Chemical, electrochemical, and structural aspects of the ruthenium complexes Ru(η-arene)Cl2(P) (where arene = benzene, [2.2]paracyclophane and P = triphenylphosphine, rac-[2.2]paracyclophanylphosphine)

Article abstract of DOI:10.1021/om010763a

Reaction of diphenyl[2.2]paracyclophanylphosphine, rac-PPh₂(C₁₆H₁₅) (1), with [Ru(η-arene)Cl₂]₂ (where arene = C₆H₆, [2.2]paracyclophane (C₁₆H₁₆)) in a 2:1 ratio affords the half-sandwich complexes Ru(η-arene)Cl₂{PPh₂(C₁₆H₁₅)} (arene = C₆H₆ (2), C₁₆H₁₆ (3)) in high yield. In solution, the structures of 2 and 3 have been probed and assigned using 2D NMR speetroscopy and the structure of the [2.2]paracyclophane derivative, 3, has been established in the solid-state by single-crystal X-ray diffraction. Cyclic voltammetry and steady-state voltammetry of 2 in 0.25 M [ⁿBu₄N] [PF₆]/CH₂Cl₂ shows that the complex undergoes a chemically reversible, one-electron oxidation and an irreversible, two-electron reduction. The voltammetry of the related complex [Ru(η⁶-C₆H₆)Cl₂(PPh₃) ] (4), recorded under analogous conditions, is similar both in terms of the processes displayed and the potentials at which they occur.

Full text of DOI:10.1021/om010763a

924
Organometallics 2002, 21, 924-928
Ch em ica l, Electr och em ica l, a n d Str u ctu r a l Asp ects of th e
Ru th en iu m Com p lexes Ru (η-a r en e)Cl2(P ) (Wh er e
Ar en e ) Ben zen e, [2.2]P a r a cyclop h a n e a n d
P ) Tr ip h en ylp h osp h in e,
r a c-[2.2]P a r a cyclop h a n ylp h osp h in e)
Rajiv Bhalla,† Clive J . Boxwell,† Simon B. Duckett,† Paul J . Dyson,*,†
David G. Humphrey,‡ J onathan W. Steed,§ and Priya Suman|
Department of Chemistry, The University of York, Heslington, York YO10 5DD, U.K.,
Department of Chemistry, Monash University, Clayton, Victoria 3168, Australia,
Department of Chemistry, King’s College London, Strand, London WC2R 2LS, U.K., and
Department of Chemistry, Imperial College of Science, Technology and Medicine,
South Kensington, London SW7 2AY, U.K.
Received August 20, 2001
Reaction of diphenyl[2.2]paracyclophanylphosphine, rac-PPh2(C16H15) (1), with [Ru(η-
arene)Cl2]2 (where arene ) C6H6, [2.2]paracyclophane (C16H16)) in a 2:1 ratio affords the
half-sandwich complexes Ru(η-arene)Cl2{PPh2(C16H15)} (arene ) C6H6 (2), C16H16 (3)) in high
yield. In solution, the structures of 2 and 3 have been probed and assigned using 2D NMR
spectroscopy and the structure of the [2.2]paracyclophane derivative, 3, has been established
in the solid-state by single-crystal X-ray diffraction. Cyclic voltammetry and steady-state
voltammetry of 2 in 0.25 M [nBu4N][PF6]/CH2Cl2 shows that the complex undergoes a
chemically reversible, one-electron oxidation and an irreversible, two-electron reduction. The
voltammetry of the related complex [Ru(η6-C6H6)Cl2(PPh3)] (4), recorded under analogous
conditions, is similar both in terms of the processes displayed and the potentials at which
they occur.
In tr od u ction
using [2.2]PhanePhos have been ascribed to steric
effects emanating from the C2-symmetric chiral envi-
ronment imposed by the [2.2]paracyclophane backbone.
