Conformational behaviour of dinuclear Rh(I) complexes of the open-chain tetrapyrrolic ligand 2,2′-bidipyrrin (H2BDP)

Article abstract of DOI:10.1016/j.jorganchem.2005.05.024

The reaction of 2,2′-bidipyrrins H₂BDP with the Rh ^I complexes [Rh(COD)(μ-OMe)]₂ and [Rh(CO) ₂(μ-Cl)]₂ yields the neutral species [{Rh(COD)} ₂BDP] (7, 8) and [{Rh(CO)₂}₂

Full text of DOI:10.1016/j.jorganchem.2005.05.024

Journal of Organometallic Chemistry 690 (2005) 5290–5299
www.elsevier.com/locate/jorganchem
Conformational behaviour of dinuclear Rh(I) complexes
of the open-chain tetrapyrrolic ligand 2,20-bidipyrrin (H2BDP)
*
Martin Bro¨ring , Esther Consul Tejero
´
Fachbereich Chemie, Philipps-Universita¨t Marburg, Hans-Meerwein-Straße, 35032 Marburg, Germany
Received 7 February 2005; received in revised form 2 May 2005; accepted 2 May 2005
Available online 29 June 2005
Abstract
The reaction of 2,20-bidipyrrins H2BDP with the RhI complexes [Rh(COD)(l-OMe)]2 and [Rh(CO)2(l-Cl)]2 yields the neutral
species [{Rh(COD)}2BDP] (7, 8) and [{Rh(CO)2}2BDP] (2, 9), respectively. Treatment of the COD complexes with carbon monox-
ide results in the exchange of all COD ligands against CO. Ligand exchange studies on the carbonyl complexes 2 and 9 with different
phosphane donors reveal the regioselective exchange of one CO per metal ion. In most cases, the reaction is accompanied by a large
conformational change of the tetrapyrrole from a syn to an anti conformation. This conformational change was resolved by a
combination of NMR spectroscopy and X-ray diffraction studies.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Oligopyrroles; Conformational control; Rhodium
1. Introduction
or Rh(CO)(PR3)-fragment was employed in order to
obtain crystalline derivatives and therefore the struc-
tural proof for a new macrocycle [7]. Some important
examples are given in Scheme 1. Besides the rather large
number of macrocyclic compounds only one report
about rhodium complexes of open-chain tetrapyrroles
has been published so far [8]. This is surprising, since
structural information on open-chain oligopyrroles is
still rare, and, in addition, special reactivity schemes
of these complexes can be deduced from the redox prop-
erties of open-chain oligopyrroles and group 9 cations
[9].
Our first attempts to fill this gap made use of the
artificial open-chain tetrapyrrole 2,20-bidipyrrin
(H2BDP) [10] and produced the puzzling result, that
either mono- or dinuclear Rh(I) complexes 3 and 2
of the H2BDP ligand 1, or mononuclear Rh(III) com-
plexes 4 of a macrocycle related to the corrin are
formed, depending on the Rh(I) precursor used
(Scheme 2) [11]. From a simple sterical argument it
could be deduced, that dinuclear Rh(I) species are in
Rh(CO)2-fragments have been of frequent use in the
chemistry of oligopyrrolic macrocycles. They were first
introduced by Ogoshi in 1972, when the mechanism of
porphyrin metalation was in question [1]. So-called sit-
ting-atop (SAT) intermediates [2] were proposed to be
vital in this respect, and Ogoshiꢀs compounds were the
first structurally characterized species, for which this
particular feature was observed [3]. Later on rhodium(I)
complexes of especially porphyrin and corrole deriva-
tives were much studied with respect to the analogy with
vitamin B12 [4], the ability of anion sensing [5], and the
finding of CH-activation processes [6].
In more recent years, the complexation of non-
natural cyclic oligopyrroles with the planar Rh(CO)2-
*
Corresponding author.
E-mail address: martin.broering@chemie.uni-marburg.de
(M. Bro¨ring).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.05.024

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M. Bro¨ring, E. Consul Tejero / Journal of Organometallic Chemistry 690 (2005) 5290–5299
5291
N
L' N
H
N
L N
H
C6H5
C6F5
C6F5
C6H5
C6H5
N
H
Rh
Rh
CO OC
N
N
L
L
O
N
N
N
Rh
Rh
N
N
OC
CO
H
N
C6F5
C6H5
L = CO, L' = PPh3
L = CO
Scheme 1. Selected oligopyrrolic macrocycles characterized via Rh(CO)L derivatives.
N
N
N
N
[(CO) RhCl]
2
2
N
N
M
M
M
H
N
N
N
N
N
N
M
M = Rh(CO)
N
N
2
N
N
N
N
N
H
2
M
II
N
[(COD)RhCl]
N
H
N
H
2
N
N
H
M
III
I
N
N
N
N
Scheme 3. Prominent conformations of 2,20-bidipyrrin and metal
chelates.
