Sterically Crowded Tin Acenaphthenes - Organometallics (ACS

Article pubs.acs.org/Organometallics

Sterically Crowded Tin Acenaphthenes Marie-Luise Lechner, Kasun S. Athukorala Arachchige, Rebecca A. M. Randall, Fergus R. Knight, Michael Bühl, Alexandra M. Z. Slawin, and J. Derek Woollins* EaStCHEM School of Chemistry, University of St Andrews, St Andrews, Fife KY16 9ST, Scotland S Supporting Information *

ABSTRACT: The synthesis of crowded peri-5-bromo-6-(organostannyl)acenaphthenes is described. Reaction of 5,6-dibromoacenaphthene with 1 equiv of n-BuLi at −40 °C in diethyl ether followed by addition of the appropriate organotin reagent at 0 °C gave 5bromo-6-(triphenylstannyl)acenaphthene (1), 5-bromo-6-(chlorodiphenylstannyl)acenaphthene (2), bis(6-bromoacenaphthen-5-yl)diphenylstannane (3), bis(6-bromoacenaphthen-5-yl)dibenzylstannane (4), bis(6-bromoacenaphthen-5-yl)dibutylstannane (6), and bis(6-bromoacenaphthen-5-yl)dichlorostannane (7) in low to medium yields (10−56%). 4 was converted into 5-iodo-6-bromoacenaphthene (5) by stirring overnight in the presence of a large excess of iodine. The new compounds were fully characterized spectroscopically. 119Sn NMR spectra suggest and interaction between the tin atoms and the neighboring peri halogen atoms. Single-crystal X-ray studies on 1−4 and 6−8 revealed Sn···X distances which are significantly less than the sum of the van der Waals radii, while DFT calculations indicate Wiberg bond indices of up to 0.11. Furthermore, there is evidence of the onset of 3c−4e bonding, though according to natural population analysis, the charge on tin is close to +2 in all compounds studied. Electrostatic interactions may thus be another important driving force for the close Br···Sn interactions, along with the small covalent (donor−acceptor) contributions.

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INTRODUCTION The nature of chemical bonds and atomic interactions is of central importance in chemistry as well as materials science. Although covalent and ionic bonds are thought to be well understood, even simple systems can reveal unexpected complexity.1−4 Weak intermolecular and intramolecular interactions, which are likely to be important in emerging areas of chemistry such as mechanostereochemistry, are not fully understood and are therefore an intriguing field of study. A wide range of interactions such as hydrogen bonding, ion−ion interactions, van der Waals forces, ion−dipole interactions, π−π stacking, and dipole−dipole interactions have become increasingly recognized in recent years.5,6 Furthermore, less common interactions have emerged such as CH···O and CH···π6 (nonconventional hydrogen bonding) and short van der Waals forces between halogen and chalcogen congeners.5−10 Weak interactions between heavy elements constrained in congested environments have attracted great attention over the past decade. Sterically restricted systems involving heteroatoms at distances shorter than the sum of van der Waals radii undergo steric compression arising from nonbonded interactions as a result of direct overlap of orbitals.11−13 The distinguishing features of peri substitution are evident when examining the proximity effects of ortho substitution in benzenes14 and bay substitution in phenanthrenes.15 While ortho- and peri-substituted species regularly give species with bridging geometries,16−21 the closer proximity of the interacting atoms or groups in peri-substituted frameworks allows a relaxed geometry to form via the formation of a direct bond between the two peri atoms (Figure 1).22−27 The bay-substituted © 2012 American Chemical Society

Figure 1. Ortho substitution in benzenes, peri substitution in acenaphthenes and naphthalenes, and bay-region disubstitution in phenanthrene. The preferred method of achieving a relaxed geometry for each motif is shown in the lower diagrams.

conformation of phenanthrenes forces the interacting atoms to even closer distances (ca. 2.0 Å), limiting their chemistry with single-atom-bridged species to afford the preferred relaxed geometry.28 Disubstituted naphthalenes and acenaphthenes are ideally suited for the study of noncovalent interactions, due to their rigid backbones and their short “natural” peri distance (2.44 Å). The molecular geometry in the peri region is determined by competition between attractive (covalent and weak) forces and repulsive forces resulting from the spatial requirements of the fully occupied MOs of the substituents. Apart from clear-cut Special Issue: F. Gordon A. Stone Commemorative Issue Received: December 17, 2011 Published: March 5, 2012 2922

dx.doi.org/10.1021/om201253t | Organometallics 2012, 31, 2922−2930

Organometallics

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bc:5′,6′-fg]-(1,5)distannocin was reported65 in 1991 by reacting 5,6-dilithioacenaphthene with dimethyldichlorostannane. Unfortunately, no crystal structures of these compounds were reported. Here, we report the synthesis and comprehensive structural study of various 5-bromo-6-(organostannyl)acenaphthenes. Alkyl- as well as aryl-substituted organotin chlorides were used as starting materials. Apart from synthetic studies, geometry optimizations in the gas phase and NBO calculations were performed for all compounds.

