Synthesis of Intramolecularly Coordinated Aluminum and Gallium

Article pubs.acs.org/Organometallics

Synthesis of Intramolecularly Coordinated Aluminum and Gallium Compounds for the Preparation of [1]Ferrocenophanes Nora C. Breit,† Travis Ancelet,†,§ J. Wilson Quail,‡ Gabriele Schatte,‡ and Jens Müller*,† †

Department of Chemistry and ‡Saskatchewan Structural Sciences Centre, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada S Supporting Information *

ABSTRACT: Two different ligands equipped with pyridine donor moieties, (2-H 4C5N)(Me3Si)2C (R′) and (2-H4C5N)(Me3Si)(Me)C (R″), were applied in the preparation of aluminum and gallium dihalides that could be employed in salt metathesis reactions with 1,1′dilithioferrocene. R′GaCl2 (1) was accessible from LiR′ and GaCl3 (21%), whereas the respective aluminum compound R′AlCl2 (3Cl) and its bromine analogue R′AlBr2 (3Br) could only be prepared through the intermediate species R′AlMe2 (2) by the addition of Me3SnCl and Br2, respectively. An improved synthesis of the ligand precursor R″H, (2-H 4C5N)(Me3Si)(Me)CH), is described. Attempted syntheses of R″AlX2 starting from LiR″ and AlCl3 or ClAlMe2 gave the bis-ligand compounds R″2AlCl (4) and R″2AlMe (6), respectively. As deduced from proton NMR spectroscopy, the formation of 6 proceeded through the intermediate R″AlMe2 (5) and was facilitated in the presence of tmeda. The formation of 4 and 6, respectively, is diastereospecific, as only rac isomers were formed (R,R-Λ and S,S-Δ). Molecular structures of compounds 2, 3Br, and 6 were determined by single-crystal X-ray analysis. Salt metathesis of the dihalides 1, 3Cl, and 3Br with 1,1′-dilithioferrocene gave the respective galla- and alumina[1]ferrocenes (7 and 8). Neither compound could be isolated and were only identified by 1H NMR spectroscopy in reaction mixtures. Analytically pure polymers (7 n) of low molecular weight were found and investigated by DLS (Mw = 8.3 ± 2.5 kDa; DPw = 17 ± 5).

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Chart 1. Strained [1]Metallacyclophanes (Left) and Unstrained [1.1]Metallacyclophanes (Right)

INTRODUCTION Metallopolymers are a growing class of functional materials showing unique properties stemming from the presence of metal atoms.1 Ring-opening polymerization (ROP) of strained sandwich compounds is one of the most effective methods for the preparation of well-defined metallopolymers.1c,2 Siliconbridged [1]ferrocenophanes are the best known class of strained sandwich compounds, and different methodologies for ROPs have been developed over the last two decades. 1c Of particular interest is the living anionic ROP of dimethylsila[1]ferrocenophane, which can be used to prepare block copolymers.3 Self-assembly of these block copolymers in block-selective solvents leads to cylindrical micelles, with a core-forming poly(ferrocenylsilane) block. These micelles are living, with both ends of the PFS cylinders being active, and addition of further block-copolymer unimers gives larger micelles of uniform lengths. This process has been termed crystallization-driven living self-assembly and opens possibilities to control the dimensions of new functional materials on the nanometer scale.4 Since 2005, we have investigated strained sandwich compounds with aluminum or gallium in bridging positions, aiming to explore new polymeric materials through ringopening polymerization (ROP) (Chart 1). All of our strained species were prepared by salt metathesis reactions between dilithio sandwich compounds and the respective aluminum or gallium dichlorides RECl2. The bulkiness of the ligand R plays a crucial role, not only for the outcome of these salt metathesis © 2011 American Chemical Society

reactions but also for the reactivity of the resulting sandwich compounds. If the bulky, intramolecularly coordinating, trisyltype ligands Pytsi and Me2Ntsi (Chart 2) were employed, strained aluminum- or gallium-bridged [1]vanadarenophanes,5 [1]chromarenophanes, 5 [1]ferrocenophanes, 5 , 6 [1]molybdarenophanes,7 and [1]ruthenocenophanes8 could be isolated. However, if nonbulky ligands of the “one-armed” phenyl type (Ar′; Chart 2) were used to stabilize group 13 elements in bridging positions, nonstrained [1.1]metallacyclophanes resulted from respective salt metathesis reactions.9 Received: July 25, 2011 Published: November 2, 2011 6150

dx.doi.org/10.1021/om200680d | Organometallics 2011, 30, 6150−6158

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Chart 2

Scheme 1

Attempts to polymerize aluminum- and gallium-bridged [1]ferrocenophanes and [1]ruthenocenophanes either failed or resulted in sluggish polymerizations.8 These results indicated that the bulkiness of trisyl-type ligands (Chart 2), which was required for the synthesis of strained sandwich compounds, was hindering the ROP of those species. Recently, we successfully used a ligand with an intermediate bulkiness (Mamx; Chart 2)10 for the preparation of a galla[1]ferrocenophane. 11 This gallium-bridged ferrocenophane showed an unexpectedly high reactivity and escaped its isolation through ROP to give a poly(ferrocenylgallane).11 This result illustrated that increasing the bulkiness of the “one-armed” phenyl ligand by switching from an Ar′ ligand to the Mamx ligand (Chart 2) changes the outcome of the respective salt metathesis reactions and strained [1]ferrocenophanes instead of [1.1]ferrocenophanes are formed. In the course of these investigations, we set out to decrease the steric requirements of the Pytsi ligand (Chart 2) to access aluminum- or gallium-bridged [1]ferrocenophanes of reactivity higher than those that were stabilized with the Pytsi ligand. In this report, we describe syntheses of aluminum and gallium species equipped with R′ and R″ ligands, as shown in Chart 3.

