Synthetic and reactivity studies of hetero-tri-anionic sodium zincates

The synthesis and characterisation of several sodium zincate complexes is reported. The all-alkyl monomeric sodium zincate (PMEDTA)·Na(μ-CH2SiMe3)ZntBu2 2, is prepared by combining an equimolar quantity of tBu2Zn, nBuNa and PMDETA (N,N,N′,N′′,N′′-pentamethyldiethylenetriamine)]. A similar approach was used to prepare and isolate the unusual dimeric zincate [(PMEDTA)·Na(μ-nBu)ZntBu2]2 3. When an equimolar mixture of nBuNa, tBu2Zn and TMP(H) (2,2,6,6-tetramethylpiperidine) are combined in hexane, the hetero-tri-leptic TMP(H)-solvated zincate (TMPH)Na(μ-TMP)(μ-nBu)ZntBu 4 was forthcoming. Complex 4 can also be prepared using a rational approach [i.e., utilising two molar equivalents of TMP(H)]. When TMEDA is reacted with an equimolar mixture of nBuNa, tBu2Zn and TMP(H), the monomeric sodium zincate (TMEDA)Na(μ-TMP)(μ-nBu)ZntBu 5 was obtained – this complex is structurally similar to the synthetically useful relation TMEDA)·Na(μ-TMP)(μ-tBu)Zn(tBu) 1. By changing the sodium reagent used in the synthesis of 5, it was possible to prepare (TMEDA)Na(μ-TMP)(μ-Me3SiCH2)ZntBu 6. By reacting 5 with cis-DMP(H) (cis-2,6-dimethylpiperidine), the zincate could thermodynamically function as a amide base, to give the transamination product (TMEDA)Na(μ-cis-DMP)(μ-nBu)ZntBu 7, although no crystals could be grown. However, when HMDS(H) (1,1,1,3,3,3-hexamethyldisilazane) or PEA(H) [(+)-bis[(R)-1-phenylethyl]amine] is reacted with 5, crystalline (TMEDA)Na(μ-HMDS)(μ-nBu)ZntBu 8 or (TMEDA)Na(μ-PEA)(μ-nBu)ZntBu 9 are isolated respectively. With PNA(H) (N-phenylnaphthalen-1-amine) the reaction took a different course and resulted in the formation of the dimeric sodium amide complex [(TMEDA)Na(PNA)]2 10. When reacted with benzene, it appears that a TMEDA-free variant of 5 functions thermodyanically as an nBu base to yield the previously reported (TMEDA)Na(μ-TMP)(tBu)Zn(μ-C6H4)Zn(tBu)(μ-TMP)Na(TMEDA) 11. Finally when reacted with TEMPO (2,2,6,6-tetramethylpiperidinyloxy), 5 undergoes a single electron transfer reaction to form (TMEDA)Na(μ-TMP)(μ-TEMPO)ZnnBu 12

Palladium(II) complexes with a phosphino-oxime ligand: synthesis, structure and applications to the catalytic rearrangement and dehydration of aldoximes

The treatment of [PdCl2(COD)] (COD = 1,5-cyclooctadiene) with 1 and 2 equivalents of 2-(diphenylphosphino)benzaldehyde oxime in dichloromethane at room temperature led to the selective formation of [PdCl2{κ2-(P,N)-2-Ph2PC6H4CH[double bond, length as m-dash]NOH}] (1) and [Pd{κ2-(P,N)-2-Ph2PC6H4CH[double bond, length as m-dash]NOH}2][Cl]2 (2), respectively, which represent the first examples of Pd(II) complexes containing a phosphino-oxime ligand. These compounds, whose structures were fully confirmed by X-ray diffraction methods, were active in the catalytic rearrangement of aldoximes. In particular, using 5 mol% complex 1, a large variety of aldoximes could be cleanly converted into the corresponding primary amides at 100 °C, employing water as solvent and without the assistance of any cocatalyst. Palladium nanoparticles are the active species in the rearrangement process. In addition, when the same reactions were performed employing acetonitrile as solvent, selective dehydration of the aldoximes to form the respective nitriles was observed. For comparative purposes, the catalytic behaviour of an oxime-derived palladacyclic complex has also been briefly evaluated.This work was supported by Spanish MINECO (projects CTQ2013-40591-P, CTQ2013-43446-P and CTQ2014-51912-REDC) and Gobierno del Principado de Asturias (project GRUPIN14-006). L.M.-R. and E.T.-M. thank MINECO, MECD and ESF for the award of FPI and FPU fellowships, respectively

