The d4/d3 redox pairs [MX(CO)(η-RCCR)Tp′] z (z = 0 and 1): Structural consequences of electron transfer and implications for the inverse halide order

Article abstract of DOI:10.1039/b611472e

The d⁴ halide complexes [MX(CO)(η-RCCR)Tp′] {X = F, Cl, Br or I; R = Me or Ph; M = Mo or W; Tp′ = hydrotris(3,5- dimethylpyrazolyl)borate} undergo one-electron oxidation to the d³ monocations [MX(CO)(η-RCCR)Tp′]⁺, isolable for M = W, R = Me. X-Ray structural studies on the redox pairs [WX(CO)(η-MeCCMe)Tp′] ^z (X = Cl and Br, z = 0 and 1), the ESR spectra of the cations [WX(CO)(η-RCCR)Tp′]⁺ (X = F, Cl, Br or I; R = Me or Ph), and DFT calculations on [WX(CO)(η-MeCCMe)Tp′]^z (X = F, Cl, Br and I; z = 0 and 1) are consistent with electron removal from a HOMO (of the d⁴ complexes) which is π-antibonding with respect to the W-X bond, π-bonding with respect to the W-C(O) bond, and δ-bonding with respect to the W-C_alkyne bonds. The dependence of both oxidation potential and ν(CO) for [MX(CO)(η-RCCR)Tp′] shows an inverse halide order which is consistent with an ionic component to the M-X bond; the small size of fluorine and its closeness to the metal centre leads to the highest energy HOMO and the lowest oxidation potential. In the cations [MX(CO)(η-RCCR)Tp′] ⁺ electronegativity effects become more important, leading to a conventional order for Cl, Br and I. However, high M-F π-donation is still facilitated by the short M-F distance. The Royal Society of Chemistry.

Full text of DOI:10.1039/b611472e

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www.rsc.org/dalton | Dalton Transactions
ꢀ z
4
3
The d /d redox pairs [MX(CO)(g-RC≡CR)Tp ] (z = 0 and 1): structural
consequences of electron transfer and implications for the inverse halide order†
a
a
a
a
a
Christopher J. Adams, Ian M. Bartlett, Susannah Carlton, Neil G. Connelly,* David J. Harding,
a
a
a
a
b
Owen D. Hayward, A. Guy Orpen, Elena Patron, Christopher D. Ray and Philip H. Rieger‡
Received 8th August 2006, Accepted 19th October 2006
First published as an Advance Article on the web 31st October 2006
DOI: 10.1039/b611472e
4
ꢀ
The d halide complexes [MX(CO)(g-RC≡CR)Tp ] {X = F, Cl, Br or I; R = Me or Ph; M = Mo or W;
ꢀ
3
Tp = hydrotris(3,5-dimethylpyrazolyl)borate} undergo one-electron oxidation to the d monocations
ꢀ
+
[
MX(CO)(g-RC≡CR)Tp ] , isolable for M = W, R = Me. X-Ray structural studies on the redox pairs
ꢀ
z
[
(
(
WX(CO)(g-MeC≡CMe)Tp ] (X = Cl and Br, z = 0 and 1), the ESR spectra of the cations [WX(CO)
ꢀ
+
g-RC≡CR)Tp ] (X = F, Cl, Br or I; R = Me or Ph), and DFT calculations on [WX(CO)
ꢀ z
g-MeC≡CMe)Tp ] (X = F, Cl, Br and I; z = 0 and 1) are consistent with electron removal from a
4
HOMO (of the d complexes) which is p-antibonding with respect to the W–X bond, p-bonding with
respect to the W–C(O) bond, and d-bonding with respect to the W–Calkyne bonds. The dependence of
ꢀ
both oxidation potential and m(CO) for [MX(CO)(g-RC≡CR)Tp ] shows an inverse halide order which
is consistent with an ionic component to the M–X bond; the small size of fluorine and its closeness to
the metal centre leads to the highest energy HOMO and the lowest oxidation potential. In the cations
ꢀ
+
[
MX(CO)(g-RC≡CR)Tp ] electronegativity effects become more important, leading to a conventional
order for Cl, Br and I. However, high M–F p-donation is still facilitated by the short M–F distance.
ꢀ
ꢀ
Introduction
[Mo(CO)
(
2
(g-RC≡CR)Tp ][PF
6
] or [W(CO)
2
(g-RC≡CR)Tp ][BF
]X (X = F, Br, I and NCS)
or thf, followed by column chro-
4
]
n
R = Me or Ph) with [NBu
4
The structural characterisation of the two redox pairs
or [N(PPh ]Cl in CH Cl
3
)
2
2
2
z
6
5 1
[
Cr(CO)
2
(g-PhC≡CPh)(g-C
6
z
Me
5
H)] (z = 0 and 1) (d /d ) and
matography, has given a wide range of analogous complexes
ꢀ
ꢀ
[Mo(CO)
2
(g-PhC≡CPh)Tp ] {z = 0 and 1, Tp = hydrotris(3,5-
ꢀ
[
MX(CO)(g-RC≡CR)Tp ] 1–18 (Scheme 1) in ca. 40–70% yield.
5
4 2
dimethylpyrazolyl)borate} (d /d ) established that stepwise re-
These complexes were characterised by elemental analysis, IR
moval of two electrons from a HOMO antibonding with respect to
1
13
spectroscopy and cyclic voltammetry (Table 1), H and C NMR
6
the metal–alkyne bond in the d complex leads to the conversion
of the alkyne from a two- to a three- to a four-electron donor.
We now show that one-electron oxidation of the d halide
ꢀ
spectroscopy and, in the cases of [WCl(CO)(g-MeC≡CMe)Tp ]
ꢀ
1
1, [WBr(CO)(g-MeC≡CMe)Tp ] 12 and [W(NCS)(CO)(g-Me-
4
ꢀ
C≡CMe)Tp ] 14, by X-ray crystallography (see below). In CH
2
Cl
2
ꢀ
complexes [MX(CO)(g-RC≡CR)Tp ] (M = Mo or W) gives the
the IR spectrum of each complex shows one m(CO) absorption in
3
ꢀ
+
d cations [MX(CO)(g-RC≡CR)Tp ] . The electron is removed
from an orbital strongly p-antibonding with respect to the M–X
bond, p-bonding with respect to the M–C(O) bond and weakly
d-bonding with respect to the M–alkyne bond; the alkyne remains
bound as a four-electron donor. In addition, ESR spectroscopic
and DFT studies have shed light on the observed inverse halide
order whereby the order of ease of oxidation of [MX(CO)(g-
−1
the range 1875–1940 cm . The carbonyl bands of the tungsten
−1
complexes 10–18 are ca. 25–30 cm lower in energy than those
of the molybdenum analogues 1–9, and those for the MeC≡CMe
−1
complexes are 12–16 cm lower than for the PhC≡CPh analogues.
ꢀ
3
RC≡CR)Tp ] is F > Cl > Br > I.
Results and discussion
The synthesis of [MX(CO)(g-RC≡CR)Tpꢀ]
ꢀ
The complex [WI(CO)(g-MeC≡Me)Tp ] has been made
4
previously but a general method involving the reaction of
a
School of Chemistry, University of Bristol, Bristol, UK BS8 1TS E-mail:
neil.connelly@bristol.ac.uk; Fax: 0117 929 0509; Tel: 0117 928 8162
b
Department of Chemistry, Brown University, Rhode Island, RI, 02912, USA
†
Electronic supplementary information (ESI) available: Table S1: Pro-
13 1
ton and C{ H} NMR spectroscopic data for 1–18. See DOI:
1
‡
0.1039/b611472e
Deceased.
ꢀ
Scheme 1 Complexes [MX(CO)(g-RC≡CR)Tp ].
