Formation and isomerization of cis, cis-Ir(H)2( - Ph)(CO)(PPh3)2 and cis, cis-Ir(H)( - Ph)2(CO)(PPh3)2 in oxidative addition of hydrogen and phenylacetylene to trans-Ir(CO)( - Ph)(PPh3)2

Article abstract of DOI:10.1016/S0277-5387(98)00358-1

Oxidative addition of H-R (H - Ph and H₂) to trans-Ir( - Ph)(CO)(PPh₃)₂ (2) gives the initial products, cis, cis-Ir(H)( - Ph)₂(CO)(PPh₃)₂ (3a) and cis, cis-Ir(H)₂( - Ph)(CO)(PPh₃)₂ (3b), respectively. Both cis-bis(PPh₃) complexes, 3a and 3b undergo isomerization to give the trans-bis(PPh₃) complexes, trans, trans-Ir(H)( - Ph)₂(CO)(PPh₃)₂ (4a) and cis, trans-Ir(H)₂( - Ph)(CO)(PPh₃)₂ (4b). The isomerization, 3b→4b is first order with respect to 3b with k₁=6.37×10^-4 s^-1 at 25°C under N₂ in CDCl₃. The reaction rate (k₁) seems independent of the concentration of H₂. A large negative entropy of activation (ΔS^≠=-24.9±5.7 cal deg^-1 mol^-1) and a relatively small enthalpy of activation (ΔH^≠=14.5±3.3 kcal mol^-1) were obtained in the temperature range 15~35°C for the isomerization, 3b→4b under 1 atm of H₂.

Full text of DOI:10.1016/S0277-5387(98)00358-1

Polyhedron 18 (1999) 811–815
Formation and isomerization of cis, cis-Ir(H)2(-≡-Ph)(CO)(PPh3)2 and cis,
cis-Ir(H)(-≡-Ph)2(CO)(PPh3)2 in oxidative addition of hydrogen and
phenylacetylene to trans-Ir(CO)(-≡-Ph)(PPh3)2
*
Chong Shik Chin , Moonhyun Oh, Gyongshik Won, Haeyeon Cho, Dongchan Shin
Department of Chemistry, Sogang University, Shinsoo-dong, Mapo-ku, Seoul 121-742, South Korea
Received 23 June 1998; accepted 24 September 1998
Abstract
Oxidative addition of H–R (H-≡-Ph and H2) to trans-Ir(-≡-Ph)(CO)(PPh3)2 (2) gives the initial products, cis, cis-Ir(H)-
(-≡-Ph)2(CO)(PPh3)2 (3a) and cis, cis-Ir(H)2(-≡-Ph)(CO)(PPh3)2 (3b), respectively. Both cis-bis(PPh3) complexes, 3a and 3b undergo
isomerization to give the trans-bis(PPh3) complexes, trans, trans-Ir(H)(-≡-Ph)2(CO)(PPh3)2 (4a) and cis, trans-Ir(H)2-
(-≡-Ph)(CO)(PPh3)2 (4b). The isomerization, 3b→4b is first order with respect to 3b with k156.3731024 s21 at 258C under N2 in
CDCl3. The reaction rate (k1) seems independent of the concentration of H2. A large negative entropy of activation (DS±5224.965.7
cal deg21 mol21) and a relatively small enthalpy of activation (DH±514.563.3 kcal mol21) were obtained in the temperature range
15|358C for the isomerization, 3b→4b under 1 atm of H2.
1999 Elsevier Science Ltd. All rights reserved.
Keywords: Iridium(I,III) complexes; Oxidative addition; cis-(PPh3)2 complexes; Isomerization; Intramolecular rearrangement
1. Introduction
tained with A being an electron withdrawing group such as
a halogen [7,8,10,11], RCN [9,13] or OClO3 [20,21]
whereas cis isomers (C and C9) are observed when A is an
electron donating group such as H [15,17,18], Me, Ph [14],
carborane [19] or OMe [14] (Eq. (1)). The isomer, C
seems to be a kinetic product as it readily undergoes
isomerization to give the more stable T [18,19,31] and C9
The stereochemistry of oxidative addition of H–R to
transition metals (M) to produce the H–M–R moiety is of
interest to many chemists working in the field of homoge-
neous catalysis with metal complexes [1–3]. It may
provide valuable information on the metal catalyzed
hydrogenation, hydroformylation, hydrosilylation and
polymerization of unsaturated compounds with respect to
the direction of H2 addition and consequently the structure
of the products [4–6].