examples of bonding or repulsion between the peri atoms, there are many intermediate species where arguments about the existence of attractive forces are of interest. As a consequence of the peri geometry, substituents other than hydrogen experience considerable strain.29 In-plane as well as out-of-plane distortion often results in buckling of the ring system, leading to a significant change of the ideal geometry of naphthalenes. Weak atomic interactions and bond formation between the peri atoms can reduce this steric strain considerably.28,30−33 In our initial investigations of sterically crowded systems we utilized the special peri-substituted geometry and stability of the rigid naphthalene backbone. Our early work focused on dichalcogenide ligands34−39 and unusual phosphorus compounds.25,40−44 More recently we have reported the synthesis and structural study of chalcogen−chalcogen,45−47 halogen− chalcogen,48−51 and mixed-donor phosphorus−chalcogen52−55 naphthalenes, while more recent work has examined group 16 acenapthene systems.56,57 We have reviewed the literature for group 15 and 16 systems.58,59 Recent calculations60 predict significant E···E bonding in peri-substituted systems where there are suitable R groups such that donor−acceptor bonds may become possible. We have also noted significant structural features which support delocalized 3c−4e bonding in a number of group 15/16 systems.56−59 We were interested to establish if our observations on group 15/16 chemistry applied to heavier group 14 systems. There has been a recent report32 of the X-ray structure of Nap(I)(SnPh3) which displayed an Sn···I distance of 3.46 Å, but overall there are surprisingly few group 14 peri-substituted systems, though not surprisingly most examples involve carbon or silicon at the peri positions. Disilyl naph(SiR3)2 compounds have been described32,33 (SiR3 = SiH3, SiMe3, SiH2Ph). Mixed substituted molecules have also been reported where simple intramolecular donor−acceptor bonds are clearly important (Figure 2,) and this encouraged us that suitable peri substituted

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RESULTS AND DISCUSSION All new compounds were synthesized by reacting 5,6dibromoacenaphthene with 1 equiv of n-BuLi at −40 °C in diethyl ether and subsequent addition of the appropriate organotin compound. To test the methodology, we first used Ph3SnCl (eq 1) to prepare 1 in fair yield (32% after recrystallization).

The analogous reaction between dialkyltin dichlorides or SnCl4 and 5-bromo-6-lithioacenaphthene proved quite sensitive to the stoichiometry. Surprisingly, we found that for R = Bu, Bz, Cl when we used a 1:1 ratio of acenaphthene and the dialkyltin dichloride, both chlorides were substituted by a bromoacenaphthenyl group (eq 2) to give 4, 6, and 7 in variable yields (12.5− 56%). For diphenyldichlorostannane a mixture of the monosubstituted 5-bromo-6-(chlorodiphenylstannyl)acenaphthene (2; 23% yield) and the disubstituted bis(6bromoacenaphhten-5-yl)diphenylacenaphthene (3) was obtained. Using a 2:1 ratio of acenaphthene to diphenyltin dichloride, 3 was obtained as the main isolated product in poor yield (10%). We investigated the reactivity of bis(6bromoacenaphthenyl)dibenzylstannane (4) and bis(6bromoacenaphthenyl)dichlorostannane (7) (eq 3). 4 was readily converted into 5-iodo-6-bromoacenaphthene (5) by stirring overnight in the presence of a large excess of iodine, though the same procedure with 7 did not lead to any reaction at all. Reaction of 4 with SnCl 4 gives bromo-6(dichlorobenzylstannyl)acenaphthene (8). It is noteworthy that, though the exchange rate of aryl groups is reported to be higher than that of benzyl groups,66 an acenaphthenyl as well as a benzyl group is exchanged by a chloride here. Stepwise reaction of 4 with n-BuLi and SnCl4 also yields 8 (21% yield), indicating that n-BuLi prefers to react with the tin center followed by a ligand exchange reaction. The replacement of the second bromine on the acenaphthene seems to be less favorable. In contrast to the case for 4, we noted that, in general, 7 proved to be surprisingly unreactive. For example, 1H NMR indicates that 7 does not react with n-BuLi under the conditions used here. Organotin chlorides are known to form tin−tin bonds when reacted with activated magnesium.67,68 However, we observed no reaction for 7 even after stirring for a

Figure 2. Examples of peri-substituted molecules stabilized by intramolecular interactions.61−63

molecules might demonstrate weak covalent bonding and in particular 3c−4e delocalized frameworks. Introducing organotin substituents into an acenaphthene structure can be challenging, due to the large van der Waals radius of tin (2.17 Å). Only two such compounds have been reported in the literature to date. 5-(Tributylstannyl)acenaphthene was synthesized in 198964 by reacting 5bromoacenaphthene with the sodium salt of tributylstannane. The synthesis of 5,5,12,12-tetramethyldiacenaphtho[5,62923


