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Inorganic and Organometallic Chemistry
Introduction
The activity of the group comprises the synthesis, characterization and reactivity studies of
inorganic, organometallic and intermetallic compounds of actinides and lanthanides and ion
molecule reactions with the same elements, in order to understand the influence of the
electronic configuration and of the size of these elements in the chemical behaviour of their
compounds. Due to the type of chemistry we are dealing with, we extended our work to the
chemistry of rhenium, with the aim of developing compounds that could be used as
intermediates in reactions directed to organic synthesis and that can be models for compounds
with 99m
Tc to be used as radiopharmaceuticals. These activities are supported by X-ray
diffraction analysis for structural studies and thermochemical studies for determination of
metal-ligand bond disruption enthalpies. The gas-phase reactions of metallic, intermetallic and
oxide ions involving lanthanides and actinides with organic substrates are studied by means of
Fourier transform ion cyclotron resonance spectroscopy.
The work done during 1996 in the domain of organometallic compounds allowed to
accomplish the study of the reactivity of the system UCl2(HBpz3)2 towards several organic
substrates. The analogous UCl2(Bpz4)2 system is now under investigation. The introduction of
more sterically hindered polypyrazolylborate ligands, such as [HB(3-tBupz)3] and [HB(3-
Mespz)3] allowed the synthesis of new systems of U (IV) and Ln(II) and their reactivity is
being studied.
The synthesis of alkoxides of lanthanides that could be active in some catalytic
transformations was also studied. We were trying to get alkoxides of low nuclearity using
alcohols with additional ether or amine functions. The compounds were tested in the
carboxylation reaction of methanol but probably due to the highly aggregated structures
obtained, the compounds did not show to be active in this particular transformation. The only
compound which showed to be active in this reaction was the ytterbium:nickel (1:1) alloy.
78% of conversion of methanol to dimethylcarbonate was achieved by reacting the alloy with
methanol under CO2.
The reactivity of oxo-complexes of rhenium towards several neutral substrates was studied as
well as the properties of rhenium (V) diolates. Attempts to prepare 99m
Tc analogues have been
done.
The work in the gas-phase included studies of the reactivity of lanthanide and actinide metal
and oxide ions with hydrocarbons, alcohols and phenols. Comparative studies with alkaline-
earth ions were made due to the similarity of these elements with lanthanides in low oxidation
states. The studies undertaken provided further examples confirming the relevance of the
accessibility of reactive electronic configurations to the reactivity of lanthanide and actinide
ions with organic molecules. Formation of f-d intermetallic ions was achieved and these
species may be available for future studies of the influence of the d element in the reactivity
with organic molecules. Reactivity of several lanthanide oxide cluster ions with small
oxygenated molecules was also studied. Collaborative work has extended the gas-phase
research to studies of transition metal ions.
Inorganic and Organometallic Chemistry ________________________________________________________
8
Research Team
Researchers – 12 * (10 PhD)
Research Students – 4
BSc Last Year Students – 4
Technicians – 2
* 2 Post-doctoral
Publications:
Journals – 7
Special Publ. – 1
Conf. Commun.: 10
Internal Reports: 1
Theses:
PhD – 1
MSc – 1
Lic. – 4
________________________________________________________ Inorganic and Organometallic Chemistry
9
f - Element Chemistry
Hydrocarbyl Derivatives of [UCl2{HB(pz)3}2]: Synthesis, Characterization
and Reactivity Studies Towards Protic Substrates and Ketones
M. Paula C. Campelloa, Maria José Calhorda
c, Ângela Domingos
a, Adelino Galvão
b,
João
Paulo Leala, A.Pires de Matos
a and Isabel Santos
a
aDepartamento de Química, ITN, 2686 Sacavém Codex, Portugal
bDepartamento de Engenharia Química, Instituto Superior Técnico, 1096 Lisboa Codex, Portugal
cI. T. Q. B., R. da Quinta Grande 6, Apt. 127, 2780 Oeiras, Portugal and Faculdade de Ciências,
Edifício C4, Campo Grande, 1700 Lisboa
Abstract
The reaction of [UCl2{HB(pz)3}2] (1) with lithium alkyls LiR (R=Me, CH2SiMe3, C6H4-o-
CH2NMe2) in the 1:1 or 1:2 molar ratio affords the compounds [UClR{HB(pz)3}2] (pz=
C3H3N2, R=Me (2), CH2SiMe3 (3), C6H4-o-CH2NMe2 (4)) and [UR2{HB(pz)3}2] (R=Me (5),
CH2SiMe3 (6)), respectively in 60-80% yield. Complex 2 can also be obtained (60%, yield) by
redistribution at room temperature between the complexes 1 and 5. Compounds 2, 3 and 4
react with pzH providing [UCl(pz){HB(pz)3}2] (7) in almost quantitative yield and 5 and 6
react also with pzH leading to [U(pz)2{HB(pz)3}2] (8). The alkoxide [U(OC6H4-o-
OMe)2{HB(pz)3}2] (9) was synthesized by reacting 5 or 6 with guaiacol. By reacting the
clorohydrocarbyls 2, 3 or 4 with excess of acetone the aldolate
[UCl(OCMe2CH2(C=O)Me){HB(pz)3}2] (11) was obtained, due to the activation of -CH
bond of acetone; however, for 3 the reaction is not clean and a mixture of (11) and
[UCl(OCMe2CH2SiMe3){HB(pz)3}2] (12) is always obtained. Stoichiometric amounts of
acetone insert into the metal-carbon bonds of 2 and 5 yielding [UCl(OtBu){HB(pz)3}2] and
[U(OtBu)2{HB(pz)3}2], respectively, while the insertion product
[U(OCMe2CH2SiMe3)2{HB(pz)3}2] (10) can only be obtained when 6 reacts with excess of
this substrate. (9) crystallizes from toluene/hexane in the triclinic space group P1 with unit
cell dimensions a=12.295 (2) Å, b=12.640(2) Å, c=13.994(2) Å, =76.10(1)º, =72.50(1)º,
=80.71(1)º, V=2004(2) Å3and Z=2. Recrystallization of a mixture containig
[UCl(OtBu){HB(pz)3}2] and 11 led to a decomposition product which has been characterized
by X-ray structural analysis as [UCl(Hpz)(OtBu){(-O)B(-pz)(pz)2}]2 (13): monoclinic
P21/n, a=13.701(3) Å, b=11.337(2) Å, c=14.857(4) Å, =104.65(2)º, V=2233(1) Å3 and Z=2.
