Correlation of Metal Spin State with Catalytic Reactivity: Polymerizations Mediated by α‐Diimine–Iron Complexes

Shaver, Michael P.; Allan, Laura E. N.; Rzepa, Henry; Gibson, Vernon C.

doi:10.1002/ange.200502985

Cited by 16 publications

(13 citation statements)

References 21 publications

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“…An important example is provided by the complexes in Scheme 3, which are highly active pre-catalysts for the polymerization of styrene [13]. Activation of the complexes with (2-chloroethyl)benzene affords five-coordinate iron(III) active catalysts [LFeCl 2 (C 2 H 4 Ph)], where L is the α-diimine chelate.…”

Section: Methodsmentioning

confidence: 99%

“…Such considerations can also have a bearing on organometallic catalysis, where first-row transition ions are increasingly playing a role [12]. An important example is provided by the complexes in Scheme 3, which are highly active pre-catalysts for the polymerization of styrene [13]. Activation of the complexes with (2-chloroethyl)benzene affords five-coordinate iron(III) active catalysts [LFeCl2(C2H4Ph)], where L is the α-diimine chelate.…”

Section: Methodsmentioning

confidence: 99%

“…In contrast, the five-coordinate activated species formed from B have a reduced, intermediate spin state (S = 3 /2). This strongly disfavors atom transfer chemistry, leading to a much slower catalytic chain transfer process yielding low molecular-weight polymer product [13]. The difference is caused by the inductive effect of the ligand phenyl substituents in B, which promote iron→diimine back bonding sufficiently to induce a spin state flip [14].…”

Section: Methodsmentioning

confidence: 99%

“…Structures of alkene polymerization pre-catalysts that proceed by rapid atom radical transfer polymerization (A) or a slow chain transfer reaction (B; R = cyclohexyl or tertbutyl) [13].…”

Section: Methodsmentioning

confidence: 99%

“…While it is well understood how factors such as metal oxidation state and coordination geometry control Δoct and spin state (see Scheme 3. Structures of alkene polymerization pre-catalysts that proceed by rapid atom radical transfer polymerization (A) or a slow chain transfer reaction (B; R = cyclohexyl or tertbutyl) [13].…”

Section: Methodsmentioning

confidence: 99%

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The Effect of Ligand Design on Metal Ion Spin State—Lessons from Spin Crossover Complexes

2016

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Abstract:The relationship between chemical structure and spin state in a transition metal complex has an important bearing on mechanistic bioinorganic chemistry, catalysis by base metals, and the design of spin crossover materials. The latter provide an ideal testbed for this question, since small changes in spin state energetics can be easily detected from shifts in the spin crossover equilibrium temperature. Published structure-function relationships relating ligand design and spin state from the spin crossover literature give varied results. A sterically crowded ligand sphere favors the expanded metal-ligand bonds associated with the high-spin state. However, steric clashes at the molecular periphery can stabilize either the high-spin or the low-spin state in a predictable way, depending on their effect on ligand conformation. In the absence of steric influences, the picture is less clear since electron-withdrawing ligand substituents are reported to favor the low-spin or the high-spin state in different series of compounds. A recent study has shed light on this conundrum, showing that the electronic influence of a substituent on a coordinated metal ion depends on its position on the ligand framework. Finally, hydrogen bonding to complexes containing peripheral N-H groups consistently stabilizes the low-spin state, where this has been quantified.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…Structures of alkene polymerization pre-catalysts that proceed by rapid atom radical transfer polymerization (A) or a slow chain transfer reaction (B; R = cyclohexyl or tertbutyl) [13].…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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The Effect of Ligand Design on Metal Ion Spin State—Lessons from Spin Crossover Complexes

2016

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Einelektronenreaktionen von Übergangsmetallkomplexen in der radikalischen Polymerisation

Poli

2006

Angewandte Chemie

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Kontrollierte radikalische Polymerisationen sind vor allem dank der Entwicklung effizienter Übergangsmetallkatalysatoren für die radikalische Atomtransferpolymerisation möglich geworden. Eine weitere Methode zur kontrollierten radikalischen Polymerisation ist die metallorganische Radikalpolymerisation, bei der es zur reversiblen Bildung von Metall‐Kohlenstoff‐Bindungen kommt. Übergangsmetallkomplexe können außerdem katalytische Kettentransfers bewirken, einen Prozess, der unter Abstraktion von Wasserstoffatomen verläuft. Dieser Kurzaufsatz diskutiert die Rolle von Einelektronenreaktionen von Übergangsmetallkomplexen bei metallvermittelten kontrollierten radikalischen Polymerisationen.