Oxidative cis-addition of H–R to trans-IrA(CO)(PPh3)2
(1) [7–22] and related complexes such as IrA(CO)(p–p)
(p–p5bidentate diphosphines) [23–30] and trans-
IrA(CO)(PMe3)2 [31] has been extensively studied in
order to establish the reaction pathways in connection with
the thermal stability of the intermediates and products.
Experimental work [8,9,12–23,25–31] as well as theoret-
ical calculations [10,11,24] have been made to characterize
the intermediates observed and predicted in the oxidative
reaction. Trans isomers (T and T9) are exclusively ob-
1The C type isomer was not observed in the reaction of trans-
Ir(-≡-R)(CO)(PPh3)2 (2) with H-≡-R. The final product, trans, trans-
Ir(H)(-≡-R)2(CO)(PPh3)2 (4a) was incorrectly reported as cis, trans-
Ir(H)(-≡-R)2(CO)(PPh3)2 (4a9) [20] (see Section 3 for the characteriza-
tion of 4a and Ref. [32] which describes 4a9 in detail).
2It was reported that (i) the reaction of IrH(CO)(PPh3)3 with H-≡-R in
refluxing benzene gave cis dihydrido complex, Ir(H)2(-≡-R)(CO)(PPh3)2
(A) for which no spectral data were reported, (ii) A readily loses H2 to
give Ir(-≡-R)(CO)(PPh3)2 (B) in refluxing benzene and (iii) B does not
react with H2 at 1 atm, but reacts with H2 at 50 atm and 708C in the
presence of PPh3 to give IrH(CO)(PPh3)3 [20]. From the thorough
investigation, however, we found that the reaction of Ir(-≡-
Ph)(CO)(PPh3)2 (2) with H2 at 1 atm and 258C readily gives the cis
dihydride, cis,trans-Ir(H)2(-≡-Ph)(CO)(PPh3)2 (4b) which can be isolated
in high yield (85%) (see text and Section 3 for the procedure and spectral
and elemental analysis data).
*
Corresponding author.
0277-5387/99/$ – see front matter
PII: S0277-5387(98)00358-1
1999 Elsevier Science Ltd. All rights reserved.

812
C.S. Chin et al. / Polyhedron 18 (1999) 811–815
[19]. Reversible reductive elimination and oxidative addi-
tion of H–R have been suggested for the isomerization as
shown in Eq. (2) [17–19,31]. To the best of our knowl-
edge, however, no kinetic study has been reported for the
isomerization of C to T.
In the course of our investigation on reactions of trans-
Ir(-≡-Ph)(CO)(PPh3)2 (2), we found that C isomers are
1
generated in the reactions of 1 with H2 [32] and H-≡-Ph2
and undergo isomerization to give T isomers at a rate
appropriate for the kinetic measurements at room tempera-
ture.
2. Results and discussion
2.1. Formation of cis, cis-Ir(H)(-≡-Ph)2(CO)(PPh3 )2
(3a)
Fig. 1. 1H-NMR spectral changes in the hydride region during the
isomerization, cis, cis-Ir(H)(-≡-Ph)2(CO)(PPh3)2 (3a)→trans, trans-
Ir(H)(-≡-Ph)2(CO)(PPh3)2 (4a) in CDC13 at 258C: 2 h (a), 10 h (b) and
24 h (c) after the addition of H-≡-Ph into the solution of trans-Ir(-≡-
Ph)(CO)(PPh3)2 (2).
