Synthetic, Spectroscopic, and Electrochemical Studies of the Isomerically-Rich [M(CO)2(P2P′)X]+/0 (M = Mn, Re; X = Cl, Br; P2P′ = η3-Ph2P (CH2)2P(Ph)(CH2)2PPh2) System: Structural Characterization of a Novel Pair

Article abstract of DOI:10.1021/ic961295d

Reaction of Mn(CO)₅X (X = Cl, Br) with Ph₂P(CH₂)₂P(Ph)(CH₂) ₂PPh₂ (P₂P') in refluxing xylene led to the formation of isomerically pure cis,mer-Mn(CO)₂(η³-P₂P/)X. Cyclic voltammograms in dichloromethane (0.1 M Bu₄NPF₆) show a reversible one-electron oxidation (process 1, E_1/2 = 0.142 V) to give cis,mer-[Mn(CO)₂(P₂P')X]⁺, However, in acetone (0.1 M Bu₄NPF₆) at room temperature, process 1 is not reversible and an additional redox process 4 (E_1/2 = 0.048 V) is observed. Process 4 is not observed at low temperatures, and at higher temperatures in acetone it merges with process 1 and also a new reversible redox couple (process 5, E_1/2 = -0.411 V) appears. A combination of electrolyses, chemical oxidation, and subsequent reduction, coupled with IR and ³¹P NMR spectroscopies and electrospray mass spectrometry (ESMS), is used to show that processes 1, 4, and 5 are all associated with redox and interconversion reactions of different isomers of Mn(CO)₂(P₂P')X and [Mn(CO)₂-(P₂P')⁺. Other irreversible processes due to oxidation of the different isomers of [Mn(CO)₂(P₂P')X]⁺ are observed at very positive potentials. Reaction between Re(CO)₅X and P₂P' in refluxing mesitylene gives a soluble product and a small amount of precipitate. The major soluble product was identified as cis,mer-Re(CO)₂(P₂P')X, and the oxidative chemistry is similar to that of the manganese analogues. The precipitate consists of five compounds, one of which was cis,mer-Re(CO)₂(P₂P')X. The new compounds A - D were identified as follows: A is cis,mer-{Re(CO)₂(P₂P')X}₂, a dimeric species with bridging P₂P' ligands. The spectroscopic data for B indicated that it was a form of cis,mer-Re(CO)₂(P₂P')X, but not the same as the major product. Compound C is cis/fac-Re(CO)₂-(P₂P')X, and compound D was shown to be fac-[Re(CO)₃(P₂P')]X. The crystal structures of cis,mer-Re(CO)₂-(P₂P')C1 (I) and cis,mer-Re(CO)₂(P₂P')Cl(II) show the compounds to be diastereoisomers with the same mer geometry of the P₂P' ligand, which of necessity generates a cavity formed by three phenyl rings on one side of the rhenium atom. The coordination geometry of the two compounds differ only by the interchange of the mutually trans chloro and carbonyl ligands. In (I) the carbonyl ligand is within the cavity and in (II) the chloro ligand is within the cavity.

Full text of DOI:10.1021/ic961295d

Inorg. Chem. 1997, 36, 1181-1193
1181
Synthetic, Spectroscopic, and Electrochemical Studies of the Isomerically-Rich
[M(CO)2(P2P′)X]+/0 (M ) Mn, Re; X ) Cl, Br; P2P′ ) η3-Ph2P(CH2)2P(Ph)(CH2)2PPh2)
System: Structural Characterization of a Novel Pair of Diastereoisomers of
cis,mer-Re(CO)2(P2P′)Cl
Alan M. Bond,*,1,2 Ray Colton,1,2 Robert W. Gable,3 Maureen F. Mackay,1 and
Jacky N. Walter1
School of Chemistry, La Trobe University, Bundoora, Victoria 3083, Australia, and School of
Chemistry, University of Melbourne, Parkville, Victoria 3052, Australia
ReceiVed October 25, 1996X
Reaction of Mn(CO)5X (X ) Cl, Br) with Ph2P(CH2)2P(Ph)(CH2)2PPh2 (P2P′) in refluxing xylene led to the
formation of isomerically pure cis,mer-Mn(CO)2(η3-P2P′)X. Cyclic voltammograms in dichloromethane (0.1 M
Bu4NPF6) show a reversible one-electron oxidation (process 1, E1/2 ) 0.142 V) to give cis,mer-[Mn(CO)2(P2P′)X]+.
However, in acetone (0.1 M Bu4NPF6) at room temperature, process 1 is not reversible and an additional redox
process 4 (E1/2 ) 0.048 V) is observed. Process 4 is not observed at low temperatures, and at higher temperatures
in acetone it merges with process 1 and also a new reversible redox couple (process 5, E1/2 ) -0.411 V) appears.
A combination of electrolyses, chemical oxidation, and subsequent reduction, coupled with IR and 31P NMR
spectroscopies and electrospray mass spectrometry (ESMS), is used to show that processes 1, 4, and 5 are all
associated with redox and interconversion reactions of different isomers of Mn(CO)2(P2P′)X and [Mn(CO)2-
(P2P′)X]+. Other irreversible processes due to oxidation of the different isomers of [Mn(CO)2(P2P′)X]+ are observed
at very positive potentials. Reaction between Re(CO)5X and P2P′ in refluxing mesitylene gives a soluble product
and a small amount of precipitate. The major soluble product was identified as cis,mer-Re(CO)2(P2P′)X, and the
oxidative chemistry is similar to that of the manganese analogues. The precipitate consists of five compounds,
one of which was cis,mer-Re(CO)2(P2P′)X. The new compounds A-D were identified as follows: A is cis,mer-
{Re(CO)2(P2P′)X}2, a dimeric species with bridging P2P′ ligands. The spectroscopic data for B indicated that it
was a form of cis,mer-Re(CO)2(P2P′)X, but not the same as the major product. Compound C is cis,fac-Re(CO)2-
(P2P′)X, and compound D was shown to be fac-[Re(CO)3(P2P′)]X. The crystal structures of cis,mer-Re(CO)2-
(P2P′)Cl(I) and cis,mer-Re(CO)2(P2P′)Cl(II) show the compounds to be diastereoisomers with the same mer
geometry of the P2P′ ligand, which of necessity generates a cavity formed by three phenyl rings on one side of
the rhenium atom. The coordination geometry of the two compounds differ only by the interchange of the mutually
trans chloro and carbonyl ligands. In (I) the carbonyl ligand is within the cavity and in (II) the chloro ligand is
within the cavity.
Introduction
the existence of relatively stable [M(CO)2(η3-P2P′)X]+ com-
plexes. The numerous isomerically related products of elec-
The reactions between Mn(CO)5X (X ) Cl, Br, I) and the
triphosphine Ph2P(CH2)2P(Ph)(CH2)2PPh2 (P2P′) have been
investigated by two groups of workers. King and co-workers4
synthesized Mn(CO)2(η3-P2P′)Br, while Butler and Coville5,6
have prepared Mn(CO)3(η2-P2P′)X and Mn(CO)2(η3-P2P′)X. The
only structural information previously available for the dicar-
bonyl complexes is from the IR spectra which show the carbonyl
groups to be cis.
In this paper, Mn(CO)2(η3-P2P′)X and the previously un-
reported rhenium analogues Re(CO)2(η3-P2P′)X (X ) Cl, Br)
compounds have been fully characterized by IR and multinuclear
(31P, 13C) magnetic resonance spectroscopies. The electro-
chemical behavior of these complexes has been investigated on
both the voltammetric and coulometric time scales and reveal
trochemical and chemical redox reactions associated with the
[M(CO)2(η3-P2P′)X]+/0 system have been isolated and identified
by a range of techniques, including multinuclear magnetic
resonance and IR spectroscopies and electrospray mass spec-
trometry. X-ray crystallography has been used to characterize
two novel diasteroisomers of cis,mer-Re(CO)2(η3-P2P′)Cl.
In all of the compounds described in this paper, the ligand
P2P′ is bound to the metal as a tridentate ligand so the prefix
η3 will be omitted in all subsequent representations of the
formulas.
Experimental Section
Materials and Preparations. All solvents were Analytical Reagent
grade. Manganese and rhenium carbonyls and P2P′ (Strem) were used
as supplied. The pentacarbonyl halides were prepared by interaction
of the carbonyls with halogen.7 Mn(CO)5X and 1 mol equiv of P2P′
were heated in refluxing xylene for 1 h. Upon cooling the solution,
yellow needles (Cl) or orange needles (Br) separated out. The liquid
was decanted off, and the needles were recrystallized from dichloro-
methane/hexane to give yellow needles of Mn(CO)2(P2P′)X. Re(CO)5X
and 1 mol equiv of P2P′ were heated in refluxing mesitylene for several
X Abstract published in AdVance ACS Abstracts, February 1, 1997.
(1) La Trobe University.
(2) Present address: Department of Chemistry, Monash University,
Clayton, Victoria 3168, Australia.
(3) University of Melbourne.
(4) King, R. B.; Kapoor, P. N.; Kapoor, R. N. Inorg. Chem. 1971, 10,
1841.
(5) Butler, I. S.; Coville, N. J.; Spendjian, H. K. J. Organomet. Chem.
1972, 43, 185.
(6) Coville, N. J.; Butler, I. S. J. Organomet. Chem. 1973, 57, 355.
(7) Colton, R.; McCormick, M. J. Aust. J. Chem. 1976, 29, 1657.
S0020-1669(96)01295-5 CCC: $14.00 © 1997 American Chemical Society

