Water-soluble phosphines: Part XII. Pd catalyzed PC coupling reactions: a novel synthetic route to cationic phosphines with para- and meta-guanidiniumphenyl moieties

Mono- and bifunctional guanidinium phosphines (3c, 4a, 4b, 5a–5d, 5f) containing para-and meta-guanidiniumphenyl moieties C6H4NHC(NH2)(NR2)+ (R=H, Me) are accessible in high yields by Pd catalyzed PC coupling reactions between iodophenyl guanidines IC6H4NHC(NH)NR2 (meta-, para-isomers; R=H, Me) and phenyl- or diphenylphosphine. The X-ray structure of 3c·MeOH (space group P212121) has been determined, showing a planar guanidinium group in a NHO and NHCl hydrogen bridged arrangement. Pd(II) and Mo(0) complexes of 5c have been synthesized. The influence of the cationic guanidinium group on the electronic and steric parameters of 5c is discussed. A comparative study of 5c, phosphonated and sulfonated phosphine ligands in the biphasic Pd catalyzed Suzuki-type coupling between m-bromophenyldiphenyl phosphine oxide and para-tolylboronic acid shows 5c to be less active than Ph2PC6H44-PO3Na2.