Synthesis and solid-state isomerisation reactions of diag- and lat-(η5-C5H4R)Re(CO)(L)X2

Article abstract of DOI:10.1016/S0022-328X(97)00700-6

Reaction of diag- or lat- (i.e. trans or cis)(η⁵-C₅H₄R)Re(CO)₂X ₂ (R=Me, t-Bu, SiMe₃; X=Br, I) with isocyanides, phosphites and triphenyl phosphine proceeded rapidly at room temperature (r.

Full text of DOI:10.1016/S0022-328X(97)00700-6

Journal of Organometallic Chemistry 556 (1998) 111–118
Synthesis and solid-state isomerisation reactions of diag- and
lat-(p5-C5H4R)Re(CO)(L)X2
Lin Cheng, Neil J. Coville *
Centre for Applied Chemistry and Chemical Technology, Department of Chemistry, Uni6ersity of the Witwatersrand, Pri6ate Bag 3, WITS 2050,
Johannesburg, South Africa
Received 9 September 1997
Abstract
Reaction of diag- or lat- (i.e. trans or cis)(p5-C5H4R)Re(CO)2X2 (R=Me, t-Bu, SiMe3; X=Br, I) with isocyanides, phosphites
and triphenyl phosphine proceeded rapidly at room temperature (r.t.) in the presence of Me3NO to give (p5-C5H4R)Re(CO)(L)X2
(L=CNC6H3Me2, P(OMe)3, P(OiPr)3, P(OPh)3, PPH3) in good yields (typically\75%) with the diagonal isomer as the dominant
(\90%) product. The diag-(p5-C5H4R)Re(CO)(L)X2 isomer were readily converted into the lateral isomer in excellent yield
(\70%) by directly heating solid diag-(p5-C5H4R)Re(CO)(L)X2 under nitrogen below its melting point. Solution phase
isomerisation in CHCl3 or C6D6 (r.t., visible light irradiation) also proceeded from the diag to the lat isomer. The solid-state
reaction between diag-(p5-C5H4Me)Re(CO)[P(OPh)3]Br2 and excess NaI surprisingly gave diag-(p5-C5H4Me)Re(CO)2I2 in quanti-
tative yield, revealing both Re–P and Re–Br bond cleavage. The new complexes, diag- and lat-(p5-C5H4R)Re(CO)(L)X2, have
been fully characterized by elemental analysis and IR and NMR spectroscopy. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Rhenium; Cyclopentadienyl; Carbonyl substitution; Isomerization; Solid-state
1. Introduction
ment on these complexes reported to date. The method
used to prepare lat-(p5-C5H5)Re(CO)(L)Br2 by reflux-
ing diag-(p5-C5H5)Re(CO)2Br2 with three equivalents of
phosphites in toluene gave modest results (yields were
only 35–45%) [2]. The reactions of the pentamethylcy-
clopentadienyl rhenium complexes Cp*Re(CO)2X2
(X=Cl, Br, I) with P(OMe)3 in refluxing toluene were
studied by Klahn et al and it was found that
Cp*Re(CO)2[P(OMe)3], not the carbonyl substitution
The chemistry of cyclopentadienyl half-sandwich rhe-
nium complexes has been developed over the past three
decades [1]. In this time many cyclopentadienyl four-
legged piano stool rhenium complexes have been pre-
pared, and the solution isomerization behavior and the
chemical reactivity of these complexes have been stud-
ied [3–8]. However, it is only since 1976 that King and
Reimann successfully separated the diagonal and lateral
(i.e. trans and cis) isomers of (p5-C5H5)Re(CO)2Br2 [2].
The carbonyl substitution reactions of cyclopentadi-
enyl dicarbonyldihalides rhenium complexes have been
little exploited. Indeed as far as we aware, the King and
Reimann description of the reaction of diag-(p5-
C5H5)Re(CO)2Br2 with different phosphites, P(OR)3,
and isocyanides is the only example of the CO replace-
product,
was
the
dominant
product
[9].
Cp*Re(CO)(PMe3)X2 (X=Cl, Br, I) and cis-
Cp*Re(CO)(L)I2 (L=P(OMe)3, P(OPh)3, PMe3,
PMe2Ph) have rather been prepared indirectly by oxida-
tive-addition of X2 to the dinitrogen complexes
Cp*Re(CO)(L)N2 [10], or by Me3NO induced decar-
bonylation of cationic [cis-Cp*Re(CO)2(L)I]+ [11].
Recently the first thermal solid-state isomerization
reaction of (p5-C5H4R)Re(CO)2Br2 (R=Me) was re-
ported by us [4] but work on related complexes (R=t-
* Corresponding author.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00700-6

112
L. Cheng, N. J. Co6ille / Journal of Organometallic Chemistry 556 (1998) 111–118
Bu, SiMe3, etc.) indicated that the reaction may not be
general. To further explore the generality of this un-
usual solid-state reaction [12] the substituted complexes
(p5-C5H4R)Re(CO)(L)X2, have been considered for
study. Trimethylamine N-oxide has been shown to be a
valuable synthetic reagent in the preparation of substi-
tuted metal carbonyl complexes [13] and its use for
preparing new rhenium complexes seemed feasible.