1182 Inorganic Chemistry, Vol. 36, No. 6, 1997
Bond et al.
hours. Upon cooling the solution, a small amount of white solid
precipitated and was filtered off and washed with hexane. Subsequently
this solid was dissolved in dichloromethane and separated into five
components by chromatography on silica as described in the text.
Hexane was added to the filtered solution of mesitylene to precipitate
a solid which was recrystallized from dichloromethane/hexane to yield
crystals of Re(CO)2(P2P′)X.
Table 1. Crystal Structure Data for Isomers of
cis,mer-Re(CO)2(P2P′)Cl
cis,mer-(I)‚CH2Cl2
cis,mer-(II)
formula
Mr
C37H35Cl3O2P3Re
897.1
C36H33ClO2P3Re
812.2
colorless
monoclinic
P21/c
color
cryst syst
space group
colorless
monoclinic
P21/n
Electrochemical Methods. Conventional voltammetric measure-
ments were typically obtained with 1.0 mM solutions of compound in
dichloromethane (0.1 M Bu4NPF6) or acetone (0.1 M Bu4NPF6), using
a Cypress Systems (Lawrence, KS) Model CYSY-1 computer controlled
electrochemical system or a BAS 100A electrochemical analyzer
(Bioanalytical Systems, West Lafayette, IN). The working electrode
was a glassy carbon disk (0.5 mm radius), the auxiliary electrode was
a platinum wire, and the reference electrode was Ag/AgCl (saturated
LiCl in dichloromethane (0.1 M Bu4NPF6)) separated from the test
solution by a salt bridge. The reversible voltammetry of an ap-
proximately 1.0 mM ferrocene (Fc) solution in the same solvents was
used as a reference redox couple, and all potentials are quoted relative
to Fc+/Fc. Steady-state voltammograms were recorded using a 12.5
µm radius platinum microdisk electrode. Solutions were purged with
solvent-saturated nitrogen before voltammetric measurements and then
maintained under an atmosphere of nitrogen during measurements.
Bulk electrolysis experiments were undertaken with either a PAR
Model 273 potentiostat or the BAS 100 A electrochemical analyzer
using a large platinum basket working electrode and a platinum gauze
auxiliary electrode separated from the test solution by a salt bridge
and the same reference electrode as used in the voltammetric studies.
Spectroscopic Methods. NMR spectra were recorded on a Bruker
AM 300 spectrometer, 31P at 121.496 MHz in dichloromethane or
acetone and 13C at 75.469 MHz in CDCl3 solution. The high-frequency
positive convention is used for chemical shifts with external 85% H3PO4
and internal TMS references, respectively. Infrared spectra were
recorded on a Perkin-Elmer FT-IR 1720X or a Perkin-Elmer 1430 IR
spectrometer.
Electrospray Mass Spectrometry. Electrospray mass spectra of
cationic complexes were obtained with a VG Bio-Q triple quadrupole
mass spectrometer using a water/methanol/acetic acid (50:50:1) mobile
phase. Solutions of the compounds (2.0 mM in dichloromethane) were
mixed, if necessary, with oxidant or sodium acetate as described in
the text. The mixed solution was then diluted 1:10 with methanol and
immediately injected directly into the spectrometer via a Rheodyne
injector fitted with a 10 µL loop. A Pheonix 20 micro LC syringe
pump delivered the solution to the vaporization nozzle of the electro-
spray source at a flow rate of 5 µL min-1. Nitrogen was used as the
drying gas and for nebulization with flow rates of approximately 3 L
min-1 and 100 mL min-1, respectively. The voltage on the first
skimmer (B1) was usually 40 V, but higher voltages were used to induce
collisionally activated fragmentations as described in the text. Peaks
are identified by the most abundant mass in the isotopic mass
distribution. In all cases the agreement between experimental and
theoretical isotopic mass patterns was good.
a, Å
b, Å
c, Å
18.749 (3)
32.307 (6)
18.978 (3)
107.76 (2)
10 948 (7)
12
13.898 (4)
15.845 (1)
15.443 (5)
105.14 (1)
3283 (1)
â, deg
vol, Å3
Z
4
F(calc), g/cm3
cryst dimens (distance in
mm from centroid)
1.633
1.643
(-1 -2 1) 0.173
(1 2 -1) 0.226
(-1 -1 -2) 0.165
(121) 0.123
(-1 2 1) 0.140
(1 -2 -1) 0.140
(110) 0.12
(-1 -1 0) 0.12
(-1 1 0) 0.12
(1 -1 0) 0.12
(100) 0.107
(-1 0 0) 0.107
(001) 0.313
(0 0 -1) 0.313
293
temp, K
293
radiation, Å (graphite
monochrometer)
F(000)
Mo KR (λ )
0.710 69)
5328
Mo KR (λ )
0.710 69)
1608
µ, cm-1
37.1
40.1
transmn factors
max 0.4654,
min 0.3434
2.2 < 2θ < 50.0
18 769
16 453
0.0326
max 0.5103,
min 0.3700
2.0 < 2θ < 50.0
6000
5003
0.0303
2θ limits
no. of reflns collecd
no. of unique reflns
Ramal
no. of unique reflcns
used (I > 2σ(I))
refinement
12 464
4664
full matrix
0.0398
0.0863
1.008
full matrix
0.0187
0.0475
1.059
a
R1
b
Rw
GOFc
a Ramal ) σ|Fo2 - Fo (mean)|/σFo . R1 ) ∑(|Fo| - |Fc|)/∑|Fo|). b Rw
2
2
) [∑(Fo - Fc2)2]/∑wFo ]}1/2, where w ) [σ2Fo + (0.0331P)2
+
2
2
2
2
50.86P]-1 for cis,mer-(I) and [σ2Fo + (0.0296P)2 + 0.9028P]-1 for
cis,mer-(II) with P ) (Fo + 2Fc2)/3). c GOF ) {[∑w(Fo - Fc2)]2/(n
- m)}1/2, where n is the number of reflections used in the refinement
and m is the number of parameters refined.
2
2
thermal parameters of a Cl atom (Cl9) of one dichloromethane molecule
in the structure of cis,mer-(I) indicated a strong libration. To
approximate this effect, the coordinates of this atom were split into
eight components and each given an occupancy factor of 0.125 (see
Table 7). To decrease computational time only the 12 464 terms for
which I g 2σI were used in the refinement of the structure of cis,mer-
(I). Extinction corrections were not applied to the data, but one term
(-1 0 2) was omitted from the final refinements of cis,mer-(II).
Crystal Structure Determinations for cis,mer-Re(CO)2-
(P2P′)Cl(I)‚CH2Cl2 and cis,mer-Re(CO)2(P2P′)Cl(II). Crystallo-
graphic Data. Crystals of the two compounds identified as cis,mer-
Re(CO)2(P2P′)Cl were obtained by slow evaporation of dichloromethane/
hexane solutions of the complexes at room temperature. Intensity data
were collected on an Enraf-Nonius CAD-4 Mach S diffractometer at
20 °C. Crystal data for both structures are given in Table 1.
Structure Determination and Refinement. Analytical absorption
corrections were applied to the intensities before structure solution.
The positions of the rhenium atoms were derived from vector maps,
and the sites of the remaining non-hydrogen atoms were determined
from successive difference maps using SHELX-76.8 The structures
were refined against F2 with SHELX-93.9 Hydrogen atoms were
included at idealized positions using C-H bond lengths of 0.97 and
0.93 Å for the methylene and phenyl hydrogens, respectively. The
Results and Discussion
The chemistry of the Mn(CO)5X/P2P′ system is somewhat
different to that of Re(CO)5X with P2P′, so it is convenient to
describe the chemistry of the two metals separately.
A. Reactions of Mn(CO)5X with P2P′. Spectroscopic
evidence (Table 2) outlined below shows that the reaction of
both carbonyl halides with P2P′ gives only a single isomer of
the product previously characterized as Mn(CO)2(P2P′)X. The
infrared spectrum of Mn(CO)2(P2P′)Br shows two carbonyl
stretches of approximately equal intensities, whose positions
agree with literature values.4,5 This spectrum shows that the
carbonyl groups are mutually cis. Its 31P NMR spectrum
consists of two peaks of relative intensities 1:2, both of which
are shifted considerably to high frequency compared with the
positions of the resonances for the free ligand,10 which confirms
that all three phosphorus atoms are coordinated to the metal
(8) Sheldrick, G. M. SHELX-76, Program for Crystal Structure Deter-
mination; Cambridge University: Cambridge, U.K., 1976.
(9) Sheldrick, G. M. SHELX-93, Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Germany, 1993.

Isomerically-Rich [M(CO)2(P2P′)X]+/0
Inorganic Chemistry, Vol. 36, No. 6, 1997 1183
Table 2. IR and NMR Data for All [Mn(CO)2(P2P′)X]+/0 Compounds
δ(31P),a ppm
compound
ν
CO, cm-1
P′
P2
δ(13C),b ppm
temp(NMR), °C
cis,mer-Mn(CO)2(P2P′)Cl
cis,mer-[Mn(CO)2(P2P′)Cl]+
cis,fac-Mn(CO)2(P2P′)Cl
cis,fac-[Mn(CO)2(P2P′)Cl]+
trans-Mn(CO)2(P2P′)Cl
1936, 1866
2033, 1960d
119.0
87.0
226c
22
125.7
134.4
119.0
129.2
137.3
49.7
69.4
85.9
49.5
70.1
-80
22
2052, 1060d
1893
1973
trans-[Mn(CO)2(P2P′)Cl]+
cis,mer-Mn(CO)2(P2P′)Br
cis,mer-[Mn(CO)2(P2P′)Br]+
cis,fac-Mn(CO)2(P2P′)Br
cis,fac-[Mn(CO)2(P2P′)Br]+
trans-Mn(CO)2(P2P′)Br
1936, 1866
227.1, 225.3
22
2031, 1960d
-80
22
2048, 1960d
1893
1970
trans-[Mn(CO)2(P2P′)Br]+
a In CH2Cl2 solution. b In CDCl3 solution. c May be two overlapping resonances. d Value only approximate due to overlap with peak due to
trans+.
B. Electrochemical Studies. (i) Cyclic Voltammetry. All
voltammetric data are summarized in Table 3; the potentials
quoted are relative to the reversible Er1/2 value for the Fc+/Fc
couple. Unless stated otherwise, voltammograms were recorded
using a 0.5 mm radius glassy carbon disk macroelectrode.
Figure 2a shows an oxidative cyclic voltammogram (scan rate,
200 mV s-1) for a 1.0 mM solution of cis,mer-Mn(CO)2(P2P′)Cl
in dichloromethane (0.1 M Bu4NPF6) at 20 °C. On the first
scan an oxidative response (process 1) is observed and the
corresponding reduction response (process 1′) is seen on the
reverse scan. Second and subsequent scans are identical, and
the response remains reversible at all scan rates (100-50 000
mV s-1) and temperatures (-20 to +50 °C) examined. A
steady-state voltammogram at a platinum disk microelectrode
(radius, 12.5 µm) shows that the limiting current for process 1
is similar to that obtained for the oxidation of an equimolar
solution of Mn(CO)3(dpe)Br (dpe ) Ph2PCH2CH2PPh2), which
is known12 to be a one-electron oxidation. The redox process
1 may therefore be assigned as
cis,mer-[Mn(CO)2(P2P′)Cl]+ + e- h
cis,mer-Mn(CO)2(P2P′)Cl (1)
Figure 1. Four possible geometrical isomers of Mn(CO)2(P2P′)X (X
) Cl, Br). The phenyl and methylene group have been omitted for
clarity.
Figure 2b shows that at more positive potentials there are
two further oxidation responses, both irreversible, a very small
peak labeled process 2 and a larger response labeled process 3.
These features will be discussed in more detail below.
In acetone (0.1 M Bu4NPF6) subtly different responses are
observed in oxidative cyclic voltammograms of cis,mer-
Mn(CO)2(P2P′)Cl at 20 °C. Figure 2c is a cyclic voltammogram
(scan rate, 200 mV s-1) over a limited potential range, and it
shows only process 1 on the first oxidative scan, but on the
reverse scan a small response (process 4′) is observed as well
as process 1′. Second and subsequent scans under these
conditions show an additional oxidative response (process 4).
However, scans at -30 °C (scan rate, 200 mV s-1) show only
processes 1 and 1′, indicating that the formation of the species
responsible for processes 4 and 4′ is a kinetically controlled
step. This was confirmed by experiments at 20 °C using a scan
rate of 5000 mV s-1, and again processes 4 and 4′ were absent
because the kinetically controlled reaction(s) was outrun by the
electrochemical timescale.
and also that the terminal phosphorus atoms remain chemically
equivalent. Since it is known that P2P′ may coordinate to metals
in both fac and mer configurations,11 there are four possible
isomers of Mn(CO)2(P2P′)X, as shown in Figure 1, if only the
geometry of the donor atoms about the metal is considered. The
trans isomer is eliminated on the basis of the infrared spectrum
and the cis,fac-(I) isomer is discarded on the basis of the 31P
NMR spectrum since it would have three non-equivalent
phosphorus atoms. The cis,fac-(II) and cis,mer isomers may
be distinguished by their 13C NMR spectra (carbonyl region).
The observed 13C NMR spectrum of Mn(CO)2(P2P′)Br shows
two carbonyl resonances which unequivocally determine the
structure to be cis,mer. The spectroscopic data for Mn(CO)2-
(P2P′)Cl are very similar to those of cis,mer-Mn(CO)2(P2P′)Br
except that the 13C NMR spectrum shows only one resonance
in the carbonyl region. However, the signal is rather broad and
is probably two superimposed signals. Electrochemical data
given below strongly indicate that both compounds are the same
isomer, so it will be assumed that Mn(CO)2(P2P′)Cl is also
cis,mer.
Figure 2d shows an oxidative cyclic voltammogram (scan
rate, 200 mV s-1) at 20 °C for cis,mer-Mn(CO)2(P2P′)Cl in
acetone (0.1 M Bu4NPF6) over a wider potential range.
Processes 2 and 3 previously observed in dichloromethane are
(10) Colton, R.; Tedesco, V. Inorg. Chim. Acta 1992, 202, 95.
(11) Bond, A. M.; Colton, R.; Feldberg, S. W.; Mahon, P. J.; Whyte, T.
Organometallics 1991, 10, 3320.
(12) Bond, A. M.; Colton, R.; McCormick, M. J. Inorg. Chem. 1977, 16,
155.

