Water Soluble Cationic Phosphine Ligands Containing m-Guanidinium Phenyl Moieties. Syntheses and Applications in Aqueous Heck Type Reactions

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Abstract
Cationic phosphine ligands containing m-guanidinium phenyl substituents {Ph3-nP[C6H4-m-NHC(NH2)(NMe2)]n}n+ nCl- (n = 1−3) (17a−c) have been obtained by addition of dimethylcyanamide to the amino groups of tertiary (m-aminophenyl)phosphines in acidic medium. The tertiary (m-aminophenyl)phosphines Ph3-nP(C6H4-m-NH2)n (4a−c) were prepared by reaction of (3-[N,N-bis(trimethylsilyl)amino]phenyl)magnesium chloride (1) with chlorophosphines Ph3-nPCln followed by deprotection of the bis(trimethylsilyl)amino groups with methanol. Using a similar protected group synthesis as above, the secondary (m-aminophenyl)phosphine Ph(H)PC6H4-m-NH2 (7) could be prepared as well. It may be employed as a building block for the syntheses of chiral bidentate phosphine ligands (11, 14, and 15) bearing m-aminophenyl substituents. The guanidinium phosphines 17b and 17c are readily soluble in water. A comparative study of 17b and 17c, the aryl alkyl guanidinium phosphines 18 and 19, and TPPTS (P(C6H4-m-SO3Na)3) in the aqueous phase palladium-catalyzed C−C coupling reaction between p-iodobenzoate and (trifluoroacetyl)propargylamine shows 17b to be of surmounting activity.