In our studies we selected [2.2]paracyclophane as a
substituent group in mono-phosphines, anticipating that
it would provide electronic effects that are conducive to
catalysis. We noticed that when [2.2]cyclophanes are η6-
coordinated to metal centers, the redox potentials of
both oxidation3 and reduction4 become more facile as
the extent of inter-ring overlap, and hence π-π overlap,
increases. In [2.2]orthocyclophane there is no π-π
overlap, in [2.2]metacyclophane there is partial π-π
overlap, and in [2.2]paracyclophane there is consider-
able π-π overlap. Since many catalytic cycles involve
both oxidative-addition and reductive-elimination steps,
we postulated that the presence of [2.2]paracyclophane
may make these steps more facile and therefore enhance
catalytic activity. With this in mind we prepared several
paracyclophanylphosphines, including rac-diphenyl[2.2]-
paracyclophanylphosphine, rac-PPh2(C16H15). Monosub-
stituted [2.2]paracyclophane derivatives are inherently
chiral, but since chiral mono-phosphines offer no ad-
vantages over bis-phosphines, resolution of rac-PPh2-
(C16H15) into optically pure isomers was not attempted.
Initial studies were concerned with the structural
characterization of some palladium5 and platinum6
derivatives of the new phosphine. In this paper we
Phosphines are important ligands in transition-metal-
catalyzed reactions and the electronic and steric effects
of the phosphine have a pronounced influence on the
organic transformation that take place at the transition-
metal center.1 The search for new phosphine ligands
that will enhance the rate, yield, or specificity of organic
transformations remains an active field of research. A
large number of new phosphine ligands are reported
each year, but very few prove to be superior to those
currently available for use in catalysis. A relatively
recent example of a new bis-phosphine ligand that has
showed catalytic activity superior to that of other
available phosphines is 4,12-bis(diphenylphosphino)[2.2]-
paracyclophane, (PPh2)2(C16H14) or [2.2]PhanePhos,2 in
which the high activity and enantioselectivities obtained
* To whom correspondence should be addressed. E-mail: pjd14@
york.ac.uk.
† The University of York.
‡ Monash University.
§ King’s College London.
| Imperial College of Science.
(1) For example see: (a) Tolman, C. A. Chem. Rev. 1977, 77, 313.
(b) van Leeuwen, P. W. N. M.; Kamer, P. C. J .; Reek, J . N. H.; Dierkes,
P. Chem. Rev. 2000, 100, 2741.
(2) (a) Pye, P. J .; Rossen, K.; Reamer, R. A.; Tsou, N. N.; Volanta,
R. P.; Reider, P. J . J . Am. Chem. Soc. 1997, 119, 6207. (b) Dyer, P. W.;
Dyson, P. J .; J ames, S. L.; Martin, C. M.; Suman, P. Organometallics
1998, 17, 4344. (c) Rossen, K.; Pye, P. J .; Maliakal, A.; Volante, R. P.
J . Org. Chem. 1997, 62, 6462. (d) Pye, P. J .; Rossen, K.; Reamer, R.
A.; Volanta, R. P.; Reider, P. J . Tetrahedron Lett. 1998, 39, 4441. (e)
Burk, M. J .; Hems, W.; Herzberg, D.; Malan, C.; Zanotti-Gerosa, A.
Org. Lett. 2000, 2, 4173.
(3) Bond, A. M.; Dyson, P. J .; Humphrey, D. G.; Lazarez, G.; Suman,
P. J . Chem. Soc., Dalton Trans. 1999, 443.
(4) Plitzko, K.-D.; Boekelheide, V. Organometallics 1988, 7, 1573.
