Synthesis of the sterically crowded cycloheptatrienyl complexes [M(CO)(PPh3)2(η-C7H7)] + (M = Mo or W): X-ray crystal structures of [W(CO)(PPh 3)2(η-C7H7)][BF4] and [W(CO)2(PPh3)(η-C7H7)][BF 4]

Article abstract of DOI:10.1016/j.jorganchem.2006.01.013

The first examples of complexes of the sterically crowded, bis(triphenylphosphine) auxiliary M(PPh₃)₂(η-C ₇H₇) (M = Mo or W) have been synthesised. [Mo(CO)(PPh ₃)₂(η-C₇H₇)][PF₆] (1) was obtained by low-temperature reaction of [MoMe(CO)(PPh₃)(η- C₇H₇)] with [Ph₃C][PF₆] in the presence of PPh₃. The tungsten analogue [W(CO)(PPh₃) ₂(η-C₇H₇)][BF₄] (3) was formed by reaction of [WI(CO)(PPh₃)(η-C₇H₇)] with Ag[BF₄] in acetone followed by addition of PPh₃. An X-ray crystallographic structural comparison of complex 3 with its mono-phosphine counterpart, [W(CO)₂(PPh₃)(η-C₇H ₇)][BF₄] ? CH₂Cl₂ (4) reveals that the principal structural differences between 3 and 4 resulting from replacement of a carbonyl ligand by PPh₃ are: (i) an increase in the sum of the angles between the tripodal ligands and (ii) an elongation of the W-PPh₃ bond length (from 2.4950(12) A? in 4 to 2.5360(6) and 2.5496(6) A? in the bis(phosphine) complex 3).

Full text of DOI:10.1016/j.jorganchem.2006.01.013

Journal of Organometallic Chemistry 691 (2006) 1879–1886
www.elsevier.com/locate/jorganchem
Synthesis of the sterically crowded cycloheptatrienyl
complexes [M(CO)(PPh3)2(g-C7H7)]+ (M = Mo or W): X-ray
crystal structures of [W(CO)(PPh3)2(g-C7H7)][BF4]
and [W(CO)2(PPh3)(g-C7H7)][BF4] Æ CH2Cl2
Emma C. Fitzgerald, Richard W. Grime, Heather C. Knight, Madeleine Helliwell,
*
James Raftery, Mark W. Whiteley
School of Chemistry, University of Manchester, Brunswick Street, Manchester M13 9PL, UK
Received 18 November 2005; received in revised form 10 January 2006; accepted 10 January 2006
Available online 17 February 2006
Abstract
The first examples of complexes of the sterically crowded, bis(triphenylphosphine) auxiliary M(PPh3)2(g-C7H7) (M = Mo or W) have
been synthesised. [Mo(CO)(PPh3)2(g-C7H7)][PF6] (1) was obtained by low-temperature reaction of [MoMe(CO)(PPh3)(g-C7H7)] with
[Ph3C][PF6] in the presence of PPh3. The tungsten analogue [W(CO)(PPh3)2(g-C7H7)][BF4] (3) was formed by reaction of [WI(CO)-
(PPh3)(g-C7H7)] with Ag[BF4] in acetone followed by addition of PPh3. An X-ray crystallographic structural comparison of complex
3 with its mono-phosphine counterpart, [W(CO)2(PPh3)(g-C7H7)][BF4] Æ CH2Cl2 (4) reveals that the principal structural differences
between 3 and 4 resulting from replacement of a carbonyl ligand by PPh3 are: (i) an increase in the sum of the angles between the tripodal
˚
˚
ligands and (ii) an elongation of the W–PPh3 bond length (from 2.4950(12) A in 4 to 2.5360(6) and 2.5496(6) A in the bis(phosphine)
complex 3).