Extended Hückel molecular orbital calculations provided some information on the bonding
capabilities of the [U{HB(pz)3}2] fragment compared to [U(C5Me5)2] and on the vulnerability
of the poly(pyrazolyl)borate ligands to nucleophilic attack.
Journal of Organometallic Chemistry (in press).
Inorganic and Organometallic Chemistry ________________________________________________________
10
Synthesis of lanthanide complexes coordinated by an asymmetric
cyclopentadienyl ligand
A.A. Trifonova, P. Van de Weghe
a, J. Collin
a, A. Domingos
b, I. Santos
b
a Laboratoire de Synthése Asymétrique, URA, ICMO, Université Paris-sud, 91405 Orsay, France
b Departamento de Química, Instituto Tecnológico e Nuclear, 2686 Sacavém Codex, Portugal
Abstract
The synthesis and characterization of bis- and monocyclopentadienyl lanthanide iodides
(S)-Cp’2 LnI (Ln = Sm, 3; Ln = La, 4) and (S)-Cp’LnI2 (THF)n’ (Ln = Sm, n = 3, 5; Ln = La,
n = 2, 6) coordinated by an asymmetric cyclopentadienyl ligand (Cp’ =
C5H4CH2CH(CH3)OCH2Ph) have been carried out. Variable-temperature NMR study
compounds 3 and 4 reveals a fluxional process in solution. The X-ray crystal structure
analysis of 3 shows a bent metallocene structure with intramolecular coordination to the
oxygen atoms of the side chains of both cyclopentadienyl ligands. For monocyclopentadienyl
complexes, intramolecular coordination is observed only for the lanthanum complex 6. All
compounds exhibit activity for the catalysis of Diels-Alder reactions.
Journal of Organometallic Chemistry (in press).
Current Work
Reduction of Copper-Lanthanide oxides catalysts derived from LnCu2
intermetallics and their catalytic behaviour in mesityl oxide hydrogenation
D. Ballivet-Tkatchenkoa J. Branco
b and A. Pires de Matos
b
a Institut de Recherches sur la Catalyse, Avenue Albert Einstein 2, 69626 Villeurbanne Cedex, France
b Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
Abstract
The reduction under hydrogen of the oxidized intermetallics described by the formulas
CeO2.2CuO and Ln2CuO4.3CuO (Ln = La, Pr, Nd) was followed by thermo-
gravimetric/differential thermal analysis (TG/DTA) and by temperature programmed
reduction (TPR). These techniques confirm two mass losses over 473 - 1173 K corresponding
the first to the reduction of the CuO phase and the second to the reduction of the ternary
phases as shown by X-ray powder diffraction (XRD). Energy dispersive X-ray analysis (EDX)
on several particles gave a Cu:Ln ratio close to that of the oxidized intermetallic compounds.
A two step treatment - oxidation followed by reduction - allows us to obtain catalysts which
are supported copper on lanthanide oxides. It was found that the reduction step does not alter
the copper composition on the surface resultant from the previous oxidation. These systems
proved to be active in the hydrogenation of mesityl oxide, being the only product the saturated
ketone.
To be submitted to J. Phys. Chem.
________________________________________________________ Inorganic and Organometallic Chemistry
11
Catalytic behaviour of LnCu2 intermetallics and derived supported
Copper-Lanthanide oxide catalysts in propionitrile hydrogenation
D. Ballivet-Tkatchenko,a J. Branco,
b and A. Pires de Matos
b
a Institut de Recherches sur la Catalyse, Avenue Albert Einstein 2, 69626 Villeurbanne Cedex,
France b Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
Abstract
The intermetallic compounds LnCu2 (Ln=La, Ce, Pr, Nd) and the derived copper-lanthanide
oxide catalysts CeO2.2Cu and Ln2O3.4Cu (Ln = La, Pr, Nd), show high selectivity for the
hydrogenation of propionitrile into the primary amine. The intermetallic compounds are
essentially good catalytic precursors and the derived copper-lanthanide oxide catalysts show
higher activity than the parent compounds. They show also higher selectivity for the primary
amine than copper catalysts obtained from impregnation of different supports with metallic
copper.
To be submitted to J.Catal.
Uranium (IV) complexes with polypyrazolylborate ligands
Ângela Domingosa, Noémia Marques
a, Manuela Silva
a, and Swiatoslaw Trofimenko
b
a Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
b E. I. Du Pont de Nemours & Company, Inc., Experimental Station, Wilmington, Delaware 19880-0302
During the last years we have been studying the reactivity of the U-C bond of -hydrocarbyl
uranium (IV) complexes of general formula UCl2RTpMe2 (TpMe2 = HB(3,5-Me2pz)3. Since it
was found that the reactivity patterns were dependent of the size of the R group, it will be of
interest to determine which effect in the reactivity could be achieved by changing the steric
and/or electronic requirements of the ancillary ligands. We have decided to use the ligand
TpMs
(TpMs
=[HB(3-Mespz)3] ), one of the so-called 2nd
generation Trofimenko’s ligands. The
reaction of UCl4 with Tl[HB(3-Mespz)3] when performed in CH2Cl2 or THF yielded the
complex UCl3[(HB(3-Mespz)2(5-Mespz)] (1) (HB(3-Mespz)2(5-Mespz)=TpMs
*) due to
isomerization of the TpMs
ligand. 1 undergoes metathetical reactions with K[N(SiMe3)2] and
LiC6H4CH2NMe2 to yield the corresponding UCl2XTpMs
* compounds. The crystal and
molecular structures of 1 and 2 were determined by means of X-ray diffraction analysis.
