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

Abstract

Divalent bis(phosphinimino)methanide lanthanide complexes of composition [{(Me 3SiNPPh 2) 2CH}EuI(THF)] 2 and [{(Me 3SiNPPh 2) 2CH}YbI(THF) 2] have been prepared by a salt metathesis reactions of K{CH(PPh 2NSiMe 3) 2} and LnI 2. Further reactions of these complexes with [K(THF) n N(PPh 2) 2] led selectively to the heteroleptic amido complexes [{(Me 3SiNPPh 2) 2CH}Ln{(Ph 2P) 2N}(THF)] (Ln = Eu, Yb). The ytterbium complex can also be obtained by reduction of [{CH(PPh 2NSiMe 3) 2}Yb{(Ph 2P) 2N}Cl] with elemental potassium. The single crystals of [{(Me 3SiNPPh 2) 2CH}Ln{(Ph 2P) 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, MI 2 (M = Ca, Sr, Ba) was reacted with K{CH(PPh 2NSiMe 3) 2} to give [{(Me 3SiNPPh 2) 2CH}CaI(THF) 2], [{(Me 3SiNPPh 2) 2CH}SrI(THF)] 2, and [{(Me 3SiNPPh 2) 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(PPh 2NSiMe 3) 2} − ligand acts as tridentate donor forming a long methanide carbon metal bond. Thus, all complexes presented can be considered as organometallic compounds. [{(Me 3SiNPPh 2) 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.