η2-Coordination of a Phosphaalkyne to an Amino Olefin Nickel Complex and Regioselective Catalyzed Cyclooligomerization to Dewar 1,3,5-Triphosphabenzene

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Abstract

We report herein an efficient synthesis of a Dewar-triphosphabenzene derived from [2+2+2] cycloaddition of three phosphaalkyne molecules promoted by an amino olefin Ni0 complex as the catalyst. Amino diolefin NiI complex 1 serves as a precursor complex that reacts with triphenylmethylphosphaethyne under reducing conditions at low temperature to give Ni0 complex 3 with a coordinated phosphaalkyne in a η2-mode. The structure of 3 was determined by X-ray diffraction methods and suggests a bonding situation for the phosphaalkyne that is between a side-on coordinated C≡P molecule and a metallaphosphacyclopropene structure. The reaction of 3 with a 10-fold excess of phosphaethylene under reducing conditions at room temperature resulted in the formation of 2,4,6-tris(triphenylmethyl)-Dewar-1,3,5-triphosphabenzene (4) in good yield.

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