The linear tetraphos ligand prP4 (1,1,4,8,11,1-hexaphenyl-1,4,8, 11-tetraphosphaundecane, Ph2PCH2CH2P(Ph)CH 2CH2CH2P(Ph)CH2CH 2PPh2): Synthesis and characterization of cis- and trans-[Fe(NCS)2(prP4)]

Article abstract of DOI:10.1021/om030579k

The stereochemistry of prP₄ (l,l,4,8,11,11-hexaphenyl-l,4,8,11- tetraphosphaundecane) and its coordination properties in mononuclear complexes are explored. The free ligand is obtained as a mixture of meso and rac diastereomers from the reaction of dilithium 1,3-bis(phenylphosphido)propane- tetrakis(tetrahydrofuran) ( Lippp ) with 2 equiv of l-chloro-2(diphenylphosphino)ethane. Reaction of prP₄ with FeCl ₂ and KSCN leads to cis- and trans-[Fe(NCS)₂(prP ₄)] complexes of the meso and the rac ligands; the composition of this mixture has been fully analyzed. The iron isothiocyanato complexes cis-α- and trans-[Fe(NCS)₂(rac-prP₄)] have been characterized by X-ray structure determinations. The ³¹P NMR spectrum of the free tetraphos ligand shows an AA'XX' coupling scheme with three groups of signals centered at -20.6 and -20.7 ppm and at -12.4 ppm, which belong to the rac and meso isomers, respectively. ³¹P NMR spectra of the cis and trans iron isothiocyanato complexes of rac-prP₄ exhibit AA'XX' patterns as well, which can be reproduced by simulation, trans[Fe(NCS) ₂(meso-prP₄)] is identified by its ³¹P NMR spectrum, which is similar to that of its rac counterpart. On the basis of NMR spectroscopy it is found that the cis-α complex of the rac ligand converts into the trans-rac complex with a half-life of approximately 2 days. Infrared and Raman spectra of the cis-α and trans isomers of [Fe(NCS) ₂(rac-prP₄)] reveal characteristic differences in the region of the C-N stretching vibrations.