Cyanide bridged multimetallics derived from extended arrays of alkaline earth, rare earth, and transition metals: A study from complexes to catalysts.

摘要

Several new cyanide bridged bimetallic compounds were synthesized for use as novel heterogeneous catalysts. With this in mind specific metal -- metal combinations were chosen. In the search for bimetallic catalyst precursors containing either cobalt or iron, two new alkaline earth(II) hexacyanometalate(III) complexes, (DMF)14Sr3[M(CN)6]2 (DMF = N,N-dimethylformamide; M = Co or Fe), were synthesized using a novel preparation utilizing both DMF and H2O as solvents. Several new alkaline earth(II) tetracyanometalate(II) (DMF)nAeM(CN) 4 (Ae = Sr, Ba, and Ca; M = Pd and Pt) were synthesized as well. The strontium palladium containing complexes were converted to bimetallic heterogeneous catalysts and served as excellent hydrodechlorination catalysts.;In view of their use as catalytic precursors, several experiments were devised to study rare earth(III) tetracyanometalate(II) [(DMF)5Ln] 2[M(CN)4]3 (M = Ni, Pd, and Pt) combinations. A new synthesis, again utilizing H2O, was devised to reduce synthesis time from two weeks to a few days. Several new complexes containing interstitial K2M(CN)4 units were synthesized. The rare earth to catalytic metal ratio (2:3 in the previously studied complexes) was changed to one to one by varying reaction conditions and new (DMF)5LnXM(CN) 4 (X = Cl- or NO3-) complexes were synthesized. All complexes were characterized by IR, elemental analysis, and single crystal X-ray diffraction.;Supported bimetallic catalysts were prepared using a novel reduction method. A solution of ammonia borane in tetrahydrofuran replaced hydrogen as the reducing agent in the conversion of the precursors into SiO2 supported catalysts. XPS studies of these catalysts confirm that both metals from the precursor material are reduced by ammonia borane. A model Suzuki coupling reaction was used to test these new catalysts. These studies confirm that YbPd/SiO2 reduced with ammonia borane from the precursor [(DMF) 5Yb]2[Pd(CN)4]3 is an active catalysts in the Suzuki coupling of phenylboronic acid with 4'-iodoacetophenone.