXXX American Chemical Society

Trip = C6H2-2,4,6-iPr3.

Special Issue: Applications of Electrophilic Main Group Organometallic Molecules Received: July 26, 2013

A

dx.doi.org/10.1021/om400736e | Organometallics XXXX, XXX, XXX−XXX

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(3) and 2.6362(6) Å (5). These bond lengths can be compared with the P−Sn bond length of 2.663(1) Å in the threemembered cycle A. They lie in the range of published P−Sn bond lengths and belong to the group of longer distances.18−26 In compound 3 we find a much shorter contact between the P atom and the Sn(II) atom, Sn−P = 2.7489(4) Å, in comparison to the ortho-Sn(IV)-substituted phosphinophenyl molecule D (Chart 2), Sn−P = 3.125(4) Å.9,27,28 Therefore, the angles at

Scheme 2. Formation of the Acenaphthene-Based Lewis Pair 5a

Chart 2. a

a

Trip = C6H2-2,4,6-iPr3.

solvents. Crystal structure and refinement data are given in the Supporting Information. In Figures 1 and 2 the molecular a

R = [C6H3-2,6-(NMe2)2].

the carbon atoms inside the four-membered ring (Sn−P−C− C) are smaller in 3 than in D (3, P−C2−C1 = 108.81(9)°, C2−C1−Sn = 108.11(9)°; D, P1−C6−C1 = 113.1(13)°, Sn1− C1−C6 = 117.9(12)°). Obviously the Sn(II) atom in 3 exhibits a much stronger Lewis acidity than the Sn(IV) atom in D. Intramolecular Lewis pairs in ortho-substituted benzene derivatives were also studied in the case of P−B and Sn−N interactions (E and F in Chart 2).12,29 Since the presented Sn− P interaction in the acenaphthene Lewis pair 5 is the first interaction between these elements in peri position, we can only compare this interaction with a variety of other element− element interactions studied also in peri position at acenaphthene or naphthalene.10−12,14 Following the geometrical considerations made by Woollins for peri-substituted acenaphthene derivatives, we found a very small splay angle of 0.7°, indicating a Sn−P interaction.30 The displacements from the mean acenaphthene plane to the same side of 0.4 Å (Sn atom) and 0.01 Å (P atom) and the buckling of the acenaphthene framework (central torsion angles 2 and 1°) lie in the range of published substitution derivatives.30 Sn−N interactions were found in a bis(naphthyl)tin(II) compound, and weak interactions between bromine and tin(IV) atoms were studied in an acenaphthene derivative.10,31 NMR Spectroscopy. Selected NMR spectroscopic data for A, 3, 5, and D are given in Table 1. The 119Sn NMR resonances of the Sn(II)−P Lewis pairs A, 3, and 5 (Chart 3) show a tendency to resonate at higher field with increasing ring size. The same tendency has been observed for dialkylamino base stabilized stannylenes: the molecule with the four-membered ring shows a 119Sn signal at 442 ppm, and the signal for the

Figure 1. ORTEP plot of the molecular structure of 3. Hydrogen atoms have been omitted; ellipsoids are given at the 50% probability level. Interatomic distances (Å) and bond angles (deg): Sn−P = 2.7489(4), Sn−C1 = 2.235(1), Sn−C3 = 2.233(1), P−C2 = 1.809(1), C1−C2 = 1.403(2); C1−Sn−P = 62.5(1), Sn−P−C2 = 78.9(1), C3− Sn−C1 = 105.8(1), C3−Sn−P = 100.1(1), P−C2−C1 = 108.8(1), C2−C1−Sn = 108.11(9), C4−C1−Sn = 133.1(1), C5−C2−P = 128.4(1), P−C2−C1−Sn = 13.4(1).

