Half-sandwich Cp Research Articles

Theoretical investigation of mechanism and ligand effects on half-sandwich iridium complexes for direct reductive amination

The reaction mechanisms of direct reductive amination catalyzed by half-sandwich Cp*Ir complexes and the possible side reactions — transfer hydrogenation of ketones and N-formylation of amines have been explored by density functional theory (DFT). The reaction involves two steps: (1) the hydridoiridium formation as a rate-determining step, and (2) the hydride transfer to obtain amines. The relationships between the structure and activity of Cp*Ir complexes were analyzed by natural population analysis (NPA), Bader's atoms in molecules theory (AIM) and frontier molecular orbital (FMO). In general, the picolinamidato ligands are more favorable than the sulfonamidato ones due to the electronic effect. The catalyst with the phenyl ring bearing functional groups on the N-amide exerts the positive effect on the catalytic activity. Furthermore, the electron-donating group on the pyridine ring provides better performance owing to the higher NPA charge on the Ir atom, the lower electron density at the Ir-Cl bond critical point, and the destabilization of the highest occupied molecular orbital (HOMO).

Recent Development in the Synthesis and Catalytic Application of Iridacycles.

Cyclometallated complexes are well-known and have found many applications. This article provides a short review on the progress made in the synthesis and application to catalysis of cyclometallated half-sandwich Cp*Ir(III) complexes (Cp*: pentamethylcyclopentadienyl) since 2017. Covered in the review are iridacycles featuring conventional C,N chelates and less common metallocene and carbene-derived C,N and C,C ligands. This is followed by an overview of the studies of their applications in catalysis ranging from asymmetric hydrogenation, transfer hydrogenation, hydrosilylation to dehydrogenation.

Construction of organometallic trefoil knots and one-dimensional chains featuring half-sandwich Cp*Rh corner units and an abnormal zwitterion ligand

An abnormal flexible O-coordinated zwitterion ligand L shows self-adaptive conformation behaviour in chemical self-assembly. Two trefoil knots were obtained with C-shaped ligand L and two novel 1D chains were obtained with Z-shaped ligand L.

Synthesis, characterization and photodynamic activity of half-sandwich rhodium(III) complexes with curcuminoids.

Half-sandwich Cp*-Rh complexes containing curcuminoids ([Rh(η5-Cp*)(L)(Py)]PF6, 1-3, L = curcuminoid ligands L1-L3) were prepared, characterized and studied for anticancer activity. Complex 1 was structurally characterized by single-crystal X-ray crystallography. Complex 3 presented excellent photodynamic anticancer effect in light (>400 nm) showing IC50 values of 7.5 and 4.3 μM against HepG2, SKOV3 and HeLa, respectively, along with the 12.4, 7.9 and 4.7-fold lower toxicity in the dark. Confocal fluorescence images show that the complex primarily targeted mitochondrial localization. These results suggest that the complex 3 was a valuable agent with higher efficacy for chemotherapy and photodynamic therapy, which can achieve real-time image guidance in cancer therapy for the fluorescence of the complex as imaging signals. This investigation provides a valuable route to design novel half-sandwich Cp*-Rh complexes with higher efficacy for photodynamic anticancer chemotherapy.

Novel half-sandwich rhodium(III) and iridium(III) photosensitizers for dual chemo- and photodynamic therapy.

