Synthesis and oxidation of chiral rhenium phosphine methyl complexes of the formula (η5-C5Me5)Re(NO)(PR3)(CH 3): In search of radical cations with enhanced kinetic stabilities

Article abstract of DOI:10.1016/S0022-328X(00)00528-3

Reactions of racemic [(η⁵-C₅Me₅)Re(NO)(NCCH ₃)(CO)]⁺ BF^-₄ and phosphines PR₃ (R = C₆H₅ a; 4-C₆H₄CH₃ b; 4-C₆H₄-t-C₄H₉ c; 4-C₆H₄C₆H₅ d; 4-C₆H₄OCH₃ e; C-C₆H₁₁ f) give the phosphine carbonyl complexes [(η⁵-C₅Me₅)Re(NO)(PR₃)(CO)] ⁺ BF^-₄ (5a-5f⁺ BF^-₄; 55-95%). These are treated with LiEt₃BH and then BH₃·THF to give the phosphine methyl complexes (η⁵-C₅Me₅)Re(NO)(PR₃)(CH ₃) (2a-2f, 50-86%). Cyclic voltammetry shows that the new compounds 2b-2f undergo chemically reversible one-electron oxidations that are thermodynamically more favorable than that of 2a (ΔE○ = 0.07, 0.07, 0.01, 0.09, 0.22 V; CH₂Cl₂). The radical cations 2^?+ X^- can be generated with Ag⁺ X^- or (η⁵-C₅H₅)₂Fe^?+ X^- (X^- = PF^-₆, SbF^-₆), as evidenced by IR and ESR spectra, but are labile and efforts to isolate pure salts fail. Reaction of 2a and TCNE give (η⁵-C₅Me₅)Re(NO)(η ²-TCNE)(CH₃), which is crystallographically characterized and proposed to form by initial electron transfer followed by radical chain substitution.

Full text of DOI:10.1016/S0022-328X(00)00528-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 616 (2000) 44–53
Synthesis and oxidation of chiral rhenium phosphine methyl
complexes of the formula (h5-C5Me5)Re(NO)(PR3)(CH3): in search
of radical cations with enhanced kinetic stabilities
Wayne E. Meyer a, Angelo J. Amoroso a, Monika Jaeger a, Jean Le Bras a,b,
Wing-Tak Wong c, J.A. Gladysz a,b,
*
a Department of Chemistry, Uni6ersity of Utah, Salt Lake City, UT 84112, USA
b Institut fu¨r Organische Chemie, Friedrich-Alexander Uni6ersita¨t Erlangen-Nu¨rnberg, Henkestrasse 42, 91054 Erlangen, Germany
c Department of Chemistry, The Uni6ersity of Hong Kong, Pokfulam Road, Hong Kong, China
Received 23 June 2000
Abstract
Reactions of racemic [(h5-C5Me5)Re(NO)(NCCH3)(CO)]+ BF4− and phosphines PR3 (R=C6H5 a; 4-C6H4CH3 b; 4-C6H4-t-
C4H9 c; 4-C6H4C6H5 d; 4-C6H4OCH3 e; c-C6H11 f) give the phosphine carbonyl complexes [(h5-C5Me5)Re(NO)(PR3)(CO)]+ BF−4
(5a–5f+ BF4−; 55–95%). These are treated with LiEt3BH and then BH3·THF to give the phosphine methyl complexes
(h5-C5Me5)Re(NO)(PR3)(CH3) (2a–2f, 50–86%). Cyclic voltammetry shows that the new compounds 2b–2f undergo chemically
reversible one-electron oxidations that are thermodynamically more favorable than that of 2a (DE°=0.07, 0.07, 0.01, 0.09, 0.22
+
5
+
V; CH2Cl2). The radical cations 2 X− can be generated with Ag+ X− or (h -C5H5)2Fe X− (X−=PF6−, SbF−6 ), as evidenced
by IR and ESR spectra, but are labile and efforts to isolate pure salts fail. Reaction of 2a and TCNE give (h5-C5Me5)Re(NO)(h2-
TCNE)(CH3), which is crystallographically characterized and proposed to form by initial electron transfer followed by radical
chain substitution. © 2000 Elsevier Science B.V. All rights reserved.
’
’
Keywords: Rhenium; Radical cations; Cyclic voltammetry; ESR; TCNE
1. Introduction
structural and electronic properties. However, the C6
and C8 homologs are dramatically less stable. Similar
trends have been described by Lapinte with iron end-
groups [5,6]. Nonetheless, he was able to isolate the C8
radical cation [(h5-C5Me5)Fe(dppe)(CCCCCCCC)-
There is intense interest, from both fundamental and
applied standpoints, in compounds where elemental sp
carbon chains span two transition metals [1]. Our own
studies have emphasized complexes in which at least
one endgroup is the chiral rhenium fragment (h5-
C5Me5)Re(NO)(P(C6H5)3) (I), which carries 17 valence
electrons as a neutral entity [2–4]. Species with
polyynediyl chains, –(CꢀC)n–, of up to 20 carbons can
be isolated [2b]. In the case of dirhenium C4 complexes
[(h5-C5Me5)Re(NO)(P(C6H5)3)(CCCC)((C6H5)3P)(ON)-
5
+
’
(dppe)Fe(h -C5Me5)] PF−6 in analytically pure form
[5b]. This synthetic triumph has never been equaled.
Accordingly, we have sought analogs of the end-
group I that would give more stable oxidation prod-
ucts. One obvious approach would be to utilize
phosphines that are more electron releasing than
triphenylphosphine. This should lead to thermodynami-
cally more favorable oxidations and E° values. From
linear free energy considerations, the rates of several
possible types of decomposition reactions (e.g. atom
abstraction, dimerization) would likely be retarded. An-
other approach would involve bulkier phosphines,
which should sterically inhibit all types of bimolecular
reactions. Alternatively, replacement of the nitrosyl lig-
Re(h5-C5Me5)]n+ nPF6− (1n+ nPF−6 ), the radical cation
+
’
1
PF−6 and dication 12+ 2PF−6 can also be synthe-
sized and isolated [2a]. These compounds, which are
illustrated in Scheme 1, exhibit a variety of fascinating
* Corresponding author. Tel.: +49-9131-8522540; fax: +49-9131-
8526865.