10.1021/om010763a CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/07/2002

Ru(η-arene)Cl2P Complexes
Organometallics, Vol. 21, No. 5, 2002 925
Ta ble 1. 1H, 31P , a n d 13C NMR Da ta for 2 a n d 3 Recor d ed in CDCl3
a
2
3
η-C6H6 (2) or η-C16H16 (3)
5.03 (s, 6H)
88.36 (d, J P-C 3.6, 6C)
6.60 (m, 4H)
132.7 (s, 4C)
84.10 (s, 2C)
87.10 (s, 2C)
31.26 (s, 2C)
33.17 (s, 2C)
139.40 (s, 2C)
122.56 (s, 2C)
4.45 (d, 5.6, 2H)
4.24 (d, 5.6, 2H)
2.92 (m, 4H)
2.09 (m, 2H)
2.13 (m, 2H)
Ph Groups
135.99 (s, 4C)
130.98 (s,4C)
128.39 (s, 2C)
137.19 (d, J P-C 40, 2C)
8.37 (m, 4H)
7.99 (m, 4H)
7.46 (m, 2H)
7.83, 8.18 (br, 4H)
7.41, 7.34 (m, 4H)
7.36, 7.41 (m, 2H)
-, 135.6 (s, 2C)
128.1, 127.9 (s, 1C)
130.2, 129.9 (s, 1C)
137.7 (d, J P-C 40, 2C)
130.68 (d, J P-C 40, 2C)
[2.2]Paracyclophanyl Group
1
2
3
4
5
6
7
8
127.5 (d, J P-C 40, 1C)
126.95 (d, J P-C 44, 1C)
144.28 (s, 1C)
139.77 (s, 1C)
136.4 (s, 1C)
135.3 (s, 1C)
139.8 (d, J P-C 14, 1C)
131.3 (s, 1C)
132.77 (s, 1C)
138.26 (s, 1C)
132.7 (s, 1C)
132.77 (s, 1C)
139.39 (s, 1C)
34.90 (s, 1C)
8.42 (m, 1H)
143.24 (s, 1C)
145.61 (s, 1C)
137.07 (s, 1C)
135.90 (s, 1C)
140.43 (s, 1C)
132.43 (s, 1C)
133.02 (s, 1C)
139.63 (s, 1C)
131.70 (s, 1C)
136.08 (s, 1C)
138.55 (s, 1C)
35.17 (s, 1C)
8.08 (d, J P-H 18, 1H)
6.61 (m, 1H)
6.46 (dd, 8, J P-H 3, 1H)
6.58 (d, 7.4, 1H)
6.41 (dd, 7.4, J P-H 3, 1H)
5.10 (d, 6.4, 1H)
6.25 (d, 7.6, 1H)
5.21 (d, 7.5, 1H)
6.29 (d, 7.5, 1H)
9
10
11
12
13 (a)
13 (b)
14 (a)
14 (b)
15 (a)
15 (b)
16 (a)
16 (b)
6.60 (m, 1H)
6.51 (d, 7, 1H)
6.58 (m, 1H)
6.48 (m, 1H)
3.10 (m, 1H)
3.27 (m, 1H)
3.26 (m, 1H)
2.98 (m, 1H)
3.18 (m, 1H)
2.89 (ddd, 4.6, 11.9, 15, 1H)
2.00 (br, t, 11.9, 1H)
3.05 (m, 1H)
3.28 (m, 1H)
3.28 (m, 1H)
34.90 (s, 1C)
2.95 (m, 1H)
35.36 (s, 1C)
35.23 (s, 1C)
35.76 (s, 1C)
34.97 (s, 1C)
3.08 (m, 1H)
2.88 (m, 1H)
1.74 (br, 1H)
2.51 (m, 1H)
34.45 (s, 1C)
2.60 (ddd, 3.4, 11.4, 13.4, 1H)
a
Atom labels are as shown; the CH2 protons labeled “a” correspond to those on the same side of cyclophane as the P atom, and those
labeled “b” are on the opposite side. Resonances are given in units of ppm and J values in Hz.
report more fully on this ligand, describing the synthesis
and chemical, electrochemical, and structural charac-
terization of ruthenium(II)-rac-PPh2(C16H15) deriva-
tives.
fragment ions (see Experimental Section). The 31P{1H}
NMR spectra of 2 and 3 are very simple, with a singlet
resonance observed at δ 19.53 for 2 and δ 32.41 for 3.
1
In contrast, corresponding H NMR spectra are quite
complicated with signals ranging from δ 2.00 to 8.42
for 2 and from δ 1.74 to 8.08 for 3. Full assignments of
Resu lts a n d Discu ssion
1
Ru(η-C6H6)Cl2{PPh2(C16H15)} (2) and Ru(η-C16H16)-
Cl2{PPh2(C16H15)} (3) were prepared according to a
high-yielding method originally described by Zelonka for
related species.7 Two molecular equivalents of rac-
diphenyl[2.2]paracyclophanylphosphine (1) was stirred
with the appropriate dimer, [Ru(η-C6H6)Cl2]2 or [Ru(η-
C16H16)Cl2]2, in CHCl3 to afford 2 and 3, respectively.