6
2 | Dalton Trans., 2007, 62–72
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Table 1 Analytical, IR spectroscopic and electrochemical data for [MX(CO)(g-RC≡CR)Tpꢀ]
a
b
−1
Analysis (%)
IR /cm
◦
ꢀc
Complex
M
X
R
Colour
Yield (%)
C
H
N
m(CO)
E
/V
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
Mo
Mo
Mo
Mo
Mo
Mo
Mo
Mo
Mo
W
W
W
W
W
F
Me
Me
Me
Me
Me
Ph
Ph
Ph
Ph
Me
Me
Me
Me
Me
Ph
Ph
Ph
Ph
Dark green
Green
Light green
Lime green
Green
Yellow–orange
Orange
Orange
48
38
41
40
57
56
46
42
53
60
48
48.5 (48.6)
47.3 (47.0)
43.5 (43.3)
39.9 (39.9)
47.4 (47.3)
58.0 (58.3)
56.5 (56.8)
52.9 (53.1)
49.5 (49.6)
41.5 (41.2)
40.3 (40.1)
37.3 (37.4)
—
5.8 (5.7)
5.3 (5.5)
5.2 (5.1)
4.6 (4.7)
5.1 (5.3)
4.9 (5.2)
4.9 (5.1)
4.6 (4.8)
4.3 (4.4)
4.8 (4.9)
4.7 (4.7)
4.4 (4.4)
—
17.2 (17.0)
16.1 (16.4)
15.0 (15.1)
14.0 (14.0)
18.0 (18.3)
13.4 (13.6)
13.3 (13.2)
12.1 (12.4)
11.4 (11.6)
14.4 (14.4)
13.9 (14.0)
13.0 (13.0)
—
1904
1922
1925
1927
1932 (2071)
1918
1935
1938
1939
1876
1896
1899
1904
1907 (2074)
1891
1910
1913
1916
0.47
0.61
0.63
0.64
0.72
0.45
0.58
0.62
Cl
Br
I
NCS
F
Cl
Br
I
d
Orange
0.64
1
1
1
1
1
1
1
1
1
F
Dark blue
Royal blue
Blue
Light blue
Light green
Green
Brown
Brown
Brown
0.30 (1.49) [−0.06]
0.45 (1.63) [0.17]
0.46 (1.60) [0.18]
0.47 (1.57) [0.22]
0.55 (1.55) [0.18]
0.32 (1.50) [−0.04]
0.44 (1.67) [0.20]
0.47 (1.67) [0.24]
0.49 (1.64)
Cl
Br
I
NCS
F
Cl
Br
I
43
e
d
63
66
67
69
61
40.9 (40.6)
50.7 (51.0)
49.3 (49.9)
47.1 (47.0)
44.2 (44.4)
4.8 (4.5)
4.5 (4.6)
4.5 (4.5)
4.3 (4.2)
4.2 (4.0)
15.4 (15.8)
11.6 (11.9)
11.5 (11.6)
11.0 (10.9)
10.2 (10.3)
W
W
W
W
a
b
c
−1
Calculated values in parentheses. Strong absorptions in CH
2
Cl
2
.
In CH
2
Cl
2
. The peak potential, (E
p
◦ꢀ
)
ox (at a scan rate of 200 mV s ), is given in
ꢀ
+
ꢀ
2+
parentheses for the irreversible oxidation of [WX(CO)(g-RC≡CR)Tp ] to [WX(CO)(g-RC≡CR)Tp ] ; E for the reversible product wave observed after
d
e
scanning through this irreversible oxidation wave is given in square brackets. Medium intensity m(CN) band. See ref. 4.
The energies of the carbonyl bands for [MX(CO)(g-
ꢀ
RC≡CR)Tp ] increase in the order m(CO) = F < Cl < Br < I
showing increased p-donation from the metal to the CO p* orbital
in the order X = I < Br < Cl < F, the opposite to that expected
on the basis of halogen electronegativity. This trend, generally
referred to as the ‘inverse halide order’, has been commonly
5
observed and often attributed to a variation in the extent of X-to-
M p
p
–d bonding with fluoride therefore regarded as the strongest
p
6,7
p-donor of the halides. However, recent studies have suggested
that the increased ionic nature of the M–F bond, relative to that
of M–X (X = Cl, Br or I) bonds, is also important. Our studies of
this trend in 1–18 are discussed more fully below.
ꢀ
The IR spectra of [M(NCS)(CO)(g-MeC≡CMe)Tp ] (M =
Mo 5, M = W 14) also show m(CN) absorptions, at 2071 and
−
1
8
2074 cm respectively, implying that the potentially ambidentate
thiocyanate ligand acts as an N-donor. This was confirmed by an
ꢀ
X-ray structural study of [W(NCS)(CO)(g-MeC≡CMe)Tp ] 14.
ꢀ
The structure of [W(NCS)(CO)(g-MeC≡CMe)Tp ] 14
ꢀ
Fig. 1 The molecular structure of [W(NCS)(CO)(g-MeC≡CMe)Tp ] 14.
The structure of 14 is shown in Fig. 1 and important bond lengths
Hydrogen atoms have been omitted for clarity.
and angles are given in Table 2. The tungsten atom is in a pseudo-
ꢀ
3
octahedral coordination sphere with the Tp ligand j coordinated,
the thiocyanate ligand N-bound, and the alkyne and CO ligands
occupying the remaining coordination sites. The W–Calkyne bond
◦
Table 2 Selected bond lengths ( A˚ ) and angles ( ) for [W(NCS)(CO)(g-
ꢀ
MeC≡CMe)Tp ] 14
˚
lengths [1.996(10) and 2.056(10) A] are consistent with the alkyne
acting as a four-electron donor.
W(1)–C(1)
W(1)–C(4)
W(1)–C(5)
W(1)–N(7)
C(4)–C(5)
C(1)–O(1)
C(2)–N(7)
C(2)–S(1)
1.944(10)
2.056(10)
1.996(10)
2.061(8)
1.310(11)
1.168(11)
1.180(10)
1.603(10)
N(7)–W(1)–C(1)
N(7)–W(1)–C(4)
N(7)–W(1)–C(5)
C(1)–W(1)–C(4)
C(1)–W(1)–C(5)
C(4)–W(1)–C(5)
C(5)–C(4)–C(3)
C(4)–C(5)–C(6)
W(1)–N(7)–C(2)
N(7)–C(2)–S(1)
93.5(4)
100.1(3)
103.8(3)
70.7(4)
107.9(4)
37.7(3)
141.2(11)
137.4(11)
165.1(7)
179.0(9)
9.8
9
The alkyne is aligned approximately parallel to the
carbonyl ligand, as observed for [WI(CO)(g-alkyne)Tp ]
ꢀ
4
[
alkyne
=
PhC≡CMe,
MeC≡CCHMe(CH
2
)
4
I
and
10
Me(PhCH
2
)HCC≡CCHMeCH(OH)Ph ] and [WX(CO)(g-
ꢀ
PhC≡CPh)Tp ] (X = Cl and Br, see below) with b, the angle
◦
between the C≡C and M–C(O) vectors, 9.8 In addition, the
a
metal-bound alkyne carbon closer to the carbonyl ligand is also
closer to the metal. Such an alignment optimises the p-donor and
p-acceptor interactions of the alkyne with the metal dp orbitals
b
a
b = the angle between the C≡C and M–C(O) vectors.
Dalton Trans., 2007, 62–72 | 63
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whilst also allowing interaction of the dp orbital with the carbonyl
9
p* orbital.
NMR spectroscopy
1
13
1
ꢀ
The H and C{ H} NMR spectra of [MX(CO)(g-RC≡CR)Tp ]
–18 (see ESI†) are very similar to those reported previously
1
ꢀ
4
for [WI(CO)(g-MeC≡CMe)Tp ] and have been assigned by
1
comparison. In each H spectrum, the six methyl groups in the
ꢀ
3
- and 5-positions of the pyrazolyl rings of the Tp ligand give
rise to six separate singlets, between 1.26 and 2.94 ppm, and the
pyrazolyl protons in the 4-positions are observed as three singlets,
between 5.61 and 6.08 ppm, indicating three inequivalent pyrazolyl
1
3
1
rings. The C{ H} NMR spectra show up to six resonances (some
ꢀ
are coincident) for the methyl groups of the Tp ligand, between
1
1 and 19 ppm, three for the carbon atoms in the 4-positions of
the three pyrazolyl rings, at 106–109 ppm, and six for the 3- and
-carbons of the pyrazolyl rings, between 143 and 155 ppm. Both
5
1
13
1
the H and C{ H} NMR spectra are therefore consistent with
ꢀ
Fig. 2 Double scan CV of [WCl(CO)(g-PhC≡CPh)Tp ] 16 at a Pt
an asymmetric (chiral) metal centre. Indeed, the optical isomers
electrode in CH Cl .
2
2
ꢀ
10
of [WI(CO)(g-MeC≡CMe)Tp ] have been separated. In addition,
1
3
the C chemical shifts for the metal-bound alkyne carbons (two for
each complex), at 194–219 ppm, are consistent with four-electron
the second irreversible oxidation wave at (E
reversible product wave at 0.20 V.
p
)
ox = 1.67 V, and the
9
alkynes.
The first oxidation potentials for the molybdenum complexes
ꢀ
Each of the but-2-yne complexes [MX(CO)(g-MeC≡CMe)Tp ]
1–9 are more positive (by ca. 0.15 V) than those of the tungsten
1
(
1–5 and 10–14) shows two sharp singlets in both the
H
analogues 10–18, and no second wave is observed in the range
.0–1.8 V (although ill-defined reduction waves are observed close
1
3
1
NMR (in the range 2.71–3.39 ppm) and C{ H} NMR spec-
tra (between 18 and 23 ppm) for the alkyne methyl sub-
stituents, suggesting that no alkyne rotation occurs at ambient
temperature; variable-temperature NMR spectroscopic studies
also showed a high barrier to alkyne rotation for [WI(CO)(g-
0
to the background wave of the supporting electrolyte). For a given
metal and alkyne, the halide complexes are more difficult to oxidise
in the order F < Cl < Br < I, in agreement with the trend for m(CO)
and a further manifestation of the inverse halide order.
ꢀ
4
ꢀ
10
◦ꢀ
PhC≡CH)Tp ] and [WI(CO)(g-MeC≡CMe)Tp ]. By contrast,
As well as the qualitative dependence of both m(CO) and E
1
the H NMR spectrum of the cyclopentadienyl analogue
(
for the first oxidation wave) on the halide, plots of these two
[
MoBr(CO)(g-MeC≡CMe)(g-C
5
H
5
)] revealed alkyne rotation at
parameters for each of the four series of complexes [MX(CO)(g-
11
room temperature.