1
M = Rh(COD)
3
2. Results and discussion
Cl
2.1. Crystallographic analysis of a H2BDP ligand
N
N
[(COE) RhCl]
2
2
Rh
N
N
The most prominent coordination modes found in
BDP complexes of four coordinate metal ions are the
distorted square I and the distorted tetrahedron II
(Scheme 3) [12]. The tetrapyrrolic ligand therefore
adopts either a conjugated pseudomacrocyclic syn con-
formation as in I or a non-conjugated conformation
with orthogonal dipyrrin subunits as in II. In contrast
to this, the ligand H2BDP itself usually resides in a
planar and conjugated anti conformation III. This was
deduced for the solution from 2D NMR experiments
[10b] and has now been proven for the solid state by
an X-ray diffraction study on the 3,30,4,40-tetraethyl-
8,80,9,90,10,100-hexamethyl-derivative 5 [10b].
Cl
H3C
4
Scheme 2. Visitor ligand-dependent metalation reactions of 2,20-
bidipyrrins.
a sterical dilemma, in that the visitor ligands of the
Rh(I) centres of each dipyrrin fragment are in close
contact with the methyl termini, and with the respec-
tive other metalated dipyrrin fragment of the complex.
Non-planar species residing in one of two limiting con-
formations, a pseudomacrocyclic syn conformation and
a stretched anti conformation (similar to I and III in
Scheme 3), can therefore be expected. Since the barrier
of interconversion between the syn and anti form is
presumably high, we expected an influence of the
respective conformation on the ability to form macro-
cycles like 4. This paper summarizes our results
on the conformational features of dinuclear Rh(I)
complexes of 2,20-bidipyrrin ligands.
Suitable crystals from 5 were obtained by slow evap-
oration from dichloromethane under argon. Complex 5
ꢀ
forms green cubes with a metallic luster, space group P1,
˚
˚
˚
a = 4.6919(6) A, b = 10.5834(13) A, c = 14.281(2) A,
a = 75.849(15)ꢁ, b = 83.730(16)ꢁ, c = 83.427(15)ꢁ, Z = 1.
Fig. 1 shows the molecular structure and Table 1 gives
selected bond lengths and distances. Complex 5 crystal-
lizes with two identical dipyrrin subunits. The most
prominent structural finding is the proof for the planar

´
M. Bro¨ring, E. Consul Tejero / Journal of Organometallic Chemistry 690 (2005) 5290–5299
5292
bered chelate rings. The alternative binding of metal
ions via a N2,N20-chelate, on the other hand, appears
to be conformationally disfavoured.
2.2. Metalation reactions of 1 and 6 with Rh(I)
precursors and crystallographic analysis of the neutral
[{Rh(CO)2}2BDP] complex 2
For the complexation studies the two known H2BDP
derivatives 1 and 6 were chosen [10b]. The octaethyl di-
methyl derivative 1 is sterically similar to 5 and serves as
the working horse in all of our bidipyrrin studies, while
the dipropyl tetraethyl dimethyl derivative 6 was intro-
duced as a ligand with reduced steric hindrance in the
anti conformation (Scheme 4). The preparation of
[{Rh(CO)2}2BDP]complexes of ligands 1 and 6 was suc-
cessfully carried out in two different ways, either starting
from [Rh(COD)(l-OMe)]2 and successive treatment of
the isolated COD complexes 7 and 8 with CO, or di-
rectly using [Rh(CO)2(l-Cl)]2 as the precursor (Scheme
4). The new compounds [{Rh(COD)}2BDP] (7 and 8)
as well as [{Rh(CO)2}2BDP] (2 and 9) were obtained
in 70–95% yield as dark green-brown crystals with a
metallic sheen and could be fully characterized by
NMR, IR and mass spectroscopy. By a temperature
dependent 1H NMR spectroscopic analysis we were able
to show, that all isolated complexes display a stable,
non-dynamic conformation in solution up to 80 ꢁC.
Additional attempts were undertaken in order to pre-
pare mononuclear Rh(I) complexes of 2,20-bidipyrrins
by the use of stoichiometric amounts of Rh(I) precur-
sors. These experiments were not successfull, and the de-
sired mononuclear species were obtained only as tlc
detectable short-lived constituents of mixtures. The high
propensity of all mononuclear species to undergo fast
hydrolytic cleavage prevented their isolation and spec-
troscopic characterization.
Fig. 1. Molecular structure of 3,30,4,40-tetraethyl-8,80,9,90,10,100-hexa-
methyl-2,20-bidipyrrin (5) (numbering scheme deviating from the
nomenclature).
Table 1
˚
Selected bond lengths (A) and bond angles (ꢁ) for 5, 2 (mean values)
and 18
Complex
5
2
18
˚
Bond lengths (A)
M–N1
M–N2
2.094(3)
2.078(3)
1.843(5)
1.859(4)
2.093(7)
2.100(6)
1.748(11)
M–CCO1
M–CCO2
M–P
2.280(3)
6.288
Mꢀ ꢀ ꢀM
3.1985
C2–N1
N1–C5
1.3312(18)
1.398(2)
1.378(2)
1.341(5)
1.403(4)
1.372(5)
1.402(5)
1.383(4)
1.365(4)
1.459(5)
1.348(10)
1.427(10)
1.367(11)
1.386(10)
1.412(9)
1.372(8)
1.436(13)
C5–C6
C6–C7
1.4062(19)
1.3784(18)
1.3592(16)
1.441(3)
C7–N2
N2–C10
C10–C100
Bond angles (ꢁ)
N1–M–N2
87.86(11)
94.35(15)
171.14(15)
84.7(3)
88.4(5)
N1–M–CCO
N1–M–CCO
N1–M–P
1
2
168.9(2)
172.9(5)
N2–M–CCO1
N2–M–CCO
N2–M–P
176.61(17)
92.42(14)
2
Also unsuccessfull were attempts to transform the
dinuclear Rh(I) complexes 2, 7, 8 and 9 into pseudomac-
rocyclic mononuclear Rh(III) species by means of iodine
oxidation or photooxidation with CCl4 [14]. These pro-
cedures represent standard protocols in porphyrinoid
rhodium chemistry, but lead to decomposed material
only when applied to bidipyrrin chemistry.
