Terminal and Super-Basic Parent Imides of Hafnium

A dinuclear hafnium complex containing the parent imido ligand [(PN)(PNC)Hf=NH{mu(2)-K}](2) (2) (PN-=(N-(2-(PPr2)-Pr-i-4-methylphenyl)-2,4,6-Me3C6H2; PNC2-=(N-(2-(PPr2)-Pr-i-4-methylphenyl)-2,4,6-CH2Me2C6H2), was prepared by reduction of the bisazide trans-[(PN)(2)Hf(N-3)(2)] (1) with two equiv of KC8. Encapsulation of K+ in 2 with crown-ether or cryptand affords the first discrete salt [K(encap)][(PN)(PNC)Hf equivalent to NH] (encap=18-crown-6(THF)(2), 3; 2,2,2-Kryptofix, 4), featuring a terminal parent imide and possessing some of the shortest Hf-N bond lengths known to date. DFT calculations revealed formation of 2 to proceed via an extremely basic monomeric nitrido, [(PN)(2)Hf equivalent to N](-)(A), having a computed pK(BH+) of similar to 57 followed by heterolytic splitting of an inert 1,2-CH bond of a benzylic methyl group across the Hf equivalent to N triple bond in A. An electronic structure analysis reveals A to possess a covalent Hf equivalent to N triple bond and of super-basic character. We also showcase reactivity of the Hf equivalent to NH bond with various electrophiles.

Automated summary

A dinuclear hafnium complex with a parent imido ligand was synthesized by reduction reaction and exhibited short Hf-N bond lengths. DFT calculations revealed the formation mechanism of the complex and showcased its reactivity with various electrophiles.