E-mail address: gladysz@organik.uni-erlangen.de (J.A. Gladysz).
0022-328X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00528-3

W.E. Meyer et al. / Journal of Organometallic Chemistry 616 (2000) 44–53
45
2. Results
2.1. Syntheses of phosphine complexes
The previously reported preparation of triphenyl-
phosphine complex 2a is shown in Scheme 2 [7].
Analogous procedures were found to work well for
other phosphines. First, the readily available cationic
dicarbonyl complex [(h5-C5Me5)Re(NO)(CO)2]+ BF−4
(3+ BF−4 ) [7] was combined with iodosobenzene in
acetonitrile to give the isolable monocarbonyl solvent
complex [(h5-C5Me5)Re(NO)(NCCH3)(CO)]+ BF−4 (4+
BF−4 ). This was subsequently treated, with or without
purification, with 1–2 equivalents of the phosphines
b–f (Scheme 2). The triarylphosphines b, e, which
feature electron-releasing p-methyl or p-methoxy
groups, are commercially available. The bulkier p-t-bu-
tyl homolog c is easily prepared [10], as is the p-phenyl
system d [11]. The latter was selected more for size and
possible crystallinity-enhancing characteristics than for
electronic properties. Tri(cyclohexyl)phosphine f is
commercially available, and distinctly more electron
releasing than triphenylphosphine [12].
Workups gave the new carbonyl phosphine com-
plexes [(h5-C5Me5)Re(NO)(PR3)(CO)]+ BF−4 (5b–5f+
BF−4 ) as air stable yellow powders. No attempts were
made to optimize yields, which ranged from 95% to
55%. Complexes 5b–5f+ BF−4 were characterized by
microanalysis, mass spectrometry, IR and NMR (1H,
13C, 31P) spectroscopies, as described in Section 4. In all
cases, properties closely matched those of the
triphenylphosphine complex 5a+ BF4−. The 13C-NMR
Scheme 1. Interconversion of the dirhenium C4 complexes 1n+ nPF6−
.
and, which is a good p acceptor, by a more basic ligand
should help. However, a three-electron donor would be
required, a somewhat less flexible or tunable ligand
class. This overall strategy can best be implemented by
substituting a two-electron donor ligand, and simulta-
neously changing to a metal with an additional valence
electron. In this way one arrives at the iron cyclopenta-
dienyl bis(phosphine) endgroups of Lapinte [5] and
related ruthenium systems of Bruce [6].
We set out to build the necessary foundation for
preparing C6 and C8 analogs of 1n+ nX− with more
electron releasing and bulkier phosphines. The first
objective was to synthesize methyl complexes of the
formula (h5-C5Me5)Re(NO)(PR3)(CH3) (2). The parent
triphenylphosphine compound (h5-C5Me5)Re(NO)(P-
(C6H5)3)(CH3) (2a) [7] is a key precursor to all higher
polyynediyl homologs of 1 [2,3]. The second objective
was to characterize the oxidation potentials of 2, and
conduct exploratory preparative reactions. We noted
earlier that cyclic voltammograms of 2a show chemi-
cally reversible one-electron oxidations [3a]. However,
attempts to isolate radical cations 2a + X− have to date
’
failed. Improved kinetic stabilities with any of the new
phosphine ligands would likely be mirrored in the
corresponding C6 and C8 dirhenium radical cations.
In this paper, we report syntheses of five new com-
plexes of the formula 2, each featuring a readily avail-
able phosphine that is a stronger donor and/or bulkier
than triphenylphosphine. Their oxidation potentials
+
and reactions that give labile radical cations 2 X−
’
are described. In the following paper [8], we report the
isolation and crystal structure of one such radical
cation, and diverse supporting experiments that help to
interpret its physical and chemical properties. In future
papers [9], we will detail analogous complexes of new,
heretofore unprecedented classes of phosphines, and
their successful applications to the carbon chain com-
plex chemistry outlined above.
Scheme 2. Synthesis of rhenium phosphine complexes.

46
W.E. Meyer et al. / Journal of Organometallic Chemistry 616 (2000) 44–53
spectra showed doublets for the CO ligands at 209.9 to
201.0 ppm (JCP=7.9–8.5 Hz). The IR wCO and wNO data
are summarized in Table 1. The tri(cyclo-
hexyl)phosphine complex 5f+ BF4− gave slightly lower
values, indicating enhanced backbonding to the car-
bonyl and nitrosyl ligands, consistent with the high
phosphine basicity. The tri(p-(phenyl)phenyl)phosphine
complex 5d+ BF4− gave slightly higher values. The
others gave values that were identical within experimen-
tal error.
C5Me5)Re(NO)(PR3)(CH3) (2b–2f) in 50–86% unopti-
mized yields. The one-step NaBH4 reduction used in the
cyclopentadienyl series [13] afforded poorer yields.
Complexes 2b–2f were air sensitive red powders or
crystals that were stored under nitrogen. Their benchtop
stabilities were noticeably greater in the arid Salt Lake
City climate than the humid Erlangen, Germany cli-
mate. They were characterized analogously to 5b–5f+
BF−4 , and properties closely matched those of 2a. The
13C-NMR spectra of 2b–2f showed doublets for the
methyl ligands at −21.6 to −27.3 ppm (JCP=6.6–8.7
Hz). The IR wNO values (Table 1) showed a greater
spread than with 5b–5f+ BF−4 . Analogous sequences
were conducted with PMe3 and P(CH2CH2-n-C6F11)3
Complexes 5b–5f+ BF4− were treated with LiEt3BH
and then BH3·THF (Scheme 2). This two-step reduc-
tion, which involves an intermediate formyl complex [7],
gave the target methyl phosphine complexes (h5-
Chart 1. Cyclic voltammetry data for methyl complexes 2a–f.

W.E. Meyer et al. / Journal of Organometallic Chemistry 616 (2000) 44–53
47
Table 1
complexes 2e and 2f. The latter was the easiest to
oxidize, comparable to the dirhenium C4 complex 1
(Scheme 1). The separations of the anodic and cathodic
peaks varied from 70 to 120 mV, reflecting fine points
and gradations of reversibilities that remain under
investigation.
