Synthesis and structural aspects of M-allyl (M = Ir, Rh) complexes

Article abstract of DOI:10.1016/j.jorganchem.2007.07.053

The synthesis, characterization and chemistry of novel η³-allyl metal complexes (M = Ir, Rh) are described. The structures of compounds (C₅Me₄H)Ir(PPh₃)Cl₂ (1), (C₅Me₄H)Ir(PPh

Full text of DOI:10.1016/j.jorganchem.2007.07.053

Journal of Organometallic Chemistry 692 (2007) 5125–5132
www.elsevier.com/locate/jorganchem
Synthesis and structural aspects of M-allyl (M = Ir, Rh) complexes
Akella Sivaramakrishna, Emma Hager, Feng Zheng, Hong Su,
*
Gregory S. Smith, John R. Moss
Department of Chemistry, University of Cape Town, Rondebosch 7701, Cape Town, South Africa
Received 10 May 2007; received in revised form 23 July 2007; accepted 23 July 2007
Available online 8 August 2007
Abstract
The synthesis, characterization and chemistry of novel g3-allyl metal complexes (M = Ir, Rh) are described. The structures of com-
pounds (C5Me4H)Ir(PPh3)Cl2 (1), (C5Me4H)Ir(PPh3)(g3-1-methylallyl)Br (3a), (C5Me4H)Ir(g4-1,3,5-hexatriene) (8), and (C5Me5)Rh-
(g3-1-ethylallyl)Br (5d) have been determined by X-ray crystallography. Structural comparisons among these complexes are discussed.
It is found that the neutral metal allylic complex [Cp*IrCl(g3-methylallyl)] (5) ionizes in polar solvents to give [Cp*Ir(g3-methyl-
allyl)]+Clꢀ (6) and reaches equilibrium (5 ꢀ 6) at room temperature. Addition of tertiary phosphine ligands to neutral complexes such
as [Cp*Ir(g3-methylallyl)Cl], results in the formation of stable ionic phosphine adducts. Factors such as solvent, length of carbon chain,
temperature and light are discussed with respect to the formation, stability and structure of the allyl complexes.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Metal-(g3-allyl) complexes; Transmetalation reactions; Ligand addition reactions; Structure comparison; Thermolysis studies
1. Introduction
as reactants has been reported [7]. The catalytic asymmetric
hydrogenation of a-functionalized ketones using chiral
Ru(II)-allyl complexes has also been reported [8]. A good
knowledge of the structural aspects of these compounds
is important in understanding the reactivity patterns in
detail. The present work describes the synthesis, structural
characterization and reactivity of some allylic iridium(III)
and rhodium(III) complexes.
Transition metal g3-allyl compounds display a rich
chemistry [1] and are widely encountered both as synthetic
reagents and in catalysis. There has also been much interest
shown in elucidating the structures and stereodynamic
behaviour of g3-allyl metal complexes in solution [2].
Investigations on potential applications of these types of
complexes in asymmetric synthesis as well as in heteroge-
neous catalysis have been carried out [3]. For example,
tris(allyl)rhodium complexes with a variety of metal oxide
supports have been reported as catalysts [4]. g3-Allyl palla-
dium complexes have been studied extensively, partly
because of the extremely useful palladium-catalyzed reac-
tions of nucleophiles with allylic substrates [5]. It has also
been shown that the bulky ligand substituents can cause
modifications to the structure and solution behaviour of
the stable allylic metal complexes [6]. The reactivity of rho-
dium and iridium allylic complexes with various substrates
2. Results and discussion
Our original efforts were aimed at preparing and charac-
terizing a series of iridium and rhodium alkenyl com-
pounds with an M–C r-bond and a pendant alkene
group. However, some of the products of the reactions of
1 with 1-alkenyl Grignard reagents were shown to be the
metal allyl complexes. It has been found that the com-
pound 2 is air-sensitive in the solid state and decomposes
rapidly in solution, particularly in chlorinated solvents
(Eq. (1)) [9]. The analogous reaction involving the rhodium
precursor with 1-alkenyl Grignard reagent showed that the
PPh3 ligand was eliminated from the metal sphere (as
*
Corresponding author. Tel.: +27 21 650 2535; fax: +27 21 689 7499.
E-mail address: John.Moss@uct.ac.za (J.R. Moss).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.07.053

5126
A. Sivaramakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 5125–5132
indicated by 31P NMR) in solution as the allylic structure
formation was more predominant.
