Ru(II) and Rh(III) porphyrin complexes of primary phosphine-substituted porphyrins

Article abstract of DOI:10.1039/b402083a

Primary alkynyl phosphine porphyrins were prepared by AlHCl₂ reduction of the corresponding alkynyl phosphonates. Dephosphorylation of the alkyne proved to be a major side reaction. Using LiAlH₄ as reducing agent, the alkyne was found to be partially reduced to give the trans-alkenyl phosphine selectively. The primary phosphines coordinate to both ruthenium(II) and rhodium(III) porphyrins and readily form bis-phosphine complexes. The ¹H and ³¹P NMR spectra for the ruthenium complexes show a pattern characteristic of an [AX₂]₂ spin system with an unusually large ²J_PP coupling constant of 620.6 Hz. The IR spectrum of the complex (PAPH₂)Ru(CO)(porphyrin) (PAPH₂ = phenylacetylenephosphine) indicates weak σ-donor properties of the ligand. In contrast to the corresponding tertiary phosphine complexes, the bis-phosphine complexes with both ruthenium(II) and rhodium(III) porphyrins are more stable than the mono-phosphine complexes, as judged by NMR spectroscopy, and they can also be detected in the gas phase by LDI-TOF MS. In all cases the complexes could not be isolated and they degrade within hours at ambient temperatures when kept in solution. These compounds may therefore not be suitable for the construction of larger multiporphyrin systems, but their accessibility makes it possible to study their coordination behaviour with other transition metals.

Full text of DOI:10.1039/b402083a

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P A P E R
Ru(II) and Rh(III) porphyrin complexes of primary
phosphine-substituted porphyrinsy
Eugen Stulz,*a Michael Maue,b Sonya M. Scott,b Brian E. Mannc and Jeremy K. M. Sanders*b
a
Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland.
E-mail: eugen.stulz@unibas.ch; Fax: þ41-61-2670976; Tel: þ41-61-2671147
b
University Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge, UK
CB2 1EW. E-mail: jkms@cam.ac.uk; Fax: þ44-1223-336017; Tel: þ44-1223-336411
c
Department of Chemistry, University of Sheffield, Sheffield, UK S3 7HF.
E-mail: B.Mann@sheffield.ac.uk; Fax: þ44-114-2229346; Tel: þ44-114-2229332
Received (in Montpellier, France) 10th February 2004, Accepted 1st April 2004
First published as an Advance Article on the web 19th July 2004
Primary alkynyl phosphine porphyrins were prepared by AlHCl2 reduction of the corresponding alkynyl
phosphonates. Dephosphorylation of the alkyne proved to be a major side reaction. Using LiAlH4 as reducing
agent, the alkyne was found to be partially reduced to give the trans-alkenyl phosphine selectively. The primary
phosphines coordinate to both ruthenium(II) and rhodium(III) porphyrins and readily form bis-phosphine
1
complexes. The H and 31P NMR spectra for the ruthenium complexes show a pattern characteristic of an
[AX2]2 spin system with an unusually large 2JPP coupling constant of 620.6 Hz. The IR spectrum of the complex
(PAPH2)Ru(CO)(porphyrin) (PAPH2 ¼ phenylacetylenephosphine) indicates weak s-donor properties of the
ligand. In contrast to the corresponding tertiary phosphine complexes, the bis-phosphine complexes with both
ruthenium(II) and rhodium(III) porphyrins are more stable than the mono-phosphine complexes, as judged by
NMR spectroscopy, and they can also be detected in the gas phase by LDI-TOF MS. In all cases the complexes
could not be isolated and they degrade within hours at ambient temperatures when kept in solution. These
compounds may therefore not be suitable for the construction of larger multiporphyrin systems, but their
accessibility makes it possible to study their coordination behaviour with other transition metals.
complexes formed from both the model phosphine PAPH2
and the phosphine porphyrins with ruthenium and rhodium
porphyrins.
