Coordination behaviour in transition metal complexes of asymmetric NPN ligands

Two bicyclic, chiral aminophosphine ligands, namely 4R, 9R-1,3-bis(pyridin-2-ylmethyl)-2-(2-propyl)octahydro-1H-1,3,2-benzodiazaphosphole (1) and 4R, 9R-1,3-bis(pyridin-2-ylmethyl)-2-(2-ethoxy)octahydro-1H-1,3,2-benzodiazaphosphole (2) have been prepared from 1R, 2R-diaminocyclohexane and the appropriate dichlorophosphine and the nature of their coordination to a number of transition metals explored. Ligand 1 coordinates to Pd(II) and Pt(II) as a terdentate donor to give complexes of the type [M(κ3-N,P,N-1)Cl]+ whereas ligand 2 favours bidentate κ2-P,N coordination to give the complexes M(κ2-P,N-2)Cl2. The study of the coordination chemistry of the NPN ligand 1 is frustrated by its ready decomposition to an unknown species which appears to be promoted by transition metals. The ligand 2 does not undergo such a transformation and its metal chemistry is more readily examined. Aside from the Pt(II) and Pd(II) complexes above, 2 has been coordinated to Cr(0) and Mo(0) in the octahedral complexes M(κ2-P,N-2)(CO)4 and Au(I) in linear Au(κ1-P-2)Cl. All the complexes have been fully characterised by spectroscopic and analytical techniques including a single-crystal X-ray structure analysis of [Pt(κ3-N,P,N-1)Cl]Cl, 3.

Two bicyclic, chiral aminophosphine ligands have been prepared and the nature of their coordination to a number of transition metals explored. Ligand 1 has an exocyclic 2-propyl substituent on the P-donor and coordinates to Pd(II) and Pt(II) to give [M(κ3-N,P,N-1)Cl]+ whereas ligand 2 with an exo-ethoxy group at P favours bidentate κ2-P,N coordination to give the complexes M(κ2-P,N-2)Cl2.Figure optionsDownload as PowerPoint slideResearch highlights
► The stability of two bicyclic aminophosphines depends on the nature of the exocyclic P-substituent.
► The P-alkyl derivative is less stable than the P-alkoxy relative.
► Aminophosphines possess two pyridine secondary donors.
► Mixed N,P,N donor systems coordinate in either a terdentate or bidentate fashion depending on the exocyclic P-substituent.