Photodynamic therapy has emerged as a promising treatment for cancer and other malignancies. Design of photosensitizers with two different action mechanisms may be an essential strategy for the improvement of the efficacy of phototherapeutic drugs. The objective of this study was to evaluate the anticancer photo- and chemocytotoxic effects of the novel half-sandwich rhodium(III) and iridium(III) photosensitizers. A series of novel half-sandwich Cp*-Rh(III) and Cp*-Ir(III) complexes containing 9-anthraldehyde thiosemicarbazones, (Cp*)M(L)Cl (M = Rh or Ir, L = 9-anthraldehyde thiosemicarbazones), were compared for cell uptake and photo- and chemocytotoxic effects against human prostate carcinoma (PC3) and human ovarian carcinoma (SKOV3) cell lines. Cp*-Ir(III) complexes, (Cp*)Ir(L)Cl, showed remarkable phototoxic behavior against human ovarian adenocarcinoma SKOV3 cells (IC50 = 2.7 and 2.3 μM, respectively, λirr > 400 nm), as well as the 7.4 and 5.3-fold lower toxicity in the dark, implying possibility of dual action as chemo- and phototherapeutic agents. The complexes, which present a synergistic effect with good properties of both the Cp*-Rh(III) and Cp*-Ir(III) chemotherapeutic effect and the anthracene photodynamic therapy efficiency, show great potential as a new generation of light activated dual-action anticancer agents for photodynamic therapy.

Mechanistic insights and computational design of half-sandwich iridium and rhodium complexes for hydrogenation of quinoline

DFT calculations reveal a stepwise proton and hydride transfer mechanism for the hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline catalysed by half-sandwich Cp*Ir(NHC) complexes.

Dehydrogenation of Dimethylamine–Borane Catalyzed by Half-Sandwich Ir and Rh Complexes: Mechanism and the Role of Cp* Noninnocence

Half-sandwich Cp*RhIII complexes (Cp* = η5-1,2,3,4,5-pentamethylcyclopentadienyl) supported by 2,2′-bipyridine or 4,4′-di-tert-butyl-2,2′-bipyridine catalyze dehydrogenation of dimethylamine–borane (Me2NH·BH3) to produce H2 and dimethylamino–borane dimer (Me2N—BH2)2 with turnovers of 2200. The IrIII analogues, on the other hand, display dramatically poorer catalytic activity. Mechanistic inferences drawn from stoichiometric reactions and DFT calculations suggest noninnocent involvement of the Cp* moiety as a proton shuttle.

Synthesis and structural studies of half-sandwich Cp* rhodium and Cp* iridium complexes featuring mono, bi and tetradentate nitrogen and oxygen donor ligands

A series of Cp*Rh and Cp*Ir complexes of various nitrogen and oxygen donor ligands were synthesized and characterized. Mono, bi and tetradentate ligands were used to synthesize mononuclear and dinuclear complexes. Schiff base derivatives of picolinic hydrazine and 5-aminoquinoline were used in the synthesis of complexes 1–8. Among the ligands used for complexation, L1 and L2 act as bidentate, L3 as monodentate and L4 as tetradentate in forming the corresponding complexes. All the complexes were characterized by spectroscopic techniques and the structures of complexes 2, 3, 5 and 7 were unambiguously characterized by single crystal X-ray crystallography. Complexes 2 and 7 were found to have $${\uppi }$$ - $${\uppi }$$ stacking interactions and solvent to complex interactions, respectively. Metal-mediated deprotonation of N-H and monodentate binding of nitrogen are attributed to the formation of neutral complexes whereas ionic complexes are formed by (N,O) bonding. SYNOPSIS Half-sandwich Cp* rhodium and Cp* iridium complexes of Schiff base derivatives of picolinic hydrazine and 5-aminoquinoline were synthesized, characterized and their structures studied by single crystal X-ray analysis. Various binding modes of the complexes were unambiguously confirmed.

Active Cp*Iridium(III) Complex with ortho-Hydroxyl Group Functionalized Bipyridine Ligand Containing an Electron-Donating Group for the Production of Diketone from 5-HMF

Diketones are ubiquitous blocks for organic synthesis. This work shows a highly active catalyst for the production of diketone 1-hydroxyhexane-2,5-dione (HHD) by hydrogenation of 5-hydroxymethylfurfural (5-HMF), a biobased platform chemical. Half-sandwich Cp*Ir complexes with ortho-hydroxyl group functionalized bipyridine ligands were synthesized and found to exhibit remarkably high catalytic activity for this reaction in acidic water. The HHD formation rate was further increased when the bipyridine ligands of Cp*Ir complexes were modified by an electron-donating group. A bipyridine ligand with both dimethylamino and ortho-hydroxyl groups achieved a HHD formation turnover frequency (TOF) of 31 560 h–1 by H2 and a TOF of 6140 h–1 by formic acid, representing 180-fold and 3 000-fold over the activities of the best reported results, respectively.