98.6(2)
87.9(4)
CCO1–M–CCO
CCO1–M–P
2
85.05(17)
Torsion angles (ꢁ)
N2–C10–C100–N20
C2–C10–C100–C20
P–Cx–Cx0–P0
180.00
180.00
47.31
17.98
57.59
64.89
67.07
Single crystals of the carbonyl complex 2 were ob-
tained from dichloromethane by slow evaporation under
argon. 2 forms a dichloromethane solvate as dark blue-
green cubes with a metallic luster, space group P21/c,
and stretched anti conformation of free base 2,20-bidi-
pyrrins in the solid state. A similar conformation was re-
ported earlier for a related hexapyrrole [13]. The linear
conformation is apparently not capable of binding metal
ions in the classical fashion due to the fact, that both
chelating NHꢀ ꢀ ꢀN units are blocked by one of the ethyl
substituents (on C9, C90) of the opposite dipyrrin sub-
unit. Deprotonated H2BDPs will therefore act as two-
compartment ligands for monocationic metal complex
fragments, yielding dinuclear complexes with six-mem-
˚
˚
˚
a = 12.1400(9) A, b = 39.025(4) A, c = 9.1365(7) A,
b = 104.915(9)ꢁ, Z = 4. Fig. 2 shows the molecular struc-
ture and Table 1 gives selected bond lengths and dis-
tances. Due to the presence of one molecule of
dichloromethane per formula, the two [Rh(CO)2dipyr-
rin] fragments of 2 differ slightly in their molecular struc-
ture. Mean values for bond lengths and bond angles are
therefore used in the discussion.

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M. Bro¨ring, E. Consul Tejero / Journal of Organometallic Chemistry 690 (2005) 5290–5299
5293
R
R
R'
R'
N
N
M
M
N
N
[(COD)Rh(OMe)]
2
7
Et
8
H
M = Rh(COD)
CO
R
R
R
R'
R'
R' Et nPr
N
H
N
H
N
N
[(CO) RhCl]
2
2
R
R
R'
R'
1
6
R
Et
H
N
N
R' Et nPr
M
M
N
N
2
Et
9
H
M = Rh(CO)
2
R
R' Et nPr
Scheme 4. Preparation of dinuclear carbonyl and COD complexes.
The syn conformation of complex 2 is achieved in the
way, that both metalated dipyrrin subunits are bent in a
contra-rotating wing-like fashion, so that the torsion an-
gle at the central bipyrrole N2–C10–C100–N20 is as high
as 47.31ꢁ, but the torsion angle C2–C10–C100–C20,
which describes the overall tilt much better, is as low
as 17.98ꢁ. In this arrangement the Rh(CO)2 fragments
of 2 organize above and below the mean tetrapyrrole
plane and escape most of the steric encumbrance of
the constrained centre of the molecule.
The special geometry of complex 2 causes a short
˚
Rhꢀ ꢀ ꢀRh contact of 3.1985 A, posing the question,
whether an attractive metal–metal interaction between
the rhodium atoms directs the syn conformation ener-
getically. Theoretical work done on related square
planar d8 systems suggest, that attractive metal metal
interactions can be found only for ML4 fragments
eclipsed towards each other [15]. For 2 a mean torsion
angle L–Rh–Rh0–L0 of ca. 65ꢁ is found, pointing
against an attractive interaction in this case. The same
conclusion can be drawn from the finding of only two
IR absorptions for the Rh(CO)2 fragments of 2
at 2060 and 1996 cmꢁ1. Within the scenario of a
Rh–Rh bond a strongly coupled system of all four
CO stretches should be expected. For these reasons
we believe, that the observation of the syn conforma-
tion of 2 is solely based on sterical interactions be-
tween the different ligands and does not indicate any
attractive dispersion interaction between the two metal
centres.
Fig. 2. Molecular structure of [{Rh(CO)2}2BDP] (2) (numbering
scheme deviating from the nomenclature).
The rhodium(I) ion is unsymmetrically coordinated
˚
by two nitrogen donors at 2.078 and 2.094 A, and by
˚
two carbonyl ligands at 1.843 and 1.859 A, respectively.
These values and the angles at Rh, which generally devi-
ate less than 5ꢁ from the ideal 90ꢁ, fit well into the expec-
tations for porphyrinoid rhodium(I) complexes and
therefore bear no surprise. The same is true for the
C–C and C–N bond lengths within the tetrapyrrole
ligand backbone of 2, which displays the same pattern
with the central pyrrole type C4N rings and the terminal
pyrrolenin substructures as was seen for the free base 5.