Introduction
In recent studies, we have used diphenyl phosphine-substituted
alkynyl porphyrins for the construction of linear and cyclic
multiporphyrinic arrays via coordination of the phosphorus
to ruthenium(II) or rhodium(III) porphyrins.1,2 The coordina-
tion of tertiary phosphines to transition metal porphyrins is
well-documented and many complexes have been studied in
solution and, in some cases, also in the solid state.3,4 The
binding of a primary phosphine to a metalloporphyrin, on
the other hand, has not been reported to date. Indeed, reports
on coordination compounds of primary phosphines are
scarce,5–7 although some air-stable primary phosphines have
been reported.8 Primary phosphines are expected to be weaker
donors than tertiary phosphines due to an increased s charac-
ter of the P lone pair orbital.6,9 The acidic P–H bond is suscep-
tible to deprotonation giving phosphido species.7,10 Given the
rich electrochemistry of Ru(II) and Rh(III) porphyrins,3 the
coordination of a primary phosphine to these acceptor
porphyrins might yield complexes of unusual reactivity.
Attachment of a diphenyl phosphine group to a porphyrin is
readily achieved using an alkynyl linker.1 Thus, the report by
Guillemin et al.11 on a primary phenylalkynyl phosphine
(PAPH2 , Scheme 1) and its tungsten pentacarbonyl complex
attracted our interest. This ligand is comparable with other
simple phenylalkynyl phosphines and phosphonites, which
we have previously used to study the coordination of phos-
phorus to ruthenium and rhodium porphyrins.2b,12,13 Here,
we report on the synthesis of a porphyrin substituted with a
primary alkynyl phosphine, as well as on the NMR and IR
spectroscopic and mass spectrometric investigations of the
Results and discussion
Synthesis of the phosphine porphyrins
The synthetic route to the porphyrins substituted with a pri-
mary alkynyl phosphine is outlined in Scheme 1. The reduction
step is adapted from the reported synthesis of PAPH2 .11,14
Both meta- and para-substituted alkynyl porphyrins can be
phosphonylated by our general route via formation of a
Grignard-type cadmium-alkynyl complex1 and using chloro-
diethyl phosphate as electrophile. In this way, the phos-
=
phonates Por–C C–P(O)(OEt) (Por ¼ porphyrin, 1) are
=
2
accessible in 20 to 30% overall yield. The characteristic phos-
phorus chemical shift is dP ¼ ꢀ5 ppm, which is independent
of the substitution pattern (meta vs. para) and of the metalla-
tion state. A major side product was isolated by column chro-
matography and identified by NMR spectroscopy (dP ¼ ꢀ19
ppm) and MALDI-TOF MS as the bis-porphyrin phosphinate
ꢁ
=
(Por–C C) P(O)OEt. The bis-porphyrin phosphinate was
2
=
present in up to 40% yield. Adding the Grignard reagent to
a solution of the chlorophosphate did not alter the distribution
of the products. The desired products can be obtained as free-
base (Fb-1), zinc(II) (Zn-1) or nickel(II) (Ni-1) porphyrinates.
However, since the difference in the substitution pattern on
the meso-aryl group (meta- vs. para-alkyne) does not have a
significant influence on the coordination behaviour of phos-
phine substituted porphyrins,1 we focused on the meta-substi-
tuted zinc porphyrin (Zn-1) and the para-substituted nickel
porphyrin (Ni-1) as representative phosphine porphyrins.
y Dedicated to the memory of Bhaskar G. Maiya.
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Scheme 1 Synthesis of the primary phosphines. Reagents and conditions: (i) LiHMDA, CdCl2 , ClP(O)(OEt)2 , THF, ꢀ78 ꢁC; (ii) LiAlH4 , THF,
ꢀ78 ꢁC; (iii) LiAlH4 , AlCl3 , THF, ꢀ78 ꢁC.
3
addition of one equivalent of hydrogen. The JHH value for
The phosphonates could be reduced to the corresponding
primary phosphines (2) and (3) according to the procedure
described by Guillemin et al.11 using a mixture of LiAlH4
and AlCl3 . The reaction resulted in almost quantitative
conversion and showed only one single product by TLC.
