Dynamic ¹⁵N NMR studies of iron phosphine complexes containing coordinated dinitrogen

Abstract

15 N-labelled sites using an inversion-transfer-recovery experiment. Exchange between the metal-bound and terminal nitrogen atoms of coordinated N 2 was also monitored by magnetization transfer and this could proceed by N 2 dissociation or by an intramolecular process.

Testing the Push–Pull Hypothesis: Lewis Acid Augmented N2 Activation at Iron

“…The protonation reaction is >95% selective; only a 4% yield of trans- Fe(H)(depe) 2 (N 2 ) + is observed by 31 P and 15 N NMR spectroscopy. 12,22 In contrast, subjection of 1 to identical reaction conditions in the absence of B(C 6 F 5 ) 3 affords iron hydrides, indicating that protonation occurs exclusively at the iron center. 23 The monoprotonated product ( 3 ) contains a structurally unique Fe–NN(B)H unit and was characterized by X-ray crystallography, NMR, and IR spectroscopy.…”

“…NMR spectra of 2 at room temperature contain a sharp 11 B resonance at −6.35 ppm, consistent with a tetrahedral boron center. The 15 N NMR spectrum of an 15 N 2 -labeled derivative of 2 suggests significant polarization of the N 2 unit induced by the LA: the Δδ for the iron-bound and terminal N atoms increases from 5 to 109 ppm ( 1 : N α −45.2, N β −40.5; 2 : N α −10.5, N β −119.8 ppm). The significant upfield shift of N ß (−74.6 ppm), as opposed to the downfield shift N α (+30.0 ppm), suggests increased localization of electron density at the terminal nitrogen atom …”

15N NMR Spectroscopy in Structural Analysis: An Update (2001 - 2005)

“…A rather small 2 J( 31 P, 15 15 N NMR spectra exhibited separate signals for the metal-bound and terminal nitrogen atoms of the coordinated dinitrogen [60]. 2 J( 31 P, 15 N) coupling constants (50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60) were detected in coordination compounds formed by the reaction of 9-methyladenine with cisplatinum(II) complexes containing dimethyl(phenyl) phosphanes as ancillary ligands [61].…”

“…Brough et al [326] have recently reported the 15 N NMR chemical shifts of 15 N-labeled [60]fullerene-pyrrolidine-Noxides. Conclusive evidence for the formation of an N-oxide moiety is provided by the NMR characterization of a novel [60]fulleropyrrolidine N-oxide, showing an 15 N resonance 85 ppm deshielded compared with that of the related pyrrolidine derivative.…”

“…The 15 N-labeled iron dinitrogen complexes trans-[FeH(N 2 )(PP) 2 ][BPh 4 ] (PP = 1,2-bis(diphenylphosphino) dimethylphosphino)ethane) and cis-[FeH(N 2 )(PP) 2 ][BPh 4 ]have been prepared in situ[60] by the exchange of the unlabeled coordinated dinitrogen with 15 N 2 . The 15 N spectra exhibit separate signals for the metal-bound and terminal N atoms of the coordinated N 2 .An 15 N NMR study[383] of the 15 N-labeled ligand H4dota-15 NHSO 2 R, where R = p-tolyl, and their Eu 3+ and La 3+ complexes has shown that the coordination of the Nsulfonylacetamide arm involves the O-atom of the carbonyl rather than the N-atom, since very small 15 N coordination shifts were observed: -23 ppm (Eu 3+ complex) and +11 ppm (La 3+ complex).…”