Abstract
Sulfonation of (diphenylphosphinothioyl)ferrocene (1) with chlorosulfonic acid in acetic anhydride affords the crude sulfonic acid Ph2P(S)fcSO(3)H (2; fc = ferrocene-1,1'-diyl), which can be efficiently purified and isolated after conversion to Ph2P(S)fcSO(3)(HNEt3) (3). Methyl triflate/P(NMe2)(3) can be used to convert compound 3 to the stable sulfonate salt Ph(2)PfcSO(3) (HNEt3) (4) and Ph2P(Me)fcSO(3) (5) as a minor, zwitterionic byproduct.
Alternatively, compound 4 can be prepared by lithiation of 1'-(diphenylphosphino)-1-bromoferrocene (6; Ph(2)PfcBr) and trapping of the lithiated intermediate with SO3. NMe3.
Reactions of [(L-NC)PdX](2)and [(L-SC)PdX](2), where X = Cl, AcO, L-NC = 2-[(dimethylamino-kappa N)methyl]phenyl-kappa C-1, and L-SC = 2[(methylthio-kappa S)methyl]phenyl-kappa C-1, with 4 uniformly produced the bis-chelate complexes [(L-NC)Pd(Ph(2)PfcSO(3)-kappa O-2,P)] (7) and [(L-SC)Pd(Ph(2)PfcSO(3)-kappa O-2,P)] (8), respectively. The reaction of [PdCl2(MeCN)(2)] with 4 afforded the bis(phosphine) complex trans-(Et3NH)(2)[PdCl2 (Ph(2)PfcSO(3)-kappa P)(2)] (9).
Complexes 7-9 were used as defined catalyst precursors for the Suzuki- Miyaura cross-coupling of boronic acids with acyl chlorides to give ketones. Reactions of aromatic substrates in the presence of Na3PO4 and 9, the base and Pd source that showed the best performance, in a toluene/water biphasic system provided the coupling products in good yields; however, aliphatic substrates typically resulted in poor conversions.
Extensive tests of the reaction scope revealed that the transposition of the substituents between the reaction partners can have a substantial effect on the yield of the coupling product in otherwise complementary reactions, which highlights the importance of the judicious choice of starting materials for this particular reaction.