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Ligand Topology Effects on Olefin Oxidations by Bio‐Inspired [Fe II (N 2 Py 2 )] Catalysts
Author(s) -
MasBallesté Rubén,
Costas Miquel,
van den Berg Tieme,
Que Lawrence
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200600453
Subject(s) - catalysis , topology (electrical circuits) , chemistry , ligand (biochemistry) , olefin fiber , stereochemistry , dihydroxylation , octahedron , trifluoromethanesulfonate , medicinal chemistry , crystallography , crystal structure , enantioselective synthesis , organic chemistry , combinatorics , receptor , mathematics , biochemistry
Linear tetradentate N 2 Py 2 ligands can coordinate to an octahedral Fe II center in three possible topologies ( cis ‐α, cis ‐β, and trans ). While for the N,N′ ‐bis(2‐pyridylmethyl)‐1,2‐diaminoethane (bpmen) complex, only the cis ‐α topology has been observed, for N,N′ ‐bis(2‐pyridylmethyl)‐1,2‐diaminocyclohexane (bpmcn) both cis ‐α and cis ‐β isomers have been reported. To date, no facile interconversion between cis ‐α and cis ‐β topologies has been observed for iron(II) complexes even at high temperatures. However, this work provides evidence for facile interconversion in solution of cis ‐α, cis ‐β, and trans topologies for [Fe(bpmpn)X 2 ] (bpmpn= N,N′ ‐bis(2‐pyridylmethyl)‐1,3‐diaminopropane; X=triflate, CH 3 CN) complexes. As reported previously, the catalytic behavior of cis ‐α and cis ‐β isomers of [Fe(bpmcn)(OTf) 2 ] with respect to olefin oxidation depends dramatically on the geometry adopted by the iron complex. To establish a general pattern of the catalysis/topology dependence, this work presents an extended comparison of the catalytic behavior for oxidation of olefins of a family of [Fe(N 2 py 2 )] complexes that present different topologies. 18 O labeling experiments provide evidence for a complex mechanistic landscape in which several pathways should be considered. Complexes with a trans topology catalyze only non‐water‐assisted epoxidation. In contrast, complexes with a cis ‐α topology, such as [Fe(bpmen)X 2 ] and [Fe(α‐bpmcn)(OTf) 2 ], can catalyze both epoxidation and cis ‐dihydroxylation through a water‐assisted mechanism. Surprisingly, [Fe(bpmpn)X 2 ] and [Fe(β‐bpmcn)(OTf) 2 ] catalyze epoxidation via a water‐assisted pathway and cis ‐dihydroxylation via a non‐water‐assisted mechanism, a result that requires two independent and distinct oxidants.