1
|
Lastowski RJ, Yarranton JT, Zhu L, Vogiatzis KD, Girolami GS. Three-Center M-H-B Bonds Are Strong Field Interactions. Synthesis and Characterization of M(CH 2NMe 2BH 3) 3 Complexes of Titanium, Chromium, and Cobalt. J Am Chem Soc 2023; 145:23585-23599. [PMID: 37851538 DOI: 10.1021/jacs.3c07336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2023]
Abstract
We describe new compounds of stoichiometry M(CH2NMe2BH3)3 (M = Ti, Cr, and Co), each of which contains three chelating boranatodimethylaminomethyl (BDAM) ligands. In all three compounds, the BDAM anion, which is isoelectronic and isostructural with the neopentyl group, is bound to the metal center at one end by a metal-carbon σ bond and at the other by one three-center M-H-B interaction. The crystal structures show that the d1 titanium(III) compound is trigonal prismatic (or eight-coordinate, if two longer-ranged M···H interactions with the BH3 groups are included), whereas the d3 chromium(III) compound and the d6 cobalt(III) compounds are both fac-octahedral. The Cr and Co compounds exhibit two rapid dynamic processes in solution: exchange between the Δ and Λ enantiomers and exchange of the terminal and bridging hydrogen atoms on boron. For the Co complex, the barrier for Δ/Λ exchange (ΔG⧧298 = 10.1 kcal mol-1) is significantly smaller than those seen in other octahedral cobalt(III) compounds; DFT calculations suggest that Bailar twist and dissociative pathways for Δ/Λ exchange are both possible mechanisms. The UV-vis absorption spectra of the cobalt(III) and chromium(III) species show that the ligand field splittings Δo caused by the M-H-B interactions are unexpectedly large, thus placing them high on the spectrochemical series (near ammonia and alkyl groups); their nephelauxetic effect is also large. The DFT calculations suggest that these properties of M-H-B interactions are in part a consequence of their three-center nature, which delocalizes electron density away from the metal center and reduces electron-electron repulsions.
Collapse
Affiliation(s)
- R Joseph Lastowski
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | - Jonathan T Yarranton
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Lingyang Zhu
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| | | | - Gregory S Girolami
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States
| |
Collapse
|
2
|
Salvadori E, Chiesa M, Buonerba A, Grassi A. Structure and dynamics of catalytically competent but labile paramagnetic metal-hydrides: the Ti(iii)-H in homogeneous olefin polymerization. Chem Sci 2020; 11:12436-12445. [PMID: 34123229 PMCID: PMC8162776 DOI: 10.1039/d0sc04967k] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Accepted: 09/24/2020] [Indexed: 11/29/2022] Open
Abstract
Metal hydride complexes find widespread application in catalysis and their properties are often understood on the basis of the available crystal structures. However, some catalytically relevant metal hydrides are only spontaneously formed in situ, cannot be isolated in large quantities or crystallised and their structure is therefore ill defined. One such example is the paramagnetic Ti(iii)-hydride involved in homogeneous Ziegler-Natta catalysis, formed upon activation of CpTi(iv)Cl3 with modified methylalumoxane (MMAO). In this contribution, through a combined use of electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) and hyperfine sublevel correlation (HYSCORE) spectroscopies we identify the nature of the ligands, their bonding interaction and the extent of the spin distribution. From the data, an atomistic and electronic model is proposed, which supports the presence of a self-assembled ion pair between a cationic terminal Ti-hydride and an aluminate anion, with a hydrodynamic radius of ca. 16 Å.
