The transition-metal chemistry of amidinatosilylenes, -germylenes and -stannylenes

• The synthesis, reactivity and catalytic activity of transition-metal derivatives of heavier tetrylene amidinates (amidinato-HT–TM complexes) are reviewed.
• Most of the hitherto reported amidinato-HT–TM complexes are silylene or germylene derivatives.
• Amidinato-HTs are strong electron-donating ligands, stronger than N-heterocyclic carbenes (NHCs) in many cases.
• The electronic and steric properties of amidinato-HTs can be easily tuned.

The transition-metal (TM) chemistry of heavier tetrylenes (HTs), also known as heavier carbene analogs, group 14 metalenes or group 14 metalylenes (compounds containing Si, Ge, Sn or Pb in +2 oxidation state), has experienced an exponential growth in the last few years because new families of HTs have emerged to the main-group chemistry arena. One of these families is characterized by the presence of an amidinato group attached to the group 14 element. Although the first report dealing with amidinato-HT–TM complexes appeared only seven years ago, nearly one hundred TM complexes containing amidinato-HT ligands are currently known and, remarkably, some of them have already been recognized as catalyst precursors for useful transformations of organic substrates (Sonogashira, Kumada and Negishi cross-couplings, ketone hydrosilylations, cycloadditions, arene C–H borylations, etc.). Thus, amidinato-HTs have emerged as promising alternatives to widely used classical ligands, such as phosphines or N-heterocyclic carbenes. This review comprehensively surveys the TM chemistry of amidinato-HTs published up to the end of 2014, examining not only the synthesis and characterization of these complexes, but paying special attention to reactivity studies, theoretical investigations and catalytic applications.

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