Cleavage of palladium metallacycles by acids: A probe for the study of the cyclometalation reaction

Full text of DOI:10.1002/(sici)1521-3773(19990115)38:1/2<147::aid-anie147>3.0.co;2-i

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Symp. 1993, 69, 1 ± 17; e) C. Hilger, M. Dräger, R. Stadler, Macro-
molecules 1992, 25, 2498 ± 2501; f) P. Bladon, A. C. Griffin, Macro-
molecules 1993, 26, 6604 ± 6610; g) L. M. Wilson, Macromolecules
1994, 27, 6683 ± 6686; h) C. B. St. Pourcain, A. C. Griffin, Macro-
molecules 1995, 28, 4116 ± 4121.
H. R. Allcock, F. W. Lampe, Contemporary Polymer Chemistry,
2nd ed., Prentice-Hall, New Jersey, 1990, pp. 508 ± 511) and not by
gelation in a poor solvent, which has also yielded fibers by self-
organization: a) C. F. van Nostrum, S. J. Picken, A.-J. Schouten,
R. J. M. Nolte, J. Am. Chem. Soc. 1995, 117, 9957 ± 9965; b) M.
de Loos, J. van Esch, I. Stokroos, R. M. Kellogg, B. L. Feringa, J. Am.
Chem. Soc. 1997, 119, 12675 ± 12676; c) N. Kimizuka, S. Fujikawa, H.
Kuwahara, T. Kunitake, A. Marsh, J.-M. Lehn, J. Chem. Soc. Chem.
Commun. 1995, 2103 ± 2104. Linear hydrogen-bonded supramolecular
aggregates have been formed into fibers from the molten state.[2f±h] For
a review on fiber theory, see H. L. Needles, Handbook of Textile
Fibers, Dyes, and Finishes, Garland STPM, New York, 1981, pp. 1 ± 27.
[16] N. Yamaguchi, L. M. Hamilton, H. W. Gibson, Angew. Chem. 1998,
110, 3463 ± 3466; Angew. Chem. Int. Ed. 1998, 37, No. 23.
[3] a) R. P. Sijbesma, F. H. Beijer, L. Brunsveld, B. J. B. Folmer,
J. H. K. K. Hirschberg, R. F. M. Lange, J. K. L. Lowe, E. W. Meijer,
Science 1997, 278, 1601 ± 1604; b) F. H. Beijer, H. Kooijman, A. L.
Spek, R. P. Sijbesma, E. W. Meijer, Angew. Chem. 1998, 110, 79 ± 82;
Angew. Chem. Int. Ed. 1998, 37, 75 ± 78.
[4] P. R. Ashton, P. J. Campbell, E. J. T. Chrystal, P. T. Glink, S. Menzer,
D. Philp, N. Spencer, J. F. Stoddart, P. A. Tasker, D. J. Williams,
Angew. Chem. 1995, 107, 1997 ± 2001; Angew. Chem. Int. Ed. Engl.
1995, 34, 1865 ± 1869.
[5] Based on the assumption that the complexation at the ammonium ion
moieties of 7 are independent of each other the association constant
for pseudorotaxane formation between the ammonium ion moieties of
7 and DB24C8 in [D6]acetone/[D3]chloroform (1/1) at 228C was
[17] J.-P. Leblanc, H. W. Gibson, Tetrahedron Lett. 1992, 33, 6295 ± 6298.
1
calculated as 3.5 Â 102 m by single point measurement (slow ex-
1
change) by using H NMR spectroscopy.
[6] The NOESY spectra of 1:1 stoichiometric solutions of 3a and 7 could
not be recorded at concentrations greater than 1.0m because of
overloading of the analogue to digital converter.
Cleavage of Palladium Metallacycles by Acids:
A Probe for the Study of the Cyclometalation
Reaction**
[7] The average molecular weight of 9 was calculated on the assumption
that the cyclic oligomers such as 2:2 and 3:3 complexes were absent. It
is noteworthy that linear polymerization is highly favored over
cyclization at high solution concentrations (for example, 1.0m). For
reviews on cyclization versus linear polymerization, see a) G. Odian,
Principles of Polymerization, 3rd ed., Wiley, New York, 1991, p. 73;
b) S. C. Hamilton, J. A. Semlyen, Polymer 1997, 38, 1685 ± 1691.
Therefore, the assumption of the absence of the oligomeric cyclic
complexes is valid in the more concentrated solutions. The percentage
of ammonium ion units l in 9 is equal to 100 minus the percentage of
ammonium ion units d in 8 (l ‡ d ˆ 100) The ratio of the percentage of
ammonium ion units l in 9 to the percentage of uncomplexed
ammonium ion units u is equal to 2n (n ˆ degree of aggregation).