Key IR data (cm−1, CH2Cl2)
Complex
wNO
wCO
5a+ BF−4
5b+ BF−4
5c+ BF−4
5d+ BF−4
5e+ BF−4
5f+ BF−4
2a
2b
2c
2d
2e
1741
1743
1743
1745
1742
1737
1606
1603
1601
1606
1594
1599
2002
2002
2002
2006
2001
1993
Preparative oxidations were investigated next. Both
silver and ferrocenium cations are effective with 1 [2].
Accordingly, 2a–2d, 2f and Ag+ PF6− (1 equivalent) or
5
+
(h -C5H5)2Fe X− (X−=PF6− or SbF−6 ; 1–1.5 equiv-
alent)[17] were combined in CH2Cl2 as shown in Chart
2. In all cases, solutions darkened. IR monitoring
showed shifts of the wNO bands from 1599–1606 to
1710–1720 cm−1, consistent with the reduced back-
’
2f
bonding that would be expected in radical cations
+
’
2a–2d, 2f
X−. This is approximately twice the shift
[14]. Data on these carbonyl and methyl complexes,
which did not advance the objectives of this study and
were only partially characterized, are presented else-
where [15].
found upon generation of the mixed valence radical
cation 1
+
’
PF−6 (Scheme 1), in which the positive
charge is delocalized between two rheniums. The prod-
ucts were stable for hours in solution at room tempera-
ture. Repeated efforts were made to isolate or
2.2. Oxidations
crystallize these species. The PF−6 salts were not stable
+
in the solid state, but solid 2a SbF−6 was stable for
’
Cyclic voltammograms of 2b–2f were recorded in
CH2Cl2. The conditions and data are summarized in
Chart 1 [16] which contains a representative trace. All
5–15 min under nitrogen.
Additional evidence for the formation of 2 + X− was
’
sought. Thus, representative ESR spectra were
complexes exhibited chemically reversible one-electron
recorded, as illustrated in Chart 2. Sextets were ob-
served, similar to a spectrum of 2a
+
+
’
PF−6 reported
’
oxidations, presumably representing radical cations 2
X−, and no further reversible oxidations at potentials
as high as 1.2 V. All were thermodynamically easier to
oxidize than 2a. The E° values tracked the IR wNO
earlier [3a]. The individual lines were broad, and the
Aiso,Re values ranged from 185 to 206 G (a, 197; b, 185;
c, 198; d, 206; f, 193 G). The multiplicity follows from
the 5/2 nuclear spin of the principle rhenium isotopes
values, except for
a
reversal with the tri(p-
methoxyphenyl)phosphine and tri(cyclohexyl)phosphine
(
185Re, 187Re), which have nearly identical magnetic
Chart 2.

48
W.E. Meyer et al. / Journal of Organometallic Chemistry 616 (2000) 44–53
Table 2
Crystallographic data for 6
Molecular formula
Fomula weight
C17H18N5ORe
494.57
Crystal dimensions (mm)
Crystal system
Space group
0.22×0.24×0.34
Monoclinic
P21/n
Unit cell dimensions
,
a (A)
9.294(1)
13.728(1)
14.089(1)
91.22(2)
1797.2(2)
4
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
T (K)
296
1.828
1.80
67.78
Dcalc (g cm−3
)
Scheme 3. Reaction with TCNE.
Dfound (g cm−3) (CH3I/CCl4)
Absorption coefficient (cm−1
F(000)
)
moments. Importantly, the Aiso,Re values are approxi-
952
mately twice that of the delocalized dirhenium radical
+
cation 1 PF−6 (98 G). No other couplings have ever
Diffractometer
Radiation (A)
2q Range (°)
Scan type
MAR research image plate
0.71073 (Mo–Ka)
2.0–51.3
ꢀ-rotation
65
8
120
’
,
been resolved in this series of compounds. Two isomeric
rhenium centered radicals of the formula [Re(CO)3-
(P(C–C6H11)3)2] gave Aiso,Re values of 190 and 156 G,
respectively [18].
No. of frames
Exposure per frame (min)
Detector distance (mm)
Index ranges (h, k, l)
Reflections collected
Independent reflections
Observed reflections
Weighting scheme
R, Rw
Goodness-of-fit
D/| (max)
Number of parameters
0–11, 0–16, −17–17
31488
2.3. Reaction with TCNE
3336 (Rint=0.038)
2231 [I\3|(I)]
w=1/|2(Fo), p=0.002
0.036, 0.030
S=2.20
0.01
226
1.10
In the course of the exploratory oxidation chemistry
described above, 2a and TCNE were combined in ben-
zene as shown in Scheme 3. TCNE is well known to serve
as a one-electron oxidant. However, it is thermodynam-
a
5
+
’
ically more difficult to reduce than (h -C5H5)2Fe X−,
with a difference of 270 mV in CH3CN [16b]. Hence, it
is a weaker oxidant, and the E° data in Chart 1 indicate
−3
,
D/z (max) (e A
)
a R=ꢀ(ꢁꢁFoꢁ−ꢁFcꢁꢁ)/ꢀ(ꢁFoꢁ); Rw=[ꢀ(w(ꢁFoꢁ−ꢁFcꢁ)2/ꢀ(wꢁFoꢁ )]1/2
.
2
that it would not necessarily give complete conversion to
2a TCNE −. Interestingly, an IR spectrum showed a
rapid and quantitative reaction, with a much larger shift
of the wNO band (1606 to 1753 cm−1) than for the
oxidations in Chart 2. A crystalline, diamagnetic
product 6 was isolated in high yield. The 1H and
13C-NMR spectra showed methyl ligand signals that
were no longer coupled to phosphorus. No 31P-NMR
signal could be detected. A strong IR band at 2234 cm−1
suggested the presence of cyano groups. Mass spectral
and microanalytical data were consistent with the for-
mulation (h5-C5Me5)Re(NO)(h2-TCNE)(CH3) (6).
In order to establish unequivocally the identity of 6,
a crystal structure was determined as outlined in Table
2 and Section 4. Fig. 1 confirms the proposed formula-
tion, and Table 3 lists key bond lengths and angles.
Structural features and mechanistic implications are
analyzed below.