Uranium compounds with Poly(pyrazolyl)borate ligands: attempts to
prepare Uranium cations
Alexandra Rolo de Oliveira, A.Pires de Matos and Isabel Santos
Departamento de Química, ITN, 2686 Sacavém CODEX, Portugal
We have been trying to prepare uranium cations by reacting the compounds
[UCl2{HB(pz)3}2], [UClR{B(pz)4}2] and [UR2{B(pz)4}2] (R=CH3, CH2SiMe3) with AgBPh4
or NHEt3BPh4. Some compounds were obtained, but their full characterization needs crystals
suitable for X-ray crystallographic analysis.
Inorganic and Organometallic Chemistry ________________________________________________________
12
Chemistry of Uranium compounds containing the fragment "U{B(pz)4}2"
M. Paula Campello, Ângela Domingos, A.Pires de Matos and Isabel Santos
Departamento de Química, ITN, 2686 Sacavém CODEX, Portugal
Reactions of [UCl2{B(pz)4}2] (1) with LiMe, LiCH2Ph, LiCH2CMe3, LiC6H4-o-CH2NMe2
and LiCH2C6H4-o-NMe2 have been studied in different stoichiometries. Generally, we
observed reduction of the metal, but in the case of LiMe the complex [UClMe{B(pz)4}2] was
isolated and characterized. We also studied the possibility of preparing compounds with U-S
bonds. The complex [U(SiPr)2{B(pz)4}2] has been isolated and characterized, including by X-
ray crystallographic analysis.
Synthesis of Sm (II) and Yb(II) complexes
Irene Lopes, Ângela Domingos, and Noémia Marques Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
We have been studying the capability of the bulkier poly(pyrazol-1-yl)borates, [HB(3-
Mespz)3]- and [HB(3-
tBupz)3]-, to stabilize compounds of lanthanides in low coordination
numbers. Amide and thiolate derivatives of the compounds YbI[HB(3-Mespz)3](thf)2 and
YbI[HB(3-tBupz)3](thf) were obtained, but reactivity studies are still scarce. In some cases the
complexes formed were not stable and disproportionate yielding Yb[HB(3-tBupz)3]2. Due to
accidental presence of HCl in the course of one reaction, crystals of [Yb{(HB(3-Mespz)2(5-
Mespz)}(-Cl)]2 were obtained. The isomerization of the ligand [HB(3-Mespz)3], that must be
related with lability of the M-N bonds induced by the electron withdrawing effect of the
mesityl substituents of the pyrazolyl rings, seems to be a way to decrease steric overcrowding
around the metal centre.
We studied also the ability of the complexes LnTpMe2
(Ln=Sm, Eu; TpMe2
=HB(3,5-Me2pz)3)
to reduce organic substrates. The quinones can be reduced in two one-electron steps.
SmTpMe2
Me2 and EuTpMe2
react with 1,4-benzoquinone in the molar ratio 1:1 to yield the
Ln(III) compounds, LnTpMe2
(OC6H4O). When the reaction is carried in the molar ratio 2:1, the
quinone can be reduced by two samarium centres yielding the complex (SmTpMe2
)2(-
OC6H4O). Due to its lower reducing power, the Eu compound can not reduce the second one-
electron step of the quinone and only EuTpMe2
(OC6H4O) is formed, remaining the excess of
EuTpMe2
unreacted.
SmTpMe2
reduces also benzophenone to yield the ketyl SmTpMe2
(OCPh2) and E2R2 reagents to
yield Sm TpMe2
(ER) compounds.
The compound SmTpMe2
can not reduce protic substrates, but using iodine as a catalyst,
several Sm(III) complexes of the type SmTpMe2
X (X=OPh, pz) could be obtained.
________________________________________________________ Inorganic and Organometallic Chemistry
13
Synthesis and characterization of alkoxides and aryloxides of lanthanides
Joaquim Branco, José Manuel Carretas , Adelaide Carvalho, Ângela Domingos, Maria Teresa
Duarte, Joaquim Marçalo, Noémia Marques, António Pires de Matos Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
Alkoxides are known for almost all the elements, but the structural chemistry of these
compounds is dominated by the formation of polymeric structures. Due to the large ionic radii
of the lanthanides, the formation of multinuclear species is still more general for lanthanide
alkoxides, leading to compounds with low solubility and reactivity.
In order to get lanthanide alkoxides of low nuclearity we have been using bulky phenoxo
ligands ([OC6H2Me3-2,4,6]-, [OC6H3Bu
t-2,6]
-, [OC6H2Bu
t-2,6-Me-4]
- and [OC6H2Bu
t3-2,4,6]
-)
or phenoxo ligands bearing an additional ether or amine function ([OC6H4-OCH3-2]-,
[OC6H2-(CH2NMe2)2-2,6-Me-4)]-.and [OC6H2-(CH2NMe2)-2-Me3-3,5,6]-). We have been
using several synthetic routes. Conventional routes such as : a) the alcoholysis of a lanthanide
tris[bis(trimethylsilyl)amido] compound, Ln(N(SiMe3)2)3 ,(Ln=La, Eu, Yb), with HOC6H4-
OCH3-2, HOC6H2-(CH2NMe2)2-2,6-Me-4) and HOC6H2-(CH2NMe2)-2-Me3-3,5,6] in hexane
or toluene solutions at 0 ºC, b) the reaction between LnCl3 (Ln=La, Eu, Yb) and the
potassium salt of the phenoxo ligands [OC6H2Me3-2,4,6]-, [OC6H3Bu
t-2,6]
-, [OC6H2Bu
t-2,6-
Me-4]- and [OC6H2Bu
t3-2,4,6]
- in THF at room temperature and the ammoniacal route c) the
reaction of Yb or Eu metal in liquid ammonia at -78 ºC with 3 equiv. of HOC6H4-OCH3-2.
