Highly distorted d8 -rhodium(+I) and d10 -rhodium(-I) complexes: Synthesis, reactivity, and structures in solution and solid state

Article abstract of DOI:10.1039/b002906h

A synthesis of the new ligand 5-diphenylphosphanyl-10-methyl-5H-dibenzo[a,d]cycloheptene (^metropp^ph) was developed in order to prepare highly distorted tetra-co-ordinated rhodium(+I) complexes. The ligand ^metropp^ph

Full text of DOI:10.1039/b002906h

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Highly distorted d8-rhodium(+ I) and d10-rhodium(ÔI) complexes:
synthesis, reactivity, and structures in solution and solid state
Stephan Deblon, Heinz Ruegger, Hartmut Schonberg, Sandra Loss, Volker Gramlich and
Hansjorg Grutzmacher*
L aboratory of Inorganic Chemistry, ET H-Centre, Universitatstrasse 6, CH-8092 Zurich,
Switzerland. E-mail: gruetzmacher=inorg.chem.ethz.ch; Fax: ]41 1 632 10 90
Received (in Montpellier, France) 10th April 2000, Accepted 16th June 2000
First published as an Advance Article on the web 23rd October 2000
A synthesis of the new ligand 5-diphenylphosphanyl-10-methyl-5H-dibenzo[a,d]cycloheptene (metroppph) was
developed in order to prepare highly distorted tetra-co-ordinated rhodium(]I) complexes. The ligand metroppph
contains a cycloheptatriene ring in a rigid boat conformation such that a Ph P and an oleÐnic binding site are
2
perfectly arranged for transition metal complexation. Four equivalents of metroppph react with [Rh (l-Cl) (cod) ] in
2
2
2
the presence of KPF to yield almost quantitatively [Rh(]I)(metroppph) ]PF , which was isolated in the form of
6
2
6
dark red-violet crystals. A crystal structure analysis reveals that the co-ordination sphere of the rhodium centre in
[Rh(]I)(metroppph) ]` deviates strongly from a square planar arrangement (r \ 42¡). One methyl group in
2
2
[Rh(]I)(metroppph) ]` can be deprotonated by KOBut to give the allyl complex [Rh(allyltroppph)(metroppph)]. This
complex has a structure that may be best described as a distorted trigonal bipyramid. The boron hydride
[BEt H]~ and organolithium reagents, LiR, react with [Rh(allyltroppph)(metroppph)] in allylic alkylation reactions to
3
yield anionic rhodate complexes [Rh(RCH2troppph)(metroppph)]~ (R \ H, Me, n-Bu, Ph) that formally have a d10
valence electron conÐguration. The rhodate [Rh(metroppph) ]~ can be obtained directly by reduction of cation
2
[Rh(metroppph) ]` with alkali metals. In a sym-proportionation reaction [Rh(metroppph) ]` and [Rh(metroppph) ]~
2
2
2
give the neutral d9-[Rh(metroppph) ] radical (K \ 1.1 ] 107), which is not stable but decomposes with loss of H to
2
2
give the allyl complex [Rh(allyltroppph)(metroppph)]. The structures in solution of [Rh(metroppph) ]`,
2
[Rh(allyltroppph)(metroppph)], and [Rh(nBuCH2troppph)(metroppph)]~ were determined by NMR techniques, which
reveal that (i) they match the solid state structures and (ii) are rather similar to each other. This fact may explain
the remarkable electronic Ñexibility of the rhodium centre, which changes reversibly its formal oxidation state from
]I to 0 to [I at rather low negative potentials (*E01 \ [0.882 V; *E02 \ [1.298 V).
The chemistry of rhodium and iridium complexes in formally
low oxidation states, that is 0 and [I, is comparatively little
studied. In early works, strongly electron withdrawing ligands
L like CO1 and Ñuorophosphanes2 were used for the synthesis
planar conÐguration towards a tetrahedron.8 We expected
that the ground state of the cation would be more destabilised
than that of the product by such a distortion, leading to a
lowering of the reduction potential. As will be seen later, this
is not observed. However, we succeeded in the preparation of
a strongly distorted tetra-co-ordinated rhodium complex and
the chemistry of this compound and its derivatives is reported
in this paper. In particular, the synthesis of a new substituted
tropp ligand and a new method to prepare d10-rhodate com-
plexes by nucleophilic attack on an allyl moiety co-ordinated
to a rhodium(]I) centre are described.
of [ML ]~ anions (M \ Rh, Ir) with a formal d10 valence
4
electron count on the metal. Only recently, the Ðrst stable
rhodium and iridium d10-complexes with chelating phos-
phanes were prepared.3a,b The synthesis of stable monomeric
d9-[ML ] complexes was also only recently achieved.3b,4
4
These 17-electron complexes may have interesting properties
as catalysts for the photolytic cleavage of water.5
We have designed tropylidenylphosphanes (tropp)6 as a
new ligand system to allow the synthesis of stable rhodium4a
and iridium4b complexes in their formal oxidation states 0 and
[I. These complexes were completely characterised including
X-ray analyses, which allowed us to study structural changes
caused by the addition or abstraction of single electrons (see
Results and discussion
Synthesis of metroppph
also ref. 3b). Furthermore, these [M(tropp) ]m complexes
(M \ Rh, Ir; m \ ]1, 0, [1) show very low redox potentials
The introduction of a methyl group into the oleÐnic unit of
the central seven-membered ring of tropp, which co-ordinates
to the metal centre, should increase the steric congestion and
hence enforce a distorted co-ordination sphere. The synthesis
of this new tropp ligand is outlined in Scheme 1. Starting from
the readily available dibenzosuberenone 1, 10-bromo-5H-
dibenzo[a,d]cyclohepten-5-one 2 was prepared by bromina-
tion of the double bond and subsequent HBr elimination.9 In
the next step, the ketone functionality was protected by ketali-
sation using glycol in the presence of para-toluenesulfonic acid
(pTosOH). In contrast to the literature procedure10 this con-
version gave almost quantitatively compound 3. Reaction of 3
2
[M`1/M0: [1.0 V (M \ Rh), [0.97 V (M \ Ir); M0/M~1:
[1.2 V (M \ Rh), [1.4 V (M \ Ir) vs. Ag/AgCl], which
make them indeed potentially interesting as redox catalysts.
The vast structural data available for tetra-co-ordinated d8-
rhodium(]I) complexes show these to be square planar,
which is also supported by molecular orbital calculations.7
With the aim to provoke an even more anodic shift of the
reduction potentials of rhodium tropp complexes, we wanted
to prepare tetra-co-ordinated cationic rhodium(]I) com-
pounds that are signiÐcantly distorted from their square
DOI: 10.1039/b002906h
New J. Chem., 2001, 25, 83È92
83
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Scheme 1 Synthesis of metroppph.
with excess Mg turnings in THF gave the corresponding Grig-
nard reagent, which was reacted with an excess of methyl
iodide. After addition of concentrated aqueous HCl and reÑux
for about 12 h, 10-methyl-5H-dibenzo[a,d]cyclohepten-5-one
4 was obtained in very good yield (90%) while the known
procedure gave only 37% overall yield.10 The suberenone
derivative
4 was reduced by modifying the literature
procedure10 and then transformed into 5-chloro-10-methyl-
dibenzo[a,d]cycloheptene 5. The addition of diphenylphos-
phine in toluene, followed by an aqueous work-up under basic
conditions, led cleanly to the desired 5-diphenylphosphanyl-
10-methyldibenzo[a,d]cycloheptene 6 as a racemic mixure of
Scheme 2 Synthesis of the cationic rhodium bis(metroppph) complex
9.
the
R and S isomers in 86% isolated yield after re-
mixed dimer [Rh (l-Cl) (troppph)(cod)] was directly observed.
crystallisation from acetonitrile. Following our simpliÐed
nomenclature,4,6 we name this ligand metroppph where the
superscript in front (me) indicates substituents bonded to the
C2C bond of the seven-membered ring and the superscript at
the end denotes the substituents bonded to phosphorus.
