Preparation and Characterization of 1,3-Butadiene and Isoprene Complexes, W₂(OCH₂^tBu)₆(diene)(py), and Studies of the Selective Hydrogenation of 1,3-Dienes

Abstract

In hydrocarbon solutions W 2 (OCH 2 t Bu) 6 (py) 2 , 1, and 1,3-butadiene and isoprene reversibly form adducts W 2 (OCH 2 t Bu) 6 (diene)(py), compounds 2 (diene ) 1,3-butadiene) and 3 (diene ) isoprene). The structures of 1, 2, and 3 are reported. For 1 there is a central O 3 NWt WNO 3 core with W-W ) 2.334(1) Å, and each W atom is in a distorted square-based pyramidal environment with the WtW bond in the apical site. In 2 and 3 there is a common W 2 O 6 C 4 N core wherein the diene adopts a novel mode of coordination, µ,η 1 ,η 4 . One W atom is coordinated to five oxygen atoms and the bridging carbon atom of the µ-diene ligand, while the other is bonded to three oxygen atoms, a pyridine nitrogen, and four carbon atoms of the diene. The structure may be viewed as being derived from a confacial bioctahedron with two bridging OR ligands and one bridging alkyl. In this view the diene can be considered as a µ-metalated π (η 3 -)allyl or a 2-ligand. The W-W distances are 2.471(1) Å in 2 and 2.464(1) Å in 3, consistent with a (WdW) 8+ core. The isoprene structure 3 reveals a disorder involving primarily the location of the isoprene C-Me group over two sites. The variabletemperature 1 H and 13 C{ 1 H} NMR spectra reveal the dynamic equilibria involving 1 + the diene and 2 and 3. The spectra of 2 and 3 are entirely reconcilable with the solid-state structures, and for the deuterated complexes W 2 (OCD 2 t Bu) 6 (diene)(py) all the 1 H signals of the diene are assigned by a combination of COSY and HETCOR spectra. For 3 there exists a mixture of the two isomers, differing with respect to the position of the isoprene C-Me group as seen in the solid-state structure. These interconvert by a reversible dissociative pathway. Though other 1,3-dienes have not been found to form adducts, we have found selective 1,2-hydrogenation to give 3-enes in the presence of W 2 (OCH 2 t Bu) 6 (py) 2 . This hydrogenation is not restricted to dienes but is also observed for cis-cyclic olefins. The addition of D 2 to norbornene reveals the stereospecific cis-addition at the endo sites. The addition of D 2 to 1,3-butadiene and isoprene gives CH 2 DCHDCHdCH 2 and CH 2 DCHDCMedCH 2 , respectively. These results are discussed in terms of other substrate activations by W 2 (OR) 6 compounds and other hydrogenation reactions.

Ring Opening Metathesis Polymerization of Norbornene and Derivatives by the Triply Bonded Ditungsten Complex Na[W2(µ-Cl)3Cl4(THF)2]·(THF)3

“…This peak may be assigned to the equivalently bound olefinic protons of an η 4 -NBD ligand, either bridging the two tungsten atoms (1a) or chelating at one of them (1'a, Scheme 2). In support of formation of 1a is the considerable insight on alkyne activation at bimetallic metal-metal bonded Group 6 centers [33,51,52], and in this particular case, the formation of [W 2 (µ-Cl) 3 (R = Me, Ph) deriving from the reaction of 1 with internal alkynes [53]; also, a limited number of representative alkene and diene interactions [54][55][56][57][58][59][60].…”

A New Donor‐Stabilized Ditungsten Amido Alkoxido Species: Synthesis, Crystal Structure, Fluxionality, and Grafting onto Silica

“…1 H 2D double quantum MAS spectrum of 4 using excitation/reconversion pulse train of two rotor periods (100 μs) (800.13 MHz, 20 kHz spinning speed, pulse RF = 80 kHz). 13 C CP MAS NMR signals are reminiscent of those of the molecular precursor (Figure 8). Signals of the pyridine carbons appear at 171.8, 150.0, 135.9, and 119.3 ppm.…”

“…H atoms are omitted for clarity. 97.81 (13) Each tungsten of the dimer adopts a distorted squareplanar coordination [the sum of angles is 348.8(5)°], composed of two dimethylamido and one chelating pyridylalkoxido ligands. The two tungsten-based fragments are connected by a C 2 axis, which intersects the compound at the center of the W-W triple bond.…”

“…Two other peaks are observed at δ = 57.9 and 48.2 ppm, a range corresponding to WNMe groups. Indeed, the 13 C CP MAS NMR spectrum of ϵSi-O-[W 2 (NMe 2 ) 5 ] comprises three peaks at δ = 58.2, 47.8, and 37.6 ppm. [9] Other WNMe signals may be hidden under the broad peak centered at δ = Figure 8.…”

“…[9] Other WNMe signals may be hidden under the broad peak centered at δ = Figure 8. 13 C CP MAS spectrum of 4 (100.6 MHz; * denotes rotation peaks).…”