The synthesis, characterisation and reactivity of 2- phosphanylethylcyclopentadienyl complexes of cobalt, rhodium and iridium

Article abstract of DOI:10.1039/b512054c

2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C ₅R′₄(CH₂)₂PR₂] (R = Et, R′ = H or Me, R = Ph, R′ = Me), have been prepared from the reaction of spirohydrocarbons C₅R′₄(

Full text of DOI:10.1039/b512054c

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PAPER
www.rsc.org/dalton | Dalton Transactions
The synthesis, characterisation and reactivity of
2-phosphanylethylcyclopentadienyl complexes of cobalt,
rhodium and iridium†
Ann C. McConnell,a Peter J. Pogorzelec,b Alexandra M. Z. Slawin,a Gary L. Williams,c
Paul I. P. Elliott,c Anthony Haynes,c Andrew C. Marra and David J. Cole-Hamilton*a
Received 24th August 2005, Accepted 18th October 2005
First published as an Advance Article on the web 21st November 2005
DOI: 10.1039/b512054c
2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C5Rꢀ4(CH2)2PR2]
(R = Et, Rꢀ = H or Me, R = Ph, Rꢀ = Me), have been prepared from the reaction of spirohydrocarbons
C5Rꢀ4(C2H4) with LiPR2. C5Et4HSiMe2CH2PMe2, was prepared from reaction of Li[C5Et4] with
Me2SiCl2 followed by Me2PCH2Li. The lithium salts were reacted with [RhCl(CO)2]2, [IrCl(CO)3] or
[Co2(CO)8] to give [M(C5Rꢀ4(CH2)2PR2)(CO)] (M = Rh, R = Et, Rꢀ = H or Me, R = Ph, Rꢀ = Me; M =
Ir or Co, R = Et, Rꢀ = Me), which have been fully characterised, in many cases crystallographically
as monomers with coordination of the phosphorus atom and the cyclopentadienyl ring. The values
of mCO for these complexes are usually lower than those for the analogous complexes without the bridge
between the cyclopentadienyl ring and the phosphine, the exception being [Rh(Cpꢀ(CH2)2PEt2)(CO)]
(Cpꢀ = C5Me4), the most electron rich of the complexes. [Rh(C5Et4SiMe2CH2PMe2)(CO)] may
be a dimer. [Co2(CO)8] reacts with C5H5(CH2)2PEt2 or C5Et4HSiMe2CH2PMe2 (L) to give binuclear
complexes of the form [Co2(CO)6L2] with almost linear PCoCoP skeletons. [Rh(Cpꢀ(CH2)2PEt2)(CO)]
and [Rh(Cpꢀ(CH2)2PPh2)(CO)] are active for methanol carbonylation at 150 ◦C
and 27 bar CO, with the rate using [Rh(Cpꢀ(CH2)2PPh2)(CO)] (0.81 mol dm−3 h−1) being higher than
that for [RhI2(CO)2]− (0.64 mol dm−3 h−1). The most electron rich complex, [Rh(Cpꢀ(CH2)2PEt2)(CO)]
(0.38 mol dm−3 h−1) gave a comparable rate to [Cp*Rh(PEt3)(CO)] (0.30 mol dm−3 h−1), which was
unstable towards oxidation of the phosphine. [Rh(Cpꢀ(CH2)2PEt2)I2], which is inactive for methanol
carbonylation, was isolated after the methanol carbonylation reaction using [Rh(Cpꢀ(CH2)2PEt2)(CO)].
Neither of [M(Cpꢀ(CH2)2PEt2)(CO)] (M = Co or Ir) was active for methanol carbonylation under these
conditions, nor under many other conditions investigated, except that [Ir(Cpꢀ(CH2)2PEt2)(CO)] showed
some activity at higher temperature (190 ◦C), probably as a result of degradation to [IrI2(CO)2]−.
[M(Cpꢀ(CH2)2PEt2)(CO)] react with MeI to give [M(Cpꢀ(CH2)2PEt2)(C(O)Me)I] (M = Co or Rh)
or [Ir(Cpꢀ(CH2)2PEt2)Me(CO)]I. The rates of oxidative addition of MeI to [Rh(C5H4(CH2)2PEt2)(CO)]
and [Rh(Cpꢀ(CH2)2PPh2)(CO)] are 62 and 1770 times faster than to [Cp*Rh(CO)2]. Methyl
migration is slower, however. High pressure NMR studies show that [Co(Cpꢀ(CH2)2PEt2)(CO)] and
[Cp*Rh(PEt3)(CO)] are unstable towards phosphine oxidation and/or quaternisation under methanol
carbonylation conditions, but that [Rh(Cpꢀ(CH2)2PEt2)(CO)] does not exhibit phosphine degradation,
eventually producing inactive [Rh(Cpꢀ(CH2)2PEt2)I2] at least under conditions of poor gas mixing.
The observation of [Rh(Cpꢀ(CH2)2PEt2)(C(O)Me)I] under methanol carbonylation conditions suggests
that the rhodium centre has become so electron rich that reductive elimination of ethanoyl iodide
has become rate determining for methanol carbonylation. In addition to the high electron density at
rhodium.
Introduction
aEaStCHEM, School of Chemistry, University of St. Andrews, St. Andrews,
Fife, UK KY16 9ST. E-mail: djc@st-and.ac.uk; Fax: +44-1334-463808;
Tel: +44-1334-463805
The carbonylation of methanol to ethanoic acid is one of the most
successful industrial applications of homogeneous catalysis.1–3 The
first process to be developed was based on cobalt, but required
very forcing conditions (600–700 bar, 250 ◦C).4 In the mid 1960’s
Monsanto developed a rhodium based process in which the
active species is [RhI2(CO)2]−.5–8 This operates under much milder
bCatalyst Evaluation and Optimisation Service, EaStCHEM, School of
Chemistry, University of St. Andrews, St. Andrews, Fife, UK KY16 9ST
cDepartment of Chemistry, University of Sheffield, Dainton Building, Brook
Hill, Sheffield, UK S3 7HF. E-mail: a.haynes@sheffield.ac.uk; Fax: +44-
114 222 9346; Tel: +44-114 2229326
† Electronic supplementary information (ESI) available: Kinetic data and
crystal structures. See DOI: 10.1039/b512054c
◦
conditions (30 bar, 180 C). The most recent developments have
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involved [IrI2(CO)2]− promoted by e.g. [RuI2(CO)3].9 In all cases,
the mechanism involves oxidative addition of MeI, formed from
a reaction of methanol with HI, meaning that highly electron
rich metal centres are required. In the case of the rhodium
based system, this oxidative addition to [RhI2(CO)2]− is the rate
determining step, despite the estimate of Forster that oxidative
addition of MeI to the anionic [RhI2(CO)(EPh3)]− is faster by
a factor of 105 than to the neutral [RhI(CO)(EPh3)2] (E = P,
As, Sb).10 The other steps in the catalytic cycle are fast and the
short lifetime of many of the intermediates ensures the very high
selectivity (>99%) to the desired ethanoic acid.
the chelate effect should ensure a higher stability constant for
phosphine coordination. In this paper, we describe the synthesis
of such ligands, their coordination to Co, Rh and Ir, studies of
the rate of reaction of some of these complexes with MeI and
the use of the resulting complexes in methanol carbonylation. A
preliminary report of some of these results has appeared.20
Experimental
Microanalyses were by the University of St. Andrews microan-
alytical service. Infrared spectra were obtained using a Nicolet
Protege 460 Fourier Transform Spectrometer with CsI optics. The
infrared spectrometer was interfaced to a personal computer via
the OMNIC operating system. GCMS analysis was carried out
using a Hewlett Packard GC system with a 5973 mass selective
detector fitted with a 5% phenyl methyl siloxane capilliary column.
Carbon, proton and phosphorus NMR spectra were recorded on
a Bruker AM 300 NMR spectrometer, a Bruker Avance 300 or
a Varian 300 NMR spectrometer. The two-dimensional spectra
were recorded on a Bruker Avance 300. Broad band decoupling
was used for 13C spectra and 31P spectra. 1H and 13C NMR spectra
were referenced internally to deuteriated solvents and are reported
relative to TMS. 31P chemical shifts are to high frequency of
external H3PO4 (85%).
All manipulations were performed in a nitrogen atmosphere,
unless otherwise stated, using standard Schlenk line and catheter
tubing techniques. Nitrogen/argon was passed through a glass
column containing Cr(II) absorbed onto silica, prior to use. All
gases were purchased from BOC gases. All solvents were freshly
distilled and dried; petroleum ether (bp 40–60 ◦C), tetrahydro-
furan and diethyl ether were distilled over sodium diphenylketyl.
Dichloromethane was distilled over calcium hydride.
The metal complexes [RhCl(CO)2]2, [Co2(CO)8], [IrCl(CO)-
(PPh3)2] and [IrCl(CO)3]n were all purchased from Strem. Di-
ethylphosphine and diphenylphosphine were both purchased
from Strem. Cyclopentadiene, tetramethylcyclopentadiene, n-
butyllithium, dichlorodimethylsilane, methyl iodide, acetic acid
and methyl acetate were all purchased from Aldrich. Deuteriated
solvents were purchased from Cambridge Isotope Laboratories,
degassed by repeated freeze–pump–thaw cycles under high vac-
uum or by deoxygenation with dry argon/nitrogen prior to
use. [Rh(C5H4(CH2)2PPh2)(CO)] was prepared by a published
method.21
In order to try to increase the rate of the reaction even further,
we11–14 and others1 have investigated using highly electron donating
ligands to increase the electron density on the metal and hence
increase the rate of the oxidative addition step. This strategy has
proven effective in that the rate has been increased but, especially
when using tertiary phosphines, the catalysts are rather unstable.
In the case of PEt3,11 where the active species is [RhI(CO)(PEt3)2],
the rate of methanol carbonylation at 150 ◦C in the presence of 17%
added water is 1.5 times that using [RhI2(CO)2]−, but the rate drops
to the same as that using [RhI2(CO)2]−, over a period of 15 min.
The rate of oxidative addition of MeI to [RhI(CO)(PEt3)2] at room
temperature is 57 times that to [RhI2(CO)2]−, whilst the migration
of the methyl group onto CO is 38 times faster for [RhMeI3(CO)2]−
than for [RhMeI2(CO)(PEt3)2]. Despite this, oxidative addition of
MeI is rate determining in both cases. The deactivation of the
PEt3 containing catalyst is caused by loss of the PEt3 groups,
which are mainly oxidised to Et3PO, with only a small amount of
quaternisation to [Et3MeP]I and [Et3PH]I being observed. High
activity with better stability has been observed using bidentate
ligands involving at least one P donor,15–18 but the best results are
obtained if the ligand is unsymmetrical.16,17 Phosphine oxidation
is still a concern over longer reaction times. There has been one
report of a non-phosphine based ligand which gives high rate
and good stability. This involves the multifunctinal thiophene-
2,5-(carboxylatomethylenebenzotriazole) ligand.19 Because of the
problems associated with phosphine ligands, we attempted to
increase the electron density on the metal by using highly
electron donating pentamethylcyclopentadienyl (Cp*) ligands.
[Cp*Rh(CO)2] proved to be highly active for the carbonylation of
methyl ethanoate to ethanoic anhydride,13 but the most promising
results were obtained using [Cp*Co(CO)2] in the presence of
PEt3.14 At 100 bar and 120 ◦C, this system gave an initial rate
of methanol carbonylation of 44 mol dm−3 h−1, 1.5 times the rate
using the same concentration of [RhI2(CO)2]− under the same
conditions and faster t◦han obtained in the commercial rhodium
based systems at 180 C (ca. 20 mol dm−3 h−1). This catalytic
system was again not stable and after 200 s a period of inactivity
(400 s) was followed by a prolonged reaction with a rate of
2.5 mol dm−3 h−1. Although the actual catalytically active species
were not identified, it was proposed that the fast step was catalysed
by [Cp*Co(CO)(PEt3)] and the slower step by [Cp*Co(CO)I]−.
Unusually, the PEt3 appeared to transfer between cobalt atoms
without being quaternised as [CoI(CO)2(PEt3)2] was isolated from
the final solution of a catalytic reaction at low water content and
crystallographically characterised.