Ph3P
Ph3P
Cl
Cl
Et2O
n
n
BrMg(CH2)nCH2CH=CH2
n = 1, 2
a
Cp*
Cp*
1
2
CH2Cl2 or
CHCl3
ð1Þ
Br-
Ph3P
Cp*
R
3a, R = Me,
3a', R = Et
55.4. 55.22. 55.0. 44.88. 44.6. 44.44. 44.22. 44.0. 33.88. 33.66. 33.4. 33.2.233.0. 22.8. 22.6. 22.4. 22.22. 22.0. 11.8. 11.6. 11.4.4 11.2.2 11.0. 00.8. 00.6.
Grignard reagents with short alkenyl chains (viz
BrMgCH2CH@CH2 and BrMgCH2CH2CH@CH2) gave
metal–allyl halides in good yields on reaction with
[Cp*MX2]2 (where M = Ir, Rh) as shown in Scheme 1.
These unexpected (g3-allyl-metal) complexes, 5a–d are ob-
tained by an irreversible rearrangement of the initially
formed M-alkenyl complexes. It was found that the neutral
allylic complex, 5 and the cationic allylic complex, 6 are in
equilibrium in solution. The formation of 5b (M = Ir) in
the solid state was identified by X-ray crystal structural
analysis. But we could not solve this structure completely
as there are errors associated with the space group identifi-
cation. We also find that ionization becomes more favored
as ꢀthe size of the halide ligand increases (i.e. Iꢀ >
Br > Clꢀ) (Scheme 1, where Cp*Ir = (C5Me4H)Ir and
Cp*Rh = (C5Me5)Rh).
The conversion of neutral metal allylic complexes to
ionic metal complexes was observed at room temperature
in the polar solvents (chloroform, dichloromethane and
methanol). It is evident that the chloride and bromide
ligands are not sufficiently labile to effect the dissociation
of the complex in non-polar solution. For example, the
1H NMR of 5b (where M = Ir) revealed a significant differ-
ence in the chemical shifts of the methyl protons of tetram-
b
55.4.4 55.2.2 55.0.0 44..88 44.6.6 44.4. 44..22 44.0.0 33.8.8 33.6.6 33.4.4 33.22. 33.0.0 22..88 22.6.6 22.4.4 22..22 22.00. 11.8.8 11.6.6 11.4.4 11.22. 11.0.0 00.88. 00.66.
Fig. 1. (a) Compound 5b in CDCl3; (b) compound 5b in C6D6.
ethylcyclopentadienyl, depending on the solvent used. In
polar solvents, three different signals were observed. The
spectrum of the same compound in non-polar solvent
showed two signals for the methyl protons. The position
of the methyl protons of tetramethylcyclopentadiene in 5b
(M = Ir) appears at d 1.44 and 1.43 in C6D6 whereas in
CDCl3 the same compound showed peaks at 1.79, 1.83,
1.87 (1:2:1) (see Fig. 1). It was observed that the tetrameth-
ylcyclopentadienyl hydrogen shifts significantly downfield
to d 4.83 in CDCl3 and in C6D6 appears at d 4.15.
The equilibrium dissociation increases with decreasing
temperature and the position of equilibrium is readily
controlled by variation of solvent polarity, temperature,
and replacement of chloro-ligand by better leaving groups.
These results are supported by the 1H NMR spectra of the
corresponding metal–allyl compounds.
Cp*
X
X
(i)
Cp*
Cl
n
M
M
M
Cp*
X
X
Cp*
Cp*
4, n = 1, 2
n
X
Ir
Ir
M = Ir, X = Cl, Br, I, Cp* = C5Me4H;
M = Rh, X = Cl, Br, Cp* = C5Me5.
+
(i)
(ii)
R
7a, R = Et
7b, R = C3H7;
n = 3 or 4
Cl
9
Cl
Cl
X-
M+
Cp*
Cl
X
Ir
Ir
R
R
Cp*
Cp*
Cp*
M
Cp*
(ii)
(iii)
Ir
6a, R = H, M =Rh, X = Br;
6b, R = CH3; M = Ir, X = Cl;
6c, R = CH3, M = Rh, X = Br;
6d, R = Et, M = Rh, X = Br.
5a, R = H, M =Rh, X = Br;
5b, R = CH3; M = Ir, X = Cl;
5c, R = CH3, M = Rh, X = Br;
5d, R = Et, M = Rh, X = Br.
8
Scheme 1. (i) Et2O, BrMg(CH2)nCH@CH2 (n = 1, 2); (ii) benzene or
toluene; (iii) CHCl3 or MeOH.
