Insertion of Symmetric Alkynes into the σ[Pd–C(sp 2 , Ferrocene)] Bond of Palladacycles with [C(sp 2 , Ferrocene),N,S(Thienyl)] – Pincer Ligands

A study of the reactivity of [Pd({(η 5 ‐C 5 H 3 )–CH=N–(CH 2 ) n –(C 4 H 3 S)}Fe{η 5 ‐C 5 H 5 })Cl], n = 2 ( 1e ) or 1 ( 1f ), with symmetric alkynes R 1 –C≡C–R 1 (R 1 = CO 2 Me, Et or Ph) has allowed us to achieve the di‐μ‐chloro‐bridged complexes [Pd({(MeO 2 C–C=C–CO 2 Me)(η 5 ‐C 5 H 3 )–CH=N–(CH 2 ) n –(C 4 H 3 S)}Fe{η 5 ‐C 5 H 5 })μ‐Cl] 2 , n = 2 ( 3e ) or 1 ( 3f ), and the mononuclear derivatives [Pd({(MeO 2 C–C=C–CO 2 Me)(η 5 ‐C 5 H 3 )–CH=N–(CH 2 ) n –(C 4 H 3 S)}Fe{η 5 ‐C 5 H 5 })Cl(PPh 3 )], n = 2 ( 4e ) or 1 ( 4f ), [Pd({(R 1 –C=C–R 1 ) 2 (η 5 ‐C 5 H 3 )–CH=N–(CH 2 ) n –(C 4 H 3 S)}Fe{η 5 ‐C 5 H 5 })Cl],R 1 = CO 2 Me, n = 2 ( 5e ) or 1 ( 5f ), R 1 = Et, n = 2 ( 6e ) or 1 ( 6f ), or R 1 = Ph, n = 2 ( 7e ), and [Pd({(Ph–C=C–Ph) 2 (η 5 ‐C 5 H 3 )–CH=N–(CH 2 )–(C 4 H 3 S)}Fe{η 5 ‐C 5 H 5 })Cl(PPh 3 )] ( 7f· 1/2Ph–C≡C–Ph). With MeO 2 C–C≡C–CO 2 Me, mono‐ ( 3e , 3f , 4e and 4f ) and bis‐insertion complexes ( 5e and 5f ) were obtained, whereas for R 1 –C≡C–R 1 with R 1 = Et or Ph, only bis‐insertion products ( 6e , 6f , 7e and 7f ) were isolated. These studies also proved that 1e and 1f , which have a labile Pd–S(thienyl) bond, are more prone to undergo the insertion of R 1 –C≡C–R 1 (R 1 = CO 2 Me, Et or Ph) than their analogues with [C(sp 2 , ferrocene), N, X] – [X = O, N(amine) or S(thioether)] pincer ligands.