1184 Inorganic Chemistry, Vol. 36, No. 6, 1997
Bond et al.
temp,
Table 3. Cyclic Voltammetric Data for Oxidation of cis,mer-Mn(CO)2(P2P′)X Compounds at a Glassy Carbon Disk Electrode
cis,mer-Mn(CO)2(P2P′)Cl
cis,mer-Mn(CO)2(P2P′)Br
ox
red
a
ox
red
a
scan rate,
mV s-1
Ep
,
Ep
,
E1/2
,
temp, scan rate,
°C
mV s-1
Ep
,
Ep
,
E1/2,
process
1
V vs Fc+/Fc V vs Fc+/Fc V vs Fc+/Fc
V vs Fc+/Fc V vs Fc+/Fc V vs Fc+/Fc
°C
In Dichloromethane
0.140
200
0.181
0.099
20
200
200
200
200
200
200
200
0.202
0.196
0.826
1.178
0.094
-0.032
1.046
0.116
0.108
0.159
0.152
20
-30
20
2
3
4
5
6
200
200
0.803
1.153
b
-0.391
1.023
20
20
20
20
0.014
-0.108
0.054
200
200
-0.459
-0.425
20
20
-0.070
20
20
In Acetone
1
1
1
1
2
3
4
5
6
200
200
200
5000
200
200
200
200
200
0.177
0.190
0.193
0.216
0.771
0.961
0.083
-0.375
1.073
0.099
0.116
0.113
0.106
0.138
0.153
0.153
0.161
-30
20
50
20
20
20
20
20
20
200
200
0.216
0.202
0.126
0.098
0.171
0.150
20
55
200
200
200
200
200
0.817
0.994
0.108
-0.368
1.054
20
20
20
20
20
0.013
-0.447
0.048
0.411
0.038
-0.442
0.073
-0.405
a Calculated from the value of (Epox + Epred)/2, where Epox and Epred are the oxidation and reduction peak potentials, respectively, associated with
the designated processes under the stated conditions. b Process 4 cannot be observed in CH2Cl2 at 20 °C.
again observed, but process 2 is more pronounced in acetone.
The relationship between processes 2 and 4 will be discussed
later. Process 3, which is close to the solvent limit, remains
irreversible at all temperatures and scan rates examined. It
seems likely that process 3 is a further oxidation of cis,mer-
[Mn(CO)2(P2P′)Cl]+ to a highly unstable 16-electron Mn(III)
complex, thus explaining its irreversibility, and process 3 will
not be considered further.
(ii) Bulk Electrolysis. Exhaustive bulk oxidative electrolysis
of a dichloromethane (0.4 M Bu4NPF6) solution of cis,mer-
Mn(CO)2(P2P′)Cl was carried out at a platinum gauze working
electrode at a potential of 0.270 V vs Fc+/Fc (slightly more
positive than process 1). The appearance of the solution
changed from yellow to orange. A reductive cyclic voltam-
mogram of the oxidized solution shows that process (E1/2
)
0.142 V) is now absent, but a reversible couple is observed at
-0.425 V vs Fc+/Fc. This is the same potential as the small
response labeled process 5 seen in the cyclic voltammograms
for cis,mer-Mn(CO)2(P2P′)Cl in acetone (0.1 M Bu4NPF6) at
50 °C. Scanning to more positive potentials shows a new
irreversible response at 1.023 V vs Fc+/Fc (process 6), while
processes 2 and 3 seen for cis,mer-Mn(CO)2(P2P′)Cl are absent.
The voltammogram remains unchanged on the second and
subsequent scans. The sign of the current in a steady-state
voltammogram at a platinum microelectrode after the electrolysis
shows that the species in solution giving rise to process 5 is in
the oxidized form. Comparison of the limiting current with that
for an equimolar solution of Mn(CO)3(dpm)Br shows that
process 5 is a one-electron process. The IR spectrum of the
oxidized solution exhibits a single peak in the carbonyl region
An oxidative cyclic voltammogram (scan rate, 200 mV s-1
)
of cis,mer-Mn(CO)2(P2P′)Cl in acetone (0.1 M Bu4NPF6) at 55
°C does not exhibit process 4′, but there is a small new reductive
response at -0.459 V vs Fc+/Fc (process 5′) and the second
and subsequent scans show the corresponding oxidation response
at -0.391 V (process 5). Redox process 5 is a weak feature in
the cyclic voltammograms of cis,mer-Mn(CO)2(P2P′)Cl but is
more pronounced for cis,mer-Mn(CO)2(P2P′)Br, and it will be
discussed in more detail for that compound.
An oxidative cyclic voltammogram (scan rate, 200 mV s-1
)
at 20 °C for cis,mer-Mn(CO)2(P2P′)Br in dichloromethane (0.1
M Bu4NPF6) as given in Figure 3a, shows processes 1 and 1′
as for cis,mer-Mn(CO)2(P2P′)Cl, but process 4′ is also promi-
nent, whereas this process was not observed for the chloro
complex in this solvent. Process 2 (not shown) is also observed
at more positive potentials. Process 4′ (and processes 4 and 2)
can be removed by cooling the solution to -30 °C.
In acetone (0.1 M Bu4NPF6) under similar conditions, process
4′ is quite prominent on the first scan, as shown in Figure 3b,
and the corresponding oxidative component (process 4) is seen
on the second scan. On heating the acetone solution of cis,mer-
Mn(CO)2(P2P′)Br, cyclic voltammograms show that processes
1′ and 4′ shift closer together and at 40 °C appear as a single
broad response, and the reduction response 5′ becomes apparent.
At 55 °C the cyclic voltammogram of cis,mer-Mn(CO)2(P2P′)-
Br in acetone (Figure 3c) shows a much sharper response for
processes 1 and 1′ (and 4, 4′) and processes 5′ and 5 are well-
defined.
at 1973 cm-1
.
Exhaustive bulk reductive electrolysis was then performed
on the originally oxidized solution, and the color of the solution
changed from orange to pink. A subsequent cyclic voltammo-
gram shows the same redox couple for process 5, but a steady-
state voltammogram at a platinum microelectrode shows that
the species in solution is now in the reduced form. The IR
spectrum of the reduced solution shows a single carbonyl
absorption at 1893 cm-1, and the 31P NMR spectrum of the
solution shows two signals (1:2). The IR data strongly indicates
a trans configuration for the carbonyl groups, and the NMR
spectrum is consistent with this formulation. Thus, process 5
is assigned to the redox couple
trans-[Mn(CO)2(P2P′)Cl]+ + e- h trans-Mn(CO)2(P2P′)Cl
(2)
The compounds giving rise to processes 4 and 5 cannot be
assigned on the basis of the cyclic voltammograms alone, but
they are identified as other isomers of Mn(CO)2(P2P′)X on the
basis of additional information obtained from the experiments
described below.
Many previous studies11-14 of group 6 and group 7 18-
electron cis- or fac-carbonyl species have shown that upon
(13) Bond, A. M.; Colton, R.; Jackowski, J. J. Inorg. Chem. 1975, 14, 274.

Isomerically-Rich [M(CO)2(P2P′)X]+/0
Inorganic Chemistry, Vol. 36, No. 6, 1997 1185
Figure 3. Oxidative cyclic voltammogram (scan rate, 200 mV s-1
)
Figure 2. Oxidative cyclic voltammograms (scan rate, 200 mV s-1
)
for 1 mM cis,mer-Mn(CO)2(P2P′)Br solutions at a glassy carbon
electrode (radius 0.5 mm) (a) in dichloromethane (0.1 M Bu4NPF6) at
20 °C, (b) in acetone (0.1 M Bu4NPF6) at 20 °C, and (c) in acetone
(0.1 M Bu4NPF6) at 55 °C.
for 1 mM cis,mer-Mn(CO)2(P2P′)Cl solutions at a glassy carbon
electrode (radius 0.5 mm) at 20 °C (a) in dichloromethane (0.1 M
Bu4NPF6) over a restricted potential range, (b) under similar conditions,
over an extended potential range, (c) in acetone (0.1 M Bu4NPF6) over
a restricted potential range, and (d) similar conditions, over an extended
potential range.
C. Chemical Oxidation at Room Temperature. The
chemical oxidants NOBF4 and (BrC6H4)3NSbCl6 (“magic blue”)
were used to oxidize solutions of cis,mer-Mn(CO)2(P2P′)X.
(i) Monitoring by IR Spectroscopy and Electrochemistry.
Immediately after addition of NOBF4 to a dichloromethane
solution of cis,mer-Mn(CO)2(P2P′)Br the IR spectrum shows a
weak peak at 2052 cm-1 and three strong absorptions at 2033,
1973 (assigned to trans-[Mn(CO)2(P2P′)Br]+), and 1960 cm-1
(shoulder). A reductive cyclic voltammogram of the solution,
while all four IR peaks are present, shows the three reversible
processes corresponding to processes 1, 4, and 5. However,
after addition of the reductant cobaltocene to the oxidized
solution, a voltammogram displays only processes 1 and 5, and
the IR spectrum after reduction shows a stretch at 1893 cm-1
(assigned to trans-Mn(CO)2(P2P′)Br) and also stretches at 1936
and 1866 cm-1 due to the starting material cis,mer-Mn(CO)2-
(P2P′)Br.
oxidation the resulting 17-electron species isomerize to the trans-
or mer-carbonyl configuration, often on the voltammetric time
scale. Thus, it is reasonable to observe a similar isomerization
in the present case. In the present case the rate of isomerization
is too slow to be observed on the voltammetric time scale at
room temperature, but sufficiently fast for the isomerization to
be complete on the electrolysis time scale. The overall reaction
scheme may be represented by the following version of the
square scheme
cis,mer-Mn(CO)2(P2P′)Cl
cis,mer-[Mn(CO)2(P2P′)Cl]+ + e–
slow
trans-Mn(CO)2(P2P′)Cl
trans-[Mn(CO)2(P2P′)Cl]+ + e–
(3)
When the IR spectrum of the solution containing cis,mer-
Mn(CO)2(P2P′)Br and NOBF4 is monitored over several min-
utes, the intensities of the peaks at 2052, 2033, and 1960 cm-1
decrease, while that of the stretch at 1973 cm-1 increases until
this is the only peak in the spectrum. Reduction of this solution
with cobaltocene gives an IR spectrum which contains only the
stretch at 1893 cm-1 assigned to trans-Mn(CO)2(P2P′)Br, as
found for the bulk electrolysis experiments. Experiments in
acetone give similar results as do those using magic blue as the
oxidant, although in this case an irreversible reduction is
Isomerization of trans-Mn(CO)2(P2P′)Cl to cis,mer-Mn(CO)2-
(P2P′)Cl was not observed. Process 6 is due probably to further
oxidation of trans-[Mn(CO)2(P2P′)Cl]+ to an unstable 16-
electron Mn(III) species and will not be considered further.
Exactly analogous observations were made for the bulk oxida-
tion of cis,mer-Mn(CO)2(P2P′)Br, and all data are given in Table
3.
(14) Bond, A. M.; Carr, S. W.; Colton, R. Inorg. Chem. 1984, 23, 2343.