An intermediate is initially generated and slowly dis-
appears during the reaction of 2 with phenylacetylene,
which is unambiguously seen by the 1H-NMR spectral
changes (see Fig. 1). This intermediate is identified as the
cis-(PPh3)2 species, 3a [Eq.(3)]. The doublet of the
doublet at d 210.40 ppm strongly suggests the hydride
being trans to one PPh3 (JP–H 5161.2 Hz) and cis to the
other PPh3 (JP–H 514.7 Hz) of 3a. The triplet at d 28.78
ppm clearly suggests both of PPh3 being cis to the hydride
(JP–H 514.7 Hz) of the final product, 4a. The cis-
bis(alkynyl) structure (3a) is the preferred one to the
trans-bis(alkynyl) species (3a9) for the following reason.
The trans OC–Ir–A bond axis is supposed to be main-
tained when the C type isomers are formed since H–R has
to approach metal with its bond axis parallel to the P–Ir–P
axis of 2 to cause bending of the P–Ir–P axis only
[10,18,19,24,27,28].
The chemical shift of a hydride coordinated to a transition
metal largely depends on the nature of the trans ligand and
has been very useful for the characterization of iridium
compounds such as cis, trans-Ir(H)2(L)(CO)(PPh3)2 (L5
RCN, CO, OClO3, SiR3, carborane, etc.), trans-Ir(H)(-≡-
The characterization of trans, trans-Ir(H)(-≡-
R)2(CO)(PPh3)2, 4a is straightforward according to the
1H-, 13C-, and 31P-NMR spectral data (see also Section 3).

C.S. Chin et al. / Polyhedron 18 (1999) 811–815
813
R)(L)(CO)(PPh3)2, (L5RCN, OClO3), cis, trans-Ir(H)(-
≡-R)2(CO)(PPh3)2 and related compounds [8,9,13–
20,32,33]. The hydride trans to CO is seen at relatively
lower field, d 27.0|210.2 ppm for the related iridium
compounds [8,13,16,19]. The signal due to the hydride
trans to alkynyl group (-≡-Ph) in cis, trans-Ir(H)(-≡-
Ph)2(CO)(PPh3)2 (4a9) is observed at d 210.01 ppm [32].
The triplet at d 28.78 ppm is, therefore, assigned to the
hydride trans to the CO in 4a. The 13C-NMR spectral data
also support the trans-bis(alkynyl) moiety for 4a. While
the 13C-NMR spectrum of the cis-bis(alkynyl) complex,
4a9 shows a broad signal at d 82.6 (br, Ir–Ca≡C–) and two
signals at d 108.7 (s) and 109.1 (s) (Ir–C≡Cb 2 ) [32], the
trans-bis(alkynyl) complex, 4a shows only one signal for
each of Ca and Cb of the two trans (symmetric) alkynyl
groups at d 82.0 (t, Ir–Ca≡C–) and 109.5 (s, Ir–C≡Cb
)
2
ppm.
2.2. Formation of cis, cis-Ir(H)2(-≡-Ph)(CO)(PPh3 )2
(3b)
The reaction of 2 with H2 also produces an intermediate
that is generated at the early stage of the reaction and
slowly disappears to give a stable product as seen in Fig. 2.
The intermediate and the final product are identified as the
cis-(PPh3)2 complex, cis, cis-Ir(H)2(-≡-Ph)(CO)(PPh3)2
(3b) and trans-(PPh3)2 complex, cis, trans-Ir(H)2(-≡-
Ph)(CO)(PPh3)2 (4b), respectively (see below).
It is evident that the multiplet-like signal centered at d
210.30 ppm is due to the two hydrides of the inter-
mediate, 3b, and the two doublets of the triplet at d 29.54
and 211.59 ppm are due to the two hydrides of the stable
final product, 4b. The Ir(H)2(P)2 moiety of 3b seems to be
in a same plane with the two PPh3 being cis to each other
and the two hydrides being also cis to each other. The
pattern of the signal centered at d 210.30 ppm is evidently
due to the AA9XX9 spin system of the cis-Ir(H)2(PPh3)2
moiety of 3b where the two hydrides are chemically
equivalent but magnetically different. The same type of
pattern (AA9XX9) has been observed at d 29.52 and
210.8 ppm for cis, cis-Ir(H)2(CO)(carborane)(PPh3)2 [14]
and cis, cis-Ir(H)2(Me)(CO)(PPh3)2 [19], respectively,
and was assigned to the two hydrides of cis, cis-
Ir(H)2(PPh3)2 moieties.
