New Synthetic Routes to Tris(pentaalkylcyclopentadienyl)lanthanide Complexes Including the X-ray Crystal Structure of (C₅Me₄Et)₃Sm¹

Abstract

The synthetic chemistry leading to tris(pentamethylcyclopentadienyl)samarium complexes has been examined to determine why some routes fail and to develop routes superior to the first synthesis from (C5Me5)2Sm and 1,3,5,7-cyclooctatetraene (COT). (C5Me5)2Sm(THF) fails as a reagent since (C5Me5)3Sm reacts with any THF present to form the ring-opened product (C5Me5)2Sm[O(CH2)4C5Me5](THF). However, (C5Me5)2Sm(OEt2) reacts cleanly with COT to form (C5Me5)3Sm and (C5Me5)Sm(C8H8). A more efficient synthesis involves the reaction of (C5Me5)2Sm(OEt2) with (C5Me5)2Pb which generates (C5Me5)3Sm in >90% yield. This route has been used to synthesize the more sterically crowded tris(pentaalkylcyclopentadienyl) complex (C5Me4Et)3Sm, which shows that the limit of steric crowding in this class has not yet been realized. X-ray crystallographic study of (C5Me4Et)3Sm revealed a trigonal planar arrangement of ring centroids around samarium with an average Sm−C(C5Me5) distance of 2.834 Å. Two ethyl groups point toward samarium with a minimum Sm−C distance of 3.620(13) Å.

Zur Elektronenstruktur metallorganischer Komplexe der f-Elemente LIX. Spektrochemische und nephelauxetische Effekte sowie experimentorientierte MO-Schemata (im f-Bereich) pseudo-trigonal-planarer (substituierter) Tris(η5-cyclopentadienyl)neodym(III)-Komplexe und eines THF-Monoaddukts

“…Während die unsubstituierten Tris(cyclopentadienyl)lanthanoid(III)-Verbindungen (Ln(Cp) 3 ) der Anfangsglieder der Ln-Serie polymer sind [2], und somit ihre optischen Spektren schwerlich kristallfeldtheoretisch analysiert werden können, haben die entsprechenden hö her alkylierten oder silylierten Derivate monomere Strukturen [2][3][4][5][6][7]. Die Ln 3+ -Zentralionen dieser Verbindungen sind pseudo(w)-trigonal-planar koordiniert [2][3][4][5][6][7], so daß jeweils ein effektives Kristallfeld (KF) der Symmetrie D 3h vorliegt.…”

“…Die Ln 3+ -Zentralionen dieser Verbindungen sind pseudo(w)-trigonal-planar koordiniert [2][3][4][5][6][7], so daß jeweils ein effektives Kristallfeld (KF) der Symmetrie D 3h vorliegt.…”

Lewis‐Acid Stabilized Organoimide Complexes of Divalent Samarium, Europium, and Ytterbium

“…The feasibility of such thermally stable divalentl anthanide imides prompted us to further investigate into their redox chemistry.I np revious studies 1e À -oxidation agents, such as halogenating agents, [40] organothallium, [47] or organolead [48,49] compounds have been used for Ln II -to-Ln III conversions. As half-sandwich Ln III imide complexeso ft he type [Cp*Ln(NR)] (Cp* = C 5 Me 5 )p ose attractive targetc ompounds, we were par-ticularlyi nterested in reagents capable of oxidative Cp* ligand transfer.Similar to organothallium(I) compounds, organolead(II) compounds can act as such oxidation and ligand transfer reagents, [47] which is also demonstrated by their redox potentials of Tl I /Tl 0 À0.34 Va nd Pb II /Pb 0 À0.13 V( PbSO 4 /Pb 0 ,S O 4 2À at À0.36 V).…”

Reactivity of the metal–cyclopentadienyl (indenyl, fluorenyl and cycloheptatrienyl) bonds

“…The alkyl-like reactivity of the (C 5 Me 5 ) 3 Ln complexes without elimination of pentamethylcyclopentadienyl group has been investigated with CO [45][46][47], THF [47][48][49][50][51], PhCN [51], PhNCO [51], and CO 2 [47]. In these reactions, (C 5 Me 5 ) 3 Ln can react initially as if an g 5 -C 5 Me 5 g 1 -C 5 Me 5 equilibrium occurs as shown in Eq.…”

“…All the lanthanides (C 5 Me 5 ) 3 Ln (Ln = La, Ce, Pr, Nd, Sm) react with THF to form the ring-opened products (C 5 Me 5 ) 2 Ln[O(CH 2 ) 4 C 5 Me 5 ](THF) but more rigorous conditions are required for increasing the size of the metal complex (Scheme 12) [47][48][49][50][51]. (C 5 Me 5 ) 2 Ln(g 1 -C 5 Me 5 )-(THF) is initially formed and then the coordinated THF could be Lewis acid-activated to nucleophilic attack by the adjacent C 5 Me 5 group.…”