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A Unified Treatment of the Relationship Between Ligand Substituents and Spin State in a Family of Iron(II) Complexes

et al. 2016

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The influence of ligands on the spin state of ametal ion is of central importance for bioinorganic chemistry,and the production of base-metal catalysts for synthesis applications. Complexes derived from [Fe(bpp) 2 ] 2+ (bpp = 2,6-di{pyrazol-1-yl}pyridine) can be high-spin, low-spin, or spin-crossover (SCO) active depending on the ligand substituents.Plots of the SCO midpoint temperature (T1 = 2 )i ns olution vs.t he relevant Hammett parameter showt hat the low-spin state of the complex is stabilized by electron-withdrawing pyridyl ("X") substituents,b ut also by electron-donating pyrazolyl ("Y") substituents.M oreover,w hen as ubset of complexes with halogeno Xo rYs ubstituents is considered, the two sets of compounds instead show identical trends of asmall reduction in T1 = 2 for increasing substituent electronegativity.D FT calculations reproduce these disparate trends,w hich arise from competing influences of pyridyl and pyrazolyl ligand substituents on Fe-L s and p bonding.The ability of first-row transition ions to adopt different spin states in strong or weak ligand fields is of great importance to their catalysis and reactivity. [1][2][3] Fore xample,f undamental mechanistic steps in biological and synthetic oxidation catalysis involve ac hange in spin state at an iron catalyst center, described as two-state reactivity.[3] Catalysts with different resting spin states follow different pathways through these two-state processes,l eading to altered reactivity and product distributions.[4] Similar considerations also apply for "base-metal" catalysts for organometallic reactions, [5] which give access to high-spin active species with different reactivity patterns compared to conventional precious-metal catalysts. [6,7] Another consequence of spin-state dichotomy is the phenomenon of spin crossover (SCO), where am olecular or framework compound exhibits atransition between high-and low-spin states under aphysical stimulus. [8,9] SCO compounds have been developed into versatile molecular switches for molecular materials chemistry and nanoscience. [9,10] Ther elationship between chemical structure and spin state is central to these phenomena. [2,11] Asterically crowded ligand sphere generally leads to high-spin complexes. [12] However,t he effect of ligand electronic character on metalion spin state is less clear-cut, with electron-withdrawing substituents being reported to stabilize either the lowspin [13][14][15][16] or the high-spin state [17,18] in different series of compounds.W hile the literature includes data from solution and the solid-state,t hese effects are best quantified by solution measurements which determine ac omplexs spin state in the absence of crystal-packing effects or any other influences from ar igid solid lattice. [19] We report herein ac omprehensive study to resolve this contradiction, through as urvey of twenty-five complexes from the [Fe(bppfamily (bpp X,Y = a2 ,6-di(pyrazol-1-yl)pyridine derivative; Scheme 1).[20] Our results show that substituents at the X and Ysites ...

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Correlation of Metal Spin State with Catalytic Reactivity: Polymerizations Mediated by α‐Diimine–Iron Complexes

Cited by 16 publications

References 21 publications

The Effect of Ligand Design on Metal Ion Spin State—Lessons from Spin Crossover Complexes

The Effect of Ligand Design on Metal Ion Spin State—Lessons from Spin Crossover Complexes

Einelektronenreaktionen von Übergangsmetallkomplexen in der radikalischen Polymerisation

A Unified Treatment of the Relationship Between Ligand Substituents and Spin State in a Family of Iron(II) Complexes

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