Modular Synthesis of Phosphino Hydrazones and Their Use as Ligands in a Palladium-Catalysed Cu-Free Sonogashira Cross-Coupling Reaction.

Invited for this month's cover is the group of Evamarie Hey-Hawkins at Leipzig University. The cover picture shows the three different bonding modes (mono-, bi- and tridentate) of the modular ligand towards palladium(II) or platinum(II), illustrated with Winston who kindly served as the model. The cat has three binding sites (mouth, front paws and hind paws = P, N and pyridine) to bind the metal dichloride fragment. When all three are used in a tridentate bonding mode, one chlorido ligand is cleaved off. Cover design by Dr. Christoph Selg. More information can be found in the Research Article by Evamarie Hey-Hawkins and co-workers.

Modular Synthesis of Phosphino Hydrazones and Their Use as Ligands in a Palladium-Catalysed Cu-Free Sonogashira Cross-Coupling Reaction.

Phosphino hydrazones represent a versatile class of nitrogen-containing phosphine ligands. Herein, we report a modular synthesis of phosphino hydrazone ligands by hydrazone condensation reaction of three different aryl hydrazines with 3-(diphenylphosphino)propanal (PCHO). Complexation reactions of these phosphino hydrazone ligands with palladium(II) and platinum(II) were investigated and the catalytic activity of the palladium(II) complexes was explored in a Cu-free Sonogashira cross-coupling reaction achieving yields up to 96 %. Additionally it was shown that the catalytically active species is homogeneous.

Metal phosphine aldehyde complexes and their application in Cu-free Sonogashira and Suzuki-Miyaura cross-coupling reactions.

Transition metal coordination chemistry and catalysis are rife with phosphine ligands. One of the rather less studied members of the phosphine ligand family are phosphine aldehydes. We have synthesised 3-(diphenylphosphino)propanal (PCHO) with a slight modification of the known procedure and studied its complexation behaviour with palladium(II) and platinum(II). The catalytic activity of the palladium(II) phosphine aldehyde complexes was investigated in Cu-free Sonogashira and Suzuki-Miyaura cross-coupling reactions. Furthermore, the homogeneous nature of the catalytically active species was confirmed.

Heterobimetallic Pd/Mn and Pd/Co complexes as efficient and stereoselective catalysts for sequential Cu-free Sonogashira coupling-alkyne semi-hydrogenation reactions.

A series of heterobimetallic PdII/MII complexes (MII = Mn, Co) were synthesised and tested as precatalysts for sequential Sonogashira coupling-alkyne semi-hydrogenation reactions to form Z-aryl alkenes. The carbometalated heterobimetallic PdII/CoII complex CoPdL3' demonstrated an apparent cooperative effect compared to the corresponding monometallic counterparts. This compound was identified as a potent single-molecule catalyst for the one-pot Cu-free Sonogashira coupling of aryl bromides with terminal alkynes followed by chemo- and stereoselective semi-hydrogenation of the alkyne intermediate using NH3·BH3 as a hydrogen source. Furthermore, different aromatic substrates have been tested to show the generality of the reaction for the synthesis of Z-alkenes, including biologically active combretastatin A-4. In addition, the homogeneous nature of the catalytically active species was demonstrated.