The Chemistry of Ca^II and Yb^II: Astoundingly Similar But Not Equal!

Abstract

The structures and chemical behavior of heavier alkalineearth metal complexes (Ca, Sr, and Ba) [1] have often been compared to that of early d-and f-block metal complexes. [2][3][4][5][6][7][8][9][10][11] In particular, parallels with "hot" lanthanide(ii) complexes [12] have been observed. Lanthanide complexes are d 0 species with a limited radial extension of their f orbitals. Therefore, orbital factors do not affect their chemistry as much as in transition-metal chemistry. As for complexes of the heavier alkaline-earth metals, their bonding and structures are mainly determined by electrostatic and steric factors.There is ample evidence for the striking similarity in the chemistry of Ca II and Yb II : 1) crystal structures of Ca and Yb analogues are always isomorphous and have exceptionally similar cell constants, [7,8,10] 2) the observation of nearly identical IR spectra of Ca and Yb analogues suggests a striking similarity in bonding, [2] 3) analogous Ca and Yb complexes display similar gas-phase behavior: electron-diffraction studies of [Cp *2 Ca] (Cp* is pentamethyl cyclopentadiene) and [Cp *2 Yb] reveal similar Cp* centroid -M-Cp* centroid angles of 154 (3)8 and 158(4)8, respectively, [13] and 4) analogous reactivities of Ca II and Yb II complexes have been reported. [8,9] These parallels in the chemistry of Ca and Yb complexes prompted us to repeat the calcium chemistry recently reported by us, but with ytterbium. The substitution of Ca for Yb in benzylcalcium-based initiators for stereoselective styrene polymerization [15,20] and an investigation of its polymerization chemistry is here of special importance.The syntheses and crystallization of the Yb II complexes were greatly facilitated by the strong similarity with their calcium analogues: in all cases exactly the same procedures as for their Ca analogues were followed. The Yb II complexes 1(Yb)-5(Yb) were prepared and the structures of 1(Yb)-

On the Initiation Mechanism of Syndiospecific Styrene Polymerization Catalyzed by Single‐Component ansa‐Lanthanidocenes

“…Keywords: homogeneous catalysis · lanthanides · polymerization · reaction mechanisms · styrene based on ytterbium, [8] scandium, [9] and neodymium [10] were shown to feature very high activity and syndiospecificity. In particular, some of us reported that neutral allyl neodymocene complexes of general formula [{Cp''CMe 2 Flu'}NdA C H T U N G T R E N N U N G (h 3 -allyl)A C H T U N G T R E N N U N G (ether) n ] (Cp'' = 3-R 1 C 5 H 3 , R 1 = H (Cp'), tBu; Flu' = 9-C 13 H 8 ; allyl = CH 2 CHCH 2 ; ether = THF, Et 2 O, n = 0,1) (1) are single-component (i.e., they do not require any co-activator), single-site catalysts which are effective under industrially relevant conditions (bulk styrene, high temperature);…”

An Extremely Bulky Tris(pyrazolyl)methanide: A Tridentate Ligand for the Synthesis of Heteroleptic Magnesium(II) and Ytterbium(II) Alkyl, Hydride, and Iodide Complexes

“…Attention then turned towards the preparation of heteroleptic calcium(II) amides and alkyls that could be subsequently treated with iodinating agents to give [{C(3-Ad-5-Mepz) 3 ly) and display similar coordination chemistry. [20] Therefore, it seemed unlikely that a stable ytterbium(II) iodide complex incorporating the [C(3-Ad-5-Mepz) 3 [5a] Although no identifiable products could be isolated from any of these reactions, we believe that compound 8 holds significant potential for inorganic chemists as a precursor to related sterically protected ytterbium(II) systems.…”

Compositional variations in monomeric trimethylsilylated allyl lanthanide complexes

“…Because the ionic radii of calcium and ytterbium differ only slightly (Ca(II), 1.00 Å ; Yb(II), 1.02 Å for CN 6) [6], bond distances and angles of the ligands in their respective complexes are usually similar [32]. An argument has been made that the longer Yb-C bonds reflect bond weakening arising from the filled f 14 shell of the Yb(II) ion [4].…”