the main product of this reaction was the known salt [R′ 2 Ga][GaCl 4 ], which precipitates from the reaction mixture.12h Several attempts to adopt this method to prepare the aluminum analogue of species 1 failed. Only the known species R′2AlCl could be identified as a product of the reaction.12e However, as shown in Scheme 1, the targeted aluminum compound 3Cl can be synthesized through a twostep process. First, the dimethyl species 2 was prepared by quenching LiR′ with Me2AlCl, which was then converted to the chloride 3Cl by the addition of ClSnMe3 (Scheme 1). The reaction of species 2 with bromine gave the bromide 3Br. Similar procedures had been applied for group 13 dihalides of the type REX2 before.13 The formation of the intermediate 2 is nearly quantitative, and the crude reaction product was used for the subsequent chlorination or bromination, resulting in isolated yields of 75% and 76% for 3Cl and 3Br, respectively. As expected, compounds 1, 2, 3Cl, and 3Br all show similar signal patterns in their NMR spectra that are consistent with Cssymmetric species in solution. Molecular Structures of 2 and 3Br. Crystals suitable for single-crystal X-ray analysis were obtained for the dimethyl compound 2 and the bromide 3Br (Figures 1 and 2; Table 1). As expected, both species are monomers in the solid state, with nitrogen acting as an electron donor toward the Lewis acidic aluminum. The Al−N bond lengths of 1.984(2) and 1.996(2) Å for 2 and 1.936(4) Å for 3Br are not strikingly different from values found in the related species (Pytsi)AlMe2 (2.0034(18) Å),14 (Pytsi)AlCl2 (1.9383(16) Å),15 and (Me2Ntsi)AlCl2 (1.975(2) Å)16 (see Chart 2 for Pytsi and Me2Ntsi). It is apparent from the thermal ellipsoid plots in Figures 1 and 2 that the most unusual structural parameter is the small bite angle of ligand R′, which was found to be 70.66(8) and 70.60(8)° for the dimethyl species 2 and 73.38(18)° for the bromide 3Br. For the known species [R′2Al][AlCl4]12e and R′2GaCl12h similar bite angles of 72.7(9) and 73.2(7)° (Al species) and 65.6(1) and 67.2(2)° (Ga species) were reported. In the molecular structures of 2 and 3Br the pyridine ring is tilted toward the aluminum atom, as illustrated by comparing C7−C2−C3 angles (130.4(2)−130.2(4)°) with C7−C2−N1 angles (110.45(18)−110.9(4)°). It seems that the deviation from an idealized angle of 120° by almost 10° is caused by the donor-bond interaction between nitrogen and aluminum. Synthesis of Species 4−6. As mentioned before, the bulkiness of ligands R of aluminum or gallium dihalides of the

Chart 3

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RESULTS AND DISCUSSION

Synthesis of Species 1−3. The R′ ligand (Chart 3) had been employed for the synthesis of various transition-metal and main-group compounds.12 Among those species are aluminum and gallium compounds equipped with two R′ ligands (R′2ECl and [R′2E][ECl4]).12e,h However, the starting dihalides R′EX2, which were needed for the preparation of new [1]ferrocenophanes, were unknown in the literature. Following a literature procedure, 12i the ligand precursor 2-[bis(trimethylsilyl)methyl]pyridine (R′H) (Scheme 1) was synthesized by deprotonating 2-picoline with nBuLi followed by addition of chlorotrimethylsilane. Following a lithiation protocol described in the same reference, 12i R′H was deprotonated in situ and reacted with GaCl3 in diethyl ether to give the new gallium dichloride species 1 (Scheme 1). However, compound 1 could only be isolated in a yield of 21%; 6151


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R″H can either be lithiated using nBuLi with 1 equiv of tmeda or using tBuLi. If in situ prepared LiR″ was reacted with AlCl3 in Et2O, instead of the expected aluminum dichloride R″AlCl2, only R″2AlCl (4) could be isolated through crystallization in a moderate yield of 42%. 1H NMR spectra of reaction mixtures showed in addition to the signals of 4 another set of signals of an unknown compound with a pattern that would be expected for the targeted dichloride R″AlCl2. However, as the isolation of this second compound failed, we can only speculate that it might be R″AlCl2. These results were independent of the order of addition of starting species. As in the case of the R′ ligand (Scheme 1), we intended to synthesize the targeted R″AlCl2 through a respective dimethyl species (5 in Scheme 2). Similar to the case of the targeted dichloride R″AlCl2, only the bis-ligand species could be isolated (6 in Scheme 2). When the reaction was followed by 1H NMR spectroscopy, peaks revealing the presence of the targeted species 5 were not found; only signals for a methylaluminum species and coordinated tmeda were found in addition to those of compound 6.17 In order to avoid the presence of tmeda, the ligand precursor R″H was lithiated using tBuLi in Et2O. After the addition of Me2AlCl, resulting reaction mixtures showed two signal patterns for R″-containing products in 1H NMR spectra. One pattern revealed the presence of species 6, while the second pattern could tentatively be assigned to the targeted dimethyl species 5.18 However, isolation of 5 using common techniques failed in all cases and only the bis-ligand species 6 could be isolated. If tmeda was added to reaction mixtures, the intensity of proton NMR signals of compound 6 increased, while those of 5 decreased. Obviously, species 5 readily exchanges ligands to form 6 and AlMe3 and this process is facilitated through trapping AlMe3 with tmeda. Using the same conditions that led to the isolation of the aluminum species 4 (Scheme 2), the preparation of R″GaCl2 was attempted using both methods of lithiation (nBuLi/tmeda and tBuLi/Et2O; see Scheme 2). Isolation of a product was attempted by sublimation, crystallization from various solvents, and precipitation from a toluene solution into hexanes, but all attempts proved unsuccessful. Even changing the ratio of LiR″ to GaCl3 to 2:1 in order to isolate the species R″2GaCl did not give a definite result. Interestingly, both species 4 and 6 show only one signal pattern for the R″ moiety: four multiplets in the aromatic region (Py) and two singlets in the aliphatic region (Me and SiMe 3). That the isolated compound 6 is indeed the bis-ligand species is apparent by measured intensity ratios between the signals for the MeAl moiety and those of the ligand R″. However, from this pattern alone an identification of species 4 as R″2AlCl is impossible, because the targeted molecule R″AlCl2 should show the same pattern. However, the peak in the mass spectrum with the highest m/z ratio at 418 [M+] clearly reveals the composition of species 4. Of course, the ligand precursor R″H with one stereogenic carbon atom was synthesized as a racemate. Therefore, one can expect species 4 and 6 to be a mixture of isomers due to the presence of two stereogenic carbon atoms per molecule. Furthermore, a trigonal-bipyramidal geometry with the two N-donor atoms in axial positions with an idealized C2 symmetry can exist as a Δ or a Λ enantiomer (Chart 4). With each ligand containing one stereogenic carbon atom, three pairs of enantiomers are expected: R,R-Δ/S,S-Λ (C2 symmetry), R,R-Λ/S,S-Δ (C2 symmetry), and R,S-Δ/S,R-Λ (C1 symmetry) (Scheme 3). Donor−acceptor bonds between nitrogen and aluminum or