2
2
We did not assign the NMR signals to the di†erent isomers
nor determine the isomeric distribution. Crystals of 8 suitable
for an X-ray analysis were not obtained. Note that in this
context, the structure of [Rh (l-Cl) (troppph) ] containing the
2
2
2
unsubstituted troppph ligand was determined earlier and the
major isomer showed the two phosphorus atoms in a cis
arrangement.12 When 8 is dissolved in a co-ordinating solvent
like THF or MeCN, only one broadened 31P resonance is
observed at 103.5 ppm [1J(103Rh31P) \ 203 Hz].
Synthesis of d8-rhodium metroppph complexes
The metroppph ligand rac-6 reacts quantitatively with the
chloro-bridged binuclear rhodium cyclooctadiene (cod)
complex 7 at room temperature to give an orange methylene
chloride solution that contains a mixture of all possible dia-
stereomers of the rhodium complexes 8, as indicated by the
Even when a large excess of rac-6 is reacted with 7 at ele-
vated temperatures, no bis(metroppph) type complexes are
formed, in contrast to reactions with the non-methyl-substi-
31P NMR data given below (Scheme 2). The isomers cis-C -8
tuted ligand troppph, for which [RhCl(troppph) ] is
2
2
and trans-C -8 contain a C rotation axis, cis-meso-8 a mirror
obtained.4a,12
However,
when
potassium
hexa-
2
2
plane and trans-i-8 an inversion centre as symmetry elements
and therefore each isomer should give rise to one 31P reso-
nance signal split into a doublet by 103RhÈ31P coupling.
Indeed, in the 31P NMR spectrum recorded at room tem-
perature only two exchange broadened doublets are seen,
which upon cooling to [70 ¡C split into four doublets [1:
d31P 110.3, 1J(103Rh31P) \ 212 Hz, 50%; 2: d31P 110.0,
Ñuorophosphate, KPF , is added to an acetonitrile solution
6
of 8, the dark red-violet bis(metroppph) complex 9 forms.
Complex 9 is obtained in about 86% isolated yield; it is
soluble in CH Cl and acetonitrile but poorly soluble in THF.
2
2
It can be crystallised by layering CH Cl or CH CN solutions
2
2
3
with n-hexane. In solution, exclusively one isomer can be
detected by NMR spectroscopy. The 103RhÈ31P coupling con-
stant [1J(103Rh31P) \ 192 Hz is indicative of a cis isomer
whereas the trans isomer [1J(103Rh31P) \ 132 Hz] is pre-
dominant (80%) in solutions of the [Rh(troppph) ]` cation.4
Interestingly, some of the protons of the annelated benzo
1J(103Rh31P) \ 209
1J(103Rh31P) B 207
Hz,
Hz,
35%;
10%;
3:
4:
d31P
d31P
109.4,
109.5,
1J(103Rh31P) B 207 Hz, 50%]. In an 1H-NOESY NMR spec-
trum, it is seen that every isomer does exchange with every
other component. Regarding the di†erent possible conÐgu-
rations of 8 in Scheme 2, apart from an intermolecular process
via the solvated complex [RhCl(metroppPh)S] A (S \ CH Cl ),
2
groups and the phenyl substituents bonded to the phosphorus
centres within each metroppph ligand show quite distinct 1H
NMR signals in comparison to the uncomplexed ligand. For
the ortho phenyl protons a (d \ 5.50) and b (d \ 7.65) (Fig. 1)
in particular, this di†erence is signiÐcant and amounts to 2.15
ppm. It should be noted that this large di†erence is observed
not only for the ortho protons but also for the entire phenyl
rings. Indeed, for the latter, a remarkably di†erent shielding is
observed as a consequence of the conformation and arrange-
ment of the phenyl substituents with respect to each other and
to the benzo groups of the cycloheptatriene unit. A NMR
2
2
an intramolecular process via B can explain the pair-wise
exchange between cis-C -8 and trans-C -8 on one hand and
2
2
cis-meso-8 and trans-i-8 on the other.11 All other exchanges
must proceed via intermolecular pathways on which interme-
diates A or higher nuclear complexes like C, which subse-
quently collapse to give all possible stereoisomers, may
appear. Note that when [Rh (l-Cl) (cod) ] 7 is added, it also
2
2
2
exchanges with all other components although none of the
84
New J. Chem., 2001, 25, 83È92

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crystallographic details are given in Table 1, selected bond
lengths and angles are listed in Table 2. In Fig. 2, an ORTEP
3 plot13 of the cation of 9 is shown.
The two phosphorus centres occupy the cis positions if an
idealised square planar conformation is taken into consider-
ation. However, the co-ordination sphere of the rhodium
centre is strongly distorted towards a tetrahedron. The angle
r between the two planes that run through each phosphorus
centre, the rhodium centre and the midpoint of each of the
metal-bound C2C bonds amounts to 42¡. Hence, the co-
ordination is halfway between a square plane (r \ 0¡) and a
tetrahedron (r \ 90¡) and is to our knowledge the second
strongest deviation observed to date for tetra-co-ordinated d8-
rhodium complexes.8 While the RhÈP distances [mean
2.241(1) A; max. di†erence D: 0.054 A] lie within the usual
range (B2.30 A),14 the steric congestion is more clearly seen in
the unusually long RhÈC distances [mean: RhÈC4: 2.426(4)
A, D \ 0.066 A; RhÈC5: 2.371(4) A, D \ 0.146 A], which are
about 0.24 A longer than the usually observed bond lengths
(B2.15 A).14 The variation of the individual RhÈP or RhÈC4/
C5 bonds expressed by the di†erence D between the shortest
and longest bond is also considerable.14 The co-ordinated
C2C bonds [mean: 1.375(6) A] are not very elongated when
compared to the free ligand.6 The sum of bond angles around
the carbon centre C4 shows only a weak pyramidalisation (by
less than 4¡), indicating only a weak d ] p(p) back donation
from the metal centre to the C2C unit.
Fig. 1 Schematic representation of the cation of complex 9. a and b
denote the set of di†erent ortho-phenyl protons on each P centre. For
a detailed picture of the structure see Fig. 2.
determination of the three-dimensional solution structure
reveals that one phenyl ring deÐnes a plane with the RhÈP
bond vector. This brings the ortho protons a into a deshield-
ing region (indicated by x in Fig. 1) due to the magnetic
anisotropy of the rhodium nucleus. The latter is caused by the
d -type orbital at Rh(]I), which induces an unusually high
z2
frequency. On the other hand, the NOE between the PCH
proton and the ortho protons b is remarkably weak, consistent
with a dihedral angle between the corresponding phenyls of
ca. ^90¡ with respect to the RhÈP bond. In this conforma-
tional arrangement, the protons b are subject to a two-fold
shielding anisotropy e†ect: (i) intraligand (y ) due to the
1
neighbouring benzo group of the tropylidene unit and (ii)
interligand (y ) due to a parallel arrangement of equivalent
2
phenyl rings on each ligand in such a way that the protons of
one ring lie in the shielding region of the other.
