Methods to synthesize diphosphines with different substituents on the two phosphorus centers are limited, particularly for the synthesis of unsymmetric bis(dialkylphosphine) ligands. Herein is reported a modular and high-yielding synthesis of borane-protected unsymmetric 1,3-bis(diphosphino)propanes containing either two dialkylphosphine moieties or one dialkylphosphine and one diphenylphosphine group. The method relies on sequential phosphine substitution on 1,3-dibromopropane. The borane-protected diphosphines are readily converted to bis(phosphonium salts), which serve as convenient preligands. Palladium(II) complexes of di-tert-butyl(3-(dicyclohexylphosphino)propyl)phosphine (tBuCyPP), di-tert-butyl(3-(diisobutylphosphino)propyl)phosphine (tBuiBuPP), and diisobutyl((3-(dicyclohexylphosphino)propyl)phosphine (CyiBuPP) have been prepared. The tBuiBuPP and CyiBuPP complexes have been structurally characterized and their structural properties compared to symmetric (1,3-diphosphinopropane)palladium dichloride structures.