PMID- 17474744
OWN - NLM
STAT- PubMed-not-MEDLINE
DCOM- 20070725
LR  - 20070523
IS  - 0002-7863 (Print)
IS  - 0002-7863 (Linking)
VI  - 129
IP  - 21
DP  - 2007 May 30
TI  - Palladium-catalyzed asymmetric phosphination. Scope, mechanism, and origin of 
      enantioselectivity.
PG  - 6847-58
AB  - Asymmetric cross-coupling of aryl iodides (ArI) with secondary arylphosphines 
      (PHMe(Ar'), Ar' = (2,4,6)-R3C6H2; R = i-Pr (Is), Me (Mes), Ph (Phes)) in the 
      presence of the base NaOSiMe3 and a chiral Pd catalyst precursor, such as 
      Pd((R,R)-Me-Duphos)(trans-stilbene), gave the tertiary phosphines PMe(Ar')(Ar) in 
      enantioenriched form. Sterically demanding secondary phosphine substituents (Ar') 
      and aryl iodides with electron-donating para substituents resulted in the highest 
      enantiomeric excess, up to 88%. Phosphination of ortho-substituted aryl iodides 
      required a Pd(Et-FerroTANE) catalyst but gave low enantioselectivity. 
      Observations during catalysis and stoichiometric studies of the individual steps 
      suggested a mechanism for the cross-coupling of PhI and PHMe(Is) (1) initiated by 
      oxidative addition to Pd(0) yielding Pd((R,R)-Me-Duphos)(Ph)(I) (3). Reversible 
      displacement of iodide by PHMe(Is) gave the cation 
      [Pd((R,R)-Me-Duphos)(Ph)(PHMe(Is))][I] (4), which was isolated as the triflate 
      salt and crystallographically characterized. Deprotonation of 4-OTf with NaOSiMe3 
      gave the phosphido complex Pd((R,R)-Me-Duphos)(Ph)(PMeIs) (5); an equilibrium 
      between its diastereomers was observed by low-temperature NMR spectroscopy. 
      Reductive elimination of 5 yielded different products depending on the 
      conditions. In the absence of a trap, the unstable three-coordinate phosphine 
      complex Pd((R,R)-Me-Duphos)(PMeIs(Ph)) (6) was formed. Decomposition of 5 in the 
      presence of PhI gave PMeIs(Ph) (2) and regenerated 3, while trapping with 
      phosphine 1 during catalysis gave Pd((R,R)-Me-Duphos)(PHMe(Is))2 (7), which 
      reacted with PhI to give 3. Deprotonation of 1:1 or 1.4:1 mixtures of cations 
      4-OTf gave the same 6:1 ratio of enantiomers of PMeIs(Ph) (2), suggesting that 
      the rate of P inversion in 5 was greater than or equal to the rate of reductive 
      elimination. Kinetic studies of the first-order reductive elimination of 5 were 
      consistent with a Curtin-Hammett-Winstein-Holness (CHWH) scheme, in which 
      pyramidal inversion at the phosphido ligand was much faster than P-C bond 
      formation. The absolute configuration of the phosphine (SP)-PMeIs(p-MeOC6H4) was 
      determined crystallographically; NMR studies and comparison to the stable complex 
      5-Pt were consistent with an RP-phosphido ligand in the major diastereomer of the 
      intermediate Pd((R,R)-Me-Duphos)(Ph)(PMeIs) (5). Therefore, the favored 
      enantiomer of phosphine 2 appeared to be formed from the major diastereomer of 
      phosphido intermediate 5, although the minor intermediate diastereomer underwent 
      P-C bond formation about three times more rapidly. The effects of the diphosphine 
      ligand, the phosphido substituents, and the aryl group on the ratio of 
      diastereomers of the phosphido intermediates Pd(diphos*)(Ar)(PMeAr'), their rates 
      of reductive elimination, and the formation of three-coordinate complexes were 
      probed by low-temperature 31P NMR spectroscopy; the results were also consistent 
      with the CHWH scheme.
FAU - Blank, Natalia F
AU  - Blank NF
AD  - Contribution from the 6128 Burke Laboratory, Department of Chemistry, Dartmouth 
      College, Hanover, New Hampshire 03755, USA.
FAU - Moncarz, Jillian R
AU  - Moncarz JR
FAU - Brunker, Tim J
AU  - Brunker TJ
FAU - Scriban, Corina
AU  - Scriban C
FAU - Anderson, Brian J
AU  - Anderson BJ
FAU - Amir, Omar
AU  - Amir O
FAU - Glueck, David S
AU  - Glueck DS
FAU - Zakharov, Lev N
AU  - Zakharov LN
FAU - Golen, James A
AU  - Golen JA
FAU - Incarvito, Christopher D
AU  - Incarvito CD
FAU - Rheingold, Arnold L
AU  - Rheingold AL
LA  - eng
PT  - Journal Article
DEP - 20070503
PL  - United States
TA  - J Am Chem Soc
JT  - Journal of the American Chemical Society
JID - 7503056
EDAT- 2007/05/04 09:00
MHDA- 2007/05/04 09:01
CRDT- 2007/05/04 09:00
PHST- 2007/05/04 09:00 [pubmed]
PHST- 2007/05/04 09:01 [medline]
PHST- 2007/05/04 09:00 [entrez]
AID - 10.1021/ja070225a [doi]
PST - ppublish
SO  - J Am Chem Soc. 2007 May 30;129(21):6847-58. doi: 10.1021/ja070225a. Epub 2007 May 
      3.