David Palomas | Queen Mary, University of London (original) (raw)

Papers by David Palomas

The reaction of a series of dinucleating bis(β-diketiminate) pro-ligands with mesitylcopper in th... more The reaction of a series of dinucleating bis(β-diketiminate) pro-ligands with mesitylcopper in the presence and absence of mono and diphosphines has allowed the isolation of a new series of dicopper(I) complexes. Inclusion of trans-1,2-cyclohexyl (1), 2,6-pyridyl (2), and 2,2’-oxydiaryl (3) spacers between the β-diketiminate units has been studied. The isolation of three new copper(I) phosphine complexes [1·Cu2(PPh3)2], [2·Cu2(PPh3)2] and [3·Cu2(PPh3)2] is reported. While these compounds display large Cu⋯Cu separations of 5.4–7.9 Å in the solid state, solution data are consistent with a large degree of conformational freedom. Modification of the monophosphine to a diphosphine, DPPE, allowed the isolation of the novel 11-membered bimetallic macrocycle [2·Cu2(DPPE)] containing both a binucleating nitrogen based ligand and a chelating diphosphine. While acetonitrile adducts of this series could also be generated in situ, under forcing conditions reaction of the 2,6-pyridyl bridged ligand with mesityl copper led to the formation [2·Cu2]2. This latter complex is a dimer of dicopper(I) units in which the bis(β-diketiminate) ligand now binds four copper(I) centers through not only the expected κ2-N,N’-chelation but also κ1- and η2-binding of the central pyridine through orthogonal Cu–N and Cu–arene interactions. Reversible coordination of alkenes, pyridine and quinoline to the copper cluster was identified allowing the isolation
and structural characterisation of a further series of dinuclear complexes [2·Cu2(pyridine)2], [2·Cu2(cyclopentene)2] and [2·Cu2(norbornene)2]. Solution studies allow quantification of the reversible binding event through a van’t Hoff analysis. Both solution and the solid state data suggest a weak anagostic interaction exists in the latter two alkene complexes of copper(I). The new complexes have been
characterized by X-ray diffraction, multinuclear NMR spectroscopy and CHN analysis

A series of Cu-, Fe-and Fe/Cu-containing zeolite (ZSM-5, beta, Y) catalysts were prepared to inve... more A series of Cu-, Fe-and Fe/Cu-containing zeolite (ZSM-5, beta, Y) catalysts were prepared to investigate the effect of zeolite's physicochemical properties on the total oxygenates production and MeOH selectivity from the partial methane oxidation using H 2 O 2 as oxidizing agent. The NH 3-TPD studies have shown that the zeolite type and Si/Al molar ratio are correlated with the acid sites strength and concentration. The latter surface property was proved to have a strong influence on the oxygenate productivity. In particular , a significant increase of the methanol production was observed when lowering Si/Al ratio in the ZSM-5, Fe/ZSM-5, Cu/ZSM-5 and Cu–Fe/ZSM-5 catalysts. This can be explained by the increased amount of Brønsted acid sites capable of accommodating the active catalyst (Fe species). The Fe-only ZSM-5 catalysts exhibited the highest catalytic activity (total oxygenated products) with HCOOH being the major product, whereas the presence of only Cu was found to suppress the production of MeOOH and HCOOH. On contrary , the deposition of both Fe 3? and Cu 2? results to a switch in selectivity and the target product, MeOH, was observed in *80 % selectivity. In the case of Cu-only ZSM-5 catalysts, a similar activity to methanol was observed regardless the copper source and synthesis method. The activity/selectivity findings of the present study confirm and complement the conclusions of the previous work by Hammond et al. (ACS Catal 3:689, 2013; ACS Catal 3:1835, 2013; Angew Chem Int Ed 51:5129, 2012; Chem Eur J 18:15735, 2012) over the well-studied Cu–Fe–zeolite system, providing also complete material balance based on both gas and liquid reaction products. Graphical Abstract Keywords Partial oxidation of methane Á ZSM-5 zeolite Á Acidity Á Methanol production

Catal. Sci. Technol., 2015

A series of multimetallic copperIJII) complexes have been re-investigated for methane oxidation wi... more A series of multimetallic copperIJII) complexes have been re-investigated for methane oxidation with H 2 O 2 . The preparation and properties of trinuclear copperIJII) complexes of the form ijCu 3 IJtriazole) n IJOH 2 ) 12−n ] (n = 8, 10) are reported. While these complexes are trimeric in the solid-state, 1 H NMR studies suggest that facile ligand dissociation occurs in solution. The oxidation of cyclohexane with H 2 O 2 catalyzed by ijCu 3 IJtriazole) n IJOH 2 ) 12−n ] (n = 8, 10) is compared against a literature known oxo-centered tetrameric cluster (Angew. Chem., Int. Ed., 2005, 44, 4345) and these catalysts display moderate activities. The series have also been investigated in methane oxidation at 30 bar and 40°C. Analytical techniques including a solvent suppression 1 H NMR method have been applied to quantify the liquid-and gas-phase products. The multimetallic copperIJII) complexes and copperIJII) nitrate control samples produce only methanol and CO 2 . While TONs for methanol production range from 1.4-4.6 in all cases approximately 50 times the amount of CO 2 is produced relative to methanol. We conclude that selectivity is a determining factor in methane oxidation under these conditions and should be considered in future studies. 4108 | Catal. Sci. Technol., 2015, 5, 4108-4115

