Well-defined imidotitanium alkyl cations: agostic interactions, migratory insertion vs.[2+2] cycloaddition, and the first structurally authenticated AlMe3 adduct of any transition metal alkyl cation

Bolton, Paul D.; Clot, Eric; Cowley, Andrew R.; Mountford, Philip

doi:10.1039/b504567c

Cited by 60 publications

(52 citation statements)

References 33 publications

(23 reference statements)

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“…These characteristics strongly suggest that an additional α‐agostic interaction involving a C18−H18 bond must be operative in 3 . To our knowledge, this is the first spectroscopic evidence for multiple α‐agostic interactions in this class of heterobimetallic adducts . Even if the diastereotopic CH 2 protons of the bridging ethyl group cannot undergo mutual exchange (as do the hydrogens of Me18 in 2 ), they alternate between agostic and nonagostic positions during interconversion between 3 syn and 3 anti .…”

Section: Resultsmentioning

confidence: 94%

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

Tensi

Froese

Kuhlman

et al. 2020

Chemistry A European J

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Heterobimetallic complexes with inequivalent bridging alkyl chains are very often invoked as key intermediates in many catalytic processes, yet their interception and structural characterization are lacking. Such complexes have been prepared from reactions of the cationic cyclometalated hafnocene [CpPrCpCH2CH2CH2 Hf][B(C6F5)4] (1) with main group metal alkyls to afford the corresponding hetero‐bridged cationic products, [CpPrCpCH2CH2(μ-CH2) Hf(μ‐R)E(R)n][B(C6F5)4] (E=Al or Zn; R=Me, Et, or iBu). NMR and DFT studies demonstrate that both bridging alkyls establish agostic interactions with Hf, which are appreciably stronger for ethyl rather than methyl groups. Hf–Al and Hf–Zn distances are surprisingly short and only slightly longer than computed Hf–Al or Hf–Zn single bond lengths (2.80 Å). Finally, a reaction of [CpPrCpCH2CH2(μ-CH2) Hf(μ‐Me)Zn(Me)][B(C6F5)4] with excess ZnMe2 yields an unprecedented heterotrimetallic species, [(CpPr)2Hf(μ‐Me)(ZnMe)(μ3‐CH2)ZnMe][B(C6F5)4], the detailed structure of which is elucidated by a combination of NMR spectroscopic methods and molecular calculations.

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Section: Resultsmentioning

confidence: 94%

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

Tensi

Froese

Kuhlman

et al. 2020

Chemistry A European J

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“…56 The less sterically protected monomethylcyclopentadienyl compound Ti(h-C 5 H 4 Me)(N-2,6-C 6 H 3 Me 2 ){MeC(N i Pr) 2 } (11) was also formed cleanly (71% yield as a green oil after high vacuum distillation). The methylcyclopentadienyl-benzamidinate analogue Ti(h-C 5 H 4 Me)(N-2,6-C 6 H 3 Me 2 ){PhC(NSiMe 3 ) 2 } (12) was also made by room temperature imido ligand exchange starting from the tert-butyl imido compound 5 (58% yield). In contrast, the pentamethylcyclopentadienyl-benzamidinate com- pound Ti(h-C 5 Me 5 )(N t Bu){PhC(NSiMe 3 ) 2 } (3) does not undergo imide exchange reactions with anilines even after several days at 80 • C (benzene-d 6 ).…”

Section: Synthesis Of New Cyclopentadienyl-amidinate Aryl Imido Compo...mentioning

confidence: 99%

Reactions of cyclopentadienyl-amidinate titanium imido compounds with CO2: cycloaddition-extrusion vs. cycloaddition-insertion