We have no evidence for the formation of penta co-
ordinated [Rh(tropp) L]` complexes (L \ MeCN or THF)
2
even though such species are formed with sterically less
encumbered tropp-type ligands.4c Indeed, the exclusive forma-
tion of the chiral (C symmetry) R,R and S,S isomers, respec-
2
tively, was established by an X-ray analysis (vide infra). The
meso isomer is not observed, probably because of even higher
steric congestion, which prevents its formation. In the 103Rh
NMR spectrum of a CH Cl solution of 9, one sharp reso-
2
2
nance signal (triplet) at ]162 ppm is observed, which is
typical for 16-electron rhodium tropp complexes.
Structure of [Rh(metroppph) ]PF Æ 2CH CN (9)
2
6
3
The salt [Rh(metroppph) ]PF 9 crystallises with two crystallo-
2
6
graphically independent pairs of enantiomers in the unit cell.
All bonds and angles are equal within the limits of experimen-
tal accuracy and we discuss therefore only one of the two
cations. Additionally, two acetonitrile molecules are included,
which have no close contact with the rhodium centre. Further
Fig. 2 Molecular structure of one of the crystallographically inde-
pendent cations of 9. Hydrogen atoms are omitted for clarity. Selected
bond lengths and angles are given in Table 2.
Table 1 Crystallographic data of compounds 9 and 10
9
10
Chemical formula
Formula weight
Crystal system
Space group
a/A
b/A
c/A
a/¡
C
H
F NP Rh
C
H
Cl
P Rh
58 49 6
3
55.5 45.40 1.50 2
942.45
1069.80
Triclinic
P1
Orthorhombic
C2/c
45.90(5)
10.159(10)
19.773(19)
90
102.27(8)
90
9009(16)
8
293(2)
4.842
4804
10.844(2)
20.697(4)
22.722(5)
91.629(13)
91.462(13)
101.890(12)
4985.7(17)
4
b/¡
c/¡
U/A
Ž
3
Z
T /K
293(2)
0.501
k/mm~1
ReÑections collected
Independent reÑections
Final R indices [I [ 2p(I)]
28 990
14 653 [R(int) \ 0.0378]
4620 [R(int) \ 0.0428]
R
wR
2
0.036
0.072
0.046
0.113
1
New J. Chem., 2001, 25, 83È92
85

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Table 2 Selected bond lengths (A) and angles (¡) of the two crystallo-
graphically independent cations of 9
an X-ray analysis (Fig. 4) and we reasonably assume that this
structure corresponds to the major isomer 10 (see Scheme 3)
observed in solution. However, when pure re-crystallised 10 is
dissolved in CH Cl , both isomers are again found in the
same ratio (28 : 1). Because of the similarity of the 31P NMR
data, we assign to the minor component 10@ a structure in
which the intact metroppph ligand has rotated by 180¡ when
compared to the major product. Consequently, the methyl
Rh1ÈP1
Rh1ÈP1a
Rh1ÈC5
Rh1ÈC4
Rh1ÈC5a
Rh1ÈC4a
P1ÈC17
P1ÈC23
P1ÈC1
2.226(1)
2.260(1)
2.337(4)
2.362(4)
2.404(4)
2.451(4)
1.818(5)
1.819(4)
1.878(4)
1.372(6)
1.825(5)
1.830(4)
1.858(4)
1.380(6)
Rh1bÈP1c
Rh1bÈP1b
Rh1bÈC5c
Rh1bÈC4c
Rh1bÈC5b
Rh1bÈC4b
P1bÈC23b
P1bÈC17b
P1bÈC1b
C4bÈC5b
P1cÈC23c
P1cÈC17c
P1cÈC1c
2.212(1)
2.266(2)
2.341(4)
2.381(4)
2.401(4)
2.508(4)
1.812(5)
1.839(4)
1.874(4)
1.373(6)
1.817(4)
1.819(4)
1.872(4)
1.375(6)
2
2
group points towards the CH terminus of the allyl moiety as
2
shown in Scheme 3. For this isomerisation, an interesting
possibility would have consisted of an intra-molecular depro-
tonation of the methyl substituent of one tropp ligand by the
allyl group of the other. However, 2D-NOESY spectra show
no cross-peaks for the corresponding protons and hence give
no indication for such a phenomenon.
C4ÈC5
P1aÈC23a
P1aÈC17a
P1aÈC1a
C4aÈC5a
C4cÈC5c
Most informative are the heteronuclear correlations. For
the 103RhÈ1H HMQC (heteronuclear multiple quantum
coherence) NMR data of rhodium metroppph complexes, the
three expected 103RhÈ1H cross-peaks per inequivalent ligand
are found for the protons of the PCH and the oleÐnic H and
Me group. However, there is an additional cross-peak for 10,
P1ÈRh1ÈP1a
P1ÈRh1ÈC5
P1AÈRh1ÈC5
P1ÈRh1ÈC4
P1aÈRh1ÈC4
C5ÈRh1ÈC4
94.18(4)
90.2(1)
166.7(1)
90.1(1)
133.3(1)
34.0(1)
167.0(1)
89.7(1)
88.8(1)
96.2(1)
134.5(1)
89.3(1)
96.6(2)
P1cÈRh1bÈP1b
P1cÈRh1bÈC5c
P1bÈRh1bÈC5c
P1cÈRh1bÈC4c
P1bÈRh1bÈC4c
C5cÈRh1bÈC4c
P1cÈRh1bÈC5b
P1bÈRh1bÈC5b
C5cÈRh1bÈC5b
C4cÈRh1bÈC5b
P1cÈRh1bÈC4b
P1bÈRh1bÈC4b
C5cÈRh1bÈC4b
C4cÈRh1bÈC4b
C5bÈRh1bÈC4b
C23bÈP1bÈC17b
C23bÈP1bÈC1b
C17bÈP1bÈC1b
C23bÈP1bÈRh1b
C17bÈP1bÈRh1b
C1bÈP1bÈRh1b
C23cÈP1cÈC17c
C23cÈP1cÈC1c
C17cÈP1cÈC1c
C23cÈP1cÈRh1b
C17cÈP1cÈRh1b
C1cÈP1cÈRh1b
93.44(4)
90.8(1)
169.8(1)
89.7(1)
136.8(1)
33.8(1)
164.1(1)
89.2(1)
89.3(1)
99.1(1)
131.8(1)
89.8(1)
94.3(2)
119.1(1)
32.4(1)
104.2(2)
99.6(2)
103.3(2)
110.7(1)
125.8(1)
110.1(1)
106.9(2)
100.7(2)
103.3(2)
110.7(1)
122.6(1)
110.3(1)
P1ÈRh1ÈC5a
P1aÈRh1ÈC5a
C5ÈRh1ÈC5a
C4ÈRh1ÈC5a
P1ÈRh1ÈC4a
P1aÈRh1ÈC4a
C5ÈRh1ÈC4a
C4ÈRh1ÈC4a
C5aÈRh1ÈC4a
C17ÈP1ÈC23
C17ÈP1ÈC1
indicating the formation of a CH unit with diastereotopic
2
protons rather than an additional Me group. The low fre-
quency 103Rh shift (d \ [370) is consistent with the formula-
tion of an g3-allyl moiety. This is further conÐrmed by the
13C, 1H one- and multiple-bond correlations showing a ter-
tiary C5H, quaternary C4 and secondary C16H with
2
119.3(2)
33.0(1)
d \ 61.7, 103.0 and 58.1, respectively (see Fig. 3). Such values
are typically encountered for g3-allyl groups.
