DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 1043–1044 1043 A leaving group strategy for the selective functionalisation of an imido Sn(II) cubane Belén Galán, Marta E. G. Mosquera,* Julie S. Palmer, Paul R. Raithby and Dominic S. Wright * Chemistry Department, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW. E-mail: dsw1000@cus.cam.ac.uk Received 23rd February 1999, Accepted 24th February 1999 Controlled hydrolysis of the cubane [SnNtBu]4 with H2O in thf–MeCN provides a direct route to the oxo complex [Sn4(NtBu)3O], reaction of which with naphNHLi (naph 5 1-naphthyl) gives the heteroleptic cubane [Sn4- (NtBu)3(Nnaph)] as the sole product.In original studies by Veith,1 imido Sn(II) cubanes of the type [SnNR]4 1 were found to be readily accessible from the reaction of [{Me2SiNtBu}2Sn] with primary amines.2 These species prove to be valuable precursors for the preparation of heterometallic complexes containing Sn(II) imido and phosphinidene anions, such as [Li?thf ]4[{Sn(m-PCy)}2(m-PCy)]2 in which the four Li1 cations are coordinated by a metallacyclic [{Sn- (m-PCy)}2(m-PCy)]2 42 unit.3 However, although it has been found that the intact oxo cubane [Sn4(NtBu)3O] 2 can function as an ether-like donor ligand in the adduct [{Sn4(NtBu)3O}? AlMe3],4 nothing has so far been reported concerning the reactivity or synthetic utility of the cubane itself.A current interest of ours has involved uncovering new synthetic strategies which will allow the selective synthesis of a range of main group complexes.5 In contrast to the previous report that the oxo cubane [Sn4(NtBu)3O] 2 cannot be obtained from the hydrolysis of [SnNtBu]4 1a with H2O,5a we have now found that 2 is readily prepared in high yield from this reaction if MeCN–thf is employed as the solvent (rather than solely thf as used in the previous study).This discovery facilitates a leaving group strategy by which imido cubanes 1 can be converted regioselectively into monosubstituted, heteroleptic cubanes [Sn4(NR)3(NR9)], as exemplified by the formation of [Sn4- (NtBu)3(Nnaph)] 3 (naph = 1-naphthyl) from the controlled hydrolysis of [SnNtBu]4 with H2O followed by the substitution of the oxo group of 2 with naphNHLi.† The latter reaction relies on the greater polarity of the Sn–O bonds compared to the Sn–N bonds in 2 and is driven thermodynamically by the formation of LiOH (Scheme 1).It is noteworthy that 3 cannot be obtained from the reaction of the cubane 1 with naphNHLi under similar conditions and that the reaction of 1 with excess naphNHLi results in [Li(thf )4]1[(tBuN)Sn3(Nnaph)3Li?thf ]2 only after reflux.3 As far as we are aware, although hydrolytic substitution reactions of organo–oxo compounds of Sn(IV) with amines and alcohols have been employed in the preparation of amide and alkoxide complexes,6 the reaction of a metallated primary amine or similar species (with the elimination of LiOH) is a novel one.The low-temperature crystal structure of 3‡ shows it to consist of discrete cubane units, [Sn4(NtBu)3(Nnaph)] (Fig. 1). Despite the incorporation of one diVerent imido substituent into the cubane framework, only minor distortions in the Sn4N4 core have been introduced. The internal angles at the Sn (mean 81.18) and N (mean 98.38) centres are similar to those observed previously in [SnNtBu]4 1d and other homoleptic cubanes.2 However, although the majority of the Sn–N bonds of the core fall in a similar range to those present in [SnNtBu]4,1d the bonds to the aryl–imido group are on the whole longer [Sn(2,3,4)– N(4) 2.218(4)–2.224(4) Å; cf. 2.181(4)–2.203(4) Å for the other Sn–N bonds]. This pattern can be seen as arising from the greater electron acceptor ability of the naph group compared to the tBu groups, allowing some degree of dispersion of the negative charge on the naphN imido centre into the aromatic Fig. 1 ORTEP10 drawing of the structure of 2. Thermal ellipsoids are at the 40% probability level. Selected bond lengths (Å) and angles (8): Sn(1)–N(1) 2.197(4), Sn(1)–N(2) 2.203(4), Sn(1)–N(3) 2.199(4), Sn(2)– N(1) 2.185(4), Sn(2)–N(2) 2.187(4), Sn(2)–N(4) 2.224(4), Sn(3)–N(2) 2.199(4), Sn(3)–N(3) 2.181(4), Sn(3)–N(4) 2.218(4), Sn(4)–N(1) 2.194(4), Sn(4)–N(3) 2.191(4), Sn(4)–N(4) 2.219(4), C(4)–N(4) 1.415(7); range N–Sn–N 80.7(1)–81.7(2) (mean 81.1), range Sn–N–Sn 97.6(2)– 99.7(2) (mean 98.3).Scheme 1 (i) H2O (1 equivalent), MeCN–thf, 278 8C, 2tBuNH2; (ii) naphNHLi, thf, 2LiOH.1044 J. Chem. Soc., Dalton Trans., 1999, 1043–1044 substituent and resulting in correspondingly weaker Sn–N bonds. The synthetic strategy outlined above