Scheme 2. (i) Et2O, BrMg(CH2)nCH@CH2 (n = 3, 4); (ii) Et2O,
BrMg(CH2)4CH@CH2, reflux at 45 ꢁC, 5 h.

A. Sivaramakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 5125–5132
5127
In contrast, the Grignard reagents with longer alkenyl
chains gave different products at ꢀ78 ꢁC, i.e. mainly 7,
which contains one pendant alkenyl chain along with an
g3-allylic group (Scheme 2). Reactions of [Cp*IrCl2]2
(Cp* = g5-C5Me5 or g5-C5Me4H) with [BrMg(CH2)4CH@
CH2] in diethylether at 45 ꢁC gave [Cp*Ir(g4-C6H10)] (8) as
the final product formed from a reaction involving C–H
activation of an alkenyl chain (Scheme 2).
alkenes to their corresponding 2-alkenes (Eq. (3)). Further
studies of these reactions are under way [11].
X
Cp*
M
ð3Þ
, 100οC, 90h,Toluene
A single crystal of 8 suitable for the X-ray diffraction
analysis was obtained and the structure reveals trigonal
planar coordination at the Ir atom. The corresponding rho-
dium reaction of [Cp*RhCl2]2 with [BrMg(CH2)3CH@
CH2] gave only [Cp*RhBr(g3-C5H9)] [5d] and no C–H
activation was observed.
2.1. Structural aspects
The average M–C bond distances of the metal–cyclo-
pentadienyl rings in complexes 3a, 8 and 5d, are
˚
˚
˚
2.2102 A, 2.2354 A and 2.2380 A, respectively, somewhat
longer than the corresponding distances in compound 1
X
Cl-
Cp*
˚
(average 2.1958 A). This might be due to the electronic
CHCl3
Cp*
M
M+
effect of the central metal. The distances between the
metal and the centroid of the cyclopentadienyl ring vary,
depending on the nature of metal. The shortest metal-
centroid distance among these complexes is found in
+
PPh3
Ph3P
M = Ir, Rh
Cp* = C5Me5 or C5Me4H
5b, R = CH3, M = Ir, X = Br;
5c, R = CH3, M = Rh, X = Br;
3a, R = CH3, M = Ir, X = Br;
3b, R = CH3, M = Rh, X = Br;
˚
compound 1 as 1.824(2) A. The presence of donor
ð2Þ
ligands such as PPh3 or alkenes has a significant effect
on the metal-centroid distances (see Table 1). The posi-
tive charge on the iridium atom in compound 3a did
not induce any significant change in the metal–carbon
distances of the allylic carbon atoms around the metal
as compared with the neutral complex, 5d (average dis-
In order to expand the relatively unexplored ligand addition
chemistry of these metal allyl compounds, investigations
into their reactivities with various types of ligands were car-
ried out. It was found that these stable allyl complexes, 5a–d
or 6a–d are unreactive at 25 ꢁC with the P, N and O
(P = PPh3, N = CH3CN, and O = tetrahydrofuran) donor
ligand systems even after several days. The stability is a
likely consequence of the restricted motion of the allyl
ligands as they satisfy the 18eꢀ rule and the resulting
blockage of further reaction pathways. A similar trend
was observed with the rhodium complexes. The synthesis
of iridium and rhodium analogs demonstrated that their
reactions with a variety of phosphine ligands yielded their
corresponding phosphine derivatives under refluxing condi-
tions (Eq. (2)). However, on refluxing for several hours, the
neutral compound, 5b (M = Ir) was converted to an ionic
compound, 3a (see Eq. (2)). The structure of 3a with bro-
mide counter anion was confirmed by X-ray structural char-
acterization. As reported earlier [10], these g3-allyl metal
complexes with an unsymmetrical ligand environment can
show different conformations such as syn- and anti-,
depending on the orientation of the allyl ligand with respect
to the other ligands in the complex (Chart 1).
On addition of PPh3 to an NMR tube containing a
solution of Cp*Rh(III)(g3-1-ethylallyl)Br (5d) in C6D6
and subsequent heating for several hours, the 31P NMR
spectrum shows two doublets at 47.51 (J = 165 Hz) and
48.09 ppm (J = 166 Hz) indicative of Cp*Rh(III)(PPh3)-
(g3-1-ethylallyl)Br. The appearance of 2 doublets may be
due to the presence of syn- and anti- isomers. In a similar
way, the formation of Cp*Rh(III)(g3-1-methylallyl)-
(PPh3)Br was observed when PPh3 was added to a solution
of Cp*Rh(III)(g3-1-methylallyl)Br14 [5c] in C6D6.