Interconversion of Formic Acid and Carbon Dioxide by Proton-Responsive, Half-Sandwich Cp*IrIII Complexes: A Computational Mechanistic Investigation

Dihydrogen (H2) has many desirable features as a fuel, but utilization of H2 is limited due to storage and transportation problems. A promising solution to these issues is reversible storage of hydrogen in the form of liquid-phase chemicals such as formic acid (FA), which could be accomplished by the development of efficient and robust catalysts. Recently, proton-responsive, half-sandwich Cp*IrIII (where Cp* = pentamethylcyclopentadienyl anion) complexes capable of reversible hydrogen storage via interconversion between H2/CO2 and formic acid/formate in water have been reported. This interconversion is performed via CO2 hydrogenation and FA dehydrogenation reactions and modulated by the pH of the medium. We report the results of a computational investigation of the mechanistic aspects of reversible hydrogen storage via two of these catalysts: namely, [Cp*Ir(4DHBP)]2+ (4DHBP = 4,4′-dihydroxy-2,2′-bipyridine) and [Cp*Ir(6DHBP)]2+ (6DHBP = 6,6′-dihydroxy-2,2′-bipyridine). Distinct features of the catalytic c...

Synthesis, Solid-State Structures, and Computational Studies of Half-Sandwich Cp*BeX (X = Cl, Br, I) Compounds

The solid-state structures of half-sandwich beryllium complexes Cp*BeX (X = Cl (1), Br (2), I (3)) are described. All attempts to synthesize Cp*BeF (4) by reaction of 1–3 with several fluorinating reagents such as AgF2, XeF2, 4-FC6H4IF2, AgF, NaF, and Me4NF failed. However, the reaction of 3 and AgF in resulted in the unexpected synthesis of the known beryllocene Cp*2Be (5). Quantum-chemical calculations were performed to investigate the electronic structures of 1–4.

Positional Effects of Hydroxy Groups on Catalytic Activity of Proton-Responsive Half-Sandwich Cp*Iridium(III) Complexes

Proton-responsive half-sandwich Cp*Ir(III) complexes possessing a bipyridine ligand with two hydroxy groups at the 3,3′-, 4,4′-, 5,5′-, or 6,6′-positions (3DHBP, 4DHBP, 5DHBP, or 6DHBP) were systematically investigated. UV–vis titration data provided average pKa values of the hydroxy groups on the ligands. Both hydroxy groups were found to deprotonate in the pH 4.6–5.6 range for the 4–6DHBP complexes. One of the hydroxy groups of the 3DHBP complex exhibited a low pKa value of <0.4 because the deprotonation is facilitated by the strong intramolecular hydrogen bond formed between the generated oxyanion and the remaining hydroxy group, which in turn leads to an elevated pKa value of ∼13.6 for the second deprotonation step. The crystal structures of the 4- and 6DHBP complexes obtained from basic aqueous solutions revealed their deprotonated forms. The intramolecular hydrogen bond in the 3DHBP complex was also observed in the crystal structures. The catalytic activities of these complexes in aqueous phase reactions, at appropriate pH, for hydrogenation of carbon dioxide (pH 8.5), dehydrogenation of formic acid (pH 1.8), and transfer hydrogenation reactions using formic acid/formate as a hydrogen source (pH 2.6 and 7.2) were investigated to compare the positional effects of the hydroxy groups. The 4- and 6DHBP complexes exhibited remarkably enhanced catalytic activities under basic conditions because of the resonance effect of the strong electron-donating oxyanions, whereas the 5DHBP complex exhibited negligible activity despite the presence of electron-donating groups. The 3DHBP complex exhibited relatively high catalytic activity at low pH owing to the one strong electron-donating oxyanion group stabilized by the intramolecular hydrogen bond. DFT calculations were employed to study the mechanism of CO2 hydrogenation by the 4DHBP and 6DHBP complexes, and comparison of the activation free energies of the H2 heterolysis and CO2 insertion steps indicated that H2 heterolysis is the rate-determining step for both complexes. The presence of a pendent base in the 6DHBP complex was found to facilitate the rate-determining step and renders 6DHBP a more effective catalyst for formate production.

