New class of .sigma.-bonded aliphatic aza-macrocyclic complexes of transition metals: synthesis and x-ray crystal structures of nitrogen-bridged [(TiN4C12H24)2] and the oxo-bridged species [(N4C12H25)TiOTi(N4C12H25)]

Olmstead, Marilyn M.; Power, Philip P.; Viggiano, Michael

doi:10.1021/ja00347a084

Cited by 34 publications

(8 citation statements)

References 5 publications

(7 reference statements)

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“…They have also been invoked as a possible surface termination of Fe 2 O 3 (0 0 0 1) [20], even though ferryl species are relatively rare. Titanyl species are known to exist in Ti(IV) complexes [22,24,[58][59][60], and Ti@O groups have been invoked as important reaction centers in titanium-containing zeolites [61,62], although their presence has been questioned in Ref. [21].…”

Section: Discussionmentioning

confidence: 99%

Structure, defects, and impurities at the rutile TiO2(011)-(2×1) surface: A scanning tunneling microscopy study

et al. 2006

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Section: Discussionmentioning

confidence: 99%

Structure, defects, and impurities at the rutile TiO2(011)-(2×1) surface: A scanning tunneling microscopy study

et al. 2006

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“…After preliminary contributions that revealed the ability of anionic derivatives of cyclam to coordinate to Group 4 transition metals as diamido diamine donor sets, our research focused on the chemistry of zirconium complexes anchored by dianionic trans -dibenzyl cyclam ancillary ligands . A large variety of (Bn 2 Cyclam)Zr(X)(Y) compounds (Bn = benzyl or substituted benzyl; X = Y or ≠ Y) and several catalytic applications were established.…”

Section: Introductionmentioning

confidence: 99%

Cooperative Metal–Ligand Hydroamination Catalysis Supported by C–H Activation in Cyclam Zr(IV) Complexes

et al. 2018

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Complexes of the type (R2Cyclam)ZrCl2 (where R = CH2C(H)CH2 (All), CH2C(Me)CH2 (MeAll), and PhCH2 (Bn)) react with suitable Grignard reagents to produce the corresponding alkyl derivatives (R2Cyclam)ZrR′2 (R′ = Me, CH2Ph). Thermally induced double metalation of the pending arms of the cyclam ligand led to the formation of complexes ((CHC(H)CH2)2Cyclam)Zr, 14, ((CHC(Me)CH2)2Cyclam)Zr, 15, or ((C6H4CH2)2Cyclam)Zr, 16. These reactions proceed through C(sp2)–H bond activation and R′H elimination and convert the original dianionic tetracoordinated cyclam-based ligands in tetraanionic hexacoordinated ligands that establish two new Zr–C bonds. The cleavage of the Zr–C bonds may be readily achieved by treatment of the bis(ortho-metalated) species 16 with protic substrates (tert-butanol, phenol, thiophenol, aniline, benzophenone hydrazone, pyrazole, and N,N′-diphenylhydrazine), to give rise to (Bn2Cyclam)ZrX2 complexes (X = OtBu, OPh, SPh, NHPh, NHNCPh2, C3H3N2, N,N′-PhNNPh). In catalytic conditions, complexes (All2Cyclam)Zr(NMe2)2, 14, 15, or 16 convert 2,2-diphenyl-pent-4-enylamine to 2-methyl-4,4-diphenylpyrrolidine with 100% selectivity and conversion values varying between 61 and 88% in 4.5 h, at 115 °C. Complexes 14 and 15, which display metalated allyl and methallyl pending groups on the cyclam ring, are the most active species (1.7 < TOF < 2.0 h–1). The mechanism of this reaction was studied by density functional theory that revealed two competitive paths, one proceeding through an imido intermediate and another that occurs via an amido ligand. Both cases represent cooperative mechanisms with active participation of the cyclam, as proton exchange between the coordinated substrate and the ligand side arm with reversible C–H activation is a crucial feature of the mechanism.

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“…The two µ-oxo-bridges present in the aggregate were found to be dissimilar, with the Ti1-O9-Ti2 angle close to linear at 173.4(2) • , while the Ti3-O18-Ti4 is significantly distorted at 148.6(2) • . The linear Ti1-O9-Ti2 bond showed a greater degree of Ti-O π-bonding than in the bent Ti3-O18-Ti4 bond due to Ti1 and Ti2 being more electron deficient metal centres [31]. This difference is also represented in the average Ti-N bond lengths at 2.252(2) Å and 2.295(1) Å for Ti1/2 and Ti3/4, respectively.…”

Section: Synthesis Of Ti and Zr Clustersmentioning

confidence: 92%

Polymetallic Group 4 Complexes: Catalysts for the Ring Opening Polymerisation of rac-Lactide

et al. 2021

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Five novel air- and moisture-stable polymetallic Ti and Zr amino acid-derived amine bis(phenolate) (ABP) complexes were synthesised and fully characterised, including X-ray crystallographic studies. The reaction of the ABP proligands with Ti or Zr alkoxides has resulted in the formation of polymetallic aggregates of different nuclearity. The steric bulk on the pendant arm of the ligand was found to play a critical role in establishing the nuclearity of the aggregated complex. Sterically, less-demanding groups, such as H or Me, facilitated the formation of tetrametallic Ti clusters, bridged by carboxylate groups, while increased steric bulk (tBu) led to the formation of binuclear μ-oxo-bridged species. The isolated complexes were employed as catalysts for the ring opening polymerisation (ROP) of rac-lactide. Overall, the Ti catalysts were all active with the smaller, bimetallic Ti aggregates exhibiting relatively faster rates. A monometallic, bis(ABP) Zr complex was found to exert remarkable ROP activity, albeit with limited control over the tacticity and molecular weight distribution of the polymer. A further oxo-bridged Zr cluster was shown to display a previously unprecedented trimetallic structure and achieved a moderate rate in the ROP of rac-lactide.

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New class of .sigma.-bonded aliphatic aza-macrocyclic complexes of transition metals: synthesis and x-ray crystal structures of nitrogen-bridged [(TiN4C12H24)2] and the oxo-bridged species [(N4C12H25)TiOTi(N4C12H25)]

Cited by 34 publications

References 5 publications

Structure, defects, and impurities at the rutile TiO2(011)-(2×1) surface: A scanning tunneling microscopy study

Structure, defects, and impurities at the rutile TiO2(011)-(2×1) surface: A scanning tunneling microscopy study

Cooperative Metal–Ligand Hydroamination Catalysis Supported by C–H Activation in Cyclam Zr(IV) Complexes

Polymetallic Group 4 Complexes: Catalysts for the Ring Opening Polymerisation of rac-Lactide

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