Thus, we decided to study the carbonyl substitution
reactions of (p5-C5H4R)Re(CO)2X2 using Me3NO as a
decarbonylating reagent. The results of this study are
described below. The solid-state and solution diag–lat
isomerization reactions of the new complexes are also
reported.
phosphine, tributyl phosphine and pyridine resulted in
decomposition of starting materials.
2.2. Thermal solid-state isomerization of
diag-(p5-C5H4R)Re(CO)(L)X2
Solid diag-(p5-C5H4R)Re(CO)(L)X2 (50 mg) in a 25
ml round-bottom flask was heated under nitrogen in an
oil bath at temperatures at least 10–15°C below their
melting points for 0.5–6 h. No decomposition was
observed. The solid residues were then dissolved in
CH2Cl2 and chromatographed on a silica gel column.
The composition of the new lateral isomers was confi-
rmed by IR and NMR spectroscopy. The yields, as well
as the spectroscopic and analytical data for the lat-(p5-
C5H4R)Re(CO)(L)X2 complexes are listed in Tables
1–3.
2. Experimental
The lat-(p5-C5H4R)Re(CO)(PPh3)X2 complex decom-
posed on a silica gel column and purification of the
complex was achieved by recrystalization from a mix-
ture of dichloromethane and hexane at −15°C.
The diagonal and lateral (p5-C5H4R)Re(CO)2Br2
(R=Me, t-Bu, SiMe3) complexes were prepared by the
literature methods [4]. 2,6-dimethylphenylisocyanide,
phosphites and phosphines were used as supplied by
Fluka or Merck. Trimethylamine N-oxide dihydrate
(Aldrich) was used as received. All reactions were car-
ried out using standard Schlenk techniques under nitro-
gen. Solvents were dried by conventional methods,
distilled under nitrogen, and used immediately. Melting
points were recorded on a Kofler hot stage melting
point apparatus. IR spectra were measured on a Midac
FTIR spectrometer, usually in KBr cells (solutions).
NMR spectra were measured on a Bruker AC 200
spectrometer operating at 200 MHz. Microanalysis
were carried out at the CSIR, Pretoria, South Africa.
2.3. Thermal solid-state halogen exchange reaction of
diag-(p5-C5H4Me)Re(CO)2Br2 with excess NaI
Diag-(p5-C5H4Me)Re(CO)2Br2 (200 mg, 0.416 mmol)
and NaI (1.25 g, 8.31mmol) were dissolved in acetone
in a 25 ml round-bottom flask. The solvent was then
removed by rotatory evaporation, and the residue was
dried under vacuum (0.1 mmHg) at 25°C and heated
under nitrogen in an oil bath at 100–105°C for 18 h.
After column separation (silica gel, 1:1 CH2Cl2/hexane),
red microcrystaline diag-(p5-C5H4Me)Re(CO)2I2 (239
mg, 100% yield) was obtained. IR (wco, CH2Cl2): 1982
cm−1, 2043 cm−1. 1H-NMR (CDCl3): 2.44 ppm (s, 3H,
CH3); 5.59 ppm (t, 2H, Cp); 5.71 ppm (t, 2H, Cp).
2.1. Preparation of diag-(p5-C5H4R)Re(CO)(L)X2
Diag- or lat-(p5-C5H4R)Re(CO)2X2 (100 mg, 0.174–
0.208 mmol) (R=Me, t-Bu, SiMe3; X=Br, I) and 1.1
equivalents of ligand L (L=CNC6H3Me2, P(OMe)3,
P(OiPr)3, P(OPh)3, PPh3) were dissolved in 15 ml
CH2Cl2 under nitrogen. Me3NO·2H2O (two to five
equivalents) was added to the above magnetically
stirred solution. The reactions were monitored by IR
spectroscopy and were complete within 30 min. Solvent
was removed by vacuum rotatory evaporation to leave
a red residue, which was dissolved in CH2Cl2 and
chromatographed on a silica gel column (2×50 cm)
prepared in hexane. Successive elution with 1:1 CH2Cl2/
hexane gave first diag-(p5-C5H4R)Re(CO)(L)X2 from a
red band, then a small amount (B5%) of lat-(p5-
C5H4R)Re(CO)(L)X2 from a brown band. The yields,
as well as the spectroscopic and analytical data for
diag-(p5-C5H4R)Re(CO)(L)X2 are listed in Tables 1
and 2.
2.4. Thermal solid-state reaction of
diag-(p5-C5H4Me)Re(CO)[P(OPh)3]Br2 with excess NaI
Diag-(p5-C5H4Me)Re(CO)[P(OPh)3]Br2
(80
mg,
0.105 mmol) and NaI (314 mg, 2.10 mmol) were dis-
solved in acetone in a 25 ml round-bottom flask. The
solvent was then removed by rotatory evaporation, and
the residue was dried under vacuum (0.1 mmHg) at
25°C and heated under nitrogen in an oil bath at
125–130°C for 16 h. After column separation (silica
gel, 1:1 CH2Cl2/hexane), diag-(p5-C5H4Me)Re(CO)2I2
(30 mg, 0.052 mmol, 49.5% yield) was obtained as the
only carbonyl product. IR (wco, CH2Cl2): 1982 cm−1
,
1
2043 cm−1. H-NMR (CDCl3): 2.44 ppm (s, 3H, CH3);
Similar reactions with triethyl phosphine, triisopropyl
5.59 ppm (t, 2H, Cp); 5.71 ppm (t, 2H, Cp).