ꢀ
RC≡CR)Tp ] (M = W, R = Me and Ph; M = Mo, R = Me
1
9
ꢀ
The F NMR spectra of [MF(CO)(g-PhC≡CPh)Tp ] show
singlets at −42 (M = Mo) and −95 (M = W) ppm with the latter
2
and Ph) (Fig. 3) are linear (correlation coefficients, R , are 0.97,
1
9
183
showing tungsten satellites {J( F W) = 26 Hz}.
Electrochemistry
Each of the cyclic voltammograms (CVs) of 1–18, at a platinum
disc electrode in CH
2
2
Cl (Table 1), shows one fully reversible
oxidation wave, between 0.30 and 0.72 V (except for [MoF(CO)(g-
ꢀ
PhC≡CPh)Tp ] 6 for which the process is only reversible at scan
−
1
4
rates above 100 mV s ). The oxidation of the (formal) d neutral
3
complexes to the d cations therefore contrasts markedly with
the reversible reduction of the parent dicarbonyl d complexes
4
ꢀ
+
5
ꢀ
2
[M(CO)
2
(g-RC≡CR)Tp ] to d [M(CO)
2
(g-RC≡CR)Tp ].
The tungsten complexes 10–18 also show a second oxidation
wave, between 1.49 and 1.67 V, its irreversibility implying that
2
ꢀ
2+
the d -complex [WX(CO)(g-RC≡CR)Tp ] is unstable under the
electrochemical conditions. For 10–17 this second oxidation is
accompanied by a reversible wave, in the range −0.04 to 0.24 V, due
ꢀ
+
to the reduction of a secondary product, [WFX(g-RC≡CR)Tp ] ,
which will be described elsewhere. All of these features are
ꢀ
◦ꢀ
ꢀ
exemplified in the double scan CV of [WCl(CO)(g-PhC≡CPh)Tp ]
Fig. 3 Plots of E vs. m(CO) for [MX(CO)(g-RC≡CR)Tp ] (X = F, Cl,
1
6 which shows (Fig. 2) the first reversible oxidation wave at 0.44 V,
Br or I).
6
4 | Dalton Trans., 2007, 62–72
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0
.99, 0.99 and 0.98 respectively) as are plots for a given alkyne
over, the molybdenum analogues 1–9, with m(CO) higher than the
tungsten analogues 10–18, undergo very rapid decarbonylation on
2
(
0
including both Mo and W) (i.e. R = Me and Ph, R = 0.99 and
.97). Interestingly, the peak potentials for the second irreversible
chemical oxidation with [Fe(g-C
and 4, intermediates were detected, presumably 2 and 4 , showing
very high energy carbonyl bands at 2114 and 2095 cm respec-
5
H
4
COMe)(g-C
5
+
H
5
)][BF ]. (For 2
4
ꢀ
+
oxidation of [WX(CO)(g-RC≡CR)Tp ] are in the order F <
I < Br < Cl, more nearly that expected on the basis of halide
electronegativities (except for F).
−
1
tively.) Moreover, the cyclopentadienyl analogues [MX(CO)(g-
RC≡CR)(g-C
5
H
5
)], which show yet higher energy carbonyl bands
The chemical oxidation of [MX(CO)(g-RC≡CR)Tpꢀ]
and irreversible oxidation waves in their CVs, are also rapidly
12
decarbonylated on oxidation.
On the basis of the potentials determined by cyclic voltammetry,
ꢀ
+
−
4
The CVs of [WX(CO)(g-RC≡CR)Tp ][BF
4
]
10 [BF
] –
4
ꢀ
the first oxidation of d [MX(CO)(g-RC≡CR)Tp ] 1–18 should be
+
−
4
1
8 [BF
]
show the same pattern as those of the corresponding
accomplished using relatively mild oxidants. Thus, the addition of
neutral complexes, but with the reversible oxidation in the
latter being a reversible reduction in the former. However,
one equivalent of [Fe(g-C
sten complexes 10–13 in CH
and subsequent purification of the precipitate using CH
5
H
4
COMe)(g-C
5
H
5
)][BF
4
] to the tung-
2
2
Cl , followed by addition of n-hexane
+
−
+
−
for 15 [BF
4
] –17 [BF
4
]
an additional small wave is observed
2
Cl
2
–n-
between −0.04 and 0.24 V, at a potential identical to that of the
ꢀ
hexane, gave the stable salts [WX(CO)(g-MeC≡CMe)Tp ][BF
4
]
product wave observed after the second oxidation of [WX(CO)(g-
+
−
+
−
4
1
0 [BF
4
] –13 [BF
] which were fully characterised by elemental
ꢀ
ꢀ
2+
PhC≡CPh)Tp ] to [WX(CO)(g-PhC≡CPh)Tp ] . (The CV of
analysis, IR (Table 3) and ESR spectroscopy, cyclic voltammetry
+
1
6 [BF
4
] is shown in Fig. 4 as an example.) As will be described
+
+
and, in the case of 11 and 12 , X-ray crystallography (see below).
The same oxidation reaction with 15–18 gave the salts [WX(CO)(g-
elsewhere in more detail, these products are of the form [WFX(g-
ꢀ
+/0
13
PhC≡CPh)Tp ] (X = F, Cl or Br). Other fluoride complexes
ꢀ
+
−
+
−
PhC≡CPh)Tp ][BF
4
−
] 15 [BF
4
] –18 [BF
4
] which, in the cases of
−
have been obtained similarly by the abstraction of F from
+
−
+
1
5 [BF
4
] –17 [BF
4
] , were contaminated with small amounts of
ꢀ
[
WFX(g-PhC≡CPh)Tp ][BF
4
] (X = F, Cl or Br) as inseparable
+
−
4
by-products. The fluoride complex, 15 [BF
] , is the least stable of
the salts, decomposing in a few days even in the solid state under a
+
−
nitrogen atmosphere. However, the iodide complex 18 [BF
4
] was
isolated pure (Table 3).
The IR carbonyl bands of 10–13 and 15–18 are shifted to
−
1
considerably higher energy, by ca. 160 (X = I) to 190 cm (X =
+
−
+
−
+
−
+
−
4
F), on oxidation to 10 [BF
4
] –13 [BF
4
] and 15 [BF ] –18 [BF ]
4
and are then in the order F ∼ I < Br < Cl, in agreement with the
electrochemical data. Furthermore, the energy of m(CO) shows
a decreasing sensitivity of the carbonyl ligand in [WX(CO)(g-
ꢀ
RC≡CR)Tp ] to the effect of oxidation, with D(CO), the difference
between m(CO) for the neutral and cationic complexes, in the order
−
1
−1
−1
−1
F (189 cm ) > Cl (180 cm ) > Br (175 cm ) > I (160 cm ) for
the but-2-yne complexes. This suggests that the contribution of
ꢀ
+
the carbonyl ligand to the SOMO of [WX(CO)(g-RC≡CR)Tp ] ,
ꢀ
and by implication the HOMO of [WX(CO)(g-RC≡CR)Tp ], is
greatest for X = F and least in X = I.
The carbonyl stretching frequencies for the diphenylacetylene
ꢀ
Fig.
4
Cyclic voltammogram of [WCl(CO)(g-PhC≡CPh)Tp ][BF
4
]
+
−
+
−
4
+
complexes 15 [BF
4
] –18 [BF
] are higher than those for the but-
+
ꢀ +
1
6 [BF
4
] in CH
2
Cl
2
. showing [WFCl(g-PhC≡CPh)Tp ] (*) as an im-
+
−
−
2
-yne complexes 10 [BF
4
] –13 [BF
4
] . Thus, the correspondingly
purity. The wave centred at 0.74 V (#) is due to the calibrant
weaker W–CO bonds lead to more ready decarbonylation. More-
[Fe(g-C
5
H
4
5 5
COMe)(g-C H )].
ꢀ
Table 3 Analytical and IR spectroscopic data for [MX(CO)(g-RC≡CR)Tp ][BF
4
]
a
b
−1
Analysis (%)
IR /cm
Complex
M
X
R
Colour
Yield (%)
C
H
N
m(CO)
+
−
c
1
1
1
1
1
1
1
1
0 [BF
4
4
4
4
4
4
4
4
]
]
]
]
]
]
]
]
W
W
W
W
W
W
W
W
F
Me
Me
Me
Me
Ph
Ph
Ph
Brown
51
41
47
69
72
33
34.1 (34.2)
4.3 (4.1)
4.2 (4.1)
3.6 (3.9)
3.7 (3.6)
—
—
—
11.3 (11.6)
12.1 (12.3)
11.2 (11.5)
10.6 (10.8)
—
—
—
2065
2076
2074
2064
2071
2084
2082
2074
+
−
−
−
−
−
−
−
1 [BF
Cl
Br
I
Dark green
Dark green
Dark purple
Red–brown
Black
Black
Black
35.1 (35.1)
33.0 (32.9)
31.2 (30.9)
—
—
—
+
2 [BF
+
3 [BF
+
d
5 [BF
F
+
d
6 [BF
Cl
Br
I
+
d
7 [BF
42
53
+
8 [BF
Ph
40.1 (40.0)
3.0 (3.6)
9.4 (9.3)
a
b
c
d
ꢀ
Calculated values in parentheses. Strong absorptions in CH
2
Cl
2
.
