An official website of the United States government
Abstract The conventional synthetic approach to transition metal pincer complexes calls for the preparation of the tridentate pincer (pro)ligand first, with subsequent introduction of the transition metal center as the last step. This work demonstrates that the alternative synthetic logic, where the central main group element is introduced last, can be applicable to a number of PEP pincer complexes (E=B, Al, Si, P) derived from phosphinophenols and phosphinopyrroles. This approach obviates the need to isolate well‐behaved propincer precursors, and instead relies on the formation of phosphine‐metal adducts first, whose nature determines the stoichiometry of the needed main group reagent to complete the synthesis.
more »
« less
Pincer-supported metal/main-group bonds as platforms for cooperative transformations
Electron-rich late metals and electropositive main-group elements (metals and metalloids) can be combined to provide an ambiphilic façade for exploring metal–ligand cooperation, yet the instability of the metal/main-group bond frequently limits the study and application of such units. Incorporating main-group donors into pincer frameworks, where they are stabilized and held in proximity to the transition-metal partner, can allow discovery of new modes of reactivity and incorporation into catalytic processes. This Perspective summarizes common modes of cooperativity that have been demonstrated for pincer frameworks featuring metal/main-group bonds, highlighting similarities among boron, aluminium, and silicon donors and identifying directions for further development.
more »
« less
- Award ID(s):
- 1552591
- PAR ID:
- 10312224
- Date Published:
- Journal Name:
- Dalton Transactions
- Volume:
- 50
- Issue:
- 45
- ISSN:
- 1477-9226
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The first examples of a CNC pincer ligands with a central pyridinol derived ring were recently reported. The differences in catalytic reactivity between CNC ligands with a central pyridine ring vs. a pyridinol derived ring are substantial and highly active and robust catalysts have been synthesized and studied. In these pincer ligands, the 4-substituent can be OMe, OH, or O-, and these latter two options allow for altered catalyst properties as a function of proton concn. Catalytic studies have used ruthenium(II), nickel(II), and other transition metals. We have made metal complexes that can be protonated or deprotonated reversibly in situ to switch on or off the photocatalytic performance towards CO2 redn. Furthermore, the methoxy group on the pyridine ring offers unique catalysis advantages not seen with the unsubstituted analog. Our best catalysts offer selective CO formation, >300 turnover cycles, and a 40 h lifetime. Steric and electronic ligand effects are being studied with these catalysts by exptl. and computational methods.more » « less
-
The catalytic hydroboration of imines, nitriles, and carbodiimides is a powerful method of preparing amines which are key synthetic intermediates in the synthesis of many value-added products. Imine hydroboration has perennially featured in notable reports while nitrile and carbodiimide hydroboration have gained attention recently. Initial developments in catalytic hydroboration of imines and nitriles employed precious metals and typically required harsh reaction conditions. More recent advances have shifted toward the use of base metal and main group element catalysis and milder reaction conditions. In this survey, we review metal and nonmetal catalyzed hydroboration of these unsaturated organic molecules and group them into three distinct categories: precious metals, base metals, and main group catalysts. The TON and TOF of imine hydroboration catalysts are reported and summarized with a brief overview of recent advances in the field. Mechanistic and kinetic studies of some of these protocols are also presented.more » « less
-
We systematically investigated iodine–metal and iodine–iodine bonding in van Koten’s pincer complex and 19 modifications changing substituents and/or the transition metal with a PBE0–D3(BJ)/aug–cc–pVTZ/PP(M,I) model chemistry. As a novel tool for the quantitative assessment of the iodine–metal and iodine–iodine bond strength in these complexes we used the local mode analysis, originally introduced by Konkoli and Cremer, complemented with NBO and Bader’s QTAIM analyses. Our study reveals the major electronic effects in the catalytic activity of the M–I–I non-classical three-center bond of the pincer complex, which is involved in the oxidative addition of molecular iodine I2 to the metal center. According to our investigations the charge transfer from the metal to the σ* antibonding orbital of the I–I bond changes the 3c–4e character of the M–I–I three-center bond, which leads to weakening of the iodine I–I bond and strengthening of the metal–iodine M–I bond, facilitating in this way the oxidative addition of I2 to the metal. The charge transfer can be systematically modified by substitution at different places of the pincer complex and by different transition metals, changing the strength of both the M–I and the I2 bonds. We also modeled for the original pincer complex how solvents with different polarity influence the 3c–4e character of the M–I–I bond. Our results provide new guidelines for the design of pincer complexes with specific iodine–metal bond strengths and introduce the local vibrational mode analysis as an efficient tool to assess the bond strength in complexes.more » « less
-
The first examples of a CNC pincer ligands with a central pyridinol derived ring were recently reported. The differences in catalytic reactivity between CNC ligands with a central pyridine ring vs. a pyridinol derived ring are substantial and highly active and robust catalysts have been synthesized and studied. In these pincer ligands, the 4-substituent can be OMe, OH, or O , and these latter two options allow for altered catalyst properties as a function of proton concn. Catalytic studies have used ruthenium(II), nickel(II), and other transition metals. We have made metal complexes that can be protonated or deprotonated reversibly in situ to switch on or off the photocatalytic performance towards CO redn. Furthermore, the methoxy group on the pyridine ring offers unique catalysis advantages not seen with the unsubstituted analog. Our best catalysts offer selective CO formation, >300 turnover cycles, and a 40 h lifetime. Highly active self-sensitized catalysts have recently been developed. Steric and electronic ligand effects are being studied with these catalysts by exptl. and computational methods.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1DT02739E