The FAB mass spectra of 2 and 3 recorded in positive
mode show strong peaks corresponding to the parent
ion, and the [M - Cl]+ ion along with additional
the H and 13C NMR spectra are listed in Table 1.
Electr och em ica l In vestiga tion s. The redox behav-
ior of 2 and the triphenylphosphine analogue [Ru(η-
C6H6)Cl2(PPh3)] (4) have been investigated using cyclic
voltammetry and steady-state voltammetry. The cyclic
voltammogram of 2, recorded in 0.25 M [nBu4N][PF6]/
dichloromethane, is shown in Figure 1. A scan from 0
to +1.5 V at 100 mV s-1 reveals a chemically reversible
process at E1/2 ) +1.40 V, with ∆Ep ) 70 mV. This
process corresponds to a one-electron oxidation, as
judged by steady-state voltammetry of a solution con-
taining equimolar amounts of 2 and a complex known
to undergo a chemically reversible one-electron process.
The oxidation of 2, and related [Ru(η-C6H6)Cl2(PR3)]
compounds, can be considered as a metal-based RuII/III
(5) (a) Dyer, P. W.; Dyson, P. J .; J ames, S. L.; Suman, P.; Davies, J .
E.; Martin, C. M. Chem. Commun. 1998, 1375. (b) Dyson, P. J .; Steed,
J . W.; Suman, P. Cryst. Eng. Commun. 1999, 2.
(6) Suman, P.; Dyer, P. W.; Dyson, P. J .; J ames S. L.; Steed, J . W.
New J . Chem. 1998, 22, 1311.
(7) Zelonka, R. A.; Baird, M. C. Can. J . Chem. 1972, 50, 3063.

926 Organometallics, Vol. 21, No. 5, 2002
Bhalla et al.
Ta ble 2. Electr och em ica l Da ta for 2 a n d 4a
complex
E1/2/Vb ∆Ep/mVb Ip,c/Ip,a
c
[Ru(η-C6H6)Cl2{PPh2(C16H15)}] (2) +1.40 70 (rev)
-1.48 irrev
1.0
[Ru(PPh3)Cl2(η-C6H6)] (4)
+1.36 110 (rev)
-1.47 irrev
1.0
a
Measured in 0.25 mol dm-3 [nBu4N][PF6]/CH2Cl2, vs Ag/AgCl,
against which Fc0/+ is measured at +0.55 V. Abbreviations: rev
b
) reversible, irrev ) irreversible. E1/2 ) (Ep,a + Ep,c)/2, ∆Ep
)
c
Ep,a - Ep,c
S. Anal. Chem. 1966, 38, 1406.
.
Ip,c/Ip,a evaluated by the method given in: Shain, R.
