Vom Lithium-Derivat des Aminodi-tert-butylfluorsilans zu Cyclodi-, -tri- und -tetrasilazanen

Synthesis of heteroatomic bridged paracyclophanes

Heteroatomic bridged paracyclophanes were obtained by two independent synthetic approaches. The required precursors consist of para R₂SiCl (R = Me, iPr) substituted aromatic rings (2 and 4). They were subsequently functionalised by using NH₃, [LiPH₂(dme)] or LiAl(PH₂)₄. In the case of the Me-substituted species 2, the reaction with NH₃ directly yielded the Si₂N bridged paracyclophane 5. The Si₂P incorporated derivative 10 was obtained by lithiation of p-C₆H₄(SiiPr₂PH₂)₂ (9) and subsequent salt metathesis with the chlorosilane 4. The second approach involves the use of GaEt₃ in the formation of four membered (GaPn)₂ cycles (Pn = N, P). p-[C₆H₄{SiiPr₂N(H)GaEt₂}₂]₂ (11) and p-[C₆H₄{SiiPr₂P(H)GaEt₂}₂]₂ (12) represent the first examples of stable (GaPn)₂cis isomers as the trans species did not appear in solution. Although 11 and 12 show a similar coordination pattern, they differ in the orientation of the aromatic systems: in the solid structure, 11 adopts a - for paracyclophanes so far unique - T-shape conformation of the phenyl rings, while 12 shows the predominant coplanar orientation. All cyclophanes were characterized by X-ray diffraction, elemental analysis, NMR and IR spectroscopy.

Polymorphism in Lithium Amides: A Structural and Theoretical Study. Synthesis, Mechanism, and NMR Studies of the Lithiation of N,N'-Di-tert-butylethylenediamine

The lithiation of N,N'-di-tert-butylethylenediamine by MeLi in benzene has been shown by (1)H NMR spectroscopy to proceed via the partially lithiated species [cis-{Li[&mgr;-N(t-Bu)CH(2)CH(2)N(H)t-Bu]}(2)], 2, and [{Li[N(t-Bu)CH(2)CH(2)N(H)t-Bu]}(2)Li{N(t-Bu)CH(2)CH(2)Nt-Bu}Li], 3, prior to the formation of the dilithiated species {Li[N(t-Bu)CH(2)CH(2)Nt-Bu]Li}, 4. The solid state structures of 2, 3, and a dimeric form of 4 (4a) have been determined. A sparingly soluble form of 4 (4b) has also been isolated which has a proposed polymeric ladder structure. These structures are discussed with respect to the alternatives available for the aggregation of the dilithiated species; stacking to form dimeric Li(4)N(4) cages and laddering to form Li(n)()N(n)() ladders. Ab initio molecular orbital calculations give insight into the energetics of these aggregates and the possible structures adopted by solvated and unsolvated dilithium ethylenediamide complexes. Crystals of 2 are monoclinic, of space group C2/c (No. 15), a = 19.222(7), b = 8.734(2), c = 17.149(5) Å, beta = 119.40(1) degrees, Z = 4. Crystals of 3are monoclinic, of space group P2(1)/c (No. 14), a = 9.836(8), b = 17.821(3), c = 21.78(2) Å, beta = 101.57(4) degrees, Z = 4. Crystals of 4a are monoclinic, of space group P2(1)/c (No. 14), a = 15.990(7), b = 10.0162(9), c = 16.42(1) Å, beta = 104.49(2) degrees, Z = 4. Crystals of 6 are monoclinic, of space group P2(1)/c (No. 14), a = 10.124(8), b = 17.861(3), c = 22.21(2) Å, beta = 102.05(4) degrees, Z = 4.