102.6(2)
102.8(2)
101.6(2)
125.0(1)
111.8(1)
110.3(1)
105.4(2)
101.8(2)
102.6(2)
110.2(1)
124.6(1)
109.8(1)
After having identiÐed some structural features of the
complex, we now turn to an analysis of the solution structure.
As such, the two-bond coupling constants between ligand
atoms are the most valuable tool in the determination of the
conÐguration at the rhodium centre. In this respect,
2J(31P31P) \ 29 Hz indicates a cis arrangement of the P1 and
P1a centres. Within the constraints of an assumed trigonal
bipyramid, this means that either both phosphorus are equa-
torial or one is equatorial and the other one axial. Placing the
allyltropp ligand with its P1 centre in an axial position brings
both allyl termini C5 and C16 in equatorial positions. Hence,
the angle between these two carbon atoms and the P1a
nucleus of the metropp would have similar values. However,
this is in contrast to the observed coupling constants
C23ÈP1ÈC1
C17ÈP1ÈRh1
C23ÈP1ÈRh1
C1ÈP1ÈRh1
C23aÈP1aÈC17a
C23aÈP1aÈC1a
C17aÈP1aÈC1a
C23aÈP1aÈRh1
C17aÈP1aÈRh1
C1aÈP1aÈRh1
Synthesis of the allyl complex [Rh(allyltroppph)(metroppph)] (10)
When potassium tert-butoxide is added to a solution of R,R-9
(S,S-9) in THF (Scheme 3) an immediate colour change from
deep red to intense orange occurs and 10, 10@ are formed
quantitatively.
2J(31P13C) of 41.8 and 11.0 Hz for the CH and CH carbons,
2
In the reaction solution, only two products are observed by
31P NMR in a ca. 28 : 1 ratio, showing each signal as a
doublet of doublets [major: d 31P 88.0, 1J(103Rh31P) \ 172.0
Hz, 79.0 1J(103Rh31P) \ 159 Hz; 91.7 1J(103Rh31P) \ 168 Hz,
81.4 1J(103Rh31P) \ 158 Hz]. The very similar chemical shifts
and coupling constants observed suggest the formation of two
structurally related isomers.
Recrystallisation from CH Cl Èn-hexane gave complex 10
Fig. 3 Schematic representation of 10 illustrating two- and multiple-
bond correlations.
2
2
in almost quantitative yield. The structure was determined by
Scheme 3 Synthesis of the allyl complex 10 and allylic alkylation giving 12aÈd.
86
New J. Chem., 2001, 25, 83È92

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Table 3 Selected bond lengths (A) and angles (¡) of 10
respectively. Indeed, the former value indicates a transoid
arrangement. Accordingly, the allyl C5H carbon is most prob-
ably located in an axial position trans to the P1a centre of the
Rh1ÈC4
Rh1ÈC5a
Rh1ÈC5
Rh1ÈP1a
Rh1ÈC16
Rh1ÈC4a
Rh1ÈP1
P1ÈC17
2.168(4)
2.203(5)
2.208(4)
2.278(2)
2.293(6)
2.295(4)
2.341(2)
1.823(5)
P1ÈC23
P1ÈC1
1.839(5)
1.889(4)
1.839(4)
1.843(5)
1.879(4)
1.437(6)
1.424(6)
metropp ligand. Consequently, the allyl C16H and the oleÐnic
P1aÈC17a
P1aÈC23a
P1aÈC1a
C4ÈC5
2
bond are equatorial. A retention of the chirality of the ligands
requires that the angle C5aÈRhÈP1 be larger than C4aÈRhÈP1.
This is indeed reÑected by the larger coupling constant values
[2J(31P13C) \ 21.8 Hz] for the C5aH carbon relative to the
C4aMe [2J(31P13C) \ 10.3 Hz].
C4aÈC5a
The NOE results are fully consistent with these results, the
oleÐnic H at C5a is close to both anti protons Ha of the allyl
moiety, whereas the syn proton Hs shows a short separation
to the ortho proton of the in-plane phenyl group attached to
the intact metroppph ligand. On the basis of the NMR data,
with the exception of phenyl ring Ñips (rather than rotations),
the solution structure can be assumed as being quite static,
showing no indication of the dynamic behaviour often
encountered in allyl and penta co-ordinated organometallic
chemistry.
C4ÈRh1ÈC5a
C4ÈRh1ÈC5
109.1(2)
C5ÈRh1ÈP1
88.9(1)
101.0(1)
122.0(1)
111.6(1)
102.0(2)
99.4(2)
100.3(2)
121.0(2)
122.7(1)
107.3(1)
100.2(2)
101.0(2)
103.8(2)
121.9(1)
119.1(2)
108.2(2)
38.3(2)
90.6(2)
123.2(1)
90.4(1)
159.8(1)
37.0(2)
86.5(2)
64.1(2)
95.9(1)
135.0(2)
36.8(2)
100.9(2)
91.9(1)
122.8(2)
90.1(1)
147.4(1)
P1aÈRh1ÈP1
C16ÈRh1ÈP1
C4aÈRh1ÈP1
C17ÈP1ÈC23
C17ÈP1ÈC1
C5aÈRh1ÈC5
C4ÈRh1ÈP1a
C5aÈRh1ÈP1a
C5ÈRh1ÈP1a
C4ÈRh1ÈC16
C5aÈRh1ÈC16
C5ÈRh1ÈC16
P1aÈRh1ÈC16
C4ÈRh1ÈC4a
C5aÈRh1ÈC4a
C5ÈRh1ÈC4a
P1aÈRh1ÈC4a
C16ÈRh1ÈC4a
C4ÈRh1ÈP1
C23ÈP1ÈC1
C17ÈP1ÈRh1
C23ÈP1ÈRh1
C1ÈP1ÈRh1
C17aÈP1aÈC23a
C17aÈP1aÈC1a
C23aÈP1aÈC1a
C17aÈP1aÈRh1
C23aÈP1aÈRh1
C1aÈP1aÈRh1
The allyl complexes 10,10@ do not react with water or
alcohol and resists treatment with diluted acetic acid.
However, when stronger acids like HO CCF , aqueous
2
3
HPF , or HBF are added, a clean re-protonation occurs and
6
4
the cationic complex 9 is reformed quantitatively.
C5aÈRh1ÈP1
Structure of [Rh(allyltroppph)(metroppph)] (10)
mode. An alternative possibility would have been a r(g1),p(g2)-
An ORTEP 3 plot of the structure of 10 is shown in Fig. 4.
Crystallographic details are given in Table 1, selected bond
lengths and angles are listed in Table 3. The rhodium centre
lies within a highly distorted co-ordination sphere, which we
describe here as trigonal pyramidal where P1a, C5 occupy the
axial positions (P1aÈRh1ÈC5 159.8¡) and the oleÐnic unit
C4a2C5a, P1, and C16 the equatorial positions.
The intersection of the plane deÐned by P1a, Rh1 and the
midpoint of the C4a2C5a unit and the P1ÈRh1ÈC4 plane,
gives an angle r of 78¡. The phosphorus rhodium distances
[RhÈP1 2.341(2); RhÈP1a 2.278(2) A] fall within the expected
range, while the oleÐnic [Rh1ÈC5a 2.203(5); Rh1ÈC4a 2.295(4)
A] and the allylic [Rh1ÈC5 2.208(4); Rh1ÈC4 2.164(4);
Rh1ÈC16 2.293(6) A] bond lengths are longer than usually
observed. Both the C2C and the allyl group are unsymmetri-
enyl mode in which the CH group is r-bonded and the C2C
2
unit p-bonded to the rhodium centre (see, however, ref. 15b).