The redox behavior of 4 is very similar to that of
compound 2, and the results from voltammetric mea-
surements are summarized in Table 2. Both complexes
display a quasi-reversible one-electron oxidation and an
irreversible two-electron reduction. The small difference
in E1/2 potentials (error (0.01 V) for the oxidation
processes of 2 and 4 suggests that the cyclophane
substituent on the phosphine does not influence the net
electron donor ability of PPh2(C16H15) (1) to any signifi-
cant extent, such that the electronic parameter øI,9 for
C16H15 is in effect similar to that for C6H5. Since the
difference in the basicity of 1 and PPh3 is negligible, it
is possible that the former phosphine may be suited to
catalytic processes which are initiated by dissociation
of the phosphine. For example, alkyl-alkyl coupling in
cis-(alkyl)2PdII(PR3)2 complexes is inhibited by excess
phosphine and it is therefore considered to be initiated
by the rate-determining dissociation of the phosphine
ligand, producing a three-coordinate intermediate.10
Solid -Sta te Str u ctu r e of 3. The structures of some
square-planar palladium and platinum complexes car-
rying the diphenyl[2.2]paracyclophanylphosphine ligand
have been previously established, and in each case some
unusual features have been observed.5,6 Single crystals
of 3 suitable for the X-ray diffraction analysis were
grown from a solution of CH2Cl2-Et2O (1:1) by slow
evaporation. The asymmetric unit of 3 contains two
molecules (a and b), which differ in the enantiomer of
the coordinated phosphine; the structure of 3a is shown
in Figure 2. The structures of the triphenylphosphine
analogues of 2 and 3 have been reported previously,11
and the gross molecular structures of the three com-
pounds are not dissimilar. The structures of 3a and 3b
are unique in that one [2.2]paracyclophane π-bonds to
the ruthenium atom, while the other is σ-bonded to the
phosphine atom and therefore interacts indirectly with
the ruthenium atom. This allows comparisons to be
made between the two [2.2]paracyclophane entities
within the same molecule. The inter-centroid distance
between the two rings in the π-bonded ligand is 2.914
Å in 3a and 2.900 Å in 3b, which is close to that
observed in Ru(η-C16H16)Cl2(PPh3) (2.97 Å). The mag-
nitude of the gap between the two decks in [2.2]-
paracyclophane has been discussed before, following the
structural characterization of [2.2]paracyclophane and
the first π-complex, Cr(CO)3(η-C16H16).12 Coordination
F igu r e 1. Cyclic voltammetry of [Ru(η-C6H6)Cl2{PPh2-
(C16H15)}] (2) in 0.25 M [nBu4N][PF6]/CH2Cl2 at 290 K (scan
rate 100 mV s-1): (a) scan from 0 to +1.5 V; (b) scan from
0 to -1.5 V.
process, as shown in eq A. Although chemically revers-
[Ru(η6-C6H6)Cl2(PR3)] T
[Ru(η6-C6H6)Cl2(PR3)]+ + e- (A)
ible on the cyclic voltammetric time scale (scan rate 10
mV s-1), the oxidation of 2 is irreversible on the bulk
electrosynthetic time scale. When the oxidation of 2 was
performed in an optically transparent thin-layer elec-
trolysis cell, the changes in the electronic spectrum were
monitored as the electrolysis progressed. The UV/vis
spectrum of 2 in CH2Cl2 contains a band at ∼27 100
cm-1. Upon oxidation spectral changes occurred without
retention of isosbestic points, and rereduction failed to
regenerate the starting spectrum. An irreversible reduc-
tion wave is detected at Ep,c ) -1.48 V in the cyclic
voltammogram of 2 upon scanning from 0 to -1.5 V at
100 mV s-1. The wave remains irreversible at fast scan
rates (up to 5 V s-1) and at low temperature (220 K)
and overall involves two electrons, as shown by steady-
state voltammetry at a microdisk electrode, where the
limiting current for the reduction is approximately twice
that for the 20/+ oxidation wave. This irreversible two-
electron wave is thought to correspond to a metal-based
process, as shown in eq B. Studies of bis-arene systems,
[Ru(η6-C6H6)Cl2(PR3)] + 2e- T
[Ru(η4-C6H6)Cl2(PR3)]2- f decomposition (B)
(9) (a) Tolman, C. A. J . Am. Chem. Soc. 1970, 92, 2953. (b) Golovin,
M. N.; Rahman, M. M.; Belmonte, J . E.; Giering, W. P. Organometallics
1985, 4, 1981.
(10) (a) Ozawa, F.; Ito, T.; Yamamoto, A. J . Am. Chem. Soc. 1980,
102, 6457. (b) Ozawa, F.; Kurihara, K.; Fujimori, M.; Hidaka, T.;
Toyoshima, T.; Yamamoto, A. Organometallics 1989, 8, 180.
(11) Elsegood, M. R. J .; Tocher, D. A. Polyhedron 1995, 14, 3147.
