Preparation and Characterization of 1,3-Butadiene and Isoprene Complexes, W2(OCH2tBu)6(diene)(py), and Studies of the Selective Hydrogenation of 1,3-Dienes
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- 作者：Jane T. Barry ; John C. Bollinger ; Malcolm H. Chisholm ; Katherine C. Glasgow ; John C. Huffman ; Eric A. Lucas ; Emil B. Lubkovsky ; and William E. Streib
- 刊名：Organometallics
- 出版年：1999
- 出版时间：June 7, 1999
- 年：1999
- 卷：18
- 期：12
- 页码：2300 - 2308
- 全文大小：180K
- 年卷期：v.18,no.12(June 7, 1999)
- ISSN：1520-6041
文摘
In hydrocarbon solutions W2(OCH2tBu)6(py)2, 1, and 1,3-butadiene and isoprene reversiblyform adducts W2(OCH2tBu)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 O3NW
f">WNO3 core with W-W = 2.334(1) Å, and each W atom is in a distorted square-basedpyramidal environment with the Wf">W bond in the apical site. In 2 and 3 there is a commonW2O6C4N core wherein the diene adopts a novel mode of coordination, 
f">,
fchars/eta.gif" BORDER=0 >1,fchars/eta.gif" BORDER=0 >4. One W atomis coordinated to five oxygen atoms and the bridging carbon atom of the f">-diene ligand,while the other is bonded to three oxygen atoms, a pyridine nitrogen, and four carbon atomsof the diene. The structure may be viewed as being derived from a confacial bioctahedronwith two bridging OR ligands and one bridging alkyl. In this view the diene can be consideredas a f">-metalated fchars/pi.gif" BORDER=0 > (fchars/eta.gif" BORDER=0 >3-)allyl or a 2- ligand. The W-W distances are 2.471(1) Å in 2 and2.464(1) Å in 3, consistent with a (W=W)8+ core. The isoprene structure 3 reveals a disorderinvolving primarily the location of the isoprene C-Me group over two sites. The variable-temperature 1H and 13C{1H} NMR spectra reveal the dynamic equilibria involving 1 + thediene and 2 and 3. The spectra of 2 and 3 are entirely reconcilable with the solid-statestructures, and for the deuterated complexes W2(OCD2tBu)6(diene)(py) all the 1H signals ofthe diene are assigned by a combination of COSY and HETCOR spectra. For 3 there existsa mixture of the two isomers, differing with respect to the position of the isoprene C-Megroup as seen in the solid-state structure. These interconvert by a reversible dissociativepathway. Though other 1,3-dienes have not been found to form adducts, we have foundselective 1,2-hydrogenation to give 3-enes in the presence of W2(OCH2tBu)6(py)2. Thishydrogenation is not restricted to dienes but is also observed for cis-cyclic olefins. The additionof D2 to norbornene reveals the stereospecific cis-addition at the endo sites. The addition ofD2 to 1,3-butadiene and isoprene gives CH2DCHDCH=CH2 and CH2DCHDCMe=CH2,respectively. These results are discussed in terms of other substrate activations by W2(OR)6compounds and other hydrogenation reactions.
f">WNO3 core with W-W = 2.334(1) Å, and each W atom is in a distorted square-basedpyramidal environment with the Wf">W bond in the apical site. In 2 and 3 there is a commonW2O6C4N core wherein the diene adopts a novel mode of coordination, f">,fchars/eta.gif" BORDER=0 >1,fchars/eta.gif" BORDER=0 >4. One W atomis coordinated to five oxygen atoms and the bridging carbon atom of the f">-diene ligand,while the other is bonded to three oxygen atoms, a pyridine nitrogen, and four carbon atomsof the diene. The structure may be viewed as being derived from a confacial bioctahedronwith two bridging OR ligands and one bridging alkyl. In this view the diene can be consideredas a f">-metalated fchars/pi.gif" BORDER=0 > (fchars/eta.gif" BORDER=0 >3-)allyl or a 2- ligand. The W-W distances are 2.471(1) Å in 2 and2.464(1) Å in 3, consistent with a (W=W)8+ core. The isoprene structure 3 reveals a disorderinvolving primarily the location of the isoprene C-Me group over two sites. The variable-temperature 1H and 13C{1H} NMR spectra reveal the dynamic equilibria involving 1 + thediene and 2 and 3. The spectra of 2 and 3 are entirely reconcilable with the solid-statestructures, and for the deuterated complexes W2(OCD2tBu)6(diene)(py) all the 1H signals ofthe diene are assigned by a combination of COSY and HETCOR spectra. For 3 there existsa mixture of the two isomers, differing with respect to the position of the isoprene C-Megroup as seen in the solid-state structure. These interconvert by a reversible dissociativepathway. Though other 1,3-dienes have not been found to form adducts, we have foundselective 1,2-hydrogenation to give 3-enes in the presence of W2(OCH2tBu)6(py)2. Thishydrogenation is not restricted to dienes but is also observed for cis-cyclic olefins. The additionof D2 to norbornene reveals the stereospecific cis-addition at the endo sites. The addition ofD2 to 1,3-butadiene and isoprene gives CH2DCHDCH=CH2 and CH2DCHDCMe=CH2,respectively. These results are discussed in terms of other substrate activations by W2(OR)6compounds and other hydrogenation reactions.