However, 1H NMR and MALDI-TOF MS analysis of the
collected fraction from column chromatography showed that
some dephosphorylation occurred, so that in some samples
up to 50% of the free alkyne was present. Due to the inherent
instability of the primary phosphine towards both isomerisa-
tion and oxidation, and due to the identical Rf values of the
two compounds on silica, these could not be separated. There-
fore, micro-analytical data such as elemental analysis or
HRMS could not be obtained. The primary alkynyl phosphine
porphyrins show a characteristic 31P NMR chemical shift of
Hb $ Hc could not be resolved due to the broadened multiplet
resonances, but the alkene Zn-2 was shown to be the trans iso-
mer using 2D NOESY experiments. Through-space NOE con-
nectivities between both alkene protons and the aryl group
could be detected, but not from the PH2 group (Fig. 1). Char-
acteristic NOEs were found for Ha to Hb , Hb to Hd and He ,
and for Hc to Hd and He . The phosphine protons resonate
at dH ¼ 3.54 ppm as a doublet of doublets (1JPH ¼ 200 Hz,
3JHH ¼ 5 Hz). The 31P NMR spectrum showed a resonance
at dP ¼ ꢀ136 ppm, which appears in the proton-coupled spec-
2
trum as a triplet of triplets (1JPH ¼ 200 Hz, JPH ¼ 12 Hz,
3JPH ¼ 12 Hz, Fig. 1), where the coupling constants to the
two vinyl protons have identical values.15
The primary phosphines are highly unstable and must be
handled under an inert atmosphere. Chloroform as solvent
should be avoided, because the release of acid induces degrada-
tion of the compounds within a few hours. The phosphine
porphyrins are best dissolved in benzene and can be stored
in a frozen matrix of benzene at ꢀ20 ꢁC.
1
dP ¼ ꢀ178 ppm (t, JPH ¼ 214 Hz, Fig. 1). These values are
essentially identical to those for PAPH2 (dP ¼ ꢀ176 ppm, t,
1
1JPH ¼ 215 Hz). In the H NMR spectrum, the PH2 group is
1
at dH ¼ 3.78 ppm (d, JPH ¼ 214 Hz). This corresponds to a
small low-frequency shift compared to the resonance found
1
in PAPH2 (dH ¼ 3.96 ppm, d, JP-H ¼ 215 Hz). In decoupled
spectra, the resonances for both the phosphorus and the
phosphine protons appear as singlets.
NMR spectroscopy of (PAPH2)2Ru-4
When LiAlH4 was used as sole reducing agent, the partially
reduced alkene phosphine was isolated. The double bond
shows characteristic proton resonances at dH ¼ 7.11 and
6.50 ppm (Fig. 1); the MALDI-TOF MS confirmed the
To get an understanding of the coordination behaviour of pri-
mary alkynyl phosphines to metalloporphyrins, we first inves-
tigated the affinity of Ru-4 towards PAPH2 . When mixing
Fig. 1 Part of the 400 MHz 1H NMR spectra of (a) Ni-3 and (b) Zn-2; the insets show the 161.9 MHz 31P NMR spectra of the phosphines. The
marked (*) signals arise from the corresponding dephosphorylated alkyne porphyrins. Arrows in the structure of Zn-2 indicate selected through-
space NOE connectivities.
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PAPH2 with Ru-4 (C6D6), new signals could be observed in
1
both the H NMR and 31P NMR spectra. The 1H{31P} NMR
spectrum showed a new singlet at dH ¼ ꢀ0.60 ppm. This
low-frequency shift is consistent with the binding of the
phosphorus in the shielding region of the porphyrin. In the
31P{1H} NMR spectrum, three signals could be found, namely
a sharp singlet at dP ¼ ꢀ102 ppm and two broad resonances at
dP ¼ ꢀ119 and ꢀ178 ppm, the latter being the resonance of
the free PAPH2 (Fig. 2). These broadened signals indicate a
dynamic exchange between the free phosphine and the bound
PAPH2 in the mono-phosphine complex of the form (PAPH2)-
Ru(CO)(por).13 Displacement of the carbonyl ligand yields the
bis-phosphine complex (PAPH2)2Ru(por), which seems to be
much more kinetically inert than the mono-phosphine com-
plex. Despite all attempts made, the final complex could not
be isolated. Usually, the complex degraded during the crystal-
lisation procedure and the solutions turned from green to
black overnight. However, the complex can be stored in a
frozen C6D6 matrix at ꢀ20 ꢁC.
The H and 31P (1H coupled) NMR spectra of the PH2 sig-
1
Fig. 3 (a) A partial experimental 400 MHz 1H NMR spectrum of
(PAPH2)2Ru-4 in d6-benzene showing the signal due to the PH2
protons. (b) The calculated spectrum of the PH2 protons, calculated
nal showed a pattern characteristic of an [AX2]2 spin system
(Figs. 3 and 4). This was analysed using WINDAISY and a
2
fit was obtained using the parameters JPP ¼ 620.6 Hz,
2
as an [AX2]2 spectrum with the parameters JPP ¼ 620.6 Hz,
3
2
1JPH ¼ 340.8 Hz and JPH ¼ 3.8 Hz. JPP is remarkably
large when compared with the 229 and 308 Hz reported for
[RuCl2(CO)2(PHtBu2)2]16 (isomers).
