The reaction between orthodiphenylphosphinobenzaldehyde and [(η5-C5Me5)MCl(μ-Cl)]2 (M=Rh and Ir)

Article abstract of DOI:10.1016/j.ica.2003.12.026

The benzaldehyde functionalized phosphine Ph₂PC ₆H₄CHO-2 underwent reaction with [(η⁵- C₅Me₅)MCl(μ-Cl)]₂ (M=Rh, Ir) to form (η⁵-C₅Me₅)MCl₂

Full text of DOI:10.1016/j.ica.2003.12.026

Inorganica Chimica Acta 357 (2004) 2870–2874
www.elsevier.com/locate/ica
The reaction between orthodiphenylphosphinobenzaldehyde
and [(g5-C5Me5)MCl(l-Cl)]2 (M ¼ Rh and Ir)
*
Mark Nieuwenhuyzen, Graham C. Saunders
School of Chemistry, QueenÕs University Belfast, David Keir Building, Belfast BT9 5AG, UK
Received 17 December 2003; accepted 26 December 2003
Available online 28 January 2004
Abstract
The benzaldehyde functionalized phosphine Ph2PC6H4CHO-2 underwent reaction with [(g5-C5Me5)MCl(l-Cl)]2 (M ¼ Rh, Ir) to
form (g5-C5Me5)MCl2(jP-Ph2PC6H4CHO-2), which underwent activation of the aldehyde C–H bond to form (g5-
C5Me5)MCl(jP; jC-Ph2PC6H4CO-2). Formally the reaction involves oxidative addition of C–H across the metal and reductive
elimination of HCl. The structure of (g5-C5Me5)RhCl(jP; jC-Ph2PC6H4CO-2) has been determined by single-crystal X-ray dif-
fraction.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Rhodium; Iridium; 2-Diphenylphosphinobenzaldehyde; Oxidative addition; Acyl
1. Introduction
methyl complexes of iron [12], cobalt and nickel [9], in
which methane is reductively eliminated.
The benzaldehyde-functionalized phosphine 2-diph-
enylphosphinobenzaldehyde (1), commonly binds to
transition metals as either a monodentate jP ligand [1–
5] or a chelating bidentate jP; jO ligand [2,6,7], but
more complicated bonding modes are known [8]. Ad-
ditionally, the aldehyde C–H bond of 1 can undergo
chelate-assisted oxidative addition across the metal to
give an acylhydride complex containing a chelating
jP; jC ligand (Scheme 1) [2–5,7,9–13]. Oxidative addi-
tion of 1 can also occur to give dinuclear complexes with
bridging acyl and hydride ligands [14]. Complexes con-
taining the cyclic MPC6X4C(O) motif have also be
formed by addition of CO to orthometallated complexes
[15] and by reactions at the a-carbon of coordinated
jC; jP-CXYC6H4PPh2 [16]. For some acylhydride
complexes, in which a suitable ligand (X) is coordinated
to the metal, reductive elimination of HX can occur
returning the metal to the original formal oxidation
state. This has been observed in the reactions of 1 with r
Addition of the aldehyde C–H bond across the metal
has been observed for complexes of all group 9 and 10
metals, usually in a low oxidation state. In particular a
number of rhodium(III) [2,5,11,13] and iridium(III) [3]
acylhydride complexes have been prepared by the reac-
tion between 1 and rhodium(I) and iridium(I) com-
plexes. To date there have been no reports of subsequent
reductive elimination or formation of an acyl complex
by the reaction between 1 and a rhodium(III) or irid-
ium(III) complex.
Here we report the reactions between 1 and the
complexes [(g5-C5Me5)MCl(l-Cl)]2 (M ¼ Rh, Ir).
2. Experimental
2.1. Physical measurements
1H, 19F and 31P NMR spectra were recorded using
Bruker DPX300 and DRX500 spectrometers. 1H
(300.01 or 500.13 MHz) were referenced internally using
the residual protio solvent resonance relative to SiMe4
(d 0) and 31P (121.45 or 202.46 MHz) externally to 85%
H3PO4 (d 0). All chemical shifts are quoted in d (ppm),
* Corresponding author. Tel.: +44-28-9027-4682; fax: +44-28-9027-
2117.
