Bulky Group 2 Octaphenylmetallocenes and Direct Access to Calcium and Ytterbium Pseudo-Grignard Complexes

Abstract

The reaction between Mg( n Bu) 2 and C 5 Ph 4 H 2 in toluene at 100−110 °C yielded octaphenylmagnesocene, [Mg-(C 5 Ph 4 H) 2 ], which has two parallel Cp rings despite the steric bulk of the ligands. The redox-transmetalation/protolysis (RTP) reaction between calcium metal, HgPh 2 , and C 5 Ph 4 H 2 in thf afforded the bent calcium sandwich complex [Ca-(C 5 Ph 4 H) 2 (thf)]. Two rare calcium and ytterbium pseudo-Grignard complexes, [M(C 5 Ph 4 H)(μ-Br)(thf) 2 ] 2 , were prepared from RTP reactions of the corresponding metal, PhHgBr, and C 5 Ph 4 H 2 in thf. Reduction of the calcium bromide complex by KC 8 in the presence of 18-crown-6 afforded the charge-separated potassium compound [K(18-crown-6)(thf) 2 ][C 5 Ph 4 H], but no Ca I species were detected.

Crystal structure of 1,1′,2,2′,4,4′-hexaisopropylmagnesocene

“…Therefore, many crystal structures of magnesocenes are actually of donor complexes, such as magnesocene mono-and bis(tetrahydrofuran) adduct, Cp 2 MgÁ(thf) and Cp 2 MgÁ(thf) 2 (Lehmkuhl et al, 1986;Jaenschke et al, 2003;Kim et al, 2007). Nevertheless, solvent-free crystal structures are also known, especially in case of highly substituted magnesocenes (Morley et al, 1987;Gardiner et al, 1991;Weber et al, 2002;Vollet et al, 2003;Deacon et al, 2015;Mu ¨ller et al, 2021). Hanusa and coworkers had reported the synthesis of 1,1 0 ,2,2 0 ,4,4 0 -hexaisopropylmagnesocene, 3 Cp 2 Mg, -calcocene, 3 Cp 2 Ca, -strontocene, 3 Cp 2 Sr, and -barocene, 3 Cp 2 Ba (the triisopropylcyclopentadienide ligand is commonly abbreviated as ' 3 Cp'), via treatment of potassium 1,2,4-triisopropylcyclopentadienide, 3 CpK, with the corresponding metal(II) bromide or iodide and described the magnesocene to be oily or waxy in composition (Burkey et al, 1993(Burkey et al, , 1994.…”

Cyclopentadienyl Complexes of the Alkaline Earths in Light of the Periodic Trends

“…[Cp Me 2 Mg] (Cp Me =C 5 MeH 4 ) and [Cp (SiMe3) 2 Mg] (Cp (SiMe3) =C 5 (SiMe 3 )H 4 ) are viscous non‐distillable liquids with pyrophoric nature [27a] . [Cp CHMePh 2 Mg] [14a] (Cp CHMePh =C 5 (CHMePh)H 4 ) and [Cp Ph4 2 Mg] [35] (Cp Ph4 =C 5 Ph 4 H) are η 5 /η 5 linear sandwiches, isostructural with [Cp t Bu 2 Mg] and [Cp Me4 2 Mg], [25] respectively. [Cp Me4 t Bu 2 Mg] (Cp Me4 t Bu =C 5 Me 4 t Bu) on the other hand, with increased steric pressure compared to [Cp* 2 Mg], is bent like [Cp t Bu3 2 Mg] and [Cp (SiMe3)3 2 Mg] [25] .…”

“…The molecules are typically monomeric or dimeric depending on the sterics, while a few polymeric barium iodides are known [33b,81] . Figure 7 shows a consolidated list ordered in a Cp’ ring‐wise manner, [14a,20b,29a,33b,35,37,41,44–45,51b,53,81–82] but a detailed case to case comparison could be complicated and ineffective as four different variables (Cp’, M, X, and the co‐donors) are involved. However, a gross periodic pattern is still apparent where the smaller Mg has more examples with the sterically less bulky or less substituted Cp’ rings, while it is opposite for the larger Ca to Ba.…”

Functionalised Alkaline Earth Iodides from Grignard Synthons “PhAeI(thf)n” (Ae = Mg‐Ba)

“…Direct metal reactions have been almost exclusively used to prepare symmetrically substituted complexes, and their utility for the direct preparation of unsymmetrically substituted complexes is limited. The RTP synthesis of [{Ca(Cp Ph4 )(Br)(thf) 2 } 2 ] (Cp Ph4 = C 5 Ph 4 H – ) from calcium, Cp Ph4 H and [HgPhBr] is a rare example of such a direct metal reaction yielding a bifunctional complex (Scheme ).…”

“…Metal based synthesis of alkaline earth complexes via redox transmetallation/protolysis (RTP) and the synthesis of lanthanoid formamidinate and pyrazolate complexes by protolysis of lanthanoid pseudo‐Grignard synthons …”