Thus, this equation yields n ˆ (100% d/2u). From the n value and
the repeat unit mass (1980 Da) the number average molar mass Mn of
9 was calculated.
[8] A mixture of acetone/chloroform (1/1) was added to a flask containing
3a (1.1233g) and 7 (0.8568 g) until complete dissolution occurred. The
solution was slowly concentrated and vacuum dried to afford 9, which
was then diluted with acetone/chloroform (1/1) to 0.50 mL.
[9] Similar effects have been observed in a supramolecule assembled
from a heteroditopic precursor. See N. Yamaguchi, D. S. Nagvekar,
H. W. Gibson, Angew. Chem. 1998, 110, 2518 ± 2520; Angew. Chem.
Int. Ed. 1998, 37, 2361 ± 2364.
Â
Â
Juan Campora,* Jorge A. Lopez, Pilar Palma,* Pedro
Valerga, Edzard Spillner, and Ernesto Carmona*
The cyclometalation reaction[1] constitutes one of the first
known examples of C ± H bond activation, which is a major
achievement of organometallic chemistry.[2] Of particular
interest is the cyclometalation of a pendant aromatic ring, a
process that constitutes a good model for C ± H activation and
has in addition led to many useful synthetic applications.[3±6]
Despite the number of studies devoted to this transforma-
tion,[7] contemporary work continues to provide important
mechanistic information.[1a] A recent account by Canty and
van Koten has pointed out the formal relationship that may be
established between the cyclometalation reaction and the
protonation of M ± CH3 and M ± C6H5 bonds,[8] as well as the
possible intermediary role of arenonium ions in both proc-
esses.[8, 9] Here we provide experimental evidence in support
[10] The 1H NMR spectrum of a 1:1 stoichiometric solution of 1b and
dibenzylammonium hexafluorophosphate at 1.0 Â 10 2 m in [D6]ace-
tone/[D3]chloroform (1/1) did not show extra sets of signals from slow
exchange or changes in the chemical shifts from fast exchange. The m-
phenylene linkage prevents pseudorotaxane formation in solution.
[11] The solutions were frozen at 938C with an acetone ± ethanol/liquid
nitrogen bath and the solvents were removed under high vacuum to
give yellow ± orange solids.
Â
Â
[*] Dr. J. Campora, Dr. P. Palma, Prof. Dr. E. Carmona, Dr. J. A. Lopez,
E. Spillner
Â
Departamento de Química Inorganica
Instituto de Investigaciones Químicas
Universidad de SevillaÐ
Consejo Superior de Investigaciones Científicas
Â
C/ Americo Vespucio s/n., Isla de la Cartuja, E-41092 Sevilla (Spain)
[12] To eliminate sample history the freeze-dried samples were initially
Fax : (‡ 34)95-4460565
heated to 1008C and cooled to 308C at the rate of 108Cmin 1. They
E-mail: guzman@cica.es
1
were then heated at 108Cmin and the DSC thermograms were
Dr. Pedro Valerga
Departamento de Ciencia de Materiales,
recorded.
2
[13] The 1H NMR spectra of equimolar solutions of 3a and 7 at 1.0 Â 10
,
Â
Â
Ingeniería Metalurgica y Química Inorganica
0.10, and 0.50m in [D6]acetone/[D3]chloroform (1/1) were essentially
unchanged from 40 to 608C. Below this temperature the 1H NMR
spectra of the solutions were unable to be recorded because of partial
freezing of the solvents. Thus, Mn values of the freeze-dried ( 938C)
samples were estimated by simple integration of relevant signals of the
spectra recorded at 408C.
Â
Facultad de Ciencias, Universidad de Cadiz
Â
Apdo 40, E-11510 Puerto Real, Cadiz (Spain)
Â
Â
[**] Financial support from the Direccion General de Investigacion
Â
Científica y Tecnica (Project PB96-0824) and Junta de Andalucía is
gratefully acknowledged. J.A.L thanks the CONACYT and the
University of Guanajuato (Mexico) for a studentship. E.S. was an
Erasmus student in our laboratory from the University of Hamburg.
We thank Professors M. Brookhart and R. A. Andersen for helpful
discussions during their sabbatical stays in our laboratory as Iberdrola
Visiting Professors. Thanks are also given to Iberdrola for making
their stay possible.
[14] A similar dimeric cyclic species has recently been reported: P. R.
Ashton, I. Baxter, S. J. Cantrill, M. C. T. Fyfe, P. T. Glink, J. F.
