Polyfunctional Phosphine Ligands. Synthesis of 7-Diphenylphosphino-2,4-dimethyl-1,8-naphthyridine and its Co-ordination Properties

DOI: 10.1039/DT9920002367

Source and publish data:

Journal of the Chemical Society, Dalton Transactions p. 2367 - 2374 (1992)

Update date:2022-09-26

Topics:

Authors:

Grassi, Maria

Munno, Giovanni De

Nicolo, Francesco

Schiavo, Sandra Lo

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Article abstract of DOI:10.1039/DT9920002367

The new trinucleating ligand 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine (dpnapy) has been prepared and its co-ordination chemistry with rhodium(I) complexes investigated.Reactions with <2> (cod = cycloocta-1,5-diene) lead to different products depending on the ligand to metal ratio.The P-monodentate ligand complex 1 is formed when a 2:1 ligand:dimer ratio is used.The cod region of the 1H and 13C NMR spectra of 1 is temperature dependent.The fluxional behaviour can be explained by the formation of a five-co-ordinate intermediate displaying rapid intramolecular exchange of the cod olefinic and CH2 protons.A lower activation energy process, not frozen at 215 K, is also observed.At room temperature (r.t.) the two-dimensional 1H and 31P chemical exchange spectra indicate a further slower dynamic equilibrium 1 <*> 2 with loss of dpnapy.The binuclear complex <2(μ-dpnapy)> 2, in which dpnapy acts as bridging bidentate ligand using the phosphorus and the terminal nitrogen atoms, is the reaction product when a 1:1 ligand:dimer ratio is used.The 1H and 13C NMR data for complex 2 are consistent with a dimeric structure of low symmetry.Complex 2 is also involved in several dynamic processes.At r.t. the two-dimensional 1H chemical exchange spectrum shows a slow general scrambling of the cod olefinic protons and the presence of the equilibrium 2 <*> 1 with participation of <2>.The ligand reacts with <2> giving as the only isolable product the metallocycle <2>*2CH2Cl2 3.The reaction proceeds through several steps involving the formation of cis-dicarbonyl intermediates as indicated by IR and NMR spectra.The structure of 3 has been determined by X-ray crystallography.It consists of two Rh(CO)Cl units, joined together by two dpnapy molecules in a head-to-tail arrangement.