Boryl Ancillary Ligands: Influencing Stability and Reactivity of Amidinato-Silanone and Germanone Systems in Ammonia Activation.

While the nucleophilic addition of ammonia to ketones is an archetypal reaction in classical organic chemistry, the reactivity of heavier group 14 carbonyl analogues (R2E=O; E=Si, Ge, Sn, or Pb) with NH3 remains sparsely investigated, primarily due to the synthetic difficulties in accessing heavier ketone congeners. Herein, we present a room-temperature stable boryl-substituted amidinato-silanone {(HCDippN)2B}{PhC(tBuN)2}Si=O (Dipp=2,6-iPr2C6H3) (together with its germanone analogue), formed from the corresponding silylene under a N2O atmosphere. This system reacts cleanly with ammonia in 1,2-fashion to give an isolable sila-hemiaminal complex {(HCDippN)2B}{PhC(tBuN)2}Si(OH)(NH2). Quantum chemical calculations reveal that the formation of this sila-hemiaminal is crucially dependent on the nature of the ancillary ligand scaffold. It is facilitated thermodynamically by the hemi-lability of the amidinate ligand (which allows for the formation of an energetically critical intramolecular N⋅⋅⋅HO hydrogen bond within the product) and is enabled mech-anistically by a process in which the silanone initially acts in umpolung fashion as a base (rather than an acid), due to the strongly electron-releasing and sterically bulky nature of the ancillary boryl ligand.

An Isolable Three-Coordinate Germanone and Its Reactivity.

A rare three-coordinate germanone [IPrN]2 Ge=O (IPrN=bis(2,6-diisopropylphenyl)imidazolin-2-imino) was successfully isolated. The germanone has a rather high thermal stability in arene solvent, and no detectable change was observed at 80 °C for at least one week. However, high thermal stability of [IPrN]2 Ge=O does not prevent its reactivity toward small molecules. Structural analysis and initial reactivity studies revealed the highly polarized nature of the terminal Ge=O bond. Besides, the addition of phenylacetylene, as well as O-atom transfer with 2,6-dimethylphenyl isocyanide make it a mimic of nucleophilic transition-metal oxides. Mechanism for O-atom transfer reaction was investigated via DFT calculations, which revealed that the reaction proceeds via a [2+2] cycloaddition intermediate.

The Preparation of Complexes of Germanone from a Germanium µ-Oxo Dimer.

Complexes of germanone containing formal Ge=O→M bonds (M=Zn, B, Ge, Sn) were isolated and characterized. The compounds were prepared through a novel synthetic route using a germanium µ-oxo dimer 3 as the starting material. This method circumvents the need to employ germanones to prepare complexes of germanones.