Stoddart, A. J. P. White, D. J. Williams, Angew. Chem. 1998, 110,
1344 ± 1347; Angew. Chem. Int. Ed. 1998, 37, 1294 ± 1297.
[15] It must be noted that these fibers were formed in a manner analogous
to that used for covalently bonded macromolecules (dry spinning:
Angew. Chem. Int. Ed. 1999, 38, No. 1/2
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HN(SiMe3)2, NaX
PMe3
c
Me3P
Me3P
Me3P
Me3P
[H(OEt2)2]BAr4
Pd
Pd
NaN(SiMe3)2
BAr4
a
HX
Me3P
X
CH2CMe2Ph
2
Pd
4
PMe3
b
PMe3
1
X = Cl (1a), OAc (1b), OTf (1c)
HOTf
Me3P
TfO
Pd
[HPMe3]OTf
X = OTf (1c)
3
Scheme 1.
of this proposal by: 1) the synthesis of the palladacycle 2
(Scheme 1) by the base-induced metalation of the neophyl
derivatives trans-[Pd(CH2CMe2Ph)X(PMe3)2] (X ˆ Cl, 1a;
OAc, 1b; OTf, 1c) and 2) the study of the reverse reaction,
namely the protonation of 2 to produce compounds of types 1
and 3 or the aryl derivative [Pd(C6H4-o-CMe3)(PMe3)3]BAr4
(4, Arˆ 3,5-C6H3(CF3)2, Scheme 1). As discussed below one
of the intermediates in our system is a cationic species B
(Scheme 2), in which the highly electrophilic palladium center
is stabilized by an auxiliary p,h1 interaction with the ipso
carbon atom of the phenyl group.[10]
Thus, the relatively short Pd ± Cipso distance of about 2.38 Š is
indicative of a p-bonding interaction. Since the ortho carbon
atoms are farther apart (the shortest Pd ± Cortho distances being
2.61(2) and 2.53(1) Š in the two independent molecules,
respectively), the coordination of the ring can be described as
approximately p,h1. This is in accord with a similar observa-
Â
tion by Falvello, Fornies, and co-workers in the complex cis-
[Pd(C6F5)2(NMe2CH2C6H5)],[10a] although for other related
Pd ± arene complexes p,h2 coordination of the arene ligand
has been proposed.[10c,d]
In contrast with the behavior exhibited by the analogous
NiII and PtII neophyl derivatives, which convert readily into
the corresponding metallacycles,[7c, 11a] the bis(alkyl) complex
[Pd(CH2CMe2Ph)2(PMe3)2] fails to give a product of this
kind,[11b] even though related palladacyclic species can be
easily prepared.[12] Nonetheless, metallacycle 2 can be formed
by treatment of the neophyl complexes 1 with a strong base
such as NaN(SiMe3)2 (Scheme 1, reaction a). This method
parallels the previously reported synthesis of other related
palladium metallacycles.[12] The cyclometalation reaction can
be readily reversed by treating 2 with stoichiometric amounts
of HX (X ˆ Cl, OAc, HTfO) to give 1. This regioselectivity is
the same as that found in the analogous Ni metallacycle.[11a]
The triflate complex 1c is very labile and, whereas it has been
fully characterized in solution, it could not be isolated in pure,
crystalline form. If two equivalents of triflic acid (HOTf) are
used, high yields of the crystalline complex 3 are obtained
along with [HPMe3]OTf (Scheme 1, reaction b). This latter
transformation can also be reversed; the addition of PMe3 to
solutions of 3 regenerates the neophyl compound 1c.
Figure 1. ORTEP representation of one of the two crystallographically
independent molecules of 3.
Table 1. Selected bond lengths [Š] and angles [8] for 3.
Molecule A
Molecule B
The structure proposed for 3 on spectroscopic grounds has
been confirmed by X-ray studies. Figure 1 shows an ORTEP
view of one of the two crystallographically independent
molecules of 3 that are contained in the unit cell.[13] The most
interesting aspect of this highly distorted square-planar
structure is undoubtedly the coordination mode of the
neophyl ligand. The Pd ± CH2 bond has a normal length (ca.
2.02 Š) but the neophyl backbone bends in such a way that
the phenyl ring comes close to the Pd atom (Figure 1, Table 1).
