A regioselectively 1, 1',3 ,3'-tetrazincated ferrocene complex displaying core and peripheral reactivity

Regioselective 1,1′,3,3′-tetrazincation [C-H to C-Zn(tBu)] of ferrocene has been achieved by reaction of a fourfold excess of di-t-butylzinc (tBu2Zn) with sodium 2,2,6,6-tetramethylpiperidide (NaTMP) in hexane solution manifested in the trimetallic iron-sodium-zinc complex [Na4(TMP)4Zn4(tBu)4{(C5H3)2Fe}], 1. X-ray crystallographic studies supported by DFT modelling reveal the structure to be an open inverse crown in which two [Na(TMP)Zn(tBu)Na(TMP)Zn(tBu)]2+ cationic units surround a {(C5H3)2Fe}4- tetraanion. Detailed C6D6 NMR studies have assigned the plethora of 1H and 13C chemical shifts of this complex. It exists in a major form in which capping and bridging TMP groups interchange, as well as a minor form that appears to be an intermediate in this complicated exchange phenomenon. Investigation of 1 has uncovered two distinct reactivities. Two of its peripheral t-butyl carbanions formally deprotonate toluene at the lateral methyl group to generate benzyl ligands that replace these carbanions in [Na4(TMP)4Zn4(tBu)2(CH2Ph)2{(C5H3)2Fe}], 2, which retains its tetrazincated ferrocenyl core. Benzyl-Na π-arene interactions are a notable feature of 2. In contrast, reaction with pyridine affords the crystalline product {[Na·4py][Zn(py∗)2(tBu)·py]}∞, 3, where py is neutral pyridine (C5H5N) and py∗ is the anion (4-C5H4N), a rare example of pyridine deprotonated/metallated at the 4-position. This ferrocene-free complex appears to be a product of core reactivity in that the core-positioned ferrocenyl anions of 1, in company with TMP anions, have formally deprotonated the heterocycle

Anionic polymerisation of MMA using novel S-block organometallic initiators

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Structural basis for regioisomerization in the alkali-metal-mediated zincation (AMMZn) of trifluoromethyl benzene by isolation of kinetic and thermodynamic intermediates

Performed with a desire to advance knowledge of the structures and mechanisms governing alkali-metal-mediated zincation, this study monitors the reaction between the TMP-dialkylzincate reagent RTMEDA)Na(TMP)(Bu-t)Zn(Bu-t)] 1 and trifluoromethyl benzene C6H5CF3 2. A complicated mixture of products is observed at room temperature. X-ray crystallography has identified two of these products as ortho- and meta-regioisomers of heterotrianionic RTMEDA)Na(TMP)(C6H4-CF3)Zn(Bu-t)], 3-ortho and 3-meta, respectively. Multinuclear NMR data of the bulk crystalline product confirm the presence of these two regioisomers as well as a third isomer, 3-para, in a respective ratio of 20:11:1, and an additional product 4, which also exhibits ortho-zincation of the aryl substrate. Repeating the reaction at 0 C gave exclusively 4, which was crystallographically characterized as [{(TMEDA)(2)Na}(+)(Zn(C6H4-CF3)(Bu-t)(2)}(-)}. Mimicking the original room-temperature reaction, this kinetic product was subsequently reacted with TMP(H) to afford a complicated mixture of products, including significantly the three regioisomers of 3. Surprisingly, 4 adopts a solvent-separated ion pair arrangement in contrast to the contacted ion variants of 3-ortho and 3-meta. Aided by DFT calculations on model systems, discussion focuses on the different basicities, amido or alkyl, and steps, exhibited in these reactions, and how the structures and bonding within these isolated key metallic intermediates (prior to any electrophilic interception step), specifically the interactions involving the alkali metal, influence the regioselectivity of the Zn-H exchange process

Structural Basis for Regioisomerization in the Alkali-Metal-Mediated Zincation (AMM<i>Zn</i>) of Trifluoromethyl Benzene by Isolation of Kinetic and Thermodynamic Intermediates

