Pentaisopropyl Cyclopentadienyl: An Overview across the Periodic Table

Abstract

Cyclopentadienide (Cp) groups are among the most popular ligands in organometallic chemistry. Sterically demanding substitution patterns on the Cp ring can have an important effect on the ligand properties and there are many examples of metal complex which are only stable and isolatable with sterically demanding Cp ligands, carrying alkyl or aryl groups. Among these sterically demanding Cp ligands, pentaisopropylcyclopentadienide is the bulkiest pentaalkyl derivative and has been utilized in main group, as well as transition metal and rare‐earth element chemistry for several decades.

Bulking up CpBIG: A Penta-Terphenyl Cyclopentadienyl Ligand

“…40 The higher degree of aggregation is presumably prevented by the high steric bulk of 1. In comparison to the structure of 4-n-Bu-Cp BIG K, 1-K features a slightly longer K1−Cp(centroid) distance [1-K: 2.707(1) Å; 4n-Bu-Cp BIG K: K1−Cp(centroid), 2.6464(17) Å; K3−Cp-(centroid), 2.6601(16) Å; K2−Cp(centroid), 2.6738 (19) Å]. 40 The cyclopentadiene to arene plane-to-plane twist angles in 1-K range from 44.38(6)°to 50.79(6)°, which is significantly lower than in the case of 1-Na•thf and in agreement with the increased ionic radius of K compared to Na.…”

“…These properties led to isolation of metal complexes that were previously unstable with Cp ligands, e.g., decamethyltitanocene (Figure B) . Moreover, the introduction of even bulkier substituents such as tert -butyl or iso- propyl groups has led to cyclopentadienyls with still stronger steric demand such as C 5 H 2 t Bu 3 (Cp‴) and C 5 i Pr 5 . − The former ligand has recently been used for the synthesis of unusual metallocene anions, , while the latter ligand has recently received attention through its capability to stabilize a dysprosium metallocene single-molecule magnet [(η 5 -C 5 i Pr 5 )­(Cp*)­Dy]­[B­(C 6 F 5 ) 4 ] showing magnetic hysteresis up to 80 K and the linear uranocene [(η 5 -C 5 i Pr 5 ) 2 U]. , …”

Introducing the Perfluorinated Cp* Ligand into Coordination Chemistry

“…Cyclopentadienyl anions (Cp) are by number the most common organic ligands for transition metals, explaining their ubiquity in organometallic chemistry. Given a variety of Cp derivatives, most of them are electron rich and act as strong π‐donor ligands due to (per)alkylation[ 1 , 2 ] or (per)arylation. [ 3 , 4 ] Of particular interest is the commonly used [C 5 (CH 3 ) 5 ] − ligand, better known as Cp*, which finds for example application in highly oxidized transition metal complexes.…”

Back to the future of organolanthanide chemistry

“…8), 74 a ligand previously used for the formation of Ln(Cp iPr5 ) 2 (Ln = Sm, Eu, Yb). 77,191,192 The modulation of the Cp substituents leads to variations in the complexes' geometry, directly impacting the magnetic properties. Additionally, the strategy was extended to non-classical divalent lanthanide complexes featuring a linear geometry (Fig.…”