E-mail address: g.saunders@qub.ac.uk (G.C. Saunders).
0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.12.026

M. Nieuwenhuyzen, G.C. Saunders / Inorganica Chimica Acta 357 (2004) 2870–2874
2871
O
H
X
O
O
H
ML n
PPh2
ML n
- HX
+ MLn X
PPh2
PPh2
1
Scheme 1.
using the high frequency positive convention, and cou-
pling constants in Hz. LSIMS mass spectra were re-
corded on a VG Autospec X series mass spectrometer.
Elemental analyses were carried out by ASEP, The
School of Chemistry, QueenÕs University Belfast.
652.12740. m(C@O): 1624 cmꢀ1. NMR data are given in
Table 1.
2.3.3. Crystal structure determination of (g5-
C5Me5)RhCl(jP; jC-PPh2C6H4CO-2) (2a)
A
crystal of 2a with approximate dimensions
2.2. Materials
0.20 ꢁ 0.18 ꢁ 0.16 mm was grown from dichlorome-
thane. Crystal data and a summary of data collection
and refinement parameters are given in Table 3. The
molecular structure is shown in Fig. 1. Selected bond
distances and angles are listed in Table 2. Data were
collected on a Bruker SMART diffractometer using the
SAINTNT software with Mo Ka radiation. Lattice
parameters were determined from a least squares re-
finement of 5381 reflections. The structure was solved by
direct methods and refined on F 2 by full matrix least
squares. All nonhydrogen atoms were refined with an-
isotropic thermal parameters. The hydrogen atoms were
The compounds [(g5-C5Me5)RhCl(l-Cl)]2 and
Ph2PC6H4CHO-2 (1) (Aldrich) were used as supplied.
[(g5-C5Me5)IrCl(l-Cl)]2 was prepared as described [17].
2.3. Preparations
2.3.1. (g5-C5Me5)RhCl(jP; jC-PPh2C6H4CO-2) (2a)
A solution of [(g5-C5Me5)RhCl(l-Cl)]2 (0.13 g, 0.22
mmol) and 1 (0.13 g, 0.44 mmol) in dichloromethane (40
cm3) was left at room temperature for 72 h. The volume
was reduced to 15 cm3 by rotary evaporation and hex-
ane (15 cm3) added. Further concentration by rotary
evaporation afforded crystals of 2a. Yield: 0.17 g
(68.7%). Anal. Calc. for C29H29ClOPRh: C, 60.8; H, 5.2.
Found: C, 61.9; H, 4.95%. LSIMS: 562 (62) (Mþ), 499
(100) ([M–Cl–CO]þ). Found for Mþ 562.06696
C29H3259ClOPRh requires 562.06996. m(C@O): 1642
cmꢀ1. NMR data are given in Table 1.
ꢀ
placed in calculated positions (C–H 0.96 A), assigned
fixed isotropic thermal parameters at 1.2 times for C–H
the equivalent isotropic Uij (1.5 for methyl) of the atoms
to which they are attached and allowed to ride on their
respective parent atoms. All calculations were per-
formed using SHELXTL [18].
3. Results and discussion
2.3.2. (g5-C5Me5)IrCl(jP; jC-PPh2C6H4CO-2) (2b)
A solution of [(g5-C5Me5)IrCl(l-Cl)]2. (0.14 g, 0.18
mmol) and 1 (0.11 g, 0.37 mmol) were treated as for 2a.