1186 Inorganic Chemistry, Vol. 36, No. 6, 1997
Bond et al.
Table 4. Electrospray Mass Spectrometric Data at Low Ion Source Energies
compound
additive
ions (m/z)
cis,mer-Mn(CO)2(P2P′)Cl
cis,mer-Mn(CO)2(P2P′)Br
cis,mer-Re(CO)2(P2P′)Cl(I)
NOBF4
NOBF4
NOBF4
magic blue
NOBF4
[Mn(CO)2(P2P′)Cl]+ (680); [Mn(CO)2(P2P′)]+ (645); [Mn(P2P′)Cl]+ (624)
[Mn(CO)2(P2P′)Br]+ (726); [Mn(P2P′)Br]+ (670); [Mn(CO)2(P2P′)]+ (645)
[Re(CO)2(P2P′)Cl]+ (812);a [Re(CO)(NO)(P2P′)Cl]+ (814)b
[Re(CO)2(P2P′)Cl]+ (812)
cis,mer-Re(CO)2(P2P′)Br(I)
[Re(CO)2(P2P′)Br]+ (856);a [Re(CO)(NO)(P2P′)Br]+ (858)b
[Re(CO)2(P2P′)Br]+ (856)
magic blue
[Re(CO)2(P2P′)Br2]+ (937)
cis,mer-Re(CO)2(P2P′)Cl(I)
cis,mer-Re(CO)2(P2P′)Br(I)
cis,mer-{Re(CO)2(P2P′)Cl}2
Br2
Br2
magic blue
NaOAc
NOBF4
NOBF4
[Re(CO)2(P2P′)ClBr]+ (891)
[Re(CO)2(P2P′)Br2]+ (937)
[{Re(CO)2(P2P′)Cl}2]+ (1624)
[Na + {Re(CO)2(P2P′)Cl}2]+ (1647)
[Re(CO)2(P2P′)Cl]+ (812)
cis,mer-Re(CO)2(P2P′)Cl(II)
cis,mer-Re(CO)2(P2P′)Br(II)
[Re(CO)2(P2P′)Br]+ (856)
a Immediately after addition of NOBF4. b Some minutes later.
observed close to the trans+/0 couple which is assigned to the
reduction of Sb(V) to Sb(III) from the anion of magic blue.
The chloro complex cis,mer-Mn(CO)2(P2P′)Cl behaves simi-
larly. Thus, chemical oxidation of cis,mer-Mn(CO)2(P2P′)X
also produces trans-[Mn(CO)2(P2P′)X]+, which may be reduced
to trans-Mn(CO)2(P2P′)X, as in the bulk electrolysis experi-
ments.
(P2P′)X]+ as the base peak in the mass spectrum, together with
weaker peaks due to species formed by loss of either the two
carbonyl groups or a halogen atom. Increasing the ion source
energy increased the relative intensities of these fragment peaks,
indicating that they are formed by collisions within the ion
source. Although these spectra confirm that [Mn(CO)2(P2P′)X]+
ions exist in the oxidized solutions, they can give no information
of the isomers present. All ESMS data are given in Table 4,
where peaks are identified by the most abundant mass in the
isotopic mass pattern. In all cases excellent agreement was
observed between experimental and theoretical isotopic mass
distributions.
D. Chemical Oxidation at Low Temperature. A steady-
state voltammogram at a platinum microelectrode of a solution
of cis,mer-Mn(CO)2(P2P′)Cl in dichloromethane (0.1 M Bu4NPF6)
after oxidation with NOBF4 at -30 °C shows process 1 as the
dominant feature, and only a small response is observed for
process 4. Low-temperature IR facilities are not available to
us, but the IR spectrum recorded quickly at room temperature
shows two strong absorptions at 2033 and 1960 cm-1 of
approximately equal intensities, but there is also a small peak
at 2052 cm-1. These data strongly suggest that the strong
absorptions at 2033 and 1960 cm-1 are due to the oxidized
component of process 1, that is cis,mer-[Mn(CO)2(P2P′)Cl]+,
while the weak peak at 2052 cm-1 is associated with the less
abundant oxidative component of process 4. Monitoring the
IR spectrum of this solution over several minutes at 20 °C
reveals a decrease in these three peaks and a concomitant growth
of a stretch at 1973 cm-1 due to trans-[Mn(CO)2(P2P′)Cl]+.
However, the peaks at 2033 and 1960 cm-1 remain the same
intensity relative to each other, confirming they are associated
with the same compound.
These experiments show that on the shorter time scale at least
three oxidation products of cis,mer-Mn(CO)2(P2P′)X are present
in solution and upon reduction after a short time cis,mer-
Mn(CO)2(P2P′)X and trans-Mn(CO)2(P2P′)X are identified. This
indicates that one likely oxidation product is cis,mer-[Mn(CO)2-
(P2P′)X]+. Longer time scale experiments show the isomer-
ization of cis,mer-[Mn(CO)2(P2P′)X]+ to trans-[Mn(CO)2-
(P2P′)X]+ proceeds to completion as expected from previous
studies of 17-electron carbonyl systems.11-14 However, there
is another species in solution (corresponding to process 4) which
remains to be identified. The IR absorptions of this so far
unidentified oxidation product and cis,mer-[Mn(CO)2(P2P′)X]+
cannot yet be assigned between the absorptions at 2052, 2033,
and 1960 cm-1
.
(ii) 31P NMR Spectroscopy. The 31P NMR spectrum of a
solution of cis,mer-Mn(CO)2(P2P′)Cl to which a small amount
of NOBF4 has been added consists of several broad peaks.
However, when cobaltocene is added, the peaks become sharp
and are resolved into the resonances for cis,mer-Mn(CO)2(P2P′)-
Cl and two new signals of relative intensities 1:2 which are
assigned to trans-Mn(CO)2(P2P′)Cl, previously identified from
bulk electrolysis and chemical oxidation experiments. A similar
experiment with isolated trans-Mn(CO)2(P2P′)Cl confirmed that
its NMR peaks broadened on addition of magic blue, and after
subsequent addition of cobaltocene only the sharp peaks of
trans-Mn(CO)2(P2P′)Cl were observed in the spectrum. This
experiment showed that no trans to cis isomerization occurs in
either the 17- or 18-electron compounds on this time scale.
Broadening of the NMR peaks of both cis,mer-Mn(CO)2(P2P′)-
Cl and trans-Mn(CO)2(P2P′)Cl in the solution of cis,mer-
Mn(CO)2(P2P′)Cl after addition of NOBF4 suggests that electron
self-exchange is occurring between the 17- and 18-electron
species, which is fast on the NMR time scale. Previous studies14
have shown that fast electron exchange occurs only between
isostructural species, and therefore it is likely that the broadening
of the peaks of cis,mer-Mn(CO)2(P2P′)Cl is due to exchange
with some cis,mer-[Mn(CO)2(P2P′)Cl]+ present in solution,
rather than with the trans-[Mn(CO)2(P2P′)Cl]+ which is known
to be present also.
When a sample of the oxidized solution which had been kept
at -30 °C is reduced with cobaltocene at -30 °C, the IR
spectrum shows only the peaks at 1936 and 1866 cm-1 due to
cis,mer-Mn(CO)2(P2P′)Cl, showing that the kinetically controlled
isomerization which produces trans-[Mn(CO)2(P2P′)Cl]+ is
slowed significantly so that no trans-Mn(CO)2(P2P′)Cl (νCO
)
1893 cm-1) is produced upon reduction with cobaltocene.
A steady-state voltammogram at a platinum microelectrode
obtained at -25 °C of a solution originally containing cis,mer-
Mn(CO)2(P2P′)Cl in acetone (0.1 M Bu4NPF6) after addition
of NOBF4 at -60 °C is similar to that observed in dichloro-
methane except that process 4 is enhanced. The IR spectrum
of this solution shows a broad peak at 2032 cm-1 with a shoulder
at ∼2050 cm-1 and a peak at 1959 cm-1. The peaks at 2032
and 1959 cm-1 have already been assigned to cis,mer-
[Mn(CO)2(P2P′)Cl]+, and the peak at 2050 cm-1 is stronger than
in dichloromethane, confirming that it is associated with the
more abundant oxidized species associated with process 4.
(iii) Electrospray Mass Spectrometry. The electrospray
mass spectra of solutions of both cis,mer-Mn(CO)2(P2P′)Cl and
cis,mer-Mn(CO)2(P2P′)Br to which had been added some
NOBF4 both showed the appropriate intact cation [Mn(CO)2-

