Disparate reactivity from isomeric {Me 2 C(CH 2 N CHpy) 2 } and {Me 2 C(CH NCH 2 py) 2 } chelates in iron complexation

Hulley, Elliott B.; Williams, Valerie A.; Morris, Wesley D.; Wolczanski, Peter T.; Hernández‐Burgos, Kenneth; Lobkovsky, Emil; Cundari, Thomas R.

doi:10.1016/j.poly.2014.07.039

Cited by 8 publications

(11 citation statements)

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“…Subsequent dimerization via attack of the nucleophilic eneamide on the electrophilic imine of another titanium intermediate would lead directly to 3 . Related nucleophile/electrophile couplings of 1,3-di-(2-pyridyl)-2-azaallyl (smif) constituents and others − have been postulated as nonradical alternatives in the C–C bond forming steps illustrated in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…Carbon–carbon bond formation is often a consequence of redox noninnocence (RNI) that induces radical character in certain ligands. − In many cases, a relatively simple coupling of carbon radicals occurs to form a single new bond, but sometimes the reactivity can be complicated. Figure illustrates some unusual C–C bond forming events discovered in these laboratories. − In A , the Ti(III) complex, (smif){Li(smif–smif)}Ti, was shown to contain one C–C bond derived from coupling of smif (smif = 1,3-di(2-pyridyl)-2-azaallyl) ligands that were reduced during the course of its synthesis. One mode of its decomposition generated dimer [(smif 2– )Ti III ] 2 (μ-κ 3 ,κ 3 - N , N (py) 2 -smif,smif), which contained two new C–C bonds that can be construed as arising from coupling of a singlet diradical, or alternatively, a nucleophile/electrophile coupling .…”

Section: Introductionmentioning

confidence: 98%

“…Five-membered eneamide rings are generated from coupling of 1,3-di(2-pyridyl)-2-azaallyl components of the original chelate concomitant with dehydrogenation. Perhaps the most intriguing example is found in D , where attempts at chelation of M(II) diamides with Me 2 C(CHNCH 2 –py) 2 led to the creation of 3 new C–C bonds, a metal–metal bond, and six new stereocenters as {Me 2 C(CHNCH-py) 2 }M 2 (M = Cr, Co, Ni) were formed. , …”

Section: Introductionmentioning

confidence: 99%

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Oxidative Additions to Ti(IV) in [(dadi)^4–]Ti^IV(THF) Involve Carbon–Carbon Bond Formation and Redox-Noninnocent Behavior

et al. 2019

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An attempt at transferring the imide of (dadi)TiNAd (2NAd, dadi 2− , dadia product that features four new C−C bonds to two new carbons. Mechanistic evaluation of its formation led to oxidative addition studies of SnX 4 (X = Cl, Br, I) and RX to (dadi)Ti(THF) (1-THF, dadi 4− ), in which the oxidation occurs at the dadi ligand. Products include (dadi)TiX 2 (2-X 2 , X = Cl, Br, I) and the imine-triamide (R-ita)TiX (5-RX, R = Me, Bn; X = Cl, Br; Rita = [{−CH 2 N(1,2-C 6 H 4 )N(2,6-i Pr 2 -C 6 H 3 )}{CRN(1,2-C 6 H 4 )N(2,6-i Pr 2 -C 6 H 3 )}]). Studies of the RX additions, including implementation of radical clocks, pointed toward concerted process(es). Rearrangements of 2-X 2 and 2NAd revealed a new tridentate benzimidazole diamide chelate (bida) structurally characterized in (bida)TiCl 2 (4-Cl 2 ) and (bida)TiNAd (OPMe 2 Ph) (6). The nature of various products suggests that the (dadi n )Ti core can act as a nucleophile (n = 4), electrophile (n = 2), or as a radical center (n = 3) under certain conditions.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Oxidative Additions to Ti(IV) in [(dadi)^4–]Ti^IV(THF) Involve Carbon–Carbon Bond Formation and Redox-Noninnocent Behavior

