Anti-Bimetallic Complexes of Divalent Lanthanides with Silylated Pentalene and Cyclooctatetraenyl Bridging Ligands as Molecular Models for Lanthanide-Based Polymers

Summerscales, Owen T, Jones, Simon C, Cloke, F Geoffrey N and Hitchcock, Peter B (2009) Anti-Bimetallic Complexes of Divalent Lanthanides with Silylated Pentalene and Cyclooctatetraenyl Bridging Ligands as Molecular Models for Lanthanide-Based Polymers. Organometallics, 28 (20). pp. 5896-5908. ISSN 0276-7333

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Abstract

The new pentalene antibimetallic compounds [MCp*(THF)](2)(mu,eta(5):eta(5)-C8H41,4-SiiPr3) were prepared for M = Eu (1), Yb (2) from the one-pot reaction of MI2(THF)(x) and KCp* and the subsequent addition of 2 equiv of C8H41,4-SiiPr3[K](2) in THF. The related series of COT1,4-SiiPr3-bridged triple-deckers [MCp*(THF)(x)](2)(mu,eta(8):eta(8)-COT1,4-SiiPr3) (M = Eu, x = 0 (3); M = Yb, x = 0 (4); M = Sm, x = 1 (5)) were synthesized similarly; additionally, the base-free derivative with M = Sm and x = 0 (6) could be prepared by reaction of [SmCp*(mu-I)(THF)(2)](2) with COT1,4-SiiPr3[K](2) in toluene with heating. The solid-state structures, as determined by X-ray diffraction, show antibimetallic arrangements in which the divalent lanthanide centers are held oil opposing sides of a planar bridging ligand. The pentalene ligand coordinates in an approximate eta(5):eta(5) mode, with the metal centers slipped toward the wingtip carbons, whereas the COT ligand is bound in an eta(8):eta(8) fashion with the metal centers aligned with the centroid of the bridging ligand. Electronic spectroscopy suggests the Eu and Yb pentalene complexes have a smaller f-d gap than their COT analogues, indicating a greater extent of through-ligand metal-metal interaction in the pentalene species. [EuCp*(THF)(x)](2)(mu-COT1,4-SiiPr3) displays a weak green-yellow emission in THF solution (lambda(max) 509 nm, Phi(em) < 0.1%) upon excitation in the UV, consistent with a 4f(6)5d(1) -> 4f(7) emission process, with a short lifetime indicative of Eu-Eu coupling through the bridging COT ligand. Cyclic voltammetry reveals that 1, 3, and 4 decompose rapidly upon oxidation, although the monocation 2(+) appears to be stable in THF solution. Through-ligand Yb-Yb coupling is suggested by the electrochemical data for 2, of magnitude similar to that observed for its transition-metal analogues. However, unfortunately, attempts to further quantify this conclusion by spectroscopic investigation of 2(+) were unsuccessful.

Item Type: Article
Schools and Departments: School of Life Sciences > Chemistry
Depositing User: Geoff Cloke
Date Deposited: 06 Feb 2012 19:52
Last Modified: 14 May 2012 14:18
URI: http://sro.sussex.ac.uk/id/eprint/22719
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