The Zirconium Benzyl Mediated C−N Bond Cleavage of an Amino-Linked N-Heterocyclic Carbene

Hu, Yucheng; Tsai, Chung-Chih; Shih, Wei-Chih; Yap, Glenn P. A.; Ong, Tiow‐Gan

doi:10.1021/om900971c

Cited by 36 publications

(6 citation statements)

References 46 publications

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“…Zirconium complexes supported by bis-amido NHC tridentate ligands are known as well. For instance, amine or alkyl elimination reaction of tridentate carbene 73 with Zr(IV) alkyl/amido precursors provided access to various Zr(IV)–NHC adducts. − Note that carbene 73 is a stable entity and may be readily generated via deprotonation of the appropriate azolium precursor. For instance, aminolysis of Zr(NMe 2 ) 4 with carbene 73 afforded the corresponding κ 3 -(bis-amido–NHC) chelate complex 74 in good yield (Scheme ).…”

Section: Early Transition Metal Complexesmentioning

confidence: 99%

Group 1 and 2 and Early Transition Metal Complexes Bearing N-Heterocyclic Carbene Ligands: Coordination Chemistry, Reactivity, and Applications

2014

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Section: Early Transition Metal Complexesmentioning

confidence: 99%

Group 1 and 2 and Early Transition Metal Complexes Bearing N-Heterocyclic Carbene Ligands: Coordination Chemistry, Reactivity, and Applications

2014

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“…They have been successfully applied to a large range of catalytic reactions such as olefin metathesis, C–C coupling, and hydrosilylation . In contrast, early-transition-metal NHC complexes, particularly in their highest oxidation state, have yet to be studied in the same depth. − Only a small number of Ti NHC complexes have been reported. ,,,,,,,,− Successful applications of Ti NHC complexes were as efficient catalysts for ethylene and rac -lactide polymerization. ,,,, …”

Section: Introductionmentioning

confidence: 99%

Synthesis of Titanium CCC-NHC Pincer Complexes and Catalytic Hydroamination of Unactivated Alkenes

2012

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The previously reported amine elimination methodology using group 4 tetrakis(dimethylamido) starting materials for the synthesis of CCC-NHC pincer Zr and Hf complexes has been extended to include Ti. Use of excess Ti(NMe 2 ) 4 with 1,3bis(3-butylimidazol-1-yl)benzene diiodide (1) yielded (1,3-bis(3-butylimidazol-1-yl-2-idene)-2-phenylene)bis(dimethylamido)iodotitanium(IV) (2), which subsequently reacted with CH 2 Cl 2 to afford (1,3-bis(3-butylimidazol-1-yl-2-idene)-2-phenylene)trichlorotitanium(IV) (3). Combining complex 2 with TMSCl yielded complex 3 along with the geometric isomers of (1,3-bis(3butylimidazol-1-yl-2-idene)-2-phenylene)dichloroiodotitanium(IV) (4a,e). The salt, 1,3-bis(3-butylimidazol-1-yl)benzene dichloride (5), was reacted with Ti(NMe 2 ) 4 in a stoichiometric amount to yield (1,3-bis(3-butylimidazol-1-yl-2-idene)-2phenylene)dichloro(dimethylamido)titanium(IV) (6), while use of excess Ti(NMe 2 ) 4 yielded (1,3-bis(3-butylimidazol-1-yl-2idene)-2-phenylene)chlorobis(dimethylamido)titanium(IV) ( 7). An efficient direct synthesis of trichloro complex 3 was accomplished by reacting the chlorobis(dimethylamido)titanium complex 7 with TMSCl. The catalytic activity of the bis(dimethylamido)iodotitanium complex 2 and chlorobis(dimethylamido)titanium complex 7 toward the hydroamination/ cyclization of unactivated alkene-amines was also evaluated.

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“…C−N activation has now been observed in a number of both early (Y, Zr) and late (Rh, Ir, Pd) metal NHC complexes . However, these reactions either involve poorly defined metal complexes generated in situ using imidazolium salt precursors or take place under highly forcing or heterogeneous conditions.…”

Section: Introductionmentioning

confidence: 99%

Experimental and Computational Investigation of C−N Bond Activation in Ruthenium N-Heterocyclic Carbene Complexes

et al. 2010

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A combination of experimental studies and density functional theory calculations is used to study C-N bond activation in a series of ruthenium N-alkyl-substituted heterocyclic carbene (NHC) complexes. These show that prior C-H activation of the NHC ligand renders the system susceptible to irreversible C-N activation. In the presence of a source of HCl, C-H activated Ru(I(i)Pr(2)Me(2))'(PPh(3))(2)(CO)H (1, I(i)Pr(2)Me(2) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) reacts to give Ru(I(i)PrHMe(2))(PPh(3))(2)(CO)HCl (2, I(i)PrHMe(2) = 1-isopropyl-4,5-dimethylimidazol-2-ylidene) and propene. The mechanism involves (i) isomerization to a trans-phosphine isomer, 1c, in which hydride is trans to the metalated alkyl arm, (ii) C-N cleavage to give an intermediate propene complex with a C2-metalated imidazole ligand, and (iii) N-protonation and propene/Cl(-) substitution to give 2. The overall computed activation barrier (ΔE(++)(calcd)) corresponds to the isomerization/C-N cleavage process and has a value of +24.4 kcal/mol. C-N activation in 1c is promoted by the relief of electronic strain arising from the trans disposition of the high-trans-influence hydride and alkyl ligands. Experimental studies on analogues of 1 with different C4/C5 carbene backbone substituents (Ru(I(i)Pr(2)Ph(2))'(PPh(3))(2)(CO)H, Ru(I(i)Pr(2))'(PPh(3))(2)(CO)H) or different N-substituents (Ru(IEt(2)Me(2))'(PPh(3))(2)(CO)H) reveal that Ph substituents promote C-N activation. Calculations confirm that Ru(I(i)Pr(2)Ph(2))'(PPh(3))(2)(CO)H undergoes isomerization/C-N bond cleavage with a low barrier of only +21.4 kcal/mol. Larger N-alkyl groups also facilitate C-N bond activation (Ru(I(t)Bu(2)Me(2))'(PPh(3))(2)(CO)H, ΔE(++)(calcd) = +21.3 kcal/mol), and in this case the reaction is promoted by the formation of the more highly substituted 2-methylpropene.

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The Zirconium Benzyl Mediated C−N Bond Cleavage of an Amino-Linked N-Heterocyclic Carbene

Cited by 36 publications

References 46 publications

Group 1 and 2 and Early Transition Metal Complexes Bearing N-Heterocyclic Carbene Ligands: Coordination Chemistry, Reactivity, and Applications

Group 1 and 2 and Early Transition Metal Complexes Bearing N-Heterocyclic Carbene Ligands: Coordination Chemistry, Reactivity, and Applications

Synthesis of Titanium CCC-NHC Pincer Complexes and Catalytic Hydroamination of Unactivated Alkenes

Experimental and Computational Investigation of C−N Bond Activation in Ruthenium N-Heterocyclic Carbene Complexes

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