1,2,3,4-Tetramethyl-5-(2-chloroethyl)cyclopentadiene22
1,2,3,4-Tetramethylcyclopentadiene (30.5 g, 0.25 mol) was dis-
solved in diethyl ether (700 cm3) and cooled to 0 ◦C. n-BuLi
(160 cm3, 1.6 mol dm−3, 0.26 mol in hexane) was added dropwise
over 2 h and the solution was stirred at room temperature for
18 h. 1-Bromo-2-chloroethane (36.0 g, 0.25 mol) was added to the
mixture all at once and the resulting mixture stirred for 30 days
at room temperature (reaction was followed by GCMS). Water
(100 cm3) was added to the reaction mixture and the phases
were separated. The organic layer was washed once with saturated
aqueous NaCl solution (50 cm3), dried over MgSO4, filtered and
the solvent removed in vacuo. The product was a pale yellow oil
(32.0 g) which according to GCMS contained approximately 50%
of geminal isomers and 50% of non-geminal isomers.
Assuming that the initial highly active cobalt based catalyst
was [Cp*Co(CO)(PEt3)], we reasoned that its stability might be
improved if we connected the phosphine to the Cp* ligand, since
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1,2,3,4,-Tetramethylbicyclo[2,4]hepta-1,3-diene22
temperature for 3 days. The THF was removed in vacuo and the
residue washed with petroleum (50 cm3 × 2) to leave a white solid
1,2,3,4-Tetramethyl-5-(2-chloroethyl)cyclopentadiene (32.0 g) was
dissolved in THF (300 cm3). The solution was cooled to −60 ◦C
and n-BuLi (115 cm3, 1.6 mol dm−3, 0.18 mol in hexane) was
added dropwise with stirring. The reaction mixture was brought
to room temperature and stirred for 40 h. The THF was removed
in vacuo and the residue dissolved in diethyl ether (200 cm3).
Water (100 cm3) was added and the two phases were then
separated. The organic layer was washed with water (100 cm3). The
combined water layers were extracted with diethyl ether (50 cm3).
The combined organic layers were washed with saturated NaCl
(50 cm3), dried over NaSO4, filtered and the solvent removed
in vacuo to give a pale yellow oil (27.0 g). This mixture of
spirohydrocarbon and geminal isomers was purified using column
chromatography (silica gel 60, mobile solvent petroleum) to give
the pure spirohydrocarbon product as a pale yellow oil (14.8 g,
40%). 1H NMR (300 MHz, C6D6) d 1.95 (s, 6H, CH3), 1.6 (s, 6H,
CH3) and 1.1 (s, 4H, CH2). 13C NMR (75.45 MHz, C6D6) d 134.37
(s, CCH3), 134.06 (s, CCH3), 38.05 (C ring), 12.11 (s, CH3), 11.22
(s, CH2) and 9.31 (s, CH3).
1
(3.7 g, 90% yield). H NMR (300 MHz, d8-THF) d 7.39 (m (b),
4H, PhH ortho), 7.25 (m(b), 6H, PhH meta and para), 2.40 (s (vb),
2H, CH2 (10)), 2.04 (s (vb), 2H, CH2 (11)) and 1.73 (s(vb), 12H,
CH3 (6,7,8,9)). 13C NMR (75.4 MHz, d8-THF) d 141.40 (d, 2JCP
=
14.70 Hz, Ph (C) meta), 133.80 (d, 1JCP = 17.30 Hz, Ph (C) ortho),
128.90 (m, Ph (C) para), 112.50 (d, 3JCP = 14.96 Hz, ring C (5)),
106.80 (s, ring C (1,4)), 106.10 (s, ring C (2,3)), 32.26 (s, CH2 (11)),
23.55 (d, 1JCP = 17.48 Hz, CH2 (10)) and 11.23 (s, CH3 (6,7,8,9)).
1
31P { H} NMR (121.43 Hz, d8-THF) d −15.10 (b).
(2-P,P-Diethylphosphinoethyl)cyclopentadienyl lithium23
LiPEt2 (0.77 g, 6.5 mmol) was dissolved in THF (40 cm3) and
refluxed with bicyclo[2,4]hepta-1,3-diene (0.65 g, 7.03 mmol) for
1 h. The solvent was removed in vacuo and the residue washed
with petroleum (50 cm3 × 2) to leave a white solid (0.98 g, 80%
yield).1H NMR (300 MHz, d8-THF) d 5.52 (d (b), 2H, C5H4),
1,2,3,4-Tetramethyl-5-(2-P,P-diethylphosphinoethyl)-
cyclopentadienyl lithium
LiPEt2 (1.15 g, 12.0 mmol) was dissolved in THF (50 cm3) and
stirred with the spirohydrocarbon (2.0 g, 13.5 mmol) at room
temperature for 3 days. The THF was removed in vacuo and the
residue washed with petroleum (50 cm3 × 2) to leave a white
solid (2.55 g, 87% yield). Most of the lithium salts were highly
air sensitive and were characterised spectroscopically. H NMR
(300 MHz, d8-THF) d 2.27 (s(b), 2H, CH2 (10)), 1.76 (s(b), 12H,
CH3 (6,7,8,9)), 1.40 (m(b), 4H, CH2CH3), 1.33 (m, 2H, CH2 (11))
5.45 (d (b), 2H, C5H4), 2.61 (m, 2H, CH2 (7)), 1.65 (m, 2H, CH2
(6)), 1.35 (m, 4H, CH2 (8,10)) and 1.10 (m, 6H, CH3 (10,11)). 13
C
=
NMR (75.43 MHz, d8-THF) d 102.28 (d, ring C), 31.11 (d, JCP
9.21 Hz, CH2 (6)), 27.29 (d, JCP = 13.81 Hz, CH2 (7)), 19.43 (d,
2
JCP = 11.5 Hz, CH2 (8,9)) and 10.16 (d, JCP = 12.66 Hz, CH3
1
(9,11)). 31P NMR (121.4 MHz, d8-THF) d −25.05.
Preparation of 1,2,3,4-tetra(ethyl)cyclopentadiene24
and 1.06 (dt, 3JHH = 7.42 Hz, 3JHP = 13.83 Hz, 6H, CH2CH3). 13
C
An aqueous solution (50%) of NaOH (1050 g, 26.25 mol) was
cooled to 10 ◦C. Aliquat 336 (32.0 g, 79.0 mmol) and freshly
cracked cyclopentadiene (51.0 g, 0.77 mol) were added to this
cooled solution with constant stirring using a mechanical stirrer.
The reaction mixture was stirred for 15 min. Ethyl bromide
(344 g, 3.19 mol) was added over 1 h at 10 ◦C. The mixture
was stirred for 1 h at room temperature then heated to 35 ◦C
for a further 6 h. Stirring was stopped and the mixture allowed
to separate into two phases. The water layer was drawn off and
fresh NaOH solution (50%, 1050 g, 26.25 mol)) added. The
mixture was stirred for a further 5 h at room temperature. Stirring
was stopped and the organic phase separated from the aqueous
NMR (75.4 MHz, d8-THF) d 113.06 (d, 3JCP 11.51 Hz, ring C (5)),
1
106.81 (s, ring C (1,4)), 105.85 (s, ring C (2,3)), 30.33 (d, JCP
=
14.37 Hz, CH2 (11)), 22.97 (d, 2JCP = 13.26 Hz, CH2 (10)), 19.86
(d, 1JCP = 13.81 Hz, CH2CH3), 11.22 (s, CH3 (6,7,8,9)) and 10.45
(d, 2JCP = 13.27 Hz, PCH2CH3). 31P NMR (121.4 Hz, d8-THF) d
−21.93 (b). For numbering scheme see Scheme 1.
1,2,3,4-Tetramethyl-5-(2-P,P-diphenylphosphinoethyl)-
cyclopentadienyl lithium22
LiPPh2 (2.3 g, 12.0 mmol) was dissolved in THF (50 cm3) and
stirred with the spirohydrocarbon (50) (2.0 g, 13.5 mmol) at room
Scheme 1 Synthesis of CpꢀH(CH2)2PR2 (R = Et or Ph) and metal complexes of the related anion. (i) BuLi, THF; (ii) Br(CH2)2Cl, Et2O, 30 d, geminal
isomers removed by chromatography; (iii) LiPR2, THF, −60 ◦C, 3 d; (iv) aqueous work-up; (v) BuLi; (vi) M = Co, [Co2(CO)8], 170 ◦C; M = Rh,
[RhCl(CO)2]2; M = Ir, [IrCl(CO)3]n or [IrCl(CO)(PPh3)2].
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phase. The product was distilled (11 mbar, 90 ◦C) to give 1,2,3,4-
tetra(ethyl)cyclopentadiene as a pale yellow oil (60 g, 44% yield).
CH2 (10)), 1.36 (m, 4H, CH2CH3) and 1.04 (dt, 3JHP = 17.53 Hz,
3JHH = 7.73 Hz, 6H, CH2CH3). 13C NMR (75.4 MHz, C6D6) d
195.94 (dd, 1JCRh = 87.48 Hz, 2JCP = 20.72 Hz, CO (16)), 107.96
(m, ring(5)), 99.96 (m, ring (1,4)), 97.44 (s, ring (2,3)), 46.17 (d,
1JCP = 24.17 Hz, CH2 (11)), 23.44 (d, 1JCP = 25.32 Hz, CH2CH3),
20.36 (d, 2JCP = 2.30 Hz, CH2 (10)), 11.90 (s, CH3 (7,8)), 11.59 (s,
CH3 (6,9)) and 8.93 (s, CH2CH3). 31P NMR (121.4 MHz, CD2Cl2)
d 76.30 (d, JPRh = 189.21 Hz, PEt2). For numbering scheme see
Scheme 1. IR (petroleum ether) kmax 1898 cm−1. Found C 52.69, H
7.75%; C16H26OPRh requires C 52.18%, H 7.12%.
1H NMR (300 MHz, CD2Cl2) d 2.75 (s, 2H, CH2), 2.34 (q, 3JHH
=
3
7.58 Hz, 4H, CH2), 2.23 (q, JHH = 7.58 Hz, 4H, CH2), 1.06 (t,
3JHH = 7.54 Hz, 6H, CH3) and 1.01 (t, 3JHH = 7.54 Hz, 6H, CH3).
13C NMR (75.4 MHz, CD2Cl2) d 141.80 (s, ring C), 139.55 (s, ring
C), 42.30 (s, CH2 (ring)), 22.12 (s, CH2), 19.54 (s, CH2) and 15.81
(s, CH3).
1-Chloromethyl(dimethyl)silyl-2,3,4,5-tetraethylcyclopentadiene
A solution of n-BuLi in hexane (35 cm3, 1.6 mol dm−3, 56 mmol)
was added dropwise to a solution of tetra(ethyl)cyclopentadiene
(10.0 g, 56 mmol) in THF (300 cm3) at 0 ◦C. The solution was
stirred for 2 h before the addition of Me2SiCl2 (15.11 g, 56.0 mmol)
at −90 ◦C. The mixture was stirred overnight at room temperature.
The THF was removed in vacuo and the resulting oily solid
extracted with petroleum (50 cm3 × 2). The solvent was removed
in vacuo from the filtra◦te and the yellow oil was distilled under
reduced pressure at 80 C to give a pale yellow oil (13.1 g, 88%
yield). 1H NMR (300 MHz, C6D6) d 3.42 (s (b), 1H, CH), 2.41 (m
Carbonyl(j2-1-diphenylphosphinoethyl-2,3,4,5-
tetramethylcyclopentadienyl)rhodium(I)
A solution of [RhCl(CO)2]2 (0.2 g, 0.52 mmol) in THF (50 cm3)
was treated dropwise with a solution of Cpꢀ(CH2)2PPh2Li (0.38 g,
1.12 mmol) in THF (10 cm3). Immediately on addition of the
ligand to the dimer solution, a colour change from pale yellow
to dark red was noted. The mixture was refluxed for 8 h. The
solvent was removed in vacuo and petroleum added (50 cm3).
After filtration to leave a white solid (LiCl), the red solution was
evaporated in vacuo to approximately half volume (25 cm3) and
(b), 4H, CH2), 2.26 (q, 3JHH = 7.72 Hz, 4H, CH2), 0.99 (t, 3JHH
=
◦
7.72 Hz, 12H, CH3) and 0.19 (s, 6H, SiCH3). 13C NMR (75.4 MHz,
C6D6) d 143.71 (s, ring), 139.90 (s, ring), 56.30 (s, CH), 21.92 (s,
CH2), 19.68 (s, CH2), 15.83 (s, CH3) and 1.03 (s, SiCH3).
cooled to −78 C to yield red crystals (0.17 g, 45% yield). H
NMR (300 MHz, CD2Cl2) d 7.67 (m, 4H, PhH), 7.50 (m, 6H,
PhH), 3.45 (dt, 3JHH = 6.94 Hz, 3JHP = 10.97 Hz, 2H, CH2 (11)),
1
3
3
2.23 (dt, JHH = 6.92 Hz, JHP = 29.10 Hz, CH2 (10)), 1.88 (d,
JHP = 5.29 Hz, CH3 (7,8)) and 1.59 (s, 6H, CH3 (6,9)). 13C NMR
(75.4 MHz, CD2Cl2) d 135.40 (s, PhC), 133.80 (s, C(Ph)), 132.03
(s, PhC), 129.67 (d, JCP = 10.4 Hz, PhC), 114.20 (m, ring (3,2)),
109.40 (m, ring (1,4)), 84.10 (m, ring (5)), 46.50 (d, JCP = 31.2 Hz,
CH2 (11)), 19.49 (s, CH2 (10)), 9.68 (s, CH3 (7,8)) and 9.22 (s, CH3
(6,9)). 31P NMR (121.4 MHz, CD2Cl2) d 52.12 (d, JPRh = 174.99 Hz,
PRh). For numbering scheme, see Scheme 1. IR (petroleum ether)
kmax 1933 cm−1. Found: C 62.49%, H 5.53%; C24H26OPRh requires
C 62.08%, H 5.64.