Full characterization of most of the compounds was not achieved due to the lack of crystals
suitable for X-ray diffraction studies. However, recrystallization from thf/hexane mixtures of
the products obtained by reacting YbCl3 with KOC6H4-OCH3-2 or by reacting ytterbium
metal in liquid ammonia with HOC6H4-OCH3-2 provided crystals for X-ray diffraction
analysis. The compound was formulated as the polymeric [Yb6(3-OH)4(OC6H4-2-OCH3)2(-
OC6H4--OCH3)10(OC6H4--OCH3)2].
We have also been exploring the capability of metallic ytterbium and europium to be
activated by ammonia gas. When ammonia gas is bubbled through a suspension of metal
pieces (Yb, Eu), in a solution of the phenol (C6H2Me3-2,4,6-OH, C6H3But-2,6-OH and
C6H2But3-2,4,6-OH) in THF, the evolution of H2 on the surface of the metal and the
dissolution of the metal is observed. After several hours of stirring, all the metal pieces have
been consumed and a solution is obtained. After the work-up the products were characterized
by several techniques. Unfortunately, this characterization is not completed because we didn't
get crystals to make X-ray crystallographic studies. The reactions of ytterbium and europium metals with several alcohols (methanol, ethanol and
isopropanol) were also studied by this method. Surprinsingly, the metallic europium reacted
directly with the alcohols without amonia gas. Work is in progress in order to get crystals to
complete the characterization of the trivalent ytterbium alkoxides and of the divalent
europium alkoxides.
Some of the compounds formed in these reactions were tested as catalysts in the reaction of
the carboxylation of the methanol to obtain dimethylcarbonate, an industrially important
product.
The ytterbium, europium and rhenium alkoxides {"M(OC6H4-OCH3-2)3", M=Yb, Eu;
"M(OC6H2-N(CH3)2-2-CH3-4,6)", M=La, Yb; ReOBPz4(OCH3)2} and the intermetallic
compounds {YbNi, YbCu} obtained by ammoniacal synthetic route were tested in batch
conditions (50 0C/50 bar), but they did not show activity for this reaction. However, ytterbium
: nickel (1:1) alloys obtained by MVS showed to be active, with 78% of conversion of
methanol to dimethyl carbonate.
Inorganic and Organometallic Chemistry ________________________________________________________
14
Rhenium Chemistry
Synthesis, Characterization and Study of the Redox Properties of
Rhenium(V) Diolates. Attempts to Prepare some 99m
Tc Analogues
Dina Nunesa, Ângela Domingos
a, António Paulo
a, Luciana Patrício
a, Isabel Santos
a,
M. Fernanda N. N. Carvalhob, and Armando J. L. Pombeiro
b
a Departamento de Química e Radioisótopos, ITN, 2686 Sacavém Codex, Portugal
b CQE, Complexo 1, Instituto Superior Técnico, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal
Abstract
Rhenium(V) diolate complexes of the type [ReO(diolate){3-B(pz)4}] (diolate =
OCH(CH3)CH2O2-
(3), OCH(CH3)CH(CH3)O2-
(4), OC(CH3)2C(CH3)2O2-
(5) OCH2CH2CH2O2-
(6), OC6H10O2-
(7) and OCH2CH2CH2CH2O2-
(8),) have been obtained by reacting [ReO{3-
B(pz)4}(OMe)2] (1) with the corresponding diols, in CH2Cl2, or by one step preparation using
[ReOCl3(PPh3)2], K[B(pz)4] and the respective diols. These compounds have been
characterized by elemental analyses, IR, 1H NMR spectroscopy and, in some cases, by mass
spectrometry. The redox properties of these and related complexes were studied by cyclic
voltammetry and by controlled potential electrolysis. 1 crystallizes from methanol in the
monoclinic space group P21/c with cell parameters a=10.539(2) Å, b=13.556(2) Å, c=12.153
(2) Å, =92.04(2)º, V=1735.2(5) Å3, Z=4. The possibility of preparing some diolate
99mTc
analogues was also evaluated and will be described.
Submitted to Inorganic Chemistry.
Current Work
Trans-Dioxo Rhenium Complexes
António Paulo, Ângela Domingos and Isabel Santos* Departamentos de Química e Radioisótopos, ITN, 2686 Sacavém Codex, Portugal
We have been studying the reactivity of the complex [ReO(-O){B(pz)4}]2 (1) towards neutral
substrates. In this type of reactions we observed the formation of trans-dioxo complexes. The
structural characterization of trans-[ReO2{2-B(pz)4}(pyridine)2] has been made and the the
affinity of the rhenium for neutral phosphorous donor ligands is beeing studied.
________________________________________________________ Inorganic and Organometallic Chemistry
15
Synthesis, Characterization and Reactivity Studies of Rhenium Complexes
with Cores [Re≡N]2+
and [Re=O2]+
K. Rajender Reddy and Isabel Santos Departamento de Química, ITN,2686 Sacavém Codex, Portugal
We have been investigating the reactivity of poly(pyrazolyl)borates of the type K[H2B(pz*)2]
(pz* = pyrazolyl, 3,5-dimetilpyrazolyl) and K[B(pz)4] with rhenium compounds with the
core [Re=O].1-3
It was found that the reactions depend on the number of hydrogens
coordinated to the boron, on the substituints in the pyrazole ring and on the nature of the
solvent. To evaluate whether these reactions depend on the electronic properties of the metal,
we extend our studies to rhenium compounds with the cores [Re≡N]2+
and cis-[Re=O2]+.
We studied reactions of K[B(pz)4] with cis-[ReO2(PPh3)2I] and cis-[ReO2(py)4]+ in
different solvents. The compounds obtained are under characterization, and we are trying to
get single crystals for X-ray crystallographic analysis.
1- António Paulo, Ângela Domingos, A.Pires de Matos, Isabel Santos, M. Fernanda Carvalho,
A. Pombeiro, Inorg. Chem. 1994, 33, 4729.
2- António Paulo, Ângela Domingos, Joaquim Marçalo, A.Pires de Matos and Isabel Santos,
Inorg. Chem. 1995, 34, 2113.
