Preparations of Saturated N-P-N Type Secondary Phosphine Oxides and their Applications in Cross-Coupling Reactions

A series of cyclohexane-1,2-diamine (3a-3d) and benzene-1,2-diamine derivatives (3e-3h) were prepared. Followed by hydrolysis, the reaction of 3a-3c with PCl3 successfully led to the formation of corresponding metastable saturated heteroatom-substituted secondary phosphine oxides (HASPO 4a-4c), a tautomer of the saturated heteroatom-substituted phosphinous acid (HAPA). Whereas ambient-stable diamine-coordinated palladium complexes were obtained, HAPA-coordinated palladium complexes were not successfully synthesized. The molecular structures of HASPO 4c, Pd(OAc)(2)(3a), PdBr2(3b) and Pd(OAc)(2)(3c) and [Cu(NO3)(3d)(+)][NO3-] were determined by single-crystal X-ray diffraction method. Catalysis of in-situ Suzuki-Miyaura cross-coupling reactions for aryl bromides and phenylboronic acid using diamine 3a as ancillary ligand showed that the optimized reaction condition at 60 degrees C is the combination of 2 mmol% 3a/3.0 mmol KOH/1.0 mL 1,4-dioxane/1 mmol% Pd(OAc)(2). Moreover, moderate reactivity was observed when using aryl chlorides as substrates (supporting information). When diamine 3d was employed in Heck reaction, good tolerance of functional groups of aryl bromides were observed while using 4-bromoanisole and styrene as substrates. The optimized condition for Heck reaction at 100 degrees C is 3 mmol% 3d/3.0 mmol CsF/1.0 mL toluene/3 mmol% Pd(OAc)(2). In general, cyclohexane-1,2-diamine derivatives exhibited better catalytic properties than those of benzene-1,2-diamines.