1-Dimethylphosphinomethyl(dimethyl)silyl-2,3,4,5-
tetraethylcyclopentadiene
(C5Et5H)SiMe2Cl (5.9 g, 0.020 mol) was dissolved in THF
(100 cm3) and cooled to −78 ◦C. This was treated dropwise with a
solution of LiCH2PMe2 (1.80 g, 0.020 mol) in THF (50 cm3). The
solution was stirred for 24 h at room temperature. The THF was
removed in vacuo and petroleum ether (100 cm3) was added to the
residue. After filtration the petroleum was removed in vacuo to give
a sticky oily product (4.5 g, 66% yield). 1H NMR (300 MHz, C6D6)
d 3.36 (s (b), 1H, CH), 2.41 (m, 8H, CH2), 1.18 (t, 3JHH = 6.80 Hz,
Carbonyl(j2-diethylphosphinoethylcyclopentadienyl)rhodium(I)
2
2
12H, CH3), 0.99 (d, JHP = 4.00 Hz, 6H, PCH3), 0.47 (d, JHP
=
3 Hz, 2H, CH2P) and 0.22 (s, 6H, SiCH3). 13C NMR (75.4 MHz,
C6D6) d 141.59 (s, C ring), 140.95 (s, C ring), 49.67 (s, CH), 22.26
(s, CH2), 19.75 (s, CH2), 18.51 (d, JCP = 18.85 Hz, PCH2) 17.10 (d,
JCP = 28.1 Hz, PCH3), 15.30 (s, CH3), 15.1 (s, CH3) and −0.70 (s,
SiCH3). 31P NMR (121.40 MHz, C6D6) d −53.90.
A solution of [RhCl(CO)2]2 (0.20 g, 0.52 mmol) in THF (50 cm3)
was treated dropwise with a solution of Cp(CH2)2PEt2Li (0.21 g,
1.12 mmol) in THF (10 cm3). Immediately on addition of the
ligand to the dimer solution, a colour change from pale yellow
to dark red was noted. The mixture was refluxed for 8 h. The
solvent was removed in vacuo and petroleum added (50 cm3).
After filtration to leave a white solid (LiCl), the red solution was
evaporated in vacuo to approximately half volume (25 cm3) and
Carbonyl(j2-1-diethylphosphinoethyl-2,3,4,5-
tetramethylcyclopentadienyl)rhodium(I)
◦
1
cooled to −78 C to yield red crystals (0.14 g, 70% yield). H
A solution of [RhCl(CO)2]2 (0.2 g, 0.52 mmol) in THF (50 cm3)
was treated dropwise with a solution of Cpꢀ(CH2)2PEt2Li (Cpꢀ =
C5Me4, 0.27 g, 1.12 mmol) in THF (10 cm3). Immediately on
addition of the ligand to the dimer solution, a colour change from
pale yellow to dark red was noted. The mixture was refluxed for 8 h.
The solvent was removed in vacuo and petroleum added (50 cm3).
After filtration to leave a white solid (LiCl), the red solution was
evaporated in ◦vacuo to approximately half volume (25 cm3) and
cooled to −78 C to yield red crystals (0.17 g, 65% yield). 1H NMR
(299.9 MHz, C6D6) d 2.37 (dt, 3JHP = 9.61 Hz, 3JHH = 7.07 Hz, 2H,
NMR (299.9 MHz, C6D6) d 5.59 (m, 2H, H (ring)), 5.46 (m, 2H,
H (ring)), 2.04 (m, 2H, CH2 (7)), 1.81 (dt, 2JHP = 28.26 Hz, 3JHH
=
=
7.30 Hz, CH2 (6)), 1.35 (m, 4H, CH2 (8,10)) and 1.04 (dt, 3JHP
17.84 Hz, JHH = 7.53 Hz, CH3 (9,11)). 13C NMR (75.4 MHz,
3
2
C6D6) d 195.10 (dd, JCRh = 88.63 Hz, JCP = 20.72 Hz, CO),
112.0 (s, C (5)), 87.22 (m, C (2,3)), 85.89 (m, C (1,4)), 46.23 (d,
1
JCP = 25.32 Hz, CH2 (7)), 24.69 (s, CH2 (6)), 24.23 (dd, JCP
=
2
27.62 Hz, JCRh = 2.30 Hz, CH2 (8,10)) and 9.57 (s, CH3 (9,11)).
31P NMR (121.4 MHz, C6D6) d 80.29 (d, 1JPRh = 191.31 Hz, PEt2).
For numbering scheme, see the free ligand. IR (petroleum ether)
kmax1938 cm −1. Found C 46.94%, H 6.35%; C12H19OPRh requires
C 46.17%, H 5.81%.
CH2 (11)), 2.18 (d, JHP = 2.95 Hz, 6H, CH3, (7,8)), 2.13 (d, JHRh
=
2
3
0.7 Hz, 6H, CH3 (6,9)), 2.03 (dt, JHP = 26.98 Hz, JHH 6.95 Hz,
9 4 | Dalton Trans., 2006, 91–107
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Carbonyl(j2-1-dimethylphosphinomethyl(dimethyl)silyl-2,3,4,5-
tetraethylcyclopentadienyl)rhodium(I)
Hexacarbonylbis(2-(2ꢀ,3ꢀ,4ꢀ,5ꢀ-tetramethylcyclopentadienylethyl)-
diphenylphosphine)dicobalt(0)
A solution of [RhCl(CO)2]2 (0.2 g, 0.52 mmol) in THF (50 cm3)
was treated dropwise with a solution of C5Et4SiMe2CH2PMe2Li
(0.35 g,1.12 mmol) in THF (10 cm3). Immediately on addition
of the ligand to the dimer solution, a colour change from pale
yellow to dark red was noted. The solution was stirred at room
temperature for 1 h and the solvent was removed in vacuo.
Petroleum was added to the oily solid (50 cm3). After filtration to
leave a white solid (LiCl) the red/brown solution was evaporated
in vacuo to approximately half volume (25 cm3) and cooled to
−78 ◦C, −40 ◦C and −2 ◦C. This failed to yield crystals. The
solution was reduced in vacuo to give a red/brown oil (0.21 g, 62%
A solution of [Co2(CO)8] (0.15 g, 0.44 mmol) and 1,3-
cyclohexadiene (0.05 g, 0.66 mmol) in methylene chloride (25 cm3)
was treated dropwise with a solution of CpꢀH(CH2)2PPh2 (0.3 g,
0.89 mmol) in THF (25 cm3). The mixture was refluxed for 4 h.
The solvent was removed in vacuo and petroleum added (50 cm3)
to the red oil. After filtration, the red solution was cooled to 2 ◦C
for several days to yield red/brown crystals (0.14 g, 35% yield). 1H
NMR‡ (300 MHz, CD2Cl2) d 7.55 (m, 10H, PhH), 2.67 (s (b), 1H,
CH), 2,43 (m (b), 2H, CH2 (10)), 1.92 (m (b), 2H, CH2 (11)) and
1.67 (m (b), 12H, CH3). 13C NMR‡ (Bruker, CD2Cl2) d 202.75 (t,
J = 9.77 Hz, CO), 139.95 (s, ring C), 137.25 (s, ring C), 134.21
(s, ring C), 132.29 (m, PhC), 130.82 (m, PhC), 129.14 (m, PhC),
56.12 (d, 1JCP = 15.86 Hz, CH2 (11)), 52.09 (s, CH), 22.50 (s, CH2
(10)), 11.80 (s, CH3) and 11.20 (s, CH3). 31P NMR (121.4 MHz,
CD2Cl2) d 61.17 (s, PPh), 59.87 (m, PPh) and 59.57 (m, PPh). IR
(CH2Cl2) kmax 1973 and 1951 cm−1.
3
yield).1H NMR (300 MHz, C6D6) d 2.62 (dq, JHH = 7.33 Hz,
Hexacarbonylbis(2,3,4,5-tetramethyl(dimethyl)silylmethyl)-
(dimethyl)phosphinedicobalt(0)
A
solution of [Co2(CO)8] (0.27 g, 0.81 mmol) and 1,3-
3
2JHH = 14.70 Hz, 2H, CH2 (6a,9a)), 2.45 (dq, JHH = 7.33 Hz,
cyclohexadiene (0.090 g, 1.2 mmol) in THF (25 cm3) was
treated dropwise with a solution of C5Et4HSiMe2CH2PMe2 (0.5 g,
1.6 mmol) in THF (25 cm3). The mixture was refluxed for 5 h. The
solvent was removed in vacuo and petroleum added (50 cm3) to
the red oil. After filtration, the red solution was cooled to 2 ◦C
for several days to yield red/brown crystals (0.30 g, 41% yield). 1H
NMR (300 MHz, C6D6) d 2.95 (s (b), 1H, CH), 2.36 (m, 4H, CH2),
2.07 (m, 4H, CH2), 1.05 (b, 12H, CH3), 0.88 (b, 6H, PCH3), 0.77
(b, 4H, CH2P) and 0.28 (s, SiCH3). 13C NMR (75.4 MHz, C6D6)
d 203.92 (m, CO), 142.27 (s, C ring), 140.73 (s, C ring), 49.86 (s,
CH), 22.66 (d, JCP = 27.90 HZ, PMe2), 22.09 (s, CH2), 19.63 (s,
CH2), 18.29 (b, PCH2), 16.25 (s, CH3), 16.02 (s, CH3) and 0.46
(s, SiCH3). 31P NMR (121.4 MHz, C6H6) d 32.26. IR (petroleum
ether) kmax 1969 and 1951 cm−1.
2JHH = 14.70 Hz, 2H, CH2 (6b,9b)), 2.39 (qt (b), 3JHH = 7.33 Hz,
J = 1.33 Hz, 4H, CH2 (7,8)), 1.58 (dd, 2JHP = 13.39 Hz, 3JHRh
=
1.07 Hz, 2H, CH2 (16)), 1.35 (t, 3 JHH = 7.33 Hz, 6H, CH3 (10,13)),
1.32 (dd, 2JHP = 10.18 Hz, 3JHRh = 1.59 Hz, 6H, CH3 (17,18)), 1.19
(t, 3JHH = 7.33 Hz, 6H, CH3 (11,12)) and 0.40 (s, 6H, CH3 (14,15)).
13C NMR (75.4 MHz, C6D6) d 196.40 (dd, JCRh = 86.3 Hz, JCP
=
25.1 Hz, CO), 36.25 (d, JCP = 13.11 Hz, CH2 (16)), 23.70 (d,
JCP = 26.88 Hz, CH3 (17,18)), 21.22 (s, CH3 (10,13)), 20.80 (s, CH3
(11,12)), 19.82 (s, CH2 (6,9)), 18.28 (s, CH2 (7,8)) and 1.10 (s, CH3
(14,15)). 31P NMR (121.4 MHz, C6 D6) d 15.22 (d, JPRh = 185.37
Hz). IR (petroleum ether) kmax 2029, 1967 and 1928 cm−1.
Carbonyl(j2-1-diethylphosphinoethyl-2,3,4,5-
tetramethylcyclopentadienyl)iridium(I)
Hexacarbonylbis(2-(2ꢀ,3ꢀ,4ꢀ,5ꢀ-tetramethylcyclopentadienylethyl)-
diethylphosphine)dicobalt(0)
A solution of [Ir(PPh3)2(CO)Cl] (0.79 g, 1.0 mmol) in THF
(30 cm3) was treated dropwise with a solution of Cpꢀ(CH2)2PEt2Li
(0.34 g, 1.4 mmol) in THF (20 cm3). The mixture was refluxed
for 3 h. The solvent was removed in vacuo and petroleum added
(50 cm3). After filtration to leave a white solid (LiCl), the yellow
solution was evaporated in vacuo to approximately half volume
(25 cm3) and cooled to 2 ◦C for several days to yield yellow crystals
A
solution of [Co2(CO)8] (0.30 g, 0.89 mmol) and 1,3-
cyclohexadiene (0.14 g, 1.8 mmol) in THF (25 cm3) was treated
dropwise with a solution of CpꢀH(CH2)2PEt2 (0.43 g, 1.8 mmol)
in THF (25 cm3). This solution was transferred to an autoclave
using standard Schlenk techniques under carbon monoxide. The
autoclave was pressurized to approximately 20 bar of carbon
monoxide and heated to 100 ◦C for 60 min. The solvent was
removed in vacuo and petroleum added (50 cm3) to the red oil.
