Structural Analysis of Zincocenes with Substituted Cyclopentadienyl Rings

Abstract

New zincocenes [ZnCp'(2)] (2-5) with substituted cyclopentadienyl ligands C(5)Me(4)H, C(5)Me(4)tBu, C(5)Me(4)SiMe(2)tBu and C(5)Me(4)SiMe(3), respectively, have been prepared by the reaction of ZnCl(2) with the appropriate Cp'-transfer reagent. For a comparative structural study, the known [Zn(C(5)H(4)SiMe(3))(2)] (1), has also been investigated, along with the mixed-ring zincocenes [Zn(C(5)Me(5))(C(5)Me(4)SiMe(3))] (6) and [Zn(C(5)Me(5))(C(5)H(4)SiMe(3))] (7), the last two obtained by conproportionation of [Zn(C(5)Me(5))(2)] with 5 or 1, as appropriate. All new compounds were characterised by NMR spectroscopy, and by X-ray methods, with the exception of 7, which yields a side-product (C) upon attempted crystallisation. Compounds 5 and 6 were also investigated by (13)C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp' ligands, while 3 and 4 exhibit slipped-sandwich geometries. Compounds 5 and 6 have rigid, eta(5)/eta(1)(sigma) structures, in which the monohapto C(5)Me(4)SiMe(3) ligand is bound to zinc through the silyl-bearing carbon atom, forming a Zn--C bond of comparable strength to the Zn--Me bond in ZnMe(2). Zincocene 5 has dynamic behaviour in solution, but a rigid eta(5)/eta(1)(sigma) structure in the solid state, as revealed by (13)C CPMAS NMR studies, whereas for 6 the different nature of the Cp' ligands and of the ring substituents of the eta(1)-Cp' group (Me and SiMe(3)) have permitted observation for the first time of the rigid eta(5)/eta(1) solution structure. Iminoacyl compounds of composition [Zn(eta(5)-C(5)Me(4)R)(eta(1)-C(NXyl)C(5)Me(4)R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl=2,6-dimethylphenylisocyanide) have also been obtained and characterised.

New Racemic and Single Enantiopure Hybrid Scorpionate/Cyclopentadienyl Magnesium and Zinc Initiators for the Stereoselective ROP of Lactides

“…17 Additionally, the Zn(1)−C(13) bond length of 2.191(3) Å is consistent with that previously observed in zincocenes with parallel [η 5 /η 1 (π)] and nonparallel [η 5 /η 1 (σ)] cyclopentadienyl rings. 17 4) Å] can be considered as nonbonding. 11a,17 It is worth noting that the coordination to zinc in this complex, in the solid state, is through the carbon atom C (13).…”

Zincocene and Dizincocene N‐Heterocyclic Carbene Complexes and Catalytic Hydrogenation of Imines and Ketones

“…To that end, the parent octamethyl-and bis(trimethylsilyl)zincocenes, [Zn(Cp Me4 ) 2 ] and [Zn-(Cp TMS ) 2 ], which are known to be coordination polymers in the solid state, were prepared and converted with NHCs (Scheme 1). [21] Although the reported syntheses used [LiC 5 H 4 SiMe 3 ] and [Mg(C 5 Me 4 H) 2 ] as metathesis reagents, the present approach is similar to that reported for analogous ZnCp* 2 derivatives. [18] Thus, the pro-ligands Cp R H were treated with 1.2 equivalent of NaH and subsequently reacted with ZnCl 2 .…”

“…Because the above‐described previous results demonstrated that NHCs can stabilize cyclopentadienyl–zinc hydrides, we sought to probe related systems. To that end, the parent octamethyl‐ and bis(trimethylsilyl)zincocenes, [Zn(Cp Me4 ) 2 ] and [Zn(Cp TMS ) 2 ], which are known to be coordination polymers in the solid state, were prepared and converted with NHCs (Scheme ) 21. Although the reported syntheses used [LiC 5 H 4 SiMe 3 ] and [Mg(C 5 Me 4 H) 2 ] as metathesis reagents, the present approach is similar to that reported for analogous ZnCp* 2 derivatives 18.…”

“…This is likely a consequence of steric effects, and a similar binding was observed for the parent compound [Zn(Cp TMS ) 2 ] n . [21] The overall observed complex geometry is reminiscent of the paddle-wheel nature of 6.…”

Assembly of ethylzincate compounds into supramolecular structures

“…Dicyclopentadienylzinc, for example, gives rise to polymeric zigzag chains, which are interconnected through CH/p-interactions into a three-dimensional network [32]. Bis(2,3,4,5-tetramethylcyclopentadienyl)zinc forms similar chains, but there is no evidence of CH/p-interactions, and no network is formed [33]. In di(2-methylallyl)zinc, a three-dimensional supramolecular network is obtained through coordination of four methylallyl groups to each zinc; two through primarily covalent ZneC s-bonds, and two additional methylallyl ligands from adjacent molecules coordinate to the zinc atom through their psystems [34].…”