Also, the sum of bond angles at C4 (360¡) when compared to
C4a (353.3¡) is in line with the g3-description of the allyl
group.
In summary, it can be concluded that the solution structure
of 10 and its solid state structure (vide infra) are very closely
related.
Synthesis of d10-rhodate complexes
The nucleophilic attack on co-ordinated allyl groups has been
widely studied, in particular for cationic 16-electron palladium
complexes, [Pd(C R )L ]`.16 Little is known about the corre-
3 5
2
sponding reaction of isoelectronic but neutral rhodium com-
plexes. In recent work, it was shown that rhodium complexes
cally bound to the rhodium centre (D
B 0.09 A). However,
RhhC
the almost equal CÈC bond lengths [C4ÈC5 1.437(6); C4ÈC16
1.421(6) A] within the allyl moiety, when compared to the cor-
responding distances in the intact metroppph ligand [C4aÈC5a
1.424(6); C4aÈC16a 1.513(7) A], clearly indicate the g3 binding
of the Wilkinson type prepared in situ from [RhCl(PPh ) ]
3 3
and P(OR) may have an interesting synthetic potential as
3
catalysts for allylic alkylation reactions.15 However, it was
proposed that p(g3)-allyl intermediates are not the reactive
species but rather a r(g1),p(g2)-enyl complex with a formal
oxidation state of ]III on the rhodium centre.15b
In this context, the reaction of the rhodium(]I) complex 10
with various nucleophiles LiR 11aÈd was particularly inter-
esting (Scheme 3). Note that 10 is within formal concepts an
electronically saturated 18-electron metal complex in which
the g3-coordination mode of the allyl moiety is clearly estab-
lished. In view of the vast literature available on the nucleo-
philic attack on 16-electron complexes, which are mostly
cationic, this reaction seemed not that evident with the neutral
18-electron complex 10. However, in all cases the nucleophile
attacks the CH terminus of the co-ordinated allyl moiety and
2
the d10-rhodate complexes 12aÈd are formed. The syntheses of
12a and 12c proceeded even at room temperature within less
than 5 min. The two complexes were isolated as highly
oxygen- and water-sensitive deep burgundy-red micro-
crystalline substances. The formation of the compounds 12b
and 12d is slow and these could only be characterised by
NMR spectroscopy in solution. Other nucleophiles like
amides, alcoholates, or thiolates did not react. During these
reactions, the formal valence electron count does not
changeÈall complexes are 18-electron speciesÈand the
formal oxidation state of the rhodium centre is diminished
Fig. 4 Molecular structure of 10. Hydrogen atoms are omitted for
clarity. Selected bond lengths and angles are given in Table 3.
New J. Chem., 2001, 25, 83È92
87

View Article Online
from ]I to [I. Consequently, the rhodate complex 12a could
also be prepared from the cationic d8-rhodium complex 9 by
two-electron reduction with elemental lithium, sodium or pot-
assium in THF. Unfortunately, we did not succeed in growing
crystals suitable for an X-ray analysis of one of these com-
pounds.
All complexes show fairly complex NMR spectra and as an
example, complex 12c was carefully investigated by various
techniques. For this molecule the solution structure can be
determined unambiguously as there is not a single atom
related to any other by symmetry. A complete assignment of
the 103Rh, 31P, 13C, and 1H resonances was possible on the
basis of 103RhÈ1H, 31PÈ1H and 13CÈ1H one- and multiple-
bond correlations in combination with 1HÈ1H TOCSY and
NOESY measurements. Subtle e†ects, such as chirality of the
ligand, phenyl ring orientations and pentyl side chain confor-
mations could all be determined. With respect to the former
two points, it turns out that: (i) both ligands in 12c have the
same absolute conÐguration and (ii) the phenyl ring orienta-
tions are as already discussed for 9. The interligand relation-
ship is interesting because it determines the structure around
the central rhodium atom. Starting from a tetrahedral situ-
ation (see A in Fig. 5), one expects to have the oleÐnic protons
close to each other and to the ortho protons of the adjacent
arene ring of the bis(benzo)cycloheptatriene. However, this is
clearly not the case as can be seen from Fig. 6. In fact, the
distances a between the oleÐnic proton on the pentyltroppph
1
ligand group and the methyl group and from the latter to the
oleÐnic proton of the metroppph ligand, a , seem to be quite
2
similar. A similar short triangulation, b , b , to the oleÐnic
1
2
proton and one arene proton of the opposing metroppph ligand
is seen for one of the diastereotopic methylene H of the CH
pentyl group directly linked to the central seven-membered
2
Fig. 6 Contour plots of sections from the 2D NOESY spectrum
ring. This indicates a situation (B) where the tetrahedron is
strongly distorted towards a square planar arrangement.
Indeed, the structure found for the Rh(]I) compound 9 Ðts
exceptionally well with the constraints of the NOE data.
In the 103Rh spectra of 12a, a triplet centered at d \ [344
is observed. Complex 12c shows a doublet of doublets at
d \ [325. Both chemical shifts fall within the same range as
the one found for the allyl complex 10 while 16-electron
rhodium tropp complexes like 9 show resonances shifted
about 500 ppm to higher frequencies.
(400.13 MHz, q \ 600 ms) recorded for 12c. The dotted box in the
mix
lower part shows two cross-peaks due to intra-ligand NOEs between
the two oleÐnic protons and adjacent ortho-protons of the benzohep-
tene moiety. Note that cross-peaks in the opposite corners of the box
stemming from the inter-ligand NOEs expected for a regular tetra-
hedral structure are absent. The dashed boxes in the upper part of the
spectrum show cross-peaks of similar intensity from each of the two
oleÐnic protons to the methyl and to one of the diastereotopic methy-
lene protons of the pentyl group. These observations are in agreement
with the distorted structure described in the text.
oxidation states.4 In particular, the redox potentials M`1/M0
and M0/M~1 are considerably lowered (up to 1 V) when com-
pared to reported systems.17 We expected that the highly
Electrochemical investigations and observation of the
d9-rhodium tropp complex
In previous work, we have shown that the troppph ligand sta-
bilises rhodium and iridium complexes in their formally low
tetrahedrally distorted cation d8-[Rh(metroppph) ]` in
9
2
would be reduced to the corresponding d9 and d10 valence
states at even lower potentials (vide supra). The cyclic
voltammogram of 9 in THF solution (1 ] 10~3 M) contain-
ing 0.25 mol n-Bu NPF as electrolyte at room temperature
4
6
is shown in Fig. 7. Using a scan rate of 100 mV s~1,
two almost reversible redox waves at [0.882 V (*E1
\
red@ox
82 mV) and [1.298 V (*E2
\ 85 mV) are recorded
red@ox
(potentials vs. Ag/AgCl; reference: ferrocene/ferrocenium).
The Ðrst wave corresponds to the redox couple
[Rh(metroppph) ]`(9)/[Rh(metroppph) ] (13), the second to the
2
2
couple 13/[Rh(metroppph) ]~(12a) (Scheme 4).