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M. Bro¨ring, E. Consul Tejero / Journal of Organometallic Chemistry 690 (2005) 5290–5299
5294
2.3. Ligand exchange reactions with phosphane donors
In contrast to the monophosphanes, the reactions of
the CO complexes 2 and 9 with stoichiometric amounts
of the diphosphanes dppm and dppe proceed very
slowly in all cases. Of the four new compounds 15, 16,
17 and 18, only 15 and 18 could be isolated and fully
characterized. The complexes 16 and 17 were character-
ized as mixtures with the respective starting material 9
or 2 by 1H and 31P NMR. All ligand exchange reactions
are summarized in Scheme 5.
Ligand exchange reactions were carried out for the
four CO and COD complexes 2, 7, 8 and 9 with mono-
phosphanes PR3 of different size (R = Ph, Me, i-Pr) as
well as with diphosphanes Ph2P–(CH2)n–PPh2 (n = 1,
2). All attempts with the COD complexes 7 and 8 failed
due to immediate demetalation. The same was observed,
if a large excess of phosphane was reacted with the CO
complexes 2 and 9. Additionally, the reactions of mono-
phosphanes with the di-n-propyl derivative 9 yielded
very impure products and will therefore not be discussed
further.
Single crystals suitable for X-ray diffraction were ob-
tained from compound 18 by slow diffusion of pentane
into a dichloromethane solution at ꢁ30 ꢁC 18 forms
˚
brown blocks, space group I2/a, a = 23.186(3) A,
˚
˚
The treatment of [{Rh(CO)2}2BDP] (2) with 2 equiv
of PPh3 at elevated temperature resulted in a single
product 10, in which one of the two CO ligands of each
Rh(CO)2 fragment is stereoselectively exchanged. The
action of the more reactive alkyl phosphanes PR3
(R = Me, i-Pr) on 2 was found to proceed with dimin-
ished selectivity even at 0 ꢁC. In both cases mixtures
of products with one and two exchanged CO ligands,
[{Rh(CO)(PR3)}{Rh(CO)2}BDP] (11) (R = Me) or (13)
(R = i-Pr) and [{Rh(CO)(PR3)}2BDP] (12) (R = Me)
or (14) (R = i-Pr) were obtained in addition to decom-
posed material. Using 1 or 2 equiv of phosphane allows
to enrich the mixtures with either the non-symmetric
complexes 11 and 13 or the symmetric species 12 and
b = 10.2310(8) A, c = 25.752(3) A, b = 111.955(14)ꢁ,
Z = 4. Fig. 3 presents two different views of the molecu-
lar structure and Table 1 gives selected bond lengths and
distances.
The rhodium atoms in 18 are unsymmetrically sur-
˚
rounded with one CO ligand at 1.748 A, two N donors
˚
at 2.093 (N1) and 2.100 A (N2), and one P donor at
˚
2.280 A. While these bond lengths and the found angles
are within the limits of normal Rh(I) complexes, the
fact, that the P donor in 18 has replaced the inner CO
of 9, and therefore now occupies the sterically more
unfavourable position, was not expected.
The bond lengths pattern of the tetrapyrrole ligand
backbone of 18 differs remarkably from those found
for 2 or 5. Other than in these cases, the C4N rings of
18 appear electronically reorganized in the way, that
1
14, so that a H and 31P NMR spectroscopic character-
ization became possible.
N
N
N
N
PR
3
ML
M
ML'
M
N
N
N
N
M = Rh(CO)
2
10
PPh
L' PPh
11
PMe
CO
12
PMe
PMe
13
PiPr
CO
14
PiPr
PiPr
L
3
3
3
3
3
3
3
3
R
R
N
R
R
R'
R'
R'
R'
N
N
N
Ph P-R''-PPh
2
2
M
M
M
M
N
N
N
N
P
P
R''
2
9
R
Et
H
M = Rh(CO)
M = Rh(CO)
2
R' Et nPr
15
16
17
18
R
Et
H
nPr
Et
Et
H
nPr
R' Et
R'' CH
CH (CH ) (CH )
2
2
2 2
2 2
Scheme 5. Overview of ligand exchange reactions of this study.

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M. Bro¨ring, E. Consul Tejero / Journal of Organometallic Chemistry 690 (2005) 5290–5299
5295
Fig. 3. Molecular structure of [{Rh(CO)}2(l-dppe)BDP] (18). Left side: view along the bipyrrole axis C10–C100; right side: view along the
crystallographic b-axis (numbering scheme deviating from the nomenclature).
the former differences between the pyrrole type and the
pyrrolenine type substructure are mainly evened out.
The most prominent detail of the molecular structure
of 18 ist the anti conformation, in which the bidipyrrin
ligand binds to the rhodium ions. This conformation is
again achieved by a wing-like distortion of both metal-
lodipyrrin subunits. In contrast to 2, however, the two
subunits of 18 are distorted in a con-rotating way,
resulting in similar torsion angles N2–C10–C100–N20
and C2–C10–C100–C20 of 57.59ꢁ and 64.89ꢁ, respec-
tively. In order to allow the bridging diphosphane to
bind in an intramolecular fashion, both Rh(CO)P frag-
ments are situated at the same side of the tetrapyrrole.
positions 3 and 30 most significantly. The latter should
be particularly true for all complexes derived from li-
gand 1, in which diastereotopic splittings DdA,B of differ-
ing strengths should be observed for the proton
resonances of the methylene groups at C3, C30. Table
2 summarizes all relevant NMR parameters of the com-
plexes described herein.