Collapse
Affiliation(s)
- Enrico Salvadori
- Department of Chemistry, University of Turin Via Pietro Giuria 7 Torino 10125 Italy
| | - Mario Chiesa
- Department of Chemistry, University of Turin Via Pietro Giuria 7 Torino 10125 Italy
| | - Antonio Buonerba
- Dipartimento di Chimica e Biologia, Università degli Studi di Salerno Via Giovanni Paolo II, 132 I-84084 Fisciano SA Italy
| | - Alfonso Grassi
- Dipartimento di Chimica e Biologia, Università degli Studi di Salerno Via Giovanni Paolo II, 132 I-84084 Fisciano SA Italy
| |
Collapse
|
3
|
Roldan-Molina E, Padial NM, Lezama L, Oltra JE. CpTiCl 2
, an Improved Titanocene(III) Catalyst in Organic Synthesis. European J Org Chem 2018. [DOI: 10.1002/ejoc.201801120] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Esther Roldan-Molina
- Department of Organic Chemistry.; University of Granada; Campus Fuentenueva s/n, E -18071 Granada Spain
| | - Natalia M. Padial
- Department of Organic Chemistry.; University of Granada; Campus Fuentenueva s/n, E -18071 Granada Spain
| | - Luis Lezama
- Department of Inorganic Chemistry and BCMaterials. University of the Basque Country. UPV/EHU; 48080 Bilbao Spain
| | - J. Enrique Oltra
- Department of Organic Chemistry.; University of Granada; Campus Fuentenueva s/n, E -18071 Granada Spain
| |
Collapse
|
4
|
Morra E, Giamello E, Chiesa M. EPR approaches to heterogeneous catalysis. The chemistry of titanium in heterogeneous catalysts and photocatalysts. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 280:89-102. [PMID: 28579105 DOI: 10.1016/j.jmr.2017.02.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Revised: 02/09/2017] [Accepted: 02/10/2017] [Indexed: 06/07/2023]
Abstract
Paramagnetic species are often involved in catalytic or photocatalytic reactions occurring at the solid-gas interface of heterogeneous catalysts. In this contribution we will provide an overview of the wealth and breadth of information that can be obtained from EPR in the characterization of paramagnetic species in such systems, illustrating the advantages that modern pulsed EPR methodologies can offer in monitoring the elementary processes occurring within the coordination sphere of surface transition-metal ions. To do so we selected three representative systems, where titanium ions in low oxidation states act as active catalytic sites, trying to outline the methodological approaches which characterize the application of EPR techniques and the questions that can be answered and addressed relative to the characterization of heterogeneous catalytic materials.
Collapse
Affiliation(s)
- Elena Morra
- Dipartimento di Chimica, Università di Torino, Via Giuria, 7, 10125 Torino, Italy
| | - Elio Giamello
- Dipartimento di Chimica, Università di Torino, Via Giuria, 7, 10125 Torino, Italy
| | - Mario Chiesa
- Dipartimento di Chimica, Università di Torino, Via Giuria, 7, 10125 Torino, Italy.
| |
Collapse
|
5
|
Ye Q, Ziegler MS, Lakshmi KV, Don Tilley T. Titanium Imido Complexes via Displacement of -SiMe 3 and C-H Bond Activation in a Ti(III) Amido Complex, Promoted by a Cyclic (Alkyl)(Amino) Carbene (cAAC). Eur J Inorg Chem 2017; 2017:2484-2487. [PMID: 30505212 PMCID: PMC6261457 DOI: 10.1002/ejic.201700295] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Indexed: 11/08/2022]
Abstract
A strong σ-donating cyclic (alkyl)(amino) carbene (cAAC) triggers rearrangement of the silyl(aryl) amido ligand -N(SiMe3)Dipp (Dipp = 2,6-diisopropylphenyl) in the coordination sphere of titanium(III) to afford a novel zwitterionic titanium imido complex with a TiCH2SiMe2[cAAC] linkage. Reduction of this species produces a new DippN=Ti imido complex containing a cAAC-centered radical species, characterized by single crystal diffraction analysis and electron paramagnetic resonance spectroscopy.
