Lewis Acid – Base Interactions Between Bis-π-cyclopentadienyl Tungsten and Molybdenum Dihydrides, Cp₂MH₂, and some Main Group III Moieties

Abstract

Combination of the Lewis bases Cp2MH2 (where M = W or Mo) with the Group III Lewis acids AlR3 (where R = Me, Et, or Ph) and AlMe2H has yielded a series of 1:1 complexes of the type Cp2MH2•AlR3. A number of the complexes undergoes a slow elimination of hydrogen or alkane in benzene solution. Attempts to isolate mixed hydride adducts of the type, Cp2MH2•M′H3 (where M′ = Al or Ga), were unsuccessful.

Synthese und Molekülstruktur von [{Cp′(μ-η1 : η5-C5H3Me)Mo(μ-AlRH)}2] (Cp′ = C5H4Me, R =iBu, Et)

“…Wir berichten nun u È ber die Reaktion von [Cp' 2 MoH 2 ] mit HAlR 2 , die zu Molybdocenkomplexen [{Cp'(l-g 1 : (2) [14,15]. Wa Èhrend aufgrund spektroskopischer Untersuchungen das Vorliegen einer direkten M±Al-Bindung angenommen wurde [14], konnte mit der strukturellen Charakterisierung des W-Derivats [Cp 2 W(l-H) 2 -AlMe 3 ] das Vorliegen von Hydridobru È cken im Festko È rper gezeigt werden [15].…”

“…Offenbar sind Komplexe des Typs [Cp 2 MH 2 (AlR 3 )] in Lo È sung dynamisch, was durch H/D-Austausch-Experimente nachgewiesen wurde [15]. Die Verbindungen [Cp 2 MH 2 (AlR 3 )] zersetzen sich, mit Ausnahme von [Cp 2 WH 2 (AlMe 3 )], in Lo È sung langsam bei Raumtemperatur unter Alkan-Eliminierung [14]. Die 1 : 1-Komplexe der entspre-chenden Dialkylalane sind noch labiler; so ist der Mo-Komplex bei Raumtemperatur nicht isolierbar [14].…”

A comparative study on the reaction mechanisms of Cp2MH2 (M = Cr, Mo, W) with HBF4

“…Cp 2 WH 3 ·BF 4 is stable, while Cp 2 MoH 3 ·BF 4 is unstable and can liberate hydrogen and alkanes over time. [10,11] To illustrate the experimental results, reaction mechanism calculations were performed. The optimized geometric parameters of the reactants, transition states, intermediates and products on the potential energy surfaces (PES) are listed in Table 3.…”

“…On the basis of infrared spectroscopy, Shriver proposed a direct W-B bond in the Cp 2 WH 2 ·BF 3 adduct due to the very slight perturbation of the W − H stretching frequencies. [8] However, subsequent results from 1 H and 11 B NMR and X-ray structure studies dispelled this notion and demonstrated that Cp 2 WH 3 ·BF 4 rather than Cp 2 WH 2 ·BF 3 formed in the Cp 2 WH 2 + BF 3 reaction. The experimental results obtained by Braunschweig et al showed that the yield of Cp 2 WH 3 ·BF 4 is low in the Cp 2 WH 2 + BF 3 reaction.…”

Crystal and molecular structure of (pentahapto-cyclopentadienyl)hydridomolybdenum-μ-dimethylaluminum-μ-[methylaluminum-di-(μ)-pentahapto(monohapto)dimethylaluminum]-(pentahapto-cyclopentadienyl)hydridomolybdenum, [(C5H5)(C5H4)MoH]2Al3(CH3)5

“…An earlier report (Storr & Thomas, 1971) indicated that slow decomposition oft he adduct Cp2 M o H 2. A1 M e3 occurs in benzene solution at room temperature.…”