Unexpected Halide Transfer: Aluminium and the Lanthanoids

Unexpected Halide remove Aluminium and the LanthanoidsUnexpected Halide Transfer Complex Reorganisation Between Aluminium and the Lanthanoids.Glen B. Deacon, David J. Evans and Peter C. Junk.*This submission was created exploitation the RSC Communication Template (DO NOT DELETE THIS TEXT)(LINE INCLUDED FOR SPACING only DO NOT DELETE THIS TEXT)Pr(MeCN)9AlCl43.MeCN undergoes reorganisation upon the addition of an ether. In the look of recrystallisation from tetrahydrofuran, the ionic nature is lost, whereas the addition of wind ether gives reorganisation, whilst maintaining ionic character. isolation of ho seawalleptic ionic trivalent lanthanoid knottyes, under non aqueous conditions, has been investigated using northward based ligand systems 1-5. The interest surrounding these homoleptic complexes is attributed to their potential catalytic properties 3,5. Under non aqueous conditions, the use of highly labile ligands, much(prenominal) as solvent molecules, presents the curta in raising of exposing the coat centre, hence providing a site for catalysis and thus stinkpot be considered to be uprise nude 3. Complexes involving Ln3+ ions, that cig bet be considered near naked have to date been restricted to complexes such as Ln(MeCN)n3+ , with anions such as AsF6 and AlCl4 3-5.With this in mind, we have investigated the ability to access homoleptic near naked Ln3+ complexes with tetrahydrofuran (thf) ligands. Currently, no such complexes have been account for the smaller trivalent species contrary the larger divalent species, for which there is precedent viz. Sm(thf)7BPh42 6. Exploitation of the coordination abilities of invest ether has been investigated with the isolation of ScCl2(18-crown-6)FeCl4. Via Sc n.m.r it has been shown that ScCl(thf)(18-crown-6)FeCl42 and indeed subsequently Sc(thf)2(18-crown-6)FeCl43 can be synthesised even though it has not been structurally characterised. With this in mind it should whence be possible to isolate int erchangeable adducts in MeCN.Results and DiscussionHomoleptic acetonitrile Ln3+ complexes can be obtained via two pathways viz equations 1 and 2 3. It was our intention to extend this chemical science to involve homoleptic Ln3+ complexes with ether ligands in place of MeCN. In reactions analogous to equations 1 and 2 with thf in place of MeCN, we found to our surprise LnCl3(thf)2n (Ln = Pr, Nd) was the sole Ln complex isolatable. This suggests that the complex is formed by a concerted process whereby AlCl4 binds to Ln3+ let go of AlCl3, allowing binding of another AlCl4 and so on until complete halide transfer to Ln3+ occurs surrender LnCl3(thf)n (equations 3, 4). Similarly, addition of 18-crown-6 to Pr(MeCN)9AlCl43 resulted in reorganisation to (PrCl(Cl)(18-crown-6))2AlCl42.2(MeCN) (1) .Isolation of 1 illustrates there is an symmetry in solution involving Pr(MeCN)9AlCl43.(MeCN). conduction measurements show a 13 electrolyte 7.This is in contrast to that previously reported fo r the Sm complex by Hu and supported by Bnzli for which a 12 is electrolyte is reported 4,8. We believe that the complex Ln(MeCN)9AlCl43.(MeCN) undergoes rearrangement in solution ranging from a 13 down to a 12 electrolyte (equation 5).This change in coordination purlieu of the lanthanoid metal establishes the pathway to halide transfer involving a transient species tie in to that shown in Figure 1. Structural motifs similar to this have been observed for several(prenominal) lanthanoid complexes including Sm(6-C6Me6)(AlCl4)3 .toluene 9,10. The reaction is completed by the substitution of MeCN by the crown ether and cleavage of the bridging AlCl bonds in a similar fashion to that observed for reactions involving thf.Complex 1 has a nine array Pr centre that is bound to all six oxygens of the crown ether. The Pr is also bound to one terminal and a bridging chloride, and dimerises through an anastrophe centre. There is a distinct change in bond lengths in the midst of the terminal (Pr-Clter 2.715(2)) and bridging chlorides (Pr-Clbr 2.839(2) and 2.858(2)) as would be expected with similar changes identified in PrCl(-Cl)(tetraethyleneglycol)2 11. The distances for Pr-Ocrown range from 2.572(4) 2.590(7), following the same trends in the related cation (DyCl(Cl)(dibenzo18-crown-6))2(DyCl3(Cl)(MeCN))2 12, albeit with a increase of Ln-O in line with increased ionic radius between Dy and Pr.The crown ethers adopt a saddle