Conventional (-)-sparteine adducts of lithium and sodium 1,1,1,3,3,3-hexamethyldisilazide (HMDS) were prepared and characterised, along with an unexpected and unconventional hydroxyl-incorporated sodium sodiate, [(-)-sparteine·Na(-HMDS)Na·(-)-sparteine]+[Na4(-HMDS)4(OH)]--the complex anion of which is the first inverse crown ether anion

Alan R. Kennedy

Byrne

Charles T. O’Hara

Collum

Driess

Engelhardt

Gehrhus

Gemma M. Robertson

Gessner

Grüning

Henderson

Hoppe

Kennedy

Kizirian

Knizek

Lucht

Luderer

Mulvey

Natalie M. Clark

O’Brien

Pablo García-Álvarez

Power

Strohmann

Veith

English

Clark, N.M.

Garcia-Alvarez, P.

Kennedy, A.R.

O'Hara, C.T.

Robertson, G.M.

University of Strathclyde Institutional Repository

Strathprints Institutional RepositoryClark, N.M. and Garcia-Alvarez, P. and Kennedy, A.R. and O’Hara, C.T. and Robertson, G.M.(2009) Reactions of (-)-sparteine with alkali metal HMDS complexes : conventional meets theunconventional. Chemical Communications (London), 2009 (39). pp. 5835-5837. ISSN 0009-241XStrathprints is designed to allow users to access the research output of the University of Strathclyde.Copyright c© and Moral Rights for the papers on this site are retained by the individual authorsand/or other copyright owners. You may not engage in further distribution of the material for anyprofitmaking activities or any commercial gain. You may freely distribute both the url (http://strathprints.strath.ac.uk/) and the content of this paper for research or study, educational, ornot-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to Strathprints administrator:mailto:strathprints@strath.ac.ukhttp://strathprints.strath.ac.uk/Reactions of ()-sparteine with alkali metal HMDS complexes:conventional meets the unconventionalwNatalie M. Clark, Pablo Garcı´a-A´lvarez, Alan R. Kennedy, Charles T. O’Hara*and Gemma M. RobertsonReceived (in Cambridge, UK) 1st May 2009, Accepted 30th July 2009First published as an Advance Article on the web 6th August 2009DOI: 10.1039/b908722b‘Conventional’ ()-sparteine adducts of lithium and sodium1,1,1,3,3,3-hexamethyldisilazide (HMDS) were prepared andcharacterised, along with an unexpected and ‘unconventional’hydroxyl-incorporated sodium sodiate, [()-sparteineNa-(l-HMDS)Na()-sparteine]+[Na4(l-HMDS)4(OH)]—thecomplex anion of which is the ﬁrst inverse crown ether anion.Alkyl and amido alkali metal reagents, in particular therespective lithium reagents, are amongst the most utilisedcompounds in synthesis. Indeed, 95% of all synthetic trans-formations for the pharmaceutical industry are thought toinvolve a lithium reagent at some stage.1 An all-pervadingchallenge for the synthetic chemist is the generation ofoptically-active compounds in good yield and selectivity. Byincorporating a chiral diamine [such as ()-sparteine] intoalkyllithium systems, high levels of reactivity and stereo-selectivity in deprotonation, oxidation, reduction and additionreactions2–6 can be achieved. Surprisingly, the syntheticchemistry of chiral diamine complexes of alkali metal amideshas been largely neglected,7 despite increased deprotonativeselectivity of an amidolithium versus an alkyllithium towardscertain organic substrates (nucleophilic addition is a commoncompeting reaction for the latter).Turning to solid-state chemistry, the ()-sparteine adduct ofa phosphorus-functionalised alkyllithium was reported in 1989by Raston, White and coworkers.8 Recently, some key widely-utilised ()-sparteine-coordinated organolithiums have beenisolated and characterised by Strohmann et al., including theﬁrst monomeric butyllithium complex [()-sparteinetBuLi].9,10Again rather surprisingly, the solid-state chemistry of()-sparteine adducts of the alkali metal amides have thusfar been neglected. Addressing this deﬁciency, we reporthere the synthesis and characterisation of the ()-sparteineadducts of the synthetically important lithium and sodiumbis(trimethylsilyl)amides (1 and 2, respectively). In addition,we report an intriguing, highly unusual hydroxyl-incorporatedsolvent-separated hexanuclear sodium sodiate complex (3)—aresult which may perhaps shed light on the lack of researchinvolving ()-sparteine complexes of the alkali metalamides.