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Molybdenum; Tungsten; Cycloheptatrienyl; Steric crowding
1. Introduction
(PPh3)Cp*], a process not mirrored by the corresponding
Cp system. Although ring substituents may be critical in
the design of sterically crowded, half-sandwich systems,
the effect of increasing ring size is also an important factor
[3]. In the complexes [ML3(gn-CnHn)]z+ (n = 4–7) an
increase in n results in a corresponding decrease in the
sum of the angles (Ru) between the tripodal ligands L
(see Fig. 1) effectively restricting the space available to
the ligands L. In fact the magnitude of this pyramidalisa-
tion effect is not strongly dependent upon the identity of
ring-substituents, but rather it is controlled by changes in
donor/acceptor properties of the cyclopolyene with
increase in n.
Steric crowding in 18-electron organometallic complexes
is an effective strategy to facilitate ligand dissociation and
the formation of unsaturated 16-electron systems which
can exhibit catalytic properties or new patterns of reactivity
[1]. In half-sandwich systems, a key consideration is the
interplay of ring size and ring substituents with the steric
demands of other ligands in the complex. For example,
in the complexes [RuCl(PPh3)2(g-C5R5)] [R = H (Cp) or
Me (Cp*)], the enhanced reactivity of the Cp* complex to
dissociation of PPh3 has been exploited in the synthesis
of the novel neutral vinylidenes [2] [RuCl(@C@CHR0)-
The isoelectronic character of the 13-electron fragments
Ru(g-C5R5) and Mo(g-C7H7) (C7H7 = cycloheptatrienyl)
has been well documented by ourselves [4] and others
[5] and similarities in complex type and reactivity noted.
*
Corresponding author. Tel.: +44 0161 275 4634; fax: +44 0161 275
4598.
E-mail address: Mark.Whiteley@manchester.ac.uk (M.W. Whiteley).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.01.013

1880
E.C. Fitzgerald et al. / Journal of Organometallic Chemistry 691 (2006) 1879–1886
tions required to accommodate the combination of steri-
cally demanding ring and phosphine ligands in a half-
sandwich complex.
M
2. Results and discussion
L
L
φ
L
2.1. Synthetic studies
Fig. 1. Illustration of the parameter u for [ML3(gn-CnHn)]z+
.
The isolation of complexes derived from the
Mo(PPh3)2(g-C7H7) auxiliary has long been a goal of our
investigations into the chemistry of the cycloheptatrienyl
molybdenum system. However, following a number of
unsuccessful synthetic attempts using several different strat-
egies, it began to appear that such complexes were not
accessible – an observation which might easily be rationa-
lised by steric limitations. It was therefore with some sur-
prise that we identified [Mo(CO)(PPh3)2(g-C7H7)][PF6]
(1) as the product of an attempt to generate and stabilise
the carbene complex [Mo(@CH2)(CO)(PPh3)(g-C7H7)]+
from the low temperature reaction of [Mo(CH3)(CO)-
(PPh3)(g-C7H7)] with [Ph3C][PF6] [11]. The synthetic strat-
egy for formation of the desired carbene complex
[Mo(@CH2)(CO)(PPh3)(g-C7H7)]+ and subsequent stabili-
sation as a phosphonium salt is summarised in Scheme 1.
Following addition of PPh3, the reaction mixture was
warmed to room temperature and the product isolated as
a green-brown solid by recrystallisation first from thf-
diethyl ether, then CH2Cl2-diethyl ether. Characterisation
However, the chemistry of the cycloheptatrienyl molybde-
num system is clearly distinct from that of the Ru(g-C5R5)
system and this can, in part, be attributed to differences in
steric parameters. The large ring cycloheptatrienyl ligand
presents considerable steric demand at a metal centre with
an estimated cone angle (154ꢁ) [6], larger than that of both
the Cp (110ꢁ) and Cp* (142ꢁ) ligands. The experimental
consequences of the effect of increasing ring size on the
accommodation of sterically demanding tripodal ligands
are nicely illustrated by a comparison of the known
auxiliaries
RuðPR03Þ2ðg-C5R5Þ and MoðPR03Þ2ðg-C7H7Þ.