Pd1 ± P1
Pd1 ± O1
Pd1 ± C1
Pd1 ± C5
2.233(4)
Pd2 ± P2
Pd2 ± O4
Pd2 ± C15
Pd2 ± C19
2.232(4)
2.21(1)
2.02(2)
2.38(1)
2.16(1)
2.01(2)
2.39(1)
P1-Pd1-O1
P1-Pd1-C1
P1-Pd1-C5
O1-Pd1-C1
O1-Pd1-C5
C1-Pd1-C5
99.7(3)
90.2(5)
153.8(4)
170.0(5)
104.6(4)
65.4(6)
P2-Pd2-O4
99.9(3)
90.9(5)
154.0(4)
169.2(6)
104.6(5)
64.9(6)
P2-Pd2-C15
P2-Pd2-C19
O4-Pd2-C15
O4-Pd2-C19
C15-Pd2-C19
148
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The formation of 3 is particularly noteworthy because p ±
arene complexes have been proposed to be intermediates in
the activation of aromatic C ± H bonds by Pd and other
metals.[14] The recent observation by Cheng and co-workers of
the cyclometalation of a neutral palladium p ± arene complex
by treatment with sodium hydroxide in the presence of
PPh3,[1m] seems to indicate the intermediacy of this type of
complex in the cyclometalation reaction. Unfortunately,
direct cyclometalation of 3 by bases under the experimental
conditions used by Cheng et al. has proved meaningless,
because the p ± arene interaction is readily cleaved by added
PMe3.[15] Nevertheless, 3 is a robust compound that can be
dissolved in CD3OD without decomposition.[16] No H ± D
exchange, in the ortho positions of the phenyl ring could be
detected after three days at room temperature (or 6 h at
608C) in this solvent, which suggests these protons are not
labile.
basis of these data we propose that the protonation occurs
also at the aryl carbon atom to give initially compound B (that
is, the kinetic product, see below) and that B subsequently
isomerizes by a solvent-assisted rearrangement of the neophyl
ligand (Scheme 2). We are not aware of a similar role of the
solvent in related isomerizations of M ± CH2CMe2C6H5 moie-
ties.[11e, 18±20]
We have been unable to obtain experimental evidence for
the formation of intermediate A (Scheme 2), hence its
participation in the proposed reaction pathway remains
speculative. However it appears reasonable on chemical
grounds and moreover its formulation is in agreement with
recent results on organopalladium(iv) and hydridoplatinu-
m(iv) chemistry.[8, 9, 21] As a consequence of the higher kinetic
barrier to the reorientation of the strongly directional sp3
orbital of the alkyl PdCH2 carbon atom relative to the sp2 aryl
carbon atom, to form the C ± H bond,[22] hydrogen transfer to
the aryl carbon atom is expected to be kinetically more
favorable. This would yield the cationic species B, perhaps
with participation of an arenonium ion or an agostic
intermediate (not ilustrated in Scheme 2).[9, 21] Coordination
of X would convert B into compounds 1 but if X is a
noncoordinating anion, for example BAr4 , B could reverse to
the purported PdIV hydride A in a process that seems to
require the presence of Et2O or THF as a weakly coordinating
solvent. Eventually, complex A could undergo the kinetically
less-favorable 1,2 hydrogen shift to the sp3-hybridised alkyl
site, followed by phosphane substitution to give compound 4.
There are still some aspects of these transformations that are
only partially understood and the overall process of Scheme 2
may be mechanistically more complex than depicted. How-
ever in agreement with the above hypothesis, treatment of 2
with [HPMe3]BAr4 in CH2Cl2 gives [Pd(CH2CMe2Ph)-
(PMe3)3]BAr4, which converts cleanly into 4 after heating at
608C for three hours. A similar isomerization of the neophyl
ligand occurs when 1b is heated at 808C in CD3OD for three
At variance with the protonations described above, the
reaction of the metallacycle 2 with one equivalent of
[17]
[H(OEt2)2]BAr4
(Arˆ 3,5-C6H3(CF3)2) in Et2O ( 408C,
then warmed to room temperature) leads to the aryl
derivative 4, in 42% yield (Scheme 1, reaction c), together
with some as yet unidentified products. The nature of 4 would
appear to suggest a different regioselectivity for the proto-
nation reaction, namely proton attack at the sp3 alkyl carbon
atom. However, carrying out the reaction in CH2Cl2 at 408C
or, alternatively, treating the [Pd(CH2CMe2Ph)X(PMe3)2]
complexes 1a or 1c with NaBAr4, also in CH2Cl2 at low
temperature, allows the isolation of a colorless complex B
(Scheme 2, X ˆ BAr4). This complex has spectroscopic prop-
erties related to those of 3, which is indicative of a p,h1 ± arene
coordination (31P{1H} NMR: AX spin system, dA ˆ 1.8, dX ˆ
2
2
31.1, JAX ˆ 37 Hz; 13C{1H} NMR: d ˆ 33.5 (dd, JCP ˆ 65,
2
8 Hz, Pd-CH2), 123.5 (dd, JCP ˆ 12, 4 Hz, Cipso)). Dissolution
of B in Et2O or THF results in formation of the above-
mentioned mixture of 4 plus unidentified products. On the
H
Me3P
Me3P
Me3P
Me3P
X– coord.
