Dinuclear palladium–azido complexes containing thiophene derivatives: reactivity toward organic isocyanides and isothiocyanates

Abstract

Cyclopalladated tetranuclear Pd(II) complexes, [Pd₂(µ-Cl)₂(Y)]₂ (Y = L¹ or L²; H₂L¹ = di(2-pyridyl)-2,2′-bithiophene; H₂L² = 5,5″-di(2-pyridyl)-2,2′:5′,2″-terthiophene), containing two pyridyl-α, α′-disubstituted derivatives of thiophene were prepared. Treating these products with PR₃ and subsequently with NaN₃ produced the dinuclear Pd–azido complexes [(PR₃)₂(N₃)Pd–Y–Pd(N₃)(PR₃)₂] (Y = L¹ or L²) or a cyclometallated complex [(PR₃)(N₃)Pd–Y′–Pd(N₃)(PR₃)] (Y′ = C,N-L²). Reactions of these Pd–azido complexes with CN–Ar (Ar = 2,6-Me₂C₆H₃, 2,6-i-Pr₂C₆H₃) or R–NCS (R = i-Pr, Et, allyl) led to the complexes containing end-on carbodiimido groups [(PMe₃)₂(NCN–Ar)Pd–Y–Pd(NCN–Ar)(PMe₃)₂] or S-coordinated tetrazole-thiolato groups {(PMe₃)₂[CN₄(R)]S–Pd–Y–Pd–S[CN₄)(R)](PMe₃)₂}. Interestingly, when treated with elemental sulfur, the carbodiimido complexes transformed into the cyclometallated derivatives, [(PMe₃)(NCN–Ar)Pd–Y′–Pd(NCN–Ar)(PMe₃)] (Y′ = C,N-L¹, C,N-L²). We also report the preparation of linear, thienylene-bridged dinuclear Pd complexes [L₂(N₃)Pd–X(or X′)–Pd(N₃)L₂] (L = PMe₃ or PMe₂Ph; H₂X = 2,2′-bithiophene or H₂X′ = 2,2′:5′,2″-terthiophene) and their reactivity toward organic isocyanide and isothiocyanates.