()-Sparteine-coordinated 1 was prepared by reactingn-butyllithium with an equimolar quantity of HMDS(H). Thismixture was left to stir for 30 min, then one molar equivalentof ()-sparteine was added (Scheme 1).z The solution wasplaced in a freezer (28 1C) and X-ray quality crystals of 1, inmoderate-to-good yield (64%) were precipitated. In anattempt to prepare a sodium analogue of 1, n-butylsodiumwas utilised. After stirring the ()-spartiene and metal amidesolution for 30 min, a crop of crystals precipitated atambient temperature within one hour. To our surprise,X-ray crystallographic studies revealed that these crystalswere not a simple ()-sparteine adduct of NaHMDS,but an unusual hydroxyl-incorporated sodium sodiate,[()-sparteineNa(m-HMDS)Na()-sparteine]+[Na4(m-HMDS)4-(OH)] 3, despite the apparent strict use of an inertatmosphere and Schlenk techniques.This synthesis was deemed reproducible by checking the unitcell of several crystals from multiple batches of the crystallinematerial. It was assumed that the hydroxide contaminant arosefrom the reaction of the metal amide mixture with adventitiouswater which was present in the ()-sparteine. When ()-sparteinewas subjected to a vacuum for two hours prior to use—in anattempt to remove volatiles such as entrained H2O—crystals of 3were not forthcoming. Instead a microcrystalline material (2)precipitated from solution at28 1C. Unfortunately, this materialwas not suitable for X-ray crystallographic analysis. However, byScheme 1 Syntheses of 1, 2 and 3.WestCHEM, Department of Pure and Applied Chemistry,University of Strathclyde, Glasgow, UK G1 1XL.E-mail: charlie.ohara@strath.ac.uk; Tel: +44 (0)141 548 2667w Electronic supplementary information (ESI) available: NMR dataand space-ﬁlling diagrams. CCDC 730642 & 730643. For ESI andcrystallographic data in CIF or other electronic format see DOI:10.1039/b908722bThis journal is c The Royal Society of Chemistry 2009 Chem. Commun., 2009, 5835–5837 | 5835COMMUNICATION www.rsc.org/chemcomm | ChemCommDownloaded by University of Strathclyde on 21 September 2012Published on 06 August 2009 on http://pubs.rsc.org | doi:10.1039/B908722BView Online / Journal Homepage / Table of Contents for this issue1H NMR analysis of 2 in D6-benzene solution, it was evident thatthe HMDS:()-spartiene ratio was 1 : 1 (akin to 1); diﬀerent fromthe ratio for crystalline 3 in D6-benzene which was 5 : 2 (see ESIw).Crudely, these reactions show that if one molar equivalent of H2Ois present, then it consumes sixmolar equivalents of NaHMDS toform 3—possibly suggesting why ()-sparteine solvates of alkalimetal amides (in particular NaHMDS) have not yet been utilisedto any signiﬁcant degree in asymmetric synthesis. A lithiumanalogue of 3 could not be detected.X-Ray crystallographic studies reveal that 1 crystallises in thechiral space group P1 and is monomeric in the solid-state (Fig. 1).Key bond parameters are given in the ESI.w Its Li centre isthree-coordinate, adopting a distorted trigonal planar environ-ment (sum of angles around Li, 356.21). As expected thegreatest distortion from perfect trigonal planarity occurs at the()-sparteine-Li bite angle [89.9(2)1]. To the best of ourknowledge, only three monomeric LiHMDS complexes have beenpublished previously. These are a 12-crown-4,11 a PMDETA12(N0,N0,N00,N00,N0 0 0-pentamethyldiethylenetriamine and—perhapsmost pertinent to this paper—a didentate TMEDA(N0,N0,N00,N00-tetramethylethylenediamine) complex.12 TheLi–NHMDS bond distance in 1 [1.910(5) A˚] is almost identical tothat