3
1JPH ¼ 340.8 Hz and JPH ¼ 3.8 Hz.
suggest that PAPH2 (calculated pKa ¼ ꢀ3.7) is a much weaker
ligand than PPh3 (pKa ¼ 2.7).10 The lower wavenumber
observed for the PPh3 complex is consistent with this, because
PPh3 , as stronger donor, increases the electron density on the
ruthenium, thus allowing more effective back-bonding to the
pp* orbital of the CO ligands, resulting in a decreased CO
stretching frequency compared to PAPH2 .
Comparison of the IR spectra of Ru-4 and (PAPH2)Ru-4
To obtain the IR spectrum of the mono-phosphine complex, a
DCM solution of PAPH2 was titrated into a 2.0 mM solution
=
of Ru-4. The absorption of the C O IR stretching vibration of
=
Ru-4 is at n ¼ 1919 cmꢀ1 and the final spectrum of the mono-
=
=
phosphine complex (PAPH )Ru(CO)(por) showed the C O
2
absorption at n ¼ 1949 cmꢀ1 (Fig. 5). Further addition of
PAPH2 resulted in formation of the bis-phosphine complex
(PAPH2)2Ru(por), visible in the loss of the CO absorption.
Compared to other phosphine ligands such as PPh3 , which
shows a difference in the wavenumber of Dn ¼ 18 cmꢀ1 upon
binding,13 this rather large shift of Dn ¼ 30 cmꢀ1 for PAPH2
indicates very different stereoelectronic influences on the metal
from the primary phosphine compared to the tertiary phos-
phine. The s-donor properties of the ligands, which can be
approximated by the pKa of the protonated phosphine,17
Ru(II) and Rh(III) complexes of 2 and 3
To obtain the complexes of the primary phosphines, both
Ru(II) (Ru-4) and Rh(III) (Rh-5) porphyrins were dissolved in
C6D6 (5 mM each) and titrated into C6D6 solutions of Zn-2
and Ni-3 (ca. 2–3 mM each), which were immediately used
for NMR measurements. The complexation of both the alke-
nyl and the alkynyl phosphine to the ruthenium(II) and rhodiu-
m(III) porphyrins could be followed by 1H NMR spectroscopy
Fig. 4 (a) The experimental 161.9 MHz 31P NMR spectrum of
(PAPH2)2Ru-4 in d6-benzene. (b) The calculated spectrum of the PH2
31P nuclei, calculated as an [AX2]2 spectrum with the parameters
Fig. 2 161.9 MHz 31P{1H} NMR spectrum of the mixture of PAPH2
with Ru-4 in C6D6 (273 K).
1
3
2JPP ¼ 620.6 Hz, JPH ¼ 340.8 Hz and JPH ¼ 3.8 Hz.
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missing outer lines, the errors may be too large to discuss these
values in detail, yet they are similar to those of the PAPH2
complex. This sample degraded rapidly upon standing at
ambient temperature.
The vinylic phosphine Zn-2 also readily coordinates to Rh-5,
but multiple species are observed (1H NMR) immediately after
mixing the two components (Fig. 6). Analogous to the com-
2
plex with Ni-3, a signal at d ꢀ 1.45 (1JPH ¼ 377 Hz, JHH ¼ 6
6 Hz) corresponds to the coordinated primary phosphine and
the alkenyl phosphine resonates at slightly lower frequency as
the alkynyl phosphine. The origin of a second signal at d ꢀ 2.07
2
(1JPH ¼ 362 Hz, JHH ¼ 6 Hz) is unclear, as the triplet cou-
pling cannot be explained. Another signal at d ꢀ 1.79
(1JPH ¼ 155 Hz) again suggests free phosphine but located
within the shielding region of the porphyrin, thus complexa-
tion via the vinyl might explain this resonance. For this signal,
2
the JHH could not be determined due to the low resolution.
Upon mixing Ru-4 and Zn-2, no spectrum with clearly
resolved signals could be obtained.
=
C O absorption region in the IR spectra of Ru-4 (solid line)
and of (PAPH2)Ru-4 (dashed line). Spectra are recorded in CH2Cl2
Fig. 5
(2.0 mM, 25 ꢁC).
