Synthesis and Characterization of Pd(0) Complexes with Electronically Differentiated Ferrocene Diphosphane Ligands

Abstract

The strategy of modifying phosphane ligands through substituent variation has been widely applied in coordination chemistry and catalysis. This contribution focuses on unsymmetric ferrocene diphosphanes with electronically distinct phosphane moieties, Ph 2 PfcCH 2 PAr 2 (Ar=Ph, 1; 3,5-C 6 H 3 Me 2 , 2; and 3,5-C 6 H 3 (CF 3 ) 2 , 3; fc = ferrocene-1,1'-diyl), which were synthesized and converted to the corresponding selenides (1Se-3Se) and Pd(0) complexes [Pd(L-k 2 P,P')(η 2 -ma)] (5-8 for L = 1-3 and dppf, ma = maleic anhydride). All compounds were characterized by NMR spectroscopy, ESI MS and elemental analysis, and the structures of 2, 1Se • CHCl 3 , 2Se and 5 • PhMe were determined by X-ray diffraction analysis. In addition, the redox behavior of 1-3 and 5-8 was studied by cyclic voltammetry and rationalized through DFT calculations. The prepared Pd(0) complexes and their model compound [Pd(dppf-k 2 P,P')(η 2 -ma)] were employed in Pd-catalyzed CÀ H arylation of benzoxazole with chlorobenzene in n-butanol in the presence of K 3 PO 4 as the base, and the catalytic results were compared with the collected characterization data, including the 1 J PSe coupling constants determined for 1Se-3Se, as a measure of ligand basicity.