HX, S
base
–S
+S
Pd
Pd
Pd
X
X
1
Me3P
X– dissoc.
Me3P
S
2
A
B
X = BAr4
PMe3
Me3P
Me3P
Pd
BAr4
4
Scheme 2.
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spin system, dA
ˆ
27.6, dX ˆ 17.2, JAX ˆ 44 Hz; 13C{1H} NMR (CD2Cl2,
hours, with the aryl compound trans-[Pd(C6H4-o-
CMe3)(OAc)(PMe3)2] (5) being formed in good yield. Only
10% isomerization is observed after three hours in C6D6
under the same reaction conditions.
208C): d ˆ 33.0 (s, CMe3), 36.9 (s, CMe3), 151.7 (d, 2JCP ˆ 107 Hz, Cq arom.).
Received: May 5,
Revised version: July 31, 1998 [Z11819IE]
German version: Angew. Chem. 1999, 111, 199 ± 203
Keywords: C-H activation ´ metallacycles ´ palladium ´ pi
interactions ´ protonations
Me3P
AcO
CH2CMe2Ph
PMe3
Me3P
AcO
80 °C
Pd
Pd
CD3OD
[1] a) A. D. Ryabov, Chem. Rev. 1990, 90, 403; b) G. R. Newkome, W. E.
Puckett, V. K. Gupta, Chem. Rev. 1986, 86, 451; c) G. E. Kiefer, Chem.
Rev. 1986, 86, 151; d) I. Omae, Chem. Rev. 1989, 93, 155; for recent
examples of cyclometalation reactions, see e) T. Hascall, V. Murphy,
G. Parkin, Organometallics 1996, 15, 3910; f) N. S. Radu, S. L.
Buchwald, S. Berk, C. J. Burns, Organometallics 1996, 15, 3913;
g) R. H. Zambrano, P. R. Sharp, C. L. Barnes, Organometallics 1995,
PMe3
5
1b
In closing, some comments on the chemical significance of
the cationic species B seem appropriate. As noted above, B is
involved as an intermediate in both the cyclometalation and
the isomerization of the neophyl ligand although the addi-
tional participation in the key C ± H bond activation reaction
of an arenonium ion or an agostic intermediate appears likely.
The lability of B contrasts with the relative inertness of the
neutral triflate complex 3. This observation suggests that a
positive charge at the Pd center may be needed to achieve the
metalation of the pendant aromatic ring. In other words,
anion dissociation rather than phosphane dissociation could
be required for the activation of the C ± H bond in compounds
of type 1. This proposal is in agreement with previous findings
on somewhat related reactions.[23] Moreover, it is in accord
with our failure to cyclometalate the bis(alkyl) complex
[Pd(CH2CMe2Ph)2(PMe3)2].[11e]
Â
14, 3607; h) R. Bosque, C. Lopez, J. Sales, P. Tramuns, X. Solans, J.
Chem. Soc. Dalton Trans. 1995, 2445; i) J. C. Jeffrey, E. Schatz, E. H.
Tilley, M. D. Ward, J. Chem. Soc. Dalton Trans. 1995, 825; j) P. W.
Jennings, L. L. Johnson, Chem. Rev. 1994, 94, 2241; k) M. Catellani,
G. P. Chiusoli, Gazz. Chim. Ital. 1993, 123, 1; l) M. Catellani, M. C.
Fagnola, Angew. Chem. 1994, 106, 2559; Angew. Chem. Int. Ed. Engl.
1994, 33, 2421; m) C. Liu, C. S. Li, C. H. Cheng, Organometallics 1994,
13, 18.
[2] a) A. E. Shilov, G. B. Shulꢁpin, Chem. Rev. 1997, 97, 2879; b) B. A.
Arndtsen, R. G. Bergman, T. A. Morley, T. H. Peterson, Acc. Chem.
Res. 1995, 28, 154.
[3] a) A. J. Canty, Acc. Chem. Res. 1992, 25, 83; b) A. J. Canty in
Comprehensive Organometallic Chemistry II. Vol. 9 (Eds: E. W. Abel,
F. G. A. Stone, G. Wilkinson), Pergamon, Oxford, 1995, p. 225.
[4] a) R. F. Heck, Palladium Reagents in Organic Chemistry; Academic
Press, London, 1985; b) J. Vicente, J. A. Abad, J. Gil-Rubio, Organo-
metallics 1996, 15, 350; c) U. Aulwurm, J. V. Melchinger, H. Kisch,
Organometallics 1995, 14, 3385; d) J. Spencer, M. Pfeffer, N. Krystakis,
J. Fischer, Organometallics 1995, 14, 2214, and references therein.
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Chappell, D. J. Cole-Hamilton, Polyhedron 1982, 1, 739; c) G. Ingrosso
in Reactions of Coordinated Ligands (Ed.: P. S. Braterman), Plenum,
New York, 1986, p. 639; d) I. Ojima, M. Tzamarioudaki, Z. Li, R. J.
