Synthesis and Molecular Structures of 2-Trimethylsilyl-, 2-Trimethylgermyl-, and 2-Trimethylstannyl-pyridines

Abstract

F ran k R ied m iller, A le x a n d e r Jo c k isc h , H ubert S ch m id b au r* Pyridine, 2-Silyl-pyridine, 2-Germyl-pyridine, 2-Stannyl-pyridine, Molecular Structure 5-M ethyl-2-trimethylsilyl-pyridine (1) has recently been prepared via the "in situ" Grignard reaction of 1-bromo-5-methyl-pyridine with magnesium and trimethylchlorosilane in refluxing tetrahydrofuran (thf) and structurally characterized. 2-Trimethylgermyl-(2) and 2trimethylstannyl-pyridine (3) were now obtained from 2-bromo-pyridine through metallation (with /?-BuLi) and treatment of the intermediates with Me.^GeBr and Me.^SnCl, respectively, in diethylether/ thf at -70°C. The crystal and molecular structure of compound 2 has been determined by low temperature (in situ) single crystal X-ray diffraction methods. There is a significant bending of the Me.^Ge substituent towards the nitrogen heteroatom [Ge-C-N = 114.7(2)°]. This phenomenon is known from previous studies of the silicon analogue 1 to be not due to intramolecular (peripheral) Si/G e-N coordination, but to be rather an intrinsic property of the heteroarene skeleton, as also confirmed by quantum-chemical calculations. Furthermore, there is no evidence for mtermolecular coordination in the crystals. Such inter actions could also be ruled out for the solution state of 2 and 3 through variable temperature multinuclear NMR investigations.

Trihydrogermyl-substituted thiophenes

“…The 1 H and 13 C NMR spectra showed the expected resonance patterns already documented for the analogous silyl compounds. [10][11][12][13] In all three cases 73 Ge resonances were observed as broad signals without discernible 73 Ge-1 H splitting (Table 1). This result is at variance with the findings for related arylgermanes (aryl = phenyl, mesityl, etc.)…”

“…1 H NMR: δ 4.20 (s, 3 H, GeH 3 ), 6.86 (dd, 3 J HH = 5/3.5, 1 H, H 4 ), 7.01 (d, 3 J HH = 3.5, 1 H, H 3 ) and 7.14 (d, 3 J HH = 5 Hz, 1 H, H 5 ). 13 C NMR: δ 126.2 (dqd, 2 J CH = 10, 2 J CGeH = 7.5, 3 J CH = 5, C 2 ipso), 128.4 (ddd, 1 J CH = 167, 2 J CH = 10, 6 Hz, C 4 ), 131.4 (ddd, 1 J CH = 184, 2 J CH = 10, 3 J CH = 5, C 5 ) and 136.7 (ddq, 1 J CH = 167, 2 J CH = 6, 3 J CGeH = 3 Hz, C 3 ). 73 Ge NMR: δ Ϫ214.0 (br s, GeH 3 ).…”

“…1 H NMR: δ 4.24 (s, 6 H, GeH 3 ) and 7.07 (s, 2 H, H 3,4 ). 13 C NMR: δ 133.1 (dqd, 2 J CH = 10, 2 J CGeH = 7.5, 3 J CH = 5 Hz, C 2,5 ) and 138.0 (ddq, 1 J CH = 167, 2 J CH = 6, 3 J CGeH = 3 Hz, C 3,4 ). 73 Ge NMR: δ Ϫ208.0 (br s, GeH 3 ).…”

“…This work follows our earlier investigations of silylated thiophenes with simple H 3 Si substituents. 10 Silylated and germylated arenes 10, 11 and pyridines 12, 13 were also the subject of preceding experimental and structural work, which opened up new preparative routes and provided basic information about structure and bonding in aryl-and heteroarylsilanes and -germanes. Arylgermanes are important precursors for reductive coupling to give extended germane structures.…”

“…Recent crystal structure studies and quantum chemical calculations have shown, however, that there are no significant intra-or inter-molecular interactions of this kind. [10][11][12][13] The molecular geometries are governed mainly by the intrinsic electronic configuration of the heterocycles. The effects are common to all substituted species (including e.g.…”