The two doublets of the triplet at d 29.54 and 211.59
ppm for 4b are unambiguously assigned to the hydride
trans to CO and -≡-Ph, respectively, by comparison with
the spectral data observed for related iridium hydrides
[8,9,13–20,32,33]. As mentioned earlier, hydride signals in
1H-NMR spectra are quite useful in characterizing related
metal hydrides. The hydride trans to CO is usually seen at
lower field (d 27.0|210.2 ppm) [8,9,13,16,19]3 while
Fig. 2. 1H-NMR spectral changes in the hydride region during the
isomerization, cis, cis-Ir(H)2(-≡-Ph)(CO)(PPh3)2 (3b)→cis, trans-
Ir(H)2(-≡-Ph)(CO)(PPh3)2 (4b) in CDCI3 at 258C: 5 min (a), 25 min (b)
and 45 min (c) after the addition of trans-Ir(-≡-Ph)(CO)(PPh3)2 (2) into
the H2 saturated CDCl3 under 1 atm of H2.
the hydride trans to alkynyl and alkenyl groups is seen at
somewhat higher field (d 210|211 ppm) [32,33].
The 31P-NMR spectrum (CDCl3, 208C) of the mixture
of 3b and 4b shows only two singlets at d 9.55 and 28.36
ppm. The singlet at d 9.55 increases at the expense of the
one at d 28.36 ppm during the isomerization, 3b→4b.
The fact that only one singlet is observed suggests 3b as a
C type isomer rather than a C9 type one that would be
expected to show two signals in the 31P NMR spectrum.
2.3. Kinetics for the isomerization of cis, cis-Ir(H)2-
(-≡-Ph)(CO)(PPh3 )2 (3b) to cis, trans-Ir(H)2-
(-≡-Ph)(CO)(PPh3 )2 (4b)
The isomerization of 3b to 4b was followed by measur-
ing the decrease of the hydride signals of 3b as well as the
increase of the hydride signals of 4b (see Fig. 2). The
3The triplet at d 28.78 ppm has been assigned to the hydride trans to CO
in complex 4a for the same reason (see text).

814
C.S. Chin et al. / Polyhedron 18 (1999) 811–815
isomerization is first order with respect to 3b as expected
for a mainly unimolecular isomerization. The rate does not
seem to be significantly affected by the concentration of
H2: k1 is found to be (6.660.1)31024 s21 and
(6.460.1)31024 s21 under H2 (1 atm) and N2, respective-
ly, at 258C in CDCl3 (see Section 3 for detailed ex-
perimental conditions). A relatively large negative value of
the activation entropy (DS±5224.965.7 cal deg21
mol21) and a relatively small activation enthalpy (DH±5
14.563.3 kcal mol21) have been obtained from k1 in the
range 15|358C. This observation suggests that the iso-
merization, 3b→4b involves an intramolecular rearrange-
ment at least in part in the temperature range 15|358C (see
below).
An intramolecular isomerization usually involves an
intermediate (or transition state) formed by a trigonal twist
or a rhombic twist of a fluxional octahedral complex
[34–42]. The activation entropy is measured to obtaining
information on the distinction between the dissociative
(through a five coordinated intermediate) and non-dissocia-
tive (fluxional) mechanisms: Negative values (254.9|2
2.3 cal deg21 mol21) for the activation entropy were
obtained for the cis↔trans isomerization of octahedral d6
complexes, ML2(CO)4 for which intramolecular isomeri-
zation mechanisms were suggested [35–38].
It is still possible that a part of 3b undergoes isomeriza-
tion through the reaction pathway involving the reversible
reductive elimination and oxidative addition of H2 as seen
in Eq. (2). Although no evidence has been obtained for the
reaction of 2 with H2 directly (not via 3b) to give 4b, we
found that 4b very slowly loses H2 to give 2: Less than 5%
of 4b loses H2 in 5 h at 358C under N2 in CDCl3.
Further investigation seems to be needed to elucidate the
detailed mechanism of the isomerization, 3→4 when better
experimental methods become available.