Donovan, Chem. Rev. 1996, 96, 635.
[6] Applied Homogeneous Catalysis with Organometallic Compounds
(Eds: B. Cornelis, W. A. Herrmann), VCH, Weinheim, 1996.
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Organometallics 1996, 15, 4228.
Experimental Section
2 and 3: The metallacyclic precursor 2 was prepared by treating a solution
of complex 1a (0.21 g, 0.5 mmol) in THF (30 mL) at
508C with
NaN(SiMe3)2 (0.85 mL, 0.6m solution in toluene, 0.5 mmol) and was
isolated as white crystals (ca. 40% yield) from its solutions in diethyl ether
or diethyl ether/petroleum ether mixtures. Elemental analysis calcd for
C16H30P2Pd: C 49.18, H 7.68; found: C 49.22, H 7.56; 1H NMR (CD2Cl2,
208C): d ˆ 2.20 (dd, 2H, JHP ˆ 8.8, 5.7 Hz, CH2); 31P{1H} NMR (CD2Cl2,
3
208C) AX spin system, dA
ˆ
22.9, dX ˆ 27.9, JAX ˆ 23 Hz; 13C{1H} NMR
2
2
(CD2Cl2, 208C): d ˆ 52.5 (dd, JCP ˆ 95, 9 Hz, CH2), 169.2 (dd, JCP ˆ 123,
14 Hz, Cq arom.). A solution of HOTf in Et2O (3.8 mL, 0.53m, 2 mmol) was
added dropwise to a cold solution ( 808C) of a pure, crystalline sample of
this compound (0.39 g, 1 mmol) in Et2O (40 mL). The mixture was stirred
for 2.5 h at room temperature, the solvent evaporated under vacuum, and
[8] A. J. Canty, G. van Koten, Acc. Chem. Res. 1995, 28, 406.
[9] a) D. M. Grove, G. van Koten, J. N. Louwen, J. G. Noltes, A. L. Spek,
H. J. C. Ubbels, J. Am. Chem. Soc. 1982, 104, 6609; b) J. Terhijden, G.
van Koten, I. C. Vinke, A. L. Spek, J. Am. Chem. Soc. 1985, 107, 2891.
‡
the residue extracted with Et2O. The white precipitate of HPMe3 TfO was
separated by filtration, and the solution concentrated and cooled overnight
at 208C. The product was isolated as colorless crystals (290 mg, 75%).
Elemental analysis calcd for C14H22F3O3PSPd: C 36.18, H 4.77; found: C
Â
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[10] a) L. R. Falvello, J. Fornies, R. Navarro, V. Sicilia, M. Tomas, J. Chem.
Â
Â
Â
Soc. Dalton Trans. 1994, 3143; b) J. Fornies, B. Menjon, N. Gomez, M.
36.34, H 4.60; 1H NMR (CD2Cl2, 208C): d ˆ 1.46 (d, 2H, JHP ˆ 5.6 Hz,
3
Â
Tomas, Organometallics 1992, 11, 1187; c) C. S. Li, C. H. Cheng, S. L.
CH2); 31P{1H} NMR (CD2Cl2, 208C): d ˆ 2.85 s; 13C{1H} NMR (CD2Cl2,
Wang, J. Chem. Soc. Chem. Commun. 1991, 710; d) E. Wehman, G.
van Koten, T. B. H. Jastrzbeski, H. Ossor, M. Pfeffer, J. Chem. Soc.
Dalton Trans. 1988, 2975.
2
2
208C): d ˆ 24.3 (d, JCP ˆ 4 Hz, CH2), 121.8 (d, JCP ˆ 13 Hz, Cq arom.),
123.2 (s, 2CH arom.), 131.2 (s, 1CH arom.), 132.3 (s, 2CH arom.).