(0.22 g, 49% yield). 1H NMR (300 MHz, C6D6) d 2.48 (dt, 3JHP
=
9.73 Hz, 3JHH = 7.29 Hz, 2H, CH2 (11)), 2.18 (d, JHP = 2.40 Hz,
6H, CH3 ring methyl (7,8)), 2.16 (s(b), 6H, CH3 ring methyl (6,9)),
◦
3
3
After filtration, the red solution was cooled to 2 C. No crystals
1.80 (dt, JHP = 24.19 Hz, JHH = 7.29 Hz, 2H, CH2 (10)), 1.48
were isolated. 31P NMR (crude product solution) (121.4 MHz,
C6D6) d 58.20, 57.60 and 55.76. IR (petroleum ether) kmax 2078,
2009, 1993 and 1951 cm−1.
3
3
(m, CH2CH3) and 1.04 (dt, JHP = 17.79 Hz, JHH = 7.55 Hz,
6H, CH2CH3). 13C NMR (75.4 MHz, C6D6) d 181.10 (d, JCP
=
2
11.51 Hz, CO (16)), 104.65 (d, 3JCP = 9.21 Hz, ring C (5)), 94.52
(d, 2JCP = 6.91 Hz, ring C (1,4)), 93.04 (s, ring C (2,3)), 48.49 (d,
1JCP = 31.08 Hz, CH2 (11)), 24.40 (d, 1JCP = 34.53 Hz, CH2CH3),
19.66 (s, CH2 (10)), 11.87 (s, ring C), 11.41 (s, ring C) and 9.47 (s,
CH2CH3). 31P NMR (121.4 MHz, C6D6) d 37.67. For numbering
‡ Six isomers of this product exist depending on the position of the double
bond in the cyclopentadienyl ring.
scheme, see Scheme 1. IR (petroleum ether) kmax 1910 cm −1
.
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Carbonyl(j2-1-diethylphosphinoethyl-2,3,4,5-
tetramethylcyclopentadienyl)cobalt(I)
NMR (121.4 Hz, CD2Cl2) d 51.45 (d, JPRh = 157.14 Hz, PPh). For
numbering, see Scheme 1).
A solution of [Co2(CO)8] (0.36 g, 1.0 mmol) in THF (15 cm3)
was treated dropwise with a solution of Cpꢀ(CH2)2PEt2Li (0.26 g,
1.1 mmol) in THF (15 cm3). Using standard Schlenk techniques
this solution was transferred to an autoclave under nitrogen, sealed
and heated to approximately 160 ◦C for 90 min. The solvent was
removed in vacuo and petroleum added (50 cm3) to the red oil.
After filtration, the red solution was cooled to −78 ◦C to yield
dark red/brown crystals (0.17 g, 52% yield). 1H NMR (300 MHz,
(j2-1-Diethylphosphinoethyl-2,3,4,5-
tetramethylcyclopentadienyl)diiodorhodium(I)
[Rh(Cpꢀ(CH2)2PEt2)I2] was formed from reaction of
[Rh(Cpꢀ(CH2)2PEt2)(CO)] with methyl iodide, methyl ethanoate,
water and ethanoic acid (under 30 bar CO and 150 ◦C) under
catalytic conditions. The exact details of the experiment are given
1
later. H NMR (300 MHz, C6D6) d 2.47 (m, J = 7.72 Hz, 2H,
CH2CH3 (Ha), 2.05 (dt, 3JHP = 10.61 Hz, 3JHH = 7.26 Hz, 2H, CH2
(11)), 1.98 (d, JHP = 5.30 Hz, 6H, CH3 (7,8)), 1.49 (s, 6H, CH3
3
3
C6D6) d 2.31 (dt, JHP = 8.96, JHH = 7.93 Hz, 2H, CH2 (11)),
2.12 (d, JHP = 2.10 Hz, 6H, CH3 (7,8)), 2.09 (s, CH3 (6,9), 1.82
3
(6,9)), 1.25 (dt,2JHP = 27.0 Hz, JHH = 7.20 Hz, 2H, CH2 (10)),
2
3
(dt, JHP = 22.27 Hz, JHH = 7.93 Hz, 2H, CH2 (10)), 1.39 (m,
2
3
3
1.55–1.12 (m, 2H, CH2CH3 (Hb) and 0.85 (dt, JHP = 15.92 Hz,
4H, CH2CH3), 1.07 (dt, JHP = 16.64 Hz, JHH = 7.42 Hz, 6H,
CH2CH3). 13C NMR (75.4 MHz, C6D6) d 207.86 (s, CO (16)),
105.80 (d, JCP = 9.20 Hz, ring C), 94.84 (d, JCP = 4.59 Hz, ring C),
3JHH = 7.72 Hz, 6H, CH2CH3 (13,15)). 13C NMR (75.4 MHz,
2
C6D6) d 43.17 (d, JCP = 26.48 Hz, CH2 (11)), 23.22 (d, JCP
=
1
27.63 Hz, CH2CH3), 18.52 (s, CH2 (10)), 11.47 (s, CH3 (8,9)),
91.35 (s, ring C), 43.89 (d, JCP = 25.32 Hz, CH2 (11)), 22.99 (d,
2
10.72 (s, CH3 (6,7)) and 8.80 (d, JCP = 5.76 Hz, CH2CH3). 31P
1JCP = 24.17 Hz, CH2CH3), 20.10 (d, 2JCP = 6.91 Hz, CH2 (10)),
12.26 (s, ring methyl), 12.12 (s, ring methyl), 9.14 (s, CH2CH3).
31P NMR (121.4 MHz, C6D6) d 87.60 (b). For numbering, see
Scheme 1. IR (petroleum ether) kmax 1910 cm−1. Found C 59.18%,
H 8.59%; C16H26CoOP requires C 59.26%, H 8.08%.
NMR (121.4 MHz, C6D6) d 63.71 (d, 1JPRh 148.29 Hz, PEt2). For
numbering, see Scheme 1.
(j2-1-Diethylphosphinoethyl-2,3,4,5-
tetramethylcyclopentadienyl)ethanoyliodorhodium(III)
A solution of [Rh(Cpꢀ(CH2)2PEt2)(CO)] (0.10 g, 0.27 mmol) in
THF (15 cm3) was treated with an excess of methyl iodide (2 cm3,
32.1 mmol) and stirred for 4 h. The solvent was removed in vacuo
and the red solid product was recrystallised from petroleum ether
(25 cm3) (0.10 g, 75% yield). 1H NMR (299.98 MHz, C6D6)§ d 3.18
(s, 3H, C(O)CH3), 2.24–1.14§ (m, 8H, CH2 (10, 11, CH2CH3)), 2.09
(d, JHP = 5.63 Hz, 3H, CH3 (ring methyl)), 1.74 (d, JHP = 0.92 Hz,
3H, CH3 (ring methyl)), 1.43 (dd, JHP = 2.7 Hz, JHRh = 1.5 Hz,
3H, CH3 (ring methyl)), 1.34 (dd, JHP = 1.2 Hz, JHRh = 0.60 Hz,
3H, CH3 (ring methyl)), 1.02 (dt, 3JHH = 8.27 Hz, 3JHP = 9.30 Hz,
CH2CH3) and 0.56 (dt, 3JHH = 8.06 Hz, 3JHP = 9.30 Hz, CH2CH3).
13C NMR (75.4 MHz, C6D6) d 121.30 (d, JCP = 11.90 Hz, C (ring)),
110.75 (d, JCP = 12.1 Hz, C (ring)), 105.66 (s, C (ring)), 95.36 (s, C
(ring)), 84.60 (d, JCP = 7.18 Hz, C (ring)), 54.20 (s, C(O)CH3), 43.97
(d, 1JCP = 27.63 Hz, CH2 (11)), 23.39 (d, JCP = 26.48 Hz, CH2CH3),
Dichloro(j2-1-diethylphosphinoethyl-2,3,4,5-
tetramethylcyclopentadienyl)rhodium(I)
[Rh(Cpꢀ(CH2)2PEt2)(CO)] (0.050 g, 0.14 mmol) was dissolved in
CD2Cl2 (5 cm3) and stirred at room temperature for 24 h. The
product was recrystallised from benzene to give bright orange
1
crystals (0.050 g, 87% yield). H NMR (299.9 MHz, CD2Cl2) d
3
3
2.89 (dt, JHH = 7.5 Hz, JHP = 10.45 Hz, 2H, CH2 (11)), 2.31
3
3
(dt, JHH 7.5 Hz, JHP = 28.86 Hz, 2H, CH2 (10)), 2.22 (m, 2H,
CH2CH3 (Hb), 1.93 (m, 2H, CH2CH3 (Ha), 1.77 (d, JHP = 7.5 Hz,
CH3 (7,8)), 1.60 (s, 3H, CH3 (6,9)) and (dt, 3JHH = 7.16 Hz, 3JHP
=
15.5 Hz, 6H, CH2CH3). 13C NMR (75.4 MHz, CD2Cl2) d 114.20 (t,
J = 8.15 Hz, C ring), 111.28 (dd, JCP = 8.2 Hz, JCRh = 4.08 Hz, C
ring), 86.39 (dd, JCP = 7.34 Hz, JCRh = 3.26 Hz, C ring), 41.66 (dd,
2
1JCP = 27.6 Hz, JCRh = 2.87 Hz, CH2 (11)), 20.10 (s, CH2 (10)),
2
18.39 (d, JCP = 26.3 Hz, CH2CH3), 9.40 (s, CH3 (6,9)), 9.31 (d,
2
19.25 (s, CH3 (10)), 16.17 (d, JCP = 24.17 Hz, CH2CH3), 9.83
JCP = 3.12 Hz, CH3 (7,8)) and 7.64 (d, 2JCP = 5.20 Hz, CH2CH3).
31P NMR (121.4 MHz, CD2Cl2) d 72.80 (d, JPRh = 146.50 Hz). For
numbering see Scheme 1. Found C 44.62%, H 5.21%; C15H26Cl2Rh
requires C 43.82%, H 6.37%.
(s, CH3 (ring methyl)), 9.37 (s, CH3, (ring methyl)), 9.08 (s,
CH3 (ring methyl)), 8.73 (s, ring methyl) and 7.95 (s, CH2CH3).
31P NMR (121.4 Hz, C6H6) d 68.57 (d, JPRh = 167.58 Hz). IR
(petroleum ether) kmax 1629 cm−1. For numbering, see Scheme 1).
Found C 40.71%, H 5.02%; C17H29IOPRh requires C 40.02%,
H 5.73%.
Dichloro(j2-1-diphenylphosphinoethyl-2,3,4,5-
tetramethylcyclopentadienyl)rhodium(I)
Carbonyl(j2-1-diethylphosphinoethylcyclopentadienyl)-
methylrhodium(III) tetrafluoroborate
[Rh(Cpꢀ(CH2)2PPh2)(CO)] (0.050 g, 0.11 mmol) was dissolved in
CD2Cl2 (5 cm3) and stirred at room temperature for 72 h. The
product was recrystallised from benzene to give bright orange
crystals (0.030 g, 69% yield). 1H NMR (300 MHz, CD2Cl2) d 7.84
A sample of [Rh(C5H4(CH2)2PEt2)(CO)] (20 mg) was dissolved
in neat MeI which, after 10 min, was removed with a stream of
N2. The resulting sample of [Rh(C5H4(CH2)2PEt2)(C(O)Me)I] was
redissolved in CH2Cl2 and treatment with a small excess of AgBF4
to give a yellow precipitate of AgI which was removed by filtration.
The resulting solution displayed a single mCO band in the IR spec-
trum at 2059 cm−1 assigned to [Rh(C5H4(CH2)2PEt2)Me(CO)]BF4.