Table 2 shows that the agreement between the diaste-
reotopic splitting of the 3,30-situated methylene protons
DdA,B and the tetrapyrrole conformation is particularly
convincing. Apparently, only those complexes bearing
the smallest ligands, i.e., CO and PMe3, as well as the
half substituted species 13 are capable to take the syn
conformation, while all other compounds prefer the
stretched anti conformation. The analysis of further
data, however, is not so straightforward, and conclu-
sions could not be drawn. The privileged low-field posi-
tion of the dCH3 term values of all PMe3 containing
complexes, however, seems to indicate, that PMe3 occu-
pies the outer position close to the methyl termini, while
all other P donor ligands are bound to the inner posi-
tion. For a detailed analysis of the latter point further
reference material will be necessary.
˚
As a result, the Rhꢀ ꢀ ꢀRh distance of 6.288 A is rather
large.
1
2.4. H NMR analyses of ligand field geometries and
molecular conformations
The peripheral alkyl substituents of the BDP com-
plexes described in this work can in principle be used
as spectroscopic probes in order to analyse the geometry
of the ligand sphere, i.e., the site, to which the phos-
phane ligand binds, and the conformation of the tetra-
pyrrole. Two molecular positions can be of importance
in this regard (Scheme 6).
The site of ligand substitution is presumably best re-
flected by the shift of the signal of the protons of the
nearby methyl termini, while a tetrapyrrole conforma-
tional change should influence the substituents at the
The question remains, how the conformational
change from one stable conformation to the other oc-
curs during ligand exchange. We believe, that this pro-
cess is initiated by the association of the second donor
to the second rhodium centre, and that the dynamic
rearrangement of the coordination sphere of the metal
is directly coupled to the conformational dynamic of
terminal CH group
3
sensitive for ligand field geometry
L
N
M
L
N
N
L
M
C3 substituent
N
L
sensitive for tetrapyrrole conformation
Scheme 6. Schematic view on efficient spectroscopic probes for coordination geometry and tetrapyrrole conformation.

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M. Bro¨ring, E. Consul Tejero / Journal of Organometallic Chemistry 690 (2005) 5290–5299
5296
Table 2
Selected 1H NMR data for the complexes of this work (see text)
techniques and vacuum-line methods. Solvents were
dried and distilled under nitrogen prior to use. Column
chromatography was carried out under nitrogen using
either silica gel (particle size 0.063–0.200 nm) or alumina
(neutral) as stationary phase. Most chemicals were used
directly without prior purification.
Compound
dCH3 term
dH-3 DdA,B
[{Rh(CO)2}2BDP] (2)
[{Rh(COD)}2BDP] (7)
2.73
2.36
–
0.16
2.57
1.43
ca. 0.10
0.09
ca. 0.15
1.56
2.09
2.95
–
–
[{Rh(CO)(PPh3)}2BDP] (10)
[{Rh(CO)(PMe3)}{Rh(CO)2}BDP] (11)
[{Rh(CO)(PMe3)}2BDP] (12)
2.27
3.12/3.10
3.28
–
–
–
3.2. Crystal structure determination
[{Rh(CO)(Pi-Pr3)}{Rh(CO)2}BDP] (13) 2.48/2.37
–
[{Rh(CO)(Pi-Pr3)}2BDP] (14)
[{Rh(CO)}2(l-dppm)BDP] ((15)
[{Rh(CO)}2(l-dppe)BDP] (17)
[{Rh(CO)2}2BDP] (9)
2.43
2.58
2.56
2.95
2.77
2.50
2.42
–
–
Data of 2, 5 and 18 were collected at ꢁ90 ꢁC on an
IPDS-I diffractometer using monochromated Mo Ka
radiation. Data were corrected for Lorenz polarization
effects and for absorption. The structures were solved
by direct methods (5) or by the Patterson method (2,
18), using SHELXS [16], and refined by full-matrix least-
squares techniques against F2 (SHELXL) [17]. The hydro-
gen atoms of the structures were included at calculated
positions with fixed thermal parameters. All non-hydro-
gen atoms were refined anisotropically. Crystal data and
other experimental procedures and refinement parame-
ters are given in Table 3. Crystallographic data (exclud-
ing structure factors) for the structures reported in this
paper have been deposited with Cambridge Crystallo-
graphic Data Centre as supplementary material publica-
tion nos. CCDC-262833 (2), CCDC-262835 (5) and
CCDC-262834 (18). Copies of the data can be obtained
free of charge on application to CCDC, 12 Union Road,
Cambridge CB21EZ, UK [fax: (internal) +44 1223 336
033; e-mail: deposit@ccdc.cam.ac.uk].
–
6.89
6.70
6.95
7.36
[{Rh(COD)}2BDP] (8)
[{Rh(CO)}2(l-dppm)BDP] (16)
[{Rh(CO)}2(l-dppe)BDP] (18)
–
–
–
the tetrapyrrole. In other words this means, that the
sterical condition of the (unknown) transition state is
responsible for the respective conformation and the
positionally selective product formation. Theoretical
work will be necessary to further elucidate this point.