Organometallics

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The molecular structures of 1−4 and 6−8 (Tables 2−5 and Figures 3−8) reveal some interesting features. All of the compounds show significant deviation from the ideal acenaphthene structure. Splay angles (sum of the peri angles 360°, which describe the in-plane distortion of the acenaphthene) of between 14.6 and 20.5° were found. Slight out-ofplane deviation described by the torsion angles Sn−C(1)− C(9)−Br(1) and Sn−C(13)−C(21)−Br(1) are also observed (0.15−15.2°). This results in peri distances between 3.1451(15) and 3.340(3) Å. The distortion of the peri substituents causes buckling of the aromatic ring system. Deviation from the planar (180°) acenaphthene torsion angles C(6)−C(5)−C(10)−C(1) and C(4)−C(5)−C(10)−C(9) of up to 4.3° were observed (see the Supporting Information). All of the compounds are distorted from tetrahedral geometry at the tin center. A major factor in these distortions appears to be weak Sn···Br interactions. It is interesting to note that the Br···Sn−C/Cl angle is very close to 180° in all the systems studied here. The geometry of the tin center in 1 might be best described as distorted trigonal bipyramidal (Figure 3). In this regard it is interesting to note that the sum of the C(1)− Sn(1)−C(19), C(1)−Sn(1)−C(25), and C(19)−Sn(1)− C(25) angles in 1 is 344.9°; i.e., enlarged from tetrahedral (328.5°) but not large enough (360°) for a perfect tbp. The recently reported33 Nap(I)(SnPh3) has an Sn···I separation of 3.46 Å, which is very similar to that in 1, though the naphthalene system accommodates the extra bulk of the iodine atom by increased displacement of the tin and iodine atoms to opposite sides of the naphthalene plane. In contrast to 1, 2 appears to have a more distorted tbp geometry while the remaining structures are best described as pseudo-octahedral. Geometry optimization of the monosubstituted triphenylstannylacenaphthene revealed an H···Sn−C angle of 167.8°. This confirms that indeed an interaction between the peri substituents is responsible for the quasi alignment of the bromo, the tin, and one of the substituents on the tin. We have recently60 discussed the ability of peri-substituted systems to support, for example, 3c−4e bonds, and the compounds described here represent examples of the onset of this type of bonding motif. The new compounds described here might also be considered indicative of the type of geometries that reaction intermediates adopt. It is interesting to note that the Sn···Br distances vary considerably. The Sn..Br distances for 1, 3, 4, and 6 (Br trans to carbon) are in the range 3.331(3)− 3.382(5) Å. The shortest Sn···Br distances are seen for compounds 2, 7, and 8 (3.1451(15), 3.174(3), and 3.191(3) Å, respectively), where the bromine is trans to a Sn−Cl bond. Since we envisage the Sn···Br bonding as electron donation from the bromine atom into low-lying empty orbitals on the tin

couple of days. 7 also failed to react with tin tetrachloride in a Kocheskov reaction.69 The new compounds were characterized spectroscopically, and the 1H and 13C NMR spectra are as anticipated. 119Sn NMR covers a wide range of shifts (approximately 4000 to −2500 ppm),70 and even small structural changes can influence the chemical shift values. Upfield shifts in 119Sn NMR due to weak coordination of the solvent66 or by complexation of the tin organyl with, for instance, phosphonium chlorides71,72 are reported in the literature. An interaction between the peri substituents would be expected to lead to a five- or even sixcoordinated tin atom, with a consequent upfield shift in comparison to the hydrogen-substituted acenaphthene. The parent acenaphthenylstannanes are unknown, and so a comparison with the related phenyl compounds is discussed here. While the 119Sn NMR shifts of 1 and 3 are actually higher than for the phenyl analogue (Ph4Sn), a large upfield shift can be seen for 2 and even more so for 7 in comparison to Ph3SnCl and Ph2SnCl2, respectively (Table 1), consistent with a higher coordination number at the tin atom as a result of the interaction between the peri substituents. Table 1. 119Sn NMR Shifts (ppm) of Compounds 1−3 and 7 in CDCl3 and the Shift (ppm) of the Analogous Compound Where the Acenaphthene Is Replaced by a Phenyl Group66 1 2 3 7

−82 −70 −116 −132

Ph4Sn Ph3SnCl Ph4Sn Ph2SnCl2

−137 −45 −137 −32 2924


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Table 2. Selected Distances (Å) and Angles (deg) of 1−4 and 6−8 1 Sn−Cl(1) Sn−Cl(2) Sn···Br(1) Sn···Br(2) av peri dist/∑rvdW ratio (%) av ∑: peri angles av splay anglea Br(1)···Sn−C Br(2)···Sn−C Br(1)···Sn−Cl Br(2)···Sn−Cl Sn−C(acenap) Br−C(acenap) C(1)-Sn-C(13) C−Sn−C/Cl−Sn−Cl a

2

3

4

6

7

2.421(3) 3.340(3)

3.1451(15)

87.4 380.1 20.1 179.9(2)

82.2 375.6 15.6

3.328(3) 3.338(3) 87.3 380.4 20.4 174.0(3) 176.0(3)

3.299(3) 3.395(3) 87.8 380.8 20.8 175.9(2) 172.1(2)

3.394(5) 3.370(5) 88.5 380.5 20.5 175.5(3)

172.06(8) 2.157(5) 1.907(4)

2.147(11) 1.918(11) 117.5(4)

2.161(7) 1.913(8) 123.8(3) 101.1(3)

2.161(9) 1.902(6) 126.9(4) 104.9(3)

2.211(8) 1.911(9) 104.7(3) 109.6(4)

8

2.379(3) 2.390(3) 3.174(3) 3.174(3) 83.1 374.6 14.6

2.434(5) 2.364(4) 3.192(3)

176.8(2) 179.2(2) 2.142(9) 1.910(8) 142.1(4) 106.3(10)

172.21(12)

83.5 377.2 17.2

2.144(10) 1.905(10) 96.05(15)

Splay angle: (sum of the three peri angles) − 360°.