Isomerically-Rich [M(CO)2(P2P′)X]+/0
Inorganic Chemistry, Vol. 36, No. 6, 1997 1187
Table 5. IR and NMR Data for All [Re(CO)2(P2P′)X]+/0 Compounds
δ(31P),a ppm
δ(13C),b ppm
compound
ν
CO,a cm-1
P′
P2
coupling constants, Hz
cis,mer-Re(CO)2(P2P′)Cl(I)
cis,mer-Re(CO)2(P2P′)Cl(II)
cis,fac-Re(CO)2(P2P′)Cl
trans-Re(CO)2(P2P′)Cl
1941
1949
1950
1906
1968
1941
2040
1941
1950
1951
1906
1967
1942
2040
1855
1860
1886
75.6
56.7
66.9
78.5
35.0
27.0
10.7
19.6
201.6d
202.5d
196.5
189.9
JC-P ) 56
JC-P ) 62
trans-[Re(CO)2(P2P′)Cl]+
cis,mer-{Re(CO)2(P2P′)Cl}2
fac-[Re(CO)3(P2P′)]Cl
1862
1962
1860
1862
1888
21.2
65.7
74.0
53.7
67.8
78.2
38.2d, 0.8d
JP-P ) 180
27.6
32.6
25.1
8.6
cis,mer-Re(CO)2(P2P′)Br(I)
cis,mer-Re(CO)2(P2P′)Br(II)
cis,fac-Re(CO)2(P2P′)Br
trans-Re(CO)2(P2P′)Br
200.9d
201.9d
195.8
189.4
JC-P ) 49
JC-P ) 54
18.5
trans-[Re(CO)2(P2P′)Br]+
cis,mer-{Re(CO)2(P2P′)Br}2
fac-[Re(CO)3(P2P′)]Br
1862
1962
21.2
38.0d, 0.2d
JP-P ) 180
a In CH2Cl2 solution. b In CDCl3 solution.
cis,mer-Mn(CO)2(P2P′)X
cis,mer-[Mn(CO)2(P2P′)X]+ + e–
Reduction of this solution with cobaltocene was undertaken at
-60 °C, and the resulting steady-state voltammogram shows
that process 4 is still present, but now in the reduced form. The
reduced solution was kept at low temperature, and the 31P NMR
spectrum was acquired at -80 °C. It shows resonances at δ
119.0 and 87.0 ppm due to cis,mer-Mn(CO)2(P2P′)Cl and two
other signals of 1:2 relative intensities occur at δ 125.7 and
49.7 ppm. When the solution is allowed to warm to room
temperature, the NMR spectrum of the solution then shows only
the resonances due to cis,mer-Mn(CO)2(P2P′)Cl. This result
shows that the reduced form associated with process 4 is another
isomer of Mn(CO)2(P2P′)Cl which is stable only at low
temperature and rapidly converts to cis,mer-Mn(CO)2(P2P′)Cl
near room temperature. Similar experiments with cis,mer-
Mn(CO)2(P2P′)Br in acetone give analogous spectra, and all data
are recorded in Tables 2 and 3. As noted earlier, cis,fac-(I)
would give three resonances in its 31P NMR spectrum, while
the cis,fac-(II) isomer would give only two resonances (1:2
intensities). Unfortunately, both cis,fac isomers of [Mn(CO)2-
(P2P′)X]+ should have two carbonyl stretches in the IR spectrum,
but only one is observed, and it is assumed that the second is
obscured by the absorption due to cis,mer-[Mn(CO)2(P2P′)X]+
at 1960 cm-1. Attempts to observe the IR spectrum of cis,fac-
Mn(CO)2(P2P′)X were unsuccessful due the rapid isomerization
to cis,mer-Mn(CO)2(P2P′)X. Despite the difficulty with the IR
spectrum, the balance of evidence suggests that process 4 can
be assigned to the redox couple
fast
fast
cis,fac-Mn(CO)2(P2P′)X(II)
cis,fac-[Mn(CO)2(P2P′)X(II)]+ + e–
(5)
As described earlier in the voltammetry section, the use of
fast scan rates or lowering the temperature leads to the
disappearance of both processes 2 and 4 in the cyclic voltam-
mograms of cis,mer-Mn(CO)2(P2P′)X. This suggests that these
processes are both associated with the same compounds, and
process 2, which will not be considered further, is most likely
further oxidation of cis,fac-[Mn(CO)2(P2P′)X]+ to an unstable
16-electron Mn(III) species
cis,fac-[Mn(CO)2(P2P′)X(II)]+ f
cis,fac-[Mn(CO)2(P2P′)X(II)]2 + e- (6)
E. Reactions of Re(CO)5X with P2P′. It was found that
Re(CO)5X compounds did not react with P2P′ at a reasonable
rate in refluxing xylene, but reaction did occur in refluxing
mesitylene solution. Upon cooling the solution to room
temperature, a small amount of precipitate was formed but the
bulk of the material remained in solution. The precipitate was
filtered off, and its composition will be discussed later after
the identity of the soluble material has been established and its
oxidative chemistry described.
The IR spectrum of the mesitylene solution following reaction
of Re(CO)5Cl and P2P′ shows two carbonyl stretches of equal
intensities at 1941 and 1855 cm-1. These positions are similar
to those of cis,mer-Mn(CO)2(P2P′)Cl and indicate cis-carbonyl
groups. The 31P NMR spectrum shows two signals (1:2) both
shifted to higher frequency than the resonances of the free
ligand, confirming all the phosphorus atoms are coordinated to
rhenium. Addition of hexane to the mesitylene solution caused
the precipitation of a white compound which was recrystallized
from dichloromethane/hexane. The 13C NMR spectrum of this
compound dissolved in deuterochloroform exhibits two reso-
nances of equal intensities in the carbonyl region at δ 201.6
and 196.5 ppm, showing that the stereochemistry is cis,mer.
The 13C NMR signal at higher frequency appears as a doublet
(JC-P ) 56 Hz) and is therefore assigned to the carbon atom of
the carbonyl group trans to P′. The spectroscopic data indicate
the stereochemistry is the same as that for the manganese
complex, and this geometry has been confirmed in the solid
state by a crystal structure determination. Spectroscopic data
are similar for cis,mer-Re(CO)2(P2P′)Br, and details are given
in Table 5, but in the table the compounds are referred to as
cis,fac-Mn(CO)2(P2P′)X(II) h
cis,fac-[Mn(CO)2(P2P′)X(II)]+ + e- (4)
The corresponding rhenium complex, cis,fac-Re(CO)2(P2P′)X(II),
which is more stable and has been fully characterized (see later),
displays similar redox properties.
As shown in Figure 2, process 4 appears for the first time on
the reverse scan in the voltammetry of cis,mer-Mn(CO)2(P2P′)X,
and therefore the cis,fac-(II) isomer is generated in the 17-
electron configuration. However, the isomerization does not
proceed to completion (since process 1′ is also present on reverse
scans). In fact, at 55 °C in acetone this isomerization reaction
in both directions is so fast that on the electrochemical time
scale the observed response becomes an average of processes
1 and 4. Similar fast isomerizations have previously been
observed for other P2P′ complexes.11 The experiments described
above prove that in the 18-electron configuration cis,fac-(II)
rapidly isomerizes to cis,mer. The overall reactions may
therefore be summarized in a square reaction scheme

1188 Inorganic Chemistry, Vol. 36, No. 6, 1997
Bond et al.
cis,mer-Re(CO)2(P2P′)X(I) to distinguish them from another
isomer which will be described later.
The fact that more than one electron per molecule is
consumed in the oxidative electrolysis is consistent with a
disproportionation reaction of the 17e species. In group 6
carbonyl chemistry there are many examples of relatively stable
chromium 17e species, but the corresponding Mo(I) and W(I)
complexes disproportionate to M(0) and M(II).15 This reaction
is assisted by the stability of seven-coordinate, 18e, M(II)
complexes. Although the chemistry of seven-coordinate Re(III)
is not as well-explored as that of Mo(II) and W(II), a significant
number of compounds are known16 and a similar dispropor-
tionation reaction is not unexpected.
F. Electrochemical Studies. (i) Cyclic Voltammetry. The
general features of the voltammetry of cis,mer-Re(CO)2(P2P′)X
are similar to those of the manganese analogues, and only a
generalized description will be given. All voltammetric data
are given in Table 6, and the electrochemical processes are given
the same numbers as the corresponding processes for the
manganese complexes. Process 4 for cis,mer-Re(CO)2(P2P′)-
Cl is weak in dichloromethane but more pronounced in acetone
and also more pronounced for the bromo complex, as was found
for the manganese complexes. The behavior of process 4 with
temperature also parallels the behavior previously described for
solutions of cis,mer-Mn(CO)2(P2P′)X.
2cis,mer-Re(CO)2(P2P′)Br
2cis,mer-[Re(CO)2(P2P′)Br]+ + 2e–
(ii) Bulk Electrolysis. Exhaustive oxidative bulk electrolysis
of a dichloromethane (0.4 M Bu4NClO4) solution of cis,mer-
Re(CO)2(P2P′)Br(I) was undertaken at 20 °C at a platinum
working electrode and a potential of 0.400 V vs Fc+/Fc.
Monitoring by steady-state voltammetry during the course of
the electrolysis indicates that cis,mer-[Re(CO)2(P2P′)Br(I)]+ is
not stable on the longer coulometric time scale since no
reductive component was present for the redox couple 1, only
the oxidative component due to not yet oxidized cis,mer-
Re(CO)2(P2P′)Br being observed. The reductive component of
process 4 was also present together with process 5. The limiting
current associated with process 5 increased as the electrolysis
proceeded, but gradually other responses at more negative
potentials became dominant. Depending upon the experimental
conditions (concentration of cis,mer-Re(CO)2(P2P′)Cl, time of
electrolysis) the charge passed after exhaustive electrolysis was
between 1 and 2 electrons per molecule. Similar observations
were made in acetone, with Bu4NPF6 as the supporting
electrolyte and for the chloro complex cis,mer-(I).
A bulk electrolysis of cis,mer-Re(CO)2(P2P′)Br(I) in acetone
(0.1 M Bu4NClO4) was undertaken at -40 °C in an attempt to
prevent decomposition of the species associated with process
5. The responses at more negative potentials still appeared on
the longer time scale (at least 1 h) at this temperature, but a
greater proportion of the total current was associated with
process 5 than at room temperature. The oxidative electrolysis
was stopped prior to completion so that a subsequent reductive
bulk electrolysis could be undertaken while a significant amount
of the species responsible for process 5 was still present. Before
reduction the IR spectrum of the solution shows an absorption
at 1969 cm-1 as well as the bands at 1941 and 1860 cm-1 of
unoxidized cis,mer-Re(CO)2(P2P′)Br(I). After exhaustive re-
ductive bulk electrolysis at -0.150 V vs Fc+/Fc at -40 °C a
steady-state voltammogram shows process 5 is now in the
reduced form. A similar voltammogram recorded after the
solution had warmed to 20 °C shows that the relative currents
for processes 1 and 5 had not changed. The 31P NMR spectrum
of the reduced solution shows a number of peaks. The solution
was evaporated to dryness, the solid was redissolved in
dichloromethane, and the solution was then passed through a
column of silica gel. The 31P NMR spectrum of the eluant
shows resonances due to cis,mer-Re(CO)2(P2P′)Br(I) at δ 74.0
and 32.6 ppm and two other peaks (1:2) at δ 78.2 and 18.5
ppm. The IR spectrum now shows a strong absorption at 1906
cm-1. All of this evidence confirms that the redox process 5 is
due to
cis,mer-Re(CO)2(P2P′)Br +[Re(CO)2(P2P′)Br]2+
A(anion or solvent)
[Re(CO)2(P2P′)BrA]2+
(8)
This disproportionation reaction of cis,mer-[Re(CO)2(P2P′)Br]+
would be in competition with the isomerization to trans-
[Re(CO)2(P2P′)Br]+ and would lead to a mixture of products if
their rates were comparable. The experiments described so far
do not prove the existence of a disproportionation reaction, but
the consumption of more than one electron and the dependence
of electrolysis products on concentration do strongly support
the suggestion. Positive proof for the formation of Re(III)
species by chemical oxidation was obtained by ESMS.
G. Electrospray Mass Spectrometry. All ESMS data are
given in Table 4. The ES mass spectrum (B1 ) 40 V) of a
solution of cis,mer-Re(CO)2(P2P′)Cl after addition of NOBF4
shows a strong peak for the intact ion [Re(CO)2(P2P′)Cl]+ (m/z
812) provided the mass spectrum is acquired immediately after
addition of the oxidant. However, if the solution is allowed to
stand for a few minutes before injection into the spectrometer,
the signal at m/z 812 is not detected but instead a peak at m/z
814 is observed, which is assigned to the intact ion [Re(CO)-
(NO)(P2P′)Cl]+. This cation is formed by reaction of NO with
the 17-electron dicarbonyl cation, and similar reactions have
been observed previously.17 When magic blue is used to oxidize
cis,mer-Re(CO)2(P2P′)Cl, only [Re(CO)2(P2P′)Cl]+ is observed.
Collisionally activated fragmentation of [Re(CO)(NO)(P2P′)-
Cl]+ can be observed by increasing the B1 voltage. At B1 )
70 V loss of carbonyl is observed, and at B1 ) 90 V [Re(NO)-
(P2P′)]+ (m/z 751) and [Re(NO)(P2P′O)]+ (m/z ) 767) are
observed. The phosphine oxide in the latter ion is formed within
the ion source, and this reaction is commonly observed in the
ES mass spectra of phosphine complexes.18 When B1 ) 110
V, the peaks at m/z 751 and 767 are dominant, but a peak for
the intact ion [Re(CO)(NO)(P2P′)Cl]+ is still present, indicating
its considerable stability. Analogous ES mass spectra were
observed when cis,mer-Re(CO)2(P2P′)Br was oxidized with
NOBF4 and magic blue, except that with the latter oxidant in
addition to the major peak at m/z 856 due to [Re(CO)2(P2P′)-
Br]+, a small peak was observed at m/z 937 which is assigned
to the seven-coordinate Re(III) cation [Re(CO)2(P2P′)Br2]+. This
(15) (a) Bond, A. M.; Bowden, J. A.; Colton, R. Inorg. Chem. 1974, 13,
602. (b) Bond, A. M.; Colton, R.; Kevekordes, J. E.; Panagiotidou,
P. Inorg. Chem. 1987, 26, 1430.
(16) ComprehensiVe Organometallic Chemistry; Wilkinson, G., Stone, F.
G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, U.K., 1982.
(17) Connelly, N. G. J. Chem. Soc., Dalton Trans. 1973, 2183.
(18) (a) Colton, R.; Harvey, J.; Traeger, J. C. Org. Mass. Spectrom. 1992,
27, 95. (b) Colton, R.; Dakternieks, D. Inorg. Chim. Acta 1993, 208,
173.
trans-[Re(CO)2(P2P′)Br]+ + e- h trans-Re(CO)2(P2P′)Br
(7)
analogous to the manganese system, but there are side reactions
not observed with manganese.