From this study, however, it becomes apparent, why
dinuclear Rh(I) BDP complexes, other then the porphy-
rins, decay under oxidising conditions and do not form
mononuclear Rh(III) compounds. In dinuclear Rh(I)
porphyrins the strained and non-planar macrocycle
has a strong tendency to planarize, and therefore to tear
one of the metal ions inside the N4 cavity, with concom-
itant loss of the other ion. In dinuclear BDP complexes
this strain is directed outwards, so that the ligand es-
capes into a stretched conformation as soon as the metal
ions start to react. The formation of a pseudomacrocy-
clic Rh(III) complex is therefore rather improbable. In
order to explain the observation, that under particular
conditions a macrocyclic Rh(III) complex 4 is formed
from a H2BDP ligand and a Rh(I) source, we assume,
that a metal template directed ligand centered oxidation
process and ring closure reaction must occur prior to the
oxidation of the metal ion. This hypothesis is currently
under investigation.
3.3. Syntheses of complexes
3.3.1. Metalation of H2BDP ligands with Rh(I) – general
procedure
A THF solution (15 ml) of H2BDP (1 or 6) (0.6
mmol) is treated with the rhodium precursor
[Rh(CO)2Cl]2 or [Rh(COD)(OMe)]2 (0.61 mmol) and
stirred at ambient temperature. After 20 h all volatiles
are removed in vacuo, and the residue is washed repeat-
edly with small aliquots of ice-cold methanol. After dry-
ing in vacuo the products are obtained as dark to olive
green powders.
3. Experimental
3.3.1.1. [{Rh(CO)2}2BDP] (2). Yield: 95%. Anal.
Calc. for C40H48N4O4Rh2: C, 56.21; H, 5.66; N, 6.55.
1
Found: C, 56.33; H, 5.62; N, 6.29%. H NMR (C6D6,
3.1. General details
NMR spectra (1H, 13C, 31P) were recorded in C6D6 at
ambient temperature on the following spectrometer
(Bruker): ARX 300, ARX 200, and DRX 400. Chemical
shifts are given in ppm relative to the residual proton res-
onance of the solvent. Mass spectra (MALDI-TOF) were
recorded on a Bruker Biflex IV, using trans-3,5-dime-
thoxy-4-hydroxycinnamic acid as matrix. HRMS analy-
ses were obtained using ESI-MS on a QStarPulsar i.
All reactions were performed in an inert atmosphere
of either nitrogen or argon by using standard Schlenk
295 K): 7.22 (s, 2H), 2.98 (m, 2H), 2.82 (m, 2H), 2.73
(s, 6H), 2.69 (q, 4H), 2.44 (q, 4H), 2.21 (m, 4H), 1.21,
1.09, 1.05, 0.95 (4 · t, 24H). 13C NMR (C6D6, 295 K):
186.5 (d, JRhC = 65 Hz), 182.1 (d, JRhC = 67 Hz),
163.3, 152.1, 145.2, 142.2, 134.7, 132.4, 131.6, 131.3,
121.1, 18.7, 18.6, 17.6, 17.5, 16.5, 16.3, 14.5, 14.1. IR
(KBr): m (cmꢁ1) = 2056, 1992. MS (MALDI): 854 (M+).
3.3.1.2. [{Rh(COD)}2BDP] (7). Yield: 71%. HRMS
calc. for C52H72N4Rh2: 958.38667. Obs.: 958.38693;

´
M. Bro¨ring, E. Consul Tejero / Journal of Organometallic Chemistry 690 (2005) 5290–5299
5297
Table 3
Crystal data, collection and refinement details for 2, 5 and 18
Complex
2
5
18
Empirical formula
Formula weight
Crystal system
C32H42N4
482.70
Triclinic
C41H50Cl2N4O4Rh2
939.57
C62H68N4O2P2Rh2
1168.96
Monoclinic
P21/c
Monoclinic
I2/a
ꢀ
Space group
Unit cell dimensions
P1
˚
a (A)
4.6919(6)
10.5834(13)
12.1400(9)
39.025(4)
9.1365(7)
23.186(3)
10.2310(8)
25.752(3)
˚
b (A)
˚
c (A)
14.281(2)
75.849(15)
a (ꢁ)
b (ꢁ)
c (ꢁ)
83.730(16)
83.427(15)
680.68(15)
104.915(9)
111.955(14)
3
˚
V (A )
4182.7(6)
4
1.492
5665.7(11)
4
1.370
Z
1
1.178
Dcalc (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
)
0.069
262
0.961
1920
0.685
2416
h Range (ꢁ)
2.18–25.33
6405
1.74–26.08
32294
2.17–25.35
22341
4967
Reflections collected
Independant reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
2335
2335/0/172
8052
8052/0/488
4967/0/330
0.874
1.033
R1 = 0.0396, wR2 = 0.1072
R1 = 0.0504, wR2 = 0.1122
0.988
R1 = 0.0447, wR2 = 0.1129
R1 = 0.0548, wR2 = 0.1190
R1 = 0.0661, wR2 = 0.1545
R1 = 0.1224, wR2 = 0.1770
1
D = 0.26 mmu. H NMR (C6D6, 293 K): 7.31 (s, 2H),
5.79 (m, 2H), 4.96–3.85 (m, 8H), 3.22 (m, 2H), 3.04–
1.83 (m, 28H), 2.36 (s, 6H), 1.42, 1.28, 1.22, 1.17
(4 · t, 24H). 13C NMR (C6D6, 293 K): 160.9, 151.4,
143.3, 141.2, 136.4, 135.6, 133.4, 131.4, 123.8, 80.3
(2 · d, JRh–C = 9 Hz), 79.2 (d, JRh–C = 12 Hz), 75.7 (d,
JRh–C = 11 Hz), 31.7, 31.0, 29.9, 29.5, 20.4, 18.3, 18.1,
17.8, 17.4, 17.3, 16.3, 15.2, 14.7. MS (MALDI): 958
(M+).
