Reactivity of coordinatively unsaturated iron complexes towards carbon monoxide: to bind or not to bind?

Benito‐Garagorri, David; Lagoja, Irene M.; Veiros, Luı́s F.; Kirchner, Karl

doi:10.1039/c0dt01636e

Cited by 40 publications

(44 citation statements)

References 85 publications

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“…The remaining iron complex, being CO-free, is possibly high spin, which would explain the absence of detectable 31 P NMR signals. 16 Consistent with this scenario, when 2 was treated with 1 equiv of Ph 2 SiH 2 , a hydridoiron(II) species was observed after 10 min. This species was characterized by an AB quartet in its 31 P NMR spectrum and a triplet in the high-field 1 H NMR spectrum (see the Supporting Information), consistent with its assignment as HFe[P 2 O(OSiPh 2 H)](CO)(NCMe).…”

Section: ■ Introductionsupporting

confidence: 75%

Cooperative Metal–Ligand Reactivity and Catalysis in Low-Spin Ferrous Alkoxides

2015

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This report describes examples of combined Fe-and O-centered reactivity of Fe(P 2 O 2 )(CO) 2 (1), where P 2 O 2 is the diphosphinoglycolate (Ph 2 PC 6 H 4 CHO) 2 2−. This 18e low-spin ferrous dialkoxide undergoes substitution of CO to give the labile monosubstituted derivatives Fe(P 2 O 2 )(CO)-(L) (L = PMe 3 , pyridine, MeCN). Treatment of Fe(P 2 O 2 )-(CO) 2 with Brønsted acids results in stepwise O-protonation, affording rare examples of low-spin Fe(II) complexes containing alcohol ligands. Substitution reactions with amides (RC(O)NH 2 ) proceeds with binding of the carbonyl and formation of an intramolecular hydrogen bond between NH and the neighboring alkoxo ligand. This two-site binding was confirmed with crystallographic characterization of the thiourea-substituted derivative. Fe(P 2 O 2 )(CO) 2 reacts with Ph 2 SiH 2 to give the O-silylated hydrido complex, which is inactive for hydrosilylation. The monocarbonyl derivatives Fe(P 2 O 2 )(CO)(L) (L = NCMe, PMe 3 , acetamide) are precursors to catalysts for the hydrosilylation of benzaldehyde, acetophenone, and styrene. ■ INTRODUCTIONMonomeric alkoxoiron(II) complexes are rare. 1 The oxygen centers in such complexes are expected to be highly basic owing to electrostatic interactions between the metal and ligand, although the Fe−O bonds themselves remain strong. 2 The enhanced basicity of the alkoxide ligand in such complexes usually results in multinuclear complexes with bridging alkoxo ligands. For these reasons, studies on the reactivity of ferrous alkoxides are few.We recently described a one-pot synthesis of an iron(II) diphosphine-dialkoxide dicarbonyl complex Fe(P 2 O 2 )(CO) 2 (1; P 2 O 2 = (Ph 2 PC 6 H 4 CHO) 2 2− ). This complex arises by the coupling of 2 equiv of 2-diphenylphosphinobenzaldehyde (PCHO) 3 in the presence of iron(0) carbonyl reagents (eq 1; bda = benzylideneacetone). 4 Similar condensations had been observed using PCHO with low-valent tungsten and technetium. 5 Our iron system is attractive because the conversion is highly efficient and the reagents are inexpensive. As a dialkoxo iron(II) carbonyl, 1 is unique. In the previous report, 1 was shown to form stable adducts with a variety of Lewis acids, including BF 3 , which bind to the alkoxide sites. In this paper, we provide new perspectives on the O-centered reactivity of 1. These results demonstrate the high basicity of alkoxo ligands and an unprecedented activation mode of Si−H bonds by alkoxo-iron functionalities to afford a series of new hydrido-iron complexes. We also found that the diphosphino-dialkoxo iron species with labile ligands (e.g., MeCN, MeC(O)NH 2 ) are active catalysts for the hydrosilylation of aldehydes, ketones, and even alkenes. The spectroscopic features of all newly synthesized compounds are summarized in Table 1. ■ RESULTS Substitution of Fe(P 2 O 2 )(CO) 2 by Lewis Bases. The CO ligands of 1 are labile. In CH 2 Cl 2 solutions, 1 exchanges with 1 atm of 13 CO over the course of several hours (see the Supporting Information). The lability of the CO ligands ...

