Premium
One‐Electron Oxidation of a Disilicon(0) Compound: An Experimental and Theoretical Study of [Si 2 ] + Trapped by N‐Heterocyclic Carbenes
Author(s) -
Arz Marius I.,
Straßmann Martin,
Meyer Andreas,
Schnakenburg Gregor,
Schiemann Olav,
Filippou Alexander C.
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201502199
Subject(s) - electron , silicon , chemistry , physics , atomic physics , materials science , nuclear physics , organic chemistry
One‐electron oxidation of the disilicon(0) compound Si 2 (Idipp) 2 ( 1 , Idipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) with [Fe(C 5 Me 5 ) 2 ][B(Ar F ) 4 ] (Ar F =C 6 H 3 ‐3,5‐(CF 3 ) 2 ) affords selectively the green radical salt [Si 2 (Idipp) 2 ][B(Ar F ) 4 ] ( 1 ‐[B(Ar F ) 4 ). Oxidation of the centrosymmetric 1 occurs reversibly at a low redox potential ( E 1/2 =−1.250 V vs. Fc + /Fc), and is accompanied by considerable structural changes as shown by single‐crystal X‐ray structural analysis of 1 ‐B(Ar F ) 4 . These include a shortening of the SiSi bond, a widening of the Si‐Si‐C NHC angles, and a lowering of the symmetry, leading to a quite different conformation of the NHC substituents at the two inequivalent Si sites in 1 + . Comparative quantum chemical calculations of 1 and 1 + indicate that electron ejection occurs from the symmetric (n + ) combination of the Si lone pairs (HOMO). EPR studies of 1 ‐B(Ar F ) 4 in frozen solution verified the inequivalency of the two Si sites observed in the solid‐state, and point in agreement with the theoretical results to an almost equal distribution of the spin density over the two Si atoms, leading to quite similar 29 Si hyperfine coupling tensors in 1 + . EPR studies of 1 ‐B(Ar F ) 4 in liquid solution unraveled a topomerization with a low activation barrier that interconverts the two Si sites in 1 + .