L. Cheng, N. J. Co6ille / Journal of Organometallic Chemistry 556 (1998) 111–118
113
Table 1
IR and NMR spectroscopic data for diag- and lat-(p5-C5H4R)Re(CO)(L)X2 complexes
Complex
waco (cm−1
)
1H-NMRb (ppm)
Cp ring
R
L
diag-(p5-C5H4Me)Re(CO)
(CNC6H3Me2)Br2
1974
1969
1963
1989
1963
1976
1948
4.72 (t, 2H); 4.90 (t, 2H)
1.82 (s, 3H)
2.35 (s, 6H);6.63
(m, 3H)
diag-(p5-C5H4Me)Re(CO)
[P(OMe)3]Br2
4.71 (t, 2H); 4.90 (t, 2H)
4.73 (t, 2H); 4.93 (t, 2H)
4.53 (t, 2H);4.65 (t, 2H)
4.75 (t, 2H); 5.00 (t, 2H)
4.63 (t, 2H); 4.73 (t, 2H)
4.81 (t, 2H);5.09 (t, 2H)
4.84 (t, 2H); 5.10 (t, 2H)
4.56 (t, 2H); 5.28 (t, 2H)
4.62 (t, 2H);5.35 (t, 2H)
4.44 (t, 2H); 4.92 (t, 2H)
4.75 (t, 2H); 5.31 (t, 2H)
4.83 (t, 2H);5.21 (t, 2H)
4.67 (t, 2H); 5.38 (t, 2H)
4.70 (t, 2H); 5.47 (t, 2H)
4.51 (t, 2H);5.08 (t, 2H)
4.90 (t, 2H); 5.44 (t, 2H)
4.72 (m, 1H); 4.78 (m, 2H); 4.90 (m, 1H)
4.82 (m, 2H);4.94 (m, 1H); 4.95 (m, 1H)
4.97 (m, 4H)
1.80 (s, 3H)
1.84 (s, 3H)
1.64 (s, 3H)
1.82 (s, 3H)
1.82 (s, 3H)
2.00 (s, 3H)
1.15 (s, 9H)
1.18 (s, 9H)
1.19 (s, 9H)
1.06 (s, 9H)
1.20 (s, 9H)
0.18 (s, 9H)
0.27 (s, 9H)
0.28 (s, 9H)
0.16 (s, 9H)
0.26 (s, 9H)
1.76 (s, 3H)
1.76 (s, 3H)
1.82 (s, 3H)
1.73 (s, 3H)
3.48 (d, 9H)
diag-(p5-C5H4Me)Re(CO)
1.24 (s, 9H);1.27 (s,9H);4.84
(m, 3H)
[P(OiPr)3]Br2
diag-(p5-C5H4Me)Re(CO)
[P(OPh)3]Br2c
6.88–7.56 (m, 15H)
6.95–7.69 (m, 15H)
6.75–7.59 (m, 15H)
6.64–7.64 (m, 15H)
2.46 (s, 6H);6.68 (m, 3H)
3.53 (d, 9H)
diag-(p5-C5H4Me)Re(CO)
(PPh3)Br2
diag-(p5-C5H4Me)Re(CO)
[P(OPh)3]I2
diag-(p5-C5H4Me)Re(CO)
(PPh3)I2
diag-(p5-C5H4t-Bu)Re(CO) 1975
(CNC6H3Me2)Br2
diag-(p5-C5H4t-Bu)Re(CO) 1971
[P(OMe)3]Br2
diag-(p5-C5H4t-Bu)Re(CO) 1960
1.28 (d, 18H);4.89
(m, 3H)
[P(OiPr)3]Br2
diag-(p5-C5H4t-Bu)Re(CO) 1992
[P(OPh)3]Br2
6.76–7.58 (m, 15H)
6.96–7.79 (m, 15H)
2.41 (s, 6H);6.63 (m, 3H)
3.45 (d, 9H)
diag-(p5-C5H4t-Bu)Re(CO) 1963
(PPh3)Br2
diag-(p5-C5H4SiMe3)
Re(CO)(CNC6H3Me2)Br2
1976
1971
1963
1993
1956
1959
1938
1932
1959
1926
1950
1922
diag-(p5-C5H4SiMe3)
Re(CO)[P(OMe)3]Br2
diag-(p5-C5H4SiMe3)
1.26 (d, 18H);4.87
(m, 3H)
Re(CO)[P(OiPr)3]Br2
diag-(p5-C5H4SiMe3)
Re(CO)[P(OPh)3]Br2
6.76–7.57 (m, 15H)
6.64–7.96 (m, 15H)
2.14 (s, 6H);6.63 (m, 3H)
3.47 (d, 9H)
diag-(p5-C5H4SiMe3)
Re(CO)(PPh3)Br2
lat-(p5-C5H4Me)Re(CO)
(CNC6H3Me2)Br2
lat-(p5-C5H4Me)Re(CO)
[P(OMe)3]Br2
lat-(p5-C5H4Me)Re(CO)
1.12 (s, 9H);1.15 (s, 9H);4.81
(br, 3H)
[P(OiPr)3]Br2
lat-(p5-C5H4Me)Re(CO)
4.62 (d, 1H); 4.72 (d, 1H); 4.77 (d, 1H); 5.07
(d, 1H)
6.75–7.55 (m, 15H)