LDI-TOF mass spectrometry
(Fig. 6). Initially, the 1H NMR spectrum of the Ni-3/Rh-5
mixture displayed a signal for the RPH2 group at d ¼ 1.33
ppm (1JPH ¼ 403 Hz), consistent with formation of the com-
plex; some uncoordinated phosphine is still detectable. Re-
measuring the sample after allowing it to stand for 24 h at
ambient temperature showed the occurrence of new species,
though some of the initial compound was still present. A signal
due to another ruthenium adduct with RPH2 is seen whose
chemical shift values are consistent with a complexed phos-
Since laser desorption ionisation time-of-flight (LDI-TOF)
mass spectrometry is a versatile characterisation method for
metalloporphyrins and their complexes,19 we have studied
the complexes of both PAPH2 and Ni-3 with Ru-4. A mixture
of PAPH2 with Ru-4 (5 equiv of phosphine to ruthenium)
showed a peak at m/z ¼ 1087.8 for the mono-phosphine com-
ꢂ
þ
plex [(PAPH2)Ru-4] (calcd m/z ¼ 1088.5), where the CO
ligand is lost from the complex. A typical mass spectrum is
displayed in Fig. 7(a). This demonstrates that the primary
phosphine ligand is a sufficiently strong s-donor to form
complexes with Ru(II) porphyrins in the gas phase. In compar-
ison, nitrogen donors such as pyridine or DMAP only form
complexes in the gas phase when using large excess of the
ligand ( > 100 equiv).19 Upon addition of a large excess of
PAPH2 to Ru-4 (approx. 50 equivalents), the bis-phosphine
complex was still not observable; similar observations were
made with tertiary phosphines as ligands. In contrast to
measurements with tertiary phosphines, the formation of the
1
phine (d ꢀ 0.93 ppm, JPH ¼ 389 Hz). Two strong signals
appear at d ꢀ 1.30 ppm (1JPH ¼ 197 Hz) and at d ꢀ 1.33 Hz
1
(1JPH ¼ 199 Hz); the JPH values suggest free RPH2 but the
chemical shifts suggest coordination, perhaps through the
alkyne.18 However, any structural assignments of the newly
formed products are speculative.
The 1H NMR spectrum of the Ni-3/Ru-4 mixture displayed
a signal at d ꢀ 0.56 ppm, which appears to be an [AX2]2 spin
1
system (singlet in the H{31P} NMR spectrum). This spin sys-
ꢂ
þ
ruthenium dimer [Ru-4]2 was not suppressed.19
tem is consistent with the one obtained from the (PAPH2)2-
Ru(por) complex and confirms the formation of the complex
In the spectrum of a 5:1 mixture of Ni-3 and Ru-4, addi-
tional signals to the parent mass peaks of the porphyrins could
be detected at higher masses [Fig. 7(b)]. A slightly broadened
mass peak at m/z ¼ 2032.4 corresponds to the diporphyrin
2
[Ni-3/Ru-4/Ni-3]. The values obtained are JPP ¼ 603.7 Hz,
3
1JPH ¼ 339.0 Hz and JPH ¼ 6.0 Hz. However, due to the
ꢂ
þ
complex [Ni-3/Ru-4] (calcd m/z ¼ 2033.2), again with loss
of CO. More surprising is the appearance of a broad peak at
m/z ꢃ 3110, which can be assigned to the triporphyrin complex
ꢂ
þ
[Ni-3/Ru-4/Ni-3] (calcd m/z ¼ 3111.8). This contrasts to
our experience with corresponding tertiary phosphine substi-
tuted porphyrins, where the triporphyrin complexes could
not be detected.1,19 The 31P NMR spectrum of the mixture
of PAPH2 with Ru-4 (Fig. 2) suggests that the bis-phosphine
complex is more stable than the mono-phosphine complex,
in contrast to tertiary phosphines where the bis-phosphine
complex is usually thermodynamically less stable than the
mono-phosphine complex. This solution phase behaviour
seems to be retained in the gas phase for Ni-3. The same can
be observed in mixtures of Ni-3 with Rh-5 [Fig. 7(c)]: the
ꢂ
þ
peaks for the diporphyrin complex [Ni-3/Rh-5] and the
triporphyrin complex [Ni-3/Rh-5/Ni-3]
ꢂ
þ
were detected at
m/z ¼ 1793.4 (calcd m/z ¼ 1793.8) and at m/z ¼ 2874.9
(calcd m/z ¼ 2872.4), respectively. In this case, the relative
peak intensity for the free Ni-3 is significantly higher than
for Rh-5, indicating easier ion formation for Ni-3 than for
Rh-5. We had already made similar observations with different
metalloporphyrins in LDI-TOF MS.19 Another major differ-
ence compared to the measurement with Ru-4 can be seen:
the signals for the mono- and for the bis-phosphine complexes
appear to be much sharper and with a higher intensity than for
1
Fig. 6 Low-frequency region of the H NMR spectra obtained from
the mixtures of the primary phosphines with the ruthenium and
rhodium porphyrins: (a) Ni-3 and Rh-5; (b) Ni-3 and Ru-4; (c) Zn-2
and Rh-5.
