Bis(phosphinimino)methanides as ligands in divalent lanthanide and alkaline earth chemistry – synthesis, structure, and catalysis

Divalent bis(phosphinimino)methanide lanthanide complexes of composition [{(Me3SiNPPh2)2CH}EuI(THF)]2 and [{(Me3SiNPPh2)2CH}YbI(THF)2] have been prepared by a salt metathesis reactions of K{CH(PPh2NSiMe3)2} and LnI2. Further reactions of these complexes with [K(THF)nN(PPh2)2] led selectively to the heteroleptic amido complexes [{(Me3SiNPPh2)2CH}Ln{(Ph2P)2N}(THF)] (Ln = Eu, Yb). The ytterbium complex can also be obtained by reduction of [{CH(PPh2NSiMe3)2}Yb{(Ph2P)2N}Cl] with elemental potassium. The single crystals of [{(Me3SiNPPh2)2CH}Ln{(Ph2P)2N}(THF)] contain enantiomerically pure complexes. As a result of the similar ionic radii of the divalent lanthanides and the heavier alkaline earth metals some similarities in coordination chemistry of the bis(phosphinimino)methanide ligand were anticipated. Therefore, MI2 (M = Ca, Sr, Ba) was reacted with K{CH(PPh2NSiMe3)2} to give [{(Me3SiNPPh2)2CH}CaI(THF)2], [{(Me3SiNPPh2)2CH}SrI(THF)]2, and [{(Me3SiNPPh2)2CH}BaI(THF)2]2, respectively. As expected the Sr and Eu complexes and the Ca and Yb complexes are very similar, whereas for the Ba compound, as a result of the large ion radius, a different coordination sphere is observed. For all new complexes the solid-state structures were established by single crystal X-ray diffraction. In the solid-state the {CH(PPh2NSiMe3)2}− ligand acts as tridentate donor forming a long methanide carbon metal bond. Thus, all complexes presented can be considered as organometallic compounds. [{(Me3SiNPPh2)2CH}YbI(THF)2] was also used as precatalyst for the intramolecular hydroamination/cyclization reaction of different aminoalkynes and aminoolefines. Good yields but moderate activities were observed.

The reaction of K{CH(PPh2NSiMe3)2} with LnI2 (Ln = Eu, Yb) and MI2 (M = Ca, Sr, Ba) results in bis(phosphinimino)methanide metal iodidies. The lanthanide complexes were further reacted to give heteroleptic amides and were used as precatalyst for the the intramolecular hydroamination/cyclization reaction.Figure optionsDownload as PowerPoint slide