6.75–7.55 (m, 15H)
6.75–7.59 (m, 15H)
6.64–7.64 (m, 15H)
[P(OPh)3]Brc2
lat-(p5-C5H4Me)Re(CO)
(PPh3)Br2
4.51 (m, 1H); 4.71 (m, 1H);4.92 (m, 1H); 4.99 1.90 (s, 3H)
(m, 1H)
lat-(p5-C5H4Me)Re(CO)
[P(OPh)3]I2
4.43 (m, 2H); 4.69 (m, 1H);5.05 (m, 1H)
1.99 (s, 3H)
lat-(p5-C5H4Me)Re(CO)
(PPh3)I2
4.35 (m, 1H); 4.68 (m, 1H);4.91 (m, 1H); 5.00 2.12 (s, 3H)
(m, 1H)

114
L. Cheng, N. J. Co6ille / Journal of Organometallic Chemistry 556 (1998) 111–118
Table 1 (Continued)
Complex
wcao (cm−1
)
1H-NMRb (ppm)
Cp ring
R
L
lat-(p5-C5H4t-Bu)Re(CO)
(CNC6H3Me2)Br2
1957
1933
1930
1953
1924
4.98 (m, 2H); 5.11 (m, 1H);5.15 (m, 1H)
1.07 (s, 9H)
2.16 (s, 6H);6.62 (m, 3H)
lat-(p5-C5H4t-Bu)Re(CO)
[P(OMe)3]Br2
4.86 (m, 1H); 5.03 (m, 1H);5.23 (m, 1H); 5.35 1.17 (s, 9H)
(m, 1H)
3.46 (d, 9H)
lat-(p5-C5H4t-Bu)Re(CO)
5.10 (m, 1H); 5.16 (m, 1H);5.25 (m, 1H); 5.49 1.22 (s, 9H)
(m, 1H)
1.12 (s, 9H);1.15 (s, 9H);4.79
(br, 3H)
[P(OiPr)3]Br2
lat-(p5-C5H4t-Bu)Re(CO)
[P(OPh)3]Br2
4.94 (m, 1H); 5.03 (m, 1H);5.11 (m, 1H); 5.57 1.11 (s, 9H)
(m, 1H)
6.76–7.55 (m, 15H)
6.96–7.79 (m, 15H)
2.15 (s, 6H);6.62 (m, 3H)
3.45 (d, 9H)
lat-(p5-C5H4t-Bu)Re(CO)
(PPh3)Br2
4.89 (m, 1H); 4.97 (m, 1H);5.04 (m, 1H); 5.52 1.14 (s, 9H)
(m, 1H)
lat-(p5-C5H4SiMe3)Re(CO) 1958
(CNC6H3Me2)Br2
5.07 (m, 2H); 5.21 (m, 1H);5.26 (m, 1H)
0.23 (s, 9H)
lat-(p5-C5H4SiMe3)Re(CO) 1935
[P(OMe)3]Br2
5.07 (m, 1H); 5.17 (m, 1H);5.32 (m, 1H); 5.39 0.28 (s, 9H)
(m, 1H)
lat-(p5-C5H4SiMe3)Re(CO) 1931
5.25 (m, 1H); 5.31 (m, 1H);5.35 (m, 1H); 5.62 0.32 (s, 9H)
(m, 1H)
1.11 (s, 9H);1.14 (s, 9H);4.77
(br, 3H)
[P(OiPr)3]Br2
lat-(p5-C5H4SiMe3)Re(CO) 1952
[P(OPh)3]Br2
4.98 (m, 1H); 5.13 (m, 1H);5.21 (m, 1H); 5.64 0.21 (s, 9H)
(m, 1H)
6.82–7.40 (m, 15H)
lat-(p5-C5H4SiMe3)Re(CO) 1924
4.86 (m, 2H); 5.07 (m, 1H);5.67 (m, 1H)
0.28 (s, 9H)
7.35–7.80 (m, 15H)
(PPh3)Br2
a Recorded in CH2Cl2.
b Recorded in C6D6, relative to TMS: s, singlet; d, doublet; t, triplet; m, multiplet; br, broad.
c [12]e.
3. Results and discussion
Me3NO, reactions of either diag- or lat-(p5-
C5H4R)Re(CO)2X2 (X=Br, I) with isocyanides, phos-
phites and triphenyl phosphine in CH2Cl2 at room
3.1. Synthesis and characterization of diag- and
lat-(p5-C5H4R)Re(CO)(L)X2
temperature
(r.t.)
rapidly
gave
diag-(p5-
C5H4R)Re(CO)(L)X2 in good yields. Usually, a few
percent of lat-(p5-C5H4R)Re(CO)(L)X2 was also found
in the product. Detailed studies indicated that these
lateral isomers were formed by isomerization of the
diagonal products (see below).