Accordingly, whilst the bis(triphenylphosphine) auxiliary
Ru(PPh3)2(g-C5R5) is one of the cornerstones of the
organometallic chemistry of ruthenium [7], the chemistry
of bis(phosphine) cycloheptatrienyl systems MoðPR03Þ2-
ðg-C7H7Þ is dominated by complexes of the chelate phos-
phine Ph2PCH2CH2PPh2 (dppe) [4,8,9] or small cone angle
P-donor ligands such as P(OMe)3 [10]. This paper reports
the syntheses of the sterically crowded complexes [M(CO)-
(PPh3)2(g-C7H7)]+ (M = Mo or W), the first examples
of derivatives of the bis(triphenylphosphine) auxiliary
M(PPh3)2(g-C7H7), and explores the structural modifica-
1
by infrared and FAB mass spectroscopy and by H and
13C NMR spectroscopy (Table 1) revealed that the isolated
product was in fact the bis(triphenylphosphine) com-
plex [Mo(CO)(PPh3)2(g-C7H7)][PF6] (1). Data which
+
PPh3
X
[Ph3C][PF6]
thf -780C
Mo
PPh3
Mo
+
Mo
C
O
C
C
O
CH3
O
CH2PPh3
CH2
PPh3
PPh3
thf
+
+
PPh3
Mo
Mo
C
C
O
O
O
PPh3
PPh3
PPh3
1
Scheme 1.

Table 1
Microanalytical, infrared, mass spectroscopic and NMR data
Complex
Analysis (%)a
Infrared,
Mass spectral datac
1H NMR datad
PPh3
13C NMR datae
CO
m(CO) (cmꢀ1 b
)
C
H
C7H7
PPh3
C7H7
94.3
f
[Mo(CO)(PPh3)2(g-C7H7)][PF6] Æ CH2Cl2 (1)
[W(NCMe)(CO)(PPh3)(g-C7H7)][BF4] (2)
[W(CO)(PPh3)2(g-C7H7)][BF4]g (3)
55.5
(55.7)
4.0
(4.0)
1942
741 M+
7.40, m; 7.35,
m; 7.14, m
5.02, t,
J(P–H) 2.2
230.6, t,
J(P–C) 19.5
133.8–128.7
479 [M+ ꢀ PPh3]
451 [M+ ꢀ PPh3 ꢀ CO]
48.3
(48.5)
3.5
(3.6)
1931
1920
606 M+
7.47, m;
7.29, m (1.99, d,
J(P–H) 2.0, NCMe)
5.27, d,
J(P–H) 2.0
230.1, d,
J(P–C) 13.9
133.7–128.0
(3.2, NCMe)
89.8
90.7
95.4
565 [M+ ꢀ NCMe]
537 [M+ ꢀ NCMe ꢀ CO]
57.7
(57.8)
4.1
(4.1)
827 M+
7.43, m;
7.32, m; 7.13, m
5.02, t,
J(P–H) 2.4
224.6
135.2–128.9
135.0–131.1
565 [M+ ꢀ PPh3]
536 [M+ ꢀ PPh3 ꢀ CO]
[W(CO)2(PPh3)(g-C7H7)][BF4]g (4)
2016,
1967
593 M+
7.56, m; 7.35, m
5.64, d,
J(P–H) 1.8
206.4, d,
J(P–C) 13.4
565 [M+ ꢀ CO]h
a
Calculated values in parentheses; 2, N = 1.9 (2.0).
Solution spectra in CH2Cl2.
b
c
d
e
f
By FAB mass spectroscopy unless stated otherwise.
400 MHz spectra in CDCl3 unless stated otherwise.
100 MHz spectra in CDCl3 unless stated otherwise.
300 MHz 1H/75 MHz 13C NMR spectra.
NMR spectra in CD2Cl2.
g
h
MALDI spectrum.