(m, 4H, PhH), 7.43 (m, 6H, PhH), 3.50 (dt, 3JHH = 7.24 Hz, 3JHP
=
10.61 Hz, 2H, CH2 (11)), 2.30 (dt, 3JHH = 7.24 Hz, 1JHP = 29.45 Hz,
2H, CH2 (10)), 1.79 (d, JHP = 5.79 Hz, 6H, CH3 (7,8)) and 1.44
(s, 6H, CH3 (6,9)). 13C NMR (299.98 MHz, CD2Cl2) d 133.36 (d,
JCP = 9.77 Hz, PhC), 131.61 (d, JCP = 2.44 Hz, PhC), 129.14
(d, JCP = 10.99 Hz, PhC), 45.61 (d, JCP = 31.74 Hz, CH2 (11)),
18.87 (s, CH2 (10)), 9.56 (s, CH3 (7,8)) and 9.49 (s, CH3 (6,9)). 31
P
§ Unable to assign the exact methylene groups due to complicated pattern.
9 6 | Dalton Trans., 2006, 91–107
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The solvent was removed and NMR spectra of the product were
recorded in CD2Cl2. 1H NMR d 0.95 (dd, 3H, Rh–CH3, J = 2.3,
3.5 Hz), 1.04–1.22 (m, 6H, CH2CH3), 1.94–2.24, 2.39–2.72, 2.91–
3.17 (each m, 4H, 2H, 2H resp., CH2) 5.55, 5.60, 5.80, 6.05 (each
m, 1H, ring CH). 31P NMR d 72.2 (d, JRhP = 129.5 Hz).
reaction solution was quickly transferred to the IR cell and
data collection was started. The IR cell (0.5 mm pathlength,
CaF2 windows) was maintained at constant temperature by a
thermostated jacket. Spectra (2200–1600 cm−1) were scanned and
saved at regular time intervals under computer control. For the
faster oxidative addition reaction of [Rh(Cpꢀ(CH2)2PPh2)(CO)],
a rapid mixing stopped-flow infrared accessory (Hi-Tech FMA-
10) was used in combination with a Nicolet Magna 560 FTIR
instrument fitted with an MCT detector and using OMNIC
Series software. Absorbance vs. time data for the appropriate mCO
bands were extracted and analyzed off-line using Kaleidagraph
curve-fitting software. For each experiment, the decay of the
appropriate mCO band was fitted to an exponential curve, with
correlation coefficient ≥0.999, to give a pseudo-first order rate
constant. Each kinetic run was repeated at least twice to check
reproducibility, the kobs data given being averaged values with
component measurements deviating from each other by ≤5%.
Carbonyl(j2-1-diethylphosphinoethyl-2,3,4,5-
tetramethylcyclopentadienyl)methyliridium(III) iodide
A solution of [Ir(Cpꢀ(CH2)2PEt2)(CO)] (0.10 g, 0.22 mmol) in
THF (15 cm3) was treated with an excess of methyl iodide (2 cm3,
32.1 mmol) and stirred for 4 h. The solvent was removed in vacuo
and the pale yellow product was recrystallised from an ethanol
(10 cm3)/petroleum ether (2 cm3) solution (0.070 g, 53% yield).
1H NMR (CD2Cl2, 300 MHz) d 3.39 (m, 2H, CH2 (11)), 2.59 (m,
2H, CH2 (10)), 2.43 (s, 3H, CH3 (ring methyl)), 2.27 (d, JHP
=
3.07 Hz, CH3 (ring methyl)), 2.25 (m, 2H, CH2CH3), 2.02 (m, 2H,
CH2CH3), 1.92 (s, 3H, CH3 (ring methyl)), 1.85 (d, JHP = 3.07 Hz,
3
3
CH3 (ring methyl)), 1.19 (dt, JHH = 7.68 Hz, JHP = 12.08 Hz,
High pressure NMR studies
3
3
3H, CH2CH3), 1.12 (dt, JHH = 7.68 Hz, JHP = 11.52 Hz, 3H,
3
CH2CH3) and 0.62 (d, JHP = 3.84 Hz, 3H, Ir–CH3). 31P NMR
High pressure NMR studies were carried out in a sapphire tube
fitted with a titanium head. The tube was loaded using standard
Schlenk line and catheter tubing techniques.
(CD2Cl2, 121.44 MHz) d 32.07. For numbering, see Scheme 1. IR
(CD2Cl2) kmax 2038 cm−1.
In a typical procedure, [Rh(Cpꢀ(CH2)2PEt2)(CO)] (0.02 g,
0.05 mmol) was dissolved in a stock solution of D2O : ethanoic
acid : methyl ethanoate : methyl iodide (1 : 6 : 2 : 1) (2 cm3).
The resulting solution was transferred to the previously degassed
sapphire cell and pressurized with approximately 15 bar of carbon
monoxide. The cell was allowed to stand for 15 h before the first
spectrum was collected at room temperature. The temperature
was increased in increments of 10 ◦C and equilibrated at each
temperature for 30 min before a spectrum was recorded. This
process was repeated until a final temperature of 90 ◦C was
reached. The NMR cell was cooled to room temperature.
Similar techniques were used for: [Cp*Rh(PEt3)(CO)] (0.06 g,
0.20 mmol), [Rh(Cp(CH2)2PEt2)(CO)] (0.04 g, 0.13 mmol), and
[Co(Cpꢀ(CH2)2PEt2)(CO)] (0.09 g, 0.28 mmol). Similar studies
were also carried out on [Co(Cpꢀ(CH2)2PEt2)(CO)] (0.04 g,
0.13 mmol) in 2 cm3 of a stock solution of deuteriated methanol
(5 cm3) : methyl iodide (0.5 cm3) : water (0.35 cm3).
(j2-1-Diethylphosphinoethyl-2,3,4,5-
tetramethylcyclopentadienyl)ethanoyliodocobalt(III)
A solution of [Co(Cpꢀ(CH2)2PEt2)(CO)] (0.10 g, 0.31 mmol) in
THF (15 cm3) was treated with an excess of methyl iodide (2 cm3,
32.1 mmol) and stirred for 4 h. The solvent was removed in vacuo
and the red/brown solid product was recrystallised from
petroleum ether (25 cm3) (0.090 g, 66% yield). H NMR (C6D6,
1
300 MHz) d 3.41 (s, 3H, C(O)CH3), 2.28 (m, 2H, CH2 (10)), 2.00
(m, 2H, CH2CH3), 1.89 (d, JHP = 3.07 Hz, ring methyl), 1.72 (s, ring
methyl), 1.44 (m, 2H, CH2 (11)), 1.23 (d, 3H, JHP = 1.54 Hz, ring
methyl), 1.09 (m, 2H, CH2CH3), 0.96 (s, 3H, ring methyl), 0.64 (dt,
3JHH = 7.68 Hz, 3JHP = 15.62 Hz, CH2CH3) and 0.56 (dt, 3JHH
=
7.43 Hz, 3JHP = 14.34 Hz, CH2CH3). 13C NMR (C6D6, 75.4 MHz)
d 114.50 (d, JCP = 11.00 Hz, ring C), 100.90 (d, JCP = 7.31 Hz,
ring C), 98.17 (d, JCP = 5.50 Hz, ring C), 93.94 (d, JCP = 2.20 Hz,
ring C), 78.99 (s, ring C), 53.30 (d, JCP = 7.16 Hz, C(O)CH3),
39.30 (d, JCP = 26.76 Hz, CH2 (11)), 21.90 (d, JCP = 25.64 Hz,
Catalytic experiments
CH2CH3), 17.87 (d, JCP = 3.66 Hz, CH2 (10)), 13.50 (d, JCP
=
These experiments were carried out in a Hastelloy autoclave
(30 cm3) attached via a mass flow controller to a ballast vessel
(37.8 cm3) so that constant pressure and temperature could be
maintained within the autoclave. The autoclave was fitted with
a stirrer, heater, catalyst injector, internal thermocouple and
pressure transducer for the autoclave and ballast vessel.
23.60 Hz, CH2CH3), 12.23 (s, ring methyl), 9.88 (s, ring methyl),
9.13 (s, ring methyl), 7.91 (s, ring methyl), 7.81 (d, JCP = 2.34 Hz,
CH2CH3) and 7.78 (d, JCP = 2.48 Hz, CH2CH3). For numbering,
see Scheme 1. 31P NMR (C6D6, 121.44 MHz) d 69.10.
Kinetic measurements
Throughout the course of these experiments the catalyst was
either introduced to the autoclave via the catalyst injector at
temperature and pressure or added to the autoclave initially. For
the latter procedure methyl iodide was added via the catalyst
injector at temperature and pressure to initiate the reaction. A
solution was added to the thoroughly carbon monoxide flushed
autoclave (through the autoclave side-arm, via a syringe and
needle while under continuous CO flush). The autoclave was
flushed with three cycles of approximately 30 bar of carbon
monoxide and finally pressurised to 10 bar. The autoclave was
Reaction monitoring for kinetic experiments was achieved using
a Perkin-Elmer GX FTIR spectrometer (2 cm−1 resolution)
controlled by Spectrum TimeBase software. Pseudo-first order
conditions were employed, with at least a 10-fold excess of MeI,
relative to the Rh complex. A solution containing the required
concentration of MeI in CH2Cl2 was prepared in a 5 cm3 graduated
flask. A portion of this solution was used to record a background
spectrum. Another portion (typically 500 ll) was added to the
solid Rh complex in a sample vial to give a reaction solution
containing typically 5–10 mmol dm−3 [Rh]. A portion of the
◦
heated to approximately 150 C (internal temperature) and once
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semi-stabilised at approximately 150 ◦C, the pressure in the
autoclave was raised to 23 bar and the temperature again allowed
to stabilise. A second solution was added through the catalyst
injector and the pressure brought up to 27 bar. The pressure in
the ballast vessel was monitored electronically every five seconds.
After 2 h the autoclave was cooled and vented.
X-Ray crystallography
Data were collected using a Bruker SMART diffractometer,
graphite monochramated MoKa radiation (k = 0.71073 A).
˚
Lorentzian polarization and absorption corrections were per-
formed. The structures were solved by direct methods. The non-
hydrogen atoms were refined anisotropically, the hydrogen atoms
were idealized and refined isotropically using a riding model.
Structural refinements were performed with the full-matrix least-
squares method on F2 for all data.25 Full details in Table 1. The
structure determination of [Ir(Cpꢀ(CH2)2PEt2)(CO)(Me)]I proved
difficult due to poor crystal quality. We examined several different
crystals and the reported data are the most satisfactory, there are
some high residual peaks in the final Fourier map which reflects
the difficulties associated with this data collection.
Methanol carbonylation at high rhodium concentration, MeI
injection. [Rh(Cpꢀ(CH2)2PEt2)(CO)] was predissolved in MeOH
(4 cm3) to give a clear red/brown solution (0.105 mol dm−3)
which was added to the thoroughly CO flushed autoclave followed
by the H2O (0.35 cm3). The MeI (0.5 cm3) in MeOH (1 cm3)
was added via the catalyst injector at 150 ◦C and 23 bar and
the pressure brought up to a final pressure of 27 bar. The
reaction was stopped after 2 h. The autoclave was cooled and
vented; the final solution was deep red in colour and yielded
crystals of [Rh(Cpꢀ(CH2)2PEt2)I2]. The same procedure was use
for [Rh(Cp(CH2)2PEt2)(CO)] (0.076 mol dm−3).
The experimental details for the structure determinations of
[Rh(Cpꢀ(CH2)2PEt2)(CO)], [Rh(Cpꢀ(CH2)2PPh2)(CO)], [Rh(Cp-
(CH2)2PEt2)(CO)], [Rh(Cpꢀ(CH2)2PEt2)(COMe)I], [Rh(Cpꢀ-
(CH2)2PEt2)Cl2], [Rh(Cpꢀ(CH2)2PEt2)I2] (compounds 1, 2, 3, 9, 10
and 11 in ref. 19, CCDC reference numbers 197739–197744) have
already been reported.26
CCDC reference numbers 282064–282069.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b512054c
Methanol carbonylation at low [Rh], MeI injection.
[Rh(Cpꢀ(CH2)2PEt2)(CO)] (2 cm3) of
a standard solution
containing 0.023 g in MeOAc (10 cm3) (1.25 × 10−5 mol Rh)
was predissolved in MeOAc (2 cm3) to give a clear yellow
solution. This catalyst solution was added to the thoroughly
flushed autoclave along with H2O (1 cm3) and AcOH (6 cm3).
The MeI (1 cm3) was added via the catalyst injector at 150 ◦C
and 20 bar and the pressure brought to 27 bar. The reaction
was stopped after 2 h. The autoclave was cooled and vented.
The final solution was orange in colour, but darkened with time
to deep red. The same procedure was used for [Cp*Rh(CO)2]
(1.25 mol dm−3) in the presence of PEt3 (1.25 × 10−3 mol dm−3)
giving a rate of 0.49 mol dm−3 h−1, [RhCl(CO)2]2 giving a rate of
0.81 mol dm−3 h−1.