The initial approach to the preparation of monocar-
bonyl substitution products of (p5-C5H4R)Re(CO)2X2
was attempted using the King method, i.e. refluxing
(p5-C5H4R)Re(CO)2X2 and ligands, L, in benzene or
toluene [12](e). Indeed, the desired products (p5-
C5H4R)Re(CO)(L)X2 were obtained. However, we
found that the product selectivity, not unexpectedly,
was poor. The product was obtained as a mixture of
diagonal and lateral isomers, and the [diag]/[lat] ratio
varied from reaction to reaction. Further, some un-
wanted side products, which were not characterized,
were formed [9]. Catalytic carbonyl substitution using a
PdO catalyst was attempted. This catalyst has previ-
ously been successfully used to catalyze reactions be-
tween Re(CO)5X and group 15 donor ligands [14].
Numerous reactions (varying temperature, time, etc.)
indicated that PdO did not catalyse the carbonyl substi-
tution reactions of (p5-C5H4R)Re(CO)2X2.
All the diagonal isomers of (p5-C5H4R)Re(CO)(L)X2
have a red color and the lateral isomers are brown in
colour. They all dissolve in organic solvents such as
dichloromethane, chloroform, benzene and toluene, but
the lateral isomers have lower solubility.
Reaction of (p5-C5H4R)Re(CO)2X2 with L=PEt3,
PiPr3, PtBu3 or pyridine resulted in extensive decompo-
sition and no new monosubstituted neutral products
were formed. (No attempt was made to analyse the
reaction solution). This finding most certainly relates to
the stronger basic properties of these ligands [2].
The identification of the diagonal and lateral isomers
of (p5-C5H4R)Re(CO)(L)X2 was based on IR and
NMR spectroscopy and X-ray single crystal structures.
The proton patterns of the cyclopentadienyl ring reso-
nances of the diagonal isomers occur as two ‘pseudo’
Attempts to use Me3NO as a decarbonylating agent
were then undertaken. In the presence of excess

L. Cheng, N. J. Co6ille / Journal of Organometallic Chemistry 556 (1998) 111–118
115
Table 2
Analytical data for diag- and lat-(p5-C5H4R)Re(CO)(L)X2 complexes
Complex
Yield (%)
m.p. (°C)
Analysis (%)
C
H
N
diag-(p5-C5H4Me)Re(CO)(CNC6H3Me2)Br2
diag-(p5-C5H4Me)Re(CO)[P(OMe)3]Br2
diag-(p5-C5H4Me)Re(CO)[P(OiPr)3]Br2
diag-(p5-C5H4Me)Re(CO)[P(OPh)3]Br2
diag-(p5-C5H4Me)Re(CO)(PPh3)Br2
diag-(p5-C5H4Me)Re(CO)[P(OPh)3]I2
diag-(p5-C5H4Me)Re(CO)(PPh3)I2
92
75
84
89
70
60
84
96
75
75
61
76
95
76
75
84
63
—
—
—
—
—
—
—
—
—
154–156
114–116
108–110
164–166
186–188
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
32.89
32.82
20.81
20.69
29.06
29.01
39.33
39.39
41.97
42.06
35.02
35.03
37.10
36.96
36.43
36.35
25.21
24.97
32.44
32.42
41.75
41.43
44.40
44.41
33.65
33.50
22.68
22.70
30.05
30.16
39.47
39.20
41.92
42.17
32.89
32.60
20.81
20.51
29.06
29.02
39.33
39.38
41.97
42.00
35.02
35.00
37.10
37.01
36.43
36.31
25.21
32.44
32.50
41.75
41.82
44.40
43.90
33.65
33.41
22.68
22.46
2.76
2.64
2.79
2.68
4.27
3.93
2.90
2.68
3.10
2.88
2.59
2.44
2.74
2.61
3.54
3.31
3.58
3.28
4.87
4.64
3.50
3.26
3.73
3.69
3.45
3.30
3.49
3.57
4.76
4.64
3.44
3.44
3.65
3.69
2.76
2.48
2.79
2.78
4.27
4.06
2.90
2.69
3.10
2.87
2.59
2.46
2.74
2.63
3.54
3.27
3.58
4.87
4.50
3.50
3.46
3.73
3.62
3.45
3.27
3.49
3.43
2.40
2.32
a
—
176-169
142–144
123–125
126–128
124–126
172–174
144–146
diag-(p5-C5H4t-Bu)Re(CO)(CNC6H3Me2)Br2
diag-(p5-C5H4t-Bu)Re(CO)[P(OMe)3]Br2
diag-(p5-C5H4t-Bu)Re(CO)[P(OiPr)3]Br2
diag-(p5-C5H4t-Bu)Re(CO)[P(OPh)3]Br2
diag-(p5-C5H4t-Bu)Re(CO)(PPh3)Br2
diag-(p5-C5H4SiMe3)Re(CO)(CNC6H3Me2)Br2
diag-(p5-C5H4SiMe3)Re(CO)[P(OMe)3]Br2
diag–(p5-C5H4SiMe3)Re(CO)[P(OiPr)3]Br2
diag-(p5-C5H4SiMe3)Re(CO)[P(OPh)3]Br2
diag-(p5-C5H4SiMe3)Re(CO)(PPh3)Br2
lat-(p5-C5H4Me)Re(CO)(CNC6H3Me2)Br2
lat-(p5-C5H4Me)Re(CO)[P(OMe)3]Br2
lat-(p5-C5H4Me)Re(CO)[P(OiPr)3]Br2
lat-(p5-C5H4Me)Re(CO)[P(OPh)3]Br2
lat-(p5-C5H4Me)Re(CO)(PPh3)Br2
2.24
2.19
2.18
2.12
a
—
106–108
124–126
155–157
192–194
116–118
178–180
