The ruthenium-
p-cymene complexes [(
p-cymene)Ru(1,2,3,4-Me
4-NUPHOS)Cl][SbF
6] (
2a)and [(
p-cymene)Ru(1,4-Et
2-2,3-
cyclo-C
6H
8-NUPHOS)Cl][SbF
6] (
2b) have been prepared byreaction of [(
p-cymene)RuCl
2]
2 with the corresponding NUPHOS diphosphine in the presenceof NaSbF
6. The chloro ligand can be abstracted from these monocations to afford [(
p-cymene)Ru(
P,
P,
2(
C)-1,2,3,4-Me
4-NUPHOS)][SbF
6]
2 (
3a) and [(
p-cymene)Ru(
P,
P,
2(
C)-1,4-Et
2-2,3-
cyclo-C
6H
8-NUPHOS)][SbF
6]
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 star
k contrast, it proved mar
kedly more difficult to abstractthe chloro ligand from either the BIPHEP or the MeO-BIPHEP monocations [(
p-cymene)Ru(BIPHEP)Cl][SbF
6] (
4a) and [(
p-cymene)Ru(MeO-BIPHEP)Cl][SbF
6] (
4b), and even afterprolonged reaction times at elevated temperature [(
p-cymene)Ru(BIPHEP)][SbF
6]
2 (
5a) and[(
p-cymene)Ru(MeO-BIPHEP)][SbF
6]
2 (
5b) formed as a 30% mixture with unreacted
4a and
4b, 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][SbF
6] to underta
ke a comparative study, since [(
p-cymene)RuCl
2]
2 reacts with dppb under the same conditions as those used to prepare
2a,
b to affordthe bridged dimer [{(
p-cymene)RuCl
2}
2(
![](/images/entities/mgr.gif)
-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{Ph
2(O)PC(H)MeCMeCMeCMePPh
2}][SbF
6] (
7), whichcontains an unusual unsymmetrical bisphosphine monoxide pincer ligand formed by oxidationof one of the diphenylphosphino groups of 1,2,3,4-Me
4-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-Mar
kovni
kov addition of benzoic acidto 1-pentyne and 1-octyne to give the corresponding al
k-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 al
k-1-en-1-yl ester. In contrast, selectivity was reversed with catalyst mixturesgenerated from
6, which were 90% selective for Mar
kovni
kov 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-Mar
kovni
kov 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 AgSbF
6 catalyze the regio- and stereoselective anti-Mar
kovni
kov 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.