Analysed as a 0.66 CH
2
Cl
2
solvate. Yields for [WX(CO)(g-PhC≡CPh)Tp ][BF
4
]
ꢀ
contaminated with [WFX(g-PhC≡CPh)Tp ][BF
4
] (see text).
This journal is © The Royal Society of Chemistry 2007
Dalton Trans., 2007, 62–72 | 65

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fluorinated counter anions. For example, [FeF(dppe)(g-
C
5
Me
with [Fe(g-C
)][PF
5
)][PF
6
] is formed on oxidation of [Fe(dppe)(g-C
5
Me
5
)][PF ]
6
6
5
H
5
)
2
][PF
6
], and heating [MoCl(CO)(dppe)(g-
C
5
H
5
6
] in thf gave [MoClF(NCMe)(dppe)(g-C
5
H
5
)][PF ] (af-
6
14
ter crystallisation from MeCN–diethyl ether).
ESR spectroscopy
+
+
+
+
The ESR spectra of 10 –13 (Fig. 5–8) and 15 –18 were recorded
in CH Cl –thf (1 : 2) between 300 and 100 K (Table 4). The
isotropic spectra of [WX(CO)(g-RC≡CR)Tp ] (X = F, Br or I)
Br
2
2
ꢀ
+
1
9
79,81
show resolved hyperfine coupling to F (I = 1/2, 100%),
1
27
+
+
+
(
I = 3/2, 100%) or I (I = 5/2, 100%). Those of 10 –12 and 15 –
+
1
7 also have shoulders attributable to partially resolved hyperfine
1
83
coupling to W (I = 1/2, 14%). These results imply that the un-
paired electron density is largely metal-based but with significant
ꢀ
delocalisation onto the halide (cf. [M(CO)
significant unpaired electron density is localised on the alkyne ).
2
(g-RC≡CR)Tp ] where
Fig.
CH
7
ESR spectrum of [WBr(CO)(g-MeC≡CMe)Tpꢀ]+ 12 in
+
2
2
Cl
2
–thf (1 : 2) at (a) 290 K, and (b) 100 K.
ESR spectrum of [WF(CO)(g-MeC≡CMe)Tpꢀ]+ 10 in
+
Fig.
5
CH
2
Cl
2
–thf (1 : 2) at (a) 290 K, and (b) 100 K.
ꢀ
+
+
Fig. 8 ESR spectrum of [WI(CO)(g-MeC≡CMe)Tp ] 13 in CH
1 : 2) at (a) 310 K, and (b) 110 K.
2 2
Cl –thf
(
dividing the observed coupling constant by the isotropic hyperfine
coupling constant for unit spin density in the s orbital of the
15
nucleus in question shows that the spin population in this orbital
increases from fluoride to iodide, and thus that the halogen plays
an increasing part in the SOMO in that order (Table 4). This is
also consistent with the isotropic g values, which move from ca.
1
.92 for the fluoride complex to ca. 2.00 for the iodide. As metal
participation in the SOMO is responsible for the deviation of g
from 2.00, this too implies a decreasing metal participation on
descending the halogen group.
The average of g
1
, g
2
and g is similar to giso, as expected. As with
3
the isotropic spectra, the anisotropic spectra also show coupling to
both the metal and the halide nuclei (except for the chloride). The
broadness of the ESR spectra and overlapping peaks (particularly
in the case of the iodide) have meant that calculation of the
unpaired spin distributions from the ESR spectra has only been
+
Fig.
6
ESR spectrum of [WCl(CO)(g-MeC≡CMe)Tpꢀ]+ 11 in
CH
2
Cl
2
–thf (1 : 2) at (a) 290 K, and (b) 100 K.
W
+
+
The isotropic metal hyperfine coupling ꢁA ꢂ decreases in the
possible in the cases of the fluoride compounds 10 and 15 . For
order F > Br > I, suggesting a decreasing metal contribution
a singly occupied dyz SOMO, a negative value for (A
expected, and positive values for (A
− Aiso) and (A
x
allows the assignment of A as A . (Note that it does not matter
x
− Aiso) is
X
to the SOMO in that order. The ꢁA ꢂ values cannot be directly
y
z
− Aiso), which
compared with each other, but ‘normalising’ these values by
1
6
6 | Dalton Trans., 2007, 62–72
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Table 4 ESR spectroscopic data for [WX(CO)(g-RC≡CR)Tpꢀ]+
a,b
a,c
Isotropic parameters
Anisotropic parameters
‘
Normalised’ value
x d
w
x
w
x
Complex
X
R
ꢁgꢂ
ꢁA ꢂ
ꢁA ꢂ of ꢁA ꢂ
g
1
g
2
g
3
g
ave
A
A
+
1
1
1
1
1
1
1
1
0
1
2
3
5
6
7
8
F
Me
Me
Me
Me
Ph
Ph
Ph
1.924
1.936
1.957
2.002
1.926
1.940
1.963
2.007
61.4 e31.3 0.021
51.7
49.6 16.1 0.023
<100 22.8 0.034
2.031
2.035
2.036
2.050
2.033
2.037
1.875
1.905
f1.954
1.858
1.868
f1.874
1.921
1.936
1.955
—
1.923
1.938
—
40, 70, 72
, 83,
f106, 22, 18
+
+
+
+
+
+
+
f
f
f
Cl
Br
I
—
f
60, 52,
79, ,
f
f
f
f
30, ,
g
g
g
h
h
F
63
55
30
0.020
—
0.025
0.029
1.883
1f .906
1.860
1f .878
46, 65, 63
f101, 38, 0
e
f
f
f
f
Cl
Br
I
, 78,
f
f
h
h
f
f
5f 2
17
20
,
,
f
f
Ph
—
a
d
−4
−1
b
c
Recorded in CH
2
Cl
2
–thf (1:2); hyperfine coupling constants in units of 10 cm
.
At 240 K unless otherwise stated. At 100 K unless otherwise stated.
e
f
g
h
See text for ‘normalisation’. Not observed. Not determined. At 290 K. At 120 K.
1
6
in the current analysis which of A
2
and A
3
is A
y
z
and which is A . )
2
The contribution to the SOMO from the dyz orbital, (cyz) , is then
found from eqn (1):
2
(
c
yz) = −7/4{(A
x
− Aiso)/P
d
− 3/14(dg
y
+ dg
z
) − dg
x
}
(1)
−
4
−1
2
+
which, with P
d
(W) = 60.875 × 10 cm , gives (cyz) = 0.56 for 10
+
and 0.44 for 15 . With the fluoride hyperfine coupling, (A
is expected to be positive for a singly occupied p
the assignment of A as A . The fluoride p contribution (c
y
− Aiso
)
y
orbital, allowing
2
1
y
y
y
) can
be calculated from eqn (2):
2
(
c
y
) = 5/4{(A
y
− Aiso)/P
p
}
(2)
(F) = 1467 × 10− cm , gives (c
4
−1
) = 0.061 for 10
2
+
which, with P
and 0.058 for 15 .
p
y
+
4
3
The X-ray structures of the d /d redox pairs
ꢀ
z
[
WX(CO)(g-MeC≡CMe)Tp ] (X = Cl and Br, z = 0 and 1)
ꢀ
Fig. 9 The molecular structure of [WCl(CO)(g-MeC≡CMe)Tp ] 11.
5
4
The structural characterisation of the d /d redox pair [Mo-
Hydrogen atoms have been omitted for clarity.
ꢀ
z
(
CO)
2
(g-PhC≡CPh)Tp ] (z = 0 and 1) showed the SOMO of the
neutral complex to be metal–alkyne antibonding, the alkyne con-
2
verting from a four- to a three-electron donor on reduction. The
ꢀ
z
structural characterisation of [WX(CO)(g-MeC≡CMe)Tp ] (X =
4
Cl and Br, z = 0 and 1) provides insight into the HOMO of the d
3
neutral complexes (z = 0) [the SOMO of the d cations (z = 1)].
ꢀ
The structures of [WCl(CO)(g-MeC≡CMe)Tp ] 11,
ꢀ
ꢀ
+
[
1
WBr(CO)(g-MeC≡CMe)Tp ] 12, [WCl(CO)(g-MeC≡CMe)Tp ]
+
ꢀ
+
+
1
and [WBr(CO)(g-MeC≡CMe)Tp ] 12 are qualitatively
similar to each other and to that of the thiocyanate complex, 14,
+
described above. Those of 11 and 11 are shown in Fig. 9 and 10
as representative; selected bond lengths and angles for all four
complexes are given in Table 5. As in 14, the alkyne is aligned
approximately parallel to the carbonyl ligand in the neutral
species 11 and 12, with the angle between the C≡C and M–C(O)
◦
vectors, b, 7.9 and 6.8 respectively. However, on oxidation b
◦
becomes larger by, on average for the two redox pairs, ca. 14 , i.e.
+
+
to 21.6 and 22.4 for 11 and 12 , respectively. The alkyne twists
away from its ideal alignment with the carbonyl ligand in the
neutral molecules as the HOMO is half depopulated.