+
’
’
3. Discussion
Chart
1 shows that the replacement of the
Fig. 1. Molecular structure of TCNE complex 6.
triphenylphosphine ligand in 2a by more electron-re

W.E. Meyer et al. / Journal of Organometallic Chemistry 616 (2000) 44–53
49
Table 3
+
’
paper [8], when the radical cations 2 are paired with
appropriate bulky anions, dramatic stability enhance-
ments can be achieved.
,
Key bond lengths (A) and angles (°) for 6
Bond lengths
Re(1)–N(1)
Re(1)–C(2)
Re(1)–C(4)
Re(1)–C(11)
Re(1)–C(13)
N(2)–C(14)
N(4)–C(17)
C(1)–C(2)
C(1)–C(6)
C(2)–C(7)
C(3)–C(8)
C(4)–C(9)
1.755(6) Re(1)–C(1)
2.302(8) Re(1)–C(3)
2.364(7) Re(l)–C(5)
2.332(8)
2.296(8)
2.357(7)
2.171(8)
1.174(7)
1.116(9)
1.133(10)
1.44(1)
1.43(1)
1.448(10)
1.40(1)
1.541(9)
1.44(1)
1.46(1)
The reaction of 2a and TCNE (Scheme 3) highlights
yet another potential complication in the quest for
isolable 17 valence electron organometallic compounds:
their well documented substitution lability [22,23]. We
are aware of one close literature precedent for the
formation of TCNE complex 6, the replacement of an
iron carbonyl ligand shown in Scheme 4 [24]. These
investigators proposed a radical chain mechanism, con-
sistent with extensive studies by Kochi with (h5-
C5H5)M(L)(L%)(L¦) complexes related to 2 [23]. The
probable sequence of steps in both the iron and rhe-
nium reactions is generalized at the bottom of Scheme
4.
2.18(1)
Re(1)–C(12)
2.186(8) O(1)–N(1)
1.152(10) N(3)–C(15)
1.133(9) N(5)–C(16)
1.42(1)
1.49(1)
1.50(1)
1.49(1)
1.47(1)
1.49(1)
1.48(1)
1.42(1)
C(1)–C(5)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(10)
C(12)–C(14)
C(13)–C(16)
C(12)–C(13)
C(12)–C(15)
C(13)–C(17)
Re(1)–C5Me5(centroid) 1.987
Bond angles
Our TCNE complex belongs to a large class of
compounds of the general formula (h5-C5R5)M(XO)-
(h2-CꢁY)(Z), the structural and electronic properties of
which have been extensively analyzed [25]. Such com-
plexes are formally octahedral, as evidenced by the
91.2(4)° ON–Re–CH3 bond angle in 6. The conforma-
tion of the TCNE ligand maximizes overlap of the CꢁC
p* acceptor orbital with the one rhenium d orbital that
cannot backbond into the nitrosyl ligand. This lies in a
plane perpendicular to the rhenium–nitrosyl bond. Ac-
cordingly, the plane defined by rhenium and the ligat-
ing TCNE carbons makes 7.8° and 101.6° angles with
the Re–CH3 and Re–NO bonds, respectively. Struc-
tures of TCNE complexes have also been extensively
analyzed [26]. The (NC)2C–C(CN)2 bond length
N(1)–Re(1)–C(11)
N(1)–Re(1)–C(12)
C(11)–Re(1)–C(12) 120.5(4) C(11)–Re(1)–C(13)
C(12)–Re(1)–C(13) 39.9(3) Re(1)–C(12)–C(13)
Re(1)–C(12)–C(14) 114.5(5) Re(1)–C(12)–C(15)
91.2(4) N(1)–Re(1)–C(13)
91.7(3) N(2)–C(14)–C(12)
98.7(3)
176.4(10)
81.0(4)
70.6(5)
122.7(6)
177(1)
176.7(10)
115.0(7)
69.5(5)
114.0(6)
118.3(7)
Re(1)–N(1)–O(1)
N(4)–C(17)–C(13)
172.6(7) N(3)–C(15)–C(12)
176(1) N(5)–C(16)–C(13)
C(13)–C(12)–C(14) 118.2(7) C(13)–C(12)–C(15)
C(14)–C(12)–C(15) 110.8(7) Re(1)–C(13)–C(12)
Re(1)–C(13)–C(16) 115.7(5) Re(1)–C(13)–C(17)
C(12)–C(13)–C(16) 118.5(7) C(12)–C(13)–C(17)
C(16)–C(13)–C(17) 113.6(8)
leasing triaryl- or trialkylphosphines can render oxida-
tion up to 0.220 V thermodynamically more favorable.
Interestingly, while this work was in progress an elec-
trochemical study of related cyclopentadienyl iron ace-
tyl complexes (h5-C5H5)Fe(CO)(PR3)(COMe) (7) was
published [19]. The differences in E° values between the
triphenylphosphine complex 7a and tri(p-methyl-
phenyl)-, tri(p-methoxyphenyl)-, and tri(cyclohexyl)-
phosphine complexes 7b, e, f (CH3CN, 20°C: 0.028,
0.044, 0.197 V) were similar to those between 5a and
5b, e, f (0.07, 0.09, 0.22 V). An analogous trend has
been reported for the cobalt bis(phosphine) complexes
[Co(CNCMe3)3(PR3)2]+ ClO4− [20].
,
(1.49(1) A) is consistent with a metallacyclopropane
resonance form. Together with the IR wCN value of
\2200 cm−1, this indicates a formal TCNE oxidation
state of −II, and thus a formal rhenium oxidation
state of +III.