in the TMEDA complex [1.893(3) A˚]. In 1, the ()-sparteinecoordinates to the Li centre symmetrically and the meanLi–N()-sparteine bond is 2.0475 A˚, which is slighly shorter thanthe mean Li–NTEMDA bond (2.0805 A˚) in the TMEDA adduct.The NTMEDA–Li–NTMEDA bite angle in this complex [87.6(1) A˚]is similar to the corresponding angle in 1 despite the much greatersteric demands of the ()-sparteine ligand.12 Collum has meti-culously studied the solution chemistry of LiHMDS in the presenceof more than 100 synthetically-useful and commonly employedligands!13 Focusing on ()-sparteine, his studies have shown that inhydrocarbon solution with a low concentration of the diaminepresent, the chelated monomer exists, with the exclusion ofthe solvated dimer or more highly solvated monomer,13,14 anobservation which is in line with the solid state structure of 1.X-Ray crystallographic studies reveal that 3 crystallises inthe chiral space group C2, and due to its solvent separated ionpair composition, the cationic and anionic moieties of 3 will bediscussed independently. Full crystallographic details aregiven in the ESI.w The cation (Fig. 2) contains two ()-sparteinemolecules which coordinate in the usual terminal fashion totwo sodium atoms. To complete the structure of the cation, aHMDS anion bridges between the two metal centres, resultingin a distorted trigonal planar arrangement around Na1(sum of angles, 354.11). The only previously reported complexwhich incorporates both sodium and ()-sparteine is[()-sparteineNaMg(TMP)2nBu].15 The Na centre adoptsa distorted tetrahedral geometry in this complex, as aconsequence its mean Na–N()-sparteine bond distance(2.4989 A˚) is slightly longer than that in the cation of 3(2.4255 A˚). This decrease in coordination number accompaniesa slight widening of the diamine bite angle [from 72.59(6)1 to74.9(2)1 in 3].The anionic moiety of 3 (Fig. 3) consists of an almostperfectly planar eight-membered Na4N4 ring[N4–N5–N6–N5* torsion angle is 01; Na2–Na3–N3*–Na2*is 1.84(11)1] which acts as a tetranuclear host towards ahydroxyl anion guest. This guest is disordered over two sites inthe centre of the metal-amido ring (one above and one belowthe plane of the Na4N4 ring, vide infra). The mean Na–O bondlength is 2.336 A˚. In addition to the Na–O bonding within thestructure, each Na atom is bonded to two amido-N centres.The mean ‘corner’ Na–N–Na and ‘side’ N–Na–N angles of theocta-atomic ring are 81.06 and 170.961, respectively.The structures of other discrete (Na–N)4 eight-memberedrings have been published by Veith et al.16 These sodiumamides, [{RNSiMe2OSiMe2NR}2Na4] (where R istBu orSiMe3) adopt fundamentally diﬀerent structures from that ofthe anion of 3. Firstly, the rings in Veith’s complexes deviatesigniﬁcantly from planarity, the Na atoms are stabilised byinternal chelation, and of course, these complexes areelectronically neutral. Donor-free NaHMDS has been isolatedin the solid state as polymeric17 and cyclic trimeric18,19polymorphs, possibly indicating that other oligomers ofNaHMDS (perhaps a cyclic tetramer akin to donor-freeNaTMP,20 TMP is 2,2,6,6-tetramethylpiperidide) may existin solution. Despite the incorporation of OH, the meanNa–N bond distance in the anion of 3 (2.398 A˚) is essentiallyFig. 1 Molecular structure of 1. H atoms are omitted for clarity.Fig. 2 Molecular structure of the cation of 3. H atoms are omitted forclarity.Fig. 3 Molecular structure of the anion of 3. H atoms (exceptfor OH) and disorder component have been omitted for clarity.5836 | Chem. Commun., 2009, 5835–5837 This journal is c The Royal Society of Chemistry 2009Downloaded by University of Strathclyde on 21 September 2012Published on 06 August 2009 on http://pubs.rsc.org | doi:10.1039/B908722BView Onlineidentical to that in polymeric17 and cyclic18,19 NaHMDSpolymorphs (2.381 and 2.350 A˚, respectively); the meanN–Na–N