ꢀ
+
+
Fig. 10 The structure of the cation [WCl(CO)(g-MeC≡CMe)Tp ] 11 .
The most striking change upon oxidation of [WX(CO)(g-
Hydrogen atoms have been omitted for clarity.
ꢀ
MeC≡CMe)Tp ] is the shortening of the metal–halide bond, by ca.
˚
˚
˚
˚
0
.09 A [2.429(1) to 2.343(1) A and 2.595(1) to 2.503(1) A for X =
of the W–CO bond, by 0.15–0.17 A, consistent with the very large
increase in the energy of m(CO), and a slight lengthening of the
Cl and Br, respectively]. There is also a considerable lengthening
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◦
ꢀ z
Table 5 Selected bond lengths ( A˚ ) and angles ( ) for [WX(CO)(g-MeC≡CMe)Tp ]
+
a
+a
1
1 (X = Cl)
11 (X = Cl)
12 (X = Br)
12 (X = Br)
W(1)–C(1)
W(1)–C(3)
W(1)–C(4)
W(1)–X
W(1)–N (av.)
C(3)–C(4)
C(1)–O(1)
1.941(6)
2.050(6)
2.002(6)
2.429(1)
2.223(8)
1.295(8)
1.174(6)
2.087(3)
2.067(3)
2.035(3)
2.343(1)
2.179(3)
1.286(4)
1.114(4)
1.942(7)
2.051(7)
2.010(7)
2.595(1)
2.237(9)
1.312(10)
1.164(8)
2.118(5)
2.076(4)
2.027(4)
2.503(1)
2.184(6)
1.277(6)
1.080(5)
C(1)–W(1)–X
92.6(2)
70.9(2)
107.8(2)
98.4(2)
101.5(2)
37.3(2)
142.2(6)
139.3(6)
7.9
89.0(1)
73.2(1)
107.4(1)
94.1(1)
107.2(1)
36.5(1)
144.3(3)
143.8(3)
21.6
91.8(2)
69.4(3)
106.8(3)
97.6(2)
100.8(2)
37.7(3)
141.4(7)
136.6(7)
6.8
88.1(1)
73.5(2)
107.2(2)
92.2(1)
106.3(1)
36.3(2)
145.3(4)
143.4(4)
22.4
C(1)–W(1)–C(3)
C(1)–W(1)–C(4)
X–W(1)–C(3)
X–W(1)–C(4)
C(3)–W(1)–C(4)
C(4)–C(3)–C(2)
C(3)–C(4)–C(5)
b
b
a
−
b
As the [BF
4
]
salt. b = the angle between the C≡C and M–C(O) vectors.
˚
tions is also reproduced by DFT calculations on [WX(CO)(g-
RC≡CR)Tp ] (z = 0 and +1).}
W–Calkyne bonds, by 0.02–0.03 A. Unlike [Mo(CO) (g-
2
ꢀ
z
ꢀ
z
PhC≡CPh)Tp ] (z = 0 and 1), where the alkyne changed from
a four- to a three-electron donor on reduction, the W–Calkyne bond
ꢀ
z
ꢀ
z
DFT studies on the redox pairs [WX(CO)(g-MeC≡CMe)Tp ]
distances for [WX(CO)(g-MeC≡CMe)Tp ] are all between 2.00
˚
(X = F, Cl, Br or I; z = 0 and 1)
and 2.05 (z = 0) and 2.03 and 2.08 A (z = 1), indicating that
the alkyne remains a four-electron donor when the complex is
In order to understand further the electronic interactions within
–18 and the corresponding monocations, in particular the source
of the inverse halide order, DFT studies have been undertaken on
9
oxidised.
1
The observed structural changes are consistent with the HOMO
ꢀ
of [WX(CO)(g-MeC≡CMe)Tp ] being largely dyz in character and
ꢀ
z
[
WX(CO)(g-MeC≡CMe)Tp ] (X = F, Cl, Br or I; z = 0 and 1).
p-antibonding with respect to the W–X bond, p-bonding with
respect to the W–C(O) bond and weakly d-bonding with respect
to the W–alkyne bond (see Fig. 11). {This pattern of interac-
These consisted of geometry optimisations using the programme
Jaguar, followed by an analysis of the bonding using the NBO
17
18
methodology.
ꢀ
z
Because compounds [WX(CO)(g-MeC≡CMe)Tp ] (X = Cl, 11;
ꢀ
+
+
X = Br, 12) and [WX(CO)(g-MeC≡CMe)Tp ] (X = Cl, 11 ; X =
+
Br, 12 ) have been structurally characterised, a comparison can
be made between computed and measured geometries (Table 6).
Within the series of compounds, a particular type of bond is consis-
tently computed to be too long or short, but normally by less than
˚
0
.05 A; the greatest discrepancy is in the tungsten–halide distances
which are all longer in the computational models, but by less than
˚
0.1 A. One can therefore be confident that the computed geome-
tries closely match those found crystallographically, despite the
multitude of environmental factors such as crystal packing forces
and counterions that are inconsistent between the two approaches.
The NBO analysis allows calculation of the distribution of
+
+
the unpaired electron spin in the paramagnetic cations 10 –13 .
In addition it allows confirmation of the qualitative assignment
(
see Fig. 11) of orbital energy ordering, and in particular of the
4
3
HOMO/SOMO character of the d /d species as dyz with mixing
of ligand orbitals.
The DFT-derived data are consistent with the IR spectroscopic
results in that the W–C and C–O distances calculated for the
cations follow the disrupted inverse halide sequence noted in the
IR data (W–C: I < Br < Cl = F; C–O: I > Br > Cl < F) albeit
showing very small changes. The data obtained are also consistent
with the results of the analysis of the ESR spectra in that the
spin population of the tungsten atom and of the carbonyl ligand
decreases in the order F > Cl > Br > I, whilst the spin population
4
Fig. 11 Schematic diagram of the orbital interactions in
d
ꢀ
[
WX(CO)(MeC≡CMe)Tp ] (hy = r-hybrid orbital).
6
8 | Dalton Trans., 2007, 62–72
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Table 6 Computed and X-ray crystallographically determined bond distances ( A˚ ) for [WX(CO)(g-MeC≡CMe)Tp ] 10–13 and [WX(CO)(g-
ꢀ
ꢀ
+
+
+
MeC≡CMe)Tp ] 10 –13 , and calculated spin densities for the cations
+
+
+
+
Compound
X
10
10
11
11
12
12
13
13
F
F
Cl
Cl
Br
Br
I
I
Computed distances
W–X
W–C
C–O
C–C
W–C(3)
W–C(4)
1.984
1.931
2.071
1.137
1.299
2.116
2.071
2.460
1.960
1.161
1.309
2.086
2.044
2.381
2.071
1.136
1.298
2.107
2.067
2.683
1.963
1.160
1.310
2.082
2.042
2.589
2.070
1.137
1.302
2.103
2.063
2.884
1.963
1.160
1.310
2.082
2.043
2.781
2.064
1.138
1.303
2.101
2.061
1.959
1.165
1.309
2.089
2.045
X-Ray distances
W–X
W–C
C–O
C–C
W–C(3)
W–C(4)
2.429
1.941
1.174
1.295
2.050
2.002
2.343
2.087
1.114
1.286
2.067
2.035
2.595
1.942
1.164
1.312
2.051
2.010
2.503
2.118
1.080
1.277
2.076
2.027
Spin populations
W (dxy
W (dxz
W (dyz
)
)
)
0.030
0.022
0.642
0.720
0.092
0.047
0.088
0.855
0.029
0.025
0.614
0.697
0.149
0.032
0.070
0.799
0.028
0.026
0.597
0.681
0.172
0.027
0.064
0.772
0.027
0.025
0.570
0.652
0.212
0.023
0.059
0.734
W (total)
X (p
C (p
O (p
W + C + O
.
y
)
z
)
z
)
of the halide increases in this same order. In other words, on
moving from fluoride to iodide, the SOMO becomes less metal
and carbonyl derived, and more halide based. However, if this
were the only orbital responsible for the value of m(CO) then it
would be expected to increase in the order F < Cl < Br < I, which
is not observed for the cations 10 –13 , i.e. the IR spectroscopic
data do not reflect the amount of p-donation apart from for the
fluoride complex.
By contrast, the inverse halide effect appears to be disrupted
for the cation series 10 –13 and 15 –18 . As judged by their
+
+
+
+
carbonyl stretching frequencies and (irreversible) oxidation poten-
ꢀ
+
+
tials, the fluoride cations [WF(CO)(g-MeC≡CMe)Tp ] 10 and
ꢀ
+
+
[WF(CO)(g-PhC≡CPh)Tp ] 15 have the most electron rich metal
centre {i.e. the lowest value of m(CO) and the lowest oxidation
potential}. However, the remaining cations display a ‘normal’
+
+
◦
ꢀ
halide order, showing a decrease in both m(CO) and E in the
order Cl > Br > I indicating that the tungsten is most electron
As noted above, calculations of the unpaired spin distributions
+
+
6
from the ESR spectra have only been possible for 10 and 15 . For
the former, the computed values of 64.2 and 9.2% for the dyz and
rich in the iodide compounds. Likewise, Tilset et al. report that
the second oxidation potentials (which are for reversible processes)
5
+
+
p
y
orbitals respectively compare with those from the analysis of
for [FeX(dppe)(g -C
5
Me )] obey the same order as do 10 –13 and
5
+
+
the ESR spectra of 56 and 6.1%. The agreement between the two
approaches here is noticeably better than in the related compounds
15 –18 (i.e. F < Cl > Br > I). It thus appears that the inverse
halide effect is ‘switched off’ at the second redox step apart from
in the fluoride compounds in spite of the fact that, as described
ꢀ
2
[
M(CO)L(MeC≡CMe)Tp ] {L = CO or P(OCH
2
)
3
CEt}.
