Simplifying Iron–Phosphine Catalysts for Cross‐Coupling Reactions

Abstract

COGSWELL, P. M.; GOWER, N. J.; HADDOW, M. F.; HARVEY, J. N.; MURPHY, D. M.; NEEVE, E. C.; NUNN, J.; Angew. Chem., Int. Ed. 52 (2013) 4, 1285-1288, http://dx.doi.org/10.1002/anie.201207868 ; Sch. Chem., Univ. Bristol, Cantock's Close, Bristol BS8 1TS, UK; Eng.) -Roessler 23-030

Reactivity of [Ge9{Si(SiMe3)3}3]− Towards Transition‐Metal M2+ Cations: Coordination and Redox Chemistry

“…However, 2 is the first compound with an open electronic shell,i ndicating that the arrangement seemsf avorable irrespectivei fa ne lectronically open-or closed-shells ystem is present. For example, Fe + in its phosphine complexes was studied ast he active speciesinc ross-coupling reactions, [16] [Co(PPh 3 ) 3 Cl] was used as ac atalystf or cyclic dimerization of butadiene, [17] and [Ni(PPh 3 ) 3 Cl] catalyzest he isomerization of 1-pentene. The GeÀMn bonds vary between 276.79(3)pma nd 278.65(3)pma nd are thus longert han am anganese germanium single bond of 241.3 pm as found in [(CF 3 ) 3 GeÀMn(CO) 5 ], [13] which can be traced back to the high coordination number of six of the central manganese atom in 2.…”

Iron Pincer Complexes as Catalysts and Intermediates in Alkyl–Aryl Kumada Coupling Reactions

“…This is due to the strong chelating ability of the tridentate pincer ligand Bopa which, in turn, facilitates the mechanistic study. As in the Fe-TMEDA system for the coupling of less bulky Grignard reagent, the Fe(I) species (16) 19,20 and alkyl-alkyl Kumada coupling. 21 These Fe(I) species are supported by soft, neutral donors such as phosphine and N-heterocyclic carbene ligands which match well with the low-valent Fe(I) center.…”

The Role of Low Valent Transition Metal Complexes in Homogeneous Catalysis: An EPR Investigation

“…The [Fe(Bpin)(dpbz) 2 ] complex showed poor activity as a catalyst in the coupling of alkyl halides with Li[(B 2 pin 2 ( t Bu)], suggesting that it is not an active catalyst, but rather converts in solution to an active species upon reaction with the borate ion. In a similar fashion to the inverse first-order dependence on the diphosphine concentration reported above for reactions catalyzed by [FeBr(dppe) 2 ], additional equivalents of ligand had a highly deleterious effect on the [8,9,40]. Copyright (2015) American Chemical Society reaction rate using the Li[(B 2 pin 2 ( t Bu)] ion, thereby indicating that the active species is diphosphine-free.…”

“…Furthermore, the corresponding analogues based on the simpler bis(diphenylphosphino)-ethane (dppe) ligand, labelled [FeX(dppe) 2 ] (X = Cl, Br; Fig. 2d), also demonstrated excellent activity in reactions [9] where previously only dpbz catalysts had been found to be optimal. These results challenged the idea that dpbz is an electronically privileged ligand [36][37][38][39], and highlighted the requirement to develop a thorough understanding of the basic mechanisms of iron catalyzed C-C coupling reactions.…”

“…For a number of years we have exploited a number of advanced EPR and hyperfine based techniques to explore the structure-function relationships in transition metal based homogeneous catalysis, including Fe(I) for catalytic C-C bond formation [8,9], Cr(I) for ethylene oligomerisation [10], Co(II) for hydrolytic kinetic resolution [11], Ni(I) for cross coupling reactions [12] and Cu(II) for asymmetric aziridination [13]. We have demonstrated how the EPR approach can be used not only to identify the key oxidation states involved in these reactions, but also how the technique can help to unravel the complementary role of the ligands in controlling the selectivity and stability of the intermediates formed.…”