andNa–N–Na angles (100.07 and 139.701, respectively)are approximately 201 wider and 301 narrower than theirrespective counterparts in the anion of 3. This anion can bedirectly compared to a cationic crown ether complex. Whereasa neutral crown ether molecule encaptures a metal cation tobecome a cationic species, here the ‘NaHMDS tetramer’encapsulates a hydroxyl ligand forming the anion of 3. Inkeeping with the chemistry and terminology developed byMulvey et al.,21–23 this anion can be considered as the ﬁrstanionic inverse crown ether. It is presumably isolable due tothe immense steric bulk of ()-sparteine which suﬃcientlystabilises the counter-cation of 3 (see ESIw).Due to the large number of chemically distinct aliphaticH and C atoms in ()-sparteine, the 1H and 13C NMR spectrafor 1–3 are extremely complex (see ESIw). The key feature inall three spectra are that the resonances due to the diamineligand are broader and diﬀer slightly from those associatedwith the free diamine; hence, ()-sparteine appears to remainat least partially coordinated to the respective metal centres inarene solution. For 3, only one resonance is observed for theHMDS group, despite there being two chemically distinctligands in the solid-state structure. This may not be toosurprising given the similar local coordination environmentof the diﬀerent HMDS groups (in both the cation and anionHMDS bridges in a m2-fashion to two Na atoms). Lowtemperature NMR studies proved futile in resolving the twodistinct HMDS resonances.To summarise, we have opened a new frontier in alkalimetal HMDS chemistry by incorporating ()-sparteine, and atthe same time identiﬁed a problem that could occur ifnecessary puriﬁcation procedures are not employed. Inaddition, we have prepared the ﬁrst anionic inverse crownstructure, which should pave the way for the development of anew Group 1 macrocyclic/supramolecular chemistry.The authors thank D. V. Graham (X-ray crystallography)and the EPSRC (grant award no. EP/F065833/1) forgenerously sponsoring this research. This research was alsosupported by a Marie Curie Intra European Fellowship withinthe 7th European Community Framework Programme(to PGA).Notes and referencesz All reactions were carried out under a protective argon atmosphere.Synthesis of [()-sparteineLiHMDS] (1): nBuLi (1.25 mL of a 1.6 Msolution in hexanes, 2 mmol) was added to 5 mL of dried hexane in aSchlenk tube. HMDS(H) (0.42 mL, 2 mmol) was added and themixture was allowed to stir for 30 min, after which ()-sparteine(0.46 mL, 2 mmol) was added. The colourless solution was reduced involume by approximately 50% and placed in a freezer which wasoperating at 28 1C. After 48 h, small colourless X-ray quality crystalsof 1 were deposited (0.51 g, 64%). 1H NMR (400.13 MHz, 300 K,C6D5CD3): d 3.16, 2.78, 2.53, 2.33, 2.28, 1.81, 1.71, 1.5, 1.44, 1.32,1.22, 1.03, 0.89, 0.62, 0.35 ppm (SiCH3).13C NMR (100.63 MHz,300 K, C6D5CD3): d 67.6, 61.8, 60.3, 58.3, 54.4, 46.5, 35.8, 35.6, 30.4,29.0, 25.6, 25.2, 24.9, 24.7, 18.6, 7.5 ppm. 7Li NMR (155.47 MHz,300 K, C6D5CD3): d 1.50 ppm.Synthesis of ‘‘[()-sparteineNaHMDS]’’ (2): nBuNa (0.16 g,2 mmol) was suspended in 5 mL of dried hexane in a Schlenk tube.HMDS(H) (0.42 mL, 2 mmol) was added and allowed to stir for30 min, after which ()-sparteine (0.46 mL, 2 mmol), which had beensubjected to vaccum for two hours, and toluene (1 mL) were added.The colourless solution was placed in a freezer (operating at 28 1C).After 24 h, a colourless microcrystalline material (2) deposited[0.22 g, 26% (ﬁrst batch)]. 1H NMR (400.13 MHz, 300 K, C6D6): d2.77, 2.66, 2.47, 2.26, 2.14, 2.08, 1.95, 1.85, 1.62, 1.54, 1.41, 1.37, 1.23,1.10, 1.00, 0.15 ppm (SiCH3).Synthesis of [()-sparteineNa(m-HMDS)Na()-sparteine]+[Na4-(m-HMDS)4(OH)] (3): nBuNa (0.16 g, 2 mmol) was suspended in5 mL of dried hexane in a Schlenk tube. HMDS(H) (0.42 mL, 2 mmol)was added and the mixture was allowed to stir for 30 min, after which‘non-dried’ ()-sparteine (0.46 mL, 2 mmol) and toluene (1 mL) wereadded. After stirring for one hour, crystals of 3 [0.12 g, 25%(ﬁrst batch)] deposited at ambient temperature. 