Square-planar metal(II) complexes containing ester functionalised bis(phosphino)amines: mild P-N methanolysis and C_arene-H cyclometallation

Gaw, Kirsty G., Smith, Martin B., Wright, John B., Slawin, Alexandra M.Z., Coles, Simon J., Hursthouse, Michael B. and Tizzard, Graham J. (2012) Square-planar metal(II) complexes containing ester functionalised bis(phosphino)amines: mild P-N methanolysis and C_arene-H cyclometallation. Journal of Organometallic Chemistry, 699, 39-47. (doi:10.1016/j.jorganchem.2011.11.003).

Abstract

The synthesis of three new ester functionalised bis(phosphino)amines Ph₂PN{R}PPh₂ [R = C₆H₄(3-CO₂Me) 1a; C₆H₃(3,5-CO₂Me)₂ 1b; C₆H₄(4-CO₂Me) 1c] upon stoichiometric reaction of Ph₂PCl and the appropriate H₂N{R} in Et₂O is described. Reaction of 1 equiv. of 1a-c with MCl₂(cod) (M = Pt, Pd) in CH₂Cl₂ afforded the dichlorometal(II) complexes PtCl₂(1a) 2a, PtCl₂(1b) 2b, PtCl₂(1c) 2c and PdCl₂(1b) 2'b respectively. The corresponding dibromo (and diiodo) platinum(II) complexes 3b (and 4b) were synthesised, in > 80% isolated yields, from PtBr₂(cod) or PtI₂(cod). When a suspension of 2b in MeOH was stirred at r.t. for ca. 16 h the mixed complex cis-PtCl₂[Ph₂PNH{R}](Ph₂POMe) 5a [R = C₆H₃(3,5-CO₂Me)₂] was cleanly generated. Metathesis of 5a using excess NaBr or NaI in MeOH/acetone afforded cisPtBr₂[Ph₂PNH{R}](Ph₂POMe) 5b or cis-PtI₂[Ph₂PNH{R}](Ph₂POMe) 5c. Methanolysis of PtCl₂(1a) 2a at ambient temperature afforded, in low yield (18%), the regiospecific P, C-orthometallated complex cis-PtCl [Ph₂PNH{C₆H₃(3-CO₂Me)}](Ph₂POMe) 6. We speculate the C - H activated complex 6 is obtained via initial formation of cis-PtCl₂[Ph₂PNH{C₆H₄(3-CO₂Me)}](Ph₂POMe) 7. A similar observation was also found using 2c whereupon examination of the isolated solid, by P-31{H-1} NMR spectroscopy, revealed formation of three complexes namely orthometallated cis-PtCl[Ph₂PNH{C₆H₃(4-CO₂Me)}](Ph₂POMe) 9, cis-PtCl[Ph₂PNH{C₆H₄(4-CO₂Me)}](Ph₂POMe) 10 and cis-PtCl₂(Ph₂POMe)₂ 8. All new compounds reported here have been characterised by multinuclear NMR and IR spectroscopy, microanalysis and in six cases by single crystal X-ray crystallography. The X-ray structure of cis-PtCl[Ph₂PNH{C₆H₃(3-CO₂Me)}]( Ph₂POMe) 6 revealed selective C - H cycloplatination at the 6-position (as opposed to the 2-position) of the N-arene ring.

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Contributors

Author: Simon J. Coles

Author: Graham J. Tizzard

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