Figure 1. Molecular structure of 2 with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity. One of two independent molecules is shown. Selected atom−atom distances (Å) and bond angles (deg) for 2 (values in braces refer to the second independent molecule that is not shown): Al1−N1 = 1.984(2) {1.996(2)}, Al1−C7 = 2.064(2) {2.052(2)}, Al1−C14 = 1.968(3) {1.968(3)}, Al1−C15 = 1.962(3) {1.970(3)}, C2−C7 = 1.495(3) {1.490(3)}; C7−Al1−N1 = 70.66(8) {70.62(8)}, C7−Al1−C14 = 121.85(12) {117.59(11)}, C7−Al1−C15 = 121.11(13) {123.091(11)}, N1−Al1−C14 = 112.07(12) {106.71(10)}, N1− Al1−C15 = 110.80(12) {118.31(12)}, C14−Al1−C15 = 111.80(16) {112.57(12)}, C7−C2−N1 = 110.45(18) {110.30(19)}, C7−C2−C3 = 130.4(2) {130.5(2)}.

Figure 2. Molecular structure of 3Br with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected atom−atom distances (Å) and bond angles (deg) for 3Br: Al1−N1 = 1.936(4), Al1−C7 = 2.002(5), Al1−Br1 = 2.2784(14), Al1−Br2 = 2.2738(15), C2−C7 = 1.510(6); C7−Al1−N1 = 73.38(18), C7−Al1− Br1 = 124.54(15), C7−Al1−Br2 = 121.60(15), N1−Al1−Br1 = 116.35(13), N1−Al1−Br2 = 111.32(15), Br1−Al1−Br2 = 105.66(6), C7−C2−N1 = 110.9(4), C7−C2−C3 = 130.2(4).

type REX2 plays an important role in the accessibility as well as in the reactivity of [1]ferrocenophanes. It seems that less bulky groups attached to Al or Ga in strained sandwich compounds go hand in hand with a higher reactivity toward ROPs. 11 From this point of view, we were interested in the preparation of aluminum or gallium dihalides REX2 with a stabilizing ligand that is less bulky than R′ discussed before. We decided to formally replace one of the two trimethylsilyl groups of R′H by a methyl group and used 2-[1′-(trimethylsilyl)ethyl]pyridine (R″H) as a ligand precursor (Scheme 2). To the best of our knowledge, the ligand R″ has not been used as an intramolecularly stabilizing group, which is in contrast with the large number of known compounds for the R′ ligand. The precursor 6152


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Table 1. Crystal and Structural Refinement Data for Compounds 2, 3Br, and 6 3Br

2 empirical formula fw cryst size/mm3 cryst syst, space group Z a/Å b/Å c/Å β/deg V /Å3 ρ calcd/mg m−3 temp/K μ calcd/mm−1 θ range/deg no. of collected/unique rflns abs cor data/restraints/params goodness of fit R1 (I > 2σ(I))a wR2 (all data)a absolute structure param largest diff peak and hole, Δρ elect/Å−3 a

C14H28AlNSi2 293.53 0.20 × 0.15 × 0.05 orthorhombic, Pbca 16 15.9215(2) 16.2335(2) 28.9629(3) 90 7485.80(15) 1.042 173(2) 0.224 1.92−25.35 91 938/6844 φ-scan 6844/0/342 1.089 0.0502 0.1062

C12H22AlBr2NSi2 423.29 0.12 × 0.05 × 0.05 orthorhombic, P212121 4 8.3242(6) 15.0855(9) 15.2507(6) 90 1915.10(19) 1.468 173(2) 4.390 2.79−25.668 29 183/3629 multiscan 3629/0/169 1.084 0.0441 0.0877 0.031(12) 0.766 and −0.673

0.279 and −0.195

6 C21H35AlN2Si2 398.67 0.12 × 0.12 × 0.11 monoclinic, C2/c 4 16.387(5) 12.116(4) 12.202(4) 97.745(10) 2400.5(13) 1.103 173(2) 1.736 4.55−69.61 6920/2161 multiscan 2161/0/125 1.050 0.0582 0.1511 0.313 and −0.434

R1 = ∑||Fo| − |Fc||]/[∑|Fo| (Fo2 > 2σ(Fo2)); wR2 = {[∑w(Fo2 − Fc2)2]/[∑w(Fo2)2]}1/2 (all data).

Scheme 2

Scheme 3. Different Possible Isomers of R″2AlX (X = Cl (4), Me (6))a

Chart 4. Δ and Λ Isomers of a Trigonal Bipyramid of C2 Symmetry

a

The dotted line separates enantiomers, a solid line separates diastereomers, and double arrows indicate equilibria.

that only one set of signals was found for 4 and 6, respectively, shows that either the rac or the meso isomer formed specifically. Molecular Structure of 6. Compound 6 crystallizes in the monoclinic space group C2/c, showing that the rac isomers crystallized with the R,R-Λ and S,S-Δ isomers present in the asymmetric unit (Figure 3 and Table 1). The geometry around aluminum can be described as a distorted trigonal bypyramid with both N atoms in axial positions. The N1−Al1−N1* axis

gallium in 5-fold coordinated complexes break and re-form quickly in solution, allowing for equilibration between Δ and Λ isomers through a fast intramolecular exchange of both ligands (Scheme 3).19 Assuming a fast ligand exchange in species 4 and 6, one would expect to find two sets of peaks in NMR spectra, one for all rac isomers and one for all meso isomers.20 The fact 6153


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different chemical shifts, whereas both peaks for all β-protons appear downfield and are either overlapping or exhibit just a small difference in chemical shifts. 5,6,8,11 For example, compound 7 shows three signals in the typical Cp range at δ 4.22 (2 α-H), 4.29 (2 α-H), and 4.62 (4 β-H), while the aluminum compound 8 shows four signals at δ 4.10 (2 α-H), 4.28 (2 α-H), 4.66 (2 β-H), and 4.68 (2 β-H). These patterns and the chemical shifts are comparable with those for other galla- or alumina[1]ferrocenophanes which were isolable (e.g., bridging moiety Ga(Pytsi), δ 4.08 (2 α-H), 4.45 (2 α-H), 4.61 (2 β-H), 4.65 (2 β-H);6b bridging moiety Al(Pytsi), δ 3.91 (2 α-H), 4.31 (2 α-H), 4.64 (2 β-H), 4.68 (2 β-H)6a). In addition to peaks for the Cp protons, all expected NMR peaks for 7 and 8, respectively, could be unequivocally assigned (see Experimental Section and Figures S14 and S15 (Supporting Information)). In attempts to prepare and isolate the monomer 7, only the polymer 7n could be isolated and purified through precipitation with hexanes (Chart 5). Analytically pure 7n was

