Fe(<scp>iv</scp>) alkylidenes via protonation of Fe(<scp>ii</scp>) vinyl chelates and a comparative Mössbauer spectroscopic study

Lindley, Brian M.; Swidan, Ala’aeddeen; Lobkovsky, Emil; Wolczanski, Peter T.; Adelhardt, Mario; Sutter, Jörg; Meyer, Karsten

doi:10.1039/c5sc01268f

Cited by 45 publications

(37 citation statements)

References 43 publications

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“…Recent reevaluation of literature discounts the possibilityo f iron(IV)f or porphyrin complexesa nd other conjugatedl igand platforms. [58][59][60][61][62] In contrast, for tetracarbene ligand platforms, we and others have shownt hat high oxidation states on iron are possible, with examples of isolatedm etallotetrazenes, imides,a nd oxos. [20,38,63] To help confirm the oxidation state on 9 we employed electrochemistry.C omparisons of the electrochemistry of molecules 6, 7 and 9 are shown below each crystal structure (Figures 2, 3a nd 5, bottom).…”

Section: Resultsmentioning

confidence: 84%

A Chiral Macrocyclic Tetra‐N‐Heterocyclic Carbene Yields an “All Carbene” Iron Alkylidene Complex

DeJesus

Jenkins

2020

Chemistry A European J

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The first chiral macrocyclic tetra-N-heterocyclic carbene (NHC) ligand has been synthesized. The macrocycle, prepared in high yield andl arge scale,w as ligatedo ntop alladium and iron to give divalent C 2 -symmetric square planar complexes. Multinuclear NMR and single crystal X-ray diffraction demonstrated that there are two distinct NHCs on each ligand,d ue to the bridging chiral cyclohexane. Oxidationo f the iron(II) complex with trimethylamine N-oxide yielded a bridgingo xo complex.D iazodiphenylmethane reactedwith the iron(II) complex at room temperature to give ap aramag-netic diazoalkane complex;t he same reaction yieldedt he "all carbene" complexa te levated temperature. Electrochemical measurements support the assignment of the "all carbene"c omplex being an alkylidene. Notably,t he diazoalkane complex can be directly transformed into the alkylidene complex, which had not been previously demonstrated on iron. Finally,atest catalytic reactionw ithad iazoalkane on the iron(II) complex does not yield the expected cyclopropane,b ut actually the azine compound.[a] Dr.

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Section: Resultsmentioning

confidence: 84%

A Chiral Macrocyclic Tetra‐N‐Heterocyclic Carbene Yields an “All Carbene” Iron Alkylidene Complex

DeJesus

Jenkins

2020

Chemistry A European J

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“…4, and pertinent metrics are listed in the caption. The Fe-C(vinyl) distance of 1.961(2) Å is ≥0.06 Å longer than related "Fe=C" bonds in previously analyzed alkylidene cations, [7] and ≥0.06…”

Section: Treatment Of Cis-(mementioning

confidence: 69%

“…The electronic structure of mer-{ 3 bond. The three lowest energy orbitals are the standard "t 2g " set of an octahedral species, i.e., an absorption at 2116 cm -1 corresponding to the (NN) stretch, [7,23] consistent with a cationic center, and a singlet at  9.10 in the 31 P NMR spectrum, indicative of C s symmetry.…”

Section: Electronic Structure Of Mer-{ 3 -Nnc-(2-pyridyl)chnchchchmentioning

confidence: 99%

“…In the course of investigating Fe(IV) alkylidenes in these laboratories, [7,8] metathesis or cyclopropanation was observed. [7] In first row transition metal cationic complexes, the 3d orbitals can be contracted to the extent that metal-ligand multiple bonding is diminished. As a consequence, neutral iron alkylidenes were produced via nucleophilic attack at the imines of cation 1 (4-R), including several with a pendant side-arm (5-R,R').…”

