Issue 36, 2018

1,4-Dihydropyridyl complexes of magnesium: synthesis by pyridine insertion into the magnesium–silicon bond of triphenylsilyls and catalytic pyridine hydrofunctionalization

Abstract

Magnesium bis(triphenylsilyl) [Mg(SiPh3)2(THF)2]·THF (1) reacted with a stoichiometric amount of pyridine to give the magnesium 4-(triphenylsilyl)dihydropyridyl complex [Mg(NC5H5-4-SiPh3)2(THF)3] (2). Using an excess of pyridine, a mixture of magnesium dihydropyridyl [Mg(NC5H6)2(py)4] (3) and 4-(triphenylsilyl)pyridine was formed. Complex 3 underwent exchange with pyridine-d5 at 25 °C to give [Mg(NC5D5H-4)2(py-d5)4] (3-HD). Analogous reactions with Me3TACD-supported magnesium triphenylsilyls [(Me3TACD)Mg(SiPh3)] (4) and [(Me3TACD·AlEt3)Mg(SiPh3)] (6) ((Me3TACD)H = Me3[12]aneN4: 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane) with pyridine gave [(Me3TACD)Mg(NC5H5-4-SiPh3)] (5), [(Me3TACD·AlEt3)Mg(NC5H5-4-SiPh3)] (7) and a mixture of [(Me3TACD)Mg(NC5H6)] (8) and 4-(triphenylsilyl)pyridine. Complex 8 is also formed by reacting 3 with (Me3TACD)H and underwent exchange with pyridine-d5 at higher temperatures. The activation energy for the exchange is about 25 kJ mol−1 higher than that for the exchange reaction of 3 to 3-HD. Complexes 2, 3, 3-HD, 5, 7 and 8 were characterized by NMR spectroscopy and 3, 5 and 8 by single crystal structure analysis. Complex 3 was found to be slightly active in the hydrosilylation of pyridine using phenylsilane, whereas complex 8 showed no activity. Both complexes 3 and 8 were active in the hydroboration of pyridine with pinacolborane.

Graphical abstract: 1,4-Dihydropyridyl complexes of magnesium: synthesis by pyridine insertion into the magnesium–silicon bond of triphenylsilyls and catalytic pyridine hydrofunctionalization

Supplementary files

Article information

Article type
Paper
Submitted
13 4月 2018
Accepted
14 5月 2018
First published
15 5月 2018

Dalton Trans., 2018,47, 12553-12561

1,4-Dihydropyridyl complexes of magnesium: synthesis by pyridine insertion into the magnesium–silicon bond of triphenylsilyls and catalytic pyridine hydrofunctionalization

L. E. Lemmerz, T. P. Spaniol and J. Okuda, Dalton Trans., 2018, 47, 12553 DOI: 10.1039/C8DT01466C

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