ChemInform Abstract: Cyclometalated [Cp*M(C^X)] (M: Ir, Rh; X: N, C, O, P) Complexes

AbstractReview: synthesis, characterization and applications; 167 refs.

Bis-imine-cyclometalated macrocycles: synthesis, characterization and observation of solution behaviour

A novel class of cyclometalated macrocycles [(Cp*Ir)(2)(R-N=C-C(6)H(2)-C=N-R)(2)](2)(pyrazine)(2)·(OTf)(4) [R = Ph (4a), p-MeOC(6)H(4) (4b), p-MeC(6)H(4) (4c), p-ClC(6)H(4) (4d), Me (4e)]; [(Cp*Rh)(2)(R-N=C-C(6)H(2)-C=N-R)(2)](2)(pyrazine)(2)·(OTf)(4) [R = Ph (4a'), p-MeOC(6)H(4) (4b'), p-MeC(6)H(4) (4c')] and [(Cp*Ir)(2)(R-C=N-C(6)H(4)-N=C-R)(2)](2)(pyrazine)(2)·(OTf)(4) [R = Ph (5a), p-MeOC(6)H(4) (5b)] was stepwise constructed through the double-site C-H activation of aromatic bis-imine substrates. The structures of binuclear complexes and tetranuclear macrocycles were confirmed by single-crystal X-ray diffraction. Isomers were found both in binuclear species and macrocyclic complexes. Flexible substrates led to the existence of isomers for binuclear species, yet gave no isomers after macrocyclic constructions; rigid ones, in contrast, led to isomers only for macrocyclic species. The isomers of tetranuclear macrocycles were thermodynamically stable to reversible transformation on a scale of days. Robust bonding and a certain degree of rigidity were invoked to explain the existence of isomers. This is the first example, to our knowledge, in which coordinated macrocycles containing half-sandwich Cp*M (M = Ir, Rh) fragments have been constructed, without a dynamic reversible process.

Synthesis of samarium(ii) borohydrides and their behaviour as initiators in styrene and ε-caprolactone polymerisation

The bisborohydrido samarium compound Sm(BH(4))(2)(THF)(2) (1) was prepared in high yield by comproportionation between Sm and 2 equivalents of Sm(BH(4))(3)(THF)(3). Reaction of 1 with KCp* (Cp* = C(5)Me(5)) afforded the half-sandwich Cp*Sm(BH(4))(THF)(2) (2). The (1)H NMR borohydride resonances of both complexes, observed at very high field, are typical of divalent Sm compounds. X-Ray single crystal analysis revealed polymeric and dimeric molecular arrangements for 1 and 2, respectively. Complex 1 was found moderately active towards styrene polymerisation when activated with Al((i)Bu)(3), or with a borate/Al combination, whereas 2 showed no activity. Ring-opening polymerisation of epsilon-caprolactone could be performed rapidly at room temperature with both initiators. Complex 2 leads to narrow polydispersities and higher activity. Two different mechanisms, by monoelectronic transfer or by insertion into the Sm-(BH(4)) bond can be proposed.