183–185
200–202
189–191
227–229
194–196
154–156
2.40
2.34
lat-(p5-C5H4Me)Re(CO)[P(OPh)3]I2
lat-(p5-C5H4Me)Re(CO)(PPh3)I2
lat-(p5-C5H4t-Bu)Re(CO)(CNC6H3Me2)Br2
lat-(p5-C5H4t-Bu)Re(CO)[P(OMe)3]Br2
2.24
2.19
lat-(p5-C5H4t-Bu)Re(CO)[P(OiPr)3]Br2
lat-(p5-C5H4t-Bu)Re(CO)[P(OPh)3]Br2
—
—
170–172
158–160
lat-(p5-C5H4t-Bu)Re(CO)(PPh3)Br2
—
—
—
190–192
179–181
143–145
lat-(p5-C5H4SiMe3)Re(CO)(CNC6H3Me2)Br2
lat-(p5-C5H4SiMe3)Re(CO)[P(OMe)3]Br2
2.18
2.15

116
L. Cheng, N. J. Co6ille / Journal of Organometallic Chemistry 556 (1998) 111–118
Table 2 (Continued)
Complex
Yield (%)
m.p. (°C)
Analysis (%)
C
H
N
lat-(p5-C5H4SiMe3)Re(CO)[P(OiPr)3]Br2
lat-(p5-C5H4SiMe3)Re(CO)[P(OPh)3]Br2
lat-(p5-C5H4SiMe3)Re(CO)(PPh3)Br2
—
—
—
159–161
137–139
187–189
Calc.
Found
Calc.
Found
Calc.
Found
30.05
30.11
39.47
39.16
41.92
41.89
4.76
4.61
3.44
3.43
3.65
3.45
a Due to fast isomerization in solutions, the pure diagonal isomers of these complexes were not obtained.
triplet peaks while those of the lateral isomers usually
comprise of four multiplet peaks. The diagonal isomers
were also observed to have higher carbonyl stretching
frequencies than the lateral isomers. The structures of
diag- and lat-(p5-C5H4Me)Re(CO)[P(OPh)3]Br2, the
first structures of cyclopentadienyl monocarbonyl sub-
stituted dihalogen rhenium complexes, were successfully
determined by X-ray single crystal diffraction and un-
ambiguously confirmed our assignments [15].
[P(OPh)3]Br2 and excess NaI, surprisingly gave diag-
(p5-C5H4Me)Re(CO)2I2 (50% yield) instead of the ex-
pected
diag-(p5-C5H4Me)Re(CO)[P(OPh)3]I2.
The
above reactions indicate that both Re–Br and Re–
P(OPh)3 bonds can be broken during the solid-state
halogen exchange processes. These are remarkable re-
sults in that:
1. The diagonal iodo isomer has formed in the solid-
state. Previously we had not been able to intercon-
vert the iodo diag–lat isomers in the solid-state [16]
as a melt formed prior to isomerisation. However
the preference for the diagonal isomer is expected
from a consideration of the melting points of the
isomers.
3.2. Solid-state diag–lat isomerization of
(p5-C5H4R)Re(CO)(L)X2
It was found that all the diagonal isomers of (p5-
C5H4R)Re(CO)(L)X2 underwent thermal solid-state
isomerization reactions to give the corresponding lat-
eral isomers in good yields (\70%) within a few hours
(Table 3). It should be noted that the reaction tempera-
tures reported here (Table 3) are not the minimum
temperatures needed for solid-state isomerization reac-
tions. The isomerization is unidirectional, i.e. from the
diagonal to the lateral isomer; the lateral isomers re-
mained unchanged under the same reaction conditions.
Unlike the thermal isomerization reactions of (p5-
C5H4R)Re(CO)2Br2 in which the isomerization process
is strongly influenced by the cyclopentadienyl ring sub-
stituent R and the solid-state isomerization is only
observed for (p5-C5H4R)Re(CO)2Br2 (R=Me [4], iPr),
all (p5-C5H4R)Re(CO)(L)X2 underwent thermal solid-
state diag-to-lat isomerization. In these reactions the
different cyclopentadienyl ring substituent R, ligand L
and halogen X have no influence on the direction of the
solid-state isomerization process. More importantly,
our study indicates that thermal solid-state diag–lat
isomerization is a common reaction for a wide range of
cyclopentadienyl four-legged piano stool rhenium com-
plexes. Reaction of diag-(p5-C5H4Me)Re(CO)2Br2 and
excess NaI in the solid-state, under typical isomerisa-
tion conditions, gave quantitative formation of diag-
(p5-C5H4Me)Re(CO)2I2. This methodology also offers a
convenient method for the preparation of cyclopentadi-
enyl dicarbonyldiiodide rhenium complexes. Reaction
2. The yield is near quantitative in the phosphite–io-
dide exchange reaction and implies no CO is lost
when the ligand exchange occurs.