Angewandte Chemie International Edition, 2012

Dalton Transactions, 2012

The synthesis of several electron poor allenes bearing electron withdrawing substituents is descr... more The synthesis of several electron poor allenes bearing electron withdrawing substituents is described and their use as Lewis acids in the field of frustrated Lewis pair (FLP) chemistry reported. At room temperature the combination of N-heterocyclic carbenes (NHC) with the allenes under study invariably afforded the corresponding Lewis adducts; however, at -78 °C this reaction is in most of the cases inhibited and kinetically induced organic FLPs are formed. Under these conditions the activation of S-S bonds in disulfides has been achieved in excellent yields.

Angewandte Chemie International Edition, 2009

Financial support for this work is acknowledged (grant nos. CTQ2007-61048 and IB08-088). S.S.-P. ... more Financial support for this work is acknowledged (grant nos. CTQ2007-61048 and IB08-088). S.S.-P. and D.P. thank the MICINN for predoctoral FPU fellowships. We also thank Dr. ngel L. Suµrez-Sobrino for his helpful assistance with the X-ray analysis. We are grateful to the referees for their kind and helpful suggestions to improve the manuscript, particularly for the labeling experiments.

Organic Letters, 2008

Replacement of the tricyanofuran (TCF) acceptor by its stronger analogue CF 3 -TCF results in dec... more Replacement of the tricyanofuran (TCF) acceptor by its stronger analogue CF 3 -TCF results in decreased second-order optical nonlinearities in merocyanines bearing a proaromatic 1,3-dithiole donor. The TCF-containing derivatives display exceptionally high µ values up to 31000 × 10 -48 esu, unprecedented for 1,3-dithiole-based NLO-phores.

Iodocyclopentenes are formed at room temperature upon straight reaction of δ-alkynyl-β- ketoester... more Iodocyclopentenes are formed at room temperature upon straight reaction of δ-alkynyl-β-
ketoesters with I2 for several hours. Cyclizations involving terminal and substituted (alkyl,
aryl, Br, I) alkynes were accessed. Twelve examples with yields ranging from 20% up to 80%
are reported (out of them eight cases are above 60%). These results present the first
examples of the iodonium-promoted 5-endo-dig carbocyclization of active methyne
substrates onto alkynes.

The reaction of a series of dinucleating bis(β-diketiminate) pro-ligands with mesitylcopper in th... more The reaction of a series of dinucleating bis(β-diketiminate) pro-ligands with mesitylcopper in the presence and absence of mono and diphosphines has allowed the isolation of a new series of dicopper(I) complexes. Inclusion of trans-1,2-cyclohexyl (1), 2,6-pyridyl (2), and 2,2’-oxydiaryl (3) spacers between the β-diketiminate units has been studied. The isolation of three new copper(I) phosphine complexes [1·Cu2(PPh3)2], [2·Cu2(PPh3)2] and [3·Cu2(PPh3)2] is reported. While these compounds display large Cu⋯Cu separations of 5.4–7.9 Å in the solid state, solution data are consistent with a large degree of conformational freedom. Modification of the monophosphine to a diphosphine, DPPE, allowed the isolation of the novel 11-membered bimetallic macrocycle [2·Cu2(DPPE)] containing both a binucleating nitrogen based ligand and a chelating diphosphine. While acetonitrile adducts of this series could also be generated in situ, under forcing conditions reaction of the 2,6-pyridyl bridged ligand with mesityl copper led to the formation [2·Cu2]2. This latter complex is a dimer of dicopper(I) units in which the bis(β-diketiminate) ligand now binds four copper(I) centers through not only the expected κ2-N,N’-chelation but also κ1- and η2-binding of the central pyridine through orthogonal Cu–N and Cu–arene interactions. Reversible coordination of alkenes, pyridine and quinoline to the copper cluster was identified allowing the isolation
and structural characterisation of a further series of dinuclear complexes [2·Cu2(pyridine)2], [2·Cu2(cyclopentene)2] and [2·Cu2(norbornene)2]. Solution studies allow quantification of the reversible binding event through a van’t Hoff analysis. Both solution and the solid state data suggest a weak anagostic interaction exists in the latter two alkene complexes of copper(I). The new complexes have been
characterized by X-ray diffraction, multinuclear NMR spectroscopy and CHN analysis