et al. 2019

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“…35 Incorporating PI precursors into a nacnac framework 36−39 permitted the isolation of carbon radical character, leading to C−C bond formation (C), 40 but in related tetradentate ligands, electrostatic stabilization of a 14e − π-system afforded very stable Fe(II) complexes (D). 41,42 Finally, a tetradentate di-PI ligand revealed five redox states (E) that were quite stable, while the metal formally remained Ni(II). 6 The successful implementation of 2-azaallyls 34, 35,40,43 in bondforming processes 44−47 prompted an investigation into corresponding 1-azaallyls, 15,46−49 recognizing that such entities are ene-amides that can be readily prepared via condensation routes.…”

Section: ■ Introductionmentioning

confidence: 99%

First-Row Transition Metal and Lithium Pyridine-ene-amide Complexes Exhibiting N- and C-Isomers and Ligand-Based Activation of Benzylic C–H Bonds

et al. 2015

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Ene-amines Z-3-(2-pyridyl)-1-aza(2,6-i Pr 2 -Ph)propene, (pynac)H, and 2-(2-pyridyl)-1-aza(2,6-R,R′-Ph)propene, (pyEA-ArRR′)H, were synthesized by condensation procedures; corresponding lithium or potassium ene-amides were prepared via standard deprotonation protocols. Addition of 2 equiv of (pynac)H to {(Me 3 Si) 2 N} 2 Fe(THF) or 2 Li(pynac) to FeBr 2 (THF) 2 afforded (pynac) 2 Fe (1), while treatment of CrCl 2 (THF) 2 , MnCl 2 , FeBr 2 (THF) 2 , and CoCl 2 py 4 with 2 equiv of (pyEAAr i Pr 2 )K afforded pseudotetrahedral (pyEA-Ar i Pr 2 ) 2 M (2-M, M = Cr, Mn, Fe) and (pyEA-Ar i Pr 2 ) 2 Co-py (2-Co-py). Diamagnetic (κ-C,N-pyEA-Ar i Pr 2 ) 3 Co (3) was prepared in low yield (∼7%) from CoCl 2 , and its Co−C(sp 3 ) linkages are unusually low in field strength. Reactivity studies yielded little clean reactivity, but thermolysis of 2-Co-py afforded the bis-indolamide derivative {κ-N,N-N(C 6 H 3 (2-i Pr)CMe 2 C(Me)(2-py)} 2 Co (5-Co), and related thermolyses of 2-M (M = Cr, Mn, Fe), conducted on NMR tube scales, generated related 5-M (M = Cr, Mn, Fe) at roughly the same rates. This observation prompted thermolyses of (pyEA-ArRR′)Li, which rearrange to their corresponding indolamides in >90% yields. Rate studies, accompanied by KIE and EIE observations, revealed that an initial hydrogen transfer is reversible and is likely to correspond to an anionic rearrangement, whereas C−C bond formation is ratedetermining, as suggested by accompanying calculations. X-ray structure determinations of 1, 2-Fe, 2-Co-py, 3, and 5-Co were conducted. ■ INTRODUCTIONTransition metal compounds containing pyridine-imine (PI) 1−6 and pyridine-diimine (PDI) 7−19 moieties often exhibit redox noninnocent (RNI) 20−29 behavior due to multiple accessible charged states of the ligands. This capacity is most evident in first-row transition metals, where the ionic character of the metal−ligand bond limits charge distribution via covalency, and in early transition metals 29−32 that have limited redox capability. Ligands designed as PI variants consisting of 2-azaallyls, their precursors, or related chelates have led to intriguing carbon− carbon and C−X bond-forming reactions and afford examples of RNI, as illustrated in Figure 1.Compounds containing 1,3-di-2-pyridyl-2-azaallyl (smif) 33 tridentate ligands exhibit reversible and irreversible C−C bondforming reactions depending on steric factors (A), 34 while the generation of transient azaallyls within a tetradentate chelate have afforded [{Me 2 C(CHNCH-2-py) 2 }M] 2 (M = Cr, Co, Ni) dimers wherein three new carbon−carbon bonds have been formed around unique metal−metal bonds (B). 35 Incorporating PI precursors into a nacnac framework 36−39 permitted the isolation of carbon radical character, leading to C−C bond formation (C), 40 but in related tetradentate ligands, electrostatic stabilization of a 14e − π-system afforded very stable Fe(II) complexes (D). 41,42 Finally, a tetradentate di-PI ligand revealed five redox states (E) that were quite stable, while the metal formally remained Ni(II). 6 The s...

