- Pd(η3-1-PhC3H4)(η5- C5H5), an unusually effective catalyst precursor for Suzuki-Miyaura cross-coupling reactions catalyzed by bis-phosphine palladium(0) compounds
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It has previously been shown that the easily handled, heat- and air-stable compound Pd(η3-1-PhC3H4)(η5- C5H5) (Vb) reacts rapidly with a wide variety of tertiary phosphines L to produce near-quantitative yields of the corresponding Pd(0) compounds PdL2, which are widely believed to be the active species in many often-used cross-coupling catalyst systems based on Pd(PPh 3)4 (I), Pd2(dba)3 (II), PdCl 2 (III), and Pd(OAc)2 (IV). However, catalyst precursors I-IV are in fact known to preferentially generate sterically hindered, three-coordinate Pd(0) species rather than two-coordinate PdL2, and thus Vb is hypothetically expected to be a better catalyst precursor for e.g. Suzuki-Miyaura cross-coupling reactions. Utilizing the conventional Suzuki-Miyaura cross-coupling reaction of phenylboronic acid with bromoanisole, comparisons are made of the efficacies of catalyst systems based on Vb with those based on compounds I-IV (L = the representative phosphines PPh 3, PCy3, PBut3). As anticipated, catalysts generated from Vb are significantly more competent and, as a bonus, Vb makes palladium(0) complexes PdL2 available under rigorously anhydrous conditions.
- Fraser, Andrew W.,Besaw, Jessica E.,Hull, Laura E.,Baird, Michael C.
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- Enantioselective synthesis of polycyclic carbocycles via an alkynylation-allylation-cyclization strategy
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A new general three-stage strategy to access polycyclic ring systems bearing all-carbon quaternary centers with high enantioselectivity is reported. The required starting materials were readily accessed in racemic form through the α-alkynylation of ketoes
- Vita, Maria Victoria,Mieville, Pascal,Waser, Jerome
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- Pd(η3-1-PhC3H4)(η5- C5H5), an unusually effective catalyst precursor for heck-mizoroki and sonogashira cross-coupling reactions catalyzed by bis-phosphine palladium(0) compounds
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The compound Pd(η3-1-PhC3H4) (η5-C5H5) reacts essentially quantitatively with a variety of phosphines L to form cross-coupling catalysts of the type PdL2 and has recently been shown to be a much more effective catalyst precursor for Suzuki-Miyaura cross-coupling reactions in comparison to more commonly utilized precursors such as Pd(PPh3)4, Pd 2(dba)3, and Pd(OAc)2, which do not effectively generate two-coordinate species PdL2. This advantage is expected to apply also to e.g. Heck-Mizoroki and Sonogashira cross-coupling reactions, both of which are generally believed to be catalyzed by species of the type PdL 2. Therefore, comparisons of the efficacies of catalyst systems based on Pd(η3-1-PhC3H4)(η5- C5H5), Pd(PPh3)4, Pd 2(dba)3, and Pd(OAc)2 are made utilizing the conventional coupling reactions of aryl halides with methyl acrylate and styrene for Heck-Mizoroki coupling and with phenylacetylene for Sonogashira coupling. As anticipated, catalyst systems based on Pd(η3-1-PhC 3H4)(η5-C5H5) are found to be significantly more active.
- Fraser, Andrew W.,Jaksic, Bryan E.,Batcup, Rhys,Sarsons, Christopher D.,Woolman, Michael,Baird, Michael C.
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supporting information
p. 9 - 11
(2013/03/13)
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- ASYMMETRICALLY BONDED ? LIGANDS I. HINGING AWAY FROM METAL OF SUBSTITUTED ALLYLS: SYNTHESES OF 1-syn-METHYL AND -PHENYL COMPLEXES, AND THE MOLECULAR STRUCTURES OF ((η-1-Ph-C3H4)Pd(tmeda))BF4, ((η-C5H5)Pd(η-1-Ph-C3H4)), AND ((phen)Mo(CO)2(NCS)(η-1-Ph-C3H4)) AT 185 K
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Seven new complexes of (η-1-Me-C3H4) and (η-1-Ph-C3H4) with symmetric metal ligand backbones have been synthesised and spectroscopically characterised.Crystals of three of them, ((η-1-Ph-C3H4)Pd(tmeda))BF4 (4), ((η-C5H5)Pd(η-1-Ph-C3H4)) (5), and ((phen)Mo(CO)2(NCS)(η-1-Ph-C3H4)) (8), were suitable for X-ray diffraction studies. 4 is orthorhombic, Pca21, with four ion pairs in a cell of dimensions a 11.326(4), b 16.048(5) and c 9.950(3) angstroem.Using 4431 data measured at 185 K, R converged at 0.0311.Crystals of 5 are monoclinic, P21/c, with a 14.2255(19), b 5.8203(11), c 13.837(5) angstroem and β 91.287(21) deg at 185 K, Z=4. 3064 amplitudes have been used to afford R=0.0267. for 8 the monoclinic cell is a 15.658(4), b 9.473(3), c 15.666(6) angstroem, and β 113.95(3) deg, P21/a, Z=4.Low temperature (185 K) data were collected, and 3734 used to refine the structure to R=0.0362.The molecular structures of 4,5, and 8 all reveal an η-1-syn-Ph-C3H4 ligand that is asymmetrically bonded to the metal atom, such that M-C(1) > M-C(3).Analysis of intra- and intermolecular contacts strongly suggests that, at least for 5, the distortion in the metal-allyl bonding is electronic in origin.
- Murrall, Nicholas W.,Welch, Alan J.
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p. 109 - 130
(2007/10/02)
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