Collapse
Affiliation(s)
- Qing Ye
- Department of Chemistry, University of California, Berkeley, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, CA94720-1460, USA
- Department of Chemistry, South University of Science and Technology of China, Shenzhen, Guangdong 518055 (China)
| | - Micah S Ziegler
- Department of Chemistry, University of California, Berkeley, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, CA94720-1460, USA
| | - K V Lakshmi
- Department of Chemistry, University of California, Berkeley, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, CA94720-1460, USA
- Department of Chemistry and Chemical Biology and The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180, United States
| | - T Don Tilley
- Department of Chemistry, University of California, Berkeley, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, CA94720-1460, USA
| |
Collapse
|
6
|
Morra E, Maurelli S, Chiesa M, Giamello E. Rational Design of Engineered Multifunctional Heterogeneous Catalysts. The Role of Advanced EPR Techniques. Top Catal 2015. [DOI: 10.1007/s11244-015-0418-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
|
7
|
Maurelli S, Morra E, Van Doorslaer S, Busico V, Chiesa M. EPR investigation of TiCl3 dissolved in polar solvents--implications for the understanding of active Ti(III) species in heterogeneous Ziegler-Natta catalysts. Phys Chem Chem Phys 2015; 16:19625-33. [PMID: 25109263 DOI: 10.1039/c4cp02722a] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Multi-frequency continuous-wave and pulsed EPR techniques are employed to investigate Ti(III)-chloro complexes obtained by dissolving TiCl3 in anhydrous and hydrated methanol. Two distinctly different species, characterized by different g matrices are observed in the two cases. Hyperfine sublevel correlation (HYSCORE) spectroscopy is found to be a powerful method to identify the type of nuclei surrounding the Ti(3+) ion. For the first time, the hyperfine and nuclear quadrupole data of Ti(III)-bound (35/37)Cl nuclei are reported together with (1)H and (13)C hyperfine data of the coordinated methanol molecules. DFT modelling allows interpreting the measured spin Hamiltonian parameters in terms of microscopic models of the solvated species. The theoretical observable properties (g matrix, (35/37)Cl, (1)H and (13)C hyperfine tensors) are in quantitative agreement with the experiments for two families of complexes: [TiCln(CH3OH)6-n]((3-n)+) (with n ranging from 1 to 3) and [Ti(CH3OH)5(OH)](2+) or [Ti(CH3OH)5(OCH3)](2+). The first complex is observed in anhydrous methanol, while the second type of complex is observed when water is added to the solution, the presence of OH(-) and/or CH3O(-) species being promoted by water hydrolysis. The results obtained for the frozen solutions are critically compared to EPR spectra recorded for a MgCl2-supported Ti-based Ziegler-Natta model catalyst.
Collapse
Affiliation(s)
- Sara Maurelli
- University of Antwerp, Department of Physics, Universiteitsplein 1, B-2610 Wilrijk, Belgium.
| | | | | | | | | |
Collapse
|
8
|
Morra E, Maurelli S, Chiesa M, Van Doorslaer S. Probing the coordination environment of Ti3+ ions coordinated to nitrogen-containing Lewis bases. Phys Chem Chem Phys 2015. [DOI: 10.1039/c5cp03417e] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A combined EPR and DFT study on model systems reveals fingerprint 14N hyperfine and quadrupole data to identify binding of nitrogen-containing Lewis bases to Ti(iii).
Collapse
Affiliation(s)
- E. Morra
- Dipartimento di Chimica
- University of Torino Via Giuria
- 7-10125 Torino
- Italy
- University of Antwerp
| | - S. Maurelli
- Dipartimento di Chimica
- University of Torino Via Giuria
- 7-10125 Torino
- Italy
| | - M. Chiesa
- Dipartimento di Chimica
- University of Torino Via Giuria
- 7-10125 Torino
- Italy
| | | |
Collapse
|
9
|
Morra E, Giamello E, Chiesa M. Probing the redox chemistry of titanium silicalite-1: formation of tetrahedral Ti3+ centers by reaction with triethylaluminum. Chemistry 2014; 20:7381-8. [PMID: 24824439 DOI: 10.1002/chem.201304139] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Revised: 11/21/2013] [Indexed: 11/10/2022]
Abstract
Transition-metal ions with open-shell configurations hold promise in the development of novel coordination chemistry and potentially unprecedented redox catalysis. Framework-substituted Ti(3+) ions with tetrahedral coordination are generated by reductive activation of titanium silicalite-1 with triethylaluminum, an indispensable co-catalyst for heterogeneous Ziegler-Natta polymerization catalysts. Continuous-wave and pulse electron paramagnetic resonance methods are applied to unravel details on the local environment of the reduced transition metal-ions, which are shown to be part of the silica framework by detection of (29)Si hyperfine interactions. The chemical accessibility of the reduced sites is probed using ammonia as probe molecule. Evidence is found for the coordination of a single ammonia molecule. Comparison to similar systems, such as TiAlPO-5, reveals clear differences in the coordination chemistry of the reduced Ti sites in the two solids, which may be understood considering the different electronic properties of the solid frameworks.
