Syntheses and Crystal Structures of P-Transition-Metalated Iminophosphoranes, Cp*(CO)₂M{P(NPh)(OMe)₂} (M = Fe and Ru)

Abstract

The reaction of [Cp*(CO)2Fe{P(NHPh)(OMe)2}]PF6 with NaNH2 yielded the P-iron-bonded iminophosphorane Cp*(CO)2Fe{P(NPh)(OMe)2}, with deprotonation from the NHPh group on the phosphorus. The ruthenium analogue, Cp*(CO)2Ru{P(NPh)(OMe)2}, was also prepared in a similar manner. The spectroscopic properties of the metallaiminophosphoranes are quite similar to those of their PO analogue, i.e., phosphonate complexes. The X-ray structure analyses revealed that the P−N bond in Cp*(CO)2Fe{P(NPh)(OMe)2} is comparable in length to that of the ruthenium analogue, Cp*(CO)2Ru{P(NPh)(OMe)2}, and both are considerably shorter than a P−N single bond. These observations strongly suggest that the P−N bonds in the P-metalated iminophosphoranes have substantial double-bond character. The structural features of the metallaiminophosphorane of iron resemble those of the starting cation complex, indicating that their electronic structures are basically similar. The iron-iminophosphorane is thermally stable compared with its Cp analogue, which is not stable enough to isolate, suggesting that both steric and electronic factors are responsible for the stability of the Cp* complexes.

Trapping of Unsaturated Small Molecules through Cyclization with Iron−Iminophosphorane Complexes

“…The IR spectrum shows only one strong absorption band at 1943 cm -1 , assignable to a terminal carbonyl, together with absorptions at 1735, 1700 (sh), and 1577 cm -1 assignable to acyl carbonyls. The 31 P{ 1 H} NMR signal of 2 (180.2 ppm) appears fairly downfield from that of the starting complex 1 (122.3 ppm), indicating the lowered valency of the phosphorus in 2 . In the 1 H NMR spectra, 1 shows one doublet at 3.65 ppm ( J HP = 11.4 Hz) assignable to the spectroscopically identical POMe groups, while 2 shows two doublets at 3.45 ( J HP = 9.9 Hz) and 3.50 ppm ( J HP = 10.5 Hz) due to the diastereotopic POMe groups, suggesting the asymmetric geometry around the iron in 2 .…”

“…The N(1) atom in 2 has a perfectly planar geometry, which is nearly perpendicular to the adjacent phenyl ring plane, suggesting that its lone pair electrons are π-donated rather toward the olefinic carbon and/or the phosphorus atom(s). The P(1)−N(1) bond in 2 (1.7275(16) Å) is significantly longer than the corresponding PN bond in 1 (1.574(1) Å), indicative of its reduced bond order in 2 . This observation reveals that the phosphorus in 2 is thus that of coordinated phosphite in nature rather than that of metalated iminophosphorane, consistent with the 31 P{ 1 H} NMR spectrum.…”

“…We recently reported the syntheses of transition-metalated iminophosphoranes, Cp*(CO) 2 M{P(NPh)(OMe) 2 } (M = Fe ( 1 ), Ru), and demonstrated that the imino nitrogen is fairly basic …”

“…Majoral et al reported that a zirconium−iminophosphorane, which easily rearranges into an N -coordinated zirconium−phosphinoamide at room temperature, affords a variety of products by breaking the zirconium−phosphorus bond in the reactions with several reagents including some unsaturated molecules (vide infra) . Because the iron−iminophosphorane 1 is stable even at elevated temperatures, its reactions might proceed with the iron−phosphorus bond retained, to provide unprecedented heterocycles containing phosphorus, nitrogen, and transition-metal atoms, which might exhibit fascinating properties. − …”

Zinc complexes of anionic NPPN and NP(S)PN ligands and rearrangement to the isomeric NPNP and NP(S)NP ligands in mercury complexes

“…For example, iron and ruthenium complexes of the anionic ligand [(MeO) 2 P=NR] − are known, formed by the deprotonation of the aminophosphine ligand, once the ligand is coordinated to the transition metal through the phosphorus centre. 17 Similarly, Stahl and co-workers have reported some unusual nickel complexes of imidocyclodiphosphazanes. However, in that case the metal bridges both the nitrogen and the phosphorus centre to form a three-membered ring.…”