Structural and electronic studies of substituted m-terphenyl lithium complexes

Abstract

Spectroscopic and computational investigation of the effects of para-substituted m-terphenyl lithium complexes reveals significant electronic differences at the metal centre.

Structural and Electronic Studies of Substituted m-Terphenyl Group 12 Complexes

“… 50 A similar trend was observed in recent studies of the analogous lithium complexes [R-Ar # -Li] 2 (R = t -Bu, SiMe 3 , H, Cl, CF 3 ). 38 We note that the chemical shifts for H-9 are largely unaffected by the identity of the metal ( Table 2 ).…”

“…The reaction between the lithium complexes [R-Ar # -Li] 2 (R-Ar # = 2,6-{2,6-Xyl} 2 -4-R-C 6 H 2 ; R = t -Bu, SiMe 3 , Cl, CF 3 ) 38 with one equivalent of ZnCl 2 , CdCl 2 , or HgBr 2 in a toluene/THF (10:1) mixture at room temperature yielded the Group 12 diaryl species ( t -Bu-Ar # ) 2 M (M = Zn 1 , Cd 2 , Hg 3 ), (Me 3 Si-Ar # ) 2 M (M = Zn 4 , Cd 5 , Hg 6 ), (Cl-Ar # ) 2 M (M = Zn 7 , Cd 8 , Hg 9 ), and (F 3 C-Ar # ) 2 M (M = Zn 10 , Cd 11 , Hg 12 ) according to Scheme 1 . Complexes 1 – 12 were recrystallized from a −30 °C iso -hexane solution to give colorless crystals in low-to-moderate isolated yields.…”

“…This contrasts with the recently reported dimeric lithium complexes [R-Ar # -Li] 2 (R = t -Bu, SiMe 3 , H, Cl, CF 3 ), where a trend in the 1 H NMR chemical shifts of equivalent protons was linked to C–H···Li agostic interactions. 38 However, for the Group 12 complexes, bond paths corresponding to C–H···C arene interactions were observed between the H-9 protons and aromatic carbons of the flanking aryl rings situated opposite to them ( Figure S48 ). Properties of the electron density at the bond critical points for these interactions are provided in Supporting Information Table S6 .…”

“…A plot of the chemical shifts, δ, against the Hammett constants, σ para , reveals a linear correlation (Figures and S1). A similar trend was observed in recent studies of the analogous lithium complexes [R-Ar # -Li] 2 (R = t -Bu, SiMe 3 , H, Cl, CF 3 ) . We note that the chemical shifts for H-9 are largely unaffected by the identity of the metal (Table ).…”

“…This analysis did not locate any bond paths corresponding to C–H···M (M = Zn, Cd, Hg) agostic interactions, which might have accounted for the observed trend in the H-9 chemical shifts. This contrasts with the recently reported dimeric lithium complexes [R-Ar # -Li] 2 (R = t -Bu, SiMe 3 , H, Cl, CF 3 ), where a trend in the 1 H NMR chemical shifts of equivalent protons was linked to C–H···Li agostic interactions . However, for the Group 12 complexes, bond paths corresponding to C–H···C arene interactions were observed between the H-9 protons and aromatic carbons of the flanking aryl rings situated opposite to them (Figure S48).…”