Intensifying. EU (Work European Virtual Scene)

Universidad Pablo de OlavideMinisterio de Ciencia e Innovación CSO2009-06819-EUniversidad de Granada 1975-200

Axially Chiral Triazoloisoquinolin-3-ylidene Ligands in Gold(I)-Catalyzed Asymmetric Intermolecular (4 + 2) Cycloadditions of Allenamides and Dienes

The first highly enantioselective intermolecular (4 + 2) cycloaddition between allenes and dienes is reported. The reaction provides good yields of optically active cyclohexenes featuring diverse substitution patterns and up to three stereocenters. Key to the success of the process is the use of newly designed axially chiral N-heterocyclic carbene–gold catalystsThis work was supported by the Spanish MINECO (SAF2010-20822-C02, CTQ2010-15297, CTQ2010-14974, and Consolider Ingenio 2010 CSD2007-00006), the ERDF funds, the Xunta de Galicia (INCITE09209084PR, GRC2010/12), and the Junta de Andalucía (2008/FQM-3833 and 2009/FQM-4537, predoctoral fellowship to F.G.-C). H.F. acknowledges the Fundação para a Ciência e Tecnologia (FCT, Portugal) and POPH/FSE for a Ph.D. grant (Grant SFRH/BD/60214/2009)S

Structural studies of (rac)-BIPHEN organomagnesiates and intermediates in the halogen-metal exchange of 2-Bromopyridine

Four lithium magnesiate complexes (2−5) containing the dianionic (rac)-BIPHEN ligand have been prepared and characterized using X-ray crystallography and NMR spectroscopy. (THF)3·Li2Mg{(rac)-BIPHEN}nBu2, 2, (THF)3·Li2Mg{(rac)-BIPHEN}(CH2SiMe3)2, 3, and (THF)2·Li2Mg{(rac)-BIPHEN}neoPe2, 4, have been prepared by complexation of the appropriate dialkylmagnesium compound with in situ prepared Li(rac)-BIPHEN in a mixture of hydrocarbon/THF. For all structures, the Mg centers are four-coordinate (and retain the alkyl groups); however, in 2 and 3 the two Li centers have different coordination spheres (one binding to one THF molecule, the other to two). The solid-state structures of 2 and 3 are essentially isostructural with that of 4 except that both Li atoms in this molecule have equivalent coordination spheres. The solution behaviors of these three molecules have been studied by 1H, 13C, and DOSY NMR spectroscopy. During the synthesis of 2, it was discovered that a (rac)-BIPHEN-rich (or n-butyl-free) lithium magnesiate, (THF)4Li2Mg{(rac)-BIPHEN}fo2, 2b, could be isolated. The lithium precursor to 2−5, (THF)4·Li4{(rac)-BIPHEN)}2, 1, has also been isolated. Within the molecular structure of this tetranuclear complex, there are three different Li coordination environments. Finally, 2 has already shown promise as a reagent in a halogen−metal exchange reaction with 2-bromopyridine. The structural chemistry at play in this reaction was probed by X-ray crystallography and NMR spectroscopy. The organometallic intermediate pyridyl-magnesiated 5, (THF)2·Li2Mg{(rac)-BIPHEN}(2-pyridyl)2, was isolated in high yield