Work

Dinitrogen Activation with Low‐Valent Strontium

Year: 2025

Type: article

Abstract: DFT calculations on β‐diketiminate (BDI) complexes with the full series of alkaline‐earth (Ae) metals show that (BDI)AeAe(BDI) complexes of the heavier Ae metals (Ca, Sr, Ba) have long weak Ae─Ae bonds that are prone to homolytic bond cleavage. However, isolation of (BDI)Sr(μ‐N 2 )Sr(BDI) with a side‐on bridging N 2 2− dianion should thermodynamically be feasible. Attempts to stabilize such a complex with the super bulky BDI* ligand failed (BDI* = HC[(Me)C = N‐DIPeP] 2 , DIPeP = 2,6‐Et 2 CH‐phenyl). First, N 2 fixation with a Sr complex was enabled by a heterobimetallic approach. Reduction of ( DIPeP NN)Sr with potassium gave ( DIPeP NN) 2 Sr 2 K 2 (N 2 ) ( 6 ‐Sr); DIPeP NN = DIPeP N‐Si(Me) 2 CH 2 CH 2 Si(Me) 2 ‐N DIPeP . A similar Ca product was also isolated ( 6 ‐Ca). Crystal structures reveal a N 2 2− anion with side‐on bonding to Ae 2+ and end‐on coordination to K + . DFT calculations and Atoms‐In‐Molecules analyses show mainly ionic bonding. Both 6 ‐Ae complexes are synthons for hitherto unknown (BDI*)AeAe(BDI*) (Ae = Ca, Sr) and react by releasing N 2 and two electrons. Although surprisingly stable in benzene, the reduction of I 2 and H 2 is facile. Fast reaction with Teflon led to formation of crystalline [( DIPeP NN)SrKF] 2 ( 7 ), which is labile and decomposed to KF and ( DIPeP NN)Sr. Latter reactivity underscores potential use of 6 ‐Ae complexes as very strong, hydrocarbon‐soluble reducing agents.

Source: Angewandte Chemie International Edition

DOI: 10.1002/anie.202506989