Results and discussion
Ligand synthesis
Tertiary (phosphanylalkyl)cyclopentadienyl ligands have been
prepared by a variety of routes including reactions of fulvenes with
LiPR2 (R = aryl),27–31 alkylation of cyclopentadienyl anions with
3-chloropropyldiphenyl phosphine,32 reaction of a substituted cy-
clopentadienone with allylMgBr, followed by hydroboration and
oxidative hydrolysis to give the hydroxypropylcyclopentadienyl
complex which was reacted with TsCl (Ts = 4-MeC6H4SO2)
followed by LiPPh2,33 and reactions of spirohydrocarbons with
LiPR2 (R = Ph, Pri or But).22,34–37 Related ligands with an aryl
bridge have been synthesised by HF elimination from coordinated
cyclopentadienyl and fluorinated aryl phosphine ligands.38–42 We
attempted many of these routes but there were problems with all
of them except that starting from the spirohydrocarbon.
Deprotonation of tetramethylcyclopentadiene followed by re-
action with X(CH2)2Cl (X = Br or OTs) can give three isomeric
products (Scheme 1).43 There is some dispute in the literature36
as to the relative amounts of these products, but it seems
clear that largely the geminal isomers, which are unsuitable
for coordination since they cannot form cyclopentadienyl lig-
ands by deprotonation, are formed when using TsO(CH2)2Cl,
although subsequent reaction with LiPPh2 does give some
of the desired 1-(diphenylphosphanylethyl)-2,3,4,5-tetramethyl-
cyclopentadiene.34,35 Better results have been obtained using 1-
bromo-3-chloroethane, with the desired non-geminal isomer being
formed in 84% yield and the geminal isomers making up the
remaining 16%.22 In our hands, the ratio of geminal to non-
geminal isomers was closer to 1 : 1 at full conversion (30 days).
Reaction of this mixture with BuLi produced a mixture of
the desired spirohydrocarbon and other products, which were
separated by column chromatography. The spirohydrocarbon was
Methanol carbonylation at low [Rh], catalyst injection. Water
(1 cm3), AcOH (6 cm3) and MeI (1 cm3) were added to the
thoroughly flushed autoclave. The catalyst (1.25 × 10−5 mol) was
predissolved in MeOAc (2 cm3) to give a pale yellow solution.
This catalyst solution was added via the catalyst injector at 150 ◦C
and 20 bar and the pressure brought to a final pressure of
27 bar. The reaction was stopped after 2 h. The autoclave was
cooled and vented. The final solution was orange in colour, which
darkened with time to deep red. This same procedure was used for
[Rh(Cpꢀ(CH2)2PPh2)(CO)], [Cp*Rh(CO)2] (1.25 × 10−3 mol dm−3)
in the presence of PEt3 (1.25 × 10−3 mol dm−3), [RhCl(CO)2]2,
[Ir(Cpꢀ(CH2)2PEt2)(CO)] at 150 ◦C, 30 bar; 190 ◦C, 30 bar (rate =
◦
1.08 mol dm−3 h−1), [Co(Cpꢀ(CH2)2PEt2)(CO)] at 150 C, 27 bar;
150 ◦C, 100 bar; 120 ◦C, 100 bar; in all these cobalt containing
reactions, there was no gas uptake and the final solution was pale
yellow in colour.
Methanol carbonylation using [Co(Cpꢀ(CH2)2PEt2)(CO)]/PEt3
under low water conditions. [Co(Cpꢀ(CH2)2PEt2)(CO)] (0.074 g,
0.048 mol dm−3) was dissolved in PEt3 (0.44 cm3, 0.646 mol dm−3),
water (0.35 cm3) and methanol (2.58 cm3) and then added to the
thoroughly flushed autoclave. The MeI (0.475 cm3) and methanol
(1.27 cm3) were added via the injection port at 120 ◦C and 100 bar
CO. The reaction caused a pressure drop in the ballast vessel of
approximately 3 bar. The final solution was pale pink in colour.
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obtained in 45% yield. The desired (diethylphosphanylethyl)-
2,3,4,5-tetramethylcyclopentadienyl lithium was synthesised by
the reaction of the spirohydrocarbon with lithium diethylphos-
phide in THF at −60 ◦C. Similar methods were used to
prepare R2P(CH2)2C5Rꢀ4Li (R = Et or Ph, Rꢀ = H or Me).
Me2PCH2SiMe2C5Et4HLi was synthesised from the reaction of
[C5Et4H]− with Me2SiCl2 followed by LiCH2PMe2.
Complexation
Rhodium complexes. Rhodium complexes of all the ligands
described above and of the known21 [C5H4(CH2)2PPh2]− were
prepared from the reaction of [RhCl(CO)2]2 with the lithiated
phosphanylalkylcyclopentadiene in refluxing THF. In each case
only one complex, of formula [Rh(C5Rꢀ4(CH2)2PR2)(CO)] was
formed and spectroscopic properties (Table 2) confirmed that both
the phosphine and the cyclopentadienyl ligands were coordinated.
In particular, the P atom resonates at near d 80 compared with
negative values for the free protonated ligands (on Cp). The high
field shift confirms that the P atom is contained in a chelate ring of
intermediate size, in this case 512 membered.44 An unusual feature
1
of the H NMR spectrum of [Rh(Cpꢀ(CH2)2PEt2)(CO)] (Cpꢀ =
31
C5Me4), confirmed by 1H{ P} NMR studies, is that the high
frequency signal from the ring methyl groups (d 2.13, d, JHRh
=
0.7 Hz) shows coupling to Rh, whilst the low frequency signal (d
2.18, d, JHP = 2.95 Hz) shows coupling to P. We tentatively assign
the signal with the higher coupling to P as arising from the methyl
groups on C atoms more nearly trans to P, C7,8 in Scheme 1.
An aliquot of the solution taken before the start of the
reflux period showed, in addition to resonances from the final
product, extra doublets around d 40. These may arise from dimeric
complexes with bridging Cpꢀ(CH2)2PEt2 ligands. Such dimers have
previously been reported to be intermediates in the synthesis
of [Rh(C5H4(CH2)2PPh2)(CO)] and exist in cisoid and transoid
forms.21
The structures of each of the previously unreported complexes,
[Rh(C5Rꢀ4(CH2)2PR2)(CO)] (R = Et, Rꢀ = H or Me, R = Ph, Rꢀ =
Me) were confirmed crystallographically. For R = Et, Rꢀ = Me,
the structure is shown in Fig. 1, whilst for the other complexes
they are in the ESI.†
The complex [Rh(C5Et4SiMe2CH2PMe2)(CO)] was also syn-
thesised and spectroscopically characterised as having a similar
composition to those of the other complexes. The P atom resonates
at d 15 compared with −53.9 for the free ligand and 32.6
for the ligand bound only through P to cobalt. In this case,
it is less clear that the complex is monomeric and a dimer
(Fig. 2) similar to those formed initially during the synthesis of
[Rh(C5H4(CH2)2PPh2)(CO)]21 may predominate. The IR spectrum
of [Rh(C5Et4SiMe2CH2PMe2)(CO)] contains a strong carbonyl
band at 1929 cm−1, assigned to the complex, but two weaker
bands at 2029 and 1967 cm−1. The similarity of these absorptions
to those of [Cp*Rh(CO)2] (2027, 1964 cm−1) suggest that this may
arise from [Rh(C5Et4SiMe2CH2X)(CO)2] (X = Cl or PMe2). There
is some evidence that LiCH2PMe2 deprotonates C5Et4HSiMe2Cl
in competition with substitution of the SiCl bond since the 31P
NMR spectrum of a crude sample of C5Et4SiMe2CH2PMe2 also
contained a resonance from PMe3.
The values of mCO for the rhodium complexes are shown in
Table 2 along with those of the analogous complexes which do
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Table 2 Spectroscopic parameters of new ligands and complexes
Compound
dP (JRhP/Hz)
mCO (hexane)/cm−1
Li[C5H4(CH2)2PEt2]
−25.1
Li[Cpꢀ(CH2)2PEt2]
−21.9
Li[CpꢀH(CH2)2PPh2]
C5Et4HSiMe2CH2PMe2
[Rh(C5H4(CH2)2PEt2)(CO)]
[CpRh(PEt3)(CO)]
−15.1
−53.9
80.3 (191)
1938
1944
[Rh(C5H4(CH2)2PPh2)(CO)]
[CpRh(PPh3)(CO)]
1947a
1953a
1924
[Rh(Cpꢀ(CH2)2PEt2)(CO)]
[Cp*Rh(PEt3)(CO)]
76.3 (189)
52.1 (175)
1920
1933
[Rh(Cpꢀ(CH2)2PPh2)(CO)]
[Cp*Rh(PPh3)(CO)]
1947a
1928b
1910b
1910b
1629b,c
[Rh(C5Et4SiMe2CH2PMe2)(CO)]
[Co(Cpꢀ(CH2)2PEt2)(CO)]
[Ir(Cpꢀ(CH2)2PEt2)(CO)]
[Rh(Cpꢀ(CH2)2PEt2)(C(O)Me)I]
[Co(Cpꢀ(CH2)2PEt2)(C(O)Me)I]
[Ir(Cpꢀ(CH2)2PEt2)Me(CO)]I
[Rh(Cp(CH2)2PEt2)Me(CO)]BF4
[Rh(Cpꢀ(CH2)2PEt2)Cl2]
[Rh(Cpꢀ(CH2)2PPh2)Cl2]
[Rh(Cpꢀ(CH2)2PEt2)I2]
15.2 (185)
87.6
37.7
68.6 (168)
69.1
32.1
72.2 (130)
72.8 (147)
51.5 (157)
63.7 (148)
58.2, 57.6, 55.8
32.3
2038d
2059d
[Co2(CO)6(CpꢀH(CH2)2PPh2)2]
[Co2(CO)6(C5Et4HSiMe2CH2PMe2)2]
2078, 2009, 1993, 1951
1969, 1951b
a Pentane. b Light petroleum. c mC=
.
d CH2Cl2.
O
not contain the bridge between the cyclopentadienyl ring and
the phosphine. In most cases, except [Rh(Cpꢀ(CH)2PEt2)(CO)],
the complexes containing the bidentate ligands have lower
mCO values. As expected on the basis of their better electron
donating properties, ethyl groups on P cause lower mCO than
phenyl groups and methyl substituents on the cyclopentadienyl
moiety also lower mCO, the latter effect being slightly more
marked (compare [Rh(Cpꢀ(CH2)2PPh2)(CO)] (1933 cm−1)
with [Rh(C5H4(CH)2PEt2)(CO)] (1937 cm−1)). The drop in
mCO on introducing the bridge arises when an extra electron
donating group is introduced into the complexes, the (CH2)2
bridge replacing either a phenyl group on P or an H on the
cyclopentadienyl ring. In contrast, for [Rh(Cpꢀ(CH)2PEt2)(CO)],
the bridge replaces an ethyl group on P and a methyl group on the
cyclopentadienyl ring, reducing the overall number of electron
donating methyl or methylene groups and leading to a slightly
decreased electron density and higher value for mCO
.
Iridium complex. [Ir(Cpꢀ(CH2)2PEt2)(CO)] was prepared by
the reaction of Li[Cpꢀ(CH2)2PEt2] with either [IrCl(CO)(PPh3)2] or
[IrCl(CO)3]n. The X-ray crystal structure (see ESI†) is analagous
to that of the rhodium congener. The P atom resonates at lower
frequency (d 37.7) and mCO is at 1910 cm−1, somewhat lower than
that of its Rh congener, consistent with a slightly higher electron
density on the metal centre.
Fig. 1 Single crystal X-ray molecular structure and numbering scheme
for [Rh(Cpꢀ(CH)2PEt2)(CO)].
Cobalt complexes. One of the problems with synthesising
cobalt complexes analogous to those described above for rhodium
and iridium is the difficulty of finding a suitable starting material.
In principle, [CoI(CO)4] should be ideal, and has been used for
the preparation of [Co(C5H4(CH2)2PBut2)(CO)],32 but it is not
stable so has to be prepared in situ from [Co2(CO)8] and I2.45
It is difficult to remove all traces of iodine so that either the
phosphine itself or the cobalt complexes derived from it are
Fig. 2 Possible dimeric structure for [Rh(C5Et4SiMe2CH2PMe2)(CO)].
