Synthesis of lithium N-pentafluorophenyl, N'-trimethylsilyl 2-pyridylamidinate and its cyclization to lithium tetrafluoro-2-(2-pyridyl)benzimidazolate via a Me3SiF elimination. Coordination chemistry, reactivity, and mechanism.
When N-trimethylsilylpentafluoro aniline reacts with BuLi in the presence of THF or TMEDA, the corresponding THF (2) or TMEDA (4) lithium anilides are obtained. Complex 4 is monomeric in the solid state, with a distorted trigonal pyramidal coordination geometry at the lithium center. The strong C-F-->Li interaction in this complex is also accompanied by the elongation of the C-F bond. Mild heating of complex 4 with 2-cyanopyridine results in rapid evolution of Me(3)SiF to quantitatively yield the tetrafluoro-2-(2-pyridyl)benzimidazolate lithium complex (6). From the reaction mixture of complex 4 the asymmetric N-trimethylsilyl, N'-pentafluorophenyl-2-pyridylamidinate lithium complex (5) was isolated as a dormant intermediate. Complex 5 possesses several unusual bonding features with the most notably being a very short Si-N bond length and a rare kappa(1)-Z-syn amidinate bonding mode. A mechanism that includes silicon assisted C-F bond activation is proposed for the cyclization reaction based on the structural parameters of complexes 5 and 6, and on (1)H, (19)F, and (13)C NMR studies.
Aharonovich
Sinai
S
Schulich Faculty of Chemistry and Institute of Catalysis Science and Technology, Kyriat Hatechnion, Haifa, 32000, Israel.
Botoshanski
Mark
M
Eisen
Moris S
MS