type morphology with the metal residing in almost the centre of the cavity made by the O1, O3, O4, O6 (0.601) insipid and the O2, O5 (0.491) tabloid. The crown ether collapses to accommodate the smaller size of the Pr3+ which is evident in the planes derived by the oxygen atoms of the crown. The angle between plane 1 (O1, O2, O5, O6) and plane 2 (O2, O3, O4, O5) is 125.71o showing this slight closure to ensure that the oxygen atoms are all bound. This closure of the crown ether is observed for all the Ln3+ 18-crown-6 complexes in which the ang le closes from 129.74o in complex LaCl3(18-crown-6) 13 through to 68.95o in Lu(CH2(SiCH3))2(18-crown-6)(CH2(SiCH3))B(C6H5)3.C2H4Cl2 14 owing to the reduction in size of the ionic radius of the Ln centre.Notes and references every(prenominal) reactions were carried out under dry nitrogen using dry loge and standard Schlenk techniques. Solvents were dried by distillation from sodium wire/benzophenone (thf) or CaH/P2O5 (MeCN). IR and far IR entropy were obtained as described previously 15. Metal analyses were carried out by complexiometric EDTA titration with the addition of 5% sulphosalicylic acid to masquerade Al 16. Anhydrous AlCl3, LnCl3, and 18-crown-6 were supplied by Sigma Aldrich. AlCl3 was freshly sublimed previous to use. Conductivity measurements were carried out on a Crison Conductimeter 522 (serial no 3807), using a locally manufactured air-sensitive cadre. The complex Pr(MeCN)9 AlCl43 was made using previous published methods 3 and conductivity measurements were car ried out as mentioned above (367.97 S cm2 mol-1 1.097 x 10-3 mol dm-3, MeCN).1 Method A Pr(MeCN)9AlCl43. MeCN (0.20g, 0.19 mmol) and 18-crown-6 (0.20g, 0.57 mmol), was dissolved in MeCN (30 ml). The solution was touched and heat up to near boiling to assist dissolution. The resulting commons solution was then filtered and minify in-vacuo. The solution was then cooled at -30oC yielding small super C crystals. (0.21 g (81%)). m.p. 170oC(dec), C28H54Al2Cl12N2O12Pr2 calcd. Pr 10.27 found Pr 10.68%. I.r absorption (Nujol) cm-1. Unit cell collection confirms the same product as via method A.Method B A mixture of PrCl3 (0.10 g, 0.40 mmol), AlCl3 (0.16 g, 1.20 mmol) and 18-crown-6 (0.29g, 0.83 mmol), was dissolved in MeCN (30 ml). The solution was stirred and heated to near boiling to assist dissolution. The resulting green solution was then filtered and reduced in-vacuo. The solution was then cooled at -30oC yielding small green crystals. (0.44 g (87%)). m.p. 170oC(dec), C28H54Al2Cl12 N2O12Pr2 calcd. Pr 10.27 found Pr 10.42% I.r absorption (Nujol) 2291w, 2253s, 1644w, 1353s, 1291s, 1248s, 1082s, 1034s, 966s, 925w, 878w, 837s, 802w cm-1. 27Al nmr 104 ppm(AlCl4)X-ray data for complex 1 was collected on a Nonius Kappa CCD, MoK radiation, = 0.71073 , T = 123(2)K. The twist was solved and refined using the political programs SHELXS-97 17 and SHELXL-97 18 respectively. The program X-Seed 19 was used as an interface to the SHELX programs, and to prepare the figures. 1 (Pr(Cl2)(C12H24O6))2AlCl42.2(C2H3N) C28H54Al2Cl12N2O12Pr2, M = 1371.91, green prismatic, 0.40 0.40 0.30 mm, monoclinic, space group P21/n (No. 14), a = 12.377(3), b = 15.356(3), c = 14.387(3) , = 107.97(3), V = 2601.0(9) 3, Z = 2, Dc = 1.752 g/cm3, F000 = 1360, Nonius Kappa CCD, MoK radiation, = 0.71073 , T = 123(2)K, 2max = 56.6, 20600 reflections collected, 6215 queer (Rint = 0.0864). Final GooF = 1.022, R1 = 0.0478, wR2 = 0.1052, R indices based on 4182 reflections with I 2sigma(I) (refinement on F 2), 263 parameters, 0 restraints. Lp and absorption corrections applied, = 2.551 mm-1.Fig. 2 The structure of the cation PrCl(-Cl)(18C6)22+. Hydrogen atoms omitted for clarity. thermic ellipsoids shown at 35%. Coordination environment of the atom Pr(1) with applicable bond lengths () and angles(o). proportionateness transformations used to generate equivalent atoms -x+1,-y+1,-z+1. Pr(1) O(1), O(2), O(3), O(4), O(5), O(6), Cl(1), Cl(2), Cl(2), 2.572(4), 2.579(4), 2.574(3), 2.590(4), 2.588(4), 2.587(6), 2.715(2), 2.839(2), 2.858(2). Cl(1)-Pr(1)-Cl(2), Cl(2), 144.30(4), 143.18(4), Cl(2) Pr Cl(2),72.52(4).Fig.1 Proposed cation structure observed prior to ether coordination and subsequent cleavage of Al Cl bonds.1Evans, W. J. Rabe, G. W. Ziller, J. W. Inorg. Chem 1994, 33, 3072-3078.2Willey, G. R. Aris, D. R. Errington, W. Inorg. Chim. Acta 2001, 318, 97-102.3Deacon, G. B. 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