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“…The formation of a cyclopropanated backbone of (dadi) n suggested that reversible C–C bond formation could be a means of storing and releasing electrons in a redox noninnocent (RNI) fashion. ,− A possible hindrance to RNI is the transfer of a cyclopropane hydrogen subsequent to ring-opening, which would generate a nacnac fragment in place of the original diimine. The reactivity of {PhC 3 H 3 (-NC 6 H 4 -2-NAr) 2 }Ti(THF) ( 3 ) was probed via various potential oxidants and proton acceptors, and while most generated mixtures, the addition of Ph 2 CN 2 yielded a single product (>90%) that was dissymmetric.…”

Section: Resultsmentioning

confidence: 99%

Complexes of [(dadi)Ti(L/X)]^m That Reveal Redox Non-Innocence and a Stepwise Carbene Insertion into a Carbon–Carbon Bond

et al. 2018

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Disparate reactivity from isomeric {Me 2 C(CH 2 N CHpy) 2 } and {Me 2 C(CH NCH 2 py) 2 } chelates in iron complexation

Cited by 8 publications

References 64 publications

Oxidative Additions to Ti(IV) in [(dadi)^4–]Ti^IV(THF) Involve Carbon–Carbon Bond Formation and Redox-Noninnocent Behavior

Oxidative Additions to Ti(IV) in [(dadi)^4–]Ti^IV(THF) Involve Carbon–Carbon Bond Formation and Redox-Noninnocent Behavior

First-Row Transition Metal and Lithium Pyridine-ene-amide Complexes Exhibiting N- and C-Isomers and Ligand-Based Activation of Benzylic C–H Bonds

Complexes of [(dadi)Ti(L/X)]^m That Reveal Redox Non-Innocence and a Stepwise Carbene Insertion into a Carbon–Carbon Bond

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Disparate reactivity from isomeric {Me 2 C(CH 2 N CHpy) 2 } and {Me 2 C(CH NCH 2 py) 2 } chelates in iron complexation

Cited by 8 publications

References 64 publications

Oxidative Additions to Ti(IV) in [(dadi)4–]TiIV(THF) Involve Carbon–Carbon Bond Formation and Redox-Noninnocent Behavior

Oxidative Additions to Ti(IV) in [(dadi)4–]TiIV(THF) Involve Carbon–Carbon Bond Formation and Redox-Noninnocent Behavior

First-Row Transition Metal and Lithium Pyridine-ene-amide Complexes Exhibiting N- and C-Isomers and Ligand-Based Activation of Benzylic C–H Bonds

Complexes of [(dadi)Ti(L/X)]m That Reveal Redox Non-Innocence and a Stepwise Carbene Insertion into a Carbon–Carbon Bond

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Oxidative Additions to Ti(IV) in [(dadi)^4–]Ti^IV(THF) Involve Carbon–Carbon Bond Formation and Redox-Noninnocent Behavior

Oxidative Additions to Ti(IV) in [(dadi)^4–]Ti^IV(THF) Involve Carbon–Carbon Bond Formation and Redox-Noninnocent Behavior

Complexes of [(dadi)Ti(L/X)]^m That Reveal Redox Non-Innocence and a Stepwise Carbene Insertion into a Carbon–Carbon Bond