Collapse
Affiliation(s)
- Elena Morra
- Department of Chemistry, University of Torino, Via Giuria, 7, 10125 Torino (Italy), Fax: (+39) 0116707855; Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven (The Netherlands)
| | | | | |
Collapse
|
10
|
Maurelli S, Vishnuvarthan M, Berlier G, Chiesa M. NH3 and O2interaction with tetrahedral Ti3+ions isomorphously substituted in the framework of TiAlPO-5. A combined pulse EPR, pulse ENDOR, UV-Vis and FT-IR study. Phys Chem Chem Phys 2012; 14:987-95. [DOI: 10.1039/c1cp22897h] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
|
11
|
Maurelli S, Livraghi S, Chiesa M, Giamello E, Van Doorslaer S, Di Valentin C, Pacchioni G. Hydration Structure of the Ti(III) Cation as Revealed by Pulse EPR and DFT Studies: New Insights into a Textbook Case. Inorg Chem 2011; 50:2385-94. [DOI: 10.1021/ic1021802] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Sara Maurelli
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I-10125 Torino, Italy
| | - Stefano Livraghi
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I-10125 Torino, Italy
| | - Mario Chiesa
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I-10125 Torino, Italy
| | - Elio Giamello
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I-10125 Torino, Italy
| | - Sabine Van Doorslaer
- University of Antwerp, Department of Physics, Universiteitsplein 1, B-2610 Wilrijk-Antwerp, Belgium
| | - Cristiana Di Valentin
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53-20125, Milano, Italy
| | - Gianfranco Pacchioni
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53-20125, Milano, Italy
| |
Collapse
|
12
|
Uppal R, Incarvito CD, Lakshmi KV, Valentine AM. Aqueous Spectroscopy and Redox Properties of Carboxylate-Bound Titanium. Inorg Chem 2006; 45:1795-804. [PMID: 16471996 DOI: 10.1021/ic051714j] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The aqueous chemistry of Ti(III) and Ti(IV) in two different chemical environments is investigated given its relevance to environmental, materials, and biological chemistry. Complexes of titanium with the carboxylate ligands citrate and oxalate, found ubiquitously in Nature, were synthesized. The redox properties were studied by using cyclic voltammetry. All the titanium citrate redox couples are quasi-reversible. Electrospray mass spectrometry of the Ti(III) citrate solution shows the presence of a 1:2 Ti/cit complex in solution, in contrast to the predominant 1:3 Ti/cit complex with Ti(IV). The change in the coordination of the ligand to the metal on reduction may explain the quasi-reversible behavior of the electrochemistry. The redox potentials for Ti(IV) citrate in water vary with pH. At pH 7, the approximate E(1/2) is less than -800 mV. This stated change in redox properties is considered in light of the previously reported Ti(IV) citrate solution speciation. Analogous speciation behavior is suggested from the EPR spectroscopy of Ti(III) citrate aqueous solutions. The g tensors are deduced for several pH-dependent species from the simulated data. The X-ray crystal structure of a Ti(III)(2) oxalate dimer Ti(2)(mu-C(2)O(4))(C(2)O(4))(2)(H(2)O)(6).2H(2)O (3), which crystallizes from water below pH 2, is reported. Complex 3 crystallizes in a monoclinic P2(1)/c space group with a = 9.5088(19) Angstroms, b = 6.2382(12) Angstroms, c = 13.494(3) Angstroms, V = 797.8(3) Angstroms(3), and Z = 2. The infrared spectroscopy, EPR spectroscopy, and cyclic voltammetry on complex 3 are reported. The cyclic voltammetry shows an irreversible redox couple approximately -196 mV which likely corresponds to the Ti(IV)(2)/Ti(III)Ti(IV) couple. The EPR spectroscopy on solid complex 3 shows a typical S = 1 triplet-state spectrum. The solid follows non-Curie behavior, and the antiferromagnetic coupling between the two metal centers is determined to be -37.2 cm(-1). However, in solution the complex follows Curie behavior and supports a Ti(III)Ti(IV) oxidation state for the dimer.
Collapse
Affiliation(s)
- Ritika Uppal
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, USA
| | | | | | | |
Collapse
|
13
|
Effect of preparation parameters on SrTiO3±δ catalyst for the flameless combustion of methane. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/j.molcata.2004.09.023] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
14
|
Lukešová L, Horáček M, Štěpnička P, Gyepes R, Cı́sařová I, Kubišta J, Mach K. Irregular cyclization reactions in titanocenes bearing pendant double bonds. J Organomet Chem 2004. [DOI: 10.1016/j.jorganchem.2004.02.040] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|