Synthesis and Structure of an Azatrisilacyclobutane and Its Precursor, a Novel Lithium Enamide Having a Tricyclic (LiNSiO)2 Skeleton

Abstract

We report results that have a bearing on two diverse but related and currently topical areas of organometallic chemistry. The first concerns insertion of an a-hydrogen-free nitrile into an LiÀC bond, and specifically of 1-adamantyl cyanide (AdCN) into the chiral bis(silyl)methyl compound Li-[CH(SiMe 2 OMe)(SiMe 3 )] [1] to yield the lithium enamide 1. The second deals with the insertion of the thermally stable bis(amino)silylene Si[(NCH 2 tBu) 2 C 6 H 4 -1,2] (Si(NN)) 2 [2] into an LiÀN bond, and particularly of Si(NN) into 1 to afford the azatrisilacyclobutane 3, in which a transient insertion product 4 is a plausible intermediate.The reactions and conditions leading to the new colorless crystalline compounds 1 and 3 are summarized in Scheme 1. Scheme 1. Synthesis of 3 via 1.The yields (1, 64%; 3, 50 %) of X-ray quality crystalline materials were not optimized. Each of 1 and 3 revealed the parent molecular ion in the EI mass spectra and gave satisfactory microanalyses and multinuclear NMR spectra.The crystalline lithium enamide 1 is a centrosymmetric dimer (Figure 1). [3] It has a rhomboidal, planar (LiN) 2 core (the endocyclic angles at the Li atoms are wider than those at the N [5] M. [7] Representative data. 1: Yield: 51 %; m.p. > 300 8C; UV/Vis (CHCl 3 ): l max (e  10 À4 ) 573 (8.96), 555(sh), 532 (2.59), 309 (4.04), 275 (3.03) nm; FAB-MS (m-nitrobenzyl alcohol): calcd for C 24 BClF 12 N 6 : m/z: 646 [M ]. cis Isomer 2: Yield: < 1 %; m.p. > 320 8C; 1 H NMR (300 MHz, CDCl 3 ): d 10.47 ppm (s, 2 H, arom); IR (KBr): n Ä

Bis{μ-N-[(N,N-dimethylamino)dimethylsilyl]-2,6-dimethylanilido}lithium(I)

“…The molecule of (III) possesses a tricyclic ladder core. Such a feature has been observed in only a few examples, such as [LiN(SiMe 2 OMe){C(Ad) C(H)SiMe 3 }] 2 (Ad is adamantyl) and octanuclear [(hmqLi) 8 (THF) 4 ] (hmq À is the 2-hydroxy-4methylquinoline monoanion) (Antolini et al, 2002;Liddle & Clegg, 2002).…”

Recent developments in the chemistry of stable silylenes

“…This was assumed to form via LiOMe extrusion from the expected insertion product 37b to give an azadisilacyclopropane 37a, into which a further molecule of 3 inserts to form the observed product (Scheme 23) [51].…”

Crystalline Na–Si(NN) derivatives [Si(NN)= Si{(NCH2tBu)2C6H4-1,2}]: the silylenoid [Si(NN)OMe]–, the dianion [(NN)Si–Si(NN)]2–, and the radical anion c-[Si(NN)]3–

“…11 A precedent for an alkali metal methoxide extrusion reaction is found in the reaction between the lithium enamide 7 and the silylene 1 to give the ring compound 8 (Ad 5 1-adamantyl). 13 In contrast to the formation (ii in Scheme 1) of the dimeric cycloadduct 2b from NaOMe and 1 in THF, the silylene 1 and Na[N(SiMe 3 ) 2 ] gave the monomeric sodium amide Na[N(SiMe 3 ){Si(NN)SiMe 3 }(THF) 3 ]. 14 The structure of the centrosymmetric dimeric crystalline compound 2b 15 is shown in Fig.…”

“…2 ORTEP representation of 3. Selected bond lengths [A ˚] and angles [u]: Na-Si 2.964(2), Na-M(1)9 2.688(4), Si-Si9 2.480(2), Si-N(1) 1.843(3), Si-N(2) 1.834(3); N(1)-Si-N(2) 84.73(13), N(2)-Si-Si9 99.54(11), N(1)-Si-Si9 99.07(10), Si9-Si-Na 100.12(6).…”