furnishes a potential route to a range of compounds of the type [Sn4(NR)3X] (e.g., X = NH, PH, S) not previously accessible, using the corresponding cubane precursors [SnNR]4 which are readily prepared. Complex 3 is the first example of a heteroleptic imido Sn(II) cubane to be prepared and structurally characterised. The synthetic methodology involved (a leaving group strategy which is related to that commonly employed in organic synthesis) provides a rare if not unprecedented example of the selective structural modification of an oligomeric main group cage.Acknowledgements We gratefully acknowledge the EPSRC (J. S. P., P. R. R., D. S. W.) and the EU (fellowship for M. E. G. M.) and the Spanish Government (B.G.) for financial support. Notes and references † Synthesis of 2. [SnNtBu]4 1a (1.25 mmol) was prepared by the in situ reaction of tBuNH2 (0.53 ml, 5.0 mmol) with [Sn(NMe2)2] 7 (1.03 g, 5 mmol) in thf (20 ml). To this solution at 278 8C was added dropwise a solution of H2O (0.02 ml, 1.1 mmol) in MeCN (10 ml, distilled over CaH2). After full addition the mixture was allowed to warm slowly to room temperature and stirred (2 h) before filtration to remove a white precipitate.The solvent was removed under vacuum to obtain 2 as a lemon yellow powder. Yields of up to 0.78 g (89%) were obtained using this method. 1H NMR (250 MHz, d6-benzene, 125 8C): d 1.34 (Me of tBu) (Found: C, 20.2; H, 3.9; N, 5.8. Calc. for [Sn4ON3C12H27]: C, 20.5; H, 3.8; N, 6.0%). Synthesis of 3. A solution of naphNHLi (0.71 mmol) was prepared by the addition of nBuLi (0.47 ml, 1.5 mol dm23 solution in hexanes) to a solution of naphNH2 (0.102 g, 0.71 mmol) in toluene (5 ml)–thf (5 ml).The solution was added to a solution of 2 (0.59 g, 0.71 mmol). After stirring at room temperature (30 min) the solution was filtered. The solvent was removed under vacuum and was replaced by thf (3 ml) and Et2O (4 ml). Storage at 215 8C (4 d) gave brown crystals of 3. Yield 0.21 (36%). 1H NMR (250 MHz, d8-toluene, 125 8C): d 8.23 [d, 1H, J = 8.2, C(2)–H], 7.72 [dd, 1H, J = 9.3, 1.5 Hz, C(9)–H], 7.32 [m, 5H, C(3,4,6,7,8)–H], 1.48 (s, 27H, tBu) (Found: C, 32.2; H, 4.2; N, 6.8.Calc. for [Sn4N4C22H34]: C, 31.8; H, 4.1; N, 5.8%). ‡ Crystal data for 3: C22H34N4Sn4, M = 829.29, monoclinic, space group P1� (no. 2), a = 8.670(5), b = 9.703(5), c = 16.815(9) Å, a = 75.71(3), b = 81.36(4), g = 81.72(4)8, U = 1347(1) Å3, Z = 2, rcalc. = 2.045 Mg m23, l = 0.71073 Å, T = 180(2) K, m(Mo-Ka) = 3.682 mm21, F(000) = 788. Data were collected on a Stoe AED diVractometer using an oil-coated rapidly-cooled crystal 8 of dimensions 0.40 × 0.28 × 0.16 mm by the w– q method (3.56 £ q £ 22.508).Of a total of 5293 collected reflections, 3505 were independent (Rint = 0.032). The structure was solved by direct methods and refined by full-matrix least-squares on F2 to final, values of R1[F > 4s(F)] = 0.023 and wR2 = 0.057 (all data); 9 largest peak and hole in the final diVerence map 0.715 and 20.665 e Å23. CCDC reference number 186/1362. See http://www.rsc.org/suppdata/dt/1999/1043/ for crystallographic files in .cif format. 1 (a) M. Veith, M.-L. Sommer and D. Jäger, Chem. Ber., 1979, 112, 2581; (b) M. Veith and G. Schlemmer, Chem. Ber., 1982, 115, 2141; (c) M. Veith d M. Grosser, Z. Naturforsch., Teil B, 1982, 37, 1375; (d ) M. Veith and O. Recktenwald, Z. Naturforsch., Teil B, 1983, 38, 1054. 2 For other synthetic methods see: H. Chen, R. A. Bartlett, H. V. R. Dias, M. M. Olmstead and P. P. Power, Inorg. Chem., 1991, 30, 3390; R. E. Allan, M. A. Beswick, A. J. Edwards, M. A. Paver, P. R. Raithby, M.-A. Rennie and D. S. Wright, J. Chem. Soc., Dalton Trans., 1995, 1991. 3 R. E. Allan, M. A. Beswick, N. L. Cromhout, M. A. Paver, P. R. Raithby, A. Steiner, M. Trevithick and D. S. Wright, Chem. Commun., 1996, 1501. 4 M. Veith and H. Lange, Angew. Chem., Int. Ed. Engl., 1980, 19, 401; M. Veith and W. Frank, Angew. Chem., Int. Ed. Engl., 1985, 24, 223. 5 (a) M. A. Beswick, M. E. G. Mosquera and D. S. Wright, J. Chem. Soc., Dalton Trans., 1998, 2437; (b) M. A. Beswick and D. S. Wright, Coord. Chem. Rev., 1998, 176, 1373. 6 A. G. Davies, Comprehensive Organometallic Chemistry II, eds. E. W. Abell, F. G. A. Stone and G. Wilkinson, Pergamon, Oxford, 1995, vol. 2, ch. 6, p. 217. 7 M. M. Olmstead and P. P. Power, Inorg. Chem., 1984, 23, 413. 8 D. Stalke and T. Kottke, J. Appl. Crystallogr., 1993, 25, 615. 9 G. M. Sheldrick, SHELXL 93, a package for crystal structure refinement, University of Göttingen, 1993. 10 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. Communication 9/01478K