SiMe 3 N Me 3 Si M N Me 3 Si SiMe 3 SiMe 3 N Me 3 Si M N Me 3 Si SiMe 3 S S P S OMe 2a M = Ge b M = Sn 3a M = Ge b M = Sn 1 O(1) C(1) P S(1) S(2) S(3) Si(1) N(1) Si(2) N(2) Si(4) Si(3) Sn 2 Ar′PS 2 Ar′PS + Ar′PS 3 5 6 4 1 Ar′ = C 6 H 4 OMe-p SiMe 3 N Me 3 Si Sn N Me 3 Si SiMe 3 SiMe 3 N Me 3 Si Sn N Me 3 Si SiMe 3 S [2+2] 2 3b S Sn S N N SiMe 3 SiMe 3 SiMe 3 SiMe 3 7 8 2 Ge N N Bu t Bu t 1 Ge S P P S S P P S OMe OMe MeO MeO 9 10 Germylene and stannylene cleavage of Lawesson’s reagent Claire J. Carmalt, Jason A. C. Clyburne, Alan H. Cowley,* Viviana Lomeli and Brian G. McBurnett Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas, 78712, USA Lawesson’s reagent undergoes cleavage reactions with bis[bis(trimethylsilyl)amino]germanium(II) and bis[bis(tri- methylsilyl)amino]tin(II) whilst with 1,3-di-tert-butyl- 1,3,2-diazagermol-2-ylidene the product is a novel spir- ocyclic germanium derivative. Lawesson’s reagent 1 is one of the most versatile thiation reagents available and is highly effective, for example, for the conversion of aldehydes and ketones to the corresponding thio derivatives. 1 However, much less information is available regarding the interaction of 1 with transition metal 2 or main group reagents. Herein we describe the unusual reactions of 1 with some coordinatively unsaturated group 14 compounds. The reaction of 1 with stannylene 2b 3 in THF solution resulted in a > 90% isolated yield of 4b.† Interestingly, the corresponding reaction of 1 with 2a 3 produced a much smaller yield (ca. 10%) of the Ge analogue 3a. 31 P NMR and HRMS(CI + ) data were consistent with the formulae proposed above for both compounds, and 1 H and 13 C NMR spectra indicated the presence of one p-MeOC 6 H 4 and two (non- equivalent) N(SiMe 3 ) 2 groups.‡ However, in order to ascertain the atom connectivity, it was necessary to appeal to X-ray crystallography. Suitable single crystals of 3b were obtained from CH 2 Cl 2 solution. The central feature of the molecular structure of 3b§ (Fig. 1) comprises a planar PS 2 Sn ring [sum of angles = 360.00(3)°]. Such rings are rare as indicated by a search of the Cambridge Data Base which revealed only one previous example. 4 As expected, the average P–S ring bond distance [2.1125(9) Å] is longer than that of the external P–S bond [1.9315(9) Å]. Although the phosphorus and tin centres are four-coordinate, there is considerable deviation of the bond angles from the ideal tetrahedral value and the N–Sn–N angle in 3b [116.07(7)°] is larger than that in 2b [104.7(2)°]. 5 The mechanism of formation of 3a,b is not clear, but plausible routes to these products include (i) oxidative addition of 2a,b to 4, which results from symmetrical cleavage of 1, followed by addition of sulfur to phosphorus, (ii) addition of 2a,b to an ArAPS 3 (6) fragment resulting from unsymmetrical cleavage of 1, and (iii) addition of sulfur to 2a,b followed by reaction of the resulting germa- or stanna-thione with 4. In an attempt to clarify this point, 7, 6 which can be viewed as a cyclic dimer of the requisite stanna-thione 8, was treated with an equimolar quantity of 1 in CD 2 Cl 2 or C 6 D 6 solution at 25 °C. NMR ( 31 P and 1 H) assay indicated quantitative conversion to 3b. This observation is consistent with route (iii), and as such would represent a novel formal [2 + 2] cycloaddition involving PNS and SnNS bonds. 7 In sharp contrast to the results obtained with 2a, the cyclic germylene 9 8 undergoes a completely different type of reaction with 1 and affords 10 as the major product. Whilst not appropriate as a mechanism, one way of thinking of this reaction is to consider that the cyclic germylene 9 serves as a source of Ge atoms for transfer to four ArAPS (5) moieties. As pointed out above, 5 could arise via unsymmetrical cleavage of 1. The X-ray crystal structure of 10 revealed an interesting spirocyclic geometry (Fig. 2). Individual molecules of 10 reside on a crystallographic twofold axis. The GeS 2 P 2 rings are slightly puckered and the dihedral angle between the S–Ge–S planes is 81.7°. The geometry at Ge is essentially tetrahedral; Fig. 1 Molecular structure of 3b showing the atom numbering scheme. Selected distances (Å) and angles (°): P–C(1) 1.804(2), P–S(1) 1.9315(9), P–S(2) 2.1168(9), P–S(3) 2.1018(9), Sn–S(2) 2.4188(6), Sn–S(3) 2.4358(6), N(1)–Sn 2.015(2), N(2)–Sn 2.023(2), N–Si(1) 1.764(2), N–Si(2) 1.757(2), N(2)–Si(3) 1.757(2), N(2)–Si(4) 1.761(2); C(1)–P–S(1) 112.05(8), S(2)–P–S(3) 101.32(3), P–S(2)–Sn 87.17(3), P–S(3)–Sn 87.06(3), N(1)–Sn–N(2) 116.07(7), Sn–N(1)–Si(1) 122.83(10), Sn– N(1)–Si(2) 115.15(9), Sn–N(2)–Si(3) 116.33(9), Sn–N(2)–Si(4) 120.37(10), Si(1)–N(1)–Si(2) 120.73(10), Si(3)–N(2)–Si(4) 121.35(10). Chem. Commun., 1998 243 Published on 01 January 1998. Downloaded on 29/10/2014 18:35:53. View Article Online / Journal Homepage / Table of Contents for this issue