The Linear Tetraphos Ligand prP₄(1,1,4,8,11,11-Hexaphenyl-1,4,8,11-tetraphosphaundecane, Ph₂PCH₂CH₂P(Ph)CH₂CH₂CH₂P(Ph)CH₂CH₂PPh₂):  Synthesis and Characterization ofcis- andtrans-[Fe(NCS)₂(prP₄)]^†

The stereochemistry of prP(4) (1,1,4,8, 11, 1 1-hexaphenyl- 1,4,8, 1 1-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 1-chloro-2(diphenylphosphino)ethane. Reaction of prP(4) with FeCl2 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-alpha- and trans-[Fe(NCS)(2)(racprP(4))] have been characterized by X-ray structure determinations. The UP 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. P-31 NMR spectra of the cis and trans iron isothiocyanato complexes of rac-prP(4) exhibit AA'XX' patterns as well, which can be reproduced by simulation. trans[Fe(NCS)(2)(meso-prP(4))] is identified by its P-31 NMR spectrum, which is similar to that of its rac counterpart. On the basis of NMR spectroscopy it is found that the cis-alpha 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-alpha and trans isomers of [Fe(NCS)2(rac-prP4)] reveal characteristic differences in the region of the C-N stretching vibrations.