Heteroleptic Bis(amido) Ca(II) and Yb(II) NHC Pincer Complexes: Synthesis, Characterization, and Catalytic Activity in Intermolecular Hydrofunctionalization of C═C Bonds
Ivan V. Lapshin, Anton V. Cherkasov, Alexander A. Trifonov
Abstract
The treatment of 4,5-dimethyl-1,3-bis(2-pyridylmethyl)-1 H -imidazolium chloride with M[N(SiMe 3 ) 2 ] 2 (THF) 2 (M = Ca, Yb) in 1:2 molar ratio results in the formation of a carbene fragment, activation of the picolyl CH bond, and dearomatization of one of the pyridine rings and affords bis(amido) complexes [(NHC)MN(SiMe 3 ) 2 ] 2 (M = Ca ( 2 ), Yb ( 3 )) coordinated by a μ 2 -bridging pincer NHC amido ligand. Complexes 2 and 3 demonstrate high catalytic activity and excellent regio- and chemoselectivities in the intermolecular hydrophosphination of styrene with both primary and secondary phosphines. Complexes 2 and 3 enable selective addition of PhPH 2, Ph 2 PH, (CH 2 ) 4 NH, and (CH 2 ) 5 NH to para -divinylbenzene with high conversions under mild conditions. Tandem hydrophosphination/hydroamination of para -divinylbenzene was also performed.