It should be mentioned that kinetic measurements have
not been carried out for the reaction of 2 with H-≡-Ph as it
is inappropriate for kinetic measurements. The reaction is
much slower than the reaction of 2 with H2. The initial
step, the formation of 3a (2→3a) is so slow that the rate
measurements of the following isomerization, 3a→4a,
could not be made in the absence of 2. A significant
amount of unreacted 2 is observed even at the latest stage
of the isomerization, 3a→4a. Reductive elimination of
H-≡-Ph from 4a is not observed at 258C while a small
amount of H-≡-Ph has been detected in CDCl3 solution of
4a after 1 h of refluxing.
spectra were obtained on a Shimadzu IR-440 spec-
trophotometer. Elemental analyses were carried out at the
Organic Chemistry Reaction Center, Sogang University.
3.1. Syntheses
3.1.1. Ir(-C≡C-Ph)(CO)(PPh3 )2 (2)
This compound was previously prepared from the
reaction of Ir(h3-C3H5)(CO)(PPh3)2 with H-≡-Ph [20]. In
this study, it was synthesized by a new method as
described
below.
To
a
yellow
solution
of
[Ir(NCCH3)(CO)(PPh3)2]ClO4 [3 g] (0.178 mg, 0.2
mmol) and NEt3 (0.031 ml, 0.22 mmol) in CHCl3 (10 ml),
H-≡-Ph (0.024 ml, 0.22 mmol) was added under N2 and
the resulting dark brown solution was stirred for 8 min.
Hexane (70 ml) was added to the reaction mixture and the
precipitate of HNEt31ClO24 was removed by filtration.
Yellow solid 2 was obtained by vacuum distillation of the
filtrate and recrystallized by using CHCl3 and hexane. The
yield was 0.134 mg (80% based on 2). 1H NMR (CDCl3,
258C): d 6.37 (m). 13C NMR (CDCl3, 258C): d 67.7 (t,
J
J
P–C 512.5 Hz, Ir-C≡C-Ph), 109.5 (s, Ir-C≡C-Ph), 167.4 (t,
P–C 58.7 Hz, Ir–CO). 31P NMR (CDCl3, 258C): d 7.57
(s). IR (KBr, cm21): n(CO) 1993 (s), n(C≡C) 2104 (m).
Anal. Calcd for IrP2C45H35O: C, 63.89; H, 4.17. Found: C,
64.06; H, 4.21.
3.1.2. IrH(-C≡C-Ph)2(CO)(PPh3 )2 (4a)
A yellow solution of 2 (85 mg, 0.1 mmol) in CH2C12
(10 ml) was stirred in the presence of H-C≡C-Ph (11 mg,
0.11 mmol) under N2 at 258C for 10 h, during which time
the solution turned pale yellow. Cold hexane (25 ml) was
added to the solution in a dry-ice/acetone bath to precipi-
tate pale yellow microcrystals of 4a, which were collected
by filtration, washed with cold hexane (2310 ml), and
dried under vacuum. The yield was 81 mg (85%). 1H NMR
(CDCl3, 258C): d 28.78 (t, 1H, JP–H 514.7 Hz, Ir–H),
6.37 (m, 4H, ortho protons of -C≡C-Ph). 13C NMR
(CDCl3, 258C): d 82.0 (t, JP–C 512.65 Hz, Ir-C≡C-Ph),
109.5 (s, Ir-C≡C-Ph), 167.4 (t, JP–C 58.1 Hz, Ir–CO). 31
P
NMR (CDCl3, 258C): d 1.56 (s). IR (KBr, cm21): n(CO)
2020 (s), n(C≡C) 2107 (m). Anal. Calcd for IrP2C53H41O:
C, 66.65; H, 4.33. Found: C, 66.66; H, 4.41.
