Ruthenium Complexes of Six-Electron-Donor NUPHOS-Type Diphosphines: Highly Selective Catalysts for the Hydrocarboxylation of Terminal Alkynes
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- 作者：Simon Doherty ; Julian G. Knight ; Rakesh K. Rath ; William Clegg ; Ross W. Harrington ; Colin R. Newman ; Robert Campbell ; and Hiren Amin
- 刊名：Organometallics
- 出版年：2005
- 出版时间：May 23, 2005
- 年：2005
- 卷：24
- 期：11
- 页码：2633 - 2644
- 全文大小：291K
- 年卷期：v.24,no.11(May 23, 2005)
- ISSN：1520-6041
文摘
The ruthenium-p-cymene complexes [(p-cymene)Ru(1,2,3,4-Me4-NUPHOS)Cl][SbF6] (2a)and [(p-cymene)Ru(1,4-Et2-2,3-cyclo-C6H8-NUPHOS)Cl][SbF6] (2b) have been prepared byreaction of [(p-cymene)RuCl2]2 with the corresponding NUPHOS diphosphine in the presenceof NaSbF6. The chloro ligand can be abstracted from these monocations to afford [(p-cymene)Ru(P,P,
fchars/eta.gif" BORDER=0 >2(C)-1,2,3,4-Me4-NUPHOS)][SbF6]2 (3a) and [(p-cymene)Ru(P,P,fchars/eta.gif" BORDER=0 >2(C)-1,4-Et2-2,3-cyclo-C6H8-NUPHOS)][SbF6]2 (3b), respectively, in which the diphosphine coordinates as asix-electron donor, bonded through both diphenylphosphino groups and one of the doublebonds of the butadiene tether. In stark contrast, it proved markedly more difficult to abstractthe chloro ligand from either the BIPHEP or the MeO-BIPHEP monocations [(p-cymene)Ru(BIPHEP)Cl][SbF6] (4a) and [(p-cymene)Ru(MeO-BIPHEP)Cl][SbF6] (4b), and even afterprolonged reaction times at elevated temperature [(p-cymene)Ru(BIPHEP)][SbF6]2 (5a) and[(p-cymene)Ru(MeO-BIPHEP)][SbF6]2 (5b) formed as a 30% mixture with unreacted 4a and4b, respectively. The structures of 2a, as its perchlorate salt, and 2b have been determinedby single-crystal X-ray crystallography and are compared with that of their BIPHEPcounterpart 4a. Unfortunately, it has not been possible to prepare the corresponding dppbcomplex [(p-cymene)Ru(dppb)Cl][SbF6] to undertake a comparative study, since [(p-cymene)RuCl2]2 reacts with dppb under the same conditions as those used to prepare 2a,b to affordthe bridged dimer [{(p-cymene)RuCl2}2(
f">-dppb)] (6), the identity of which has been confirmedby a single-crystal X-ray study. Interestingly, 3a undergoes rapid hydrolysis in the presenceof pyridine to give [(p-cymene)Ru{Ph2(O)PC(H)MeCMeCMeCMePPh2}][SbF6] (7), whichcontains an unusual unsymmetrical bisphosphine monoxide pincer ligand formed by oxidationof one of the diphenylphosphino groups of 1,2,3,4-Me4-NUPHOS and a highly regioselectivesyn addition of Ru and H across the butadiene double bond proximate to the phosphineoxide. Dications 3a,b catalyze the regioselective anti-Markovnikov addition of benzoic acidto 1-pentyne and 1-octyne to give the corresponding alk-1-en-1-yl esters with cis-to-transratios as high as 95:5, while the corresponding BIPHEP and MeO-BIPHEP complexes weresignificantly less selective, catalyst mixtures formed from 4b giving a 70:30 mixture of cisand trans alk-1-en-1-yl ester. In contrast, selectivity was reversed with catalyst mixturesgenerated from 6, which were 90% selective for Markovnikov addition to 1-octyne, as mighthave been predicted for a ruthenium catalyst coordinated by a single phosphine, albeit one-half of a bidentate diphosphine. Catalysts based on NUPHOS diphosphines are also highlyactive and selective for anti-Markovnikov addition of benzoic acid to phenylacetylene andgive (Z)-styryl benzoate in yields of up to 85% and selectivities as high as 99:1 with noevidence for the formation of terminal olefin. In our hands, solutions formed by activationof 4a,b with AgSbF6 catalyze the regio- and stereoselective anti-Markovnikov hydrocarboxylation of phenylacetylene, which was somewhat surprising considering that an earlierreport has claimed that 5b reacts with phenylacetylene to form a stable catalytically inactivecyclometalation/insertion product.