(12) Kai, Y.; Yasnoka, N.; Kasai, N. Acta Crystallogr. 1978, B34,
2840.
e.g. [Ru(η6-C6Me6)2]2+, have suggested that two-electron
reduction results in a η6 to η4 transformation of the
coordinated arene.8
(8) Finke, R. G.; Voegeli, R. H.; Laganis, E. D.; Boekelheide, V.
Organometallics 1983, 2, 347.

Ru(η-arene)Cl2P Complexes
Organometallics, Vol. 21, No. 5, 2002 927
tions to those described previously using styrene as the
substrate. Compound 4, with the rac-diphenyl[2.2]-
paracyclophane ligand, was ca. 50% more active than
2. However, it is worth noting that in both cases the
catalyst had decomposed during the hydrogenation
reaction and that the catalytic turnover is very low (see
Experimental Section).
While these catalysis results are not very impressive,
we have found that rac-diphenyl[2.2]paracyclophane is
an extremely useful ligand in palladium-catalyzed Heck
reactions and our results from these studies will be
reported in due course.
Exp er im en ta l Section
All reactions were conducted under an atmosphere of
nitrogen using dried and degassed solvents, although the
products were air stable. The compounds [Ru(η-C6H6)Cl2]2,7
[Ru(η-C16H16)Cl2]2,14 Ru(η-C6H6)Cl2(PPh3) (4),11 and rac-PPh2-
(C16H15) (1)5a were prepared by literature methods. Mass
spectra were obtained using positive fast atom bombardment
on a Micromass Autospec instrument. NMR spectra were
F igu r e 2. Molecular structure of 3a . Bond lengths (Å):
Ru(1)-P(1) ) 2.339(2), Ru(1)-Cl(1) ) 2.423(2), Ru(1)-Cl(2)
) 2.429(2), Ru(1)-C(1) ) 2.157(9), Ru(1)-C(2) ) 2.147(8),
Ru(1)-C(3) ) 2.326(8), Ru(1)-C(4) ) 2.197(8), Ru(1)-C(5)
) 2.281(8), Ru(1)-C(6) ) 2.392(8), P(1)-C(33) ) 1.845(9),
P(1)-C(39) ) 1.823(8), P(1)-C(17) ) 1.836(9), C(1)-C(2)
) 1.394(12), C(1)-C(6) ) 1.431(12), C(2)-C(3) ) 1.417(12),
C(3)-C(4) ) 1.404(12), C(4)-C(5) ) 1.411(12), C(5)-C(6)
) 1.384(11), C(6)-C(7) ) 1.487(12), C(7)-C(8) ) 1.584(13),
C(8)-C(9) ) 1.530(14), C(3)-C(16) ) 1.493(12), C(16)-
C(15) ) 1.579(12), C(15)-C(12) ) 1.518(13), C(9)-C(10) )
1.399(13), C(9)-C(14) ) 1.380(12), C(10)-C(11) ) 1.374(13),
C(11)-C(12) ) 1.403(12), C(12)-C(13) ) 1.381(13), C(13)-
C(14) ) 1.364(13), C(17)-C(18) ) 1.401(12), C(17)-C(22)
) 1.404(13), C(18)-C(19) ) 1.391(13), C(19)-C(20) )
1.396(16),C(20)-C(21))1.336(17),C(21)-C(22))1.394(15),
C(19)-C(32) ) 1.507(16), C(32)-C(31) ) 1.587(19), C(31)-
C(28) ) 1.477(19), C(22)-C(23) ) 1.535(14), C(23)-C(24)
) 1.585(17), C(24)-C(25) ) 1.509(19), C(25)-C(26) )
1.375(19), C(25)-C(30) ) 1.395(17), C(26)-C(27) ) 1.37(2),
C(27)-C(28) ) 1.38(2), C(28)-C(29) ) 1.326(18), C(29)-
C(30) ) 1.400(17).