3.1.3. Ir(H)2(-C≡C-Ph)(CO)(PPh3 )2 (4b)
A yellow solution of 2 (85 mg, 0.1 mmol) in CH2Cl2
(10 ml) was stirred under H2 (1 atm) at 258C for 5 min,
during which time the solution turned pale yellow. Cold
hexane (25 ml) was added to the CH2Cl2 solution in a dry
ice/acetone bath to precipitate pale yellow microcrystals of
4b, which were collected by filtration, washed with cold
hexane (2310 ml), and dried under vacuum. The yield
was 75 mg (85%). 1H NMR (CDCl3, 258C): d 29.54 (td,
1 H, JP–Ha 517.25 Hz, JHa–Hb 54.12 Hz, Ir–Ha), 211.59
3. Experimental section
Reactions were carried out under N2 with the use of
standard Schlenk techniques. NMR spectra were recorded
on either Varian Gemini 200 or 300 spectrometers (1H,
200/300 MHz; 13C, 50.3, 75.5 MHz; 31P, 121.7 MHz). IR

C.S. Chin et al. / Polyhedron 18 (1999) 811–815
815
[4] B. Cornils, W.A. Hemmann, Applied Homogeneous Catalysis with
Organometallic Compounds, vols. 1 and 2, VCH, 1996, whole
chapters.
[5] J.P. Collinan, L.S. Hegedus, J.R. Norton, R.G. Finke, Principles and
Applications of Organotransition Metal Chemistry, University Sci-
ence Books, 1987, p. 523.
[6] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed.,
Wiley-Interscience, New York, 1988, p. 1224 and references therein.
[7] L. Vaska, Acc. Chem. Res. 1 (1968) 335.
(td, 1 H, JP–Hb 515.63 Hz, Ir–Hb), 6.32 (m, 2 H, ortho
protons of -C≡C-Ph). 13C NMR (CDCl3, 258C): d 88.16 (t,
J
P–C 512.34 Hz, Ir-C≡CPh), 113.87 (s, Ir-C≡CPh), 174.69
(t, JP–C 56.34 Hz, Ir–CO). 31P NMR (CDCl3, 258C): d
9.55 (s). IR (KBr, cm21): n(CO) 1968.5 (s), n(C≡C)
2064.0 (w). Anal. Calcd for IrP2C45H37O: C, 63.74; H,
4.40. Found: C, 63.73; H, 4.24.
[8] C.J. Sleigh, S.B. Duckett, B.A. Messerle, Chem. Commun. (1996)
2395.
[9] C.S. Chin, J. Yoon, J. Song, Inorg. Chem. 32 (1993) 5901.
[10] A.L. Sargent, M.B. Hall, Inorg. Chem. 31 (1992) 317.
[11] P. Zhou, A.A.Vitale, J.S. Filippo Jr., W.H. Sanders Jr., J. Am. Chem.
Soc. 107 (1985) 8049.
[12] W.M. Rees, M.R. Churchill, Y.-J. Li, J.D. Atwood, Organometallics
4 (1985) 1162.
[13] S.H. Park, H.-K. Park, C.S. Chin, Inorg. Chem. 24 (1985) 1120.
[14] J.S. Thompson, K.A. Bernard, J.P. Rappol, J.D. Atwood, Organo-
metallics 9 (1990) 2727.
[15] M. Drouin, J.F. Harrod, Inorg. Chem. 22 (1983) 999.
[16] J.F. Harrod, W.J. Yorke, Inorg. Chem. 20 (1981) 1156.
[17] J.F. Harrod, G. Hamer, W. Yorke, J. Am. Chem. Soc. 101 (1979)
3987.
[18] J.P. Fawcett, J.F. Harrod, J. Organomet. Chem. 113 (1976) 245.
[19] B. Longato, F. Morandini, S. Bresadola, Inorg. Chem. 15 (1976)
650.
3.1.4. Kinetic measurements for the isomerization of cis,
cis-Ir(H)2(-≡-Ph)(CO)(PPh3 )2 (3b) to cis, trans-Ir(H)2(-
≡-Ph)(CO)(PPh3 )2 (4b)
The reaction was followed by measuring the hydride
signals of 3b and/or 4b (see Fig. 2) under H2 and N2 in
the temperature region 15|358C in CDCl3. An automatic
acquisition program (installed on Varian Gemini 300 MHz
spectrometer; acquisition time, 1.997 s; repetition delay,
3.0 s; scan, 6) was used to collect the kinetic data by
measuring the spectra in the hydride region (d 29.0|2
12.0) at intervals of 30 s. The reactions were monitored for
30 min. (i) Under H2 (1 atm): a 50 mg of 2 was dissolved
in CDCl3 (0.5 ml) in an NMR tube under H2 (1 atm) at
258C and the reaction mixture was put in the cell compart-
ment of a Varian Gemini 300 MHz spectrometer main-
tained at 258C. Compound 2 completely underwent H2
[20] C.K. Brown, D. Georgiou, G. Wilkinson, J. Chem. Soc. (A) (1971)
3120.
