The Use of a Flexible Calix[4]arene Template to Stabilize a Cyclooctatetraindiyl Samarium-Potassium Complex

A sandwich compound of cyclooctatetraendiyl (COT)2？ samarium-potassium was synthesized and analyzed using a flexible calix[4]arene dianion. This compound, [p-tBu-calix[4]-(OMe)2(O)2]arenediyl-samarium-(η8-cyclooctatetraendiyl)-potassium (tetrahydrofurane)3, is constructed as a linear sequence L-Sm- -K- , where L, , and are specific ligands with L = O,O-dimethyl-calix[4]arene2？, = cyclo-octatetraendiyl, and = tetrahydrofurane templates. 1. Introduction For a long time, the organometallic chemistry of lanthanides (Ln) [1] has been dominated by the use of polycyclic hydrocarbons including the cyclopentadienyl anion or the cyclooctatetraendiyl dianion, as exemplified by the well-known lanthanocene [2] and complexes [3]. In the last two decades, the organometallic and redox chemistry of these hard metal ions has been extensively developed by the introduction of amido, thiolato, and aryloxo ligands as well as macrocyclic ligands, such as octa-alkyl-porphyrinogens and calix arenes [4, 5], and a number of such examples of complexes have recently been published [6–10]. Calixarenes are useful building blocks in supramolecular chemistry for complexing metallic cations [11]; the use of calix arene anions [12] brings significant peculiarities: the electron-rich environment provided by the oxygen donor atoms forms an ideal platform for developing the organometallic and redox chemistry of lanthanides, the quasi-planar arrangement of the four oxygen atoms resulting from the cone conformation of the calix allows the formation of “half-sandwich”-type metallic complexes, and it can accommodate up to 12 electrons to the metal centre depending on the degree of -donation. Therefore, it came out that an interesting analogy can be drawn between the quasi-planar calix arene polyanion and its electronically similar cyclooctatetraendiyl dianion [13] in the attempt to develop new scaffoldings in organometallic chemistry of Lanthanides. In the present study we report on the synthesis and crystallographic analysis of the mixed cyclooctatetraendiyl samarium-potassium complex: arenediyl samarium-( 8-cyclo-octatetraendiyl) potassium- , stabilized by a flexible calix arene dianion template, a compound that widens the ability of unsymmetrical calix arene as a useful and adaptable ligand in organometallic chemistry. 2. Experimental A solution of cyclooctatetraendiide dipotassium in THF [14] (8.8？mL, 0.275？M, 2.42？mmol) was added dropwise to a suspension of 2 (4.6？g, 2.47？mmol) [15] in THF (150？mL) at ？30°C. The reaction mixture was stirred overnight while slowly warming to room