˚
˚
tances are 2.1813 A and 2.1643 A for 3a and 5d, respec-
tively). Strikingly, the central carbon atom in the allylic
group is closest to the metal in both the complexes (3a
and 5d) (see Table 2). Thus, the structural features were
little affected by the coordination of a bulky PPh3 ligand
to the metal centre in compound 3a. It is interesting to
note that the metal–carbon distances for compound 8
˚
were found to be in a range 2.120–2.129 A, which is
quite close to metal–carbon sigma bond lengths. The
Ir–P bonds in 1 and 3a are almost equidistant and com-
parable with the literature reports [12]. The crystallo-
graphic data of all the compounds are given in Table 3
(see Figs. 2–5).
2.2. Thermal studies
Thermal decomposition of compounds 3a, 5b and 5d
gave a range of organic products. Unexpectedly, com-
pound 5b gave n-pentane (70%) and 1-pentene (30%) on
decomposition instead of the corresponding C4-hydrocar-
bon products. Similar trends were observed with the
compound 3a on decomposition. But compound 9 yielded
1-pentene (23%) and 2-pentene (25%), 2-hexene (40%) and
1,5-hexadiene (12%), which were analyzed by GC (Scheme
3). A similar decomposition trend was observed with the
rhodium analog, 5d. The methyl groups on pentamethylcy-
clopentadiene or tetramethylcyclopentadiene ligand
may be the source for the extra carbon atom in the organic
products after the decomposition. It is interesting to
note that the organic product distribution on thermal
Interestingly, these allylic metal complexes can act as
alkene isomerization catalysts for the conversion of 1-

5128
A. Sivaramakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 5125–5132
R
decomposition depends on the nature of the metal, whether
R
it is iridium or rhodium.
R
R
R
R
H
M = Ir, Rh
R = H, Me
R1 = H, Me, Et
3. Conclusions
R
R
R
R
In summary, the isolation and structural characteriza-
tion of thermally stable g3-allyl halide complexes of irid-
ium and rhodium has been accomplished. Results showed
that, in some cases, an equilibrium between neutral and
ionic complexes is observed, depending on the nature of
solvent. Evidence from NMR and X-ray crystallography
suggests that the C5Me5 or C5Me4H ligands cause rela-
tively little perturbation in the essential metal–allyl geome-
try. The high thermal stability of the metal–allyl complexes
is a likely consequence of the restricted motion of the allyl
ligands (as they satisfy the 18eꢀ rule) and the resulting
blocking of decomposition pathways. The interplay of ste-
ric, electronic and chelating effects is evident in the reac-
tions of phosphine ligands with (allyl)chloro metal
compounds. These allylic complexes may react with suit-
able substrates, resulting in the formation of functionalized
organic products (on decompositions). Further investiga-
tions on the influence of these factors with various metal–
allyl complexes will be carried out.
M
M
H
H
H
R1
H
R1
H
H
H
anti-
syn-
Chart 1.
Table 1
Distances between metal and the centroid of the Cp ring
˚
Compound Distance between metal and the centroid of the Cp ring (A)
1
1.824(2)
1.873(3)
1.883(2)
1.845(5)
3a
8
5d
Table 2
Selected metal–carbon bond distances of metal–allyl complexes
4. Experimental
˚
˚
3a (ionic) (A) [Iridium(III)
5d (neutral) (A) [Rhodium(III)
complex]
complex]
All reactions and manipulations were carried out under