fchars/eta.gif" BORDER=0 >2(C)-1,2,3,4-Me4-NUPHOS)][SbF6]2 (3a) and [(p-cymene)Ru(P,P,fchars/eta.gif" BORDER=0 >2(C)-1,4-Et2-2,3-cyclo-C6H8-NUPHOS)][SbF6]2 (3b), respectively, in which the diphosphine coordinates as asix-electron donor, bonded through both diphenylphosphino groups and one of the doublebonds of the butadiene tether. In stark contrast, it proved markedly more difficult to abstractthe chloro ligand from either the BIPHEP or the MeO-BIPHEP monocations [(p-cymene)Ru(BIPHEP)Cl][SbF6] (4a) and [(p-cymene)Ru(MeO-BIPHEP)Cl][SbF6] (4b), and even afterprolonged reaction times at elevated temperature [(p-cymene)Ru(BIPHEP)][SbF6]2 (5a) and[(p-cymene)Ru(MeO-BIPHEP)][SbF6]2 (5b) formed as a 30% mixture with unreacted 4a and4b, respectively. The structures of 2a, as its perchlorate salt, and 2b have been determinedby single-crystal X-ray crystallography and are compared with that of their BIPHEPcounterpart 4a. Unfortunately, it has not been possible to prepare the corresponding dppbcomplex [(p-cymene)Ru(dppb)Cl][SbF6] to undertake a comparative study, since [(p-cymene)RuCl2]2 reacts with dppb under the same conditions as those used to prepare 2a,b to affordthe bridged dimer [{(p-cymene)RuCl2}2(f">-dppb)] (6), the identity of which has been confirmedby a single-crystal X-ray study. Interestingly, 3a undergoes rapid hydrolysis in the presenceof pyridine to give [(p-cymene)Ru{Ph2(O)PC(H)MeCMeCMeCMePPh2}][SbF6] (7), whichcontains an unusual unsymmetrical bisphosphine monoxide pincer ligand formed by oxidationof one of the diphenylphosphino groups of 1,2,3,4-Me4-NUPHOS and a highly regioselectivesyn addition of Ru and H across the butadiene double bond proximate to the phosphineoxide. Dications 3a,b catalyze the regioselective anti-Markovnikov addition of benzoic acidto 1-pentyne and 1-octyne to give the corresponding alk-1-en-1-yl esters with cis-to-transratios as high as 95:5, while the corresponding BIPHEP and MeO-BIPHEP complexes weresignificantly less selective, catalyst mixtures formed from 4b giving a 70:30 mixture of cisand trans alk-1-en-1-yl ester. In contrast, selectivity was reversed with catalyst mixturesgenerated from 6, which were 90% selective for Markovnikov addition to 1-octyne, as mighthave been predicted for a ruthenium catalyst coordinated by a single phosphine, albeit one-half of a bidentate diphosphine. Catalysts based on NUPHOS diphosphines are also highlyactive and selective for anti-Markovnikov addition of benzoic acid to phenylacetylene andgive (Z)-styryl benzoate in yields of up to 85% and selectivities as high as 99:1 with noevidence for the formation of terminal olefin. In our hands, solutions formed by activationof 4a,b with AgSbF6 catalyze the regio- and stereoselective anti-Markovnikov hydrocarboxylation of phenylacetylene, which was somewhat surprising considering that an earlierreport has claimed that 5b reacts with phenylacetylene to form a stable catalytically inactivecyclometalation/insertion product.