Table 3. Crystallographic Data for Compounds 1 and 2 empirical formula formula wt temp (°C) cryst color, habit cryst dimens (mm3) cryst syst lattice params a (Å) b (Å) c (Å) β (deg) V (Å3) space group Z Dcalcd (g cm−3) F000 μ(Mo Kα) (cm−1) no. of rflns measd Rint min−max transmissn no of unique rflns (no. of variables) rfln/param ratio residuals: R1 (I > 2.00σ(I)) residuals: R (all rflns) residuals: wR2 (all rflns) goodness of fit indicator max peak in final diff map (e/Å3) min peak in final diff map (e/Å3)

1

2

C30H23BrSn 582.11 −148 colorless, platelet 0.31 × 0.18 × 0.08 orthorhombic

C24H18BrClSn 540.45 −148 colorless, prism 0.16 × 0.13 × 0.04 monoclinic

16.7705(12) 17.506(2) 16.2008(4) 4756.2(7) Pbca 8 1.626 2304 27.751 39 031 0.0703 0.623−0.801 4181 (289)

9.127(2) 16.587(4) 14.90(3) 93.06(13) 2252.5(9) P21/n 4 1.594 1056 30.373 19 184 0.1044 0.531−0.886 3963 (244)

14.47 0.0359 0.0478 0.0783 1.125 1.26 −0.54

16.24 0.0753 0.0976 0.2530 1.104 3.56 −1.27

Table 4. Crystallographic Data for Compounds 3 and 4 empirical formula formula wt temp (°C) cryst color, habit cryst dimens (mm3) cryst syst lattice params a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) space group Z Dcalcd (g cm−3) F000 μ(Mo Kα) (cm−1) no. of rflns measd Rint min−max transmissn no of unique rflns (no. of variables) rfln/param ratio residuals: R1 (I > 2.00σ(I)) residuals: R (all rflns) residuals: wR2 (all rflns) goodness of fit indicator max peak in final diff map (e/Å3) min peak in final diff map (e/Å3)

atom, an electron-withdrawing group on the tin atom would be expected to increase this interaction. The Sn−Cl bond lengths in 8 mirror this effect, with the Sn−Cl bond trans to the Sn···Br vector being shorter than the other Sn−Cl bond. DFT calculations were performed for 1−4 and for 6−8. Initial performance tests were carried out for 1,8-bis(trimethylstannyl)naphthalene, using the structure in the crystal33 as a starting geometry. Selected bond lengths and angles obtained with different effective core potentials (ECPs) and basis sets on tin are given in the Supporting Information. Because of its good performance, the B3LYP/SBKJC level was

3

4

C36H26Br2Sn 737.10 −180 colorless, prism 0.05 × 0.05 × 0.05 triclinic

C38H30Br2Sn 765.15 −148 colorless, chunk 0.21 × 0.15 × 0.05 monoclinic

10.073(5) 11.839(4) 12.381(6) 90.697(10) 109.926(12) 95.247(9) 1380.7(10) P1̅ 2 1.773 724 38.529 8596 0.0438 0.631−0.825 4719 (352)

12.467(3) 9.296(2) 26.334(6)

13.41 0.0512 0.0711 0.1396 1.087 1.01 −1.31

14.42 0.0504 0.0615 0.1635 1.152 2.52 −1.18

91.447(6) 3051.0(11) P21/c 4 1.667 1512 34.907 22 065 0.0476 0.58−0.84 5335 (370)

chosen for tin in further calculations. The calculated structures were found to be in good agreement with the crystal structures reported here. Wiberg bond indices (WBIs),40 which measure the covalent bond order, were calculated for all structures. The WBIs for 1, 3, 4, and 6 between the bromine and the tin atoms range from 0.07 to 0.09, indicating a weak interaction between those two atoms. The corresponding WBIs in 2, 7, and 8 are slightly 2925


Organometallics

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Table 5. Crystallographic Data for Compounds 6−8 6

7

8

empirical formula

C44H43Br3Sn

formula wt temp (°C) cryst color, habit

930.23 −180 colorless, platelet 0.1 × 0.1 × 0.01 triclinic

C28H24Br2 Cl2OSn 725.90 −148 colorless, platelet 0.19 × 0.10 × 0.05 triclinic

7.601(3) 15.347(7) 16.066(7) 102.200(11) 92.613(10) 100.486(10) 1794.2(12) P1̅ 2 1.722 924 40.946 11 439 0.0421 0.683−0.96 6329(433)

7.198(6) 10.31(7) 18.69(2) 81.51(3) 87.91(2) 74.41(2) 1322(2) P1̅ 2 1.824 708 42.209 11 197 0.0554 0.609−0.81 4648(307)

8.601(4) 11.173(5) 12.711(8) 75.78(4) 85.23(6) 68.82(5) 1104.1(10) P1̅ 2 1.759 576 32.252 9033 0.0616 0.469−0.908 4367(253)

14.62 0.0633

15.14 0.0498

17.26 0.1005

0.0800 0.1564 1.225 2.50

0.076 0.1443 1.127 1.16

0.1254 0.3630 1.377 1.14

−1.26

−1.40

−3.48

cryst dimens (mm3) cryst syst lattice params a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) space group Z Dcalcd (g cm−3) F000 μ(Mo Kα) (cm−1) no. of rflns measd Rint min−max transmissn no of unique rflns (no. of variables) rfln/param ratio residuals: R1 (I > 2.00σ(I)) residuals: R (all rflns) residuals: wR2 (all rflns) goodness of fit indicator max peak in final diff map (e/Å3) min peak in final diff map (e/Å3)

C19H15BrSnCl2 512.84 −148 colorless, 0.60 × 0.09 × 0.03 triclinic

Figure 4. Molecular structure of bis(6-bromoacenaphthen-5-yl)diphenylstannane (3) with ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity.

