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Tensi L, Moretti F, Amendola A, Froese RDJ, Macchioni A, Kuhlman RL, Pearson DM, Zuccaccia C. Solution Structure and Dynamics of Hf-Al and Hf-Zn Heterobimetallic Adducts Mimicking Relevant Intermediates in Chain Transfer Reactions. Inorg Chem 2024; 63:8222-8236. [PMID: 38666625 DOI: 10.1021/acs.inorgchem.4c00476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/07/2024]
Abstract
Cationic cyclometalated hafnocenes [CpPrCpCH2CH2CH2Hf][B(C6F5)4] (4Pr) and [CpiBuCpCH2CH(Me)CH2Hf][B(C6F5)4] (4aiBu and 4biBu) were synthesized from the corresponding [(CpPr)2HfMe][B(C6F5)4] (1Pr) and [(CpiBu)2HfMe][B(C6F5)4] (1iBu) complexes via C-H activation. 4aiBu, 4biBu, and 4Pr, mimicking a propagating M-polymeryl species (M = transition metal) with or without a β-methyl branch on the metalated chains, serve to investigate whether and how the nature of the last inserted olefin molecules changes the structure, stability, and reactivity of the corresponding heterobimetallic complexes, formed in the presence of aluminum- or zinc-alkyl chain transfer agents (CTAs), which are considered relevant intermediates in coordinative chain transfer polymerization (CCTP) and chain shuttling polymerization (CSP) technologies. NMR and DFT data indicate no major structural difference between the resulting heterobridged complexes, all characterized by the presence of multiple α-agostic interactions. On the contrary, thermodynamic and kinetic investigations, concerning the reversible formation and breaking of heterobimetallic adducts, demonstrate that isomer 4aiBu, in which the β-Me is oriented away from the reactive coordination site on Hf, but not 4biBu, having the β-Me pointing in the opposite direction, is capable of reacting with CTAs. Quantification of kinetic rate constants highlights that the formation process is rate limiting and that the nature of the last inserted α-olefin unit modulates transalkylation kinetics. The reaction of 4aiBu, 4biBu, and 4Pr with diisobutylaluminum hydride (DiBAlH) allows the interception and characterization of new heterobinuclear and heterotrinuclear species, featuring both hydride and alkyl bridging moieties, which represent structural models of elusive intermediates in CCTP and CSP processes, capturing the instant when an alkyl chain has just transferred from a transition metal to a main group metal, while the two metals remain engaged in a single heterobimetallic intermediate.
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Affiliation(s)
- Leonardo Tensi
- Department of Pharmaceutical Sciences, University of Perugia and CIRCC, Via del Liceo 1, 06123 Perugia, Italy
| | - Francesca Moretti
- Department of Chemistry, Biology and Biotechnology and CIRCC, University of Perugia and CIRCC, Via Elce di Sotto 8, 06123 Perugia, Italy
| | - Alessandra Amendola
- Department of Chemistry, Biology and Biotechnology and CIRCC, University of Perugia and CIRCC, Via Elce di Sotto 8, 06123 Perugia, Italy
| | - Robert D J Froese
- Core R&D, The Dow Chemical Company, 1776 Building, Midland, Michigan 48674, United States
| | - Alceo Macchioni
- Department of Chemistry, Biology and Biotechnology and CIRCC, University of Perugia and CIRCC, Via Elce di Sotto 8, 06123 Perugia, Italy
| | - Roger L Kuhlman
- The Dow Chemical Company, 230 Abner Jackson Parkway Herbert H Dow Building #2B104, Lake Jackson, Texas 77566, United States
| | - David M Pearson
- The Dow Chemical Company, 230 Abner Jackson Parkway Herbert H Dow Building #2B104, Lake Jackson, Texas 77566, United States
| | - Cristiano Zuccaccia
- Department of Chemistry, Biology and Biotechnology and CIRCC, University of Perugia and CIRCC, Via Elce di Sotto 8, 06123 Perugia, Italy
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Transition Metal-(μ-Cl)-Aluminum Bonding in α-Olefin and Diene Chemistry. Molecules 2022; 27:molecules27217164. [PMID: 36363991 PMCID: PMC9654437 DOI: 10.3390/molecules27217164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 10/19/2022] [Accepted: 10/20/2022] [Indexed: 11/06/2022] Open
Abstract
Olefin and diene transformations, catalyzed by organoaluminum-activated metal complexes, are widely used in synthetic organic chemistry and form the basis of major petrochemical processes. However, the role of M−(μ-Cl)−Al bonding, being proven for certain >C=C< functionalization reactions, remains unclear and debated for essentially more important industrial processes such as oligomerization and polymerization of α-olefins and conjugated dienes. Numerous publications indirectly point at the significance of M−(μ-Cl)−Al bonding in Ziegler−Natta and related transformations, but only a few studies contain experimental or at least theoretical evidence of the involvement of M−(μ-Cl)−Al species into catalytic cycles. In the present review, we have compiled data on the formation of M−(μ-Cl)−Al complexes (M = Ti, Zr, V, Cr, Ni), their molecular structure, and reactivity towards olefins and dienes. The possible role of similar complexes in the functionalization, oligomerization and polymerization of α-olefins and dienes is discussed in the present review through the prism of the further development of Ziegler−Natta processes and beyond.
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