1 0 0 | Dalton Trans., 2006, 91–107
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Scheme 2 Proposed mechanism of formation of [Co(Cpꢀ(CH2)2PEt2)(CO)].
susceptible to oxidation. Products of reactions of the lithiated
phosphanylethylcyclopentadienes with [CoI(CO)4] tended to be
green and were not easily characterised.
be [Co2(CO)7(Et2P(CH2)2Cpꢀ)]− (31P d 56.9), but that this converts
into the desired product by attack of the [Me4C5]− moiety onto the
cobalt atom which is already bound to P with [Co(CO)4]− (inferred
from a strong absorption in the IR at 1890 cm−1, lit.,50 1888 cm−1)
acting as the leaving group (Scheme 2). In this mechanism, the
phosphine and cyclopentadienyl ligands are coordinated to the
cobalt in the opposite order to that in the reaction of [CoI(CO)4]
with [C5H4(CH2)2PBut2]−, because the lack of a good anionic
leaving group on Co makes CO displacement by the phosphine
more facile than nucleophilic attack of the cyclopentadienyl
moiety.
Reactions of phosphanylalkylcyclopentadienes with [Co2(CO)8]
led to the formation of dimeric products of the form [Co2(CO)6-
L2], which were crystallographically characterised for L =
CpꢀH(CH)2PPh2 (Fig. 3) and C5Et4HSiMe2CH2PMe2 (ESI†), even
if they were carried out in the presence of cyclohexene, which
assists the formation of cyclopentadienyl complexes in reactions of
this kind by acting as a hydrogen acceptor.46 The X-ray structures
of both complexes show that the ligand is coordinated only
through P and that the P–Co–Co–P is almost linear (P–Co–Co =
177◦), as is usual for complexes of this type,47–49 with the carbonyl
ligands occupying the equatorial positions of a trigonal bipyramid.
The 31P NMR spectrum of [Co2(CO)6(CpꢀH(CH)2PPh2)2] shows 6
different resonances. These arise because the protonated form of
the ligand exists as a mixture of 3 different isomers, depending on
the site of ring protonation (see Scheme 1). In the dimeric complex,
the two ligands can be the same (3 resonances) or different
(6 resonances). Presumably some of the expected 9 resonances
overlap. 31P and 1H NMR studies suggest that the related complex,
[Co2(CO)7(Et2P(CH2)2CpꢀH)] (31P 55.8, 57.6, 58.2, from the three
isomers of the protonated ligand, mCO 2078, 2009,◦ 1993, 1951)
forms from [Co2(CO)8] and CpꢀH(CH2)2PEt2 at 100 C.
Catalytic carbonylation of methanol
Various of the rhodium complexes and some standards were tested
◦
for methanol carbonylation at 150 C under CO (27 bar) in the
presence of water and methyl iodide. The results are collected in
Table 3. Linear gas uptake plots were observed, suggesting
zero order dependence on [methanol] and good catalyst sta-
bility. At higher concentrations of [Rh(Cpꢀ(CH2)2PEt2)(CO)]
(0.105 mol dm−3, initial rate 11.4 mol dm−3 h−1) [Rh(Cpꢀ(CH2)2-
PEt2)I2] (X-ray structure in Fig. 4) was isolated from the final
solution, suggesting that the ligand remains intact and coordinated
Fig.
4
X-Ray molecular structure and numbering scheme for
[Rh(Cpꢀ(CH2)2PEt2)I2].
Table 3 Rate of methanol carbonylation using phosphanylethylcyclopen-
tadienyl complexesa
Fig.
3
X-Ray molecular structure and numbering scheme for
[Co2(CO6)(CpꢀH(CH)2PPh2)2].
Catalyst
Rate/mol dm−3 h−1
[Rh(CO)I2]−
0.64
0.30
0.38
0.81
0
[Co(Cpꢀ(CH2)2PEt2)(CO)] was successfully prepared, however,
by the reaction of [Co2(CO)8] with Li[Cpꢀ(CH2)2PEt2] (1 : 1) in
[Cp*Rh(PEt3)(CO)]
[Rh(Cpꢀ(CH2)2PEt2)(CO)]
[Rh(Cpꢀ(CH2)2PPh2)(CO)],
[Rh(Cpꢀ(CH2)2PEt2)I2]
◦
THF at 170 C in an autoclave. The complex was characterised
crystallographically (see ESI). The 31P NMR resonance was at d
87.6 and mCO at 1910 cm−1. IR and NMR studies of this reaction
suggest that the first complex formed at room temperature may
a For conditions, see Experimental section.
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in a bidentate fashion to Rh. This complex is presumably
formed by reaction of [Rh(Cpꢀ(CH2)2PEt2)(CO)] with 2 mol of
HI and is analogous to [RhI4(CO)2]−, which can be formed
from methanol carbonylation solutions containing [RhI2(CO)2]−
at low water concentrations2 or on cooling and depressurising.
[Rh(Cpꢀ(CH2)2PEt2)I2] was inactive for methanol carbonylation.
In the case of [Cp*Rh(PEt3)(CO)], the active species is believed
to be [Cp*Rh(CO)2] because HPNMR studies (see later) show
that all the phosphine is oxidised. Interestingly, the most active
of all the catalysts is [Rh(Cpꢀ(CH2)2PPh2)(CO)], giving a rate
(0.81 mol dm−3 h−1, [Rh] = 1.25 × 10−3 mol dm−3) slightly
higher than from [RhI2(CO)2]− (0.64 mol dm−3 h−1). The most
electron rich of the new complexes, [Rh(Cpꢀ(CH2)2PEt2)(CO)]
gives a lower rate of 0.38 mol dm−3 h−1, which is similar to that for
[Cp*Rh(PEt3)(CO)], which decomposes to [Cp*Rh(CO)2].
◦
At 150 C, [Ir(Cpꢀ(CH2)2PEt2)(CO)] showed no activity for
Fig.
5
X-Ray molecular structure and numbering scheme for
[Co(Cpꢀ(CH2)2PEt2)(C(O)Me)I].
methanol carbonylation, but slow gas uptake was observed at
190 ◦C. At this temperature, the rate was similar to that obtained
with [IrCl(CO)3]n, suggesting that [Ir(Cpꢀ(CH2)2PEt2)(CO)] is not
stable at this high temperature. [Co(Cpꢀ(CH2)2PEt2)(CO)] also
showed no activity for methanol carbonylation under any of
the following conditions (120 ◦C, 100 bar; 150 ◦C, 30 bar or
◦
150 C, 100 bar), which is consistent with the observations from
the high pressure 31P NMR studies, which show decomposition
of the complex under catalytic conditions at 60–90 ◦C. These
results suggest that the very active but unstable catalyst obtained14
from [Cp*Co(CO)2] and PEt3 may not be [Cp*Co(CO)(PEt3)] as
previously proposed. A small amount of activity was obtained
under low water conditions, but it ceased after a short time. At
the end of the reaction, the solution was pale pink, suggesting
complete catalyst degradation.
Scheme
3 General mechanism for the reactions of MeI with
[M(C5R4(CH2)2PRꢀ2)(CO)]. For M = Co and Rh the acetyl complex is
isolated whereas for M = Ir the methyl complex is obtained.
Stoichiometric reactions
In order to gain more insight into the catalytic reactions, we have
carried out a variety of stoichiometric reactions of the catalyst
precursors, backing them up with high pressure spectroscopy (see
later). Our intention was to prepare very highly nucleophilic metal
complexes in order to speed up the oxidative addition of methyl
iodide during methanol carbonylation. An initial indication of
the very high nucleophilicity of the rhodium centre came from
the observation that [Rh(Cpꢀ(CH2)2PEt2)(CO)] converted into
[Rh(Cpꢀ(CH2)2PEt2)Cl2] on standing in CD2Cl2 for 24 h. This may
proceed by initial nucleophilic attack on CD2Cl2, a reaction which
only occurs for highly nucleophilic metal centres51 or possibly
by a free radical reaction.52 [Rh(Cpꢀ(CH2)2PEt2)Cl2] was fully
characterised crystallographically (ESI†), the structure being very
similar to that for [Rh(Cpꢀ(CH2)2PEt2)I2]. That the chlorides
come from CD2Cl2 rather than HCl impurities was confirmed by
repeating the reaction using CD2Cl2, which had been pretreated
with NaHCO3. [Rh(Cpꢀ(CH2)2PEt2)Cl2] was still formed.
Fig. 6 X-Ray structure and numbering scheme for [Ir(Cpꢀ(CH2)2-
PEt2)Me(CO)]+.
ring are now inequivalent because there is no plane of symmetry
1
31
in the molecule. For the Rh complex, H{ P} studies showed
that only the two low frequency signals (d 1.34 and 1.43) are
coupled to rhodium, whilst both sets of signals are coupled to P, the
resonances at d 2.09 and 1.43 have the higher coupling constants
to P (5.4 and 2.7 Hz respectively) compared with 1.2 (d 1.34)
and 0.9 (d 1.74). The reaction of [Ir(Cpꢀ(CH2)2PEt2)(CO)] with
MeI led to the methyl complex, [Ir(Cpꢀ(CH2)2PEt2)Me(CO)]I¶
(Fig. 6), confirming the lack of migration in this iridium complex,
which can be attributed to the high strength of the Ir–C bond.
Reaction of [M(Cpꢀ(CH2)2PEt2)(CO)] (M = Co or Rh) with MeI
led smoothly to the formation of [M(Cpꢀ(CH2)2PEt2)(C(O)Me)I],
which were characterised crystallographically (Fig. 5, M = Co,
ESI† for M = Rh). These ethanoyl complexes are formed by
nucleophilic attack of the metal centre on MeI followed by
methyl migration to CO and coordination of I− (see Scheme 3).
¶ The measured crystal was of a double salt with [Ph3PMe]I. Presumably
some PPh3 from the starting [IrCl(CO)(PPh3)2] must have co-crystallised
with the batch of [Ir(Cp’(CH2)2PEt2)(CO)] used for the reaction with MeI.
1
An interesting feature of the H NMR spectra of the ethanoyl
complexes is that all four methyl groups on the cyclopentadienyl
1 0 2 | Dalton Trans., 2006, 91–107
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In the [IrI2(CO)2]− catalysed carbonylation of methanol, the rate
of methyl migration on Ir(III) is the rate determining step. In
the commercial process an iodide scavenging promoter, such
as [RuI2(CO)3], aids dissociation of I− from [IrI3(CO)2Me)]− to
allow coordination of CO giving neutral [IrI2(CO)3Me], in which
the methyl migration occurs.9,53 Despite the positive charge on
[Ir(Cpꢀ(CH2)2PEt2)Me(CO)]+ migration does not readily occur,
again confirming the very high electron density placed on the
metal by the Cpꢀ(CH2)2PEt2 ligand.
The proposed rhodium methyl complex, [Rh(C5H4-
(CH2)2PEt2)Me(CO)]+ was observed as an intermediate
during IR studies of the oxidative addition reaction (see
below) and could also be generated as its tetrafluoroborate salt,
[Rh(C5H4(CH2)2PEt2)Me(CO)]BF4 (mCO 2059 cm−1) from the reac-
tion of [Rh(C5H4(CH2)2PEt2)(C(O)Me)I] with AgBF4 in CH2Cl2.
The 1H NMR spectrum of [Rh(C5H4(CH2)2PEt2)Me(CO)]BF4
displayed a doublet of doublets for the methyl ligand, due
to coupling with both P and Rh. Separate signals were
present due to each of the four inequivalent hydrogens on the
cyclopentadienyl ring. Addition of Bu4NI to a CH2Cl2 solution of
[Rh(C5H4(CH2)2PEt2)Me(CO)]BF4 caused conversion back into
[Rh(C5H4(CH2)2PEt2)(C(O)Me)I], as judged by IR spectroscopy.
Kinetic measurements of the reactions of MeI with sev-
eral of the Rh complexes were conducted by IR spectroscopy
and a representative example of a series of spectra, for
[Rh(C5H4(CH2)2PEt2)(CO)], is given in Fig. 7. As the par-
ent rhodium(I) complex (mCO 1918 cm−1) decays, a mCO band
due to the methyl intermediate, [Rh(C5H4(CH2)2PEt2)Me(CO)]+
(2056 cm−1), grows and decays with the formation of the final
product, [Rh(C5H4(CH2)2PEt2)(C(O)Me)I]. The mC=O band of this
compound is split into two component peaks (1640, 1663 cm−1,
see Fig. 7), probably due to the ethanoyl ligand adopting two
different rotameric conformations with respect to the Rh centre.
The time dependences of the relative intensities of the IR signals
of the various species are shown in Fig. 8.