Figure 5. Molecular structure of bis(6-bromoacenaphthen-5-yl)dibenzylstannane (4) with ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity.

higher (0.10−0.11). This may reflect the effect of the presence of the chlorine atoms on the tin centers in 2, 7, and 8. In fact, when an isomer of 2 with its trans Br···Sn−Cl moiety is optimized with a corresponding cis orientation (i.e., by interchanging the Cl and one Ph substituent), the resulting

minimum is 2.2 kcal/mol higher in energy. On going from this cis isomer to the more stable trans form, the Br···Sn distance is

Figure 3. Molecular structures of 5-bromo-6-(triphenylstannyl)acenaphthene (1) (left) and 5-bromo-6-(chlorodiphenylstannyl)acenaphthene (2) (right) with ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity. 2926


Organometallics

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The Br···Sn interactions were investigated in more detail using natural bond orbital (NBO) analysis.74 For 3, 4, and 6, four polar Sn−C bonds are found among the NBOs. According to the second-order perturbation analysis, small but noticeable lp(Br)−σ*(Sn−C) donor−acceptor interactions are found in these cases, consistent with the noticeable WBIs discussed above. These donor−acceptor interactions involving the antibonding orbitals of the Sn−C bonds trans to Br are invariably larger than those involving cis Sn−C bonds and are estimated to be worth ca. 6−8 kcal/mol. Even stronger interactions of this type have been found in lighter congeners: e.g., in peri-diphosphines.60 In all the chlorides studied (i.e., 2, 7, and 8), the Sn−Cl bonds are not localized as 2c−2e bonds but rather as lone pairs on Cl (albeit with low occupancy). Even though no lp(Br)−σ*(Sn−Cl) contributions can be computed in these cases, this finding is consistent with an increased donor−acceptor interaction involving the Sn−Cl bonds and, hence, with the increased WBI approaching or exceeding 0.1. It should be noted, however, that because tin is rather electropositive, its bonds (in particular to halogens) are highly ionic in character. According to natural population analysis, the charge on tin is close to +2 in all compounds studied. Electrostatic interactions may thus be another important driving force for the close Br···Sn interactions, along with the small covalent (donor−acceptor) contributions manifest in the WBIs.

Figure 6. Molecular structure of bis(6-bromoacenaphthen-5-yl)dibutylstannane (6) with ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity.

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EXPERIMENTAL SECTION

General Procedures. All experiments were carried out under an oxygen- and moisture-free nitrogen atmosphere using standard Schlenk techniques and glassware. Reagents were obtained from commercial sources and used as received. Dry solvents were collected from a MBraun solvent system. 5,6-Dibromoacenaphthene was prepared following standard literature procedures starting from acenaphthene.75 Elemental analyses were performed by the London Metropolitan University School of Human Sciences Microanalysis Service. 1H and 13 C NMR spectra of 2, 3, and 8 were recorded on a Bruker Avance 300 MHz spectrometer. 1H and 13C NMR spectra of 1, 4, 6, and 7 were recorded on a JEOL GSX 270 MHz spectrometer. 119Sn NMR spectra were recorded on a JEOL GSX 270 MHz spectrometer. δ(H) and δ(C) were referenced to external tetramethylsilane. δ(Sn) was referenced to external tetramethylstannane. Assignments of 13C and 1H NMR spectra were made with the help of H−H COSY and HSQC experiments, performed on a Bruker Avance 300 MHz spectrometer. All NMR shifts are given in ppm, and all couplings are given in Hz. X-ray crystal structures for 4 and 8 were determined at −148(1) °C on the St Andrews Robotic Diffractometer,76 a Rigaku ACTOR-SM, Saturn 724 CCD area detector with graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å). Data for compounds 3 and 6 were collected at −180(1) °C by using a Rigaku MM007 high brilliance RA generator (Mo Kα radiation, confocal optic) and Mercury CCD system. Data for compounds 1, 2, and 7 were collected at −148(1) °C on a Rigaku SCXMini instrument with graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å). All data had intensities corrected for Lorentz, polarization, and absorption. The data for the complexes was collected and processed using CrystalClear77,78 (Rigaku). The structures were solved by Patterson or direct methods and expanded using Fourier techniques. Non-hydrogen atoms were refined anisotropically, and hydrogen atoms were refined using a riding model. All calculations were performed using CrystalStructure79 and SHELXL-97.80 These X-ray data can be obtained free of charge via www.ccdc.cam. ac.uk/conts/retrieving.html or from the Cambridge Crystallographic

Figure 7. Molecular structure of bis(6-bromoacenaphthen-5-yl)dichlorostannane (7) with ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity.

decreased from 3.44 to 3.31 Å, with a concomitant increase in the WBI from 0.07 to 0.11. Thus, a chloride in a trans position reinforces the Br···Sn interaction noticeably.

Figure 8. Molecular structure of 5-bromo-6-(dichlorobenzylstannyl)acenaphthene (8) with ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity. 2927


