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 (tBu2Zn) with sodium 2,2,6,6-tetramethylpiperidide (NaTMP) in hexane solution manifested in the trimetallic iron-sodium-zinc complex [Na4(TMP)4Zn4(tBu)4{(C5H3)2Fe}], 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 {(C5H3)2Fe}4- tetraanion. Detailed C6D6 NMR studies have assigned the plethora of 1H and 13C 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 [Na4(TMP)4Zn4(tBu)2(CH2Ph)2{(C5H3)2Fe}], 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 (C5H5N) and py* is the anion (4-C5H4N), 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.

Heterobimetallic metallation studies of N,N-dimethylphenylethylamine (DMPEA): benzylic C-H bond cleavage/dimethylamino capture or intact DMPEA complex.

Reaction of the sodium monoamido-bisalkylzincate [(TMEDA)Na(TMP)(Bu(t))Zn(Bu(t))] (TMEDA is N,N,N',N'-tetramethylethylenediamine; TMP is 2,2,6,6-tetramethylpiperidide) and the related lithium zincate [(PMDETA)Li(TMP)Zn(Bu(t))2] (PMDETA is N,N,N',N'',N''-pentamethyldiethylenetriamine) with the sensitive bio-relevant scaffold N,N-dimethylphenylethylamine, DMPEA, afforded the crystalline complexes [(TMEDA)Na(TMP)(NMe2)Zn(Bu(t))] and [(PMDETA)Li(NMe2)Zn(Bu(t))2], respectively, both of which have been characterized by NMR spectroscopic and X-ray crystallographic studies. Made by reaction of a LiTMP-(TMP)Al(Bu(i))2 mixture with DMPEA, a third dimethylamino-containing crystalline complex, the aluminate [(THF)Li(TMP)(NMe2)Al(Bu(i))2] has been similarly characterized. All three complexes can be regarded as products of cleave and capture chemistry whereby metallation at the benzylic position of DMPEA has led to a ß-elimination of an anionic Me2N fragment that has been captured by a charge balancing cationic heterobimetallic entity. While a metallated intermediate prior to the elimination has proved elusive in all of these reactions, DMPEA has been captured fully intact in the novel Lewis acid-Lewis base crystalline complex [DMPEA·Li(TMP)Zn(Me)2], which has also been characterized by the aforementioned techniques.

Concealed cyclotrimeric polymorph of lithium 2,2,6,6-tetramethylpiperidide unconcealed: X-ray crystallographic and NMR spectroscopic studies.

Lithium 2,2,6,6-tetramethylpiperidide (LiTMP), one of the most important polar organometallic reagents both in its own right and as a key component of ate compositions, has long been known for its classic cyclotetrameric (LiTMP)4 solid-state structure. Made by a new approach through transmetalation of Zn(TMP)2 with tBuLi in n-hexane solution, a crystalline polymorph of LiTMP has been uncovered. X-ray crystallographic studies at 123(2) K revealed this polymorph crystallises in the hexagonal space group P63 /m and exhibited a discrete cyclotrimeric (C3h ) structure with a strictly planar (LiN)3 ring containing three symmetrically equivalent TMP chair-shaped ligands. The molecular structure of (LiTMP)4 was redetermined at 123(2) K, because its original crystallographic characterisation was done at ambient temperature. This improved redetermination confirmed a monoclinic C2/c space group with the planar (LiN)4 ring possessing pseudo (non-crystallographic) C4h symmetry. Investigation of both metalation and transmetalation routes to LiTMP under different conditions established that polymorph formation did not depend on the route employed but rather the temperature of crystallisation. Low-temperature (freezer at -35 °C) cooling of the reaction solution favoured (LiTMP)3 ; whereas high-temperature (bench) storage favoured (LiTMP)4 . Routine (1) H and (13) C NMR spectroscopic studies in a variety of solvents showed that (LiTMP)3 and (LiTMP)4 exist in equilibrium, whereas (1) H DOSY NMR studies gave diffusion coefficient results consistent with their relative sizes.