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

Regioselective 1,1′,3,3′-tetrazincation [C–H to C–Zn(tBu)] of ferrocene has been achieved by reaction of a fourfold excess of di-t-butylzinc (tBu(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)(tBu)(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(tBu)Na(TMP)Zn(tBu)](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)(tBu)(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)(tBu)·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.