an inert atmosphere of dry nitrogen using standard Schlenk
and vacuum-line techniques. [(C5Me5)IrCl2]2, [(C5Me4H)-
IrCl2]2, (C5Me5)IrCl2(PPh3), (C5Me4H)IrCl2(PPh3), [(C5Me5)-
M–C1 = 2.199(6)
M–C2 = 2.095(8)
M–C3 = 2.250(7)
M–C11 = 2.179(12)
M–C12 = 2.090(2)
M–C13 = 2.224(13)
Table 3
Crystal data and structure refinements
Complexes
1
3a
8
5d
Empirical formula
Formula weight
C
763.73
27H28Cl2IrP Æ 1.5C6H6
C37H41BrIrP Æ H2O
806.79
C15H21Ir
393.52
C15H24BrRh
387.16
Data collection temperature (K)
113(2)
173(2)
113(2)
113(2)
Crystal system, space group
Monoclinic, P21/n
8.5748(1)
17.3081(2)
21.6573(3)
90
92.5010(10)
90
3211.17(7)
4, 1.580
Monoclinic, P21
9.8695(1)
17.8877(3)
9.9133(2)
90
112.386(1)
90
1618.23(5)
2, 1.656
Monoclinic, P21/m
5.9072(2)
13.6058(5)
8.3837(3)
90
100.656(1)
90
662.20(4)
2, 1.974
Monoclinic, P21/n
8.4782(1)
14.0621(2)
12.8601(2)
90
90.438(1)
90
1533.15(4)
4, 1.677
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z, Calculated density (Mg mꢀ3
)
)
Absorption coefficient l (mmꢀ1
F(000)
4.398
1516
5.437
800
10.053
376
3.699
776
Reflections collected/unique [Rint
Data/restraints/parameters
Goodness-of-fit on F2
]
68574/6285 [0.0623]
6285/0/366
1.080
36236/6117 [0.0718]
6117/7/370
1.040
9211/1572 [0.1011]
1572/6/79
1.047
35506/2887 [0.0687]
2887/2/156
1.193
Final R indices [I > 2r(I)]
R1 = 0.0235,
wR2 = 0.0416
R1 = 0.0360,
wR2 = 0.0450
0.00108(8)
n/a
R1 = 0.0289,
wR2 = 0.0511
R1 = 0.0392,
wR2 = 0.0538
0.0020(2)
0.004(6)
R1 = 0.0273,
wR2 = 0.0490
R1 = 0.0383,
wR2 = 0.0517
0.0017(8)
n/a
R1 = 0.0744,
wR2 = 0.1890
R1 = 0.0818,
wR2 = 0.1921
0.0064(9)
n/a
R indices (all data)
Extinction coefficient
Absolute structure parameter
Largest difference in peak and hole
1.466 and ꢀ0.613
0.987 and ꢀ0.754
2.268 and ꢀ1.397
3.452 and ꢀ1.346
ꢀ3
˚
(e A
)

A. Sivaramakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 5125–5132
5129
Fig. 2. Molecular structure of 1, showing the atom-numbering scheme.
One and half benzene solvent molecules are omitted. Ellipsoids are drawn
Fig. 4. Molecular structure of 8, showing the atom-numbering scheme.
˚
˚
Ellipsoids are drawn at 35% probability level. Selected bond lengths (A):
at 50% probability level. Selected bond lengths (A): Ir(1)–P(1) 2.3007(8);
Ir(1)–C(1) 2.225(5); Ir(1)–C(2) 2.219(4); Ir(1)–C(3) 2.275(4); Ir(1)–C(4)
2.131(4); Ir(1)–C(5) 2.129(4). Selected bond angles (ꢁ): C(1)–Ir(1)–C(4)
135.35(14); C(1)–Ir(1)–C(5) 111.31(18).
Ir(1)–Cl(1) 2.3939(7); Ir(1)–Cl(2) 2.4196(7); Ir(1)–C(1) 2.149(3). Selected
bond angles (ꢁ): P(1)–Ir(1)–C(1) 95.35(9); P(1)–Ir(1)–Cl(1) 88.46(3); P(1)–
Ir(1)–Cl(2) 93.96(3).
Fig. 3. Molecular structure of 3a, showing the atom-numbering scheme.
Fig. 5. Molecular structure of 5d, showing the atom-numbering scheme.
Bromide and a water molecule are omitted. Ellipsoids are drawn at 50%
probability level. Selected bond lengths (A): Ir(1)–P(1) 2.3015(14); Ir(1)–
(ORTEP diagram; 30% probability ellipsoids). Hydrogen atoms on the
alkyl chain are omitted for clarity. Selected bond lengths (A): Rh(1)–C(11)
˚
˚
C(1) 2.199(6); Ir(1)–C(2) 2.095(8); Ir(1)–C(3) 2.250(7). Selected bond
angles (ꢁ): P(1)–Ir(1)–C(5) 101.90(18); P(1)–Ir(1)–C(1) 90.32(15); P(1)–
Ir(1)–C(2) 107.0(2).
2.172(11); Rh(1)–C(12) 2.10(2); Rh(1)–C(13) 2.222(12); Rh(1)–C(1)
2.168(11); Rh(1)–C(2) 2.255(11). Selected bond angles (ꢁ): C(11)–Rh(1)–
Br(1) 94.9(4); C(12)–Rh(1)–Br(1) 106.2(5).