2
From the *E of the two redox processes, the formation con-
stant K of the reaction 9 ] 12a ¢ 2 13 was calculated to be
f
1.1 ] 107 at 298 K. Indeed, this reaction is the most conve-
nient way to prepare 13 (see Scheme 4). However, the
rhodium(0) complex 13 is not stable but decomposes cleanlyÈ
formally with loss of H Èat room temperature in about one
week, in 15 min at 70 ¡C, by a yet unclariÐed pathway to the
2
allyl complex 10.
Fig. 5 Schematic representation of two possible structures of 12c in
solution. (A) tetrahedral structure; (B) distorted planar structure
resembling closely the one of 9. The HH distances a , a , b , and b
Despite
the
strong
distortion
of
the
cation
[Rh(metroppph) ]` in 9, the Ðrst reduction to the neutral
2
1
2
1
2
are indicated by dotted lines.
complex 13 shifts only about 0.12 V to less negative potentials
88
New J. Chem., 2001, 25, 83È92

View Article Online
Unfortunately, the expected shift to less negative potentials
for the reduction of the d8-rhodium(]I) to d9-rhodium(0)
state is not observed. The latter complex, d9-[Rh(metroppph) ]
2
13, characterised by its deep green colour, is less stable com-
pared to the sterically less encumbered complex d9-
[Rh(troppph) ] and decomposes with formal loss of H to the
2
2
allyl complex [Rh(allyltroppph)(metroppph)] 10. This allyl
complex may be prepared more conveniently in almost quan-
titative yield from cation 9 and KOBut. Despite the electronic
saturation of 10 (18 valence electrons), nucleophilic attack by
lithium organyls, LiR, cleanly a†orded new anionic rhodate
complexes d10-[Rh(RCH2troppph)(metroppph)]~ 12aÈc in which
the R group has been incorporated into the former methyl
group of one metroppph ligand.
The structures of 9, 10 and 12c were determined in solution
by NMR techniques. All complexes are remarkably rigid;
even the phenyl groups seem to be locked into speciÐc confor-
mations. The solid state structures of cation 9 and of the allyl
complex 10 are fully conÐrmed in solution as well. Further-
more, it could be demonstrated that the anionic complex 12c
must have a structure in solution very close to the one of
cation 9, that is a structure deviating considerably from the
tetrahedral one that is expected for a tetra-co-ordinated d10-
metal centre. In summary, there is only relatively little struc-
tural change between 9, 10 and 12. This may explain some of
their properties, such as low redox potentials or facile nucleo-
philic attack on the allyl moiety, reactions by which the
formal oxidation state of the rhodium centre is changed.
Obviously the steric constraints imposed by the tropp-type
ligands make the complexes sterically rigid but the metal
centres electronically Ñexible.
Fig. 7 Cyclic voltammograms of 9 measured in THF (20 ¡C); scan
rate: 100 mV s~1; E vs. Ag/AgCl.
when compared to that of the sterically less encumbered
cation [Rh(troppph) ]`, which has
a square planar co-
2
ordination sphere.4a The second reduction appears at about
the same potential as that of this latter complex (only a slight
cathodic shift of about [0.08 V is observed). These experi-
ments clearly show that a distortion of about 40¡ is not suffi-
cient to cause a signiÐcant anodic shift of the reduction
potential in this type of rhodium complexes. Furthermore, the
electron-donating e†ect of the methyl group18 may partly
counterbalance the diminution of the Ðrst redox potential
induced by the geometric distortion.
Experimental
Conclusions
A high yield synthesis of a sterically demanding new tropyli-
dene phosphane, metroppph, was developed. This ligand
allowed the preparation of the tetra-co-ordinated cationic
rhodium complex 9, which is obtained as a racemic mixture of
the chiral R,R and S,S enantiomers exclusively. The cation 9
shows a deep red-violet colour in contrast to the bright red-
orange colour usually observed for tetra-co-ordinated cationic
d8-rhodium complexes. The co-ordination sphere deviates
strongly from planarity with r \ 42¡ being almost precisely
between a square plane (r \ 0¡) and a tetrahedron (r \ 90¡).
Comparable distorted structures were also determined for the
General methods
NMR spectra were taken on a Bruker DPX Avance Series
250È400 MHz. 1H- and 13C-chemical shifts are calibrated
against the solvent signal (CDCl : 1H-NMR: 7.27 ppm; 13C-
3
NMR: 77.23 ppm; CD Cl : 1H-NMR: 5.32 ppm; 13C-
2
2
NMR: 54.00 ppm; THF-d8: 1H-NMR: 3.58 ppm;
13C-NMR: 67.57 ppm). 31P chemical shifts are calibrated
against 85% H PO as external standard. 103Rh-NMR
3
4
spectra are referenced to N \ 3.16 MHz, where TMS appears
at exactly 100.000 000 MHz. 103RhÈ1H, 13CÈ1H correlations
were measured using standard HMQC and HMBC
(heteronuclear multiple bond coherence) methods, 31PÈ1H 2D
spectra using the COSY method with 1H detection, 1HÈ1H
TOCSY with MLEV 17 mixing and the 1HÈ1H NOESY with
a mixing time of 600 ms. All NMR spectra were measured at
ambient temperature. Cyclic voltammograms were acquired
with an EG&G potentiostat model 362. UV/Vis spectra were
neutral d9-[M(troppph) ] complexes (M \ Rh, Ir) and anionic
2
d10-[M(troppph) ]~ compounds, the parent cationic complex
2
d8-[M(troppph) ]` being planar.4
2
recorded on
a Perkin Elmer UV/Vis/NIR-spectrometer
Lambda 19 and mass spectra on a Finnigan MAT SSQ 7000
(EI: 70 eV). All chemicals were used as purchased from
Aldrich or Fluka, solvents were puriÐed and dried following
standard procedures. 10-Bromo-5H-dibenzo[a,d]cyclohepten-
5-one 2 was prepared following a literature procedure.9
Crystallographic analysis of 9 and 10
The data sets for the single-crystal X-ray studies were col-
lected on a Stoe Image Plate System (9) or a fully automated
Siemens-Stoe AED2 four-circle di†ractometer (10). All calcu-
lations were performed using the SHELXS-86 and SHELXS-
93 program suites. The speciÐc data for the crystals and
reÐnements are collected in Table 1.
Scheme
4
Disproportionation and decomposition of d9-
[Rh(metroppph) ] 13.
2
New J. Chem., 2001, 25, 83È92
89

View Article Online
CCDC reference number 440/204. See http://www.rsc./org/
suppdata/nj/b0/b002906h/ for crystallographic Ðles in .cif
format.
129.0, 128.8, 128.6, 128.55, 128.4, 128.35, 128.3, 128.2, 127.8,
127.6, 127.55, 127.5, 127.0, 126.7, 126.4, 125.3 (2CH ), 125.2
min
min
(2CH ), 123.3, 123.0, 67.4 (CHCl ), 61.1 (CHCl ), 25.0
maj
maj
(CH
), 24.3(CH
).
3 maj
3 min
Synthesis of compounds
5-Diphenylphosphanyl-10-methyl-5H-dibenzo[a,d]cyclo-
heptene (metroppph, 6). A solution of diphenylphosphane (1.85
g, 10 mmol) in dry toluene (50 ml) was slowly transferred via
syringe into a solution of 5 (2.4 g, 10 mmol) in dry toluene
(100 ml). A white precipitate formed immediately. After 2 h of
stirring, a carefully degassed 5% aqueous solution of sodium
carbonate was added, the organic layer separated, dried over
sodium sulfate and the solvent removed under reduced pres-
sure leaving crude 6. After recrystallisation from acetonitrile, 6
was obtained as colourless crystals (3.35 g, 86%). Mp: 127 ¡C.