Fig. 8 Plot of absorbance vs. time for m(CO) bands of Rh complexes
during the reaction of [Rh(C5H4(CH2)2PEt2)(CO)] with MeI (0.08 M in
CH2Cl2, 11 ◦C).
range of MeI concentrations and temperatures and are listed in the
ESI.† A linear dependence of kobs on [MeI] (Fig. 9) demonstrates
that the reaction is also first order in MeI and the second order
rate constant, k1, was obtained from the slope of this plot. Rate
constants for reactions of MeI with [Rh(C5H4(CH2)2PEt2)(CO)]
and [Rh(Cpꢀ(CH2)2PPh2)(CO)] are listed in Table 4, together with
comparative values for [Cp*Rh(CO)2] and [CpRh(CO)(PPh3)].55
These data display a clear correlation between the electron
density on the metal (as revealed by mCO in the starting material)
and the rate constant (k1) for reaction with methyl iodide.
The electron donating power of the methyl groups on the
ring and of the phosphine contribute to making the relative
rate constants (krel) increase in the order [Cp*Rh(CO)]2 (1) <
[CpRh(CO)(PPh3)] (3.3) < [Rh(C5H4(CH2)2PEt2)(CO)] (74) <
[Rh(Cpꢀ(CH2)2PPh2)(CO)] (2100). To our knowledge, the rate
Fig.
7
Series of IR spectra during the reaction of [Rh(C5H4-
(CH2)2PEt2)(CO)] with MeI (0.16 mol dm−3 in CH2Cl2, 16 ◦C).
The exponential decay of the reactant mCO band indicates a first
order dependence of rate on the parent Rh(I) complex. Values
of the pseudo first order rate constant, kobs, were measured over a
Fig. 9 Plot of kobs vs. [MeI] for the reaction of [Rh(C5H4(CH2)2PEt2)(CO)]
with MeI in CH2Cl2 at 16 ◦C.
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Table 4 Second order rate constants (25 ◦C, CH2Cl2) and activation parameters for oxidative addition of MeI to Rh(I) complexes in CH2Cl2. Values of
mCO (in CH2Cl2) are listed for comparison
Complex
mCO/cm−1
102 k1/dm3 mol−1 s−1
DH‡/kJ mol−1
DS‡/J K−1 mol−1
[Rh(C5H4(CH2)2PEt2)(CO)]
[Rh(Cpꢀ(CH2)2PPh2)(CO)]
[Rh(Cpꢀ(CH2)2PEt2)(CO)]
[Cp*Rh(CO)2]54
1917
1907
1898
7.8
223
40
33
—
2
1
−131
−128
—
6
3
—
1950, 2018
0.106
0.35
[CpRh(PPh3)(CO)]55
1957a
42
4
−151 13
a In hexane.
constant for oxidative addition of MeI to [Rh(Cpꢀ(CH2)2-
PPh2)((CO)] is the highest yet reported for a Rh(I) carbonyl
complex, surpassing that recently found for a square planar
complex containing a tridentate bis(imino)carbazolide ligand (k =
1.66 dm3 mol−1 s−1).56 Qualitative observations indicated that the
rate for [Rh(Cpꢀ(CH2)2PEt2)(CO)] is even faster, but quantitative
measurements have not been made using this complex. Activation
parameters for the oxidative addition reactions, as determined
from Eyring plots (ESI†) are also shown in Table 4. The large
negative entropies of activation are consistent with an SN2
mechanism for attack of the rhodium centre at the C atom of
MeI. The faster oxidative addition for [Rh(Cpꢀ(CH2)2PPh2)(CO)]
relative to [Rh(C5H4(CH2)2PEt2)(CO)] can be attributed to a
smaller activation enthalpy for the more electron rich complex,
perhaps indicating a stronger Rh–Me partial bond in the SN2
transition state.
a stronger preference (than in [Rh(C5H4(CH2)2PEt2)(C(O)Me)I)])
for one rotameric conformation of the ethanoyl ligand, due
to the steric bulk of the C5Me4 moiety. This is supported by
inspection of a space-filling model of the X-ray structure of
[Rh(Cpꢀ(CH2)2PEt2)(C(O)Me)I)], in which the ethanoyl ligand is
oriented so as to avoid clashes with methyl and ethyl substituents
of the Cpꢀ(CH2)2PEt2 ligand. The kinetic parameters are collected
in Table 5, along with those for [Cp*Rh(CO)2Me.57
The more electron rich metal complexes have slower rates of
methyl migration, than [Cp*RhMe(CO)2]+, but the rate constant
for [Rh(C5H4(CH2)2PEt2)Me(CO)]+ is slightly lower than for
[Rh(Cpꢀ(CH2)2PPh2)Me(CO)]+, despite the lower electron density
of the former. This may be because the higher steric bulk of the
methylated cyclopentadienyl ring and of the phenyl groups on P
promote migration to relieve steric strain. The rate constant for
methyl migration in [Rh(Cpꢀ(CH2)2PEt2)Me(CO)]+ is the slowest
of the ones measured in this study. Activation parameters for
methyl migration obtained from Eyring plots (ESI†) are shown
in Table 5. The value of DH‡ tends to increase with the donor
strength of the (C5R4(CH2)2PRꢀ2) ligand, indicating that increased
Rh → CO p back donation (accompanied perhaps by Rh–
Me bond strengthening) raises the enthalpic barrier to methyl
migration.
The experimental activation parameters can be used to extrap-
olate rate constants for oxidative addition at higher temperatures,
corresponding to the conditions of the catalytic experiments. At
◦
150 C, calculated rate constants are 15 and 150 dm3 mol−1 s−1
for [Rh(C5H4(CH2)2PEt2)(CO)] and [Rh(Cpꢀ(CH2)2PPh2)(CO)]
respectively, which are 3–4 orders of magnitude higher than
that calculated for [RhI2(CO)2]− (0.014 dm3 mol−1 s−1) at the
same temperature. These very fast rates make it unlikely that
oxidative addition remains the rate determining step in the
catalytic carbonylation cycle, as discussed later.
High pressure spectroscopic studies
The rate constants for migration of the methyl group onto CO in
[Rh(C5H4(CH2)2PEt2)Me(CO)]+, [Rh(Cpꢀ(CH2)2PPh2)Me(CO)]+
and [Rh(Cpꢀ(CH2)2PEt2)Me(CO)]+ were also measured. The
methyl complexes were generated in situ by dissolving their
Rh(I) precursors in CH2Cl2 containing a high concentration
(2 mol dm−3) of MeI. Under these conditions the oxidative
addition step was effectively complete in the time of mixing and
the methyl migration step could be monitored in isolation. The
Because the rate constants for oxidative addition of MeI for the
phosphanylethylcyclopentadienyl ligands are so high, it is possible
that the rate determining step for methanol carbonylation may
no longer be oxidative addition of methyl iodide, especially as
the rate of reductive elimination of MeC(O)I from the highly
electron rich ethanoyl complexes is likely to be substantially
reduced. We, therefore, carried out spectroscopic studies under
methanol carbonylation conditions (CO (30 bar) in ethanoic acid
containing methyl ethanoate, methyl iodide and deuteriated water,
with the same composition as used for the catalytic studies), but
at slightly lower temperature, in order to try to observe the species
present during catalysis, but also to investigate the stability of the
complexes.
mC= bands of the products [Rh(Cpꢀ(CH2)2PPh2)(C(O)Me)I] and
O
[Rh(Cpꢀ(CH2)2PEt2)(C(O)Me)I] formed at 1628 and 1623 cm−1
respectively. The former exhibits a high frequency shoulder,
possibly due to a rotameric form. The lack of well resolved
splitting of the mCO bands for these two complexes may indicate
◦
Table 5 First order rate constants (25 C, CH2Cl2/MeI (2 mol dm−3)) and activation parameters for methyl migration in Rh(III) methyl complexes.
Values of mCO (in CH2Cl2) are listed for comparison
Complex
mCO/cm−1
103 k2/s−1
DH‡/kJ mol−1
DS‡/J K−1 mol−1
[Rh(C5H4(CH2)2PEt2)(CO)Me]+
[Rh(Cpꢀ(CH2)2PPh2)(CO)Me]+
[Rh(Cpꢀ(CH2)2PEt2)(CO)Me]+
2056
2048
2044
2118, 2087
14.7
17.5
6.7
69
74
80
72
2
3
2
2
−47
−29
−20
−16
7
9
5
6
57
[Cp*Rh(CO)2Me]+
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Although [Rh(C5H4(CH2)2PEt2)(CO)] and [Cp*Rh(CO)(PEt3)]
gave 31P NMR signals from unidentified rhodium complexes at
room temperature under CO, heating the solutions to 90 ◦C led to
the formation of broad singlets at d 82 (75 at 25 ◦C) and 82 (75.5
at 25 ◦C), which we assign to the phosphine oxides, which will
give these high shifts in a protic environment.11 In both cases
small amounts of rhodium complexes were present, but these
could not be assigned to any of the complexes in the catalytic
cycle. In contrast, [Rh(Cpꢀ(CH2)2PEt2)(CO)] at room temperature
showed four doublets from rhodium containing complexes. Two
of these (d 73.8, d, JRhP = 116 Hz, 71.0, d JRhP = 134 Hz) were
from unidentified complexes, whilst the other two were from
[Rh(Cpꢀ(CH2)2PEt2)(C(O)Me)I] (d 65.2, d, JRhP = 165 Hz) and
[Rh(Cpꢀ(CH2)2PEt2)I2] (d 61.5, d, JRhP = 146 Hz). On heating
to 90 ◦C, all of these resonances were still present, with those
at d 71.0 and 61.5 dominating, but they all converted into
[Rh(Cpꢀ(CH2)2PEt2)I2] over 90 min at 90 ◦C. These results not
only confirm that the [Rh(Cpꢀ(CH2)2PEt2)] unit is more stable
than its analogue without the bridge between the cyclopentadienyl
and phosphine moieties, [Cp*Rh(PEt3)(CO)], but also that the
methyl groups on Cp are essential for this extra stability. The
observation that [Rh(Cpꢀ(CH2)2PEt2)(C(O)Me)I] is present but
not [Rh(Cpꢀ(CH2)2PEt2)(CO)], suggests that the rate of oxidative
addition has been accelerated so much in this system that reductive
elimination of MeC(O)I has become the rate determining step of
the catalytic reaction. The formation of [Rh(Cpꢀ(CH2)2PEt2)I2],
which was also isolated from catalytic reactions, is a problem,
however, because, unlike [RhI4(CO)2]−, it does not appear to be
reintroduced into the catalytic cycle by reaction with water. This is
because regeneration of the Rh(I) species in these systems occurs
by nucleophilic attack of water onto coordinated CO, which is not
possible for [Rh(Cpꢀ(CH2)2PEt2)I2], because it does not contain
CO.58
The rate of methanol carbonylation using [Rh(Cpꢀ(CH2)2-
PPh2)(CO)] was found to be higher than for [Rh(Cpꢀ(CH2)2-
PEt2)(CO)], despite the fact that the latter carries higher electron
density. This may arise if reductive elimination of MeC(O)I is rate
determining in these systems, as suggested by the HPNMR studies
using [Rh(Cpꢀ(CH2)2PEt2)(CO)], since increasing the electron
density on the metal would be expected to inhibit reductive
elimination.
High pressure NMR studies on [Co(Cpꢀ(CH2)2PEt2)(CO)] in
the catalytic solution at room temperature showed a single
resonance (d 75.2, s), which did not correspond to either
[Co(Cpꢀ(CH2)2PEt2)(CO)] or [Co(Cpꢀ(CH2)2PEt2)(C(O)Me)I] and
was not from oxidised phosphine because it changed on heating
to several peaks at d 31–59, which probably correspond to
complexes which do not contain the ligand bound through both
the cyclopentadienyl and the phosphine moieties. Similar results
were obtained under low water conditions. The signals in the final
solution are not from phosphine oxide (expected signal at d > 70),
but could be from phosphine quaternised by MeI or HI.
X-Ray crystallography
Several of the complexes have been studied by X-ray crystallog-
raphy (Table 6, Figs. 1 and 2–5). For complexes containing the
same ligand, the M–P bonds are shorter in the cobalt complexes
than in the Rh or Ir complexes, as expected on the basis of the
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sizes of the elements. The M–P bond lengths in [Rh(Cpꢀ(CH2)2-
PEt2)(CO)] (2.2157(19)), [Rh(Cpꢀ(CH2)2PPh2)(CO)] (2.2306(10))
and [Rh(Cp(CH2)2PEt2)(CO)] (2.1838(11)) can be rationalised
by considering the r-donation. The less donating PPh2 group
results in the longest M–P bond, whilst the higher electron
density on rhodium in [Rh(Cpꢀ(CH2)2PEt2)(CO)] compared with
[Rh(Cp(CH2)2PEt2)(CO)] also leads to a longer Rh–P bond.
Steric effects may also influence these bond lengths. In all of the
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Acknowledgements
We thank BP Chemicals and the EPSRC for a studentships
(A. E. C. M., P. I. P. E) and the EPSRC and Sasol for support
of an upgrade of the NMR machine.
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