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

Abstract

The electron‐rich cyclopentadienyl and the analogous indenyl and fluorenyl ligands (collectively denoted here as Cp’) have been impactful in stabilizing electron‐deficient metal centers including the highly electropositive alkaline earths. Being in the s‐block, the group 2 metals follow a major periodic variation in their atomic and ionic properties which is reflected in those Cp’ compounds. This article presents an overview of this class of compounds for all the five metals from beryllium to barium (radium is excluded for its radioactivity), highlighting their systematic variation.

Heteronuclear and Homonuclear Bimetallic Metallocenes of Alkaline Earths and Zinc

“…The novel motif of a Fe 2+ center sandwiched between two Cp rings gave birth to a new class of moleculesmetallocenes. Ferrocene derivatives have subsequently found applications in diverse fields such as catalysis, − biomedicine, − cathodic batteries, − and sensor design. − Modification or extension of the Cp rings has resulted in an array of monometallic metallocenes being isolated, with sandwich fillings of transition metals, alkali-earth metals, and actinides and lanthanides . Monometallic metallocenes typically possess a M 2+ center; however, metallocenes have been isolated with higher and lower metal oxidation states.…”

Regioselective C–H Alkylation of Aromatic Ethers with Alkenes by a Half-Sandwich Calcium Catalyst

“…The single-crystal structural characterization of the calcium anisyl complexes 8 and 9 , the KIE study, and DFT calculations shed a new light on the C–H activation and regioselective alkylation of aromatic derivatives. These results will promote the application of calcium-based catalytic systems for C–H bond activation in more fields …”

Fluorenyl-tethered N-heterocyclic carbene (NHC): an exclusive C-donor ligand for heteroleptic calcium and strontium chemistry

“…Notably, the organometallic journey of this trio began with aromatic π–carbanionic ligands, largely driven by strong cation–π interactions. 3 a ,4 Amusingly, even fluorenyl groups with a shallow potential surface give homo- and heteroleptic complexes. 4 A few fluorenyl Ca and Sr benzyls can even catalyze the polymerization of styrene.…”

“…3 a ,4 Amusingly, even fluorenyl groups with a shallow potential surface give homo- and heteroleptic complexes. 4 A few fluorenyl Ca and Sr benzyls can even catalyze the polymerization of styrene. 5 On the other hand, strongly σ-donating N-heterocyclic carbenes (NHCs), another class of ubiquitous but neutral C-donors, have given inherently weak adducts with Ca and Sr with only a few examples known.…”