Figure 2. ORTEP plot of the molecular structure of 5. Hydrogen atoms have been omitted; ellipsoids are given at the 50% probability level. Interatomic distances (Å) and bond angles (deg): Sn−P = 2.6362(6), Sn−C1 = 2.238(2), Sn−C3 = 2.269(2), P−C2 = 1.807(2), P−C4 = 1.838(2), P−C5 = 1.837(2); C1−Sn−C3 = 109.2(1), C1− Sn−P = 77.6(1), C3−Sn−P = 101.7(1), Sn−P−C2 = 100.4(1), Sn− P−C4 = 121.4(1), Sn−P−C5 = 114.6(1), C4−P−C5 = 107.0(1), C2− P−C4 = 108.0(1), C2−P−C5 = 103.8(1), C8−C2−P = 115.8(2), C6−C1−Sn = 122.9(2), C8−C1−Sn = 119.8(2), C7−C2−P = 123.7(2), C1−C8−C2 = 125.1(2).

Table 1. Selected NMR Data for Previously Reported Compounds A and D and New Molecules 3 and 5

structures of 3 and 5 are respectively depicted together with selected interatomic distances and angles. The phosphinoaryland phosphinoalkyl-substituted stannylenes 3 and 5 both form P−Sn donor−acceptor bonds in the solid state: 2.7489(4) Å

a NMR data for A8 and D.9 b31P solid-state NMR experiment: in the case of 3 in the solid-state NMR spectrum two signals were detected. The observation of two signals in the solid-state NMR spectrum of 3 is probably due to polymorphism.

compd A

a

3 5 Da

B

δ(119Sn) (ppm) 716 554 −139 −102

JSn−P (Hz)

δ(31P) (ppm)

83 364b 754 808,b 740b 1756 18 (3J)

−38.6 −50.3b −41.5 −42.1,b −46.0b 20.3 −1.0

1


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Chart 3. Three-, Four-, and Five-Membered Rings as Sn−P Lewis Pairsa

a

Figure 3. NBO results for compounds A, 3, and 5 (left to right): picture of the phosphorus lone pair orbital (left; in each case blue and red) and the tin vacant orbital (right; in each case turquoise and orange). A representation of the angle describing the relative orientation of the two orbitals is included.


stannylenes exhibiting five-membered rings appears at 169 or 178 ppm.12,31,32 The solid-state 31P NMR spectrum of 3 is in agreement with the solution NMR spectrum, indicating that the molecules in solution and in the solid state are similar. A little deeper insight into the phosphorus−tin interaction can be gained from the 119Sn NMR chemical shifts. Wrackmeyer proposed a paramagnetic deshielding contribution for tin NMR chemical shifts of tin(II) compounds.33 This contribution arises from magnetically induced charge circulation including the formally vacant Sn 5p orbital and the Sn−R bonding electrons rather than the lone pair at the tin. Taking a look at the three Lewis pairs A, 3 and 5, we see that the Sn−R bonding is largely the same. Only for the smallest ring A is the bridging substituent an sp3 carbon, and for the larger rings 3 and 5 sp2 carbons are present. We suggest the far more important influence on the paramagnetic deshielding contribution to be the different Lewis pair interaction: i.e., the donation of the phosphorus lone pair into the Sn 5p orbital. Thus, a more efficient donor−acceptor interaction would reduce the paramagnetic deshielding by hindering the charge circulation and lead to an NMR resonance shift to higher frequencies. For the three Lewis pairs A, 3, and 5 the 119Sn resonance frequency can be interpreted as an indicator for increasing efficiency of the P− Sn coordination in the row A, 3, and 5. In this series the size of the P−Sn heterocycles increases and the phosphorus substituents vary in the case of the acenaphthene derivative from phenyl to isopropyl. Thus, also the higher basicity of the isopropyl-substituted phosphane in compound 5 could be responsible for the increased efficiency of the P−Sn donation in 5. This interpretation is consistent with the results of DFT calculations (see below). Additionally, a supporting observation might be that the 1JSn−P coupling constant increases in the same order. Quantum Chemical Calculations. DFT calculations were performed on the full molecules 3 and 5 applying the functional revPBE-D3(BJ) and a triple-ζ basis set for all electrons.34−41 The Lewis pair A has been calculated previously using the same parameters.8 The geometries were optimized, and subsequently natural bond orbital (NBO) analyses were calculated with the program ADF2012,42−44 including the program NBO5.0.45 Detailed information on the computations is given in the Supporting Information. The geometries and donor−acceptor interactions were reproduced (Figure 3). Reactivity Studies. Recently we have shown that the threemembered ring A reacts with alkynes and 1-pentene at room temperature to give the five-membered cycles B and C.8 In order to compare the reactivity of the three Sn−P Lewis pairs A, 3, and 5 (Chart 3), we have studied reactions of the new molecules 3 and 5 with alkynes. Furthermore, the reactivity toward adamantyl azide was investigated. The four-membered-