Organometallics

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CHCHCBr, 3JH−H = 7.8), 7.57 (d, 2H, CHCBr, 3JH−H = 7.2), 7.16 (d, 2H, CHCHCSn, 3JH−H = 7.2), 7.88 (d, CHCSn, 2H, 3JH−H = 6.9, 3 JH−119/117Sn = 66.8/63.9). 13C{1H} NMR (75.5 MHz, CDCl3, Me4Si): δ 30.2 (2C, CH2CH2), 30.7 (2C, CH2CH2), 120.2, 120.6 (2C, CHCHBr), 121.0 (2C, CHCHCSn), 128.3, 128.8, 132.5 (2C, CHCBr), 137.6, 138.7 140.7 (CHCSn), 143.2, 145.7, 147.6, 148.1. 119 Sn{1H} NMR (100.76 MHz, CDCl3, Me4Sn): δ −116 (s, 1Sn). Anal. Found: C, 58.8; H, 3.7. Calcd for C36H26Br2Sn (Mr 737.11 g mol−1): C, 58.7; H, 3.6. Bis(6-bromoacenaphthen-5-yl)dibenzylstannane (4). Colorless crystals were obtained after recrystallization out of CH2Cl2/hexane via the diffusion method. Yield: 1.1 g; 55.9%. Mp: 149 °C. 1H NMR (270 MHz, CDCl3, Me4Si): δ 2.94 (s, 4H, PhCH2), 3.19−3.26 (m, 4H, CH2CH2), 3.26−3.33 (m, 4H, CH2CH2), 6.72−7.21 (m, 10H, SnCH2Ph), 7.51 (d, 2H, CHCHCSn, 3JH−H = 7.1), 7.58 (d, 2H, CHCHCBr, 3JH−H = 7.1), 7.72 (d, 2H, CHCBr, 3JH−H = 7.5), 7.79 (d, 2H, CHCSn, 3JH−H = 7.8). 13C{1H} NMR (67.9 MHz, CDCl3, Me4Si): δ 29.7 (2C, CH2Ph), 30.1 (2C, CH2CH2), 30.3 (2C, CH2CH2), 123.1, 127.8, 128.1, 147.2, 120.2, 120.7, 121.0, 127.9, 131.8, 132.1, 135.0, 135.9, 139.2 (CHCSn), 147.1. Anal. Found: C, 59.6; H, 4.1. Calcd for C38H30Br2Sn (Mr 765.17 g mol−1): C, 59.6; H, 4.0. 5-Iodo-6-bromoacenaphthene (5). A 0.5 g amount (0.65 mmol) of 4 was dissolved in chloroform. A large excess of iodine was added. The mixture was stirred overnight. Chloroform was evaporated. The presence of 5-iodo-6-bromoacenaphthene (5) could be proven by Xray crystallography. Bis(6-bromoacenaphthen-5-yl)dibutylstannane (6). Colorless crystals were obtained after recrystallization out of THF at −30 °C. Yield: 0.14 g; 12.5%. Mp: 114 °C. 1H NMR (270 MHz, CDCl3, Me4Si): δ 0.77 (t, 6H, CH3, 3JH−H = 7.3), 1.32 (h, 4H, CH2, 3JH−H = 7.1), 1.39−1.50 (m, 4H, CH2), 1.56 (t, 4H, 3JH−H = 6.9), 3.21−3.36 (m, 4H, CH2CH2), 3.36−3.50 (m, 4H, CH2CH2), 7.23 (d, 2H, CHCHCBr, 3JH−H = 6.3), 7.30 (d, 2H, CHCHCSn, 3JH−H = 7.0), 7.68 (d, 2H, CHCBr, 3JH−H = 7.3), 8.12 (d, 2H, CHCSn, 3JH−H = 7.0, 3 JH−119/117Sn = 69.5/66.4). 13C{1H} NMR (67.9 MHz, CDCl3, Me4Si): δ 13.6 (2C, CH3), 19.6 (2C, CH2), 27.4 (2C, CH2), 29.5 (2C, CH2), 29.8 (2C, CH2CH2), 30.3 (2C, CH2CH2), 119.9, 120.4, 121.8, 129.2, 131.0, 132.1 (CHCBr), 135.7, 140.6 (CHCSn, 1JC−Sn = 33), 147.0, 147.2. 119Sn{1H} NMR (100.76 MHz, CDCl3, Me4Sn): δ −31.4 (s, 1Sn). Anal. Found: C, 55.2; H, 4.9. Calcd for C32H34Br2Sn (Mr 697.13 g mol−1): C, 55.1; H, 4.9. Bis(6-bromoacenaphthen-5-yl)dichlorostannane (7). Three grams (9.6 mmol) of 5,6-dibromoacenaphthene was suspended in 30 mL of diethyl ether. A 3.85 mL portion of a 2.5 M solution of nBuLi was added dropwise at −40 °C. The solution was warmed to room temperature and stirred for 15 min. A 1.1 mL portion (9.4 mmol) of tetrachlorostannane was slowly added to the reaction mixture at 0 °C. The reaction mixture was warmed to room temperature and stirred overnight. The solvent was evaporated in vacuo ,and 40 mL of toluene was added. The solution was filtered, and half of the solvent was removed. The product crystallizes as small gray needles at −30 °C. Yield: 1.1 g; 35.1%. Mp: above 250 °C. 1H NMR (270 MHz, CDCl3, Me4Si): δ 3.22−3.36 (m, 4H, CH2CH2), 3.36− 3.52 (m, 4H, CH2CH2), 7.23 (d, 2H, CHCHCBr, 3JH−H = 7.3), 7.54 (d, 2H, CHCHCSn, 3JH−H = 7.7), 7.64 (d, 2H, CHCBr, 3JH−H = 7.3), 8.68 (d, 2H, CHCSn, 3JH−H = 7.3, 3JH−119/117Sn = 109.6/104.9). 13C{1H} NMR (67.9 MHz, CDCl3, Me4Si): δ 30.0 (2C, CH2CH2), 30.5 (2C, CH2CH2), 118.16, 121.1, 121.2, 126.2, 131.3, 131.9 (CHCBr), 137.8 (CHCSn, 2JC−Sn = 45.6), 141.8, 147.9, 150.3 (CSn, 1JC−Sn = 19.7). 119 Sn{1H} NMR (100.76 MHz, CDCl3, Me4Sn): δ −132.2 (s, 1Sn). Anal. Found: C, 44.1; H, 2.5. Calcd for C24H16Br2SnCl2 (Mr 653.80 g mol−1): C, 43.8; H, 2.3. 5-Bromo-6-(dichlorobenzylstannyl)acenaphthene (8). A 0.5 g portion (0.65 mmol) of 4 was suspended in 30 mL of ether. A 0.52 mL portion of a 2.5 M solution of n-BuLi in hexane was added dropwise at −40 °C. The reaction mixture was stirred for 30 min in the cold. A 0.15 mL portion (1.3 mmol) of tetrachlorostannane was added dropwise. The reaction mixture was stirred for another 30 min. Afterward it was warmed to room temperature and stirred overnight.