In summary, this paper has described our ‘first gener-
ation’ approach to longer chain homologs of the C4
dirhenium radical cation 1 + X− and dication 12+ 2X−
’
with improved stabilities. The relatively inauspicious
Although the radical cations 2 + X− are easily gener-
’
ated and spectroscopically characterized, the phosphine
ligands investigated are not in themselves sufficient to
render them easily isolable. In the absence of mechanis-
tic studies, one can only speculate on the exact prob-
lem. For example, the less bulky and less electron-rich
cyclopentadienyl radical [(h5-C5H5)Re(NO)(P(C6H5)3)-
+
’
(CH3)] PF−6 undergoes a rapid second-order decom-
position in acetonitrile (DH‡=0.1 kcal mol−1, DS‡=
−46 eu) to give methane (0.5 equivalent), the
methylidene complex [(h5-C5H5)Re(NO)(P(C6H5)3)(=
CH2)]+ PF−6 (0.5 equivalent), and the acetonitrile com-
plex [(h5-C5H5)Re(NO)(P(C6H5)3)(NCCH3)]+ PF−6 (0.5
equivalent) [21]. However, as detailed in the following
Scheme 4. Literature precedent for substitution by TCNE and proba-
ble mechanism.

50
W.E. Meyer et al. / Journal of Organometallic Chemistry 616 (2000) 44–53
+
beginnings with model compounds 2b–2f X− are in
fact mirrored in the corresponding C6 and C8 com-
plexes [15]. However, from the standpoint of a strategic
step in an ultimately successful quest [9], these data
provide an instructive example of design and tactics in
targeted organometallic synthesis.
l=13.7 (s). MS [31] 684 (5b+). Anal. Calc. for
C32H36NO2PReBF4: C 49.88, H 4.71. Found: C 49.62,
H 4.80%.
’
4.3. [(p5-C5Me5)Re(NO)(P(4-C6H4-t-C4H9)3)(CO)]+
BF−4 (5c+ BF−4 )
Reactions analogous to those for 5b+ BF4− were
conducted with CH3CN (60 ml), 3+ BF4− (0.427 g,
0.864 mmol), iodosobenzene (0.199 g, 0.907 mmol),
P(4-C6H4-t-C4H9)3 (0.548 g, 1.274 mmol) [10], and 2-
butanone (60 ml). An identical workup gave 5c+ BF4−
as a yellow powder (0.429 g, 0.478 mmol, 55%), m.p.
4. Experimental
4.1. General data
General procedures and solvent purifications were
identical to those in two recent papers [2b,27], and are
further detailed elsewhere [15]. Reducing agents,
TCNE, and phosphines for which no citations are
provided were obtained from common commercial ven-
dors and used without purification. Cyclic voltammetry
was conducted as previously described [2]. ESR mea-
surements utilized a Bruker ESP-300E spectrometer
equipped with an ER 4116 DM dual mode X-band
cavity and an Oxford Instruments ESR-900 helium flow
cryostat. Spectra were recorded at a sweep rate of 100
G s−1 and a microwave frequency of 9.65 GHz (precise
microwave frequencies were recorded for individual
spectra to ensure precise g-alignment; modulation fre-
quency and amplitude, 100 kHz and 12.6 G).
1
299–300°C dec. [30]. H-NMR (CD2Cl2) [32]: l=7.57
(dd, JHP=2.4 Hz, JHH=8.4 Hz, 3m-C6H4), 7.32 (dd,
J
HP=12.0 Hz,
C5(CH3)5), 1.34 (s, 3ArC(CH3)3). 13C{1H} l=201.6 (d,
CP=7.9 Hz, CO), 156.6 (d, JCP=2.1 Hz, p-C6H4),
JHH=8.4 Hz, 3o-C6H4), 1.94 (s,
J
133.3 (d, JCP=11.8 Hz, o-C6H4), 127.4 (d, JCP=60.2
Hz, i-C6H4), 127.0 (d, JCP=11.4 Hz, m-C6H4), 106.6 (s,
C5(CH3)5), 35.5 (s, ArC(CH3)3), 31.3 (s, ArC(CH3)3),
10.2 (s, C5(CH3)5). 31P{1H} l=12.0 (s). MS [31] 810
(5c+). Anal. Calc. for C41H54BF4NO2PRe: C 54.91, H
6.07. Found: C 54.79, H, 6.06%.
4.4. [(p5-C5Me5)Re(NO)(P(4-C6H4C6H5)3)(CO)]+ BF−4
(5d+ BF−4 )
4.2. [(p5-C5Me5)Re(NO)(P(4-C6H4CH3)3)(CO)]+ BF−4
(5b+ BF−4 )
A
Schlenk flask was charged with [(h5-
C5Me5)Re(NO)(NCCH3)(CO)]+ BF4− (4+ BF4− [7];
1.050 g, 2.070 mmol), P(4-C6H4C6H5)3 (1.070 g, 2.181
mmol) [11], and 2-butanone (10 ml). The mixture was
refluxed (3 h), and concentrated by rotary evaporation
(ca. 3 ml). The solution was poured into rapidly stirred
Et2O (200 ml). The yellow precipitate was isolated by
filtration and air dried to give 5d+ BF4− (1.870 g, 1.950
mmol, 95%), m.p. 268–270°C dec. [30]. 1H-NMR
(CD2Cl2) [32]: l=7.87 (dd, JHP=2.4 Hz, JHH=8.4
Hz, 3m-C6H4), 7.70 (br d, JHH=8.0 Hz, 3o-C6H4),
7.6–7.4 (m, 3C6H5) 2.04 (s, C5(CH3)5). 13C{1H} l=
201.0 (d, JCP=8.2 Hz, CO), 145.6 (d, JCP=2.7 Hz,
p-C6H4), 139.3 (d, JCP=1.1 Hz, i-C6H5), 134.0 (d,
A Schlenk flask was charged with CH3CN (100 ml)
and [(h5-C5Me5)Re(NO)(CO)2]+ BF4− (3+ BF−4 [7];
1.001 g, 2.020 mmol), and cooled to 0°C. Then iodo-
sobenzene (0.450 g, 2.020 mmol) [28] was added with
stirring. The cold bath was removed. The solution was
kept 3 h at room temperature [29], and the solvent was
removed by rotary evaporation. The dark oily residue
was washed with Et2O (2×50 ml). Then P(4-
C6H4CH3)3 (1.220 g, 4.011 mmol) and 2-butanone (100
ml) were added. The mixture was refluxed. After 3 h,
the solvent was removed by rotary evaporation. The
gold solid was transferred to a fritted glass funnel,
washed with hexane (10 ml) and Et2O (3×20 ml), and
dissolved in a minimum of acetone. The solution was
layered with Et2O, and stored at −20°C. After 2 days,
a yellow powder was isolated by filtration, washed with
Et2O (10 ml), and air dried to give 5b+ BF4− (1.051 g,
1.360 mmol, 68%), m.p. 247–249°C [30]. 1H-NMR
([D6]acetone) [32]: l=7.47 (br d, JHH=6.6 Hz, 3m-
C6H4), 7.34 (dd, JHP=12.0 Hz, JHH=8.0 Hz, 3o-
C6H4), 2.43 (s, 3ArCH3), 2.04 (s, C5(CH3)5). 13C{1H}
l=209.9 (d, JCP=7.9 Hz, CO), 143.7 (s, p-C6H4),
133.9 (d, JCP=12.3 Hz, o-C6H4), 131.0 (d, JCP=12.1
Hz, m-C6H4), 128.1 (d, JCP=59.8 Hz, i-C6H4), 107.2 (s,
C5(CH3)5), 21.4 (s, ArCH3), 10.1 (s, C5(CH3)5). 31P{1H}
J
CP=11.8 Hz, o-C6H4), 129.6 (s, o-C6H5), 129.2 (s,
p-C6H5), 129.0 (d, JCP=59.0 Hz, i-C6H4), 128.6 (d,
J
J
CP=11.5 Hz, m-C6H4), 127.7 (s, m-C6H5), 106.8 (br d,
CP=0.8 Hz, C5(CH3)5), 10.4 (s, C5(CH3)5). 31P{1H}
l=13.4 (s). MS [31] 870 (5d+). Anal. Calc. for
C47H42BF4NO2PRe: C 59.00, H 4.42. Found: C 58.93,
H 4.51%.