(KBr): m (cmꢁ1) = 2054.3, 1998.5. MS (MALDI): 826
(M+).
3.3.2. Ligand exchange reactions – general procedure
A solution of the carbonyl complex 2 or 9 (0.1 mmol)
in dichloromethane (10 ml) is cooled in an ice bath and
treated with 1 or 2 equiv of the respective phosphane or
diphosphane. The solution is stirred for 3 h at reflux (for
10), for 12 h at ambient temperature (for all diphos-
phane complexes), or for 30 min at 0 ꢁC (for all alkyl
phosphanes). After this time the solvent is removed in
vacuo and the residue is washed repeatedly with ice cold
pentane to leave the product as a green-to-brownish
solid.
3.3.1.3. [{Rh(COD)}2BDP] (8). Yield: 85%. HRMS
calc. for C50H68N4Rh2: 930.35537. Obs.: 930.35505;
D = ꢁ0.32 mmu. 1H NMR (C6D6, 300 K): 7.31 (s,
2H), 6.70 (s, 2H), 4.97–3.62 (m, 8H), 2.90–1.77 (m,
16H), 2.77 (s, 6H), 2.70 (q, 4H), 2.66 (q, 4H), 2.42 (m,
4H), 1.69 (m, 4H), 1.26 (t, 6H), 1.13 (t, 6H), 0.94 (t,
6H). 13C NMR (C6D6, 300 K): 160.0, 153.3, 144.0,
143.6, 138.7, 137.2, 131.7, 123.5, 118.65, 82.2 (d,
3.3.2.1. [{Rh(CO)(PPh3)}2BDP] (10). Yield: 90%.
HRMS calc. for C74H78N4O2P2Rh2: 1322.37098. Obs.:
1
1322.37159; D = 0.61 mmu. H NMR (C6D6, 293 K):
1JRhC = 15 Hz), 80.3 (2 · d, JRhC = 15 Hz), 73.9 (d,
8.11 (m, 12H), 7.48 (m, 6H), 7.39 (s, 2H), 7.36 (m,
12H), 4.85 (m, 2H), 3.42 (m, 2H), 3.15 (m, 4H), 2.73
(q, 4H), 2.42 (m, 4H), 2.27 (s, 6H), 1.73, 1.63, 1.39,
1.14 (4 · t, 24H). 13C NMR (C6D6, 293 K): 189.0 (dd,
JRh–C = 69 Hz, JP–C = 24 Hz), 159.7, 156.9, 143.6,
142.0, 135.3, 134.3, 133.5, 132.4, 132.3, 131.5, 129.4,
128.3, 123.1, 20.5, 18.7, 18.5, 18.4, 18.2, 17.4, 17.3,
16.6, 14.9. 31P NMR (C6D6, 293 K): 45.20 (d,
JRh-P = 164 Hz). IR (CH2Cl2): m (cmꢁ1) = 1978. MS
(MALDI): 1322 (M+).
1
1JRhC = 13 Hz), 29.7, 29.0, 24.7,18.9, 18.8, 18.0, 17.4,
15.8, 14.2. MS (MALDI): 930 (M+).
3.3.1.4. [{Rh(CO2)}2BDP] (9). Yield: 87%. HRMS
calc. for C38H44N4O4Rh2: 826.14724. Obs.: 826.14727;
1
D = 0.03 mmu. H NMR (C6D6, 300 K): 7.25 (s, 2H),
6.89 (s, 2H), 2.95 (s, 6H), 2.67 (m, 4H), 2.50 (q, 4H),
2.24 (m, 4H), 1.67 (q, 4H),1.10 (m, 6H), 0.99 (t, 6H),
0.92 (t, 6H). 13C NMR (C6D6, 300 K): 188.7 (d,
1JRhC = 66 Hz, CO), 184.4 (d, JRhC = 66 Hz, CO),
163.2, 154.1, 145.7, 144.9, 136.6, 136.4, 132.1, 121.4,
118.5, 28.9, 24.8, 19.5, 18.7, 18.6,17.4, 15.3, 14.0. IR
1
3.3.2.2. [{Rh(CO)(PMe3)}{Rh(CO)2}BDP] (11). 1H
NMR (C6D6, 300 K): 7.34, 7.18 (2 · s, 2H), 3.12, 3.10

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M. Bro¨ring, E. Consul Tejero / Journal of Organometallic Chemistry 690 (2005) 5290–5299
5298
(2 · s, 6H), 2.79 (m, 4H), 2.72 (m, 4H), 2.56 (m, 4H), 2.29
(m, 4H), 1.27 (m, 3H), 1.26 (m, 3H), 1.20 (t, 3H), 1.16 (t,
3H), 1.13 (t, 3H), 1.06 (t, 3H), 1.02 (m, 3H), 1.01 (m,
3H), 0.52 (m, 9H). 31P NMR (C6D6, 300 K): ꢁ1.42 (d,
1JRhP = 155 Hz).
