Water Addition to Alkynes Promoted by a Dicationic Platinum(II) Complex
摘要:
Dicationic platinum alkyne complexes were generated in situ by substitution of ethylene in [Pt(PNP)(C2H4)]-(BF4)(2) (PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) with alkynes at low temperature. The dicationic acetylene complex readily adds water to form the platina-acetaldehyde complex [Pt(PNP)(CH2CHO)BF4, which was analyzed by X-ray diffraction. H-1 and P-31 NMR. studies were performed to elucidate the mechanism of formation of [Pt(PNP)(CH2CHO)BF4. A reversible acid base equilibrium between the platina-acetaldehyde and the corresponding eta(2)-vinyl alcohol complex [Pt(PNP)(CH2= CHOH)](2+) was observed. The complexes with terminal alkynes (propyne and 1-hexyne) gave with water a mixture of Markovnikov and anti-Markovnikov addition products [Pt(PNP){CH2C(O)R-1}BF4 and [Pt(PNP){C(O)CH2R1}]BF4 (R-1 = Me, n-Bu) in a ratio of 1:4. However, with tert-butyl- and phenylacetylene C H bond activation occurred, yielding the sigma-alkynyl complexes [Pt(PNP)(C equivalent to CR2)BF4 (R-2 = t-Bu, Ph). Complexes with internal allcynes (RC)-C-3 equivalent to CR4 (R-3 = Me; R-4 = Me, n-Pr) react with water and form the corresponding beta-ketonyl complexes [Pt(PNP){(CHRC)-C-3(O)R-4}]BF4. Moderate regioselectivity was observed for 2-hexyne.
Water Addition to Alkynes Promoted by a Dicationic Platinum(II) Complex
摘要:
Dicationic platinum alkyne complexes were generated in situ by substitution of ethylene in [Pt(PNP)(C2H4)]-(BF4)(2) (PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) with alkynes at low temperature. The dicationic acetylene complex readily adds water to form the platina-acetaldehyde complex [Pt(PNP)(CH2CHO)BF4, which was analyzed by X-ray diffraction. H-1 and P-31 NMR. studies were performed to elucidate the mechanism of formation of [Pt(PNP)(CH2CHO)BF4. A reversible acid base equilibrium between the platina-acetaldehyde and the corresponding eta(2)-vinyl alcohol complex [Pt(PNP)(CH2= CHOH)](2+) was observed. The complexes with terminal alkynes (propyne and 1-hexyne) gave with water a mixture of Markovnikov and anti-Markovnikov addition products [Pt(PNP){CH2C(O)R-1}BF4 and [Pt(PNP){C(O)CH2R1}]BF4 (R-1 = Me, n-Bu) in a ratio of 1:4. However, with tert-butyl- and phenylacetylene C H bond activation occurred, yielding the sigma-alkynyl complexes [Pt(PNP)(C equivalent to CR2)BF4 (R-2 = t-Bu, Ph). Complexes with internal allcynes (RC)-C-3 equivalent to CR4 (R-3 = Me; R-4 = Me, n-Pr) react with water and form the corresponding beta-ketonyl complexes [Pt(PNP){(CHRC)-C-3(O)R-4}]BF4. Moderate regioselectivity was observed for 2-hexyne.
Mechanistic Studies on Platinum(II) Catalyzed Hydroarylation of Alkynes
作者:Christine Hahn、Mayra Miranda、Nagendra P. B. Chittineni、Trent A. Pinion、Ricardo Perez
DOI:10.1021/om5003123
日期:2014.6.23
The dicationic acetylene platinum(II) complex [Pt(PNP)(C2H2)](BF4)(2) (PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) was generated in situ by ligand substitution from the ethylene complex [Pt(PNP)(C2H4)](BF4)(2) and was reacted with a series of arenes at low temperature. Only electron-rich arenes added across the coordinated C-C triple bond and gave the corresponding arylalkenyl complexes (E)-[Pt(PNP)(CH=CHAr)]BF4 (Ar = C6Me5, C6H2Me3-2,4,6, C6H3Me2-2,6, C6H3Me2-2,4). A slow E-Z isomerization of the arylalkenyl complexes was observed. Single-crystal X-ray structure analyses were obtained for both E and Z isomers of the pentamethylbenzene derivative. The E isomers of [Pt(PNP)(CH=CHAr)]BF4 (Ar = C6Me5, C6H2Me3-2,4,6) reacted with excess HBF4 center dot Et2O to give the corresponding arylalkene complexes [Pt(PNP)(CH2=CHAr)](BF4)(2), whereas the Z isomers did not undergo immediate protonolysis. Using (E)-[Pt(PNP)(CD=CDC6Me5)]BF4 it was shown that the stereochemistry of the C-C double bond in the protonolysis product depends on the nature of the acid anion HX (X- = Cl-, BF4-). The catalytic hydroarylation was studied in solution by NMR spectroscopy. The reaction studies provide a more refined view of the individual steps proposed for the Friedel-Crafts type mechanism of the Pt-II-catalyzed intermolecular hydroarylation of alkynes.