MS m/z: 390 (M`, 42%), 205 (10-methyl-5H-dibenzo[a,d]
10-Bromo-5,5-ethylenedioxy-5H-dibenzo[a,d]cycloheptene
(3). To bromoketone 29 (14.2 g, 50 mmol) in benzene (250 ml),
ethylene glycol (50 ml) and para-toluenesulfonic acid (1.0 g)
were added and the resulting mixture was heated at reÑux for
3 days using a DeanÈStark apparatus. After cooling, tri-
ethylamine (10 ml) and then water (500 ml) were added. After
separation of the organic phase, the aqueous phase was
extracted three times with methylene chloride (100 ml). Drying
over sodium sulfate and removal of the solvent provided
crude 3 (16.3 g), which was subjected to sublimation at 150 ¡C
(0.05 mbar) to yield 15.9 g (97%) of colourless needles. Mp:
tropylium`, 100%). 31P-NMR (CDCl , 121.5 MHz):
3
d \ [11.7. 1H-NMR (CDCl , 300 MHz): d \ 7.48È7.42 (m, 1
3
H, CH ), 7.34È6.94 (m, 17 H, CH ), 7.14 (s, 1 H, 2CH), 4.80
ar
ar
172 ¡C (lit:10 172È173 ¡C). 1H-NMR (CDCl , 300 MHz):
[d, 2J(PH) \ 6.2 Hz, CHPR ], 2.51 (s, 3 H, CH ). 13C-NMR
3
2
3
d \ 8.03È7.97 (m, 1 H, CH ), 7.88È7.82 (m, 2 H, CH ), 7.73 (s,
(CDCl , 75.4 MHz): d \ 139.8 [d, J(CP) \ 8.2 Hz, C ],
ar
ar
3
q ar
1H, 2CH), 7.44È7.28 (m, 5 H, CH ), 4.27È4.15 (m, 2 H, CH
138.9 [d, J(CP) \ 8.8 Hz, C ], 138.5 [d, J(CP) \ 20.1 Hz,
ar
2
q ar
exo), 3.83È3.70 (m, 2 H, CH endo). 13C-NMR (CDCl , 75.4
C
Hz,
]), 138.1 [d, J(CP) \ 19.5 Hz, C ], 138.0 [d, J(CP) \ 5.2
2
3
q ar
q ar
MHz): d \ 139.3 (C ), 138.9 (C ), 133.7 (CH ), 132.7
q ar q ar ar
(C ), 132.3 (C ), 130.3 (CH ), 129.4 (CH ), 128.8 (CH ),
q ar q ar ar ar ar
128.2 (CH ), 127.9 (CH ), 127.7 (CH ), 124.7 (2CBr), 123.8
ar ar ar
(CH ), 106.0 (2CH), 65.0 (CH endo), 64.4 (CH exo).
ar
C
], 137.1 [d, J(CP) \ 4.6 Hz,
C
], 133.7 [d,
q ar
q ar
J(CP) \ 20.4 Hz, CH ], 133.4 [d, J(CP) \ 19.6 Hz, CH ],
ar
ar
130.4 [d, J(CP) 5.8 Hz, CH ], 129.7 [d, J(CP) \ 3.4 Hz,
ar
CH ], 129.2 [d, J(CP) \ 3.0 Hz, CH ], 129.0 [d, J(CP) \ 1.8
2
2
ar
ar
Hz, CH ], 128.3 (s, CH ), 128.2 (s, CH ), 127.8 [d,
ar
ar
ar
J(CP) \ 2.1 Hz, CH ], 127.8 [d, J(CP) \ 2.1 Hz, CH ], 127.7
10-Methyl-5H-dibenzo[a,d]cycloheptene-5-one (4). A solu-
tion of 3 (8.5 g, 26 mmol) in dry THF (150 ml) was slowly
dropped into a suspension of magnesium turnings (2.5 g, 100
mmol), activated with a small amount of iodine, in dry THF
(100 ml). After complete addition, the deep red solution was
held at 50 ¡C for 3 h. Excess magnesium was removed by Ðl-
tration and the Grignard solution was treated with methyl
iodide (3.1 ml, 7.1 g, 50 mmol). After overnight stirring, the
reaction mixture was evaporated to dryness. The residue was
taken up in THF (200 ml), Ðltered and diluted with 6 N
aqueous hydrochloric acid (100 ml). After heating at reÑux for
12 h the reaction mixture was neutralized with 20% sodium
hydroxide and extracted several times with ethyl acetate. The
combined organic phases were dried over sodium sulfate and
evaporated to yield the crude ketone 4. After distillation, the
product was obtained as a colourless oil, which crystallised
upon storage at room temperature (5.2 g, 91%). Analytical
data correspond to published data.10
ar
ar
[d, J(CP) \ 1.8 Hz, CH ], 127.3 (s, 2CH), 126.8 [d,
ar
J(CP) \ 1.0 Hz, CH ], 126.3 [d, J(CP) \ 1.3 Hz, CH ], 126.4
ar
ar
(s, 2CBr), 126.2 [d, J(CP) \ 1.5 Hz, CH ], 56.9 [d,
ar
1J(PC) \ 20.1 Hz, CHPR ], 25.0 (s, CH ).
2
3
[Rh(metroppph) ]PF (9). Phosphane 6 (850 mg, 2.25 mmol),
2
6
[Rh (l-Cl) (cod) ] 7 (247 mg, 0.5 mmol) and potassium hexa-
2
2
2
Ñuorophosphate (250 mg, 1.35 mmol) were mixed in dry ace-
tonitrile (40 ml) and then heated at reÑux for 20 min. An
immediate colour change from orange to deep red-violet was
observed. The solvent was evaporated and the residue re-
dissolved in methylene chloride (25 ml). After Ðltration, the
solution was layered carefully with toluene (50 ml) yielding
complex 9 as almost black crystals (889 mg, 86%). Single crys-
tals were obtained by storage of the reaction mixture over-
night at [24 ¡C. Selected physical data are given in Table 4.
[Rh(allyltroppph) (metroppph)] (10). Potassium tert-butoxide
(15 mg, 135 lmol), dissolved in THF (2 ml), was added to a
suspension of 9 (103 mg, 100 lmol) in THF (2 ml) providing a
clear orange solution of 10. A microcrystaline orange product
(85 mg, 95%) precipitated upon addition of hexane (10 ml).
Single crystals were grown by layering a methylene chloride
solution of 10 with hexane. Selected physical data are given in
Table 4.