Â
4: A solution of compound 2 (0.1 g, ca. 0.25 mmol) in Et2O (40 mL) was
cooled at 408C, and treated with [H(OEt2)2]BAr4 (0.25 g, 0.25 mmol)
dissolved in Et2O (10 mL). The mixture was stirred for 1 h at room
temperature. The solvent was then removed in vacuo, and the residue
extracted with Et2O (30 mL). The volume was reduced to approximately
one half and petroleum ether added until the solution became slightly
cloudy. After cooling the mixture at 208C overnight, the product was
collected as colorless crystals, which were filtered, washed with petroleum
ether, and dried (140 mg, 42%). Elemental analysis calcd for
C51H52BF24P3Pd: C 46.02, H 3.94; found: C 46.37, H 3.88; 1H NMR
(CD2Cl2, 208C): d ˆ 1.44 (s, 9H, CMe3); 31P{1H} NMR (CD2Cl2, 208C) AX2
[11] a) E. Carmona, E. Gutierrez-Puebla, J. M. Marín, A. Monge, M.
Paneque, M. L. Poveda, C. Ruiz, J. Am. Chem. Soc. 1989, 111, 2883;
b) M. C. Nicasio, PhD thesis, Universidad de Sevilla, 1993.
[12] a) D. J. Cardenas, C. Mateo, A. M. Echevarren, Angew. Chem. 1994,
Â
106, 2529; Angew. Chem. Int. Ed. Engl. 1994, 33, 2445; b) C. Mateo,
D. J. Cardenas, C. Fernandez-Rivas, A. M. Echevarren, Chem. Eur. J.
Â
Â
1996, 2, 1596.
[13] Crystallographic data for 3:
a
yellow irregular crystal of
PdC14H22F3O3PS having approximate dimensions of 0.26 Â 0.15 Â
0.34 mm was mounted in a glass capillary under argon. All measure-
ments were performed on a Rigaku AFC6S diffractometer with
150
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COMMUNICATIONS
graphite monochromated MoKa radiation; Mr ˆ 464.76; triclinic, space
group P1 (no. 2), a ˆ 11.428(3), b ˆ 17.336(4), c ˆ 10.439(5) Š, a ˆ
Spin-Orbit Coupling versus the VSEPR
Method: On the Possibility of a Nonplanar
Structure for the Super-Heavy Noble Gas
Tetrafluoride (118)F4**
98.11(3), b ˆ 104.13(3), g ˆ 106.02(2)8, Vˆ 1879(2) Š3, 1calcd
ˆ
3
1.643 gcm
,
F(000) ˆ 936, Tˆ 293 K, (l ˆ 0.71069 Š), m(MoKa) ˆ
12.0 cm 1, scan ˆ w/2V, scan rate ˆ 8.08min (in w; 3 scans), scan width
(1.10 ‡ 0.30tanV)8, 2Vmax ˆ 50.18. Of the 5734 reflections measured
through a detector aperture 6.0 mm horizontal and 6.0 mm vertical,
5455 were unique (Rint ˆ 0.120). A decay correction was applied
following the intensities of three standard reflections measured after
every 100 reflections ( 6.80% during data collection). The absorp-
tion correction was neglegible and it was not applied. The data were
corrected for Lorentz and polarization effects. A structural solution
was found by direct methods (Patterson method, MITHRIL pro-
gram).[24] The least-squares refinement was performed for a total of
415 parameters with 2976 reflections (I > 3s(I)); minimization func-
Clinton S. Nash and Bruce E. Bursten*
The discovery of the super-heavy elements 110, 111, and 112
by Armbruster and co-workers during the 1990s[1] has
stimulated new interest in the properties and chemistry of
newly discovered elements.[2, 3] Elements 110, 111, and 112
complete the 6d block of the periodic table. The next elements
likely to be discovered are the representative 7p block
elements, those with atomic numbers 113 ± 118. The last of
these, element 118, is predicted to be a noble gas with a
closed-shell 7s26d107p6 electron configuration. As such, its
properties are expected to resemble those of the heavy noble
gases Xe and Rn, which are known to form compounds with
electronegative elements such as F.[4]
tion: Sw(jFo j j Fc j )2, with least-squares weights: 4Fo2/s2(Fo2),
p
factorˆ 0.03. The non-hydrogen atoms were anisotropically refined
and the hydrogen atoms were included at idealized positions and they
were not refined. RF ˆ 0.060, Rw ˆ 0.070, GOF ˆ 2.03, maximum shift/
error: 7.26. Accurate cell dimensions were obtained by least-squares
refinement of 25 reflections ranged 13.40 < 2V< 16.448. All calcu-
lations were performed on a VAX 3520 station at the Servicio Central
Â
de Ciencias y Tecnologia de la Universidad de Cadiz. Crystallographic
data (excluding structure factors) for the structure reported in this
paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-101361 . Copies of
the data can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB21EZ, UK (fax: (‡44)1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk).