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E.C. Fitzgerald et al. / Journal of Organometallic Chemistry 691 (2006) 1879–1886
specifically indicate the presence of two equivalent triphe-
nylphosphine ligands are the triplet signal [J(P–
H) = 2.2 Hz] for the C7H7 ligand in the 1H NMR and
the triplet resonance [J(P–C) = 19.5 Hz] for the carbonyl
carbon in the 13C NMR spectrum. The FAB and electro-
spray (MeOH) mass spectra show the molecular ion with
the principal fragmentation arising from loss of PPh3; the
lability of the PPh3 ligand is also demonstrated by the elec-
trospray mass spectrum recorded in acetonitrile for which
the strongest peak corresponds to the molecular ion of
[Mo(CO)(NCMe)(PPh3)(g-C7H7)]+. Microanalytical data
for complex 1 are for the CH2Cl2 solvate; the presence of
CH2Cl2 was evident in the 1H NMR spectrum of the
complex and was also observed in samples of the tungsten
analogue of 1 (see later) if recrystallised from CH2Cl2-
diethylether.
The formation of complex 1 from [Mo(CH3)(CO)(PPh3)-
(g-C7H7)] can be rationalised as shown in Scheme 1.
The initially formed carbene ligand is displaced and the
coordination site occupied by the solvent (thf) which is sub-
sequently displaced by PPh3; alternatively the carbene may
be replaced directly by PPh3. Inspection of the literature
reveals that a similar mechanism is proposed for the reac-
tion of [Fe(Me)(CO)(PMe3)(g-C5Me5)] with [Ph3C][PF6]
in thf [12]. In this case the solvated intermediate [Fe(thf)-
(CO)(PMe3)(g-C5Me5)]+ is isolable but can undergo a sub-
sequent photochemically-induced substitution of thf by
PMe3 to yield [Fe(CO)(PMe3)2(g-C5Me5)]+. To exploit this
principle further, the synthesis and reactions of solvato
complexes of the type [M(solvent)(CO)(PPh3)(g-C7H7)]+
(M = Mo or W) were explored.
Complexes of the type [M(solvent)(CO)(PPh3)-
(g-C7H7)]+, have been reported previously (M = Mo,
solvent = NCMe), obtained by reaction of [MoI(CO)-
(PPh3)(g-C7H7)] with Ag[BF4] in acetonitrile [13]. In the
current investigation, the tungsten derivative [W(NCMe)-
(CO)(PPh3)(g-C7H7)][BF4] (2) was prepared for the first
time by reaction of [WI(CO)(PPh3)(g-C7H7)] with Ag[BF4]
in acetonitrile and characterised as detailed in Table 1.
Although these complexes establish the formation of sol-
vato systems, the NCMe ligand proved to be hard to dis-
place. Both complexes [M(NCMe)(CO)(PPh3)(g-C7H7)]+
(M = Mo or W) reacted with strongly nucleophilic
phosphines such as PMe3 in CH2Cl2 at room temperature
to give [M(CO)(PPh3)(PMe3)(g-C7H7)]+ (M = Mo, W)
although the outcome of the reaction was complicated by
competing partial displacement of PPh3. By contrast no
reaction occurred between [M(NCMe)(CO)(PPh3)-
(g-C7H7)]+ and PPh3 in CH2Cl2 at ambient temperature
or under reflux. Therefore, in an attempt to further a
rational synthesis of [M(CO)(PPh3)2(g-C7H7)]+ (M = Mo
or W), the intermediacy of complexes [M(solvent)-
(CO)(PPh3)(g-C7H7)]+ with more weakly coordinated,
oxygen-donor solvents was investigated.
solution followed by addition of diethylether led to precip-
itation of an oily solid formulated as the solvato complex
[W(acetone)(CO)(PPh3)(g-C7H7)][BF4]. The material was
too unstable to characterise fully but infrared spectroscopy
in CH2Cl2 revealed a single carbonyl band (m(CO)(CH2Cl2)
1917 cmꢀ1) shifted to high wavenumber by 6 cmꢀ1 from
that of the starting material [WI(CO)(PPh3)(g-C7H7)].