(m, 4H), 2.01 (br.s, 2H), 1.50 (br.s, 2H), 1.19, 1.18,
1.04, 1.02 (4 · t, 24H). The signals for two of the ethyl
methylene groups could not be assigned. 31P NMR
(C6D6, 300 K): 39.0 (dvt, 1NPRh = 161.3 Hz,
4
5
3NPP = 59.8 Hz, NPRh = ꢁ0.35 Hz, NRhRh = 0.0 Hz,
AA0XX0).
3.3.2.3. [{Rh(CO)(PMe3)}2BDP] (12). 1H NMR
(C6D6, 300 K): 7.24 (s, 2H), 3.28 (s, 6H), 2.85 (m,
4H), 2.75 (m, 2H), 2.66 (m, 2H) 2.61 (m, 4H), 2.35 (m,
4H), 1.33, 1.28, 1.16, 1.06 (4 · t, 24H), 0.50 (m, 18H).
3.3.2.9. [{Rh(CO)}2(l-dppe)BDP] (18). HRMS calc.
for C62H68N4O2P2Rh2: 1168.29273. Obs.: 1168.29251;
D = ꢁ0.22 mmu. 1H NMR (C6D6, 300 K): 7.93 (s,
2H), 7.87 (m, 4H), 7.63 (m, 4H), 7.36 (s, 2H), 7.08 (m,
4H), 7.01 (m, 2H), 6.79 (m, 2H), 6.69 (m, 4H), 2.79 (m,
4H), 2.60 (m, 4H), 2.42 (s, 6H), 2.26 (m, 4H), 2.06
(br.s, 2H), 1.58 (m, 4H), 1.44 (br.s, 2H), 1.21, 0.97,
0.81 (3 · t, 18H). 13C NMR (C6D6, 300 K): 191.4 (dd,
1
31P NMR (C6D6, 300 K): ꢁ3.6 (d, JRhP = 158 Hz).
3.3.2.4. [{Rh(CO)(Pi-Pr3)}{Rh(CO)2}BDP] (13). 1H
NMR (C6D6, 300 K): 7.21, 7.09 (2 · s, 2H), 4.08
(m, 2H), 3.93 (m, 2H), 2.48, 2.37 (2 · s, 6H), 0.56 (m,
6H). Further signals between 3.1 and 0.7 ppm could not
be assigned. 31P NMR (C6D6, 300 K): 56.0 (d, 1JRhP = 158
Hz).
2
1JRhC = 67 Hz, JPC = 23 Hz), 164.4, 153.8, 144.9,
142.6, 138.5, 138.0, 134.9, 131.7, 132.0, 130.3, 129.4,
128.3, 127.8, 122.4, 119.5, 29.3, 25.5, 19.4, 18.8, 18.6,
17.5, 15.3, 14.3. 31P NMR (C6D6, 300 K): 35.2 (dvt,
3.3.2.5. [{Rh(CO)(Pi-Pr3)}2BDP] (14). 1H NMR
(C6D6, 300 K): 7.05 (s, 2H), 4.59 (m, 2H), 3.03 (m,
2H), 2.80 (m, 4H), 2.50 (m, 4H), 2.43 (s, 6H), 2.05 (m,
4H), 1.69 (m, 1H), 1.23, 1.18, 1.06, 0.96 (4 · t, 24H),
0.78 (m, 12 H). 31P NMR (C6D6, 300 K): 56.6 (d,
1JRhP = 158 Hz).
1NPRh = 162.2 Hz, NPP = 51.3 Hz, NPRh = ꢁ0.28 Hz,
5NRhRh = 0.0 Hz, AA0XX0). IR (KBr): m (cmꢁ1): 1967.
MS (MALDI): 1168 (M+).
1
4
Acknowledgements
´
The authors thank Andreas Pfister, Jesu´s J. Perez
3.3.2.6. [{Rh(CO)}2(l-dppm)BDP] (15). HRMS
calc. for C63H70N4O2P2Rh2: 1182.30838. Obs.:
1182.30857; D = 0.19 mmu. H NMR (C6D6, 300 K):
Torrente and Katharina Uttinger for their help and
the Deutsche Forschungsgemeinschaft for financial
support.
1
7.83 (m, 4H), 7.08 (m, 8H), 7.05 (s, 2H), 6.99 (m, 2H),
6.71 (m, 2H), 6.51 (m, 4H), 4.77 (m, 2H), 3.50 (m,
2H), 2.68 (m, 2H), 2.58 (s, 6H), 2.54 (q, 4H), 2.47 (m,
4H), 2.29 (m, 4H), 1.18, 1.16, 1.00, 0.99 (4 · t, 24H).
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