Syntheses of titanium μ-arylimido and μ-pyridylimido complexes bearing (un)substituted cyclopentadienyl ligand

The reactions of (η 5-C 5H 4CH 2CH 2Br)TiBr 3, (η 5-C 5H 4CH 2CH 2OCH 3)TiCl 3, (η 5-C 5H 4-CH 2- cyclo-C 4H 7O)TiCl 3 and (η 5-C 5H 5)TiCl 3 with an equivalent of 2-MeOC 6H 4NHLi in the presence of Et 3N afford μ-arylimido complexes, [(η 5-C 5H 4CH 2CH 2Br)Ti(Br)(μ-NC 6H 4OCH 3-2)] 2 ( 1), [(η 5-C 5H 4CH 2CH 2OCH 3)Ti(Cl)( μ-NC 6H 4OCH 3-2)] 2 ( 2), [(η 5-C 5H 4-CH 2- cyclo-C 4H 7O)Ti(Cl)(μ-NC 6H 4OCH 3-2)] 2 ( 3), [(η 5-C 5H 5)Ti(Cl)(μ-NC 6H 4OCH 3-2)] 2 ( 4), which include intramolecular titanium and oxygen coordination. Complex 4 can also be obtained by reaction of the (η 5-C 5H 5) 2TiCl 2 with 2-MeOC 6H 4NHLi. Meanwhile refluxing of (η 5-C 5H 5) 2TiCl 2 with an equivalent of 2-Me 2NC 6H 4NMg·THF in toluene gives another μ-arylimido complex, [(η 5-C 5H 5)Ti(Cl)(μ-NC 6H 4NMe 2-2)] 2, which contains intramolecular titanium and nitrogen coordination. In addition, the analogous reactions of the above substituted half-sandwich Cp titanium complexes with PhNHLi in the presence of Et 3N lead to [(η 5-C 5H 4CH 2CH 2Br)Ti(Br)(μ-NPh)] 2, [(η 5-C 5H 4CH 2CH 2OCH 3)Ti(Cl)(μ-NPh)] 2. The addition of 2-MeC 6H 4NHLi to (η 5-C 5H 4CH 2CH 2OCH 3)TiCl 3 and (η 5-C 5H 5)TiCl 3 affords imido derivatives [(η 5-C 5H 5)Ti(Cl)(μ-NC 6H 4CH 3-2)] 2 and [(η 5-C 5H 4CH 2CH 2OCH 3)Ti(Cl)(μ-NC 6H 4CH 3-2)] 2. [(η 5-C 5H 5)Ti(Cl)(μ-NC 6H 3Me 2-2,6)] 2 is prepared by refluxing of (η 5-C 5H 5)TiCl 3 and 2,6-Me 2C 6H 3NMg·THF in toluene. The titanium μ-pyridylimido complexes, [(η 5-C 5H 5)Ti(Cl)(μ-NPy-2)] 2, [(η 5-C 5H 4CH 2CH 2OCH 3)Ti(Cl)(μ-NPy-2)] 2 and [(η 5-C 5H 4CH 2CH 2Br)Ti(Br)(μ-NPy-2)] 2, are synthesized by reactions of the above corresponding half sandwich Cp titanium complexes with an equivalent of 2-PyNHLi in the presence of Et 3N, respectively. Compound 1 crystallizes in the triclinic space group P1̄ (no. 2) with a=9.942(2), b=10.057(3), c=8.457(2) Å, α=111.28(2), β=106.71(2), γ=98.12(2)°, V=725.5(4) Å 3, Z=2. The catalytic activity and selectivity of compound 4 for the styrene polymerization is also investigated.

.pi.-Stabilized, yet Reactive, Half-Sandwich Cp*Ru(PR3)X Compounds: Synthesis, Structure, and Bonding

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXT.pi.-Stabilized, yet Reactive, Half-Sandwich Cp*Ru(PR3)X Compounds: Synthesis, Structure, and BondingTodd J. Johnson, Kirsten Folting, William E. Streib, James D. Martin, John C. Huffman, Sarah A. Jackson, Odile Eisenstein, and Kenneth G. CaultonCite this: Inorg. Chem. 1995, 34, 2, 488–499Publication Date (Print):January 1, 1995Publication History Published online1 May 2002Published inissue 1 January 1995https://doi.org/10.1021/ic00106a010RIGHTS & PERMISSIONSArticle Views460Altmetric-Citations112LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