4.5. [(p5-C5Me5)Re(NO)(P(4-C6H4OCH3)3)(CO)]+ BF−4
(5e+ BF−4 )
A reaction analogous to that for 5d+ BF4− was
conducted with 4+ BF4− (0.426 g, 0.833 mmol), P(4-
C6H4OCH3)3 (0.380 g, 1.08 mmol), and 2-butanone (20
ml). An identical workup gave 5e+ BF4− as a yellow

W.E. Meyer et al. / Journal of Organometallic Chemistry 616 (2000) 44–53
51
4.8. (p5-C5Me5)Re(NO)(P(4-C6H4-t-C4H9)3)(CH3) (2c)
powder (0.490 g, 0.598 mmol, 72%), m.p. 235–237°C
1
dec. [30]. H-NMR (CD2Cl2) [32]: l=7.26 (dd, JHP
12 Hz, JHH=9 Hz, 3o-C6H4), 7.06 (dd, JHP=1.8 Hz,
HH=9 Hz, 3m-C6H4), 3.87 (s, 3OCH3), 1.98 (s,
=
A reaction analogous to that for 2b was conducted
with THF (10 ml), 5c+ BF−4 (0.258 g, 0.287 mmol),
LiEt3BH (1.0 M in THF; 0.70 ml, 0.70 mmol), and
BH3·THF (1.0 M in THF; 1.70 ml, 1.70 mmol). An
identical workup gave 2c as an orange powder (0.123 g,
J
C5(CH3)5). 13C{1H} l=201.5 (d, JCP=8.5 Hz, CO),
162.9 (s, p-C6H4), 134.9 (d, JCP=13.1 Hz, o-C6H4),
121.7 (d, JCP=63.8 Hz, i-C6H4), 115.4 (d, JCP=12.0
Hz, m-C6H4), 106.4 (s, C5(CH3)5), 56.1 (s, OCH3), 10.3
(s, C5(CH3)5). 31P{1H} l=10.1 (s). MS [31] 732 (5e+).
Anal. Calc. for C32H36BF4NO5PRe: C 46.95, H 4.43.
Found: C 46.81, H 4.38%.
1
0.154 mmol, 53%), m.p. 271–273°C dec. [30]. H-NMR
(C6D6) [32]: l=7.70 (dd, JHP=10 Hz, JHH=8.6 Hz,
3o-C6H4), 7.20 (dd, JHP=1.8 Hz, JHH=8.7 Hz, 3m-
C6H4), 1.62 (s, C5(CH3)5), 1.40 (d, JHP=6.6 Hz,
ReCH3), 1.12 (s, 3C(CH3)3). 13C{1H} l=152.9 (d,
J
CP=2.0 Hz, p-C6H4), 134.7 (d, JCP=10.6 Hz, o-
4.6. [(p5-C5Me5)Re(NO)(P(c-C6H11)3)(CO)]+ BF−4 (5f+
BF−4 )
C6H4), 134.5 (d, JCP=50 Hz, i-C6H4; one line at 134.1,
other obscured by o-C6H4 signal), 125.7 (d, JCP=10.0
Hz, m-C6H4), 98.3 (s, C5(CH3)5), 34.9 (s, C(CH3)3),
A reaction analogous to that for 5d+ BF4− was
conducted with 4+ BF4− (0.101 g, 0.200 mmol), P(c-
C6H11)3 (0.056 g, 0.200 mmol), and 2-butanone (15 ml).
An identical workup gave 5f+ BF4− as a yellow powder
(0.103 g, 0.138 mmol, 70%), m.p. 189–190°C [30].
1H-NMR (CDCl3) [32]: l=2.18 (s, C5(CH3)5), 2.17–
1.65, 1.45–1.15 (2m, 3C6H11). 13C{1H} l=204.5 (d,
31.6 (s, C(CH3)3), 10.1 (s, C5(CH3)5), −21.8 (d, JCP
=
6.9 Hz, ReCH3). 31P{1H} l=23.2 (s). MS [31] (2c+).
Anal. Calc. for C41H57NOPRe: C 61.78, H 7.21. Found:
C 61.87, H 7.24%.