Figure 3. Molecular structure of 6 with thermal ellipsoids at the 50% probability level (only the R,R-Λ isomer is shown). Hydrogen atoms are omitted for clarity. Selected atom−atom distances (Å) and bond angles (deg) for 6: Al1−N1 = 2.1280(19), Al1−C7 = 2.056(2), Al1− C12 = 1.992(4), C2−C7 = 1.487(3); C7−Al1−N1 = 67.70(7), C7− Al1−C12 = 125.30(8), C7−Al1−N1* = 96.34(8), N1−Al1−C12 = 103.46(7), N1−Al1−N1* = 153.07(14), C7−C2−N1 = 110.2(2), C7−C2−C3 = 129.7(2). Symmetry transformation used to generate equivalent atoms (*): −x + 1, y, −z + 1/2.

Chart 5

with an angle of 153.07(14)° deviates significantly from linearity. A similar geometry was found for the related species R′2GaCl12h mentioned before, which exhibits N−Ga−N angles in the range of 159.8(1)−167.1(1)°.21 As expected, the bite angle of the R″ ligand in 6 (67.70(7)°) is very similar to that of the more bulky R′ ligand discussed above (2, 70.66(8) and 70.62(8)°; 3Br, 73.38(18); R′2GaCl,12h 65.6(1)−67.2(2)°). Similar to the case for species 2 and 3Br, the pyridyl group is tilted toward the acceptor atom by almost 10° (C7−C2−N1 = 110.2(2)° compared to C7−C2−C3 = 129.7(2)°; see Figure 3). The Al−N donor bond length of 2.1280(19) Å is expectedly longer, as in the related species 2 that exhibits only 4-fold coordinated Al atoms (Al−N, 1.984(2) and 1.996(2) Å; see Figure 1). Synthesis of [1]Ferrocenophanes. With the new gallium dichloride 1 and the aluminum dihalides 3Cl and 3Br in hand, we used salt metathesis reactions with 1,1′-dilithioferrocene to prepare new [1]ferrocenophanes (Scheme 4).

obtained from metathesis reactions where the tmeda adduct of 1,1′-dilithioferrocene had been replaced by (LiC5H4)2Fe·3thf.22 This replacement was done in another attempt to isolate the monomer 7, as it is known from tin-bridged [1]ferrocenophanes that traces of amines can initiate the ringopening polymerization.23 Both the tmeda and the thf adduct of 1,1′-dilithioferrocene resulted in the formation of 7n. The fact that only with (LiC5H4)2Fe·3thf was an analytically pure polymer 7n isolable, might be caused by the difficulty in completely removing tmeda and tmeda-containing lithium salts from 7n. For the aluminum species, only impure polymers 8n could be obtained from a metathesis reaction using the tmeda adduct of 1,1′-dilithioferrocene. Surprisingly, the use of (LiC5H4)2Fe·3thf in metathesis reactions with either 3Cl or 3Br did not yield significant amounts of 8 in solution (1H NMR spectroscopy). That 7n and 8n are both polymers was evident by the similarity of their proton NMR spectra. All peaks are broad; for example, the Cp protons give rise to one broad, structureless signal. Additional information about the chemical composition of 7n and 8n was obtained from hydrolysis experiments. When 7n or 8n were dissolved in water-containing CDCl3, the resulting 1H NMR spectra showed only FeCp2 and the ligand precursor R′H. In addition, tmeda was found for 8n, where (LiC5H4)2Fe· 2/3tmeda had been used for the synthesis. Dynamic light scattering of the pure sample 7n dissolved in thf gave a hydrodynamic radius Rh of 1.35 ± 0.20 nm (Table S1 and Figure S1 (Supporting Information)). Assuming 7n to be a random coil in a good solvent, the radius of gyration can be calculated to be 2.77 ± 0.41 (R g /Rh = 2.05). 24 For poly(ferrocenyldimethylsilane) Rg and the absolute Mw are known.25 Using this log(Mw)/log(Rg) relation as a calibration curve, compound 7n shows a Mw value of 8.3 ± 2.5 kDa corresponding to 17 ± 5 repeating units (DPw).

Scheme 4

In all metathesis reactions the strained [1]ferrocenophanes 7 and 8 formed in solution, but all attempts to isolate pure species were unsuccessful (see the Experimental Section). That the targeted strained species was formed in solution was evident from proton NMR spectroscopy. Aluminum- or gallium-bridged ferrocenophanes equipped with ligands capable of intramolecular donation (Cs point group symmetry) give rise to a typical pattern of the protons at the Cp moieties; i.e., the two signals for all α-protons appear upfield with significantly 6154