5-Chloro-10-methyl-5H-dibenzo[a,d]cycloheptene (5). To a
vigorously stirred suspension of 4 (4.4 g, 20 mmol) in meth-
anol (200 ml), a solution of sodium borohydride (760 mg, 20
mmol) and potassium hydroxide (560 mg, 10 mmol) in water
(2 ml) was added at once. After 2 h of stirring, a clear solution
was obtained, which was evaporated to dryness. The residue
was partitioned between water and methylene chloride, the
organic phase separated, dried over sodium sulfate and con-
centrated. Addition of hexane precipitated the alcohol as
colourless crystals (4.30 g, 19.4 mmol, 97%). After Ðltration
and drying, the residue was taken up in dry toluene (50 ml)
and treated dropwise with freshly distilled thionyl chloride (4.0
ml, 6.08 g, 51 mmol) at 0 ¡C. After overnight stirring, the
solvent was removed in vacuo to yield a slightly brownish oil,
which crystallised upon layering with a small amount of
diethyl ether (5, 4.41 g, 91% from 4). Compound 5 is obtained
as a mixture of exo and endo isomers. Mp: 72 ¡C. MS m/z:
242 (M`, 5%), 240 (M`, 8%), 205 (10-methyl-5H-dibenzo[a,d]
[M(THF) ] [Rh(metroppph) ]
(12a) (M = Li, x = 4;
x
2
M = Na, K, x = 6). A small piece of an alkali metal (Li, Na or
K) was added to a suspension of 9 (70 mg, 68 lmol) in THF (2
ml). Upon stirring the colour changed from deep red-violet via
brown to deep green and then to dark red. The alkali metal
was removed by Ðltration and the solution layered with 5 ml
hexane. The product was isolated as a deep red microcrystal-
line powder (65 mg, 72%). Selected NMR data are given in
Table 4.
tropylium`,100%). 1H-NMR (CDCl , 300 MHz): d \ 6.24 (s,
[Li(THF) ] [Rh(metroppph)(RCH2troppph)] (R = H 12a, Me
3
4
1 H, CHCl ), 5.60 (s, 1 H, CHCl ), 2.59 (s, 1 H, CH
),
12b, n-Bu 12c or Ph 12d). General procedure for the prep-
maj
2.53 (s, 1 H, CH
3 min
min
3 maj
). 13C-NMR (CDCl , 75.4 MHz):
aration of 12a–d by allylic alkylation is given below. To a
solution of 10 (30 mg, 34 lmol) in THF (1 ml), 0.1 ml of a
3
d \ 138.1, 137.2, 137.1, 136.6, 134.9, 132.8, 131.5, 129.9, 129.5,
90
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91

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this value to our attention. Further distorted complexes: (b)
commercially available solution of the corresponding lithium
[RhCl(CO)(PBut ) ] has the structure of a Ñattened tetrahedron:
reagent (12a: 1 M LiBEt H in THF; 12b: 2.5 M MeLi in
3 2
3
PÈRhÈP 162¡, ClÈRhÈC: 150¡: H. Schumann, M. Heisler and J.
diethyl ether; 12c: 1.6 M n-BuLi in hexane; 12d: 2 M Li in
Pickardt, Chem. Ber., 1977, 110, 1020; (c) R. L. Harlow, S. A.
Westcott, D. L. Thorn and R. T. Baker, Inorg. Chem., 1992, 31,
323, and refs. cited therein; (d) Compare also distortion angles in
other bisphosphane-bisoleÐn complexes like [Rh(cod)(R,R-
MeÈBPE)]` (r \ 24¡), [Rh(cod)(R,R-MeÈDuPhos)]` (r \ 18¡):
M. J. Burk, J. E. Feaster, W. A. Nugent and R. L. Harlow, J. Am.
Chem. Soc., 1993, 115, 10125; (e) [Ir(cod)(R,R-MeÈDuPhos)]`
(r \ 18¡): B. F. M. Kimmich, E. Somsook and C. R. Landis, J.
Am. Chem. Soc., 1998, 120, 10115; ( f ) See also: A. Miedaner, R.
C. Haltiwanger and D. DuBois, Inorg. Chem., 1991, 30, 417.
G. N. Walker and A. R. Engle, J. Org. Chem., 1972, 37, 4294.
cyclohexaneÈdiethyl ether 70 : 30) was added. In all cases, a
colour change from orange to deep red occurred. Addition of
hexane provided deep red powders (yields ranging from 60%
to 76%), which were re-dissolved in THF-d for NMR experi-
8
ments. Selected NMR data are given in Table 4.
In the case of 12c a microcrystalline product was obtained
directly from the reaction mixture after a few minutes.
Acknowledgements
This work was supported by the Swiss National Science
Foundation. S. D. thanks the GottliebÈDaimler and CarlÈ
Benz Foundation for a grant.
9
10 K. C. Pich, R. Bishop, D. C. Craig and M. L. Scudder, Aust. J.
Chem., 1994, 47, 837.
11 For clarity, the orientation of the methyl groups in A, B and C is
not speciÐed in Scheme 2. A comparable mechanism has been
proposed for isomerisation reactions in zinc thiolates containing
a
Zn (l-N)(l-S) four-membered ring: H. Grutzmacher, M.
Notes and references
2
Steiner, H. Pritzkow, L. Zolnai, G. Huttner and A. Sebald, Chem.
1
Neutral mononuclear d9-rhodium and iridium carbonyls can
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12 J. Thomaier, PhD Dissertation, University of Freiburg, Freiburg,
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13 The Ðgures were produced with the facilities included in the
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14 A. G. Orpen, L. Brammer, F. H. Allen, O. Kennard, D. G.
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[Rh(CO) ]~: P. Chini and S. Martinengo, Inorg. Chim. Acta,
4
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4
Angoletta, Chem. Commun., 1970, 532; ( f ) [Rh(CO) (PPh ) ]~
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3 2
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3
Roper, J. Am. Chem. Soc., 1968, 90, 2282 and refs. cited therein;
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16 For recent review on transition-metal-catalysed allylic alkyl-
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2
3
4
d10-M Ñuorophosphine complexes (M \ Rh, Ir):
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3 3
Patmore, Inorg. Chem., 1971, 10, 2387 and refs. cited therein;
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2 4
2
Soc., Dalton T rans., 1973, 195.
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2
(a) [Rh(Ph PÈ(CH ) ÈPPh ) ]~ (n \ 2, 3): B. Bogdanovic, W.
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2 n
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Leitner, C. Six, U. Wilczok and K. Wittmann, Angew. Chem.,
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2
Longato, L. Riello, G. Bandoli and G. Pilloni, Inorg. Chem., 1999,
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(a) H. Schonberg, S. Boulmaaz, M. Worle, L. Liesum, A. Schwei-
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Organometallics, 1995, 14, 3418; (i) [Rh(P(OiPr ) ]`: G. Pilloni,
3 4
G. Zotti and S. Zecchin, J. Organomet. Chem., 1986, 317, 357; ( j)
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3 3
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S. Zecchin, G. Pilloni and M. Martelli, J. Organomet. Chem.,
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5
6
7
(a) S. Oishi, J. Mol. Catal., 1987, 39, 225; (b) E. Amouyal, in
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J. Thomaier, S. Boulmaaz, H. Schonberg, H. Ruegger, A. Currao,
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E. A. Halevi and R. Knorr, Angew. Chem., 1982, 94, 307; Angew.
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[Rh(cod) ]`: J. Orsini and W. E. Geiger, J. Electroanal. Chem.,
2
1995, 380, 83.
18 Compare, for example, [Fe(Cp) ]/[Fe(Cp) ]` *E
\ ]450
2
2
red@ox
\ [100 mV
mV and [Fe(Cp*) ]/[Fe(Cp*) ]` *E
2
2
red@ox
(Cp \ cyclopentadienyl; Cp* \ pentamethylcyclopentadienyl):
P. Zanello in Ferrocenes, eds. A. Togni and T. Hayashi, VCHÈ
Wiley, Weinheim, 1995, p. 317.
19 Simulation software for cyclic voltammograms, version 3.03: M.
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589, distributed by Bioanalytical Systems, Inc., West Lafayette,
IN 47906, USA.
8
The strongest deviation (49.7¡) was observed by: (a) V. Di Noto,
G. Valle, B. Zarli, B. Longato, G. Pilloni and B. Corain, Inorg.
Chim. Acta, 1995, 233, 165. We thank the authors for bringing
92
New J. Chem., 2001, 25, 83È92