4.9. (p5-C5Me5)Re(NO)(P(4-C6H4C6H5)3)(CH3) (2d)
J
CP=8.5 Hz, CO), 105.9 (s, C5(CH3)5), 37.6 (d, JCP=
A reaction analogous to that for 2b was conducted
with THF (10 ml), 5d+ BF−4 (0.526 g, 0.550 mmol),
LiEt3BH (1.0 M in THF; 1.40 ml, 1.40 mmol), and
BH3·THF (1.0 M in THF; 3.30 ml, 3.30 mmol). An
identical workup gave 2d as an orange powder (0.402 g,
25.5 Hz, PCH), 30.7 (s, CH2), 30.0 (d, JCP=3.0 Hz,
CH2), 27.3 (d, JCP=3.0 Hz, CH2), 27.2 (d, JCP=3.0
Hz, CH2), 26.0 (s, CH2), 10.8 (s, C5(CH3)5). 31P{1H}
l=25.6 (s). MS [31] 660 (5f+). Anal. Calc. for
C29H48BF4NO2PRe: C 46.65, H 6.48. Found: C 46.77,
H 6.55%.
1
0.470 mmol, 71%), m.p. 165–168°C dec. [30]. H-NMR
(C6D6) [32]: l=7.81 (dd, JHP=9.9 Hz, JHH=8.4 Hz,
3o-C6H4), 7.50–7.39 (m, 12H of 3PAr3), 7.23–7.08 (m,
9H of 3PAr3), 1.66 (s, C5(CH3)5), 1.45 (d, JHP=6.9 Hz,
ReCH3). 13C{1H} (CD2Cl2) l=144.8 (d, JCP=2.7 Hz,
p-C6H4), 142.6 (d, JCP=2.0 Hz, i-C6H5), 140.4 (s,
p-C6H5), 134.9 (d, JCP=10.9 Hz, o-C6H4), 129.1 (s,
o-C6H5), 128.2 (d, JCP=46.4 Hz, i-C6H4), 127.4 (s,
m-C6H5), 127.1 (d, JCP=10.0 Hz, m-C6H4), 98.2 (d,
4.7. (p5-C5Me5)Re(NO)(P(4-C6H4CH3)3)(CH3) (2b)
A Schlenk flask was charged with THF (10 ml) and
5b+ BF−4 (0.200 g, 0.261 mmol). Then LiEt3BH (1.0 M
in THF; 0.64 ml, 0.64 mmol) was added to the suspen-
sion with stirring. After 10 min, BH3·THF (1.0 M in
THF; 0.64 ml, 0.64 mmol) was added to the honey
solution. After 0.5 h, solvent was removed from the red
solution by oil pump vacuum. The residue was ex-
tracted with a minimum of benzene. The extract was
passed through a silica gel column (2.5×6 cm). The
solvent was removed by rotary evaporation and then oil
pump vacuum to give 2b as an orange powder (0.150 g,
J
CP=2.0 Hz, C5(CH3)5), 9.8 (s, C5(CH3)5), −22.1 (d,
J
CP=6.7 Hz, ReCH3). 31P{1H} (C6D6) l=25.6 (s). MS
[31] 857 (2d+). Anal. Calc. for C47H45NOPRe: C 65.87,
H 5.29. Found: C 65.70, H, 5.51%.
4.10. (p5-C5Me5)Re(NO)(P(4-C6H4OCH3)3)(CH3) (2e)
A reaction analogous to that for 2b was conducted
with THF (10 ml), 5e+ BF−4 (0.100 g, 0.122 mmol),
LiEt3BH (1.0 M in THF; 0.25 ml, 0.25 mmol), and
BH3·THF (1.0 M in THF; 0.50 ml, 0.50 mmol). An
identical workup gave 2e as an orange powder (0.044 g,
1
0.224 mmol, 86%), m.p. 185–186°C dec. [30]. H-NMR
(C6D6) [32]: l=7.58 (dd, JHP=10.3 Hz, JHH=8.0 Hz,
3o-C6H4), 6.93 (br d, JHH=7.3 Hz, 3m-C6H4), 2.00 (s,
3ArCH3), 1.62 (s, C5(CH3)5), 1.35 (d, JHP=6.8 Hz,
ReCH3). 13C{1H} l=139.5 (s, p-C6H4), 134.4 (d,
1
0.061 mmol, 50%), m.p. 180–181°C dec. [30]. H-NMR
JCP=10.8 Hz, o-C6H4), 134.0 (d, JCP=49.1 Hz, i-
(C6D6) [32]: l=7.60 (dd, JHP=10 Hz, JHH=8.8 Hz,
3o-C6H4), 6.74 (dd, JHP=1.2 Hz, JHH=8.8 Hz, 3m-
C6H4), 3.22 (s, 3OCH3), 1.64 (s, C5(CH3)5), 1.41 (d,
C6H4), 129.1 (d, JCP=10.0 Hz, m-C6H4), 97.9 (s,
C5(CH3)5), 21.2 (s, ArCH3), 9.9 (s, C5(CH3)5), −22.1
(d, JCP=6.6 Hz, ReCH3). 31P{1H} l=24.5 (s). MS [31]
671 (2b+). Anal. Calc. for C32H39NOPRe: C 57.29, H
5.86. Found: C 57.23, H, 5.84%.
J
HP=6.7 Hz, ReCH3). 13C{1H} l=161.4 (s, p-C6H4),
136.2 (br s, o-C6H4), 129.1 (d, JCP=52 Hz, i-C6H4),
114.3 (d, JCP=9.6 Hz, m-C6H4), 98.3 (s, C5(CH3)5),

52
W.E. Meyer et al. / Journal of Organometallic Chemistry 616 (2000) 44–53
55.1 (s, OCH3), 10.4 (s, C5(CH3)5), −21.6 (d, JCP=7.0
Hz, ReCH3). 31P{1H} l=21.9 (s). MS [31] 719 (2e+).
Anal. Calc. for C32H39NO4PRe: C 53.47, H 5.47. Found:
C 53.33, H 5.44%.
5. Supplementary material
Atomic coordinates and other data for 6 have been
deposited with the Cambridge Crystallographic Data
Centre as supplementary publication CCDC no. 140673.
Copies of this information can be obtained free on
application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336033;
e-mail deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
4.11. (p5-C5Me5)Re(NO)(P(c-C6H11)3)(CH3) (2f)
A reaction analogous to that for 2b was conducted with
THF (10 ml), 5f+ BF4− (0.374 g, 0.500 mmol), LiEt3BH
(1.0 M in THF; 0.50 ml, 0.50 mmol), and BH3·THF (1.0
M in THF; 1.00 ml, 1.00 mmol). An identical workup gave
2f as an orange powder (0.210 g, 0.325 mmol, 65%), m.p.