1
addition to give 3b within 2 min according to H NMR
measurements. During these two min, the color of the
solution changed from yellow to pale yellow. Disappear-
ance of 3b and appearance of 4b were measured by
following the signals at d 210.10 (3b) and 29.54 (4b)
ppm. (ii) Under N2: N2 was thoroughly bubbled for 1 min
into a CDC13 solution containing 3b and a small amount
of 4b and 1H NMR spectral changes were measured to
follow the isomerization, 3b→4b, in the same manner as
described above.
[21] J. Peone, L. Vaska, Angew. Chem., Int. Ed. Engl. 10 (1971) 511.
[22] L. Vaska, J. Peone, Suom. Kemistil. B 44 (1971) 317.
[23] R.C. Schnabel, D.M. Roddick, Organometallics 12 (1993) 704.
[24] A.L. Sargent, M.B. Hall, M. Guest, J. Am. Chem. Soc. 114 (1992)
517.
[25] B.P. Cleary, R. Eisenberg, Organometallics 11 (1992) 2335.
[26] P.P. Deutsch, R. Eisenberg, Organometallics 9 (1990) 709.
[27] A.J. Kunin, C.E. Johnson, J.A. Maguire, W.D. Jones, R. Eisenberg,
J. Am. Chem. Soc. 109 (1987) 2963.
[28] C.E. Johnson, R. Eisenberg, J. Am. Chem. Soc. 107 (1985) 3148.
[29] C.E. Johnson, R. Eisenberg, J. Am. Chem. Soc. 107 (1985) 6531.
[30] C.E. Johnson, B.J. Fischer, R. Eisenberg, J. Am. Chem. Soc. 105
(1983) 7772.
[31] M.J. Burk, M.P. McGrath, R. Wheeler, R.H. Crabtree, J. Am. Chem.
Soc. 110 (1988) 5034.
Acknowledgements
We wish to thank the Korea Science and Engineering
Foundation (Grant No. 97-05-01-05-01-3) and the Korean
Ministry of Education (Grant No. BSRI-97-3412) for their
financial supports of this study.
[32] C.S. Chin, H. Lee, M. Oh, Organometallics 16 (1997) 816.
[33] C.S. Chin, Y. Park, J. Kim, B. Lee, Chem. Commun. (1995) 1495.
[34] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed.,
Wiley-Interscience, New York, 1988, p. 1321.
[35] D.J. Darensbourg, R.L. Gray, Inorg. Chem. 23 (1984) 2993.
[36] L. Vancea, R.K. Pomeroy, W.A. Graham, J. Am. Chem. Soc. 98
(1976) 1407.
References
[37] D.J. Darensbourg, Inorg. Chem. 18 (1979) 14.
[38] R.P. Stewart, Inorg. Chem. 18 (1979) 2083.
[39] F.A. Cotton, D.J. Darrensbourg, S. Klein, W.S. Kolthammer, Inorg.
Chem. 21 (1982) 2661.
[40] L.G. Vanquickenborne, K. Pierloot, Inorg. Chem. 20 (1981) 3673.
[41] R. Hoffman, J.M. Howell, A.R. Rossi, J. Am. Chem. Soc. 98 (1976)
2484.
[1] J.P. Coliman, L.S. Hegedus, J.R. Norton, R.G. Finke, Principles and
Applications of Organotransition Metal Chemistry, University Sci-
ence Books, 1987, p. 279.
[2] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed.,
Wiley-Interscience, New York, 1988, p. 1186 and references therein.
[3] R. Crabtree, The Organometallic Chemistry of the Transition
Metals, 2nd ed., Wiley, New York, 1994, p. 140.
[42] R.K. Pomeroy, L. Vancea, H.P. Calhoun, W.A.G. Graham, Inorg.
Chem. 16 (1977) 1508.