3- António Paulo, Ângela Domingos and Isabel Santos, Inorg. Chem. 1996, 35, 1798.
Inorganic and Organometallic Chemistry ________________________________________________________
16
Gas Phase Chemistry
Gas Phase Actinide Ion Chemistry: Activation of Alkanes and Alkenes by
Thorium Cations
Joaquim Marçalo, João Paulo Leal, and António Pires de Matos Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
Abstract
The activation of methane and of several small alkanes and alkenes by thorium cations, as
studied by FT-ICR/MS, is described. Thermalized Th+ ions dehydrogenate methane with a
rather low efficiency (k/kL = 0.02) to form ThCH2+. Th
+ ions react exothermically with the
studied alkanes (ethane, propane, n-butane, isobutane and cyclopropane) and alkenes (ethene,
propene and 1-butene): single and/or double dehydrogenation is observed for all the substrates
studied and, in the case of cyclopropane, propene and 1-butene, loss of hydrocarbons is also
observed. C–C coupling processes occur in secondary reactions of the products formed, in the
case of cyclopropane and the alkenes. This study indicates that Th+ ions are more reactive than
U+ ions. A tentative preview of 5f metal ion reactivity is also presented, based on comparisons
of the data reported herein with available data on lanthanide and uranium ions.
Int. J. Mass Spectrom. Ion Processes 157/158 (1996) 265.
________________________________________________________ Inorganic and Organometallic Chemistry
17
Studies on gas-phase chemistry of actinides - The role of f electrons in their
chemistry
António Pires de Matos and Joaquim Marçalo Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
Abstract
Recent work in our laboratories using FT-ICR mass spectrometry allowed us to compare the
gas phase reactivity of thorium ions with the data already described for uranium and the
lanthanide series ions. Based on these reactivity studies, some aspects of the role of f electrons
in the observed chemistry are addressed.
The reactivity studies of actinide ions have been practically limited to U+ and Th
+. Published
work for U+ is scarce and recent work allowed us to compare the reactivity of thorium ions
with the data already described for uranium and the lanthanide series ions. The efficiencies
and product distributions of the reactions of Th+ and U
+ ions with hydrocarbons clearly
demonstrate that Th+ is more reactive than U
+. U
+ exhibits a more rich chemistry than its
congener of the 4f series Nd+; with our work we were able to show that Th
+ is also more
reactive than its lanthanide congener Ce+.
For the actinide ions, the trends along the series are somewhat different from the lanthanide
ions. At the beginning of the series, from Ac+ to Np
+, there are several low-lying
configurations with at least two non f electrons available to the ions. In the case of Th+, the
ground state is already 6d27s. From the greater spatial extension of the 5f orbitals in the first
half of the actinide series compared to the 4f orbitals, we can as well expect a non-negligible
participation of the 5f electrons in the bonding, facilitating in this way the reactivity.
Based on these simple electronic structure arguments and also on the experimental results
already obtained for Th+ and U
+, we can anticipate that the actinide series ions Ac
+, Pa
+, Np
+
and Cm+ could bring about the activation of hydrocarbons, while for Pu
+, Am
+ and the
remainder of the actinide series ions from Bk+ to the end reduced reactivity should be
observed. Further experimental work on actinide ions is needed to get a better insight on a
possible 5f electron contribution to reactivity. Unfortunately protactinium and the
transuranium elements are extremely toxic and a dedicated instrument for gas phase chemistry
is needed. We have no knowledge of the existence of such facility. We think that the gas
phase chemistry of actinides is a subject that is worthwhile to explore and the results of the
research could complement the contribution given by condensed phase chemists to understand
the role of 5f electrons in actinide chemistry.
Extended Abstracts, CO1, Vol. I., Eds. F. David and J.C.Krupa, I.P.N., Orsay.
Communication to: 4th International Conference on Nuclear and Radiochemistry, St. Malo,
France, 8-13 September 1996.
Inorganic and Organometallic Chemistry ________________________________________________________
18
Activation of Phenol by Lanthanide Monocations in the Gas Phase
M. Pissavini, S. Géribaldi, J. Marçalo,* M. Decouzon, M. Azzaro
Groupe FT-ICR, Laboratoire de Chimie Physique Organique, Université de Nice-Sophia
Antipolis, Parc Valrose, 06108 Nice Cedex 2, France
*Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
Abstract
It is now well established that the knowledge of the phenomena of activation of organic
molecules by “naked” metal ions in the gas phase is indispensable to the understanding of
processes occurring in the condensed phase, in particular in what respects catalysis [1].
Although, and contrarily to the metals of the first two transition series, lanthanide ions have
been relatively neglected, these last years have witnessed a considerable development of
studies of the reactivity of these metals in the gas phase. Rare earth metals are being
increasingly used either in organic synthesis and in the fabrication of high-tech materials [2].
Recent work has shown that the gas phase reactivity of lanthanide, scandium and yttrium
cations toward arenes, and in particular benzene, is directly related to the ground-state electron
configuration of the cation: the metal ions presenting a d1s
1 ground state or a sufficiently weak
promotion energy to reach such a state, activate the C-H bonds of the arenes, while the others
only form adducts [3]. In our Laboratories we have shown that the reactivity of these cations
with oxygenated compounds is related to their oxophilicity, and that C-O and O-H bonds were
always activated according to different processes [4].
In this work, we have studied competitive activation reactions of C-H, C-O and O-H bonds of
phenol by three rare earth cations showing different ground-state electronic configurations
(gs) and different promotion energies (PE): Sc+ (gs: 4s
13d
1, PE = 0 eV), Y
+ (gs: 5s
2, PE = 0.15
eV) and Lu+
(gs: 6s2, PE = 1.63 eV).
Apparently, the general reactivity is similar for the three metal ions, and there is simultaneous
activation of the O-H bond and of the aromatic C-H bonds. However, the mechanisms that can
explain the activation reactions effectively depend on the metal ion.