+
+
The inverse halide order, observed by both IR spectroscopy
above, the computed SOMO in the cations 10 –13 becomes less
metal and carbonyl based on moving from fluoride to iodide
{a trend which would tend to create an inverse halide order in
and electrochemistry for 1–4, 6–13 and 15–18 has previously been
attributed to a variation in X-to-M p
recent detailed studies of the oxidation of [FeX(dppe)(g-C
p
–d
p
donation. However, more
Me )]
6
3
5
5
m(CO)}. It would seem that, in the d cations, electronegativity
(
X = F, Cl, Br, I, H or Me) suggest an alternative explanation,
effects and so inductive effects become overridingly important and
a conventional halide order is seen (for Cl, Br and I) but that the
short M–F distance facilitates sufficiently high M–F p-donation
for it to disrupt that ordering.
namely that the HOMO energy is not related to the p-donor ability
of X but is based on an ionic component to the M–X bond. The
small size of the fluorine atom, and therefore its close proximity
to the metal, plus its high residual negative charge destabilises the
t
2g orbitals of the metal which leads to a higher energy HOMO
Conclusions
and, consequently, the compound will be easier to oxidise. On
descending the halogen group, the atoms become larger and less
electronegative, and the M–X bond becomes longer and less polar,
hence stabilizing the HOMO.
ꢀ
The complexes [MX(CO)(g-RC≡CR)Tp ] (M = Mo or W; R = Me
or Ph; X = F, Cl, Br, I or NCS), synthesised by treating [M(CO)
2
(g-
ꢀ
n
RC≡CR)Tp ][BF
4
] with [NBu
4
]X (X = F, Br, I or NCS) or
This journal is © The Royal Society of Chemistry 2007
Dalton Trans., 2007, 62–72 | 69

View Article Online
[
N(PPh
3
)
2
]Cl in CH
2
Cl
2
, undergo one-electron oxidation followed
Fourier transform mode, with field stability maintained by an
external lock system. X-Band ESR spectra were recorded on a
Bruker ESP300 spectrometer equipped with a Bruker variable
temperature accessory and a Hewlett–Packard 5350B microwave
frequency counter. The field calibration was checked by measuring
the resonance of the diphenylpicrylhydrazyl (dpph) radical before
each series of spectra. Electrochemical studies were carried out
using an EG & G model 273A potentiostat in conjunction with a
three-electrode cell. The auxiliary electrode was a platinum wire
and the working electrode a platinum disc. The reference was
an aqueous saturated calomel electrode separated from the test
solution by a fine porosity frit and an agar bridge saturated with
by a second irreversible oxidation; the latter is associated with a
ꢀ
+
product wave due to the reduction of [WFX(g-PhC≡CPh)Tp ]
(
X = F, Cl or Br). The potentials for the first oxidation waves are
in the order F < Cl < Br < I, an inverse halide order also observed
in the IR spectra.
ꢀ
Chemical one-electron oxidation of [WX(CO)(g-RC≡CR)Tp ]
(
X = F, Cl, Br or I) with [Fe(g-C
5
H
4
COMe)(g-C
5
H
5
)][BF ] gives
4
ꢀ
[
WX(CO)(g-RC≡CR)Tp ][BF
4
] and, when X = F, Cl or Br;
ꢀ
R = Ph, a small amount of [WFX(g-PhC≡CPh)Tp ][BF
4
] as
an impurity. The carbonyl stretching frequencies of [WX(CO)(g-
ꢀ
−1
RC≡CR)Tp ][BF
4
] are at much higher energy (ca. 160–190 cm )
−
3
−3
than those of the corresponding neutral complexes and an inverse
halide order is not observed. The disrupted order for oxidation
potentials and m(CO) (partly the orthodox halide order, but with
deviation by the fluoride cation), and the nature of the SOMO, is
consistent with a dominant role for electronegativity (inductive)
effects in the cations, except for the fluorides in which the strength
of the M–F p bonding is sufficient partly to reverse that order.
KCl. Solutions were 1.0 × 10 mol dm in the test compound
and 0.1 mol dm in [NBu ][PF ] as the supporting electrolyte
in CH Cl . Under the conditions used, E for the one-electron
oxidation of [Fe(g-C COMe) ] or [Fe(g-C COMe)(g-C )],
−
3
n
4
6
◦
ꢀ
2
2
5
H
4
2
5
H
4
5
H
5
added to the test solutions as internal calibrants, is 0.97 and 0.74 V,
respectively.
Microanalyses were carried out by the staff of the Microanalysis
Service of the School of Chemistry, University of Bristol.
ꢀ
+
The ESR spectra of [WX(CO)(g-RC≡CR)Tp ] (R = Me or
Ph) show hyperfine coupling of the unpaired electron to both the
halide and tungsten and allow calculation of the distribution of
the SOMO between metal and ligands. The consistency between
DFT computed data and the qualitative models of SOMO type
and quantitative estimates of its distribution between metal and
ligands is notable.
Syntheses
ꢀ
[MoF(CO)(g-MeC≡CMe)Tp ] 1. To a stirred solution of
ꢀ
[Mo(CO) (g-MeC≡CMe)Tp ][PF ] (433 mg, 0.674 mmol) in
2
6
3
n
−3
CH Cl (30 cm ) was added [NBu ]F (800 ll of a 1.0 mol dm
2
2
4
The geometric data from computational DFT studies of
solution in thf, 0.8 mmol). After 5 min the mixture was evaporated
ꢀ
z
[
WX(CO)(g-RC≡CR)Tp ] (z = 0 or 1, X = F, Cl, Br or I)
to dryness in vacuo. The dark green residue was dissolved in
3
are consistent with those from X-ray crystallography (where
available). In particular, the geometric changes arising from
oxidation of the complexes are reproduced, with extensions of
W–CO and shortening of W–X bonds observed in both sets of
the minimum volume of CH Cl (ca. 2 cm ) and placed on a
2
2
silica/toluene chromatography column. Elution with diethyl ether
gave a green band which was collected and evaporated to dryness
in vacuo. Purification using CH Cl –n-hexane gave the product as
2
2
4
data consistent with a HOMO for the neutral d complexes which
a dark green solid, yield 161 mg (48%).
ꢀ
is p-antibonding with respect to the W–X bond and p-bonding
with respect to the W–C(O) bond.
The complexes [MoF(CO)(g-PhC≡CPh)Tp ] 6, [WF(CO)(g-
ꢀ
ꢀ
MeC≡CMe)Tp ] 10 and [WF(CO)(g-PhC≡CPh)Tp ] 15 {elution
with toluene–diethyl ether (1 : 1)} were prepared similarly.
Experimental
ꢀ
[
MoBr(CO)(g-MeC≡CMe)Tp ] 3. To a stirred solution of
ꢀ
The preparation, purification and reactions of the complexes de-
scribed were carried out under an atmosphere of dry nitrogen, us-
ing dried and deoxygenated solvents purified either by distillation
or by using Anhydrous Engineering double alumina or alumina–
copper catalyst drying columns. Reactions were monitored by IR
spectroscopy where necessary. Unless stated otherwise, complexes
[Mo(CO) (g-MeC≡CMe)Tp ][PF ] (437 mg, 0.675 mmol) in
2
6
3
CH Cl (30 cm ) was added [NEt ]Br (151 mg, 0.717 mmol). After
2
2
4
30 min the light green solution was evaporated to dryness in vacuo.
The green residue was dissolved in the minimum volume of CH Cl
(ca. 2 cm ) and placed on an alumina/toluene chromatography
2
2
3
column. Elution with CH Cl –toluene (1 : 1) gave a green
2
2
were (i) purified by dissolution in CH
through Celite, addition of n-hexane to the filtrate and reduction
of the volume of the mixture in vacuo to induce precipitation, and
2
Cl
2
, filtration of the solution
band which was collected and evaporated to dryness in vacuo.
Purification using CH Cl –n-hexane gave the product as a light
2
2
green solid, yield 153 mg (41%).
ꢀ
(
ii) are stable under nitrogen and dissolve in polar solvents such
The complexes [MoCl(CO)(g-MeC≡CMe)Tp ]
2
and
ꢀ
as CH
2
Cl
2
to give moderately air-stable solutions.
[Mo(NCS)(CO)(g-MeC≡CMe)Tp ] 5 were prepared similarly.
ꢀ
The compounds [Mo(CO)
2
(RC≡CR)Tp ][PF
6
] (R = Me or
2
ꢀ
4
ꢀ
Ph), [W(CO)
COMe)(g-C
by published methods.