The solvato intermediate so formed, was redissolved in ace-
tone and treated with one equivalent of PPh3. Gentle
refluxing of the reaction mixture led to the formation of
the bis(triphenylphosphine) complex [W(CO)(PPh3)2-
(g-C7H7)][BF4] (3), which was isolated as a green-brown
solid. Characterisation details for 3 including mass spectro-
1
scopic, H and 13C NMR data are presented in Table 1.
The dominant fragmentation pattern in the mass spectrum
is again initial loss of PPh3 followed by loss of CO, consis-
tent with a labile PPh3 ligand.
Although [W(CO)(PPh3)2(g-C7H7)][BF4] (3) is the
major product of the above procedure, on one occasion
the formation of small quantities of the dicarbonyl com-
plex [W(CO)2(PPh3)(g-C7H7)]+ (4), [m(CO)(CH2Cl2) 2016,
1967 cmꢀ1, see Table 1 for full characterisation data] was
also observed. The formation of 4 as a by-product in the
above reaction highlights the problems associated with an
analogous synthesis of the bis(triphenylphosphine)molyb-
denum derivative [Mo(CO)(PPh3)2(g-C7H7)][BF4] (1).
The 16-electron fragment M(CO)(PPh3)(g-C7H7)+ (M =
Mo or W) is labile to ligand exchange and much more so
where M = Mo than for the tungsten derivative where
W–CO bonds are relatively strong. Accordingly, when an
equivalent synthesis starting from [MoBr(CO)(PPh3)-
(g-C7H7)] and Ag[BF4] in acetone was attempted, extensive
decomposition occurred and the isolated product con-
tained significant amounts of silver–phosphine adducts
[Ag(PPh3)n], clearly identified by peaks in the mass spec-
trum at m/z 895, 633 with the correct isotopic pattern for
Ag [14–16]. These silver–phosphine adducts were also iso-
lated from the reaction of [MoBr(CO)(PPh3)(g-C7H7)]
with Ag[BF4] in acetone in the absence of added free phos-
phine. It is clear therefore that a successful synthesis of 1
depends upon a low temperature route to impede ligand
exchange and decomposition. For this reason the silver-
free, low temperature method, starting from [MoMe(CO)-
(PPh3)(g-C7H7)] remains the preferred route to 1.
2.2. Structural studies
To establish conclusively the identity of complexes 1 and
3 as bis(triphenylphosphine) systems and to investigate
how the sterically demanding ligand set is accommodated
at a M(g-C7H7) (M = Mo or W) centre, a structural study
was undertaken. Suitable crystals of the tungsten derivative
3, were obtained by vapour diffusion of diethyl ether into
an acetone solution of the complex. To provide data for
a direct comparison, the structure of the dicarbonyl com-
plex [W(CO)2(PPh3)(g-C7H7)][BF4] (4) as a CH2Cl2 sol-
vate, was also determined; the crystallographic data for 3
Treatment of a green, acetone solution of [WI(CO)-
(PPh3)(g-C7H7)] with Ag[BF4] resulted in an immediate
colour change to red then back to green. Filtration of the

E.C. Fitzgerald et al. / Journal of Organometallic Chemistry 691 (2006) 1879–1886
1883
Table 2
and 4 augment a very limited series of structural determina-
˚
Important bond lengths (A) and angles (ꢁ)
tions for the cycloheptatrienyl tungsten system [17,18]. The
X-ray crystal structures of [W(CO)(PPh3)2(g-C7H7)][BF4]
and [W(CO)2(PPh3)(g-C7H7)][BF4] Æ CH2Cl2, together with
the crystallographic numbering schemes are presented in
Figs. 2 and 3, respectively; important bond lengths and
angles are given in Table 2. Key comparisons between
the structures of 3 and 4 are presented in Table 3 together
with relevant data for other complexes cited in the discus-
sion below.