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Section: ■ Introductionsupporting

confidence: 75%

Cooperative Metal–Ligand Reactivity and Catalysis in Low-Spin Ferrous Alkoxides

2015

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“…We ascribe this difference to the stabilizing influence of the strong sigma-donor hydride which stabilizes CO ligands on these midvalent complexes. 28 …”

Section: Resultsmentioning

confidence: 99%

Active-Site Models for the Nickel–Iron Hydrogenases: Effects of Ligands on Reactivity and Catalytic Properties

et al. 2011

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Described are new derivatives of the type [HNiFe(SR)2(diphosphine)(CO)3]+, which feature a Ni(diphosphine) group linked to a Fe(CO)3 group via two bridging thiolate ligands. Previous work had described [HNiFe(pdt)(dppe)(CO)3]+ ([1H]+) and its activity as a catalyst for the reduction of protons. Work described in this paper focused on the effects of the diphosphine attached to nickel as well as the dithiolate bridge, 1,3-propanedithiolate (pdt) vs 1,2-ethanedithiolate (edt). A new synthetic route to these Ni-Fe dithiolates is described, involving reaction of Ni(SR)2(diphosphine) with FeI2(CO)4 followed by in situ reduction with cobaltocene. Evidence is presented that this route proceeds via metastable μ-iodo derivatives. Attempted isolation of such species led to the crystallization of NiFe(Me2pdt)(dppe)I2, which features tetrahedral Fe(II) and square planar Ni(II) centers (Me2pdt = 2,2-dimethylpropanedithiol). The new tricarbonyls prepared in this work are NiFe(pdt)(dcpe)(CO)3 (2, dcpe = 1,2-bis(dicyclohexylphosphino)ethane), NiFe(edt)(dppe)(CO)3 (3), and NiFe(edt)(dcpe)(CO)3 (4). Attempted preparation of a phenylthiolate-bridged complex via the FeI2(CO)4 + Ni(SPh)2(dppe) route gave the tetrametallic species [(CO)2Fe(SPh)2Ni(CO)]2(μ-dppe)2. Crystallographic analysis of the edt-dcpe compund [2H]BF4 and the edt-dppe compound [3H]BF4 verified their close resemblance. Each features pseudo-octahedral Fe and square pyramidal Ni centers. Starting from [4H]BF4 we prepared the PPh3 derivative [HNiFe(edt)(dppe)(PPh3)(CO)2]BF4 ([5H]BF4), which was obtained as a ~2:1 mixture of unsymmetrical and symmetrical isomers. Acid-base measurements indicate that changing from Ni(dppe) to Ni(dcpe) decreases the acidity of the cationic hydride complexes by 2.5 pKaMeCN units, from ~11 to ~13.5 (previous work showed that substitution at Fe leads to more dramatic effects). The redox potentials are more strongly affected by the change from dppe to dcpe, for example the [2]0/+ couple occurs at E1/2 = −820 for [2]0/+ vs −574 mV (vs Fc+/0) for [1]0/+. Changes in the dithiolate do not affect the acidity or the reduction potentials of the hydrides. The acid-independent rate of reduction of CH2ClCO2H by [2H]+ is ca. 50 s−1 (25 °C), twice that of [1H]+. The edt-dppe complex [2H]+ proved to be the most active catalyst, with an acid-independent rate of 300 s−1.

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“…6). 132 This reaction proceeds cleanly at room temperature and 1 bar pressure, and is both the first example of reductive cleavage of CO by a low-coordinate iron complex 133,134 and C 4 ring formation from CO with complete CuO bond cleavage. 135 The squaraines 56a-b feature broken conjugation due to the steric bulk of the aryl substituents, which forces them out-of-plane with the C 4 O 2 ring.…”

Section: Reactivity Towards Carbon Monoxidementioning

confidence: 92%