Acknowledgement: We thank Bruker-France for support.
1- Martinho Simões, J.A.; Beauchamp, J.L. Chem. Rev. 1990, 90, 629; Eller, K.; Schwarz, H.
Chem. Rev. 1991, 91, 1121; Eller, K. Coord. Chem. Rev. 1993, 126, 93.
2- Takaki, K.; Fujiwara, Y. Appl. Organomet. Chem. 1990, 4, 297; Schumann, H.; Meese-
Marktscheffel, J.A.; Esser, L. Chem. Rev. 1995, 95, 865; Hubert-Pfalzgraf, L.G. New J. Chem.
1995, 19, 727.
3- Yin, W.W.; Marshall, A.G.; Marçalo, J.; Pires de Matos, A. J. Am. Chem. Soc. 1994, 116,
8666.
4- Breton, S.; PhD Thesis, Université de Nice-Sophia Antipolis, 1995; Azzaro, M.; Breton, S.;
Decouzon, M.; Geribaldi, S. Int. J. Mass Spectrom. Ion Processes 1993, 128, 1; Geribaldi, S.;
Breton, S.; Decouzon, M.; Azzaro, M. New J. Chem. 1995, 19, 887.
Communication to: 9ème
Journée de la Chimie / Provence-Alpes-Côte d’Azur, Nice, France,
March 22, 1996.
________________________________________________________ Inorganic and Organometallic Chemistry
19
Current Work
Reactivity of alkaline earth metal and oxide ions with
pentamethylcyclopentadiene in the gas phase
Joaquim Marçaloa, António Pires de Matos
a and William J. Evans
b
a Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
b Department of Chemistry, University of California, Irvine
The gas-phase reactivity of the alkaline earth metal (Ca+, Sr
+ and Ba
+) and oxide (CaO
+, SrO
+
and BaO+) ions with pentamethylcyclopentadiene was studied by FTICR/MS, for comparative
purposes with previous results obtained with lanthanide (Ln = La - Lu) and group 3 (Sc and
Y) metal and metal oxide ions. The alkaline earth metal ions were produced by laser
desorption/ionization of metal hydroxide pellets and the oxide ions by reaction of the metal
ions with N2O introduced through pulsed valves. The organic reagent was admitted to the
instrument through a leak valve, and pulsed-in argon was used for collisional cooling of the
reagent ions. The reactivity of the metal cations was similar to the one observed before for
Sm+, Eu
+, Tm
+ and Yb
+, namely the formation of the fulvenide ion (C5Me4CH2)M
+ as main
primary product and of the metallocene ion (C5Me5)2M+ as main secondary product. These
similarities in the reactivity can be explained by the similar behaviour of the s1 ground states
of the group 2 metal ions and the fns
1 ground states (with large promotion energies to f
n-1d
1s
1
states) of the referred lanthanide ions. In the case of the metal oxide ions MO+, the reactivity
with pentamethylcyclopentadiene, being mainly determined by the strength of the M+ – O
bonds, again showed similarities with EuO+ and YbO
+ (the lanthanide ions with the weakest
M+ – O bonds, similar to the ones present in the alkaline earth oxide ions), with formation of
MOH+ as main primary product and M(C5Me5)
+ as secondary product.
Gas phase reactivity of rare earth ions with alcohols, phenols and other
oxygenated molecules
José Manuel Carretasa, Joaquim Marçalo
a, António Pires de Matos
a, Serge Geribaldi
b, Marc
Pissavinib, Michele Decouzon
b, Maurice Azzaro
b
a Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
b Laboratoire de Chimie Physique Organique, Université de Nice-Sophia Antipolis
The gas phase reactions of the rare earth ions Sc+, Y
+ and Ln
+ (Ln = La - Lu) with isopropanol
and phenol were studied by FT-ICR/MS. The metallic ions were produced by laser ionisation
of the corresponding metals and were thermalised by collisions with argon; the reagents were
introduced through leak valves to pressures of (1-5) 10-7
Torr. All the ions except Yb+
reacted exothermically with isopropanol and phenol, with formation of MO+ and MOH
+ ions
as primary products, as well as of MOC6H4+ in the case of phenol, a product resulting from
the simultaneous activation of O-H and aromatic C-H bonds. The primary product ions
participate in subsequent reactions that lead to M(OR)x(HOR)y+ species, where x = 1-2 and y
= 0-3. The detailed study of the mechanisms of the primary reactions, of the reaction
sequences, of the corresponding kinetics and of the energies involved in the various steps,
showed important differences in the relative reactivity of the metallic ions.
Inorganic and Organometallic Chemistry ________________________________________________________
20
Gas phase synthesis of lanthanide and actinide - transition metal
intermetallic ions
Maria da Conceição Vieira, Joaquim Marçalo and António Pires de Matos Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
FT-ICR/MS was used to study the formation of intermetallic ions involving metals of the f
and d blocks. In particular, the series of ions LnFe+ (Ln = La - Lu), as well as ThFe
+ and UFe
+,
were synthesized by gas phase reaction of the metal ions, produced by laser ionization of pure
metal pieces, with the volatile carbonyl complex Fe(CO)5, followed by excitation and
collision with argon of the MFe(CO)2+ product ions formed. Advantage was taken from the
potentialities of the FT-ICR/MS technique for performing kinetic studies, which showed that
significant differences in reaction efficiencies existed along the lanthanide series.
Gas phase reactivity of lanthanide oxide cluster ions with small oxygenated
molecules
Joaquim Marçaloa, António Pires de Matos
a, Hans H. Cornehl
b, Christoph Heinemann
b and
Helmut Schwarzb
a Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
b Institut für Organische Chemie, Technische Universität Berlin
The reactivity of several lanthanide (Ln = La, Pr, Eu, Tb, Ho, Tm, Lu) oxide cluster cations
LnxOy+ with O2, N2O and H2O in the gas phase was studied by FT-ICR/MS. The cluster ions
were produced by direct laser desorption/ionization of surface oxidized metal pieces or of
metal oxide pellets, and the reagents were admitted to the mass spectrometer through a leak
valve; argon, introduced through pulsed valves, was used for collisional cooling of the reagent
ions. Oxydation reactions with O2 and N2O were observed for some cluster ions, while the
reactivity with water corresponded only to adduct formation. Several effects of the formal
metal valency in the cluster ions as well as of the cluster size on the reactivity and in the
kinetics could be observed.