et al. 2009

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A combined experimental and DFT study of the reactions of cyclopentadienyl-amidinate titanium imido complexes with CO(2) is reported. Cycloaddition reactions of the aryl imido compounds Ti(eta-C(5)R(4)Me)(NAr){R(2)C(NR(1))(2)} (R = H or Me; R(1), R(2) = SiMe(3), Ph or (i)Pr, Me) with CO(2) gave the corresponding N,O-bound carbamate complexes Ti(eta-C(5)R(4)Me){N(Ar)C(O)O}{R(2)C(NR(1))(2)}. These reacted further with CO(2) by insertion into the Ti-N(Ar) bond to afford the new dicarboxylates Ti(eta-C(5)R(4)Me){OC(O)N(Ar)C(O)O}{R(2)C(NR(1))(2)} in which the original Ti=NAr bond has been completely cleaved. The X-ray structures of two of these have been determined. The CO(2) insertion reactions of the para-substituted phenyl carbamate complexes Ti(eta-C(5)Me(5)){N(-4-C(6)H(4)X)C(O)O}{MeC(N(i)Pr)(2)} (X = Me, CF(3) or NMe(2)) were first order with respect to both carbamate complex and CO(2) and the pseudo first order rate constants were effectively independent of the para substituent. The corresponding tert-butyl imido compounds Ti(eta-C(5)R(4)Me)(N(t)Bu){R(2)C(NR(1))(2)} also reacted with CO(2) to form N,O-bound carbamate complexes, Ti(eta-C(5)R(4)Me){N((t)Bu)C(O)O}{R(2)C(NR(1))(2)}. However, these did not insert a further molecule of CO(2) and instead extruded (t)BuNCO to form the crystallographically characterized oxo-bridged dimers [Ti(eta-C(5)R(4)Me)(mu-O){R(2)C(NR(1))(2)}](2). These reactions proceeded via transient terminal oxo intermediates, one of which was trapped by the addition of TolNCO (Tol = p-tolyl). DFT (B3PW91) calculations on Ti(eta-C(5)H(5))(NR){MeC(NMe)(2)} (R = Me, Ph, 4-C(6)H(4)Me, 4-C(6)H(4)NMe(2), 4-C(6)H(4)CF(3)) reacting with CO(2) showed that the second CO(2) insertion is thermodynamically favoured over isocyanate extrusion, and that the rates of the two processes are similar. Calculations on Ti(eta-C(5)R(5))(N(t)Bu){MeC(N(i)Pr)(2)} (R = H or Me) showed that increasing the steric bulk increases the thermodynamic favourability of the isocyanate extrusion process and significantly raises the activation barrier for the second CO(2) insertion, making the latter process impossible.

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“…[3][4][5][6][7] For example, this type of functionality is responsible for fundamentally important reactions such as the intermolecular activation of aliphatic (including methane) [8,9] as well as aromatic C À H bonds. [7,[10][11][12][13] The ubiquitous imide group can also participate in other processes such as cycloaddition reactions with substrates like carbon dioxide, [14][15][16][17][18][19][20][21] carbon disulfide, [14-16, 19, 22] ke-tones, [16,22,23] alkenes (intra-and intermolecularly), [24,25] A C H T U N G T R E N N U N G alkynes, [22,[24][25][26] nitriles, [23,27] isonitriles, [16,28] imines, [16,23,29,30] carbodiimides, [4,16,[30][31][32] allenes, [4,24,33] allylic alcohols, [34] and carboxamides…”

Section: Introductionmentioning

confidence: 99%

“…[36][37][38][39][40][41][42][43] As described previously, the imide functionality (in a closed-shell formalism) has also been utilized as a supporting ligand. For example, metal imides can be used as ancillary ligands for the study of important industrial reactions such as olefin metathesis [44] and polymerizations, [29,38,[44][45][46] as well as models for processes such as propylene ammoxidation [47] and hydrodenitrogenation. [2] The chemical behavior of the imide ligand is often governed by the role of the lone pair of electrons on nitrogen, which may or may not contribute to the formation of a pseudo-triple bond.…”

Section: Introductionmentioning

confidence: 99%

“…For example, this type of functionality is responsible for fundamentally important reactions such as the intermolecular activation of aliphatic (including methane)8, 9 as well as aromatic CH bonds 7. 10–13 The ubiquitous imide group can also participate in other processes such as cycloaddition reactions with substrates like carbon dioxide,14–21 carbon disulfide,14–16, 19, 22 ketones,16, 22, 23 alkenes (intra‐ and intermolecularly),24, 25 alkynes,22, 24–26 nitriles,23, 27 isonitriles,16, 28 imines,16, 23, 29, 30 carbodiimides,4, 16, 30–32 allenes,4, 24, 33 allylic alcohols,34 and carboxamides35 along with several other polar reagents 4–7. Depending on the complex, incomplete or complete metathetical reactions can often take place (even catalytically) with these types of substrates, thus leading to Wittig‐like chemistry and extrusion of organic products in which the imide group has been swiftly incorporated.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Progression of Synthetic Strategies to Assemble Titanium Complexes Bearing the Terminal Imide Group

Fout¹,

Kilgore²,

Mindiola³

2007

Chemistry A European J

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The synthesis of terminal titanium imides is described in this account. The incorporation of this functional group has evolved from more simplistic approaches to more complex or unusual methods. Past and current synthetic strategies to incorporate the terminal imide functionality are explained with particular emphasis on low-coordinate titanium environments bearing this ubiquitous but vital type of motif. More recently, the imide functionality has demonstrated to be a key intermediate for modeling important industrial processes such as the hydrodenitrogenation of crude oil.

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Well-defined imidotitanium alkyl cations: agostic interactions, migratory insertion vs.[2+2] cycloaddition, and the first structurally authenticated AlMe3 adduct of any transition metal alkyl cation

Cited by 60 publications

References 33 publications

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

Reactions of cyclopentadienyl-amidinate titanium imido compounds with CO2: cycloaddition-extrusion vs. cycloaddition-insertion

The Progression of Synthetic Strategies to Assemble Titanium Complexes Bearing the Terminal Imide Group

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