169–171°C [30]. 1H-NMR (CDCl3) [32]: l=1.85 (s,
C5(CH3)5), 2.15–1.60, 1.55–1.30 (2m, 3C6H11), 0.73 (br
s, ReCH3). 13C{1H} l=97.4 (s, C5 (CH3)5), 36.9 (d,
Acknowledgements
We thank the US National Science Foundation and
Deutsche Forschungsgemeinschaft (DFG, GL 300/1-1)
for support, and Professor R. Holz and Dr B. Bennett
(Utah State University) for assistance with the ESR
spectra.
JCP=23.2 Hz, PCH), 30.1 (s, CH2), 29.5 (s, CH2), 28.0,
27.8, 27.7 (overlapping d, 2CH2), 26.8 (s, CH2), 10.6 (s,
C5(CH3)5), −27.3 (d, JCP=8.7 Hz; ReCH3). 31P{1H}
l=18.5 (s). MS [31] 647 (2f+). Anal. Calc. for
C29H51NOPRe: C 53.84, H 7.95. Found: C 53.48, H
7.79%.
References
4.12. (p5-C5Me5)Re(NO)(p2-TCNE)(CH3) (6)
[1] Reviews covering subsections of this field: (a) M. Akita, Y.
Moro-oka, Bull. Chem. Soc. Jpn. 68 (1995) 420. (b) M.I. Bruce,
Coord. Chem. Rev. 166 (1997) 91. (c) F. Paul, C. Lapinte,
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[2] Full papers most relevant to the present study: (a) M. Brady, W.
Weng, Y. Zhou, J.W. Seyler, A.J. Amoroso, A.M. Arif, M.
Bo¨hme, G. Frenking, J.A. Gladysz, J. Am. Chem. Soc. 119
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Bartik, J.A. Ramsden, A.M. Arif, J.A. Gladysz, J. Am. Chem.
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A Schlenk flask was charged with 2a (0.063 g, 0.10
mmol) [7] and benzene (10 ml). A solution of TCNE (0.013
g, 0.010 mmol) in benzene (10 ml) was slowly added with
stirring [28]. After 1 h, the solvent was removed by oil
pump vacuum. The residue was washed with hexane
(2×5 ml) and Et2O (5 ml), and dissolved in a minimum
of CH2Cl2. The solution was layered with hexane. After
24 h, the dark yellow blocks were collected by filtration
and dried by oil pump vacuum to give 6 (0.040 g, 0.081
mmol, 81%), m.p. 232–235°C dec. IR (CH2Cl2): wCꢀN
=
2234 cm−1 w wNO=1753 s. H-NMR [32] (CD3CN):
l=2.01 (s, C5(CH3)5), 1.49 (s, ReCH3). 13C{1H}
(CD2Cl2): l=115.2, 115.1, 113.4, 113.2 (4s, 4CN), 110.0
(s, C5(CH3)5), 22.0, 11.0 (2s, 2CCN), 9.1 (s, C5(CH3)5),
0.88 (s, ReCH3). MS [31] 496 (6+). Anal. Calc. for
C17H18N5ORe: C 41.29, H 3.67. Found: C 41.48, H 3.61%.
1
4.13. Crystallography
Data were collected on 6 as outlined in Table 2. The
space group was determined from a Laue symmetry check
and systematic absences, and confirmed by subsequent
refinement. Lorentz and polarization (but no absorption)
corrections were applied. The structure was solved by
Patterson methods and expanded by Fourier difference
techniques. This model was refined by full-matrix least-
squares analysis on F, with all atoms anisotropic. Hydro-
gen atom positions were calculated. Scattering factors
were taken from the literature. Anomalous dispersion
effects were included in Fc. Calculations were performed
on a Silicon-Graphics computer, using the TEXSAN
software package.
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Organomet. Chem. 616 (2000) 54.
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[10] F.A. Cotton, S. Kitagawa, Polyhedron 7 (1988) 463.
[11] F. Mitterhofer, H. Schindlbauer, Monatsh. Chem. 98 (1967) 206;
Chem. Abstr. 66 (1967) 85825h.

W.E. Meyer et al. / Journal of Organometallic Chemistry 616 (2000) 44–53
53
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[29] In initial experiments, this reaction was monitored by IR.
[30] IR data: see Table 1.
[31] (a) positive FAB, 3-NBA/CH2Cl2; m/z for the most intense peak
of isotope envelope. (b) The parent cations are always the most
intense (100%), except for 5d+ BF4− and 2d where additional
intense peaks of m/zB400 were present.
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[15] W.E. Meyer, Ph.D. Dissertation, University of Utah, 1999.
[16] (a) A ferrocene E°% value of 0.46 V has been recommended for
standardizing data in n-Bu4N+ PF6−/CH2Cl2 to a SCE rever-
ence. (b) N.G. Connelly, W.E. Geiger, Chem. Rev. 96 (1996)
877.
[17] (a) H. Schumann, J. Organomet. Chem. 304 (1986) 341. (b) R.P.
Aggarwal, N.G. Connelly, M.C. Crespo, B.J. Dunne, P.M.
Hopkins, A.G. Orpen, J. Chem. Soc. Dalton Trans. (1992) 655
and refs. cited therein.
[18] H.W. Walker, G.B. Rattinger, R.L. Belford, T.L. Brown,
Organometallics 2 (1983) 775.
[19] A. Fernandez, C. Reyes, A. Prock, W.P. Giering, Organometal-
lics 17 (1998) 2503.
[32] NMR data were recorded on Varian 300 MHz spectrometers
(1H/13C/31P 300/75.5/121 MHz). Chemical shifts are given versus
[20] C.A.L. Becker, K.R. Barqawi, J. Coord. Chem. 34 (1995) 273.
[21] M. Tilset, G.S. Bodner, D.R. Senn, J.A. Gladysz, V.D. Parker,
J. Am. Chem. Soc. 109 (1987) 7551.
1
internal or external standards. The 4-PC6H4X 13C and H-NMR
signals are given relative to the phosphorus substituent (i/o/m/
p).
[22] For leading references, see Y. Huang, G.B. Carpenter, D.A.
.