Imine-Centered Reactions in Imino-Phosphine Complexes of Iron Carbonyls

Abstract

Fundamental reactions of imino-phosphine ligands were elucidated through studies on Ph2PC6H4CHNC6H4-4-Cl (PCHNArCl) complexes of iron(0), iron­(I), and iron­(II). The reaction of PCHNArCl with Fe­(bda)­(CO)3 gives Fe­(PCHNArCl)­(CO)3 (1), featuring an η2-imine. DNMR studies, its optical properties, and DFT calculations suggest that 1 racemizes on the NMR time scale via an achiral N-bonded imine intermediate. The N-imine isomer is more stable in Fe­(PCHNArOMe)­(CO)3 (1 OMe ), which crystallized despite being the minor isomer in solution. Protonation of 1 by HBF4·Et2O gave the iminium complex [1H]­BF4. The related diphosphine complex Fe­(PCHNArCl)­(PMe3)­(CO)2 (2), which features an η2-imine, was shown to also undergo N protonation. Oxidation of 1 and 2 with FcBF4 gave the Fe­(I) compounds [1]­BF4 and [2]­BF4. The oxidation-induced change in hapticity of the imine from η2 in [1]0 to κ1 in [1]+ was verified crystallographically. Substitution of a CO ligand in 1 with PCHNArCl gave Fe­[P2(NArCl)2]­(CO)2 (3), which contains the tetradentate diamidodiphosphine ligand. This C–C coupling is reversed by chemical oxidation of 3 with FcOTf. The oxidized product of [Fe­(PCHNArCl)2(CO)2]2+ ([4]2+) was prepared independently by the reaction of [1]+, PCHNArCl, and Fc+. The C–C scission is proposed to proceed concomitantly with the reduction of Fe­(II) via an intermediate related to [2]+.

Rational Design of Fe2(μ‐PR2)2(L)6 Coordination Compounds Featuring Tailored Potential Inversion

“…The present DFT calculations, carried out by means of the TURBOMOLE 7.2 suite, [50] explore different exchange and correlation functionals, in order to corroborate the energy trends that emerge comparing the calculated potentials for the different Fe 2 P 2 complexes. Given the similarity of these systems to classic hydrogenase models, we chose the BP86 functional, [51,52] which has been extensively used and validated for that class of compounds, [53][54][55][56] adding Grimme correction for dispersive contributions (BP86-D3). [57] Structures were also optimized using the B97-D functional (B97 re-parameterized to account for dispersions) [58] and, additionally, some molecules belonging to the set were optimized using the M06 functional (results not shown).…”

Inhibition of [FeFe]-hydrogenase by formaldehyde: proposed mechanism and reactivity of FeFe alkyl complexes

“…We assume that the main isomer (A) has trans-dibasal phosphine ligands as established by X-ray crystallography. This dominant and one minor isomer (B) both show 31…”

“…CD2Cl2 was degassed by freeze-pump-thaw cycles and dried using 4 Å molecular sieves. 1 H, 31 P{ 1 H}, and 13 C NMR spectra were recorded on Varian 500, Varian 600, Bruker 500, or Bruker Ascend 600 MHz spectrometers. Chemical shifts (δ/ppm) are referenced to residual solvent peak (5.32 ppm for 1 H and 53.84 ppm for 13 C in CD2Cl2).…”

“…Chemical shifts (δ/ppm) are referenced to residual solvent peak (5.32 ppm for 1 H and 53.84 ppm for 13 C in CD2Cl2). Chemical shifts (δ/ppm) for 31 P{ 1 H} NMR were calibrated using 85% H3PO4 as an external reference (0 ppm). Solution IR spectra were recorded on a Perkin-Elmer Spectrum 100 FTIR spectrometer.…”

“…Further relevant to stereodynamics, the exchange for the FeL3 sites is rapid in Fe(I)Fe(I) complexes, whereas bioctahedral Fe(II)Fe(II) complexes are more rigid. 24 Evidence of the process shown in Scheme 2 is provided by 31 According to IR measurements, the tautomerization is complete after 3 h at room temperature (eq 2).…”