Data center, 12 Union Road, Cambridge CB2 1EZ, U.K.: fax, (+44) 1223-336-033; e-mail, [email protected]. Geometries were fully optimized in the gas phase at the B3LYP81 level using Curtis and Binning’s 962(d) basis82 on Br augmented with a set of diffuse s and p functions and 6-31G(d) basis elsewhere. A variety of relativistic ECPs with their associated valence basis sets was trialed for tin, namely the Stuttgart−Dresden ECP83 along with its original double-ζ valence basis (augmented with a set of d-polarization functions)84 or a newer triple-ζ valence basis,85 the compact effective potential by Stevens et al. along with the SBKJC 2s3p2d valence basis86,87 as well as Hay−Wadt ECP with its recent triple-ζ valence basis (augmented with one set of polarization functions denoted LANL08d).88 Unless otherwise noted, the SBKJC results are given and discussed in this paper. Wiberg bond indices89 were obtained in a natural bond orbital analysis74 at the same level. Experimental structures from X-ray crystallography were used as the starting geometry. The computations were performed using the Gaussian 03 suite of programs.90 Reaction of 5,6-Dibromoacenaphthene with Organotin Compounds. One gram (3.2 mmol) of 5,6-dibromoacenaphthene was suspended in 30 mL of ether. A 1.3 mL portion of a 2.5 M n-BuLi solution in hexane was added dropwise at −40 °C. The reaction mixture was warmed to room temperature and stirred for 15 min. A 3.2 mmol amount of the organotin compound dissolved in 15 mL of ether was added dropwise to the reaction solution with ice cooling. The reaction mixture was stirred overnight. The solvent was removed in vacuo, and 40 mL of toluene was added. The solution was filtered. Toluene was removed in vacuo. 5-Bromo-6-(triphenylstannyl)acenaphthene (1). Colorless crystals were obtained after recrystallization from THF/hexane via the diffusion method. Yield: 0.6 g; 32%. Mp: 116 °C. 1H NMR (270 MHz, CDCl3, Me4Si): δ 3.23−3.30 (m, 2H, CH2CH2), 3.30−3.37 (m, 2H, CH2CH2), 7.17 (d, 1H, CHCHCSn, 3JH−H = 7.2), 7.23 (d, CHCHCBr, 1H, 3JH−H = 7.4), 7.29−7.36 (m, 9H, SnPh), 7.56−7.61 (m, 6H, SnPh), 7.68 (d, 1H, CHCBr, 3JH−H = 7.2), 7.74 (d, 1H, CHCSn, 3JH−H = 7.2, 3JH−119/117Sn = 64.4/61.0).13C{1H} NMR (67.9 MHz, CDCl3, Me4Si): δ 30.2 (2C, CH2CH2), 30.5 (2C, CH2CH2), 129.5, 128.7, 136.6, 137.4 (CHCSn, 2JC−Sn = 36.5), 120.6, 121.1, 128.4, 128.2, 129.1, 130.3, 132.6, 140.7, 142.5, 142.8. 119Sn{1H} NMR (100.76 MHz, CDCl3, Me4Sn): δ −82.4 (s, 1Sn). Anal. Found: C, 61.8; H, 4.1. Calcd for C30H23BrSn (Mr 582.12 g mol−1): C, 61.9; H, 4.0. 5-Bromo-6-(chlorodiphenylstannyl)acenaphthene (2). Colorless crystals were obtained after recrystallization from CH2Cl2/hexane via the diffusion method. Yield: 0.4 g; 23.1%. Mp: 132 °C. 1H NMR (300 MHz, CDCl3, Me4Si): δ 3.29−3.36 (m, 2H, CH2CH2), 3.38−3.45 (m, 2H, CH2CH2), 7.29−7.34 (m, 6H, SnPh), 7.66−7.69 (m, 4H, SnPh), 7.14 (d, 1H, CHCHCBr, 3JH−H = 7.0), 7.60 (d, 1H, CHCBr, 3JH−H = 7.0), 7.47 (d, 1H, CHCHCSn, 3JH−H = 7.1), 8.62 (d, CHCSn, 1H, 3 JH−H = 7.1, 3JH−119/117Sn = 73.9/70.6). 13C{1H} NMR (75.5 MHz, CDCl3, Me4Si): δ 30.3 (1C, CH2CH2), 30.9 (1C, CH2CH2), 114.8, 121.4, 121.7, 129.2, 130.1, 136.3, 136.5, 141.7 (CHCSn), 143.2, 147.5, 148.4, 150.1. 119Sn{1H} NMR (100.76 MHz, CDCl3, Me4Sn): δ −70.3 (s, 1Sn). Anal. Found: C, 53.5; H, 3.4. Calcd for C24H18BrClSn (Mr 540.47 g mol−1): C, 53.3; H, 3.4. Bis(6-bromoacenaphthen-5-yl)diphenylstannane (3). Two grams (6.4 mmol) of 5,6-dibromoacenaphthene was suspended in 50 mL of ether. A 2.6 mL amount of a 2.5 M n-BuLi solution in hexane was added dropwise at −40 °C. The reaction mixture was warmed to room temperature and stirred for 15 min. A 1.1 g amount (3.2 mmol) of diphenyldichlorostannane dissolved in 15 mL of ether was added dropwise to the reaction solution with ice cooling. The reaction mixture was stirred overnight. The solvent was removed in vacuo, and 40 mL of toluene was added. The solution was filtered. (Analysis of the residue revealed the presence of unreacted 5,6-dibromoacenaphthene, but increased reaction time did not improve the yield.) Toluene was removed in vacuo. The solid was recrystallized from THF. Yield: 0.23 g; 9.7%. Mp: 168−170 °C. 1H NMR (300 MHz, CDCl3, Me4Si): δ 3.23−3.31 (m, 4H, CH2CH2), 3.31−3.38 (m, 4H, CH2CH2), 7.18− 7.30 (m, 6H, SnPh), 7.48−7.55 (m, 4H, SnPh), 7.07 (d, 2H, 2928