Section: Introductionmentioning

confidence: 99%

“…One obvious disparity between complexes that enable olefin metathesis, and those in Scheme 1, are the substituents on the alkylidenes. Virtually every metal-carbon double bond that reacts with an olefin is of the type M=C(H)R. [14] In this manuscript, attempts at generating iron alkylidenes with hydrogen substituents are described, and two of the alkylidenes in Scheme 1, cation [mer-{-C,N,C-(2-C 6 H 4 )CH=N(1,2-C 6 H 4 )C( i Pr)=}Fe(PMe 3 ) 3 ][BAr F 4 ] (1, BAr F 4 -= [B(3,5-(CF 3 ) 2 -C 6 H 3 ) 4 ] -), [7] and neutral mer-{-C,N,C-(2-C 6 H 4 )CH(Bn)N(1,2-C 6 H 4 )C( i Pr)=}Fe(PMe 3 ) 3 (4-Bn) [8] are evaluated via computation. In addition, an unusual dianionic chelate was found to distribute charge rather than form an Fe(II) alkylidene, as a testament to Hoffmann's calculations, [6] and the ability of pyridine-imine/azaallyl species to stabilize charge.…”

Section: Introductionmentioning

confidence: 99%

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Fe(IV) alkylidenes are actually Fe(II), and a related octahedral Fe(II) “alkylidene” is a conjugated vinyl complex

et al. 2016

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Electronic structure calculations on previously synthesized [mer-{-C,N,C-(2-C 6 H 4)CH=N(1,2-C 6 H 4)C(i Pr)=}Fe(PMe 3) 3 ][BAr F 4 ] (1) and mer,trans-{-C,N,C-(2-C 6 H 4)CH(Bn)N(1,2-C 6 H 4)C(i Pr)=}Fe(PMe 3) 2 N 2 (4-Bn) reveal that 1 is best interpreted as Fe(II) bound to a carbenium ion, while 4-Bn has an iminovinyl unit bound to a ferrous center. Attempts to prepare L n Fe=CHR species capable of olefin metathesis or carbene transfer were obviated by alternative reactivity, although precursors mer,trans-{ 3-N,N,C-(2-py)CH=NCH 2 CH=CH}Fe(PMe 3) 2 CH 3 (6), [mer,trans-{ 3-N,N,C-2-py-CH=NCH 2 CH=CH}Fe(PMe 3) 2 CH 3 ] [PF 6-] (8 +), mer,trans-{ 3-N,N,C-2-py-CH=NCH 2 CH=CH}Fe(PMe 3) 2 I (9), mer-{ 3-N,N,C-(2-pyridyl) CHNCHCHCH}Fe(PMe 3) 3 (11), and mer-{ 3-C,N,C-(2-C 6 H 4)CH=NCH 2 CH=CH}Fe(PMe 3) 3 (12) were prepared. Related phenyl derivatives, mer,trans-{ 3-N,N,C-(2-py)CH=NC(Me) 2 CH=CH} Fe(PMe 3) 2 CH 3 (13) and [mer,trans-{ 3-N,N,C-(2py)CH=NC(Me) 2 CH=CH}Fe(PMe 3) 2 N 2 ][BAr F 4 ] (15) were prepared to test additional stability issues. Compounds 9 and 11 were structurally characterized, and metrical parameters of the latter, in addition to electronic structure calculations, suggest that it is not an alkylidene, but an Fe(II) center coordinated by a conjugated vinyl ligand with extensive delocalization in its -system.

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Two Exceptional Homoleptic Iron(IV) Tetraalkyl Complexes

et al. 2017

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The formation of the high-valent iron complex [Fe(cyclohexyl) 4 ]f rom Fe II under reducing conditions is best explained by disproportionation of at ransient organoiron intermediate which is driven by dispersive forces between the cyclohexyl ligands and the formation of short and strong Fe À C bonds.The (meta)stability of this diamagnetic complex (S = 0) is striking if one considers that it has empty d-orbitals at its disposal and contains,atthe same time,noless than twenty Hatoms available for either a-orb-hydride elimination.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: http://dx.

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Fe(iv) alkylidenes via protonation of Fe(ii) vinyl chelates and a comparative Mössbauer spectroscopic study

Abstract: Fe(iv) alkylidenes are produced via protonation of Fe(ii) vinyl chelate complexes.

Cited by 45 publications

References 43 publications

A Chiral Macrocyclic Tetra‐N‐Heterocyclic Carbene Yields an “All Carbene” Iron Alkylidene Complex

A Chiral Macrocyclic Tetra‐N‐Heterocyclic Carbene Yields an “All Carbene” Iron Alkylidene Complex

Fe(IV) alkylidenes are actually Fe(II), and a related octahedral Fe(II) “alkylidene” is a conjugated vinyl complex

Two Exceptional Homoleptic Iron(IV) Tetraalkyl Complexes

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