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(Applied Biosystem-MDS SCIEX). Elemental analyses were carried out at the Saskatchewan Structural Sciences Center at the University of Saskatchewan using a Perkin-Elmer 2400 CHN elemental analyzer; V2O5 was added to samples to promote combustion. 1H and 13C NMR spectra were recorded at 25 °C on a 500 MHz Bruker Avance spectrometer (1H, 500.2 MHz; 13C, 125.8 MHz). 1H NMR chemical shifts were referenced to residual protons of deuterated solvents (C6D6, δ 7.15; CDCl3, δ 7.26); 13C chemical shifts were referenced to δ 128.00 (C6D6) and 77.00 (CDCl3), respectively. C atoms directly bound to Al or Ga were not detected by 13C NMR spectroscopy. The absence of signals is presumably due to the effect of the electric quadrupole moment of Al or Ga on the relaxation times of directly bound carbon atoms. The IR spectrum was recorded on a Bruker Tensor 27 FTIR spectrometer. Dynamic light scattering experiments were performed using a Nano Series Malvern Zetasizer instrument (equipped with a 633 nm red laser). Samples were filtered twice through 0.2 μm syringe PTFE filters (Millex) before they were analyzed in 1 cm glass cuvettes at concentrations of 2.0, 3.0, and 4.0 mg mL−1 in thf at 25 °C. The refractive index of the polymer 7n was assumed to be 1.5 (see the Supporting Information). Species with calculated amounts of carbon in the 60% range (2, 4, and 6) showed lower than expected amounts of carbon in elemental analyses, and we speculate that the formation of SiC in the combustion process might be the main cause for these discrepancies. In addition, compounds with 4-fold coordinated group 13 elements (1, 2, 3Cl, and 3Br) are more sensitive to air than those with 5-fold coordination (4 and 6), with 2 and 3Br being the most sensitive species. This sensitivity is possibly reflected in slightly lower purities of isolated products (see 1 H NMR spectra in the Supporting Information). Furthermore, 2 is a sticky material, which handicaps the sample preparation for CHN analysis. All these factors might have contributed to the discrepancies in some of the CHN analyses. All compounds gave matching results for HRMS. Chemicals. The following reagents were used without further purification: 2-picoline (98%, Alfa Aesar), 2-ethylpyridine (97%, Alfa Aesar), nBuLi (2.5 M in hexanes, Acros Organics or Aldrich), tBuLi (1.7 M in pentane, Aldrich), Me3SiCl (98%, Alfa Aesar), GaCl3 (99.999%, Alfa Aesar), Br2 (99.8%, Alfa Aesar), Me3SnCl (97%, Aldrich), ferrocene (98%, Aldrich), Me2AlCl (1 M in hexanes, Aldrich). Aluminum trichloride (99.985%, Alfa Aesar) was sublimed prior to use; tmeda (99%, Alfa Aesar) was distilled from sodium and stored over 4 Å molecular sieves. (LiC5H4)2Fe· 2/3tmeda27 and (LiC5H4)2Fe(thf)322 were synthesized according to literature procedures. 2-[Bis(trimethylsilyl)methyl]pyridine (R′H) was prepared according to the literature,12i but Et2O instead of hexane and tmeda was used, resulting in typical yields of 79−85% (reported yield 85%). Known methods for the preparation of 2-[(1′-trimethylsilyl)ethyl]pyridine (R″H) start either with 2-ethylpyridine (a yield was not reported)28 or with 2-methylpyridine (method 1, nBuLi, Me3SiCl, 82% yield; method 2, nBuLi, MeI, 60% yield).12i We used 2-ethylpyridine as a starting compound, but in contrast to ref 28, we applied nBuLi/ tmeda in hexanes instead of nBuLi in thf for the lithiation (see details below). 2-[(1′-Trimethylsilyl)ethyl]pyridine (R″H). nBuLi in hexanes (20.5 mL, 51.3 mmol) was diluted with hexane (45 mL) and cooled to 0 °C, followed by addition of tmeda (7.0 mL, 47 mmol) and 2ethylpyridine (5.00 g, 46.4 mmol). After it was stirred at room temperature for 30 min, the reaction mixture was cooled down to 0 °C, before Me3SiCl (5.40 g, 49.7 mmol) was slowly added, followed by stirring at room temperature for 16 h. Hexanes (60 mL) and deionized water (80 mL) were added, and the phases were separated. The aqueous phase was washed with hexanes (3 × 50 mL), and the united organic phases were washed with deionized water (3 × 60 mL). Volatiles were removed under vacuum, and distillation in vacuum at an oil bath temperature of 70 °C gave a colorless oil (6.73 g, 76%). 1H NMR (CDCl3): δ −0.04 (s, 9 H, SiMe3), 1.41 (d, J = 7.5 Hz, 3 H, CH3), 2.44 (q, J = 7.4 Hz, 1 H, CH), 6.98 (m, 2 H, 3-H, 5-H), 7.52 (pst, 1 H, 4-H), 8.47 (d, 1 H, 6-H). 13C NMR (CDCl3): δ −3.2 (SiMe3), 13.7 (CH3), 32.7 (CHMeSiMe3), 119.3, 121.1 (5-C and 3C), 135.5 (4-C), 148.7 (6-C), 165.7 (2-C). Note that all 1H NMR

SUMMARY AND CONCLUSIONS Two different ligands equipped with pyridine donor moieties were used to prepare new aluminum and gallium dihalides that could be employed in salt metathesis reactions with 1,1′dilithioferrocene. In the case of the stabilizing ligand (2pyridyl)bis(trimethylsilyl)methyl (R′), the gallium species R′GaCl2 (1) was accessible with a one-step process starting from LiR′ and GaCl3, whereas the respective aluminum compound R′AlCl2 (3Cl) and its bromine analogue R′AlBr2 (3Br) could only be prepared through the intermediate dimethyl species R′AlMe 2 (2) (Scheme 1). A formal replacement of one of the two trimethylsilyl groups of the R′ ligand by a methyl group led to the less bulky R″ ligand (Scheme 2). However, attempted syntheses of R″AlX 2 species always resulted in the isolation of bis-ligand compounds R″2AlX (X = Cl (4), Me (6)). Compound 6 readily formed from the targeted dimethyl species R″AlMe2 (5) by a loss of AlMe3, a reaction that is facilitated in the presence of tmeda. Interestingly, the reaction resulting in compound 6 is diastereospecific and only the rac isomers were formed (R,RΛ and S,S-Δ; Scheme 3), as concluded from a single-crystal analysis and NMR spectroscopy. Even though the molecular structure of the chloride species 4 was not determined in the solid state, from the similarities of proton NMR spectra of 4 and 6 one can conclude that 4 also formed as the rac isomers exclusively. This stereospecificity might be caused by the steric requirements of the R″ ligand. Only in the case of the found rac isomers R,R-Λ and S,S-Δ, both Me3Si groups of the two R″ ligands are situated on the outer surface of the trigonal bipyramid while the smaller Me groups occupy the more spacerestricted inner area of the trigonal bypyramid (Scheme 3 and Figure 3). These types of Lewis acidic chiral compounds might be of interest as potential catalysts; the indium compound R2InX with a comparable structure had been prepared recently and employed for lactide polymerizations.26 Salt metathesis of the dihalides 1, 3Cl, and 3Br with 1,1′dilithioferrocene gave the galla- and alumina[1]ferrocenes 7 and 8, respectively. Even though, all attempts to isolate these species failed, their identity was clearly evident from proton NMR spectroscopy. In the case of the gallium compound 7, analytically pure polymers 7n of low molecular weight were isolated (DLS: Mw = 8.3 ± 2.5 kDa; DPw = 17 ± 5). In order to develop new metallopolymers in a controlled way through ROP of strained sandwich compounds, it is necessary to isolate and purify the starting monomer. The tested ligands in this study did not open this important avenue and, therefore, we will focus our attention on different ligand systems in the future.