ring molecule 3 reacts regioselectively with phenylacetylene at room temperature over a period of 13 days to give the sixmembered ring 6 (Scheme 3), whereas in the case of the Lewis Scheme 3. Reaction of the Benzene-Based Lewis Pair with Phenylacetylene and Adamantyl Azidea

a


pair 5 no reaction with phenylacetylene was detected even after stirring for several days at room temperature or for 1 day at 70 °C. The reaction product 6 was characterized by elemental analysis, NMR spectroscopy, and single-crystal structure analysis. By using 31P NMR spectroscopy, the progress of the reaction can easily be monitored: the starting material shows a resonance at −41.5 ppm, and the alkyne insertion product 6 exhibits a signal at −1.4 ppm. Both resonances are flanked by tin satellites, with the Sn−P coupling constants in molecule 6 being much smaller (99 Hz; 119Sn−31P and 117Sn−31P coupling are not resolved) in comparison to the coupling constants in molecule 3 (754 Hz, 119Sn−31P; 720 Hz, 117Sn−31P), which exhibits a direct Sn−P bond (Table 1). Furthermore, the 119Sn resonance shifts from 554 ppm (3) to −209 ppm (6). Phosphastannirane A (119Sn NMR: 716 ppm) shows analogous reactions with phenylacetylene to give molecule B (119Sn NMR: 100 ppm). Obviously in both cases the alkyne insertion products 6 and B (Chart 1) show a resonance in the 119Sn NMR at much higher field in comparison to the respective starting materials 3 and A. The 119Sn NMR resonance of alkyne insertion product 6 can also be compared with the signal for typical triply coordinated tin in [SnPh3]− at −98.4 ppm.46 In the case of the 31P NMR signals in analogy to the low-field shift from compound A (−38.6 ppm) to B (37.4 ppm) we detect a shift from −41.5 ppm (3) to −1.0 ppm (6). A diagnostic signal in the 1H NMR spectrum for the regioselective alkyne insertion is the resonance for the olefinic proton Sn−CH in 6, which appears at 10.04 ppm and shows coupling to the phosphorus atom (3JP−H = 53.4 Hz) and tin atom (2JSn−H = 26.7 Hz). The C


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nitrogen but in an azide group connected at phosphorus and tin.53 In the 119Sn NMR spectrum a shift to high field and a decrease in the 119Sn−31P coupling constant was detected for product 7. In Figure 5 the molecular structure determined in

respective carbon atom Sn−CHC exhibits a resonance at unexpected high frequency, beyond 200 ppm.8,47,48 In the fivemembered cycle B the respective proton shows a signal at 8.66 ppm, also with coupling to the phosphorus atom (3JP−H = 59.4 Hz) and tin atom (2JSn−H = 61.1 Hz). The molecular structure of the zwitterionic molecule 6 in the solid state (Figure 4) can

Figure 5. ORTEP plot of the molecular structure of 7. Hydrogen atoms have been omitted; ellipsoids are given at the 50% probability level. Two molecules of compound 7 together with two molecules of hexane were found in the asymmetric unit. Interatomic distances (Å) and bond angles (deg) (values for the second molecule are given in brackets): Sn−N = 2.305(4) [2.292(4)], Sn−C1 = 2.245(6) [2.213(5)], Sn−C3 = 2.321(6) [2.324(6)], P−N = 1.613(5) [1.608(4)], C1−C2 = 1.391(7) [1.408(7)], P−C2 = 1.798(5) [1.796(5)]; N−Sn−C3 = 107.2(2) [109.4(2)], C1−Sn−N = 80.3(2) [80.3(2)], C1−Sn−C3 = 103.0(2) [104.5(2)], N−P−C2 = 107.0(2) [106.5(2)], C1−C2−P = 115.9(4) [115.7(4)].