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suitable for the construction of larger multiporphyrin systems.
For this purpose, we would recommend to use either tertiary
phosphines or phosphonates, because they are stable under
standard inert atmosphere. But the accessibility of the primary
phosphine porphyrins makes it possible to study their coordi-
nation behaviour with other transition metals and probably
get more insight into the reactivity of unsaturated phosphines
in the presence of Ru(II) and Rh(III) complexes via NMR spec-
troscopy or LDI-TOF mass spectrometry. This could be of
particular interest to those working in the field of catalytic
hydrogenation of alkenes and alkynes with ruthenium and
rhodium complexes.
Experimental
General
All manipulations were performed using standard inert atmo-
sphere techniques and freshly distilled and degassed solvents
according to standard procedures; CDCl3 and C6D6 (Euriso-
top, France) were filtered over basic alumina and degassed
by purging with Ar prior to use. 3-(3-Hydroxy-3-methylbut-
1-ynyl)benzaldehyde and 4-(3-hydroxy-3-methylbut-1-ynyl)-
benzaldehyde were prepared according to literature proce-
dures.21 LiHMDA (1 M THF), ClP(O)(OEt)2 , LiAlH4 and
AlCl3 were purchased from Aldrich and used as received.
CdCl2 (Aldrich) was dried prior to use (1 mbar, 150 ꢁC, 3 h).
The general procedure for the synthesis of the acetylenic
porphyrins has been described earlier.22 Ru-4 and Rh-5 were
prepared as described previously.23
NMR spectra were recorded on a Bruker DPX250 NMR
spectrometer (250.13 MHz for 1H, solvent as internal stan-
dard; 101 MHz for 31P{1H}, H3PO4 external standard), on a
Bruker DPX400 NMR spectrometer (400.13 MHz for 1H,
solvent as internal standard; 161.98 MHz for 31P{1H},
H3PO4 external standard), or on a Bruker Avance 500 Cryo
NMR spectrometer at 500.13 MHz (1H). Abbreviations for
1H NMR spectra used are: s, singlet; d, doublet; t, triplet; q,
quartet; p, pentet; m, multiplet; b, broad. LDI-TOF mass spec-
tra were recorded on a Kompact MALDI 4 mass spectrometer
(Kratos Analytical Ltd), operated in the linear positive mode,
using neat samples.
Fig. 7 LDI-TOF MS of porphyrin complexes with primary phos-
phines: (a) mixture of PAPH2 with Ru-4; (b) mixture of Ni-3 with
Ru-4; (c) mixture of Ni-3 with Rh-5.
General procedure for the synthesis of the phosphonates
meta-Zn-1. Acetylene zinc porphyrin (100 mg, 94.3 mmmol)
was dissolved in 1.5 ml THF and cooled to ꢀ78 ꢁC. After addi-
tion of 470 ml LiHMDA (470 mmol), the solution was stirred
for 15 min, after which 86 mg CdCl2 (474 mmol) were added
and the solution was stirred for a further 30 min at ꢀ78 ꢁC.