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EXPERIMENTAL SECTION

General Procedures. Manipulations were done using standard Schlenk and glovebox techniques (N2 as inert gas), unless noted differently. Solvents were dried using a MBraun solvent purification system (Et2O, thf, toluene, hexanes) or distilled from sodium and benzophenone (C6H6) and stored under nitrogen over 4 Å molecular sieves. Solvents for NMR measurements were degassed through freeze−pump−thaw procedures and stored under nitrogen over 4 Å molecular sieves. Mass spectra were measured on a VG 70SE and are reported in the form m/z (relative intensity) [M+], where m/z is the mass observed, relative intensity is the intensity of the peak relative to the most intense peak, and M+ is the molecular ion or fragment; only characteristic mass peaks are reported. For isotopic patterns, only the mass peak of the isotopologue or isotope with the highest natural abundance is listed. Mass spectra with electron spray ionization were recorded from MeCN solutions using a QSTAR XL MS/MS system 6155


Organometallics

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(pst, 1 H, 4-H), 6.98 (d, 1 H, 6-H). 13C NMR (C6D6): δ 2.2 (SiMe3), 120.1 (5-C), 124.8 (3-C), 142.0 (4-C), 143.7 (6-C), 171.8 (2-C). EIMS (70 eV): m/z (%) 408 (33) [M+ − Me], 206.12 (24) [C10H17AlNSi+], 206.08 (100) [C10H16NSi2+], 132 (23) [C6H5AlSi+], 73 (42) [SiMe3+]. HRMS (EI; m/z): calcd for C12H22AlBr2NSi2, 422.9452; found, 422.9451 (Δ(ppm) = 0.4). Anal. Calcd for C12H22AlBr2NSi2 (423.270): C, 34.05; H, 5.24; N, 3.31. Found: C, 33.02; H, 5.22; N, 3.01. Chlorobis[1-(pyrid-2-yl)-1-(trimethylsilyl)eth-1-yl-κ 2C,N]alumane, R″2AlCl (4). In an attempt to synthesize R″AlCl2, tBuLi in pentane (2.8 mL, 4.8 mmol) was added to a solution of R″H (0.89 g, 4.7 mmol) in a mixture of hexanes (5 mL) and diethyl ether (10 mL) at −78 °C. After 45 min of stirring at −78 °C the reaction mixture was added to a −78 °C cold solution of AlCl3 (0.62 g, 4.7 mmol) in diethyl ether (15 mL) (see note below). The dry ice bath was removed and the reaction mixture stirred for 16 h at room temperature. The precipitate was filtered off, and crystalline 4 (0.41 g, 42%) was obtained from this solvent mixture at −25 °C. 1H NMR (C6D6): δ 0.22 (s, 18 H, SiMe3), 0.85 (s, 6 H, Me), 6.36 (pst, 2 H, 5-H), 6.73 (d, 2 H, 3-H), 6.93 (pst, 2 H, 4-H), 7.84 (d, 2 H, 6-H). 13C NMR (C6D6): δ −1.8 (SiMe3), 14.7 (Me), 118.8 (5-C), 120.9 (3-C), 138.3 (4-C), 144.1 (6-C), 174.7 (2-C). EIMS (70 eV): m/z (rel intens) 418 (48) [M+], 240 (41) [M+ − R″], 239 (26) [M+ − R″H], 162 (100) [R″AlCl − C5H3N], 146 (28) [C6H18Si2+], 132 (16) [R″Al+ − SiMe3], 73.0 (18) [SiMe3+]. HRMS (EI; m/z): calcd for C20H32AlClN2Si2, 418.1608; found, 418.1615 (Δ(ppm) = 1.6). Anal. Calcd for C20H32AlClN2Si2 (419.087): C, 57.32; H, 7.70; N, 6.68. Found: C, 55.35; H, 8.32; N, 6.24. Note: several attempts to prepare 4 by using a ratio of 1:2 (AlCl3:R″H) always gave 4 as the main product in a mixture with unknown species (1H NMR spectroscopy) and never resulted in isolation of pure 4 through crystallizations. Methylbis[1-(pyrid-2-yl)-1-(trimethylsilyl)eth-1-yl-κ 2C,N]alumane, R″2AlMe (6). For the attempted synthesis of compound 5 (R″AlMe2), a solution of nBuLi in hexanes (1.8 mL, 5.1 mmol) was diluted with hexanes (5 mL) and tmeda (0.55 g, 4.7 mmol) was added, followed by the addition of R″H (0.92 g, 4.7 mmol) at 0 °C. After it was stirred at room temperature for 4 h, the reaction mixture was cooled to 0 °C, and a solution of Me2AlCl in hexanes (5.2 mL, 5.2 mmol) was added. After removal of the ice bath, the reaction mixture was stirred for 16 h at room temperature. The precipitate was filtered off, and crystallization from hexanes at −25 °C yielded the product 6 (0.35 g, 37%). 1H NMR (C6D6): δ 0.13 (s, 18 H, SiMe3), 0.19 (s, 3 H, AlMe), 0.84 (s, 6 H, Me), 6.38 (pst, 1 H, 5-H), 6.76 (d, 1 H, 3-H), 6.94 (m, 1 H, 4-H), 7.77 (d, 1 H, 6-H). 13C NMR (C6D6): δ −1.8 (SiMe3), 14.9 (Me), 118.0 (5-C), 120.7 (3-C), 137.3 (4-C), 144.5 (6C), 176.5 (ipso-C) (C5H4). EIMS (70 eV): m/z (%) 398 (14) [M+], 383 (9) [M+ − Me], 220 (74) [M+ − R″], 219 [M+ − R″H], 162 (39) [C9H13AlN+], 146 (53) [C6H18Si2+], 132 (16) [MeCAl(C5H4N)+], 73 (100) [SiMe3+]. HRMS (EI; m/z): calcd for C21H35AlN2Si2, 398.2154; found, 398.2152 (Δ(ppm) = 0.5). Anal. Calcd for C 21H35AlN2Si2 (398.669): C, 63.27; H, 8.85; N, 7.03. Found: C, 64.71; H, 9.63; N, 7.17. Preparation of [1]Ferrocenophanes. Many attempts were undertaken to prepare and isolated pure 7 and 8, respectively, which are summarized here. Additions of R′EX2 to (LiC5H4)2Fe or of (LiC5H4)2Fe to R′EX2 were carried out at different temperatures (room temperature and 0, −20, −30, −50, and −78 °C), with the solvent being benzene, toluene, or diethyl ether. After completion of the reaction, the precipitates that formed were filtered off. Isolation of product 7 or 8 was attempted by crystallization from various solvents, including diethyl ether, toluene, and hexanes. Purification was also attempted by precipitations into hexane. [1-(Pyrid-2-yl)-1-(trimethylsilyl)eth-1-yl-κ 2 C,N]galla[1]ferrocenophane, R′Ga(C5H4)2Fe (7). Species 1 (0.59 g, 1.5 mmol) in benzene (7 mL) was added to a suspension of (LiC5H4)2Fe· 2/3tmeda (0.43 g, 1.5 mmol) in benzene (8 mL) at 0 °C. After stirring of the reaction mixture for 2.5 h at room temperature, the precipitate was filtered off and a 1H NMR spectrum was measured of the filtrate. 1H NMR of 7 (C6D6): δ 0.27 (s, 18 H, SiMe3), 4.22 (m, 2 H, α-H, C5H4), 4.29 (m, 2 H, α-H, C5H4), 4.62 (m,

