Ligand Control of the Metal Coordination Sphere: Structures, Reactivity and Catalysis

Abstract

Dedicated to the memory of Yves Chauvin, a most remarkable and visionary man and scientist, with gratitude for our scientific and non-scientific conversations and a very fruitful and enjoyable collaboration.Abstract -Two major aspects of coordination/organometallic chemistry are discussed in this article: (i) the use of functional chelating ligands to stabilize metal complexes while allowing easy stereodifferentiation within the coordination sphere and (ii) the choice of suitable ligands to stabilize challenging 'underligated' metal complexes with electronically highly unsaturated metal centres, thus potentially displaying unusual reactivity. In both cases, the relevance to homogeneous catalysis will be discussed.Résumé -Contrôle de la sphère de coordination des métaux par les ligands : structures, réacti-vité et catalyse -Deux aspects majeurs de la chimie de coordination/organométallique sont discutés dans cet article : d'une part, l'utilisation de ligands chélatants fonctionnels pour stabiliser des complexes métalliques en permettant une différenciation stéréoélectronique aisée au sein de la sphère de coordination et, d'autre part, la sélection de ligands adaptés à la stabilisation de complexes métalliques sous-coordinés dont les centres métalliques sont hautement insaturés électroniquement et donc potentiellement le siège d'une réactivité inhabituelle. Dans les deux cas, nous évoquerons la pertinence de ces approches en catalyse homogène.

Synthesis and Reactivity of NHC‐Stabilized Iron(II)–Mesityl Complexes

“…Formation of complexes of the type [Fe(R 2 Im) 2 Mes 2 ] was never observed using these NHCs for synthesis (Scheme ). Using these methods, the complexes [Fe(Me 2 Im)Mes 2 ] 4 , [Fe( i Pr 2 Im)Mes 2 ] 5 , [Fe( t Bu 2 Im)Mes 2 ] 6 , [Fe(Dipp 2 Im)Mes 2 ] 7 , and [Fe(Dipp 2 ImH 4 )Mes 2 ] 8 were synthesized in good‐to‐excellent yields, and they were isolated in the form of colorless microcrystalline powders. Compound 6 is highly soluble in toluene, whereas compounds 4 , 5 , 7 , and 8 only sparingly dissolve in this solvent.…”

“…of [Fe(NHC) [5a] We found it convenient to synthesize complexes of the type [Fe(NHC)Mes 2 ] for the small NHCs Me 2 Im and iPr 2 Im via ligand exchange between [Fe(NHC) 2 Mes 2 ] and [Fe 2 Mes 4 ] (Scheme 3), which has the advantages that: (i) the yields are much higher using this procedure; and (ii) this route seems to be quite general for a number of carbenes. Thus, the three-coordinate complexes [Fe(R 2 [6] and [Fe(Dipp 2 ImH 4 )Mes 2 ] 8 [14] were synthesized in good-to-excellent yields, and they were isolated in the form of colorless microcrystalline powders. Compound 6 is highly soluble in toluene, whereas compounds 4, 5, 7, and 8 only sparingly dissolve in this solvent.…”

“…The magnetic moment of [Fe(iPr 2 Im) 2 -(SPh) 2 ] 14 (5.16 μ B ) in solution is slightly higher than that, but is still in a region that accounts for a tetrahedral iron(II) complex with an S = 2 ground state. Single crystals suitable for X-ray diffraction were grown from saturated toluene solutions at -30°C (12, 13) or at room temperature (14). Complex 12 crystallizes in the monoclinic space group P2 1 /c, with one molecule in the asymmetric unit.…”

“…Molecular structure of [Fe(iPr 2 Im) 2 (μ 2 -H) 3 (3), Si2-H102 1. 45(2), Si2-H103 1.75 (3), Si2-H104 1.94 (3), Si2-H105 1.82 (3); C1-Fe-C11 92.36(10), C1-Fe-Si1 112.09(8), C1-Fe-Si2 117.32 (7), C11-Fe-Si1 89.61(8), C11-Fe-Si2 117.32 (7), Si1-Fe-Si2 109.98(4), C1-Fe-H103 88.7(12), C1- , C1-Fe-H105 87.7(10), C11-Fe-H103 95.0(12), C11- , C11-Fe-H105 171.3(10), H103-Fe-H104 88.1(16), H103- , H104-Fe-H105 92.1 (14), Si1-Fe-H103 158.5(12), Si1-Fe-H104 71.0(11), Si1-Fe-H105 82.3(10), Si2-Fe-H103 52.5(12), Si2-Fe-H104 60.1 (11) [30] [Fe(PMe 2 Ph)(CO) 3 (H)(SiPh 3 )] [2.3564(6) Å], [30] or in complexes of the type [(η 5 -C 5 R 5 )Fe(CO) 2 (SiPh 3 )] (2. 33-2.35 Å).…”

“…Hydrogen atoms have been omitted for clarity. Selected bond lengths [Å] and angles [°]: Fe-C11 2.133(4), Fe-O1 1.801(3), Fe-O1′ 1.793(3), Fe-O3 1.884(3); C11-Fe-O1 106.87(15), C11-Fe-O1′ 108.63(16), C11-Fe-O3 105.42(15), C21-O3-Fe 136.4(3), O1-Fe-O1′ 116.98(17), O1-Fe-O3 104.76(14), O1′-.…”