Figure 4. ORTEP plot of the molecular structure of 6. Hydrogen atoms have been omitted; ellipsoids are given at the 50% probability level. Interatomic distances (Å) and bond angles (deg): Sn−C1 = 2.217(2), Sn−C3 = 2.244(2), Sn−C4 = 2.195(2), C1−C2 = 1.407(2), P−C2 = 1.802(2), P−C5 = 1.798(2), C5−C4 = 1.352(2); C1−Sn−C3 = 94.52(5), C1−Sn−C4 = 89.50(6), C3−Sn−C4 = 106.3(1), Sn− C1−C2 = 123.3(1), C1−C2−P = 120.6(1), C2−P−C5 = 114.41(7), P−C5−C4 = 119.0(1), C5−C4−Sn = 126.0(1).

the solid state is depicted. The lengths of the PN (1.613(5), 1.608(4) Å) and Sn−N (2.305(4), 2.292(4) Å) bonds lie in the typical ranges for these type of bonds.53,55,56 The sums of the angles at tin, 290.56 and 292.76°, indicate a pyramidally coordinated Sn(II) atom. The chemistry of intramolecular stannylene-based Lewis pairs will be further explored, especially with respect to the influence of ring size and effects of substituents at tin and phosphorus on the reactivity.

be compared with that of a bicyclic distannide reported by Veith et al. and the structure of the insertion product of (trimethylsilyl)acetylene in phosphastannirane A.8,49 In molecule 6 a triply coordinated stannide and a tetracoordinated phosphonium cation are formed. The sum of the angles at the tin atom (285.3°) is smaller than the sum of angles in [Ph3Sn]− (290.3°) and slightly larger than the sum of angles at tin in the insertion products of the phophastannirane.8,46 This effect might be due to the ring formation: the angle C1−Sn−C4 inside the ring is the smallest angle at the tin atom in 6. The distance between the carbon atoms C4 and C5, 1.352(2) Å, is longer than a triple bond and lies in the range of reaction products of phenylacetylene with frustrated Lewis pairs: P(otol)3/B(C6F5)3 (1.346(3) Å); P(o-tol)3/Al(C6F5)3 (1.341(3) Å).50 The reactivity of the Lewis pairs 3 and 5 was also studied in reactions with adamantyl-substituted azide. At room temperature the azide reacts with the Lewis pair 3 to form a fivemembered cycle, whereas the peri-substituted Lewis pair shows no reaction (Scheme 3). The azide product 7 was characterized by elemental analysis, NMR spectroscopy, and single-crystal structure analysis. In principle two reaction pathways are possible for the reaction of the triarylphosphine-stabilized stannylene with the adamantyl azide: a Staudinger-type addition at phosphorus or the reaction with the stannylene to give a stannaimine.51−54 The Lewis pair 3 reacts with the azide with evolution of nitrogen and formation of Sn−N and PN bonds to give the five-membered cycle 7. A reaction with a further equiv was not detected, even after heating for several hours with an excess of azide reagent. This reaction should be compared with the reaction of a bis(P∧O)-chelated stannylene with adamantyl azide, which does not result in the evolution of

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CONCLUSIONS Lewis pairs with stannylenes acting as the Lewis acids and phosphines as the Lewis bases were constructed at the ortho position in benzene and peri position in acenaphthene (Chart 3). The Lewis pair exhibiting the four-membered ring is less reactive with respect to alkyne addition in comparison to phosphastannirane A (Chart 3). The acenaphthene derivative 5 shows no reaction with alkynes. Considering the reactivity and NMR spectroscopic data, we conclude that the effectiveness of the P−Sn interaction increases in the order A, 3, and 5.

