Low‐Valent Nickel and Palladium Complexes with 1,1′‐Bis(phosphanyl)ferrocenes: Syntheses and Structures of Acrylic Acid and Ethylene Complexes

Thermally stable acrylic acid complexes with low‐valent nickel or palladium of the type [(L)M(η 2 ‐CH 2 =CH‐COOH)] [ 1a : M = Ni, L = 1,1′‐bis(diphenylphosphanyl)ferrocene (dppf), 1b : M = Ni, L = 1,1′‐bis(diisopropylphosphanyl)ferrocene (dippf), 1c : M = Pd, L = dippf] were obtained by reaction of [Ni(cod) 2 ] or [(L)Pd(nb)] with acrylic acid in the presence of the phosphane ligands. X‐ray diffraction analysis of 1a and 1c , respectively display that only the olefin part is coordinated. Hydrogen bonds between two carboxyl groups result in dimers in the solid state. The isomeric nickela‐cyclic carboxylates of the type [(L)Ni(CH 2 CH 2 COO)] are stable complexes in case of 2a (L = dppf) and 2b (L = dippf) whereas the unstable compound 2c [L = 1,1′‐bis(di‐ tert ‐butylphosphanyl)ferrocene (dtbpf)] undergoes fast reductive decoupling to form CO 2 and the ethylene complex [(dtbpf)Ni(ethylene)] ( 3c ). The related complex [(dippf)Ni(ethylene)] ( 3b ) was prepared from nickel(0) complexes by ligand exchange reaction. 3b and 3c were characterized by elemental analyses, NMR spectroscopy and X‐ray structure analysis of single crystals.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)