The Reduction of [Fe(CO)₂L₂X₂] (L = P(OMe)₃, P(OiPr)₃, PEt₃; X = Br, I)—From Iron(II) to Iron(0) via Stable Iron(I) Intermediates

Abstract

The reduction of [Fe(CO),-L,X,] (L=P(OMe),, X = Br (la), I (lb); L = P(OiP&, X = Br (2a), I (2b); L = PEt,, X = Br (3a), I (3b)) with Zn in dioxane (la,b-2a,b) or PhLi in ether (3a,b) led to formation of the corresponding dicarbonyl(halo)bis(phosphorus donor)iron(I) complexes (L = P(OMe),, X = Br (4a), I (4b); L = P(OiPr),. X = Br (Sa), I (5b); L = PEt,, X = Br (6a), I (6b)). Slightly contaminated 5a,b and pure 6a,b were isolated as stable crystalline blue or blue-green complexes. Complexes 4a,b were obtained, with only minor impurities, by cornproportionation of 1 a,b and the dicarbonyl(ha1o)bis-(trimethy1phosphite)ferrate anions 7a,b and characterized in THF solution. The comproportionation products 5 a,b-6 a,b were obtained in high yields by reaction of 2a,b-3a,b with the dinitrogen complexes 13-15. Further reduction of 4a,b-6a,b or exhaustive reduction of 1 a,b-3a,b with sodium amalgam or iBuLi in THF afforded the nonisolable dicarbonyl-(halo)bis(phosphorus donor)ferrate(o) anions (7a,b-9a,b). The latter were characterized by acidification with trifluoroacetic acid or acetic acid yielding stable Results and DiscussionThe reduction of complexes 1 a,b-2a,b with excess Zn in dioxane and of complexes 3a,b with three equivalents of phenyllithium in ether proceeded with loss of one halogen substituent to afford the paramagnetic blue or green 17-electron iron@) compounds 4a,b-6a,b (Scheme 1). In the reduction of la,b with Zn, some [Fe(CO),{ P(OMe),} ,] and [ Fe(CO), { P(OMe),} 3]were isolated as by-products, in addition to 4 a,b.["] While 5 a,b could be isolated in analytically pure form, 6a,b were characterized as spectroscopically pure compounds.When sodium amalgam in THF was used as the reducing agent and the reaction temperature was kept below -30 "C, the Chem. Eur. J. 1995, I . No. 8 Q VCH Verlagsgesellschafi mhH, 0 6 9 4 5 1 Wernheim. 1995 094?-6539/95/0108-0541 S 3O.W+.25/0

Synthesis of the Five-Coordinate Ruthenium(II) Complexes [(PCP)Ru(CO)(L)][BAr‘4] {PCP = 2,6-(CH2PtBu2)2C6H3, BAr‘4 = 3,5-(CF3)2C6H3, L = η1-ClCH2Cl, η1-N2, or μ-Cl−Ru(PCP)(CO)}: Reactions with Phenyldiazomethane and Phenylacetylene

“…The combination of dinitrogen in the same coordination sphere with CO is rare. [50][51][52] Thus, we suggest that the Ru-N bond is relatively weak, a proposal that is consistent with the highly labile nature of the dinitrogen ligand of 4. Several other late transition metal dinitrogen complexes with pincer ligands have also been reported with either monodentate η 24,25 The electron density of the metal center as influenced by the "X" ligands of systems of the type [(PCP)Ru(CO)(X)] n+ (n ) 0 or 1) can be approximated by the energy of the CO absorptions.…”

Base‐Initiated Formation of FeI–PNP Pincer Complexes

“…The solution effective magnetic moments of 1.7–1.9 µ B are in agreement with a low spin d 7 center (one unpaired electron). This is in the same range as the theoretical spin‐only value (µ iso = 1.79 µ B ) and agrees with other reported Fe(I) complexes , …”

“…This is in the same range as the theoretical spin-only value (μ iso = 1.79 μ B ) and agrees with other reported Fe(I) complexes. [11,12] To further characterize all Fe(I) complexes X-band EPR spectra were recorded in THF and toluene at 293 K. Complexes of the type [Fe(PNP NH )(CO) 2 ] + and [Fe(PNP N )(CO) 2 ] display an iso- tropic triplet at g iso = 2.037-2.040 with a well-resolved hyper fine coupling to phosphorus atoms (A P = 17.8-20.2 G) ( Figure 1) and again is consistent with low-spin Fe(I) (S = ½). In fact, most reported low-spin Fe(I) systems exhibit EPR spectra with g values close to 2.0.…”

“…In fact, most reported low-spin Fe(I) systems exhibit EPR spectra with g values close to 2.0. [11,12] Based on DFT calculations it is clear that 4a is a low-spin complex with S = 1/2 adopting a distorted square-pyramidal geometry. The frontier orbitals of complex 4a are also typical of a low spin d 7 species with a square pyramidal geometry ( Figure 2).…”

Reductive elimination of halogens assisted by phosphine ligands in Fe(CO)4X2 (X=I,Br) complexes

“…Some steps suggested in Scheme 5 have already been proposed in the literature: equilibrium 5f was observed by Connelly and co-workers [26] in the oxidative elimination of Fe(CO) 3 (PPh 3 ) 2 by I 2 ; radical species [Fe(CO) 3 L 2 ] + were isolated [27] and their reactivity with nucleophiles and radicals [28] have been widely described; radicals Fe(CO) 2 L 2 X (X = Br, I) were recently isolated as intermediates in the monoelectron reduction of Fe(CO) 2 L 2 X 2 [29,30]; they are very stable in the absence of monoelectron-reducing species or radicals. The reaction between 17-electron radicals and nucleophiles to give 19-electron radicals is well documented in the literature for a few metals and, in particular, for iron [27] supporting equilibria 5b, 5c, 5d and 5e.…”