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EXPERIMENTAL SECTION

General Procedures. All manipulations were carried out with exclusion of air and moisture under an argon atmosphere using standard Schlenk techniques and gloveboxes. Solvents were purified by standard methods. Elemental analyses were performed by the Institut für Anorganische Chemie Universität Tübingen using a Vario EL analyzer and a Vario MICRO EL analyzer. The starting materials [2,6Trip2(C6H3)SnCl] (Trip = C6H2-2,4,6-iPr3),57−60 o-Li(OEt2)-phenyldiphenylphosphine,61 and 5-bromo-6-diisopropylphosphinoacenaphthene62 were synthesized following a literature procedure. All further chemicals used were purchased commercially and were not further purified. NMR. NMR spectra were recorded with a Bruker DRX-250 NMR spectrometer equipped with a 5 mm ATM probe head and operating D


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at 250.13 (1H) and 101.25 MHz (31P), a Bruker AVII+ 400 NMR spectrometer equipped with a 5 mm QNP (quad nucleus probe) head operating at 400.13 (1H), 100.13 (13C), and 161.97 (31P) MHz, and a Bruker AVII+ 500 NMR spectrometer with a 5 mm ATM probe head and operating at 500.13 (1H, Ξ = 100%), 125.76 (13C, Ξ = 25,145020%), 202.5 (31P, Ξ = 40.480742%), and 186.5 MHz (119Sn, Ξ = 37.290632%). Chemical shifts are reported in δ values in ppm relative to external TMS (1H), 85% aqueous H3PO4 (31P), and SnMe4 (119Sn) using the chemical shift of the solvent 2H resonance frequency. The proton and carbon signals were assigned by a detailed analysis of 1 H, 13C, 1H−1H COSY, 1H−13C HSQC, 1H−13C HMBC, and 13 C{1H} DEPT-135. Solid-state 31P NMR spectra were recorded with ramped amplitude cross-polarization magic-angle spinning (CP/MAS) on a Bruker DSX-200 super widebore NMR spectrometer using a 4 mm double-bearing MAS probe head. Crystallography. X-ray data for compounds 3 and 5−7 were collected with a Bruker Smart APEX II diffractometer with graphitemonochromated Mo Kα radiation. The programs used were Bruker’s APEX2 v2011.8-0, including SADABS for absorption correction and SAINT for structure solution, as well as the WinGX suite of programs version 1.70.01 or the program ShelXle, including SHELXS for structure solution and SHELXL for structure refinement.63−67 Results of the crystal structure determination are presented in the Supporting Information. Synthesis of Compound 3. (C6H3-2,6-Trip2)SnCl (800 mg, 1.26 mmol) was dissolved in a mixture of hexane (30 mL) and benzene (6 mL) to give an orange solution and cooled to −40 °C. o-Li(OEt2)phenyldiphenylphosphane (431 mg, 1.26 mmol) was suspended in hexane (10 mL) and benzene (2 mL) and added dropwise to the cooled solution. The orange solution was stirred for 3 h at room temperature and filtered through Celite, and the solvent was removed in vacuo. A light orange solid was obtained (yield 1.03 g, 95%). X-rayquality crystals were grown from a mixture of benzene and hexamethyldisiloxane. 