1H NMR (400.13 MHz,300 K, C6D5CD3): d 2.77, 2.66, 2.48, 2.30, 2.13, 2.06, 1.95, 1.86, 1.69,1.53, 1.42, 1.39, 1.25, 1.14, 1.11, 1.01, 0.48 (OH), 0.13 (SiCH3).Crystal data for 1: C21H44LiN3Si2, Mr = 401.71, triclinic, spacegroup P1, a = 7.6371(3), b = 9.1030(3), c = 10.5163(4) A˚, a =111.657(2), b= 106.120(2), g= 97.915(2)1, V= 628.71(4) A˚3, Z= 1,l = 0.71073 A˚, m = 0.151 mm1, T = 123(2) K; 15 393 reﬂections,5224 unique, Rint = 0.050; ﬁnal reﬁnement to convergence on F2 gaveR = 0.0504 (F, 4570 obs. data only) and Rw = 0.1416 (F2, all data),GOF = 1.091. Absolute conﬁguration conﬁrmed by reﬁnement ofFlack parameter to 0.08(12).Crystal data for 3: C60H143N9Na6OSi10,Mr= 1425.67, monoclinic,space group C2, a = 18.2491(4), b = 16.2717(3), c = 14.9831(3) A˚,b = 90.450(2)1, V = 4449.00(16) A˚3, Z = 2, l = 1.54184 A˚, m =1.973 mm1, T = 123(2) K; 13 781 reﬂections, 6757 unique, Rint =0.0212; ﬁnal reﬁnement to convergence on F2 gave R = 0.0435(F, 5176 obs. data only) and Rw = 0.1083 (F2, all data), GOF =0.926. Absolute conﬁguration conﬁrmed by reﬁnement of Flackparameter to 0.03(3). The OH group is modelled as disordered overtwo sites, occupancy 50 : 50.w1 D. B. Collum, Acc. Chem. Res., 1993, 26, 227.2 J.-C. Kizirian, Chem. Rev., 2008, 108, 140.3 P. O’Brien, J. Chem. Soc., Perkin Trans. 1, 1998, 1439.4 D. Hoppe and T. Hense,Angew. Chem., Int. Ed. Engl., 1997, 36, 2282.5 M. R. Luderer, W. F. Bailey, M. R. Luderer, J. D. Fair,R. J. Dancer and M. B. Sommer, Tetrahedron: Asymmetry, 2009,DOI: 10.1016/j.tetasy.2009.1003.1015.6 L. M. Engelhardt, W.-P. Leung, C. L. Raston, G. Salem, P. Twissand A. H. White, J. Chem. Soc., Dalton Trans., 1988, 2403.7 H. Doi, T. Sakai, M. Iguchi, K.-I. Yamada and K. Tomioka,J. Am. Chem. Soc., 2003, 125, 2886.8 L. T. Byrne, L. M. Engelhardt, G. E. Jacobsen, W.-P. Leung,R. I. Papasergio, C. L. Raston, B. W. Skelton, P. Twiss andA. H. White, J. Chem. Soc., Dalton Trans., 1989, 105.9 V. H. Gessner, C. Da¨schlein and C. Strohmann, Chem.–Eur. J.,2009, 15, 3320.10 C. Strohmann and V. H. Gessner, Angew. Chem., Int. Ed., 2007,46, 4566.11 P. P. Power and X. J. Xu, J. Chem. Soc., Chem. Commun., 1984, 358.12 K. W. Henderson, A. E. Dorigo, Q.-L. Liu and P. G. Willard,J. Am. Chem. Soc., 1997, 119, 11855.13 B. L. Lucht and D. B. Collum, Acc. Chem. Res., 1999, 32, 1035.14 B. L. Lucht, M. P. Bernstein, J. F. Remenar and D. B. Collum,J. Am. Chem. Soc., 1996, 118, 10707.15 A. R. Kennedy and C. T. O’Hara, Dalton Trans., 2008, 4975.16 M. Veith, S. Wieczorek, K. Fries and V. Huch, Z. Anorg. Allg.Chem., 2000, 626, 1237.17 R. Gru¨ning and J. L. Atwood, J. Organomet. Chem., 1977, 137, 101.18 M. Driess, H. Pritzkow and M. Skipinski, Organometallics, 1997,16, 5108.19 J. Knizek, I. Krossing, H. No¨th, H. Schwenk and T. Seifert, Chem.Ber., 1997, 130, 1053.20 B. Gehrhus, P. H. Hitchcock, A. R. Kennedy, M. F. Lappert,R. E.Mulvey and P. J. A. Rodger, J. Organomet. Chem., 1999, 587, 88.21 R. E. Mulvey, F. Mongin, M. Uchiyama and Y. Kondo, Angew.Chem., Int. Ed., 2007, 46, 3802.22 R. E. Mulvey, Organometallics, 2006, 25, 1060.23 R. E. Mulvey, Acc. Chem. Res., 2009, 42, 743.This journal is c The Royal Society of Chemistry 2009 Chem. Commun., 2009, 5835–5837 | 5837Downloaded by University of Strathclyde on 21 September 2012Published on 06 August 2009 on http://pubs.rsc.org | doi:10.1039/B908722BView Online

Reactions of (-)-sparteine with alkali metal HMDS complexes : conventional meets the unconventional

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Reactions of (-)-sparteine with alkali metal HMDS complexes : conventional meets the unconventional

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