A series of Cu-, Fe-and Fe/Cu-containing zeolite (ZSM-5, beta, Y) catalysts were prepared to inve... more A series of Cu-, Fe-and Fe/Cu-containing zeolite (ZSM-5, beta, Y) catalysts were prepared to investigate the effect of zeolite's physicochemical properties on the total oxygenates production and MeOH selectivity from the partial methane oxidation using H 2 O 2 as oxidizing agent. The NH 3-TPD studies have shown that the zeolite type and Si/Al molar ratio are correlated with the acid sites strength and concentration. The latter surface property was proved to have a strong influence on the oxygenate productivity. In particular , a significant increase of the methanol production was observed when lowering Si/Al ratio in the ZSM-5, Fe/ZSM-5, Cu/ZSM-5 and Cu–Fe/ZSM-5 catalysts. This can be explained by the increased amount of Brønsted acid sites capable of accommodating the active catalyst (Fe species). The Fe-only ZSM-5 catalysts exhibited the highest catalytic activity (total oxygenated products) with HCOOH being the major product, whereas the presence of only Cu was found to suppress the production of MeOOH and HCOOH. On contrary , the deposition of both Fe 3? and Cu 2? results to a switch in selectivity and the target product, MeOH, was observed in *80 % selectivity. In the case of Cu-only ZSM-5 catalysts, a similar activity to methanol was observed regardless the copper source and synthesis method. The activity/selectivity findings of the present study confirm and complement the conclusions of the previous work by Hammond et al. (ACS Catal 3:689, 2013; ACS Catal 3:1835, 2013; Angew Chem Int Ed 51:5129, 2012; Chem Eur J 18:15735, 2012) over the well-studied Cu–Fe–zeolite system, providing also complete material balance based on both gas and liquid reaction products. Graphical Abstract Keywords Partial oxidation of methane Á ZSM-5 zeolite Á Acidity Á Methanol production

Catal. Sci. Technol., 2015

A series of multimetallic copperIJII) complexes have been re-investigated for methane oxidation wi... more A series of multimetallic copperIJII) complexes have been re-investigated for methane oxidation with H 2 O 2 . The preparation and properties of trinuclear copperIJII) complexes of the form ijCu 3 IJtriazole) n IJOH 2 ) 12−n ] (n = 8, 10) are reported. While these complexes are trimeric in the solid-state, 1 H NMR studies suggest that facile ligand dissociation occurs in solution. The oxidation of cyclohexane with H 2 O 2 catalyzed by ijCu 3 IJtriazole) n IJOH 2 ) 12−n ] (n = 8, 10) is compared against a literature known oxo-centered tetrameric cluster (Angew. Chem., Int. Ed., 2005, 44, 4345) and these catalysts display moderate activities. The series have also been investigated in methane oxidation at 30 bar and 40°C. Analytical techniques including a solvent suppression 1 H NMR method have been applied to quantify the liquid-and gas-phase products. The multimetallic copperIJII) complexes and copperIJII) nitrate control samples produce only methanol and CO 2 . While TONs for methanol production range from 1.4-4.6 in all cases approximately 50 times the amount of CO 2 is produced relative to methanol. We conclude that selectivity is a determining factor in methane oxidation under these conditions and should be considered in future studies. 4108 | Catal. Sci. Technol., 2015, 5, 4108-4115

Angewandte Chemie International Edition, 2012

Dalton Transactions, 2012

The synthesis of several electron poor allenes bearing electron withdrawing substituents is descr... more The synthesis of several electron poor allenes bearing electron withdrawing substituents is described and their use as Lewis acids in the field of frustrated Lewis pair (FLP) chemistry reported. At room temperature the combination of N-heterocyclic carbenes (NHC) with the allenes under study invariably afforded the corresponding Lewis adducts; however, at -78 °C this reaction is in most of the cases inhibited and kinetically induced organic FLPs are formed. Under these conditions the activation of S-S bonds in disulfides has been achieved in excellent yields.

Angewandte Chemie International Edition, 2009

Financial support for this work is acknowledged (grant nos. CTQ2007-61048 and IB08-088). S.S.-P. ... more Financial support for this work is acknowledged (grant nos. CTQ2007-61048 and IB08-088). S.S.-P. and D.P. thank the MICINN for predoctoral FPU fellowships. We also thank Dr. ngel L. Suµrez-Sobrino for his helpful assistance with the X-ray analysis. We are grateful to the referees for their kind and helpful suggestions to improve the manuscript, particularly for the labeling experiments.

Organic Letters, 2008

Replacement of the tricyanofuran (TCF) acceptor by its stronger analogue CF 3 -TCF results in dec... more Replacement of the tricyanofuran (TCF) acceptor by its stronger analogue CF 3 -TCF results in decreased second-order optical nonlinearities in merocyanines bearing a proaromatic 1,3-dithiole donor. The TCF-containing derivatives display exceptionally high µ values up to 31000 × 10 -48 esu, unprecedented for 1,3-dithiole-based NLO-phores.

Iodocyclopentenes are formed at room temperature upon straight reaction of δ-alkynyl-β- ketoester... more Iodocyclopentenes are formed at room temperature upon straight reaction of δ-alkynyl-β-
ketoesters with I2 for several hours. Cyclizations involving terminal and substituted (alkyl,
aryl, Br, I) alkynes were accessed. Twelve examples with yields ranging from 20% up to 80%
are reported (out of them eight cases are above 60%). These results present the first
examples of the iodonium-promoted 5-endo-dig carbocyclization of active methyne
substrates onto alkynes.