Performed with a desire to advance knowledge of the structures and mechanisms governing alkali-metal-mediated zincation, this study monitors the reaction between the TMP-dialkylzincate reagent [(TMEDA)Na(TMP)(^<i>t</i>Bu)Zn(^<i>t</i>Bu)] <b>1</b> and trifluoromethyl benzene C₆H₅CF₃ <b>2</b>. A complicated mixture of products is observed at room temperature. X-ray crystallography has identified two of these products as ortho- and meta-regioisomers of heterotrianionic [(TMEDA)Na(TMP)(C₆H₄-CF₃)Zn(^<i>t</i>Bu)], <b>3</b>-<i>ortho</i> and <b>3</b>-<i>meta</i>, respectively. Multinuclear NMR data of the bulk crystalline product confirm the presence of these two regioisomers as well as a third isomer, <b>3</b>-<i>para</i>, in a respective ratio of 20:11:1, and an additional product <b>4</b>, which also exhibits ortho-zincation of the aryl substrate. Repeating the reaction at 0 °C gave exclusively <b>4</b>, which was crystallographically characterized as [{(TMEDA)₂Na}⁺{Zn(C₆H₄-CF₃)(^<i>t</i>Bu)₂}⁻]. Mimicking the original room-temperature reaction, this kinetic product was subsequently reacted with TMP(H) to afford a complicated mixture of products, including significantly the three regioisomers of <b>3</b>. Surprisingly, <b>4</b> adopts a solvent-separated ion pair arrangement in contrast to the contacted ion variants of <b>3</b>-<i>ortho</i> and <b>3</b>-<i>meta</i>. Aided by DFT calculations on model systems, discussion focuses on the different basicities, amido or alkyl, and steps, exhibited in these reactions, and how the structures and bonding within these isolated key metallic intermediates (prior to any electrophilic interception step), specifically the interactions involving the alkali metal, influence the regioselectivity of the Zn−H exchange process

Structural Basis for Regioisomerization in the Alkali-Metal-Mediated Zincation (AMM<i>Zn</i>) of Trifluoromethyl Benzene by Isolation of Kinetic and Thermodynamic Intermediates

Performed with a desire to advance knowledge of the structures and mechanisms governing alkali-metal-mediated zincation, this study monitors the reaction between the TMP-dialkylzincate reagent [(TMEDA)Na(TMP)(^<i>t</i>Bu)Zn(^<i>t</i>Bu)] <b>1</b> and trifluoromethyl benzene C₆H₅CF₃ <b>2</b>. A complicated mixture of products is observed at room temperature. X-ray crystallography has identified two of these products as ortho- and meta-regioisomers of heterotrianionic [(TMEDA)Na(TMP)(C₆H₄-CF₃)Zn(^<i>t</i>Bu)], <b>3</b>-<i>ortho</i> and <b>3</b>-<i>meta</i>, respectively. Multinuclear NMR data of the bulk crystalline product confirm the presence of these two regioisomers as well as a third isomer, <b>3</b>-<i>para</i>, in a respective ratio of 20:11:1, and an additional product <b>4</b>, which also exhibits ortho-zincation of the aryl substrate. Repeating the reaction at 0 °C gave exclusively <b>4</b>, which was crystallographically characterized as [{(TMEDA)₂Na}⁺{Zn(C₆H₄-CF₃)(^<i>t</i>Bu)₂}⁻]. Mimicking the original room-temperature reaction, this kinetic product was subsequently reacted with TMP(H) to afford a complicated mixture of products, including significantly the three regioisomers of <b>3</b>. Surprisingly, <b>4</b> adopts a solvent-separated ion pair arrangement in contrast to the contacted ion variants of <b>3</b>-<i>ortho</i> and <b>3</b>-<i>meta</i>. Aided by DFT calculations on model systems, discussion focuses on the different basicities, amido or alkyl, and steps, exhibited in these reactions, and how the structures and bonding within these isolated key metallic intermediates (prior to any electrophilic interception step), specifically the interactions involving the alkali metal, influence the regioselectivity of the Zn−H exchange process

Structurally defined zincated and aluminated complexes of ferrocene made by alkali-metal-synergistic syntheses

Reaction of ferrocene with 1 or 2 molar equiv of the synergistic-operative bimetallic sodium zincate base TMEDA·Na(μ-TMP)(μ-tBu)Zn(tBu) yields mainly mono- or dizincated complexes TMEDA·Na(μ-TMP)[μ-(C5H4)Fe(C5H5)]ZntBu (1) and [TMEDA·Na(μ-TMP)Zn(tBu)]2(C5H4)2Fe (2). Likewise, the separated pairing of Li(TMP) and (TMP)AliBu2 in the presence of THF can mono- or dimetalate ferrocene in a synergistic two-step lithiation/trans-metal-trapping protocol to give THF·Li(μ-TMP)[μ-(C5H4)Fe(C5H5)]Al(iBu)2 (4) or [THF·Li(μ-TMP)Al(iBu)2]2(C5H4)2Fe (5). In the absence of Lewis donating cosolvents, a 4-fold excess of the sodium zincate appears to produce an unprecedented 4-fold zincated ferrocene of formula Na4(TMP)4Zn4(tBu)4[(C5H3)2Fe] (3), whereas when donor solvent is withheld from the lithium/aluminum pairing, only dimetalation of ferrocene is possible. Tetrametalation seems to be inhibited by the in situ generation of TMP(H) via amido basicity, which then acts as a Lewis donor toward lithium, preventing inverse-crown formation and preferentially forming the Lewis acid–Lewis base adduct [TMP(H)·Li(μ-TMP)Al(iBu)2]2(C5H4)2Fe (6). With the exception of 3, all aforementioned complexes have been characterized by X-ray crystallography, while 1–6 have also been studied by solution NMR spectroscopic studies