1H NMR (400.13 MHz, C6D6): δ 1.18 (br s, 12H, o-CHMe2), 1.32 (d, 12H, o-CHMe2, 3JH−H = 6.7 Hz), 1.45 (d, 12H, p-CHMe2, 3JH−H = 6.9 Hz), 3.02 (sept, 2H, p-CHMe2, 3JH−H = 6.9 Hz), 3.39 (sept 4H, o-CHMe2, 3JH−H = 6.7 Hz), 6.26 (m, 1H, Ar), 6.97−7.00 (m, 2H, Ar), 7.05−7.09 (m, 6H, Ar), 7.16−7.21 (m, 1H, Ar), 7.30 (s, 4H, C6H2), 7.33−7.37 (m, 1H, p-C6H3), 7.39−7.41 (m, 2H, m-C6H3), 7.49−7.53 (m, 4H, Ar). 13C{1H} NMR (62.90 MHz, C6D6): δ 24.0 (o-CHMe2), 24.9 (p-CHMe2), 26.7 (o-CHMe2), 31.7 (oCHMe2), 35.2 (p-CHMe2), 121.8 (m-C6H2), 127.0, 127.3 (d, JP−C = 5.0 Hz), 129.0 (d, JP−C = 5.0 Hz), 130.4 (d, JP−C = 1.9 Hz), 130.7, 131.6, 132.6, 133.1 (d, JP−C = 14.6 Hz), 134.2 (d, JP−C = 12.6 Hz), 136.4 (d, JP−C = 36.9 Hz), 140.6 (i-C6H2), 143.1 (d, JP−C = 44.5 Hz), 147.5 (o-C6H2), 148.4 (p-C6H2), 148.5 (d, JP−C = 1.8 Hz), 169.8 (d, JP−C = 10.0 Hz), 180.8 (d, JP−C = 60.3 Hz). 31P{1H} NMR (101.25 MHz, C6D6): δ −41.5 (s, J119Sn−P = 754 Hz, J117Sn−P = 720 Hz); 31P CP/ MAS NMR (81.01 MHz): δ −42.1 (s, JSn−P = 808 Hz), −46.0 (s, JSn−P = 740 Hz). 119Sn{1H} NMR (93.25 MHz, C6D6): δ 554 (d, JSn−P = 754 Hz). Anal. Calcd for C54H63PSn: C, 75.26; H, 7.37. Found: C, 74.92; H, 7.57. Synthesis of Compound 5. 5-Bromo-6-(diisopropylphosphino)acenaphthene (150 mg, 0.43 mmol) in Et2O (20 mL) was treated with n-BuLi (1.6 M in hexane; 0.26 mL, 0.43 mmol) at −20 °C. The mixture was stirred at room temperature for 2 h and the resulting orange suspension was added dropwise to a cooled solution (−20 °C) of (C6H3-2,6-Trip2)SnCl (274 mg, 0.43 mmol) in Et2O (20 mL). The mixture was stirred for another 2 h at room temperature, the solvent was removed in vacuo and the residue was treated with hexane (50 mL). The resulting precipitate was filtered off and the solvent was removed in vacuo. Brown crystals were obtained after crystallization from benzene (2 mL). Yield: 256 mg (69%). 1H NMR (400.13 MHz, C6D6): δ 0.59−0.71 (m, 6H, −CHMe2), 1.00−1.12 (m, 6H, −CHMe2), 1.21−1.26 (m, 6H, Trip-CHMe2), 1.38−1.41 (m, 10H, Trip-CHMe2), 1.53 (d, 14H, Trip-CHMe2, 3JH,H = 7.04 Hz), 1.68 (br, 6H, Trip-CHMe2), 2.00 (br, 1H, −CHMe2), 2.38 (br, 1H, −CHMe2), 3.06−3.16 (m, 6H, 4 x Trip-CHMe2, 1 × CH2), 3.25 (br, 3H, TripCHMe2, 1 × CH2), 3.71 (br, 2H, Trip-CHMe2), 6.44 (d, 1H, 3JH,H = 7.03 Hz, Ar), 7.09 (d, 1H, 3JH,H = 7.12 Hz, Ar), 7.20−7.24 (m, 5H,