RhX2]2 (X = Cl, Br), (C5Me4H)Ir(PPh3)Cl2 (1) and
(C5Me5)Ir(PPh3)Cl2 were prepared as previously described
[13]. The Grignard reagents, BrMgCH2CH2CH@CH2,
BrMgCH2CH2CH2CH@CH2 and BrMgCH2CH2CH2CH2-
CH@CH2 were prepared as per the literature procedures
[14]. The solvents were commercially available and distilled
from dark purple solutions of sodium/benzophenone ketyl
1
before use. H, and 31P NMR spectra were recorded on a

5130
A. Sivaramakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 5125–5132
a
X
+
+
M
, 3 h
+
175oC
Cp*
9, M = Ir, X = Cl
5d, M = Rh, X = Br;
+
X
b
M
, 3 h
175oC
+
Cp*
5b, M = Ir, X = Cl
5c, M = Rh; X = Br
Scheme 3. Thermal decomposition of metal (g3-allyl) halide compounds.
1
Bruker DMX-400 spectrometer and all H chemical shifts
are reported relative to the residual proton resonance in
the deuterated solvents. Microanalyses were conducted
with a Thermo Flash 1112 Series CHNS-O Analyzer
instrument. The crystallographic data for all the single
crystals was collected at 113 K on a Nonius Kappa CCD
diffractometer using graphite- monochromated Mo Ka
@CH2); 4.19 (s, 1H, Cp*-H); 0.76–2.12 (m, 12H, CH2);
31P{1H} 25.8 (s). Anal. Calc. for compound C37H46IrP:
C, 62.24; H, 6.49. Found: C, 62.14; H, 6.79%.
4.2. Cp*Ir(III)(PPh3)(g3-1-methylallyl)Cl (3a)
In a Schlenk flask, PPh3 (448 mg, 1.708 mmol) was
added to 5 (690 mg, 1.708 mmol) in dichloromethane
(20 mL) at room temperature. The solution was refluxed
at 50 ꢁC for 8 h. All the volatiles were removed under the
high vacuum. Compound 3 was isolated from the reaction
mixture using p-TLC using dichloromethane as eluent. The
yellow band was extracted into dichloromethane and dried
under vacuum as a yellow crystalline solid. For 3; m.p. 98–
100 ꢁC; yield 83%; 1H NMR d 7.26–7.80 (m, 15H, Ph); 4.43
(s, 1H, Cp-H); 3.95 (m, 1H, CH); 2.95 (m, 1H, CH–CH3);
2.20 (m, 2H, –CH2), 1.81 (s, 12H, Cp-CH3), 1.52 (d, 3H,
CH3); 31P{1H} 10.5 (s). Anal. Calc. for compound
C31H35PIrCl: C, 55.88; H, 5.29. Found: C, 56.26; H,
5.45%. The corresponding bromo derivative, Cp*Ir-
(III)(PPh3)(g3-1-methylallyl)Br was obtained by refluxing
the compound 3a, Cp*Ir(III)(PPh3)(g3-1-methylallyl)Cl
with sodium bromide for 2 h in acetone. The obtained yel-
low crystalline solid was recrystallized from dichlorometh-
ane to obtain single crystals suitable to the X-ray analysis.
Anal. Calc. for compound C31H35PIrBr: C, 52.39; H, 4.96.
Found: C, 52.66; H, 5.12%.
˚
radiation (k = 0.71073 A). GC analyses were carried out
using a Varian 3900 gas chromatograph equipped with
an FID and a 30 m · 0.32 mm CP-Wax 52 CB column
(0.25 lm film thickness). The carrier gas was helium at
5.0 psi. The oven was programmed to hold at 32 ꢁC for
4 min and then to ramp to 200 ꢁC at 10 deg/min and hold
5 min. GC–MS analyses for peak identification were per-
formed using an Agilent 5973 gas chromatograph equipped
with MSD and a 60 m · 0.25 mm Rtx-1 column (0.5 lm
film thickness). The carrier gas was helium at 0.9 mL/
min. The oven was programmed to hold at 50 ꢁC for
2 min and then ramp to 250 ꢁC at 10 deg/min and hold
8 min.
