Ligand Exchange Reactions of [(tmeda)NiR2] (R = CH2CMe3, CH2SiMe3, CH2CMe2Ph) with N-Heterocyclic Carbenes and Bidentate Phosphines

Article abstract of DOI:10.1021/acs.organomet.0c00262

Bis(alkyl)nickel(II) complexes [(tmeda)NiR2] (R = CH2SiMe3 (1a), CH2CMe3 (1b), CH2CMe2Ph (1c)) can be prepared from [(tmeda)Ni(acac)2] and MgR2. This approach is equivalent to and, in some cases, even superior to the frequently employed reaction of [(py)4NiR2] with Grignard reagents. With [(tmeda)NiR2] as the starting material, ligand exchange reactions with N-heterocyclic carbenes and bidentate phosphines were explored. The reaction of [(tmeda)NiR2] with IiPr2Me2 (IiPr2Me = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) yields three different classes of products: (a) [cis-(IiPr2Me2)2Ni(CH2SiMe3)2] (2a-cis) derived from NHC by tmeda replacement, (b) [(IiPr2Me2)(κ-C:C-IiPr2MeCH2)Ni(CH2SiMe3)] (3a) as a result of C-H bond activation of one iPr group of the NHC ligand, and (c) [cis-(IiPr2Me2)2Ni(κ-C:C-CH2CMe2C6H4)] (4c-cis), in which an o-C-H bond of the neophyl ligand has been activated. Addition of depe (depe = Et2PCH2CH2PEt2) to 1a,c results in a clean tmeda replacement to give the corresponding complexes [(dppe)NiR2] (R = CH2SiMe3 (5a), CH2CMe2Ph (5c)). All compounds have been fully characterized by various spectroscopic methods and in most cases by single-crystal X-ray diffraction.