Isomerically-Rich [M(CO)2(P2P′)X]+/0
Inorganic Chemistry, Vol. 36, No. 6, 1997 1189
Table 6. Cyclic Voltammetric Data for Oxidation of cis,mer-Re(CO)2(P2P′)X Compounds at a Glassy Carbon Disk Electrodea (Scan Rate, 200
mV s-1
)
cis,mer-Re(CO)2(P2P′)Cl
cis,mer-Re(CO)2(P2P′)Br
ox
red
ox
red
Ep
,
Ep
,
E1/2
,
Ep
,
Ep
,
E1/2,
processb
V vs Fc+/Fc
V vs Fc+/Fc
V vs Fc+/Fc
V vs Fc+/Fc
V vs Fc+/Fc
V vs Fc+/Fc
In Dichloromethane
0.506
1
2
3
4
5
0.551
1.018
1.050
0.378
-0.039
0.440
0.522
0.646
0.461
0.556
0.472
0.514
1.002
0.382
0.006
0.445
0.529
0.657
0.300
-0.113
0.352
0.442
0.568
0.339
0.076
0.396
0.482
0.607
0.302
-0.108
0.359
0.447
0.577
0.342
-0.051
0.402
0.488
0.615
cis,mer-(II)
compound A
In Acetone
0.528
1
4
0.567
0.391
0.489
0.333
0.570
0.396
0.480
0.340
0.525
0.368
0.362
5
-0.046
0.448
-0.116
0.372
-0.081
0.410
-0.044
0.453
-0.114
0.379
-0.079
0.416
cis,mer-(II)
a Symbols have the same meaning as in Table 3. b Perocesses 1-5 refer to cis,mer-(I) and have the same assignments as for the manganese
compounds.
observation led to an investigation by ESMS of the oxidation
of cis,mer-Re(CO)2(P2P′)X with bromine.
The ES mass spectrum (B1 ) 40 V) of a solution of cis,mer-
Re(CO)2(P2P′)Cl after addition of a little bromine does not give
a peak for [Re(CO)2(P2P′)Cl]+ (m/z 812), but instead a peak is
observed at m/z 891 which is due to [Re(CO)2(P2P′)ClBr]+. At
higher collision energies one carbonyl group is lost. Oxidation
of cis,mer-Re(CO)2(P2P′)Br with bromine gave an analogous
spectrum with a strong peak at m/z 937 due to [Re(CO)2(P2P′)-
Figure 4. Proposed structure for cis,mer-{Re(CO)2(P2P′)X}2.
Br2]+. This oxidation of cis,mer-Re(CO)2(P2P′)X with bromine
closely resembles the formation of [M(CO)2(P-P)2X]+ cations
(M ) Mo, W; P-P ) diphosphine) by halogen oxidation of
M(CO)2(P-P)2.19
H. Other Derivatives of Re(CO)5X with P2P′. The
precipitate obtained from the reaction between Re(CO)5Cl and
P2P′ was dissolved in dichloromethane. The IR spectrum in
the carbonyl region consists of several overlapping absorptions,
and the 31P NMR spectrum of the solution displays many
resonances. The relative intensities of these signals vary
between preparations and also depend upon the reaction time,
which indicates that the solution contains a mixture of products.
However, for long reflux times (>24 h) the 31P NMR spectrum
shows only the signals due to cis,mer-Re(CO)2(P2P′)Cl(I).
phosphorus atoms on Re(I).20 This spectrum shows that there
must be two P2P′ ligands in the molecule, and the spectroscopic
data are consistent with the dimeric cis,mer stereochemistry
shown in Figure 4. An oxidative cyclic voltammogram of a
dichloromethane (0.1 M Bu4NPF6) solution of compound A
shows two reversible couples (Table 6) separated by 125 mV,
which is typical behavior for dinuclear complexes,21,22 and there
are additional irreversible processes at higher positive potentials.
A steady-state voltammogram for the two reversible processes
shows that the limiting currents are equal and similar to the
value obtained for the two reversible one-electron oxidations
for an equimolar solution of mer,mer-{Cr(CO)3(η2-dpe)}2(µ-
dpe).22 Thus these processes correspond to the consecutive
oxidations of the two rhenium atoms (eqs 7 and 8), and the
separation between the oxidation potentials suggests electronic
communication between the metal centers.
The components of the mixture were separated by chroma-
tography using a column of silica. Upon elution with dichloro-
methane and acetone a total of five compounds were isolated
from the original small amount of precipitate and identified.
The second compound to be eluted was cis,mer-Re(CO)2(P2P′)-
Cl(I), already identified as the major product of the reaction.
The other four compounds (A-D) are identified as follows, and
similar products were obtained from the reactions between
Re(CO)5Br and P2P′.
cis,mer-[{Re(CO)2(P2P′)Cl}2]+ + e- h
cis,mer-{Re(CO)2(P2P′)Cl}2 (9)
cis,mer-[{Re(CO)2(P2P′)Cl}2]2+ + e- h
cis,mer-[{Re(CO)2(P2P′)Cl}2]+ (10)
(i) Compound A. The first compound to be eluted with
dichloromethane was obtained in only very small amounts. Its
IR spectrum shows two bands at 1941 and 1862 cm-1, indicating
a cis-dicarbonyl structure. The 31P NMR spectrum consists of
three resonances of equal intensities, but two of the signals are
split into doublets with a coupling constant of 180 Hz, which
is a typical value for trans coupling between inequivalent
Unfortunately, bulk electrolysis experiments could not be carried
out on compound A due to the small amount of material
available.
(20) Carr, S. W.; Fontaine, X. L. R.; Shaw, B. L. J. Chem. Soc., Dalton
Trans. 1987, 3067.
(21) (a) Van Order, N.; Geiger, W. E.; Bitterwolf, T. E.; Rheingold, A. L.
J. Am. Chem. Soc. 1987, 109, 5680. (b) Sullivan, B. T.; Meyer, T. J.
Inorg. Chem. 1980, 19, 752. (c) Kober, E. M.; Goldsby, K. A.;
Narayana, D. N. S.; Meyer, T. J. J. Am. Chem. Soc. 1983, 105, 4303.
(22) Bond, A. M.; Colton, R.; Cooper, J. B.; McGregor, K.; Walter, J. N.;
Way, D. M. Organometallics 1995, 14, 49.
(19) (a) Snow, M. R.; Wimmer, F. Aust. J. Chem. 1976, 29, 2349. (b)
Ahmed, I.; Bond, A. M.; Colton, R.; Jurcevic, M.; Traeger, J. C.;
Walter, J. N. J. Organomet. Chem. 1993, 447, 59.