1
recorded on a Bruker DRX-400 spectrometer with H at 400.13
MHz, 31P at 161.98 MHz, and 13C at 100.1 MHz. 1H NMR
chemical shifts are reported in ppm relative to residual 1H
signals in the deuterated solvents (CDCl3, δ 7.29), 31P{1H}
NMR spectra are reported in ppm downfield from an external
85% solution of phosphoric acid. Standard gradient-assisted
heteronuclear multiple quantum correlation (HMQC), correla-
tion spectrosopy (COSY), and nuclear Overhauser effect
spectroscopy (NOESY) pulse sequences were used to obtain
two-dimensional heteronuclear correlation spectra.15
Syn th esis of Ru (η-C6H6)Cl2{P P h 2(C16H15)} (2). To [Ru-
(η-C6H6)Cl2]2 (250 mg, 0.5 mmol) in CHCl3 (15 mL) was added
rac-PPh2(C16H15) (392 mg, 1 mmol) and the reaction mixture
stirred under reflux for 2 h. The solution was cooled, and the
solvent was evaporated in vacuo to give a red-brown solid (0.43
g, 76%). The solid was recrystallized from CH2Cl2-Et2O (1:1)
to give red crystals which were characterized as 2 by spec-
troscopy.
Spectroscopic data for 2: FAB-MS m/z 642 [M]+, 607 [M -
Cl]+, 491 [M - 2Cl - C6H6]+; 31P{1H} NMR (CDCl3) 19.53 (s)
ppm; see Table 1 for other NMR data. Anal. Found (calcd): C,
56.33 (56.25); H, 3.85 (4.10).
Syn th esis of Ru (η-C16H16)Cl2{P P h 2(C16H15)} (3). To [Ru-
(η-C16H16)Cl2]2 (95 mg, 0.125 mmol) in CHCl3 (30 mL) was
added rac-PPh2(C16H15) (0.098 mg, 0.25 mmol) and the reaction
mixture stirred under reflux for 2 h. The solution was cooled,
and the solvent was evaporated in vacuo to give a red-brown
solid (0.142 g, 74%). The solid was recrystallized from CH2-
Cl2-Et2O (1:1) to give red crystals which were characterized
as 3 by spectroscopy.
Spectroscopic data for 3: FAB-MS m/z 772 [M]+, 737 [M -
Cl]+, 701 [M - 2Cl]+; 31P{1H} NMR (CDCl3) 32.41 (s) ppm;
see Table 1 for other NMR data. Anal. Found (calcd): C, 68.51
(68.39); H, 5.25 (5.35).
Cr ysta l Str u ctu r e Deter m in a tion for 3. Crystals were
mounted on a thin glass fiber using silicon grease and cooled
on the diffractometer to 100 K using an Oxford Cryostream
low-temperature attachment. A total of 90 oscillation frames
each of width 2° in φ and with 30 s exposure time were
recorded using a Nonius Kappa CCD diffractometer, with a
detector to crystal distance of 25 mm. Crystals were indexed
from the first 10 frames using the DENZO-SMN package,16
of [2.2]paracyclophane to an electron-withdrawing frag-
ment such as Cr(CO)3 results in the removal of some
π-electron density between the aromatic decks, which
allows the rings to move closer together, changing from
3.09 to 3.02 Å. The larger change observed in Ru(η-
C16H16)Cl2(PPh3) (3a and 3b) reflects the greater electron-
withdrawing effect of the ruthenium(II) ion versus the
chromium(0) atom. The distances between the rings in
the [2.2]paracyclophanyl groups of the phosphine ligands
are 2.988 and 3.006 Å, also suggesting that the π-elec-
tron density between the aromatic rings has decreased.
This could also arise from the distortion caused to the
[2.2]paracyclophanyl group, where the carbon atom
bonds to the phosphorus. This carbon atom causes the
aryl ring to adopt more of a butterfly shape, although
the torsion angle across the nonbridgehead atoms is only
ca. 1.8°. The remaining intramolecular structural fea-
tures are unremarkable, and the key bonding param-
eters are listed in the figure caption.
Com p a r ison of th e Ca ta lytic Activity of 2 a n d 4
in th e Hyd r ogen a tion of Styr en e. Ruthenium(II)-
arene compounds of formula [Ru(η6-arene)Cl2(PR3)]
have been shown to catalyze the hydrogenation of
styrene and phenylacetylene.13 The catalytic activity of
compounds 2 and 4 was compared under similar condi-
(14) Elsegood, M. R. J .; Tocher, D. A. J . Organomet. Chem. 1988,
356, C29.