ClP(O)(OEt)2 (82 mg, 474 mmol) in 1.5 ml THF were added
dropwise and the resulting solution was stirred at ꢀ78 ꢁC for
1.5 h, then warmed to room temperature and stirring was con-
tinued for 30 min. The reaction mixture was poured into a
separating funnel containing 100 ml CH2Cl2 and neutralised
with 50 ml saturated aqueous Na2CO3 . The organic phase
was washed with one portion of H2O (50 ml), dried over
MgSO4 , filtered and evaporated to dryness. Due to some
demetalation during the reaction, the crude product was mixed
with Zn(OAc)2 (50 mg) in 20 ml CHCl3–MeOH (10:1), heated
to the boiling point for 5 min and evaporated to dryness. The
residue was taken up in CH2Cl2 , filtered and the residue
washed with CH2Cl2 until colourless. Column chromatogra-
phy (silica, CH2Cl2–MeOH 20:1, Rf 0.5) afforded 62.1 mg of
meta-Zn-1 (52.1 mmol; 55%). 1H NMR (250 MHz, CDCl3):
d ¼ 10.21 (s, 2H, meso-H), 8.32 (s, 1H, Ar–H), 8.23 (d, 1H,
J ¼ 8 Hz, Ar–H), 8.03 (d, 1H, J ¼ 8 Hz, Ar–H), 7.93 (bs,
2H, Ar–H), 7.82 (bs, 1H, Ar–H), 7.77 (s, 1H, Ar–H), 4.24
(p, 4H, J ¼ 7 Hz, P–O–CH2–CH3), 3.98 (t, 8H, J ¼ 7 Hz,
hexyl-CH2), 2.46 (s, 6H, b-pyrrole CH3), 2.44 (s, 6H, b-pyrrole
the corresponding Ru-4 complexes. Thus, changing the accep-
tor porphyrin in the array has a dramatic influence on the out-
come of the mass spectrum. This could hint at different
photophysical behaviour of the arrays in the gas phase upon
irradiation with the laser.
Conclusions
The first syntheses of the primary alkenyl and alkynyl phos-
phines Ni-3 and Zn-4 are reported. The primary phosphines
can be synthesised with variable substitution pattern on the
porphyrin (meta- or para-substituted at the meso-phenyl
groups) or with variable central metal, such as Ni(II) or Zn(II).
The primary phosphines coordinate to both Ru(II) and Rh(III)
porphyrins, readily forming bis-phosphine complexes. In the
1H and 31P NMR spectra, the complex of PAPH2 with the
Ru(II) porphyrin showed a pattern characteristic of an
[AX2]2 spin system with a remarkably large 2JPP coupling con-
stant of 620.6 Hz. A similar signal pattern was obtained by
complexing Ni-3 to Ru-4.
All the complexes are unstable in solution and thus could
not be isolated. This might not be surprising given the possibi-
lity of activating alkenes and alkynes with ruthenium and rho-
dium porphyrins.20 These compounds may therefore not be
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
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CH3), 2.19 (m, 8H, hexyl-CH2), 1.75 (m, 8H, hexyl-CH2), 1.53
hexyl-CH2), 1.01 (m, 12H, hexyl-CH3). 31P{1H} NMR (101
t
t
(s, 9H, Bu–CH3), 1.51 (s, 9H, Bu–CH3), 1.47 (m, 8H, hexyl-
CH2), 1.39 (t, 6H, J ¼ 7 Hz, P–O–CH2–CH3), 1.27 (m, 8H,
hexyl-CH2), 0.92 (t, 12H, J ¼ 7 Hz, hexyl-CH3). 31P{1H}
NMR (101 MHz, CDCl3): d ¼ ꢀ5. LDI-TOF MS: m/z calcd
for C74H101N4O3PZn 1188.69, found 1189.16.
MHz, CDCl3): d ¼ ꢀ176 (1JPH ¼ 215 Hz). LDI-TOF MS:
m/z calcd for C70H93N4NiP 1078.65, found 1079.17.
NMR experiments
(PAPH2)2Ru-4. Ru-4 (50 mg, 50 mmol) was added to a solu-
tion of 60 mg (450 mmol) of PAPH2 in 100 ml dry THF and the
solution was stirred for 1 h at room temperature. The solvent
was evaporated and the dark red residue was dried in vacuo.
The solid was redissolved in 2.0 ml of C6D6 and directly used
for NMR measurements. 1H{31P} NMR (C6D6 , 500 MHz):
d ¼ 10.31 (s, 2H, meso-H), 8.20 (s, 4H, o-Ar–H), 7.99 (s, 2H,
p-Ar–H), 6.92–6.97 (m, 10H, Ar–H of PAPH2), 4.00 (m, 8H,
ethyl-CH2), 2.77 (s, 12H, b-pyrrole CH3), 1.83 (m, 12H,
hexyl-CH3), 1.48 (s, 36H, tBu–CH3), ꢀ0.6 (s, 4H, PH2).
