Intramolecular and intermolecular bromine⋯polyfluoroarene interactions: The crystal structure of bis{κC-1-(2,3,5,6-tetrafluoropyridyl)-3-benzylimidazolin-2-ylidene}tetrabromodimercury

Lane, Joseph R.; Saunders, Graham C.; Thomas, Hayden P.

doi:10.1016/j.jfluchem.2015.07.021

Cited by 1 publication

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“…In order to address the effect of an NHC supporting ligand on the activity and stereoselectivity of Me 2 GaOR(NHC), we have extended our previous studies on the synthesis, structure, and catalytic activity of this class of complexes with analogous complexes bearing asymmetric NHC ligands ( a NHCs), due to differently substituted nitrogens. Noteworthy, group 13 complexes with such a NHCs have not been reported so far, excluding group 13 metal complexes with asymmetric NHCs possessing Lewis base termini. , Noteworthy, barely any examples of main group metal complexes with asymmetric NHC, with nitrogens possessing different simple alkyl or aryl substituents, have been reported so far. , As a result, we have confirmed the supporting role of both symmetric and asymmetric NHCs and show how the structure of Me 2 GaOR(NHC) complexes, and consequently their activity and stereoselectivity in the ring-opening polymerization of rac -LA, can be tuned depending on the structure of N-heterocyclic carbenes. The effect of NHC on the activity of Me 2 GaOR(NHC) complexes have been supported by the structure–activity studies of Me(O,C NHC )GaOR, possessing monoanionic aryloxide chelate ligand with NHC functionality.…”

Section: Introductionsupporting

confidence: 67%

The Effect of Symmetric and Asymmetric NHCs on the Structure and Catalytic Properties of Dialkylgallium Alkoxides in the Ring-Opening Polymerization of rac-Lactide—Linking the Structure, Activity, and Stereoselectivity

et al. 2021

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Manipulating the structure of alkylgallium alkoxides with asymmetric N-heterocyclic carbenes (NHCs) has led to the formation of essentially "on" and "off" states of catalytic gallium centers in the ring-opening polymerization (ROP) of rac-lactide (rac-LA), and has allowed to rationalize the effect of the NHC on the activity and stereoselectivity of Me 2 GaOR(NHC) complexes. The reactions of dimethylgallium alkoxides with asymmetric NHCs, due to differently substituted nitrogens, resulted in the formation of Me 2 GaOR(SI(Dipp-Mes)The X-ray analysis of 1, 2, 4, and 5 revealed a strong effect of NHCs on their structure, manifested by the orientation of NHC with respect to Ga−C Me and Ga−O bonds, and OR alkoxide group. The latter, represented by a dihedral O−Ga−C NHC −N angle, have allowed to define the cavity required for the interaction of lactide with gallium and alkoxide groups, and subsequent insertion of lactide into the Ga−O alkoxide bond. Despite small differences between the cavities of 1 and Me 2 GaOMe(SIMes) (SIMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene), the structures of NHCs were responsible for their isoselectivities, of P m-max = 0.83 and P m-max = 0.78, respectively, in the ROP of rac-LA at −20 °C. The much smaller cavity of 4 led to a minor activity and lower isoselectivity (P m-max = 0.56 at −20 °C). Further decrease of the activity of Me(O,C NHC )GaOR (6), possessing both small cavity and, in contrast to 4, restrained rotation of Ga−C NHC bond of the chelate ligand, has supported the effect of NHC on the structure and activity of Me 2 GaOR(NHC) complexes. DFT calculations of the energy profile of the consecutive ring-opening of two lactide molecules into Ga−O alkoxide bonds of 1, 4, and Me 2 GaOMe(SIMes) have confirmed the effect of NHC on their stereoselectivity.

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