Yield: 0.15 g (63.9%). Anal. Calc. for C29H29ClIrOP: C,
53.0; H, 4.5. Found: C, 53.4; H, 4.5%. LSIMS: 652 (100)
(Mþ), 617 (47) ([M–Cl]þ), 589 ([M–Cl–CO]þ). Found
for Mþ 652.12776. C29H2935Cl193IrOP requires
3.1. Reactions between [(g5-C5Me5)MCl(l-Cl)]2 and
Ph2PC6H4CHO-2 (1)
Treatment of the complexes [(g5-C5Me5)MCl(l-Cl)]2
(M ¼ Rh, Ir) with 1 in dichloromethane at room
temperature afforded the acyl complexes [(g5-
C5Me5)MCl(jP; jC-Ph2PC6H4CO-2)] (2a M ¼ Rh, 2b
Table 1
NMR data for compounds of (g5-C5Me5)MCl(jP; jC-PPh2C6H4CO-2) (2a M ¼ Rh, 2b M ¼ Ir) and (g5-C5Me5)MCl2(jP-PPh2C6H4CHO-2) (3a
M ¼ Rh, 3b M ¼ Ir)
Compound
dP
dH(C5Me5)
dH(aryl)
dH(CHO)
2a
72.1 [d, 1J(Rh–P) 174 Hz] 1.41 [d, 4J(P–H) 2.8 Hz] 8.14 (2H, m), 7.76 (1H, m), 7.69 (1H, m), 7.50
(3H, m), 7.37 (2H, m), 7.22 (3H, m), 6.89 (2H, m)
2b
38.1 (s)
1.41 [d, 4J(P–H) 1.4 Hz] 8.11 (2H, m), 7.90 (1H, m), 7.79 (1H, m), 7.56
(3H, m), 7.44 (2H, m), 7.29 (3H, m), 6.94 (2H, m)
3a
3b
29.6 [d, 1J(Rh–P) 145 Hz] 1.39 [d, 4J(P–H) 3.6 Hz] 8.21 (1H, m), 7.3–7.9 (13H)
10.24
10.32
3.1 (s)
1.36 [d, 4J(P–H) 2.5 Hz] 8.18 (1H, m), 7.71 (4H, m), 7.63 (1H, m), 7.58
(1H, m), 7.34 (7H, m)

2872
M. Nieuwenhuyzen, G.C. Saunders / Inorganica Chimica Acta 357 (2004) 2870–2874
Table 3
Crystal data and summary of data collection for (g5-
C5Me5)RhCl(jP; jC-PPh2C6H4CO-2) (2a)
Formula
C29H29ClOPRh
562.85
triclinic
Formula weight
Crystal system
Space group
ꢁ
P1
ꢀ
a (A)
10.4569(9)
11.5486(10)
11.8255(10)
98.377(2)
93.149(1)
115.640(1)
1262.53(19)
153(2)
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
V (A )
T (K)
Z
3
ꢀ
2
0.71073
ꢀ
k (Mo Ka) (A)
Dcalc (g cm3)
1.481
0.865
l (mmꢀ1
F(0 0 0)
)
576
9089
Reflections collected
Unique reflections (Rint
Parameters refined
R1; w2 ½I > 2rðIÞꢂ
)
5381 (0.0254)
303
Fig. 1. Molecular structure of the
R
enantiomer of (g5-
C5Me5)RhCl(jP; jC-PPh2C6H4CO-2) 2a. Thermal ellipsoids are
shown at the 30% probability level. The hydrogen atoms are omitted
for clarity.
0.0406, 0.0888
0.0546, 0.1079
1.739, )0.832
1.049
R1; wR2 (all data)
3
ꢀ
Largest difference peak and hole (e A )
Goodness-of-fit on F 2
Table 2
ꢀ
Selected bond lengths (A) and angles (°) with estimated standard de-
m(C@O) as strong bands at 1642 and 1624 cmꢀ1 for 2a
and 2b, respectively. These values are similar to those of
other neutral rhodium(III) and iridium(III) complexes
of this ligand (1590–1632 cmꢀ1 [5,10,12] and 1630–1640
cmꢀ1 [3], respectively).
