Solid-State Structures of Base-Free Rubidium and Cesium Pentamethylcyclopentadienides. Determination by High-Resolution Powder Diffraction

Abstract

Powder diffractometry was carried out on the basefree salts MC 5 Me 5 (MCp*, M ) K-Cs) at room temperature and at -120°C. The powder patterns at room temperature and low temperature are identical for all compounds. The solidstate structures of RbCp* and CsCp* could be solVed. Both compounds are isomorphous. They crystallize as "multidecker structures" in the form of polymeric zigzag chains.

Crystal structure of (1,4,7,10,13,16-hexaoxacyclooctadecane-κ6 O 6) 1,2,3,4,5-pentamethyl-cyclopenta-2,4-dien-1-yl(potassium, rubidium) — ammonia (1/2), [K0.3Rb0.7(18-crown-6)]Cp*⋅2 NH3, C22H45K0.3N2O6Rb0.7

“…According to the main elemental site occupation by Rb and its preferred coordination environment by 18-crown-6 in a "sunrise" conformation [11], the cation is situated near the centre of the 18-crown-6 molecule but apart from its ring plane shifted in direction of the Cp* anion. The presence of the crown ether causes the formation of molecular units differing from pure RbCp* which forms polymeric "multidecker" strands [12], but similar to the effect of diaza-18-crown-6 on RbCp* [13]. Rb is bound to the Cp* ligand via five short Rb-C bonds between 3.055(4) Å and 3.199(3) Å very similar to those observed for the η 5 coordinations in [Rb(18crown-6)]Cp* [12] and [Rb(18-crown-6)]Cp* × thf [14].…”

“…The presence of the crown ether causes the formation of molecular units differing from pure RbCp* which forms polymeric "multidecker" strands [12], but similar to the effect of diaza-18-crown-6 on RbCp* [13]. Rb is bound to the Cp* ligand via five short Rb-C bonds between 3.055(4) Å and 3.199(3) Å very similar to those observed for the η 5 coordinations in [Rb(18crown-6)]Cp* [12] and [Rb(18-crown-6)]Cp* × thf [14]. All C atoms of the Cp* ligand are in plane and the cyclopentadienyl ring is an almost regular pentagon (C-C bond lengths between 1.394(5) Å and 1.423(5) Å, C-C-C angles between 106.9(3)°and 108.9(3)°), clearly different from the shape of the neutral Cp*-H molecule [15], suggesting that the negative charge is located at Cp*.…”

Optimised Syntheses of the Half-Sandwich Complexes FeCl(dppe)Cp*, FeCl(dppe)Cp, RuCl(dppe)Cp*, and RuCl(dppe)Cp

“…A more convenient laboratory preparation of FeCl(dppe)Cp* would avoid the use of ultrasonic irradiation, and the isolation and manipulation of air sensitive lithium [52] or pyrophoric potassium [53] pentamethylcyclopentadienides, whilst taking advantage of the ready availability of [FeCl2(dppe)]n. Although [FeCl2(dppe)2]n is commonly prepared from reaction of anhydrous FeCl2 with 1,2-bis(diphenylphosphino)ethane [41,51] it has been recently shown that [FeCl2(dppe)]n can be conveniently synthesised in high yield (ca. 80%) by treatment of FeCl2•4H2O with 1,2-bis(diphenylphosphino)ethane in acetone / chloroform mixtures [44,54] thereby avoiding the tedious preparation, or considerably greater cost, of anhydrous FeCl2 (As of March 2016 FeCl2•4H2O costs ~A$65 per mole and FeCl2 ~A$390 per mole, prices from Sigma Aldrich).…”

“…[54] Here, the following method is proposed (Scheme 1 A). Potassium pentamethylcyclopentadienide is produced in situ by reaction of pentamethylcyclopentadiene with potassium metal in refluxing toluene, [53] and precipitates from the reaction as a fine white powder. The potassium pentamethylcyclopentadienide so produced is not isolated, but rather the reaction mixture is allowed to cool, diluted with a further portion of toluene and treated with thoroughly dried [FeCl2(dppe)]n. [44,54]…”

“…Warning: Potassium pentamethylcyclopentadienide is a highly reactive material, spontaneously combustible in air. [53] The procedures described below are designed to avoid the isolation of this compound and any exposure of this material to the atmosphere must be avoided. the resulting dark mixture was stirred for 16 h. Subsequently, the reaction mixture was filtered through Celite ® and the filter cake was washed with toluene until the washings were colourless (~60 mL), the combined filtrant and washings were then concentrated to dryness, and the residue was dissolved in † Failure to deoxygenate the solvents in this procedure will lead to brown colouration of the product, presumably due to the formation of Fe(III) oxide species.…”