Organometallics The solvent was removed, and toluene was added. The mixture was filtered, and the toluene was removed in vacuo. 5-Bromo-6(dichlorobenzylstannyl)acenaphthene (8) was crystallized from THF/pentane as a THF adduct using the diffusion method. Yield: 0.07 g; 20.9%. Mp: 112 °C. 1H NMR (300 MHz, CDCl3, Me4Si): δ 3.26−3.32 (m, 2H, CH2CH2), 3.33−3.41 (m, 2H, CH2CH2), 3.62 (s, 2H, PhCH2, 3JH−119/117Sn) = 95.0/93.1), 7.20−7.34 (m, 5H, SnCH2Ph), 7.16 (d, 1H, CHCHCBr, 3JH−H = 6.4), 7.44 (d, 1H, CHCHCSn, 3JH−H = 6.8), 7.71 (d, 1H, CHCBr, 3JH−H = 7.7), 8.41 (d, 1H, CHCSn, 3JH−H = 7.1, 3JH−119/117Sn = 93.7/89.5). 13C{1H} NMR (75.5 MHz, CDCl3, Me4Si): δ 30.3 (CH2CH2), 30.9 (CH2CH2), 40.1 (SnCH2), 117.3, 121.4, 121.5, 126.7 (CHCHCBr), 129.2, 129.4, 131.4, 132.3 (CHCBr), 133.8, 136.0, 140.7 (CHCSn, 2JC−Sn = 47.4), 141.9, 148.5 (CSn, 1JC−Sn = 14.3), 151.7. 119Sn{1H} NMR (100.76 MHz, CDCl3, Me4Sn): δ −42.1 (s, 1Sn). Anal. Found: C, 44.7; H, 2.8. Calcd for C19H15BrSnCl2 (Mr 512.84 g mol−1): C, 44.5; H, 2.9. Reaction of Bis(6-bromoacenaphthen-5-yl)dibenzylstannane (4) with SnCl4. A 0.5 g portion (0.65 mmol) of 4 was mixed with 0.24 g (0.65 mmol) of Bz2SnCl2 and heated until the mixture melted. Afterward it was cooled to 50 °C. A 50 mL portion of toluene was added. The reaction mixture was refluxed for 3 h. 8 was identified as the main product by 1H and 119Sn NMR spectra. Reaction of Bis(6-bromoacenaphthen-5-yl)dichlorostannane (7) with n-BuLi. A 0.5 g portion (0.77 mmol) of 7 was suspended in 30 mL of ether. A 0.3 mL portion of a 2.5 M solution of n-BuLi in hexane was added dropwise at −40 °C. The reaction mixture was stirred for 30 min in the cold. A 0.09 mL portion (0.77 mmol) of tetrachlorostannane was added dropwise. The reaction mixture was stirred for another 30 min. Afterward it was warmed to room temperature and stirred overnight. The solvent was removed, and toluene was added. The mixture was filtered, and the toluene was removed on the rotary evaporator. 1H as well as 119Sn NMR showed only the signals of the starting material. Reaction of Bis(6-bromoacenaphthen-5-yl)dichlorostannane (7) with Mg. A 0.5 g portion (0.77 mmol) of 7 was suspended in 15 mL of THF. A 0.19 g portion (7.7 mmol) of magnesium was added. The magnesium was activated with 0.1 mL of 1,2-dibromoethane. The reaction mixture was stirred for 3 days. 119Sn NMR showed that no reaction had taken place. Reaction of Bis(6-bromoacenaphthen-5-yl)dichlorostannane (7) with SnCl4. A 0.5 g portion (0.77 mmol) of 7 was mixed with 0.09 mL (0.77 mmol) of SnCl4 and heated until the mixture melted. Afterward it was cooled to 50 °C. A 50 mL portion of hexane was added. The reaction mixture was refluxed for 5 h. 119Sn NMR showed one broad signal at −56 ppm (SnCl4) and one signal at −132 ppm which corresponds to 7. Reaction of Bis(6-bromoacenaphthen-5-yl)dichlorostannane (7) with Iodine. A 0.5 g portion of 7 was dissolved in chloroform. A large excess of iodine was added. The mixture was stirred overnight. The solvent was evaporated. The starting material remained unreacted.

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REFERENCES

This paper is dedicated to the memory of F. G. A. Stone, a giant of organometallic chemistry and a true gentleman.

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ASSOCIATED CONTENT

S Supporting Information *

Tables, figures, and CIF files giving crystallographic data, platon reports, pictures of the acenaphthenes with the according interactions, data for the tin basis set optimization, and a list of all the WBIs. This material is available free of charge via the Internet at http://pubs.acs.org.

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Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. 2929


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