3. This is the first time we have observed the replace-
ment of a neutral ligand by another neutral ligand
(phosphite by CO) in the solid-state.
Any mechanism will need to take the above informa-
tion into consideration. In a previous paper [17] we
proposed that isomerisation was achieved by a flexing
of the four ligands relative to the cyclopentadienyl ring
followed by a turnstile process as shown in Fig. 1. For
this new set of compounds it appears that both the ring
and the L ligand will provide the pivots for the 3-fold
rotation of the Br and CO ligands. This is entirely
consistent with the original proposal.
Presumably during the flexing process all metal–lig-
and bonds are weakened (even the ring–Re bonds [18])
and in the presence of appropriate ligands e.g. iodide/
iodine atom, substitution can take place. This would
lead to the unusual results obtained above. Clearly
further studies will be needed to assess both the gener-
ality of the reaction and the mechanism of the ligand
exchange.
3.3. Solution phase diag–lat isomerization of
(p5-C5H4R)Re(CO)(L)X2
Both diag- and lat-(p5-C5H4R)Re(CO)(L)X2 are sta-
ble in solution in the dark, even in the presence of
of
a
solid mixture of diag-(p5-C5H4Me)Re(CO)-

L. Cheng, N. J. Co6ille / Journal of Organometallic Chemistry 556 (1998) 111–118
117
Table 3
Thermal solid-state diag–lat isomerization of diag-(p5-C5H4R)Re(CO)(L)X2
Complex
Reaction temperature (°C)
Reaction time (h)
Yield (%)a
diag-(p5-C5H4Me)Re(CO)(CNC6H3Me2)Br2
diag-(p5-C5H4Me)Re(CO)[P(OMe)3]Br2
diag-(p5-C5H4Me)Re(CO)[P(OiPr)3]Br2
diag-(p5-C5H4Me)Re(CO)[P(OPh)3]Br2
diag-(p5-C5H4Me)Re(CO)(PPh3)Br2
140–145
100–105
95–100
1.0
2.0
6.0
5.0
2.0
2.0
1.0
2.0
2.0
2.0
2.0
1.0
2.0
2.0
0.5
86
96
81
80
72
70
94
82
70
85
85
76
70
71
75
145–150
145–150
145–150
130–135
105–110
105–110
108–110
140–145
130–135
90–95
diag-(p5-C5H4Me)Re(CO)(PPh3)I2
diag-(p5-C5H4t-Bu)Re(CO)(CNC6H3Me2)Br2
diag-(p5-C5H4t-Bu)Re(CO)[P(OMe)3]Br2
diag-(p5-C5H4t-Bu)Re(CO)[P(OiPr)3]Br2
diag-(p5-C5H4t-Bu)Re(CO)[P(OPh)3]Br2
diag-(p5-C5H4t-Bu)Re(CO)(PPh3)Br2
diag-(p5-C5H4SiMe3)Re(CO)(CNC6H3Me2)Br2
diag-(p5-C5H4SiMe3)Re(CO)[P(OiPr)3]Br2
diag-(p5-C5H4SiMe3)Re(CO)[P(OPh)3]Br2
diag-(p5-C5H4SiMe3)Re(CO)(PPh3)Br2
105–110
130–135
a Yield after isomer separation.
Fig. 1. Combined Berry–turnstile isomerization mechanism for CpML4 complexes.
phine
proceeded
rapidly
at
r.t.
to
give
excess ligand, L. Only a few percent (B5%) of the
lateral isomer forms when the chloroform or benzene
solutions of diag-(p5-C5H4R)Re(CO)(L)X2, covered
with aluminum foil, were kept at r.t. for 4 weeks.
No isomerisation was observed for lat-(p5-
C5H4R)Re(CO)(L)X2 under these conditions. However,
the solution isomerization of (p5-C5H4R)Re(CO)(L)X2
proceeds readily on irradiation with visible light in
CHCl3 or more slowly in C6H6.
As with the thermal solid-state isomerization reac-
tion, only the diag-to-lat isomerization was observed
for solutions of (p5-C5H4R)Re(CO)(L)X2. No isomer-
ization was observed for lat-(p5-C5H4R)Re(CO)(L)X2
under the same irradiation conditions. A mechanism
for the solution photochemical cis–trans isomerism of
(p5-C5Me5)Re(CO)2X2 (X=Cl, Br, I) has been re-
ported and a carbonyl dissociation–association process
has been proposed [19]. A similar mechanism may
apply here although a dissociative–associative process
involving X groups seems more likely.
diag-(p5-C5H4R)Re(CO)(L)X2
(L=CNC6H3Me2,
P(OMe)3, P(OiPr)3, P(OPh)3, PPh3) in good yields.