1190 Inorganic Chemistry, Vol. 36, No. 6, 1997
Bond et al.
Conclusive proof of the dimeric nature of compound A was
obtained from ESMS studies. The ES mass spectrum of a
solution of compound A after addition of a small amount of
magic blue gave a weak peak at m/z 1624, which corresponds
to the intact ion [{Re(CO)2(P2P′)Cl}2]+. This peak is probably
weak because magic blue would oxidize most of the compound
beyond [{Re(CO)2(P2P′)Cl}2]+. Much more positive evidence
for the dimeric structure was obtained by addition of sodium
acetate to a solution of compound A, and the ES mass spectrum
gave a strong peak for the sodium adduct [Na + {Re(CO)2-
(P2P′)Cl}2]+ at m/z 1647. On the basis of the above evidence,
compound A can be identified as cis,mer-{Re(CO)2(P2P′)Cl}2
with the structure shown in Figure 4.
the expected reversible process 4 but also another smaller
reversible response identified as process 1. At more positive
potentials the irreversible oxidation responses previously called
processes 2 and 3 are also present. On the second scan the
peak height of process 1 is now greater than that of process 4.
After several hours a cyclic voltammogram shows only proc-
esses 1 and 3, both of which are associated with cis,mer-
Re(CO)2(P2P′)Cl(I). Thus, addition of a small amount of
oxidant or simply recording a cyclic voltammogram (which
generates very small amounts of oxidized species) is sufficient
to convert cis,fac-Re(CO)2(P2P′)Cl(II) to cis,mer-Re(CO)2(P2P′)-
Cl(I). This type of behavior has been observed before23 and
can be attributed to a catalytic process as follows. Oxidation
of the cis,fac-(II) isomer with a small quantity of oxidant
generates cis,fac+ which rapidly isomerizes to cis,mer+. The
cross redox reaction
The second complex eluted from the silica column with
dichloromethane was identified by its IR and 31P NMR spectra
as cis,mer-Re(CO)2(P2P′)Cl(I).
(ii) Compound B. Further elution with dichloromethane gave
a third species (compound B) which also displays two carbonyl
absorptions in its IR spectrum. The 31P NMR spectrum shows
two resonances (1:2), and the 13C NMR spectrum shows two
carbonyl resonances with the higher frequency signal appearing
as a doublet with a coupling constant similar to that observed
for cis,mer-Re(CO)2(P2P′)Cl(I). All of the spectra are similar
to those of cis,mer-Re(CO)2(P2P′)Cl(I), although the actual
values are quite distinguishable from those of the major product
(Table 5). The ES mass spectrum of a solution of compound
B after addition of NOBF4 gave a strong peak at m/z 812 which
corresponds to the intact monomeric ion [Re(CO)2(P2P′)Cl]+.
Thus, the spectroscopic and mass spectral data suggest the
compound is another form of cis,mer-Re(CO)2(P2P′)Cl but the
difference between the two forms was not obvious. Accord-
ingly, crystal structures were determined for these compounds,
and both were indeed found to be cis,mer-Re(CO)2(P2P′)Cl. The
two isomers arise from differences associated with the phenyl
rings of P2P′ and will be discussed in the next section. To
distinguish the isomers, the major product will henceforth be
referred to as cis,mer-Re(CO)2(P2P′)Cl(I) and the minor product
as cis,mer-Re(CO)2(P2P′)Cl(II).
cis,fac-Re(CO)2(P2P′)Cl + cis,mer-[Re(CO)2(P2P′)Cl]+ h
cis,mer-Re(CO)2(P2P′)Cl + cis,fac-[Re(CO)2(P2P′)Cl]+
(11)
then occurs between cis,mer+ and the remaining cis,fac, which
generates cis,mer and more cis,fac+ which in turn isomerizes
to cis,mer+ to continue the process until all of the cis,fac is
converted to cis,mer. The same cycle is initiated also after only
a single voltammogram, but the process takes longer due to the
extremely small amount of oxidized material generated by this
kind of experiment.
(iv) Compound D. After elution of compounds A-C and
cis,mer-Re(CO)2(P2P′)Cl there were still two 31P NMR reso-
nances in the original mixture which were unaccounted for in
the isolated products, suggesting that a further species had been
retained on the column. The column was flushed with aceto-
nitrile and then water, but the resonances were still not detected
in the 31P NMR spectra of the collected fractions. After
allowing the silica to dry, it was soaked in dichloromethane
overnight and the solution then filtered. The NMR spectrum
of the solution shows the missing resonances at δ 65.7 and 27.6
ppm (1:2), and the IR spectrum shows carbonyl bands at 2040
and 1962 cm-1 with the lower frequency band being rather
broad. These absorptions are at higher frequencies than others
reported in this paper, and the spectral pattern is similar to those
for the group 6 metal complexes fac-M(CO)3(P2P′),11 both of
which suggest the compound may be fac-[Re(CO)3(P2P′)]Cl.
The ES mass spectrum of the solution provides unequivocal
proof for the presence of [Re(CO)3(P2P′)]+ since the intact ion
is observed at m/z 805. As the collision energy is raised from
40 V increasing amounts of fragmentation products are observed
(Table 4), but even at a B1 voltage of 180 V the intact ion is
still observed, showing that it has extraordinary stability. Thus,
the combination of spectroscopic and mass spectral data
identifies compound D as fac-[Re(CO)3(P2P′)]Cl.
I. Description of the Structures of cis,mer-Re(CO)2-
(P2P′)Cl(I)‚CH2Cl2 and cis,mer-Re(CO)2(P2P′)Cl(II). The
structure of cis,mer-Re(CO)2(P2P′)Cl(I)‚CH2Cl2 consists of
discrete molecules with one dichloromethane solvate molecule
associated with each molecule of the rhenium complex. There
are three independent molecules in the asymmetric unit, although
their geometries are very similar, giving a total of 12 molecules
in the unit cell. Important bond lengths and bond angles are
given in Tables 7 and 8. Figure 5 is an ORTEP24 diagram
showing the molecular geometry of cis,mer-Re(CO)2(P2P′)Cl(I)
One difference between the cis,mer isomers is seen in the
oxidative voltammetry. For a solution of cis,mer-Re(CO)2-
(P2P′)Cl(II) in dichloromethane (0.1 M Bu4NPF6) a reversible
redox couple (process 1) is observed together with a further
irreversible oxidation (process 3) at more positive potential, but
there is no indication of process 4′, in contrast to the behavior
observed for cis,mer-Re(CO)2(P2P′)Cl(I). This difference is
significant and will be discussed later.
(iii) Compound C. Compound C was removed from the
column using acetone as the eluant after removal of compounds
A and B and cis,mer-Re(CO)2(P2P′)Cl(I) with dichloromethane.
Its IR and 31P NMR spectra are identical to those observed after
cis,mer-Re(CO)2(P2P′)Cl(I) is first chemically oxidized and then
the solution reduced at low temperature, so compound C is
identified as cis,fac-Re(CO)2(P2P′)Cl(II). Clearly this compound
is kinetically more stable than its manganese analogue, which
could only be observed at low temperature in the presence of
cis,mer-Mn(CO)2(P2P′)Cl.
The IR spectrum of cis,fac-Re(CO)2(P2P′)Cl(II) shows two
carbonyl stretches at 1950 and 1880 cm-1. After addition of a
very small amount of magic blue (insufficient to oxidize all
the compound in solution), the IR spectrum shows stretches at
1941 and 1855 cm-1 and the 31P NMR spectrum shows
resonances at δ 75.6 and 35.0 ppm. These spectroscopic data
reveal that the species in solution is now cis,mer-Re(CO)2(P2P′)-
Cl(I). The first scan of a cyclic voltammogram of cis,fac-
Re(CO)2(P2P′)Cl(II) in dichloromethane (0.1 M Bu4NPF6) shows
(23) Bond, A. M.; Colton, R.; McGregor, K. Inorg. Chem. 1986, 25, 2378.
(24) Johnson, C. K. ORTEP II, Fortran Thermal Ellipsoid Plot Program;
Oak Ridge National Laboratory: Oak Ridge, TN, 1976.

Isomerically-Rich [M(CO)2(P2P′)X]+/0
Table 7. Interatomic Distances (Å) for
Inorganic Chemistry, Vol. 36, No. 6, 1997 1191
a
cis,mer-Re(CO)2(P2P′)Cl(I)‚CH2Cl2
molecule 1
molecule 2
molecule 3
Re*-Cl*
2.525 (2)
2.397 (2)
2.420 (3)
2.404 (2)
1.884 (9)
1.931 (10)
1.169 (10)
1.149 (12)
2.508 (2)
2.424 (2)
2.419 (3)
2.399 (3)
1.867 (8)
1.931 (10)
1.179 (10)
1.141 (13)
2.513 (2)
2.403 (2)
2.418 (2)
2.413 (2)
1.911 (10)
1.914 (10)
1.151 (12)
1.148 (13)
Re*-P*1
Re*-P*2
Re*-P*3
Re*-C*11
Re*-C*12
C*11-O*11
C*12-O*12
Dichloromethane Molecules
1.733 (20)
1.679 (20)
1.646 (17)
1.791 (20)
1.586 (21)
1.552 (18)
C14-C411
C15-C411
C16-C412
C17-C412
C18-C413
C19-C413
a * ) 1 for molecule 1; ) 2 for molecule 2; ) 3 for molecule 3.
Table 8. Interatomic Bond Angles (deg) for
cis,mer-Re(CO)2(P2P′)Cl(I)‚CH2Cl2
Figure 5. ORTEP diagram of cis,mer-Re(CO)2(P2P′)Cl(I)‚CH2Cl
(molecule 1) with ellipsoids scaled to 40% probability. The CH2Cl2
molecules and hydrogen atoms have been omitted for clarity.
molecule 1
molecule 2
molecule 3
Cl*-Re*-P*1
Cl*-Re*-P*2
Cl*-Re*-P*3
Cl*-Re*-C*11
Cl*-Re*-C*12
P*1-Re*-P*2
P*1-Re*-P*3
P*1-Re*-C*11
P*1-Re*-C*12
P*2-Re-P*3
P*2-Re*-C*11
P*2-Re*-C*12
P*3-Re*-C*11
P*3-Re*-C*12
C*11-Re*-C*12
Re*-C*11-O*11
Re*-C*12-O*12
85.58 (8)
81.08 (8)
83.18 (8)
178.3 (4)
90.0 (4)
81.80 (8)
161.40 (8)
93.1 (3)
99.0 (4)
81.85 (8)
99.8 (4)
171.0 (4)
98.4 (4)
95.8 (4)
82.73 (8)
81.13 (8)
82.94 (8)
176.7 (4)
92.8 (4)
81.00 (8)
159.10 (8)
100.5 (4)
97.3 (4)
81.82 (8)
98.7 (4)
173.8 (4)
93.8 (4)
82.47 (8)
81.92 (8)
85.71 (8)
177.6 (4)
92.7 (4)
81.01 (8)
160.65 (8)
99.4 (4)
95.5 (4)
82.20 (8)
96.9 (4)
173.9 (4)
92.1 (4)
100.4 (4)
88.5 (5)
Table 9. Interatomic Distances (Å) for
cis,mer-Re(CO)2(P2P′)Cl(II)
Re-Cl
Re-P2
Re-C1
C1-O1
2.506 (1)
2.412 (1)
1.892 (3)
1.153 (4)
Re-P1
Re-P3
Re-C2
C2-O2
2.411 (1)
2.395 (1)
1.933 (3)
1.154 (4)
Table 10. Interatomic Bond Angles (deg) for
cis,mer-Re(CO)2(P2P′)Cl(II)
Cl-Re-P1
Cl-Re-P3
Cl-Re-C2
P1-Re-P3
P1-Re-C2
P2-Re-C1
P3-Re-C1
C1-Re-C2
Re-C2-O2
89.87 (3)
97.62 (3)
87.2 (1)
162.96 (3)
98.3 (1)
85.7 (1)
83.9 (1)
Cl-Re-P2
Cl-Re-C1
P1-Re-P2
P1-Re-C1
P2-Re-P3
P2-Re-C2
P3-Re-C2
Re-C1-O1
93.99 (3)
178.4 (1)
81.89 (3)
88.5 (1)
82.34 (3)
178.8 (1)
97.3 (1)
98.5 (4)
87.4 (5)
176.0 (7)
176.8 (8)
89.1 (4)
177.5 (7)
179.0 (7)
174.3 (7)
177.6 (8)
Dichloromethane Molecule Angles
93.1 (1)
178.2 (3)
178.0 (3)
C14-C411-C15
C16-C412-C17
C18-C413-C19
120.9 (10)
105.1 (10)
128.0 (16)
ligand are mutually trans to each other in the overall cis,mer
stereochemistry. In structure (I) this carbonyl is enclosed in
the cavity while in structure (II) it is the chlorine which is inside
the cavity.
a * ) 1 for molecule 1; ) 2 for molecule 2; ) 3 for molecule 3.
(molecule 1), together with the atomic numbering scheme. The
hydrogen atoms are not labeled but carry the same number as
the carbon atom to which they are attached. The octahedral
coordination of the rhenium atom is derived from the two
carbonyl groups which are mutually cis, the three phosphorus
atoms of P2P′ which adopt a mer stereochemistry, and the
chlorine atom.
The structure of cis,mer-Re(CO)2(P2P′)Cl(II) also consists of
discrete molecules of the rhenium complex, but no solvate is
incorporated into this structure. There is only one rhenium
molecule is the asymmetric unit, giving four molecules in the
unit cell. Important bond lengths and bond angles are given in
Tables 9 and 10. Figure 6 is an ORTEP diagram showing the
molecular geometry of cis,mer-Re(CO)2(P2P′)Cl(II). The ster-
eochemical arrangement of ligands about the rhenium is very
similar to that in cis,mer-Re(CO)2(P2P′)Cl(I), but the differences
lie in the spatial relationships between the coordinated ligands
and the phenyl rings of P2P′. The mer configuration of P2P′
forces an arrangement of the phenyl rings such that three of
them (one from each P, the other from P′) are on one side of
the rhenium atom, and they form a cavity enclosing one of the
ligands coordinated to rhenium. The other two phenyl groups
are on the other side of the rhenium atom where there is a much
more open environment. One carbonyl group and the chlorine
The Re-P bond lengths are similar and agree with values
from previous structure determinations, as do the Re-Cl and
Re-C bond lengths.25-31 The nature of the ligand trans to the
metal-CO and metal-P bonds is known to influence these bond
distances. The Re-C bond of a carbonyl ligand trans to a
phosphorus is expected to be longer than Re-C bonds in which
the carbonyl is trans to a chlorine atom, since phosphorus has
some π-bonding ability, but the metal-halogen bond is regarded
as predominantly σ in nature. This characteristic behavior is
exhibited by both rhenium complexes, where the Re-C bond
trans to a phosphorus atom is observed to be approximately
(25) Davis, B. R.; Ibers, J. A. Inorg. Chem. 1971, 10, 578.
(26) Albano, V. G.; Bellon, P. L.; Cianai, G. J. Organomet. Chem. 1971,
31, 75.
(27) Anglin, J. R.; Calhoun, H. P.; Graham, W. A. G. Inorg. Chem. 1977,
16, 2281.
(28) Rossi, R.; Duatti, A.; Magon, L.; Cassellato, U.; Graziani, R.; Toniolo,
L. Inorg. Chim. Acta 1983, 75, 77.
(29) Lin, S. C.; Cheng, C. P.; Lee, T.-Y.; Lee, T.-J.; Peng, S. M. Acta
Crystallogr. 1986, C42, 1733.
(30) Rossi, R.; Marchi, A.; Duatti, A.; Magon, L.; Cassellato, U.; Graziani,
R. J. Chem. Soc., Dalton Trans. 1987, 2299.
(31) Lui, L.-K.; Lin, S. C.; Cheng, C. P. Acta Crystallogr. 1988, C44, 1402.