31P{1H} NMR (C6D6 , 101 MHz): d ¼ ꢀ102 (s). Signals for
some mono-complex at d ꢀ 120 (bs) and free phosphine at
d ꢀ 178 ppm (bs) were detected as well. The [AX2]2 coupling
pattern was analysed initially using the [AXn]2 spin system,
para-Ni-1. Yield 58.7 mg (49.6 mmol; 52%) from 100 mg
acetylene nickel porphyrin (95.4 mmol). 1H NMR (CDCl3 ,
500 MHz): d ¼ 9.42 (s, 2H, meso-H), 7.83 (d, J ¼ 8 Hz, 2H,
Ar–H), 7.79 (d, J ¼ 8 Hz, 2H, Ar–H), 7.68 (d, J ¼ 2 Hz,
2H, Ar–H), 7.67 (t, J ¼ 2 Hz, 1H, Ar–H), 3.94 (p, 4H, J ¼ 7
Hz, P–O–CH2–CH3), 3.63 (t, J ¼ 8 Hz, 8H, hexyl-CH2), 2.25
(s, 6H, b-pyrrole CH3), 2.23 (s, 6H, b-pyrrole CH3), 2.20
(p, J ¼ 7 Hz, 8H, hexyl-CH2), 1.58 (p, J ¼ 7 Hz, 8H, hexyl-
CH2), 1.42 (s, 18H, tBu–CH3), 1.34 (m, 16H, hexyl-CH2),
1.28 (t, 6H, J ¼ 7 Hz, P–O–CH2–CH3), 0.88 (2 ꢄ t, J1 ¼ 2
Hz, J2 ¼ 7 Hz, 12H, hexyl-CH3). 31P{1H} NMR (101 MHz,
CDCl3): d ¼ ꢀ5. LDI-TOF MS: m/z calcd for
C74H101N4O3PNi 1182.70, found 1183.03.
4
which assumes that JHH ¼ 0 H. The approximate coupling
constants were then refined using WINDAISY.
Zn-2. meta-Zn-1 (50.0 mg, 42 mmol) was dissolved in 3.0 ml
of Et2O at 0 ꢁC (ice bath). After addition of 4.8 mg LiAlH4
(126 mmol) in one portion, the red solution was stirred at
0 ꢁC for 2 h. Then, the solution was transferred via canula into
a flask containing 50 ml CH2Cl2 and 30 ml brine and the mix-
ture was stirred vigorously for 10 min. The organic phase was
separated and concentrated in vacuo. The crude product was
dissolved in ca. 2 ml THF, transferred onto a silica column
via syringe and flash chromatographed using THF as eluent.
This yielded a total of 32.5 mg of porphyrinic product.
Ni-2/Zn-3 with Ru-4/Rh-5. Solutions of 5.0 mg of the phos-
phine porphyrins (500 ml C6D6) were titrated with 5.0 mM
solutions of the acceptor porphyrins (C6D6) in 10 to 50 ml
portions and the 1H NMR spectra were recorded after each
addition. The final spectrum was obtained when virtually all
uncomplexed phosphine was consumed.
1
Acknowledgements
According to the H NMR spectrum, the mixture contained
13.4 mg Zn-2 (12.3 mmol, 30%); Rf (hexane–ethyl acetate 5:1)
0.8. 1H NMR (CDCl3 , 500 MHz): d ¼ 10.55 (s, 2H, meso-
H), 8.44 (s, 2H, Ar–H), 8.25 (m, 2H, Ar–H), 8.14 (bs, 1H,
Ar–H), 8.01 (d, J ¼ 7 Hz, 1H, Ar–H), 7.59 (d, J ¼ 7 Hz,
1H, Ar–H), 7.11 (m, 1H, alkene-H), 6.50 (m, 1H, alkene-H),
We thank Prof. J.-C. Guillemin (ENSC Rennes, France) for
many helpful comments on the synthesis of PAPH2 . Financial
support from the Swiss National Science Foundation (E.S.)
and from the EPSRC is gratefully acknowledged.
1
3
4.12 (m, 8H, hexyl-CH2), 3.54 (dd, JPH ¼ 200 Hz, JHH ¼ 5
Hz, 2H, PH2), 2.79 (s, 6H, b-pyrrole CH3), 2.71 (s, 6H, b-pyr-
role CH3), 2.44 (m, 8H, hexyl-CH2), 1.89 (m, 8H, hexyl-CH2),
1.59 (s, 18H, tBu–CH3), 1.58 (m, 8H, hexyl-CH2), 1.46 (m, 8H,
hexyl-CH2), 1.02 (m, 12H, hexyl-CH3). 31P{1H} NMR (101
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