Characterization and reactivity of transition metal oxide cluster anions in
the gas phase
Maria da Conceição Oliveira*, Maria Alzira Almoster Ferreira
* Joaquim Marçalo
+, Maria da
Conceição Vieira+
* Departamento de Química, FCUL
+ Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
Laser desorption/ionization was used in conjunction with FT-ICR/MS to produce and
characterize first-row transition metal oxide anions of the type MxOy-, with M = Mn, Fe, Co,
Ni and Cu. Metal oxide pellets were used as targets and argon, introduced through pulsed
valves, was used for collisional cooling of the reagent ions. Methanol was used to probe the
reactivity of these barely studied anionic species, uncovering important effects of the nature of
the metal and of cluster size in the reaction products formed and in the corresponding kinetic
efficiencies.
________________________________________________________ Inorganic and Organometallic Chemistry
21
Thermochemistry
Alkaline metal alkoxides
João Paulo Leala, P. Nunes
b, M. E. Minas da Piedade
b
aDepartamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
bInstituto Superior Técnico, Av. Rovisco Pais 1096 Lisboa Codex, Portugal
Abstract
In spite of the wide use of alkaline metal alkoxides (MOR, M = Li, Na, K, Rb, Cs) in synthetic
chemistry, thermochemical data for this family of compounds are scarce. The knowledge of
their enthalpies of formation, lattice energies, etc. is of key importance to predict new data and
to discuss the energetics of several reactions involving alkaline metal alkoxides. One example
is the study of the formation and reactivity of the now commonly used super-bases (mixed
aggregates of alkillithium compounds and alkaline metal alkoxides).
In this work, the enthalpies of formation in the crystalline state of a series of MOR (M= K, Cs;
R= Me, Et, n-Bu, t-Bu) compounds were measured by reaction-solution calorimetry. The
corresponding lattice energies, LUº, were also derived, and used to calculate thermochemical
radii, r-, for the alkoxi anions, from the Kapustinskii equation. The estimation of new data for
MOR compounds is discussed using the results obtained in the present work and those
previously published for LiOR and NaOR compounds.
Communication to: Reunião final do Network “Selective Processes and Catalysis Involving
Small Molecules”, ITQB, Oeiras, Portugal, April 1996.
Bond dissociation enthalpies in U-L. What’s the real value?
João Paulo Leala, Noémia Marques
a, J. Takats
b
a Instituto Tecnológico e Nuclear, Dep. Química, Est. Nac. nº 10, P-2686 Sacavém Codex, Portugal
b Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
Abstract
Uranium-ligand bond dissociation enthalpies had been widely studied in last years (see a
compilation of existing values in ref. 1). Despite of the considerable quantity of data already
known doubts about their absolute value persist. This is mainly due to the fact that
experimentally differences between two bonds are measured, and than one of them is assumed
(or estimated) and considered as an anchor being all the others related to that one.
On the present work the energetic of the U-O, U-I and U-Cl bonds in compounds of the type
UI2L{HB(dmpz)3} (L=O-tBu, I; dmpz=3,5-dimethylpirazole) and UCl3{HB(dmpz)3} have
been studied by means of oxidative reactions of UI2{HB(dmpz)3}.2thf with appropriate
reagents and using reaction solution calorimetry. The results allow a critical review of
literature data and suggest that a universal scale for uranium-ligand bond dissociation
enthalpies can be achieved.
1) J. P. Leal, J. A. Martinho Simões, J. Chem. Soc. Dalton Trans.1994, 2687.
Communication to: “XV Encontro Nacional da SPQ”, Porto, Portugal, May 1996.
Inorganic and Organometallic Chemistry ________________________________________________________
22
Potassium and Cesium alkoxides energetics
João Paulo Leal,a P. Nunes,
b M. E. Minas da Piedade
b
a Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
bInstituto Superior Técnico, Av. Rovisco Pais 1096 Lisboa Codex, Portugal
Abstract
Alkaline metal alkoxides (MOR, M = Li, Na, K, Rb, Cs) had been extensively used in
synthetic chemistry. Despite that thermochemical data for this family of compounds are
scarce. The knowledge of their energetics is crucial to predict new data and to discuss the
energetics of several reactions involving alkaline metal alkoxides [eg.: super-bases (mixed
aggregates of alkillithium compounds and alkaline metal alkoxides)].
In this work, the enthalpies of formation in the crystalline state of a series of MOR (M= K, Cs;
R= Me, Et, n-Bu, t-Bu) compounds were measured by reaction-solution calorimetry. The
corresponding lattice energies were also derived, and used to calculate thermochemical radii,
r-, for the alkoxi anions assuming a ionic lattice structure. This values allow the estimation of
new data for other MOR compounds not yet studied. Critical review of previously published
data for LiOR and NaOR compounds is also made1.
1
(a) J. P. Leal, A. Pires de Matos, J. A. Martinho Simões, J. Organometal. Chem. 1991, 403,
1; (b) J. P. Leal, J. A. Martinho Simões, J. Organometal. Chem. 1993, 460, 131.
Communication to: “XV Encontro Nacional da SPQ”, Porto, Portugal, May 1996.
________________________________________________________ Inorganic and Organometallic Chemistry
23
Surface Studies
Photon stimulated ion desorption of C2H4 adsorbed on graphite
J.M. Coquel1, T. Almeida Gasche
1,2, J. Wilkes
1,3, C. M. Friedrich
4, C.L.A. Lamont
3, M.A.