1192 Inorganic Chemistry, Vol. 36, No. 6, 1997
Bond et al.
Conclusions and General Discussion
The product of the reaction between Mn(CO)5X and P2P′ was
formulated as cis,mer-Mn(CO)2(P2P′)X on the basis of spec-
troscopic evidence. However, the results from the corresponding
rhenium system show that two forms of the cis,mer geometry
are possible, depending on the orientation of the different trans
ligands to the cavity generated by the P2P′ ligand. There is no
direct spectroscopic evidence to distinguish which isomer is
present for manganese, but all measurements indicate only one
cis,mer isomer is present. The close similarity of the complex
electrochemical behaviors of cis,mer-Mn(CO)2(P2P′)X and
cis,mer-Re(CO)2(P2P′)X(I) on the voltammetric time scale
implies they are the same isomer. The strongest evidence for
this lies in the presence of the redox couple 4,4′ for all these
compounds, but its absence, for the cis,mer-(II) isomer of the
rhenium compounds. The full significance of the absence of
processes 4,4′ for the cis,mer-(II) isomers will be discussed
below. It will be assumed, however, that the manganese
complexes are cis,mer-(I). No evidence was found for the
cis,fac-(I) isomer (Figure 1) with any compound. Presumably,
steric interaction between the halogen and a phenyl ring on the
adjacent phosphorus atom is sufficient to destabilize this isomer
in favor of cis,fac-(II). A simple rotation of the CO,CO,X face
of the octahedron in either the 17- or 18-electron state would
interconvert these isomers.
It is well-known that when 18-electron cis-dicarbonyl and
fac-tricarbonyl complexes are oxidized to the 17-electron state,
there is a tendency for them to isomerize rapidly to the trans-
and mer-carbonyl stereochemistries. Numerous examples have
been described,32 and a theoretical justification for the process
has been presented.33
Previous studies have shown that in the [M(CO)3(P2P′)]+/0
(M ) Mo, W) system there is very rapid isomerization between
fac and mer geometries in both the 17- and 18-electron
configurations,11 which was assumed to proceed via an internal
twist mechanism. This behavior was attributed to stereochem-
ical strain in both geometries, so that neither form is particularly
favorable. In the fac geometry there is steric interaction between
two phenyl rings, one from each terminal phosphorus, and in
the mer geometry there is angular strain associated with the
central phosphorus of P2P′.
The behavior of the oxidation products of cis,mer-Mn(CO)2-
(P2P′)X and cis,mer-Re(CO)2(P2P′)X(I) show features of both
these characteristic patterns. The isomerization of cis,mer+ to
trans+, which is carbonyl controlled, is slower than usual on
the voltammetric time scale, although the reaction does proceed
to completion on the longer time scale. Since this carbonyl
isomerization is slow on the voltammetric time scale, it allows
another isomerization to cis,fac+ to be observed, and this process
is controlled by the P2P′ ligand. Unlike the cis,mer+ f trans+
isomerization, which, although slow, is essentially one-way,
there is a fast isomerization between cis,mer+ and cis,fac+ as
evidenced by the behavior of processes 1,1′ and 4,4′ as a
function of temperature. In contrast, cis,mer-Re(CO)2(P2P′)X(II)
gives no evidence for any isomerization to a cis,fac isomer in
either the 17- or 18-electron state under voltammetric conditions,
so it seems likely that the presence of the larger halo ligand
within the cavity of phenyl rings prevents the operation on the
twist mechanisms which interconvert the isomers. It is this
phenomenon which allows both cis,mer isomers of Re(CO)2-
(P2P′)X to be isolated, since their interconversion must proceed
Figure 6. ORTEP diagram of cis,mer-Re(CO)2(P2P′)Cl(II) with
ellipsoids scaled to 40% probability. The hydrogen atoms have been
omitted for clarity.
0.04 Å longer than the Re-C bond trans to the chlorine. The
Re-P bond lengths are as expected shorter when these bonds
involve trans phosphorus atoms than the Re-P bonds in which
the phosphorus atom is trans to a carbonyl group, as the
carbonyl group is a strong π-acceptor. For these two rhenium
complexes there is only a marginal difference in these bond
lengths. In structure (I) the average Re-P distance involving
the phosphorus trans to a carbonyl group is 2.419 (3) Å, while
the average of the mutually trans Re-P bond lengths are 2.405
(2) and 2.408 (2) Å. For structure (II) the corresponding values
are 2.412 (1) Å compared with 2.395 (1) and 2.411 (1) Å.
The geometry of the ligands about rhenium shows a distorted
octahedral coordination in both structures, with structure (I)
showing the greater degree of distortion. The two P-Re-P
bite angles are significantly less than 90° for both structures
(average angles are 81.27 (8) and 81.96 (8)° for (I) and 81.93
(3) and 82.34 (3)° for (II)), obviously due to the strain about
the central phosphorus atom when P2P′ chelates in the mer
configuration to form two five-membered rings. Therefore,
P(*1) and P(*3) are tilted slightly towards P(*2) (* ) 1, 2, or
3 for molecules 1, 2, or 3). The P(*2)-Re(*)-C(*11) angle
in structure (I) has an average value of 97.7 (4)°, while the
corresponding angle for structure (II) is 85.7 (1)°. The average
Cl(*)-Re(*)-P(*2) angle of structure (I) is 82.9 (7)°, while
the analogous angle for structure (II) is 93.8 (3)°, which is closer
to the idealized value for octahedral geometry. Thus, in cis,mer-
Re(CO)2(P2P′)Cl(I) the chlorine atom is tilted toward P(*2),
whereas in cis,mer-Re(CO)2(P2P′)Cl(II) the chlorine atom points
slightly away from P2. The Re-C-O angles range from 174.3
(7) to 179.0 (7)° and are comparable to values obtained for other
rhenium carbonyl complexes.
Each phenyl ring of the two complexes is planar to within
experimental errors. The plane equations and deviations are
given in the Supporting Information. In structure (II), the
rhenium atom is located very close to the plane defined by P3C;
its deviation from the plane is 0.08 Å, while the other atoms
are coplanar to within 0.06 Å. However for structure (I), the
rhenium atom lies slightly further from the plane defined by
P3C, occurring at 0.19 Å from the plane for molecule 1 (other
atoms coplanar to within 0.02 Å), 0.19 Å from the plane for
molecule 2 (others coplanar to within 0.08 Å), and 0.08 Å from
the plane for molecule 3 (others coplanar to within 0.06 Å).
An examination of all possible intermolecular contacts did not
reveal any unusual features.
(32) (a) Geiger, W. E. Prog. Inorg. Chem. 1985, 33, 275. (b) Bond, A.
M.; Colton, R.; McCormick, M. J. Inorg. Chem. 1977, 16, 155. (c)
Bond, A. M.; Colton, R.; Jackowski, J. J. Inorg. Chem. 1975, 14, 274.
(33) Mingos, D. M. P. J. Organomet. Chem. 1979, 179, C29.

Isomerically-Rich [M(CO)2(P2P′)X]+/0
Inorganic Chemistry, Vol. 36, No. 6, 1997 1193
reflux times give a mixture of isomers of Re(CO)2(P2P′)Cl, but
longer reaction times (24 h) give only cis,mer-Re(CO)2(P2P′)-
Cl(I).
Diagrammatic representation of the two isomers of cis,mer-
Re(CO)2(P2P′)Cl are shown in Figure 7. Several conditions are
necessary to observe this type of isomerism and all must be
operative. (i) When coordinated, the polydentate ligand must
generate an unsymmetric environment on two sides of the metal.
(ii) None of the ligands can be labile, otherwise fluxional
coordinatively unsaturated intermediates would be formed which
would allow rapid interconversion of the isomers. (iii) There
must be two different groups in the trans positions, at least one
of which must be large enough to sterically block internal twist
mechanisms which would lead to isomerization. In cis,mer-
Re(CO)2(P2P′)Cl the halo ligand fulfills this requirement,
although the carbonyl group does allow twist mechanisms to
occur as evidenced by the M(CO)3(P2P′) systems and the
cis,mer-Re(CO)2(P2P′)Cl(I) h cis,fac-Re(CO)2(P2P′)Cl isomer-
ization.
Acknowledgment. We thank Dr. Alison Edwards, School
of Chemistry, University of Melbourne, for arranging for the
collection of crystallographic data. We thank Assoc. Prof. F.
R. Keene, James Cook University, Townsville, Australia, and
Prof. A. von Zelewsky, University of Fribourg, Switzerland,
for helpful comments on the isomerism of cis,mer-(I) and
cis,mer-(II). J.N.W. thanks the Commonwealth Government
of Australia for a Post Graduate Research Award. The financial
support of the Australian Research Council is gratefully
acknowledged.
Figure 7. Diagrammatic representations of the two isomers of cis,mer-
Re(CO)2(P2P′)Cl.
Supporting Information Available: Tables S-1-S-24 listing
positional parameters, anisotropic thermal parameters, hydrogen coor-
dinates, interatomic distances in the phenyl rings, least squares planes,
deviations from least squares planes, dihedral angles between least
squares planes, and intermolecular contacts less than 3.5 Å for both
structures, and figures showing packing diagrams for both structures
(48 pages). This material is contained in many libraries on microfiche,
immediately follows this article in the microfiche version of the journal,
can be ordered from the ACS, and can be downloaded from the Internet;
see any current masthead page for ordering information and Internet
access instructions.
via the fac isomer, if a twist mechanism is operative. The
following scheme can therefore be justified
cis,mer (I)
cis,mer (II)
(12)
cis,fac
However, these isomerizations do proceed at high tempera-
tures in refluxing mesitylene on the longer time scale since short
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