viations (e.s.d.s.) in parentheses for (g5-C5Me5)RhCl(jP; jC-
PPh2C6H4CO-2) (2a)
Cpy(1)–Rh
Rh–C(2)
Rh–C(4)
C(1)–C(2)
C(3)–C(4)
C(5)–C(1)
Rh–C(17)
Rh–P
1.885(4)
2.282(4)
2.188(4)
1.460(6)
1.456(5)
1.409(5)
2.028(4)
2.2568(11)
1.823(4)
1.217(5)
Rh–C(1)
Rh–C(3)
Rh–C(5)
C(2)–C(3)
C(4)–C(5)
Mean C–CH3
Rh–Cl
2.226(4)
2.292(4)
2.236(4)
1.410(5)
1.434(6)
1.495(6)
2.3874(10)
1.816(4)
1.830(4)
A possible mechanism for the reaction involves initial
jP coordination of 1 forming (g5-C5Me5)MCl2(jP-1)
(3a M ¼ Rh, 3b M ¼ Ir), followed by oxidative addition
of the aldehyde C–H bond forming an acylhydrido
complex. Subsequent reductive elimination of HCl
yields the product (Scheme 2(a)). Oxidative addition to
[(g5-C5Me5)MCl(l-Cl)]2 is not without precedent
[19,20]. The metal in the postulated intermediate (g5-
C5Me5)MHCl2(jP; jC-PPh2C6H4CO-2) has a valence
electron count of 20, however the 18 electron rule can be
satisfied if there is slippage of the pentamethylcyclo-
pentadienyl ring from g5 to g3 coordination. Reductive
elimination from this intermediate might be expected to
be facile because of the higher formal oxidation state of
the metals. Alternatively, loss of HCl from 2a and 2b
may not involve oxidative addition and reductive elim-
ination, but occur by either a stepwise or concerted
mechanism (Scheme 2(b)). Another possibility is that
oxidative addition of aldehyde C–H bond and reduc-
tive elimination of HCl occurs prior to phosphine
coordination (Scheme 2(c)). Unassisted oxidative addi-
tion of aldehyde C–H bonds to [Rh{j3P; jN-
(Ph2PCH2CH2)3N}]þ has been reported [21].
P–C(11)
P–C(31)
P–C(21)
C(17)–O
Cpy–Rh–Cl
121.0(1)
129.2(2)
Cpy–Rh–P
P–Rh–Cl
132.4(1)
94.28(4)
Cpy–Rh–C(17)
P–Rh–C(17)
Rh–P–C(11)
Rh–P–C(31)
C(11)–P–C(31)
Rh–C(17)–O
83.49(12)
103.54(13)
117.65(13)
107.88(18)
122.6(3)
Cl–Rh–C(17)
Rh–P–C(21)
C(11)–P–C(21)
C(21)–P–C(31)
Rh–C(17)–C(16)
81.21(11)
117.26(14)
106.14(17)
103.61(18)
118.0(3)
Cp* represents the centroid of the pentamethylcyclopentadienyl
ring defined by C(1), C(2), C(3), C(4) and C(5).
M ¼ Ir) in ca. 65% yield. The identity of the complexes
was confirmed by the analytical data, mass, NMR
(Table 1) and IR spectra, and for 2a also by single-
1
crystal Xray diffraction (Fig. 1). The H NMR spectra
contain resonances assigned to the hydrogen atoms of
the pentamethylcyclopentadienyl (d 1.41) and aromatic
rings (d 6.8–8.2), but no resonance which can be as-
signed to an aldehyde hydrogen atom. The 31P{1H}
NMR spectra show a doublet resonance at d 72.1 for 2a
and a singlet at d 38.1 for 2b. The IR spectra exhibit
In order to identify intermediates in the reaction, low
temperature in situ NMR experiments were performed.
Phosphine 1 was added to [(g5-C5Me5)RhCl(l-Cl)]2 in

M. Nieuwenhuyzen, G.C. Saunders / Inorganica Chimica Acta 357 (2004) 2870–2874
2873
a
PPh2
Cl
Cl
M
H
- HCl
M
O
Cl
PPh2
O
Cl
1/2[(η5-C5Me5)MCl2]2
H
M
+
O
b
Ph2
O
Cl
O
3a M = Rh
3b M = Ir
P
PPh2
- HCl
M
H
Cl
H
Cl
PPh2
2a M = Rh
2b M = Ir
1
c
- HCl
M
M
Cl
Cl
O
O
Cl
H
PPh2
Ph2P
Scheme 2.