Focusing initially on a comparison of the cycloheptatrie-
nyl tungsten complexes 3 and 4, the results of replacing CO
in 4 with the more sterically demanding ligand PPh3 in 3
are examined. The principal effects of increased steric
crowding at the W centre are (i) a decrease in pyramidali-
sation of the tripodal ligands (4, Ru = 254ꢁ; 3, Ru =
264ꢁ) and (ii) an elongation of the average W–P bond dis-
Complex 3
W(1)–P(1)
W(1)–P(2)
W(1)–C(8)
W(1)–C(1)
W(1)–C(2)
W(1)–C(3)
2.5360(6)
2.5496(6)
1.974(2)
2.364(2)
2.3565(19)
2.352(2)
W(1)–C(4)
W(1)–C(5)
W(1)–C(6)
W(1)–C(7)
C(8)–O(1)
2.346(2)
2.262(2)
2.323(2)
2.319(2)
1.152(2)
P(1)–W(1)–P(2)
P(1)–W(1)–C(8)
P(2)–W(1)–C(8)
W(1)–C(8)–O(1)
100.531(19)
82.60(6)
81.06(6)
Ct–W(1)–P(1)
Ct–W(1)–P(2)
Ct–W(1)–C(8)
123.5
126.8
128.6
174.8(7)
Complex 4
W(1)–P(1)
2.4950(12)
2.012(5)
2.004(6)
2.324(5)
2.346(5)
2.316(5)
W(1)–C(24)
W(1)–C(25)
W(1)–C(26)
W(1)–C(27)
C(19)–O(1)
C(20)–O(2)
2.312(5)
W(1)–C(19)
W(1)–C(20)
W(1)–C(21)
W(1)–C(22)
W(1)–C(23)
2.323(5)
2.336(5)
2.344(5)
1.138(7)
1.145(7)
P(1)–W(1)–C(19)
P(1)–W(1)–C(20)
C(19)–W(1)–C(20)
W(1)–C(19)–O(1)
83.91(15)
87.67(16)
82.5(2)
W(1)–C(20)–O(2)
Ct–W(1)–P(1)
Ct–W(1)–C(19)
Ct–W(1)–C(20)
177.4(5)
129.8
128.5
128.3
178.3(5)
Ct = centroid of C7H7 ring.
˚
˚
tance by approximately 0.05 A (from 2.495 to 2.543 A).
The increase in W–P distances contrasts with the trend in
˚
the W–CO distance which decreases from 2.004(6) A in 4
to 1.974(2) A in 3, in accord with the expected behaviour
˚
of a p-acceptor ligand as electron density at the metal
centre increases. The change in Ru from 254ꢁ to 264ꢁ essen-
tially spans the known limiting values for [ML3(g-C7H7)]z+
complexes (L = monodentate ligand) as exemplified by
[Mo(CO)3(g-C7H7)][BF4] (255ꢁ) [19] and the sterically
crowded system [MoI(CO)(PN*)(g-C7H7)] {PN* = Ph2PN-
(Me)CHMePh} (263ꢁ) [20]. Clearly both structural
responses (i) and (ii) afford more space to accommodate
the additional PPh3 ligand at the W centre as a P(1)–
W(1)–P(2) angle of 100.5ꢁ is achieved. However, there is
some evidence to suggest that the movement of the PPh3
ligands towards the C7H7 ring consistent with the increase
in Ru, may be close to a limiting case. The average W–ring
Fig. 2. Molecular structure of complex 3; BFꢀ4 counter anion omitted.
˚
carbon distance in 3 and 4 is almost identical (2.33 A).
˚
However, the range of values in 3 (2.262(2)–2.364(2) A) is
˚
much greater than observed for 4 (2.312(5)–2.346(5) A)
and closer inspection of the structure of 3 reveals that the
longest W–ring carbon distances W–C(1), W–C(2),
W–C(3) and W–C(7) are disposed towards the PPh3 ligands
whereas the shortest distance W–C(5) is located above the
carbonyl ligand. The cycloheptatrienyl ring in 3 is therefore
tilted away from the sterically crowded side of the molecule
but even this does not prevent a very short intramolecular
˚
contact between H(1) and H(20) (2.22 A); for comparison,
in 4, the closest cycloheptatrienyl ring-phosphine contact is
˚
between H(27) and H(6) (2.50 A).
