A regioselectively 1,1′,3,3′-tetrazincated ferrocene complex displaying core and peripheral reactivity

• Published in: Chemical science (Cambridge) 2020-03, Vol.11 (25), p.651-652
• Main Authors: Honeyman, Gordon W, Armstrong, David R, Clegg, William, Hevia, Eva, Kennedy, Alan R, McLellan, Ross, Orr, Samantha A, Parkinson, John A, Ramsay, Donna L, Robertson, Stuart D, Towie, Stephen, Mulvey, Robert E
• Format: Article
• Language: English
• Subjects: Anions; Chemistry; Crystallography; NMR; Nuclear magnetic resonance; Reactivity; Regioselectivity; Sodium; Toluene; Zinc compounds
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d0sc01612h

Regioselective 1,1′,3,3′-tetrazincation [C-H to C-Zn( t Bu)] of ferrocene has been achieved by reaction of a fourfold excess of di- t -butylzinc ( t Bu 2 Zn) with sodium 2,2,6,6-tetramethylpiperidide (NaTMP) in hexane solution manifested in the trimetallic iron-sodium-zinc complex [Na 4 (TMP) 4 Zn 4 ( t Bu) 4 {(C 5 H 3 ) 2 Fe}], 1 . X-ray crystallographic studies supported by DFT modelling reveal the structure to be an open inverse crown in which two [Na(TMP)Zn( t Bu)Na(TMP)Zn( t Bu)] 2+ cationic units surround a {(C 5 H 3 ) 2 Fe} 4− tetraanion. Detailed C 6 D 6 NMR studies have assigned the plethora of 1 H and 13 C chemical shifts of this complex. It exists in a major form in which capping and bridging TMP groups interchange, as well as a minor form that appears to be an intermediate in this complicated exchange phenomenon. Investigation of 1 has uncovered two distinct reactivities. Two of its peripheral t -butyl carbanions formally deprotonate toluene at the lateral methyl group to generate benzyl ligands that replace these carbanions in [Na 4 (TMP) 4 Zn 4 ( t Bu) 2 (CH 2 Ph) 2 {(C 5 H 3 ) 2 Fe}], 2 , which retains its tetrazincated ferrocenyl core. Benzyl-Na π-arene interactions are a notable feature of 2 . In contrast, reaction with pyridine affords the crystalline product {[Na·4py][Zn(py*) 2 ( t Bu)·py]} ∞ , 3 , where py is neutral pyridine (C 5 H 5 N) and py* is the anion (4-C 5 H 4 N), a rare example of pyridine deprotonated/metallated at the 4-position. This ferrocene-free complex appears to be a product of core reactivity in that the core-positioned ferrocenyl anions of 1 , in company with TMP anions, have formally deprotonated the heterocycle. A tetrazincated ferrocene complex displays divergent basicity towards aromatic substrates through either its core or peripheral ligands.