The correct prediction of the structures of noble gas
compounds was one of the great successes of the valence-
shell electron-pair repulsion (VSEPR) model of Gillespie and
Nyholm, in both its original[5] and more-refined current[6]
formulations. This simple and pedagogically useful model
correctly predicted that NgF2 and NgF4 (Ng ˆ noble gas)
should adopt linear and square-planar molecular geometries,
respectively, based on trigonal-bipyramidal and octahedral
electron-pair geometries. Herein, we will focus on the noble
gas tetrafluorides XeF4, which is known,[7] RnF4, which has
not been characterized definitively,[8] and (118)F4. Our
interest in the bonding in compounds of the super-heavy
elements stems in part from the huge spin-orbit effects
exhibited by these elements by virtue of their large atomic
numbers.[9] These relativistic effects can have a remarkable
influence on the properties of atoms and compounds of these
elements. For example, Kaldor et al. have used relativistic
coupled cluster calculations to predict that relativistic stabi-
lization of the 8s orbital causes the element 118 to have a small
electron affinity, making it unique among the noble gases.[10]
We have recently predicted that spin-orbit effects will cause
the super-heavy hydrogen halide H(117) to have an unusually
long and strong bond.[11] Here we will report that the influence
of spin-orbit effects on the bonding in (118)F4 is so great as to
favor a non-VSEPR tetrahedral structure for this molecule.
[14] a) W. D. Jones, F. J. Feher, Acc. Chem. Res. 1989, 22, 91; b) M. R. Chin,
L. Dong, S. B. Duckett, M. G. Partridge, W. D. Jones, R. N. Perutz, J.
Am. Chem. Soc. 1993, 115, 7685.
[15] Compound 3 reacts rapidly with one equivalent of PMe3 to give 1b.
[16] The 13C{1H} NMR spectra of 3 in CD2Cl2 and CD3OD are very similar.
Since the signal assigned to the Pd-bonded aromatic quaternary
carbon atom appears in both cases as a doublet (2JCP ˆ 7 Hz) the p,h1
arene interaction seems to be maintained in methanol.
[17] a) L. K. Johnson, S. Mecking, M. Brookhart, J. Am. Chem. Soc. 1996,
118, 267; b) C. M. Killian, L. K. Johnson, M. Brookhart, Organo-
metallics 1997, 16, 2005.
[18] S. I. Black, G. B. Young, Polyhedron 1984, 8, 585.
[19] a) R. F. Heck, J. Organomet. Chem. 1982, 37, 389; b) B. A. Markies, P.
Wijkens, H. Kooijman, A. Spek, J. Boersma, G. van Koten, J. Chem.
Soc. Chem. Commun. 1992, 1420.
[20] a) D. C. Griffiths, L. G. Joy, A. C. Skapski, D. J. Wilkes, G. B. Young,
Organometallics 1986, 5, 1744; b) M. E. Cucciolto, A. de Rienzi, F.
Ruffo, D. Tesauro, J. Chem. Soc. Dalton Trans. 1998, 1675.
[21] a) A. F. H. J. van der Ploeg, G. van Koten, K. Vrieze, A. L. Spek,
Inorg. Chem. 1982, 21, 2014; b) J. E. Kickham, S. J. Loeb, Organo-
metallics 1995, 14, 3584.
[22] M. J. Calhorda, J. M. Brown, N. A. Cooley, Organometallics 1991, 10,
1431; b) P. M. Maitlis, H. C. Long, R. Quyoum, M. L. Turner, Z.-Q.
Wang, Chem. Commun. 1996, 1.
[23] F. Kawataka, Y. Yoshito, I. Shimizu, A. Yamamoto, Organometallics
1994, 13, 3517.
[24] G. J. Gilmore, J. Appl. Crystallogr. 1984, 17, 42 ± 46.
[*] Prof. B. E. Bursten
Department of Chemistry, The Ohio State University
Columbus, OH 43210 (USA)
Fax: (‡1)614-688-3306
E-mail: bursten.1@osu.edu
Dr. C. S. Nash
The Glenn T. Seaborg Institute for Transactinium Science
Lawrence Livermore National Laboratory
Livermore, CA 94550 (USA)
Fax: (‡1)925-422-3610
E-mail: nash6@llnl.gov
[**] This work was supported by the Division of Chemical Sciences, US
Department of Energy (Grant DE-FG02-86ER13529), by the Ohio
Supercomputer Center, and by the National Energy Research Super-
computer Center. We are grateful to W. C. Ermler, D. C. Hoffman,
R. M. Pitzer, and P. Schwerdtfeger for helpful comments.
Angew. Chem. Int. Ed. 1999, 38, No. 1/2
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1433-7851/99/3801-0151 $ 17.50+.50/0
151