CDCl3 frozen at 195 K in an NMR tube. The mixture
was allowed to warm slowly to 224 K. At this temper-
ature the 31P{1H} NMR spectrum exhibited a doublet
resonance at d 29.6. The coupling of 145 Hz is consistent
with 1J (Rh–P) for g5-pentamethylcyclopentadienyl
rhodium(III) complexes. The 1H NMR spectrum ex-
hibited a singlet resonance at d 10.24, broad multiplets
between d 7.3 and 8.3, and a doublet at d 1.39. The
resonance at d 10.24 is at slightly lower frequency to that
of the aldehyde hydrogen atom of 1 (d 10.50). The data
are entirely consistent with (g5-C5Me5)RhCl2(jP-
PPh2C6H4CHO-2) (3a). No further reaction was ob-
served up to 273 K. At 300 K clean conversion of 3a to
2a was observed over hours. No other intermediates
were observed. In particular no hydride resonances (d 0
to )50) were observed. Similarly (g5-C5Me5)IrCl2(jP-
PPh2C6H4CHO-2) (3b) was observed at 273 K on
addition of 1 to [(g5-C5Me5)IrCl(l-Cl)]2, and clean
conversion to 2b in hours at 300 K.
angles are given in Table 2 and the crystal data and
refinement details in Table 3. The structure exhibits the
expected three-legged piano stool geometry and a ste-
reogenic rhodium atom. The unit cell contains both
enantiomers.
The pentamethylcyclopentadienyl ligand is distorted
from C5 symmetry about the Cpy–Rh axis to g3; g2
coordination with the alkene moiety trans to the acyl
carbon atom. The C(2)–C(3) and C(1)–C(5) distances
are significantly shorter than C(1)–C(2) and C(3)–C(4).
C(4)–C(5) is within 3r of all these distances. The inter-
nal C–C–C angles are the same (107.6(3)°–108.1(3)°).
The distance from rhodium to C(4), which is approxi-
mately trans to chloride (154.28(10)°) and cis to phos-
phorus (104.77(11)°), is significantly shorter than those
to C(1) and C(5), which are approximately cis to the acyl
carbon (109.06(16)° and 96.45(15)°, respectively). C(1) is
also approximately trans to phosphorus (165.24(11)°).
The distances from rhodium to C(2) and C(3), which are
trans to the acyl carbon atom (145.77(16)° and
145.77(16)°, respectively), are significantly longer than
the other three. The Rh–C(4) distance lies within the
range for Cp*RhCl2(phosphine) complexes (2.17–2.20
The observation of 3a and 3b strongly suggests 1
coordinates to the metal prior to loss of HCl and that
the mechanism in Scheme 2(c) can be ruled out. This is
supported by the observation that benzaldehyde un-
derwent no reaction with [(g5-C5Me5)RhCl(l-Cl)]2 un-
der the same conditions.
ꢀ
A) [22], but the other distances are longer, Rh–C(2) and
ꢀ
Rh–C(3) by almost 0.1 A.
The Rh–CO and C@O distances of 2.028(4) and
1.217(5) A, respectively, are typical for rhodium acyl
3.2. Structure of (g5-C5Me5)RhCl(jP; jC-Ph2PC6H4
CO-2) (2a)
ꢀ
complexes [10,23]. The Rh–M–CO bite angle of
83.49(12)° is similar to those of other rhodium(III)
complexes of jP; jC-Ph2PC6H4CO-2 [9], but the Rh–P
The structure of 2a was determined by single-crystal
X-ray diffraction Fig. 1. Selected bond distances and
ꢀ
distance of 2.2568(11) A is shorter. The Rh–Cl distance

2874
M. Nieuwenhuyzen, G.C. Saunders / Inorganica Chimica Acta 357 (2004) 2870–2874
and the Cpy–Rh–P and Cpy–Rh–Cl angles are typical of
Cp*RhCl2(phosphine) complexes [22].
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The reaction between [(g5-C5Me5)MCl(l-Cl)]2
(M ¼ Rh, Ir) and Ph2PC6H4CHO-2 leads to activation
of the aldehyde C–H bond and formal loss of HCl to
yield the neutral complexes [(g5-C5Me5)MCl(jP; jC-
PPh2C6H4CO-2)]. The reaction proceeds via the com-
plexes [(g5-C5Me5)MCl2(jP-PPh2C6H4CHO-2)]. No
other intermediates were detected.
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mation may be obtained free of charge from The Di-
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UK (fax: +441223336033; email: deposit@ccdc.cam.ac.
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