(15) Zhu, J .-M.; Smith, I. C. P. Concepts Magn. Reson. 1995, 7, 281
and references therein.
(13) Moldes, I.; de la Encarnacio´n, E.; Ros, J .; Alvarez-Larena, AÄ .;
Piniella, J . F. J . Organomet. Chem. 1998, 566, 165.
(16) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter,
C. W., Sweet, R. M., Eds.; Academic Press: New York, 1996. Vol. 276.

928 Organometallics, Vol. 21, No. 5, 2002
Bhalla et al.
and positional data were refined along with diffractometer
constants to give the final unit cell parameters. Integration
and scaling (DENZO-SMN, Scalepack)16 resulted in unique
data sets corrected for Lorentz and polarization effects and
for the effects of crystal decay and absorption by a combination
of averaging of equivalent reflections and an overall volume
and scaling correction. The space group was identified as
tetragonal I1/a from systematically absent data and confirmed
by successful refinement. The structures were solved using the
direct-methods option of SHELXS-9717 and developed via
alternating least-squares cycles and difference Fourier syn-
thesis (SHELXL-97)17 with the aid of the program RES2INS.18
All non-hydrogen atoms were modeled anisotropically, while
hydrogen atoms are assigned an isotropic thermal parameter
1.2 times that of the parent atom and allowed to ride. The
molecule of diethyl ether solvent was refined poorly (possibly
as a consequence of partial efflorescence), and DFIX restraints
were applied to the bond lengths. Hydrogen atoms were not
included in the model for this solvent molecule. All calculations
were carried out with either a Silicon Graphics Indy worksta-
tion or an IBM-compatible PC.
throughout with [nBu4N][PF6] electrolyte previously dried at
373 K under vacuum.
Hyd r ogen a tion of Styr en e. Hydrogenations were carried
using a Parr stainless steel autoclave (300 mL) fitted with
either a glass or a PTFE liner. The catalyst (0.03 mmol) was
added together with CH2Cl2 (40 mL) and styrene (2.08 g). The
autoclave was then sealed and purged with hydrogen gas
(99.9995% purity) and the reaction pressure set to 30 atm at
room temperature. The autoclave was then sealed, heated to
60 °C, and stirred for 18 h. After reaction the contents were
1
then analyzed by H NMR spectroscopy and GC. The conver-
sion using 2 was 71% and using 4 was 54%.
Ack n ow led gm en t. We thank the Royal Society for
a University Research Fellowship (P.J .D.), the EPSRC
for a studentship (P.S.), and the Australian Research
Council for an Endeavor Fellowship (D.G.H.). The
EPSRC is thanked for provision of an NMR spectrom-
eter, the EPSRC and King’s College London are also
thanked for the provision of the X-ray diffractometer,
and the Nuffield Foundation is acknowledged for the
provision of computing equipment.
Electr och em istr y of 2 a n d 4. Cyclic and steady-state
voltammetry was carried out with a Cypress Systems (Model
CS-2000) computerized electroanalytical system, in conjunction
with a nitrogn-purged one-compartment cell which supported
a platinum-disk working electrode (diameter 1.0 mm or 7 µm),
a platinum-coil counter electrode, and a Ag/AgCl reference
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data for 2a . This material is available free of
charge via the Internet at http://pubs.acs.org. Crystallographic
data (excluding structure factors) for 3 have been deposited
with the Cambridge Crystallographic Data Centre as supple-
mentary publication number CCDC-168655. Copies of the data
can be obtained free of charge on application to the CCDC, 12
Union Road, Cambridge CB2 1EZ, U.K. (fax, (+44) 1223-336-
033; e-mail, deposit@ccdc.cam.ac.uk).
electrode, for which the ferrocenium/ferrocene couple (Fc+/0
)
was measured at +0.55 V. Freshly distilled CH2Cl2 was used
(17) Sheldrick, G. M. SHELX-97; University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
(18) Barbour, L. J . RES2INS; University of Missouri, Columbia, MO,
1995-1998.
OM010763A