Reactivity of μ-azido and μ-thiocyanato bridged Schiff base palladacycles toward aromatic N-heterocycles and phosphines

Reaction of μ-azido bridged Schiff base palladacycles [Pd{(4-R)C6H3CHN–C6H3–2,6-i-Pr2}(μ-N3)]2 (R = H; OMe) with 1-methylimidazole generated different conformational mononuclear palladacycles. Complexes [Pd{(4-R)C6H3CHN–C6H3–2,6-i-Pr2}(μ-N3)]2 (R = H; OMe) reacted with bidentate 1,2-bis(4-pyridyl)-ethene to give mononuclear palladacycles. Also the reaction of [Pd{C6H4CHN–C6H3–2,6-i-Pr2}(μ-N3)]2 with 4,4′-bipyridine (bpy) produced mononuclear palladacycles. However, the reaction of [Pd{(4-MeO)C6H3CHN–C6H3–2,6-i-Pr2}(μ-N3)]2 with 4,4′-bipyridine formed a 4,4′-bipyridine bridged binuclear palladacycle [Pd{(4-OMe)C6H3CHN–C6H3–2,6-i-Pr2}(N3)]2(μ-bpy). In contrast, μ-thiocyanato bridged Schiff base palladacycles were relatively unreactive toward aromatic N-heterocycles. Only the reaction of [Pd{C6H4CHNC6H3-2,6-i-Pr2}(μ-SCN)]2 with imidazole generated a thiocyanato coordinated mononuclear Schiff base palladacycle [Pd(C6H4CHNC6H3-2,6-i-Pr2)(imidazole)(SCN)]. Moreover, reactions of μ-azido and μ-thiocyanato bridged Schiff base palladacycles with triphenylphosphine and 1,4-bis(diphenylphosphino) butane routinely formed mono- and bi-nuclear terminal azido or isothiocyanato coordinated palladacycles [Pd{(4-R)C6H3CHN–C6H3–2,6-i-Pr2}(PPh3)(N3)], [Pd{(4-R)C6H3CHN–C6H3–2,6-i-Pr2}(PPh3)(NCS)], [Pd{(4-R)C6H3–CHN–C6H3–2,6-i-Pr2}(N3)]2(μ-dppb) and [Pd{(4-R)C6H3CHN–C6H3–2,6-i-Pr2}(NCS)]2(μ-dppb) (R = H; OMe).

Graphical abstractReactivity of μ-azido and μ-thiocyanato bridged Schiff base palladacycles toward aromatic N-heterocycles and phosphines was studied. μ-Azido bridged Schiff base palladacycles toward aromatic N-heterocycles exhibited lability. In contrast, μ-thiocyanato bridged Schiff base palladacycles were relatively unreactive toward aromatic N-heterocycles.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The lability of μ-azido bridged Schiff base palladacycles toward aromatic N-heterocycles. ► Novel azido, thiocyanato or isothiocyanato coordinated Schiff base palladacycles. ► Synthesis of mono- and bi-nuclear Schiff base palladacycles with PPh3 or dppb.