Ar), 7.30−7.35 (m, 2H, Ar), 7.44 (br, 2H, Ar). 13C{1H} NMR (100.13 MHz, C6D6): δ 14.8 (br, −CHMe2), 18.0 (br, −CHMe2), 18.9 (br, −CHMe2), 19.3 (br, −CHMe2), 22.4 (s, −CHMe2), 23.5 (s, −CHMe2), 24.1 (br s, Trip-CHMe2), 24.4 (br s, Trip-CHMe2), 25.7 (br s, Trip-CHMe2), 27.5 (br s, Trip-CHMe2), 29.9 (s, −CH2), 30.4 (s, −CH2), 30.7 (br s, Trip-CHMe2), 31.2 (s, Trip-CHMe2), 34.5 (s, TripCHMe2), 117.4 (d, Ar-CH, JP−C = 5.44 Hz), 121.1 (Ar-CH), 121.6 (br s, Trip-CH), 124.4 (s, −CH−C6H3), 125.8 (d, quat. Ar, JP−C = 25.8 Hz), 131.1 (s, −CH−C6H3), 131.2 (d, Ar-CH, JP−C = 3.91 Hz), 139.2 (d, quat Ar, JP−C = 11.6 Hz), 139.7 (d, Ar-CH, JP−C = 10.23 Hz), 141.7 (s, quat. Ar), 141.9 (d, quat Ar, JP−C = 1.58 Hz), 145.0 (d, quat Ar, JP−C = 26.8 Hz), 145.9 (s, quat. Ar), 147.8 (s, quat Trip-C), 150.9 (d, quat Ar, JP−C = 2.12 Hz), 159.4 (d, quat Ar, JP−C = 9.27 Hz), 161.3 (d, quat Ar, JP−C = 11.9 Hz). 31P{1H} NMR (161.97 MHz. C6D6): δ 20.3 (s, J119Sn−P = 1742 Hz, J117Sn−P = 1666 Hz). 119Sn{1H} NMR (93.25 MHz, C6D6): δ −139 (d, JSn−P = 1756 Hz). Anal. Calcd for C54H71PSn: C, 74.56; H, 8.23. Found: C, 74.66; H, 8.31. Synthesis of Compound 6. 3 (100 mg, 0.12 mmol) was dissolved in hexane (6 mL), and phenylacetylene (18 mg, 0.174 mmol, 1.5 equiv) in hexane (3 mL) was added dropwise to the stirred solution. The solution was stirred at room temperature for 10 days, changing from clear orange to cloudy red. The reaction progress was monitored by NMR spectroscopy. Further phenylacetylene (93 mg, 0.91 mmol) was added to the solution. The reaction mixture was stirred for an additional 4 days and dried in vacuo to yield the red product. Crystallizazion from hexane at −40 °C yielded crystals suitable for elemental analysis. Red X-ray-quality crystals were grown by diffusion of pentane into a concentrated benzene solution. 1H NMR (400.13 MHz, C6D6): δ 1.23 (d, 6H, o-CHMe2, 3JH−H = 6.8 Hz), 1.36 (d, 6H, o-CHMe2, 3JH−H = 6.8 Hz), 1.41 (d, 6H, p-CHMe2, 3JH−H = 6.9 Hz), 1.42 (d, 6H, p-CHMe2, 3JH−H = 6.8 Hz), 1.43 (d, 6H, o-CHMe2, 3JH−H = 6.8 Hz), 1.53 (d, 6H, o-CHMe2, 3JH−H = 6.8 Hz), 3.07 (sept, 2H, pCHMe2, 3JH−H = 6.9 Hz), 3.54 (sept, 2H, o-CHMe2, 3JH−H = 6.8 Hz), 3.69 (sept, 2H, o-CHMe2, 3JH−H = 6.8 Hz), 6.70−6.79 (m, 4H, Ar), 6.84−6.97 (m, 6H, Ar), 7.00−7.04 (m, 2H, Ar), 7.10−7.17 (m, 3H, Ar), 7.18−7.22 (m, 1H, Ar), 7.27 (s, 1H, Ar), 7.33 (s, 4H, m-C6H2), 7.37−7.44 (m, 5H, Ar), 8.08−8.11 (m, 1H, SnCCH), 10.04 (d, 1H, SnCH, 3JP−H = 53.4 Hz, 2JSn−H = 26.7 Hz). 