values reported in ref 12i differ by 0.30−0.52 ppm in comparison to our values; all reported 13C NMR values12i differ by 0.3−0.4 ppm. Dichloro[(pyrid-2-yl)bis(trimethylsilyl)methyl-κ 2C,N]gallane, R′GaCl2 (1). R′H (6.36 g, 26.8 mmol) was added to a solution of nBuLi in hexanes (9.5 mL, 27 mmol) and diethyl ether (10 mL) at 0 °C. After 2.5 h of stirring at room temperature, the reaction mixture was cooled to −78 °C and a −78 °C cold solution of GaCl3 (4.72 g, 26.8 mmol) in diethyl ether (20 mL) was added. The cold bath was removed, and the reaction mixture was stirred for 16 h at room temperature. After the precipitate was filtered off, the amount of solvent was reduced in vacuo, and compound 1 crystallized at −25 °C (2.08 g, 21%). 1H NMR (C6D6): δ 0.16 (s, 18 H, SiMe3), 6.08 (pst, 1 H, 5-H), 6.55 (d, 1 H, 3-H), 6.74 (pst, 1 H, 4-H), 7.02 (br, 1 H, 6-H). 13 C NMR (C6D6): δ 1.4 (SiMe3), 120.6 (C-5), 122.6 (C-3), 141.2 (C4), 144.7 (C-6), 170.1 (ipso-C). EIMS (70 eV): m/z (%) 362 (18) [M+ − Me], 237 (31) [R′H+], 236 (18) [R′+], 222 (100) [R′H+ − Me], 206 (86) [C10H16NSi2+], 150 (21) [C8H12NSi+], 149 (14) [C8H11NSi+], 73 (45) [SiMe3+]. HRMS (EI; m/z): calcd for C12H22Cl2GaNSi2, 376.9894; found, 376.9914 (Δ(ppm) = 5.2). Anal. Calcd for C12H22Cl2GaNSi2 (377.110): C, 38.22; H, 5.88; N, 3.71. Found: C, 38.79; H, 6.23; N, 3.62. Identification of the byproduct [R′2Ga][GaCl4]: IR (KBr) ν GaCl 380 cm−1 (literature value 375 cm−1).12h MS (ESI): m/z (%) 541 (52) [R′2Ga]+, 238 (100) [R′HH]+. Dimethyl[(pyrid-2-yl)bis(trimethylsilyl)methyl-κ 2 C,N]alumane, R′AlMe2 (2). nBuLi in hexanes (13.0 mL, 20.8 mmol) was added dropwise to a solution of R′H (4.68 g, 19.7 mmol) in diethyl ether (20 mL) at 0 °C. After the mixture was stirred for 1 h at room temperature, Me2AlCl in hexanes (21.0 mL, 21.0 mmol) was added at 0 °C. After the reaction mixture was stirred for 16 h at room temperature, diethyl ether was removed under vacuum. The product was dissolved in hexanes (40 mL), and the solid residue was filtered off. Volatiles were removed under vacuum, and 2 was obtained as an orange oil with minor impurities (6.03 g, ∼100%). Crystals suitable for single-crystal X-ray diffraction analysis were obtained from a toluene solution at −15 °C. 1H NMR (C6D6): δ −0.16 (s, 6 H, AlMe2), 0.16 (s, 18 H, SiMe3), 6.13 (pst, 1 H, 5-H), 6.69 (d, 1 H, 3-H), 6.81 (pst, 1 H, 4-H), 7.12 (d, 1 H, 6H). 13C NMR (C6D6): δ −5.9 (AlMe2), 2.4 (SiMe3), 118.5 (5-C), 125.7 (3-C), 139.7 (4-C), 144.0 (6-C), 173.8 (ipso-C). EIMS (70 eV): m/z (%) 278 (9) [M+ − Me], 190 (21) [C9H13AlNSi+], 73 (100) [SiMe3+], 57 (15) [AlMe2+]. HRMS (EI; m/ z ): [M − Me]+ calcd for C13H25AlNSi2, 278.1341; found, 278.1340 (Δ(ppm) = 0.3). Anal. Calcd for C14H28AlNSi2 (293.531): C, 57.29; H, 9.61; N, 4.77. Found: C, 54.45; H, 9.05; N, 4.44. Dichloro[(pyrid-2-yl)bis(trimethylsilyl)methyl-κ 2 C,N]alumane, R′AlCl2 (3Cl). A solution of Me3SnCl (3.9 g, 20 mmol) in benzene (10 mL) was added to a solution of crude 2 (3.84 mmol) in benzene (20 mL) at room temperature. The reaction mixture was stirred for 16 h, before the volatiles were removed under vacuum. The obtained solid was washed with hexanes (2 × 10 mL) and dried in vacuo to yield product 3Cl (0.96 g, 75%). 1H NMR (C6D6): δ 0.18 (s, 18 H, SiMe3), 5.99 (pst, 1 H, 5-H), 6.61 (d, 1 H, 3-H), 6.71 (pst, 1 H, 4-H), 6.91 (d, 1 H, 6-H). 13C NMR (C6D6): δ 2.0 (SiMe3), 120.0 (C5), 124.6 (C-3), 142.0 (C-4), 143.7 (C-6), 172.1 (C-2). EIMS (70 eV): m/z (%) 333 (1) [M+], 318 (43) [M+ − Me], 237 (30) [R′H+], 236 (18) [R′+], 222 (99) [R′H+ − Me], 206 (100) [C10H16NSi2+], 150 (11) [C8H12NSi+], 149 (14) [C8H11NSi+], 132 (13) [C6H5AlSi+], 73 (38) [SiMe3+]. HRMS (EI; m/z): calcd for C12H22AlCl2NSi2, 333.0483; found, 333.0477 (Δ(ppm) = 2.0). Anal. Calcd for C12H22AlCl2NSi2 (334.368): C, 43.10; H, 6.63; N, 4.19. Found: C, 43.54; H, 6.62; N, 3.99. Dibromo[(pyrid-2-yl)bis(trimethylsilyl)methyl-κ 2 C,N]alumane, R′AlBr2 (3Br). A solution of Br2 (0.69 g, 4.3 mmol) in benzene (7 mL) was added dropwise to a solution of 2 (0.63 g, 2.1 mmol) in benzene (7 mL) at 0 °C. After 20 min of stirring, the volatiles were removed under vacuum. The resulting oil was washed with hexanes (15 mL) to yield 3Br with minor impurities (0.69 g, 76%). Crystals suitable for single-crystal X-ray diffraction analysis were obtained from a diethyl ether solution at −15 °C. 1H NMR (C6D6): δ 0.21 (s, 18 H, SiMe3), 6.00 (pst, 1 H, 5-H), 6.57 (d, 1 H, 3-H), 6.71 6156