2
(RC≡CR)Tp ][BF
4
] (R = Me or Ph), [Fe(g-
[MoI(CO)(g-MeC≡CMe)Tp ] 4. To a stirred solution of
19
20
ꢀ
C
5
H
4
5
H
5
)][BF
4
]
and [N(PPh
3
)
2
]Cl were prepared
[Mo(CO)
CH Cl
2
(g-MeC≡CMe)Tp ][PF
6
n
] (300 mg, 0.463 mmol) in
3
2
2
(50 cm ) was added [NBu ]I (180 mg, 0.487 mmol). After
4
IR spectra were recorded on a Nicolet 5ZDX FT spectrometer
or a Perkin Elmer Spectrum One FT-IR spectrometer fitted with
a Perkin Elmer ZnSe Universal ATR sampling accessory. Proton,
4 h the solvent was removed in vacuo. The orange–yellow residue
was dissolved in the minimum volume of toluene (ca. 3 cm ) and
placed on an alumina/toluene chromatography column. Elution
with toluene gave two bands. The faster moving, faint orange, band
was discarded; the second, green, band was collected and eva-
3
1
3
1
19
C{ H} and F NMR spectra were recorded on JEOL GX270,
Eclipse 300 or GX400 spectrometers with SiMe or CCl F (for
4
3
1
9
F) as internal standards. All spectrometers operated in the
porated to dryness in vacuo. Purification using CH
2
2
Cl –n-hexane
7
0 | Dalton Trans., 2007, 62–72
This journal is © The Royal Society of Chemistry 2007

View Article Online
gave the product as a lime green crystalline solid, yield 111 mg
40%).
in vacuo, giving the product as a brown 0.66 CH
53 mg (51%).
2
Cl solvate, yield
2
(
ꢀ
The complexes [WCl(CO)(g-MeC≡CMe)Tp ] 11 and
ꢀ
ꢀ
+
]−. To a stirred
[
WBr(CO)(g-MeC≡CMe)Tp ] 12 were prepared similarly.
[WCl(CO)(g-MeC≡CMe)Tp ][BF
4
] 11 [BF
4
ꢀ
solution of [WCl(CO)(g-MeC≡CMe)Tp ] (122 mg, 0.204 mmol)
ꢀ
[
MoCl(CO)(g-PhC≡CPh)Tp ] 7. To a stirred solution of
3
in CH
2
Cl
2
(30 cm ) was added [Fe(g-C
5
H
4
COMe)(g-C
5
H
5
)][BF ]
4
ꢀ
[
Mo(CO)
Cl
2
(g-PhC≡CPh)Tp ][PF
6
].CH
2
Cl (303 mg, 0.353 mmol)
2
(
65 mg, 0.206 mmol). After 5 min the green–brown solution was
3
in CH
2
2
(40 cm ) was added [N(PPh
3
)
2
]Cl (246 mg, 0.374 mmol).
3
filtered through Celite, n-hexane (30 cm ) was added and the
volume of the solution reduced in vacuo, inducing precipitation
of a dark green solid. The solid was purified twice by allowing
n-hexane (90 cm ) to diffuse into a concentrated solution of the
product in CH
After 1 h the orange solution was evaporated to dryness in vacuo.
The orange residue was dissolved in the minimum volume of
3
CH
2
Cl
2
(ca. 2 cm ) and placed on an alumina/toluene chromatog-
3
raphy column. Elution with CH
2
Cl
2
–toluene (7 : 3) gave an orange
3
◦
2
Cl
2
(8 cm ) at −20 C, giving dark green crystals,
band which was collected and evaporated to dryness in vacuo.
yield 57 mg (41%).
Purification using CH
2
Cl
2
–n-hexane gave the product as an orange
ꢀ
+
−
4
The complex [WBr(CO)(g-MeC≡CMe)Tp ][BF
4
] 12 [BF
] was
solid, yield 103 mg (46%).
prepared similarly.
ꢀ
The complexes [MoBr(CO)(g-PhC≡CPh)Tp ]
8
and
ꢀ
[
MoI(CO)(g-PhC≡CPh)Tp ] 9 were prepared similarly.
ꢀ
+
]−. To a stirred so-
[
WI(CO)(g-MeC≡CMe)Tp ][BF
4
] 13 [BF
4
ꢀ
ꢀ
lution of [WI(CO)(g-MeC≡CMe)Tp ] (100 mg, 0.145 mmol) in
[
W(NCS)(CO)(g-MeC≡CMe)Tp ] 14. To a stirred solution
3
ꢀ
CH Cl (20 cm ) was added [Fe(g-C H COMe)(g-C H )][BF ]
of [W(CO)
CH Cl
After 20 min the blue solution was evaporated to dryness in vacuo.
The green residue was dissolved in the minimum volume of CH Cl
ca. 3 cm ) and placed on an alumina/toluene chromatography
column. Elution with CH Cl –toluene (1 : 1) gave a blue band
which was collected and evaporated to dryness in vacuo. Purifi-
cation using CH Cl –n-hexane gave the product as a light green
solid, yield 158 mg (63%).
2
(g-MeC≡CMe)Tp ][BF
4
] (291 mg, 0.430 mmol) in
2
2
5
4
5
5
4
3
n
(42 mg, 0.134 mmol). After 10 min the solution was filtered
through Celite and evaporated to dryness in vacuo. The purple
2
2
(30 cm ) was added [NBu ]NCS (133 mg, 0.443 mmol).
4
3
residue was washed thoroughly with diethyl ether (2 × 30 cm ) to
2
2
3
remove [Fe(g-C H COMe)(g-C H )]. Purification using CH Cl –
(
5
4
5
5
2
2
diethyl ether gave the product as a dark purple powder, yield 78 mg
69%).
2
2
(
2
2
ꢀ
+
]−. To a stirred so-
[
WF(CO)(g-PhC≡CPh)Tp ][BF
4
] 15 [BF
4
ꢀ
lution of [WF(CO)(g-PhC≡CPh)Tp ] (100 mg, 0.142 mmol) in
ꢀ
3
[
WCl(CO)(g-PhC≡CPh)Tp ] 16. To a stirred solution of
CH
2
Cl
2
(15 cm ) was added [Fe(g-C
5
H
4
COMe)(g-C
5
H
5
)][BF ]
4
ꢀ
3
[
(
W(CO)
30 cm ) was added [N(PPh
2
(g-PhC≡CPh)Tp ][BF
4
] (209 mg, 0.261 mmol) in CH
2
Cl
2
(42 mg, 0.135 mmol). Addition of n-hexane (40 cm ) and reduction
3
3
)
2
]Cl (180 mg, 0.313 mmol). After 1 h
of the volume of the solution in vacuo gave an oil which was washed
3
3
the volume of the green solution was reduced in vacuo to ca. 10 cm ,
alumina was added and the mixture dried in vacuo. The residue was
placed on an alumina/toluene chromatography column. Elution
with toluene–diethyl ether (10 : 1) gave a green band which was
collected and evaporated to dryness in vacuo. Purification using
three times with n-hexane (15 cm ). The resulting brown powder
was purified using CH
2
2
Cl –n-hexane, giving the product as a red–
brown microcrystalline solid, yield (81 mg, 72%).
+
−
+
−
(
Note that complexes 15 [BF
4
] –17 [BF
4
]
could not be ob-
ꢀ
tained pure due to the presence of [WFX(g-PhC≡CPh)Tp ][BF
4
]
CH
2
Cl
2
–n-hexane gave the product as a brown solid, yield 127 mg
(
X = F, Cl or Br, respectively) as an impurity.
(
67%).
ꢀ
+
]−. To a stirred so-
[
WCl(CO)(g-PhC≡CPh)Tp ][BF
4
] 16 [BF
4
ꢀ
[
WBr(CO)(g-PhC≡CPh)Tp ] 17. To a stirred suspension of
ꢀ
lution of [WCl(CO)(g-PhC≡CPh)Tp ] (100 mg, 0.138 mmol) in
ꢀ
[
(
W(CO)
80 cm ) was added [NBu
2
(g-PhC≡CPh)Tp ][BF
4
] (250 mg, 0.312 mmol) in thf
3
CH
2
Cl
2
(25 cm ) was added [Fe(g-C
5
H
4
COMe)(g-C
5
H
5
)][BF ]
4
3
n
4
]Br (121 mg, 0.374 mmol). After heating
(
43 mg, 0.138 mmol). After 5 min the brown solution was filtered
the mixture under reflux for 10 min the dark green solution
3
through Celite, n-hexane was added (25 cm ) and the volume of
the solution reduced in vacuo, inducing precipitation of a black
was evaporated to dryness in vacuo. The residue was dissolved
3
in CH
2
Cl
2
(10 cm ), alumina was added to the solution and the
solid. The solid was purified using CH
2
Cl
2
–n-hexane and washed
mixture evaporated to dryness in vacuo. The residue was placed
on an alumina/toluene chromatography column. Elution with
toluene–diethyl ether (10 : 1) gave a green band which was collected
3
with n-hexane (2 × 20 cm ), yield 37 mg (33%).
ꢀ
+
−
4
The compounds [WBr(CO)(g-PhC≡CPh)Tp ][BF
4
] 17 [BF
]
ꢀ
+
−
4
and [WI(CO)(g-PhC≡CPh)Tp ][BF
4
] 18 [BF
]
were prepared
and evaporated to dryness in vacuo. Purification using CH
2
2
Cl –n-
similarly.
hexane gave the product as a brown solid, yield 165 mg (69%).