Structural diversity of sulfide tantalum and niobium complexes containing half-sandwich Cp*Ta and Cp*Nb fragments

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructural diversity of sulfide tantalum and niobium complexes containing half-sandwich Cp*Ta and Cp*Nb fragmentsKazuyuki Tatsumi, Yoshihisa Inoue, Hiroyuki Kawaguchi, Masaki Kohsaka, Akira Nakamura, Roger E. Cramer, William VanDoorne, Ginger J. Taogoshi, and Paul N. RichmannCite this: Organometallics 1993, 12, 2, 352–364Publication Date (Print):February 1, 1993Publication History Published online1 May 2002Published inissue 1 February 1993https://doi.org/10.1021/om00026a022RIGHTS & PERMISSIONSArticle Views216Altmetric-Citations51LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Cyclopentadienyl- and methylcyclopentadienyl-vanadium complexes containing chalcogen bridges: dechalcogenation to pseudocubane clusters

In extension of previous studies with pentamethylcyclopentadienyl (Cp★, η 5-C 5Me 5) vanadium complexes, decarbonylations in the presence of elemental chalcogens of the halfsandwich compounds CP(′)V(CO) 4 and CP(′)V(CO) 3L (L  SMe 2, MeCN) containing either the unsubstituted cyclopentadienyl (Cp, η 5-C 5H 5) or the monomethyl-substituted (Cp′, η 5-C 5H 4Me) cyclopentadienyl ring ligand have been investigated. (The notation Cp(′) indicates that both the unsubstituted (Cp) and the monomethyl-substituted (Cp′) cyclopentadienyl complexes were used.) The main products obtained from CP(′)V(CO) 3L and an excess of chalcogen were binuclear pentachalcogenides CP(′ 2V 2E 5 (bd1) (E  S, Se) and oxo-tritellurides Cp(′) 2V 2E 3O (bd4) (E  Te), respectively. Oxygen-containing side-products such as Cp★ 2V 2E 3O (E  S, Se), CP′ 2V 2S 4O and Cp′VO(S 5 were isolated from the reactions starting from CP′V(CO) 4. Chalcogen abstraction from 1 by use of one equivalent of tri(n-butyl)phosphane (P nBU 3) gave the tetrachalcogenides Cp(′) 2V 2E 4 ( 2), while further addition of P nBu 3 gave pseudocubane clusters Cp(′) 4V 4E 4 ( 7) (E  S, Se). Small amounts of trisulfides CP(′) 2V 2S 3 ( 3) were observed by 51V NMR spectroscopy in solutions of 1 and 2 in the presence of P nBu 3. Binuclear tetracarbonyl-dichalcogenides Cp(′) 2V 2(CO) 4E 2 ( 6) (E  S, Te) were made by treating solutions of CP(′)V(CO) 3(SMe 2) with H 2S and by photolysing CP(′)V(CO) 4 in the presence of either H 2S or TeP n Bu 3. The reactions Of Cp′ 2V 2(CO) 4S 2 ( 6a′) with an excess of an oligochalcogenide Na 2E 5 (E  Se, Te) gave the mixed-chalcogenide complexes Cp 2V 2E 2S 2 (E  Se ( 2d′) and Te ( 2f′)), which react with two equivalents of P nBu 3 or NiCp 2 to the pseudocubane cluster Cp′ 4V 4S 4 ( 7a′). Thermal decarbonylation of the tetracarbonyl-dichalcogenides Cp(′) 2V 2(CO) 4E 2 ( 6) in toluene solution gave the tetranuclear clusters Cp(′) 4V 4E 4 ( 7) (E  S, Te) directly. The analogous pentamethylcyclopentadienyl compounds Cp★ 4V 4E 4 ( 7★) (E  S, Te) were also prepared. The spectroscopic data for the new CpV and Cp′V complexes are compared with those of the corresponding Cp★V compounds.