Solid-state diag–lat isomerization reactions were ob-
served for all the monocarbonyl substituted rhenium
complexes (p5-C5H4R)Re(CO)(L)X2, prepared in this
study, indicating that the solid-state isomerization reac-
tion is a common phenomenon for cyclopentadienyl
four-legged piano stool rhenium complexes. The direc-
tion of the isomerisation reaction was also found to be
different from their parent complexes (p5-
C5H4R)Re(CO)2X2 in which lat-to-diag solution iso-
merization occurred. diag-(p5-C5H4R)Re(CO)(L)X2
completely isomerized into the corresponding lateral
isomers in chloroform or dichloromethane on irradia-
tion with visible light at r.t.
Acknowledgements
We wish to thank the FRD and the University of the
Witwatersrand for financial support.
4. Conclusions
References
With the assistance of Me3NO, reaction of diag- or
lat-(p5-C5H4R)Re(CO)2X2 (R=Me, t-Bu, SiMe3; X=
Br, I) with isocyanides, phosphites and triphenyl phos-
[1] (a) M.L.H. Green, G. Wilkinson, J. Chem. Soc. (1958) 4314. (b)
C.P. Casey, M.A. Andrews, D.R. McAlister, J.E. Rinz, J. Am.

118
L. Cheng, N. J. Co6ille / Journal of Organometallic Chemistry 556 (1998) 111–118
Chem. Soc. 102 (1980) 1927. (c) K.I. Goldberg, R.G. Bergman,
[11] M. Arenas, S. Silva, A. Toro, A.H. Klahn, Bol. Soc. Chil. Quim.
39 (1994) 285.
J. Am. Chem. Soc. 111 (1989) 1285. (d) W. Tam, G.Y. Lin,
W.K. Wong, W.A. Kiel, V.K. Wong, J.A. Gladysz, J. Am.
Chem. Soc. 104 (1982) 141. (e) A.H. Klahn, D. Sutton,
Organometallics 4 (1985) 198. (f) Y.X. He, R.J. Batchelor,
F.W.B. Einstein, L.K. Peterson, D. Sutton, J. Organomet.
Chem. 531 (1997) 27. (h) M.D. Cavanaugh, S.M. Tetrick, C.J.
Masi, A.R. Cutler, J. Organomet. Chem. 538 (1997) 41. (i) W.H.
Bosch, U. Englert, B. Pfister, R. Stauber, A. Salzer, J.
Organomet. Chem. 506 (1996) 273.
[12] (a) D. Braga, F. Grepioni, J. Chem. Soc. Chem. Commun.
(1996) 571. (b) D. Roberto, E. Cariati, R. Psaro, R. Ugo, J.
Organomet. Chem. 488 (1995) 109. (c) D. Roberto, E. Cariati,
R. Ugo, R. Psaro, Inorg. Chem. 35 (1996) 2311. (d) E.V.
Boldyreva, Mol. Cryst. Liq. Cryst. 242 (1994) 17. (e) L. Cheng,
N.J. Coville, Organometallics 16 (1997) 591.
[13] (a) T.Y. Luh, Coord. Chem. Rev. 59 (1984) 225. (b) J.K. Shen,
Y.C. Gao, Q.Z. Shi, F. Basolo, J. Organomet. Chem. 401 (1991)
295. (c) D.J. Blumer, K.W. Barnett, T.L. Brown, J. Organomet.
Chem. 173 (1979) 71.
[2] R.B. King, R.H. Reimann, Inorg. Chem. 15 (1976) 179.
[3] F.W.B. Einstein, A.H. Klahn-Oliva, D. Sutton, K.G. Tyers,
Organometallics 5 (1986) 53.
[4] L. Cheng, N.J. Coville, Organometallics 15 (1996) 867.
[5] G.K. Yang, R.G. Bergman, Organometallics 4 (1985) 129.
[6] D.F. Dong, J.K. Hoyano, W.A.G. Graham, Can. J. Chem. 59
(1981) 1455.
[14] A.E. Leins, N.J. Coville, J. Organomet. Chem. 407 (1991) 359.
[15] J.C.A. Boeyens, D.C. Levendis, L. Cheng, N.J. Coville, J. Chem.
Cryst., submitted.
[16] L. Cheng, N.J. Coville, unpublished results.
[17] J.M. Smith, N.J. Coville, Organometallics 15 (1996) 3388.
[18] R.G. Ball, A.K Campen, W.A.G. Graham, P.A. Hamley, S.G.
Kazarian, M.A. Ollino, M. Poliakoff, A.J. Rest, L. Sturgeoff, I.
Whitwell, Inorg. Chim. Acta. 259 (1997) 137.
[7] C.M. Nunn, A.H. Cowley, S.W. Lee, M.G. Richmond, Inorg.
Chem. 29 (1990) 2105.
[8] A.H. Klahn, C. Manzur, A. Toro, M. Moore, J. Organomet.
Chem. 516 (1996) 51.
[19] (a) R.H. Hill, B.J. Palmer, Organometallics 8 (1989) 1651. (b) W.
Xia, R.S. Hill, A.H. Klahn, C. Leiva, G.E. Buono-Core, Polyhe-
dron 15 (1996) 3093.
[9] A.H. Klahn, S. Arenas, Bol. Soc. Chil. Quim. 38 (1993) 277.
[10] A.H. Klahn, R.D. Singer, J.M. Aramini, D. Sutton, Inorg.
Chem. 28 (1989) 4217.
.