ꢀ
The complex [WI(CO)(g-PhC≡CPh)Tp ] 18 was prepared sim-
ilarly.
DFT calculations
ꢀ
+
]−. To a stirred so-
[
WF(CO)(g-MeC≡CMe)Tp ][BF
4
] 10 [BF
4
The geometries of the model compounds were optimised (as un-
restricted spin-doublets where appropriate) using B3LYP density
functional theory implemented by the programme Jaguar with
ꢀ
lution of [WF(CO)(g-MeC≡CMe)Tp ] (78 mg, 0.143 mmol) in
3
17
CH
2
Cl
2
(15 cm ) was added [Fe(g-C
5
H
4
COMe)(g-C
5
H
5
)][BF
4
]
3
(
45 mg, 0.143 mmol). Addition of n-hexane (20 cm ) to the
resulting brown solution and reduction of the volume in vacuo
induced precipitation of a brown microcrystalline solid. The solid
was washed thoroughly with n-hexane (6 × 10 cm ) and dried
the lav3p basis set for Br and I, the 6-31G** basis set for F, Cl and
other non-metals and the lacv3p basis set for the metal atoms. The
18
spin density by atom was provided by an NBO analysis. (Varying
the basis set and functional used had little effect on the results.)
3
This journal is © The Royal Society of Chemistry 2007
Dalton Trans., 2007, 62–72 | 71

View Article Online
ꢀ
ꢀ
+
−
Table 7 Crystal and refinement data for [WCl(CO)(g-MeC≡CMe)Tp ] 11, [WCl(CO)(g-MeC≡CMe)Tp ][BF
4
]
11 [BF
4
ꢀ
] , [WBr(CO)(g-
ꢀ
ꢀ
+
−
MeC≡CMe)Tp ]·CHCl
3
·C
6
H
14 12·CHCl
3
·C
6
H
14, [WBr(CO)(g-MeC≡CMe)Tp ][BF
4
] 12 [BF
4
]
and [W(NCS)(CO)(g-MeC≡CMe)Tp ] 14
+
−
+
−
4
Compound
11
11 [BF
4
]
12·CHCl
3
·C
6
H
14
12 [BF
]
14
Formula
M
C
598.59
Monoclinic
Cc (9)
18.243(4)
10.094(2)
14.012(2)
90
116.55(1)
90
173(2)
2308.1(7)
4
20
H
28
N
6
OBClW
C
685.40
Triclinic
P1 (2)
20
H
28
N
6
OB
2
ClF
4
W
C
24
H
36
N
6
OBBrCl
3
W
C
729.86
Triclinic
P1 (2)
20
H
28
N
6
OB
2
BrF
4
W
21 28 7
C H N OBSW
805.51
Triclinic
P1 (2)
10.297(3)
11.663(2
13.935(2)
88.34(1)
70.03(2)
78.05(1)
173(2)
621.22
Monoclinic
P2 /n (14)
Crystal system
¯
¯
¯
Space group (no.)
1
a/A˚
8.137(1)
8.150(2)
12.209(3)
17.020(4)
13.196(3)
90
115.10(1)
90
173(2)
2483.2(11)
4
b/A˚
c/A˚
11.770(3)
13.363(2)
87.72(1)
84.45(2)
85.24(2)
173(2)
1268.8(3)
2
4.712
11.863(2)
13.474(2)
89.03(1)
85.68(1)
85.25(2)
293(2)
1294.5(3)
2
6.059
◦
a/
b/
◦
◦
c /
T/K
U/A˚
3
1537.2(5)
2
5.346
Z
l/mm
−
1
5.144
4.763
Reflections collected
11755
13128
5733 (0.0269)
0.0199,
12294
4832 (0.0428)
0.0390,
13510
5869 (0.0464)
0.0293,
16297
Independent reflections (Rint
)
5159 (0.0405)
0.0265,
0.0437
5781 (0.1604)
0.0539,
0.0689
Final R indices
[I > 2r(I)]: R1,wR2
0.0406
0.0945
0.0571
ꢀ
Structure determinations of [WCl(CO)(g-MeC≡CMe)Tp ] 11,
3 Preliminary results were described in: I. M. Bartlett, S. Carlton, N. G.
Connelly, D. J. Harding, O. D. Hayward, A. G. Orpen, C. D. Ray and
P. H. Rieger, Chem. Commun., 1999, 2403.
ꢀ
+
−
[
WCl(CO)(g-MeC≡CMe)Tp ][BF
4
] 11 [BF
4
] , [WBr(CO)(g-
H14, [WBr(CO)
ꢀ
MeC≡CMe)Tp ]·CHCl
3
·C
6
H
14 12·CHCl
3
·C
6
4
S. G. Feng, C. C. Philipp, A. S. Gamble, P. S. White and J. L. Templeton,
ꢀ
+
−
(
(
g-MeC≡CMe)Tp ][BF
4
] 12 [BF
4
] and [W(NCS)(CO)
Organometallics, 1991, 10, 3504.
ꢀ
g-MeC≡CMe)Tp ] 14
5 P. M. Treichel, K. P. Wagner and H. J. Mueh, J. Organomet. Chem.,
1
975, C13, 86; M. Bochmann, M. Green, H. P. Kirsch and F. G. A.
ꢀ
Stone, J. Chem. Soc., Dalton Trans., 1977, 714; F. Abu-Hasanayn, A. S.
Goldman and K. Krogh-Jespersen, Inorg. Chem., 1994, 33, 5122; S. T.
Krueger, B. E. Owens and R. Poli, Inorg. Chem., 1990, 29, 2001; K. G.
Caulton, New J. Chem., 1994, 18, 25; T. Hascall, D. Rabinovich, V. J.
Murphy, M. D. Beachy, R. A. Friesner and G. Parkin, J. Am. Chem.
Soc., 1999, 121, 11402; G. M. Aston, S. Badriya, R. D. Farley, R. W.
Grime, S. J. Ledger, F. E. Mabbs, E. J. L. McInnes, H. W. Morris, A.
Ricalton, C. C. Rowlands, K. Wagner and M. W. Whiteley, J. Chem.
Soc., Dalton Trans., 1999, 4379.
Green crystals of [W(NCS)(CO)(g-MeC≡CMe)Tp ] 14 and
ꢀ
dark green crystals of [WX(CO)(g-MeC≡CMe)Tp ][BF
4
] (X =
+
−
+
−
4
Cl 11 [BF
4
] , X = Br 12 [BF
] ) were grown by allowing
n-hexane to diffuse slowly into a concentrated solution of
◦
each complex in CH
2
Cl
2
at −20 C. Similarly, blue crystals
ꢀ
of [WCl(CO)(g-MeC≡CMe)Tp ] 11 and [WBr(CO)(g-
ꢀ
MeC≡CMe)Tp ]·CHCl
3
·C
6
H
14 12·CHCl
3
·C
6
H14 were grown
from diethyl ether–n-hexane and CHCl
3
–n-hexane, respectively.
Many of the details of the structure analyses of 11, 11 [BF
6 M. Tilset, I. Fjeldahl, J.-R. Hamon, P. Hamon, L. Toupet, J.-Y.
Saillard, K. Costuas and A. Haynes, J. Am. Chem. Soc., 2001, 123,
+
−
4
] ,
9
984.
A. Mezzetti and C. Becker, Helv. Chim. Acta, 2002, 85, 2686.
8 A. H. Norbury and A. I. P. Sinha, Q. Rev. Chem. Soc., 1970, 24, 69.
J. L. Templeton, Adv. Organomet. Chem., 1989, 29, 1.
+
−
12·CHCl
3
·C
6
H
14, 12 [BF
4
] and 14 are listed in Table 7.
7
CCDC reference numbers 617290–617294
For crystallographic data in CIF or other electronic format see
9
1
0 M. B. Wells, J. E. McConathy, P. S. White and J L. Templeton,
Organometallics, 2002, 21, 5007.
1 C. Carfagna, M. Green, K. R. Nagle, D. J. Williams and C. M.
Woolhouse, J. Chem. Soc., Dalton Trans., 1993, 1761.
DOI: 10.1039/b611472e
1
Acknowledgements
1
1
2 S. Boonyuen, PhD Thesis, University of Bristol, 2005.
3 C. J. Adams, K. M. Anderson, N. G. Connelly, D. J. Harding,
A. G. Orpen, E. Patron and P. H. Rieger, Chem. Commun., 2002,
We thank the EPSRC for Studentships (D. J. H. and O. D. H.) and
the University of Bristol for Postgraduate Scholarships (I. M. B.
and E. P.)
1
30.
14 J. C. Fettinger, D. W. Keogh and R. Poli, J. Am. Chem. Soc., 1996, 118,
617.
3
1
1
1
5 J. R. Morton and K. F. Preston, J. Magn. Reson., 1978, 30, 577.
6 P. H. Rieger, Coord. Chem. Rev., 1994, 135–136, 203.
7 Jaguar 6.0, Schrodinger, LLC, Portland, Oregon, 2005.
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2 | Dalton Trans., 2007, 62–72
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