4.1. (C5Me4H)Ir(III)[(CH2)3CH@CH2]2(PPh3) (2)
Cp*Ir(PPh3)Cl2 (201 mg, 0.31 mmol) in diethylether
(15 mL) was cooled to ꢀ78 ꢁC and 1.0 mL of 1-pentenyl
Grignard reagent (1.30 M, 1.24 mmol) was added. The
solution was brought to 0 ꢁC and then stirred until the
solution became clear. The excess Grignard reagent was
removed by hydrolyzing the reaction mixture with 5 mL
of saturated aqueous NH4Cl at ꢀ78 ꢁC. The aqueous layer
was washed with 2 · 5 mL of diethylether and the organic
layer was separated by a separating funnel. The solvent
was removed under reduced pressure and the residue
recrystallized from a diethylether/hexane mixture (2 mL:5
mL) at ꢀ10 ꢁC for 48 h. The pale yellow crystalline solid
was separated by decanting the mother liquor and dried
under vacuum for several hours. For 2; m.p. 66–68 ꢁC
(decomposition); yield 77%; 1H NMR d 6.99–8.10 (m,
15H, Ph); 5.63–5.94 (m, 2H, @CH); 4.88–5.13 (m, 4H,
4.3. Cp*Rh(III)(g3-allyl)bromide (5a)
Allylmagensium bromide (1 mmol) was added to a
suspension of [Cp*RhBr2]2 (160 mg, 0.2 mmol) in 10 cm3
diethylether at ꢀ78 ꢁC. The reaction mixture was allowed
to warm to room temperature and was stirred for 3 h. Sat-
urated NH4Cl solution was added and the organic layer
extracted with benzene and dried over anhydrous MgSO4.
Removal of solvent in vacuo furnished a solid red–brown
product (110 mg, 76%). m.p. 120–122 ꢁC (decomposition).
NMR (CDCl3): d (1H) = 1.78 (s, 15H), 3.14 (d, 2Ha,

A. Sivaramakrishna et al. / Journal of Organometallic Chemistry 692 (2007) 5125–5132
5131
J = 11.7 Hz), 3.33 (d, 2Hb, J = 6.8 Hz), 3.95 (m, 1H). Anal.
Calc. for compound C13H20RhBr: C, 43.5; H, 5.6. Found:
C, 43.8; H, 5.5%. Mass spec. FAB: m/z 359 (M+), 279
(M+ ꢀ Br), 237.
6.03%. Mass spec. FAB: m/e 387 (M+), 307 (M+ ꢀ Br), 237
(M+ ꢀ Br–g3-C5H9–H).
4.7. Cp*Ir(III)(g3-1-ethylallyl)(1-pentenyl) (7)
4.4. Cp*Ir(III)(g3-1-methylallyl)Cl (5b)
In a Schlenk flask, [Cp*IrCl2]2 (316 mg, 0.411 mmol) in
diethylether (20 mL) was cooled to T = ꢀ78 ꢁC and 1-pen-
tenyl Grignard reagent (2.7 mL of 0.62 M, 1.644 mmol)
was added. The solution was brought to around 0 ꢁC and
then stirred until the solution became clear. The products
were isolated by p-TLC using dichloromethane as eluent.
The first yellow band was found to be the compound 7.
The product was obtained as yellow oil and crystallized
from n-hexane at ꢀ10 ꢁC. For 7: m.p. 66–68 ꢁC; yield
In a Schlenk flask, [Cp*IrCl2]2 (168 mg, 0.219 mmol) in
diethylether (20 mL) was cooled to T = ꢀ78 ꢁC and 1-bute-
nyl Grignard reagent (3.4 mL of 0.26 M, 0.88 mmol) was
added dropwise. The solution was brought to ca. 0 ꢁC
and then stirred until the solution became clear. The reac-
tion mixture was worked up as described for compound 2
(see above). The product was obtained as pale yellow crys-
talline solid. For 5: m.p. 110–112 ꢁC; yield 85%; 1H NMR d
4.43 (s, 1H, Cp-H); 3.95 (m, 1H, CH); 2.95 (m, 1H, CH–
CH3); 2.20 (m, 2H, –CH2), 1.81 (s, 12H, Cp-CH3), 1.52
(d, 3H, CH3). Anal. Calc. for compound C13H20IrCl: C,
38.65; H, 4.99. Found: C, 38.56; H, 5.08%.
1
48%; H NMR d 5.73–5.90 (m, 1H, @CH); 4.81–5.12 (m,
2H, @CH2) 4.23 (s, 1H, Cp-H); 4.01–4.12 (m, 1H, CH);
3.35–3.51 (m, 1H, CH); 0.85–1.97 (m, 23H, –CH2
&
CH3). Anal. Calc. for compound C19H31Ir: C, 50.52; H,
6.92. Found: C, 50.36; H, 7.08%. The second band was
1
found to be the compound 9. m.p. 108–112 ꢁC (dec); H
4.5. Cp*Rh(III)(g3-1-methylallyl)bromide14 (5c)
NMR d 4.43 (s, 1H, Cp-H); 3.95 (m, 1H, CH); 2.95 (m,
1H, CH–CH3); 2.20 (m, 2H, –CH2), 1.81 (s, 12H, Cp-
CH3), 1.52–1.61 (m, 2H, CH2); 0.92–1.06 (m, 3H, CH3).