13C{1H} NMR (100.13 MHz, C6D6): δ 22.6 (o-CHMe2), 24.0 (p-CHMe2), 24.2 (p-CHMe2), 24.4 (o-CHMe2), 25.8 (o-CHMe2), 26.0 (o-CHMe2), 30.9 (o-CHMe2), 31.2 (o-CHMe2), 34.1 (p-CHMe2), 119.0 (d, JP−C = 87.0 Hz), 119.2 (d, JP−C = 85.0 Hz), 120.4 (m-C6H2), 120.6 (m-C6H2), 124.1 (d, JP−C = 13.0 Hz), 124.2 (d, JP−C = 92.4 Hz), 124.8 (d, JP−C = 80.6 Hz), 125.3, 125.8, 128.3, 128.4 (d, JP−C = 4.3 Hz), 128.5 (d, JP−C = 11.8 Hz), 128.6 (d, JP−C = 12.4 Hz), 129.3, 132.0 (d, JP−C = 2.6 Hz), 132.4 (d, JP−C = 3.1 Hz), 132.5 (d, JP−C = 17.2 Hz), 134.2 (d, JP−C = 8.9 Hz), 134.5 (d, JP−C = 11.0 Hz), 139.0 (d, SnC(CH)CP, JP−C = 17.3 Hz), 142.8 (d, JP−C = 21.2 Hz), 143.0 (i-C6H2), 146.7 (m-C6H2), 147.0 (m-C6H2), 149.0, 164.0 (i-C6H3), 179.4 (d, SnCCP, JP−C = 21.5 Hz), 213.3 (d, SnCH, JP−C = 26.0 Hz). 31P{1H} NMR (101.25 MHz, C6D6): δ −1.4 (s, JSn−P = 99 Hz). 119Sn{1H} NMR (93.25 MHz, C6D6): δ −209 (d, JSn−P = 105 Hz). Anal. Calcd for C62H69PSn: C, 77.26; H, 7.22. Found: C, 77.10; H, 6.99. Synthesis of Compound 7. 3 (100 mg, 0.12 mmol) was dissolved in hexane (6 mL), and 1-azidoadamantane (21 mg, 0.12 mmol) in benzene (3 mL) was added dropwise to the orange solution. After 2.5 h the solvent was removed in vacuo to yield the light orange product quantitatively on the basis of NMR spectroscopy. Yellow X-ray-quality crystals were obtained from a concentrated hexane solution at −40 °C. 1 H NMR (400.13 MHz, C6D6): δ 1.37 (d, 12H, o-CHMe2, 3JH−H = 6.1 Hz), 1.48 (d, 12H, p-CHMe2, 3JH−H = 6.7 Hz), 1.52 (br s, 6H, CH2(CH)2), 1.75 (br s, 6H, NCH2CH), 1.89 (br s, 3H, NCH2CH), 3.12 (sept, 2H, p-CHMe2, 3JH−H = 6.9 Hz), 3.60 (br s, 4H, o-CHMe2), 6.91−6.96 (m, 3H, Ar), 7.06−7.22 (m, 5H, Ar), 7.27 (s, 1H, Ar), 7.32−7.35 (m, 1H, p-C6H3), 7.39−7.40 (m, 6H, m-C6H3, m-C6H2), 7.62−7.71 (m, 5H, Ar). 13C{1H} NMR (100.13 MHz, C6D6): δ 23.0 (br, o-CHMe2), 24.4 (p-CHMe2), 26.4 (o-CHMe2), 30.6 (CH(CH2)2), 31.2 (o-CHMe2), 34.8 (p-CHMe2), 36.1 (CH2(CH)2), 47.3 (d, 3JP−C = 8.0 Hz, NC(CH2)3), 56.5 (d, 2JP−C = 4.3 Hz, NC(CH2)3), 120.6 (br, m-C6H2), 124.6 (p-C6H3), 125.9 (d, JP−C = 14.1 Hz), 128.3, 129.3 (d, E


Organometallics

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JP−C = 3.6 Hz), 130.8 (d, JP−C = 21.8 Hz), 131.1 (m-C6H3), 131.4 (d, JP−C = 1.9 Hz), 132.8 (d, JP−C = 79.6 Hz), 133.8 (d, JP−C = 10.1 Hz), 135.6 (d, JP−C = 16.7 Hz), 137.4 (d, JP−C = 128.6 Hz), 141.2 (br, iC6H2), 147.1 (br, m-C6H2, p-C6H2), 177.3 (d, i-C6H3, JP−C = 2.3 Hz), 180.6 (d, SnCCP, JP−C = 23.4 Hz). 31P{1H} NMR (101.25 MHz, C6D6): δ 23.3 (s, JSn−P = 184 Hz). 119Sn{1H} NMR (93.25 MHz, C6D6): δ 275 (d, JSn−P = 187 Hz). Anal. Calcd for C64H78NPSn: C, 76.03; H, 7.78; N, 1.39. Found: C, 75.68; H, 7.74; N, 1.60.

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ASSOCIATED CONTENT

S Supporting Information *

Tables and CIF files giving details about the quantum chemical calculations and crystallographic data for the published structures. 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 L.W.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Fonds der Chemischen Industrie. REFERENCES

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