Organometallics

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Present Address § GNS Science, 30 Gracefield Road, PO Box 31312, Lower Hutt 5040, New Zealand.

4 H, β-H, C5H4), 6.31 (m, 1 H, 5-H), 6.77 (m, 1 H, 3-H), 6.91 (m, 1 H, 4-H), 7.53 (m, 1 H, 6-H). Poly(ferrocenylgallane) 7n. To 1 (0.40 g, 1.1 mmol) and (LiC5H4)2Fe(thf)3 (0.49 g, 1.2 mmol) was added toluene (7 mL). After the mixture was stirred for 7 h, the precipitate was filtered off. Hexanes (15 mL) were added to the solution, and the obtained precipitate was filtered and washed with hexanes (10 mL). After drying in vacuo a slightly orange powder was obtained (0.12 g, 25%). 1H NMR (CDCl3): δ 0.1 (br, 18 H, SiMe3), 3.5−5.0 (br, 8 H, C5H4), 7.05 (br, 2 H, Ar-H), 7.74 (br, 1 H, Ar-H), 8.22 (br, 1 H, Ar-H). Anal. Calcd for C22H30FeGaNSi2 (490.219): C, 53.90; H, 6.17; N, 2.86. Found: C, 54.18; H, 6.12; N, 2.35. [1-(Pyrid-2-yl)-1-(trimethylsilyl)eth-1-yl-κ 2C,N]alumina[1]ferrocenophane, R′Al(C 5 H 4 ) 2 Fe] (8). A suspension of (LiC5H4)2Fe· 2/3tmeda (0.55 g, 2.0 mmol) in benzene (18 mL) was added to a solution of 3Br (0.72 g, 1.7 mmol) in benzene (12 mL) at 0 °C. After the mixture was stirred at room temperature for 3 h, a 1H NMR spectrum was measured. 1H NMR of 8 (C6D6): δ 0.30 (s, 18 H, SiMe3), 4.10 (m, 2 H, α-H, C5H4), 4.28 (m, 2 H, α-H, C5H4), 4.66 (m, 2 H, β-H, C5H4), 4.68 (m, 2 H, β-H, C5H4), 6.24 (pst, 1 H, 5-H), 6.85 (d, 1 H, 3-H), 6.89 (m, 1 H, 4-H), 7.45 (m, 1 H, 6-H). Crystal Structure Determination. Single crystals of each compound were coated with Paratone-N oil, mounted using a CryoLoop (Hampton Research) or a Micromount (MiTeGenMicrotechnologies for Structural Genomics), and frozen in the cold stream of the Oxford cryojet attached to the diffractometer. Crystal data of 2 and 3Br were collected at −100 °C on a Nonius Kappa CCD diffractometer, using monochromated Mo Kα radiation (λ = 0.710 73 Å). An initial orientation matrix and cell was determined by φ scans, and the X-ray data were measured using φ and ω scans.29 Data reduction was performed with the DENZO-SMN/SCALEPACK software package.30 A multiscan absorption correction was applied (SCALEPACK).30 Crystal data of 6 were collected at −100 °C on a Bruker-AXS Proteum R Smart 6000 three-circle diffractometer using monochromated Cu Kα radiation (λ = 1.541 84 Å). An initial orientation matrix and cell was determined from ω scans, and the Xray data were measured using φ and ω scans.31 Data reduction was performed using SAINT, included in the APEX2 software package.32 A multiscan absorption correction was applied (SADABS).32 Structures were solved by direct methods (SIR-97, 2, 3Br; SIR-2004, 33 6) and refined by full-matrix least-squares methods on F 2 with SHELX-97 or SHELXTL V6.14.34 Unless otherwise stated, the nonhydrogen atoms were refined anisotropically; hydrogen atoms were included at geometrically idealized positions but not refined. The isotropic thermal parameters of the hydrogen atoms were fixed at 1.5 or 1.2 times that of the preceding carbon atom. The final refined absolute structure parameter35 (0.031(12)) for 3Br indicates that the correct absolute structure was chosen. Crystallographic data are summarized in Table 1.

ACKNOWLEDGMENTS

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REFERENCES

We thank the Natural Sciences and Engineering Research Council of Canada (NSERC Discovery Grant, J.M.) for support. We thank the Canada Foundation for Innovation (CFI) and the government of Saskatchewan for funding of the X-ray and NMR facilities in the Saskatchewan Structural Sciences Centre (SSSC). We thank Prof. Ildiko Badea (University of Saskatchewan, College of Pharmacy and Nutrition) for making the DLS instrument available for our studies.

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ASSOCIATED CONTENT S Supporting Information * CIF files giving crystallographic data for 2, 3Br, and 6, DLS data for 7n (Table S1; Figure S1), and NMR spectra of 1, 2, 3Cl, 3Br, 4, and 6−8 (Figures S2−S15). This material is available free of charge via the Internet at http://pubs.acs.org .Crystallographic data for compounds 2, 3Br, and 6 have also been deposited with the Cambridge Crystallographic Data Centre under file numbers CCDC 836327 (2), 836328 (3Br), and 836329 (6). Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax, +44-1223-336033; e-mail, [email protected]; web, http://www.ccdc.cam.ac.uk).

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AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected]. 6157


Organometallics

Article

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