Anal. Calc. for compound C14H22IrCl: C, 40.23; H, 5.31.
Found: C, 40.26; H, 5.46%.
Butenylmagnesium bromide (2.5 mmol) was added to a
suspension of [Cp*RhBr2]2 (400 mg, 0.503 mmol) in 10 cm3
diethylether at ꢀ78 ꢁC. After stirring for 1 day the reaction
was hydrolyzed with saturated NH4Cl solution and the
organic layer extracted with benzene. The solvent was
removed in vacuo and the oily red residue recrystallized
from ether/hexane. The product was isolated as orange
crystals (270 mg, 72%). The complex melts with decompo-
sition above 120 ꢁC. NMR (CDCl3): d (1H) = 1.56 (d, 3H,
J = 5.4 Hz), 1.76 (s, 15H), 3.11 (d, 1H, J = 11.2 Hz), 3.14
(d, 1H, J = 6.3 Hz), 3.76 (m, 2H). d (13C) = 9.67 (Cp*
Me), 17.90 (CH–CH3), 56.15 (d, J = 10.4 Hz, –CH2),
70.20 (d, J = 7.6 Hz, CH–CH3), 95.38 (d, J = 6.1 Hz,
CH2–CHc), 97.70 (d, J = 6.1 Hz, Cp* ring). Anal. Calc.
for compound C14H22RhBr: C, 45.06; H, 5.90. Found: C,
45.46; H, 5.76%. Mass spec. FAB: m/e 373 (M+), 293
(M+ ꢀ Br), 237.
4.8. Cp*Ir(I)(g4-1,3,5-hexatriene) (8)
In a Schlenk flask, [Cp*IrCl2]2 (406 mg, 1.085 mmol) in
diethylether (20 mL) was cooled down to T = ꢀ78 ꢁC and
1-pentenyl Grignard reagent (2.8 mL of 1.34 M,
3.75 mmol) was added. The solution was brought to
around 0 ꢁC and then stirred until the solution became
clear. To this, dppp (448 mg, 1.086 mmol) was added and
stirred for 36 h until a clear solution is formed. The reac-
tion mixture was worked up as described above. The prod-
uct was obtained as a pale yellow crystalline solid from the
1
n-hexane solution. For 8; m.p. 80–85 ꢁC; yield 70%; H
NMR 5.67–5.88 (m, 4H, @CH); 5.06 (s, 1H, Cp-H); 2.67-
2.83 (m, 4H, @CH2); 1.79–1.85 (m, 12H, Cp-CH3). Anal.
Calc. for compound C15H21Ir: C, 45.78; H, 5.38. Found:
C, 45.96; H, 5.42%.
4.6. Cp*Rh(III)(g3-1-ethylallyl)bromide (5d)
Pentenylmagnesium bromide (1 mmol) was added to a
suspension of [Cp*RhBr2]2 (160 mg, 0.2 mmol) in 10 cm3
diethylether at ꢀ78 ꢁC. After stirring for 1 day the reaction
was hydrolyzed with saturated NH4Cl solution and the
organic layer extracted with benzene. Solvent was removed
in vacuo and the oily red product was recrystallized from
dichloromethane/hexane to give orange–red crystals
(116 mg, 75 %). m.p. 118–120 ꢁC. NMR (CDCl3):
d(1H) = 1.16 (t, 3H, 7.3 Hz), 1.77 (s, 15H), 1.93 (m, 2H),
3.11 (d, 1H, 10.1 Hz), 3.14 (d, 1H, 6.4 Hz), 3.74 (m, 2H).
d(13C) = 9.72 (s, Cp* Me), 15.92 (s, H3C–CH2–), 26.12 (s,
–CH2–CH3), 56.22 (d, J = 11.5 Hz, –CH–CH2), 78.21 (d,
J = 7.6 Hz, –H2C–CH–), 93.47 (d, J = 6.1 Hz, –CH–HC-
CH2), 97.76 (d, J = 6.1 Hz, Cp* ring). Anal. Calc. for com-
pound C15H24RhBr: C, 46.55; H, 6.20. Found: C, 46.97; H,
Acknowledgement
We thank AngloPlatinum Corporation, DST Centre of
Excellence in Catalysis, C* Change, UCT, The UCT Chem-
istry EDP programme and Johnson Matthey for their sup-
port and Tanya le Roex for solving one of the crystal
structures.
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