MacDonald5, R.E. Palmer
1, A.M.C. Moutinho
6
1 Nanoscale Physics Research Laboratory, School of Physiscs and Space Research, University of
Birmingham, Edgbaston, Birmingham B 15 2 TT, U K 2 Instituto Tecnológico e Nuclear, Dep. de Química, Estrada Nacional 10, 2685 Sacavém, Portugal
3 School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH, UK
4 Cavendish Laboratory, Univ. of Cambdrige, Cambdrige CB3 OHE, UK
5 CLRC, Daresbury Laboratory, Warrington WA4 4AD, UK
6 GIDS/ CeFITeC, Dep. de Física, FCT, Univ. Nova de Lisboa; 2825 Monte da Caparica, Portugal
Abstract Photon stimulated desorption from C2H4 on highly oriented pyrolitic graphite using VUV synchroton radiation in the energy range 13-40 eV was studied. In contrast with gas phase measurements, only H
+ ions are detected. This is due to the image potential barrier to
desorption from the surface and unequal distribution of kinetic energy amongst the molecular photofragments. The yield of desorbed H
+ ions shows a threshold at 20.5 eV and a resonance
at 24 eV. This behaviour is different from the gas phase and is attributed to selective quenching of excited molecular electronic states on the surface and to chemical reactions between specific molecular dissociated fragments and the substrate.
Communication to: ECOSS 16 (16
th European Conf. on Surface Science), Sept. 1996, Genova,
Italy and also in Física 96, (10 th
Nacional Conf. of Physics), Sept. 1996, Faro, Portugal.
Sample holder for using in surface studies (77-1300 K)
Carlos M.M. Leitão1, Teresa Almeida Gasche
2, Roger Bennet
3, O. M. N. Teodoro
1, G.
Bonfait2, A.M.C. Moutinho
1
1 Centro de Física e Investigação Tecnológica (CeFITeC), Dep. de Física, FCT, Univ. Nova de
Lisboa; 2825 Monte da Caparica, Portugal 2 ITN- Instituto Tecnológico e Nuclear, Dep. de Química, Est. Nac. 10, 2685 Sacavém, Portugal
3 Nanoscale Physics Research Laboratory, School of Physiscs and Space Research, University of
Birmingham, Edgbaston, Birmingham B 15 2 TT, U K
Abstract
The construction of this sample holder have as aim to conceive a system where quick cycles
of cooling and heating would be possible, in the temperature range 77-1300 K. The sample
holder is mounted in a horizontal position. A molybdenum support will be used to mount the
sample. The heating will be done by electronic bombardment. The cooling system is a "cold
finger" type.
The sample holder is going to be used in a surface system in each several surface techniques
are available, e.g. XPS- X-Ray Photoelectron Spectroscopy; AES- Auger Electron
Spectroscopy, ESD- Electron Stimulated Desorption, TDS- thermal Desorption Spectroscopy.
The sample holder will allow not only to work at low temperatures but also to do annealing to
crystals.
Communication to: FÍSICA 96 -10 th
Nacional Conference of Physics, Faro, Portugal,
13-17 September 1996.
Inorganic and Organometallic Chemistry ________________________________________________________
24
Carbon-dioxide adsorbed on graphite: a photon stimulated desorption study
J. M. Coquel1, L. Siller
1, R. E. Palmer
1, R. Carrapa
2, A.M.C. Moutinho
2, J. Wilkes
3, C.L.A.
Lamont3, T. Almeida Gasche
4
1 Nanoscale Physics Research Laboratory, School of Physics and Space Research, University of
Birmingham, Edgbaston, Birmingham B 15 2 TT, U K; 2 Centro de Física e Investigação Tecnológica (CeFITeC), Dep. de Física, FCT, Univ. Nova de
Lisboa; 2825 Monte da Caparica, Portugal; 3 School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH, UK;
4 ITN- Instituto Tecnológico e Nuclear, Dep. de Química, Est. Nac. 10, 2685 Sacavém, Portugal
Abstract
Carbon-dioxide physisorbed on graphite at 50 K was studied by photon stimulated desorption
(PSD) graphite using VUV synchrotron radiation in the energy range 13-40 eV 1. Previous
studies showed that the physisorption of CO2 on graphite was not possible for temperatures
below 104 K 2,4. The results obtained in our studies are in contradiction with these
conclusions.
The sample was heated to 900 K. The measurements were done for different dosages of CO2,
in the range of 0.18 to 3.0 L. H+, CO
+ and O2
+ were the ions detected. In the mass
spectrometer, neither negative ions or neutral species were observed. The yield of desorbed
O2+ ions shows a threshold at 15 eV and a resonance at 25 eV. The yield of desorbed CO
+ ions
shows a small resonance at 15 eV and a threshold at 25 eV.
[1] Bennet, R.A.; Sharp, R.J. ; Guest, R.J.; Barnard, J.C.; Palmer, R.E.; MacDonald, M.A.;
Chemical Physics Letters, 98 (1992) 241.
[2] Terlain, A., Laeher, Y., Surface Science, 125 (1983) 304.
[3] Morishige, K., Molecular Physiscs, 78 (1993) 1203.
Communication to: FÍSICA 96 -10 th
Nacional Conference of Physics, Faro, Portugal,
13-17 September 1996.
________________________________________________________ Inorganic and Organometallic Chemistry
25
Special Publications
Handling of air sensitive compounds
João Paulo Leal Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
Abstract
Is quite usual in chemistry to handle compounds that react with the water and the oxygen
presents in atmosphere. Several techniques had been developed to allow the work in
environments with a composition distinct from that of the earth atmosphere, the so called
“inert atmospheres”. A general overview of such techniques is presented with special
relevance to vacuum and inert gas systems, “Schlenk” type systems and gloveboxes.
Química, 1996, 59, 56.
The strenght of a chemical bond
João Paulo Leal Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
Abstract
The strength of a chemical bond is introduced, although in a qualitative way, very early in the
curricula of most chemistry courses. But sometimes it is not fully understanded. Some
considerations about this subject are made and the definition of bond dissociation enthalpy
(D) and bond enthalpy term (E) are introduced.
Submitted to J. Chem. Ed.