Fig. 3. Molecular structure of complex 4; BFꢀ4 counter anion and solvent
One further mechanism by which steric crowding might
of crystallisation omitted.
be relieved in complex 3 is by reducing the effective cone

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E.C. Fitzgerald et al. / Journal of Organometallic Chemistry 691 (2006) 1879–1886
Table 3
Selected bond lengths and angles for complexes [RuL(CO)(PPh3)(g-C5R5)]+ and [RuL(PPh3)2(g-C5R5)]+ (R = H or Me)
˚
Complex
M–P (A)
Ru (ꢁ)
P–M–P (ꢁ)
Ref.
3
2.5360(6), 2.5496(6)
2.4950(12)
2.340(1), 2.327(1)
2.347(13), 2.361(7)
2.361(2)
2.347(2), 2.349(2)
2.341(3), 2.363(3)
2.359(3), 2.388(3)
2.335(2)
264
254
n/a
287
271
278
286
281
271
278
100.531 (19)
n/a
99.47(2)
97.8(4)
n/a
101.0(1)
99.6(1)
98.4(1)
n/a
This work
This work
[26]
[27]
[28]
[29]
[29]
[30]
[31]
4
[Ru(CO)(PPh3)2Cp]+
[Ru(CO)(PPh3)2Cp]+
[Ru(CO)2(PPh3)Cp*]+
[Ru{@C(OMe)Et}(PPh3)2Cp]+
[Ru(@C@CMePh)(PPh3)2Cp]+
[Ru{@C@CH(CO2Me)}(PPh3)2Cp*]+
[Ru{@CCH(Ph)CH2CH2O}(CO)(PPh3)Cp]+
[Ru(IC6H5Me)(CO)(PPh3)Cp]+
2.324(2)
n/a
[32]
n/a = not applicable or data not available.
angle of the PPh3 ligands. Although the Tolman cone angle
for PPh3 (145 2ꢁ) [21] is often employed in initial consid-
erations of sterics, this does not account for aspects of
ligand conformation and meshing effects and a number of
groups have studied the detailed conformation of PPh3
ligands [22] and the application of solid cone angles
[23,24]. One very useful approach is to calculate the exper-
imental cone angle of the PPh3 ligand from X-ray crystal-
lographic data for the structure under consideration
summarised in Table 3. Unfortunately, data for a direct
comparison with [Ru(CO)2(PPh3)Cp]+ are not available
but data for the Cp* analogue have been reported [28].
Comparison of structural parameters for [Ru(CO)2(PPh3)-
Cp*]+ and [Ru(CO)(PPh3)2Cp]+ reveal a large increase in
Ru from 271ꢁ to 287ꢁ through substitution of an additional
PPh3 ligand. However, in contrast to the pair of cyclohep-
tatrienyltungsten complexes 3 and 4, the change in the
Ru–PPh3 distance is much less evident (Ru–Paverage
:
+
[Ru(CO)2(PPh3)Cp ] = 2.36 A; [Ru(CO)(PPh3)2Cp]+ =
*
˚
according to the method described by Muller and Mingos
¨
˚
[25]. Using this procedure (rH, the van der Waals radius
2.34 A). Clearly this comparison must be qualified by
for hydrogen was taken as 1.00 A and the metal–phospho-
differences imposed by Cp vs. Cp* but the data in Table
3 [29–32] suggest that typical Ru–PPh3 distances in
cationic, mono-triphenylphosphine complexes [RuL(CO)-
˚
rus distance was taken as the crystallographically deter-
˚
mined W–P distance and not 2.28 A of the Tolman
+
˚
definition) the experimental cone angles for the PPh3
ligands in complexes 3 and 4 were calculated as 3
[P(1)Ph3: 134ꢁ; P(2)Ph3: 135ꢁ] and 4 (137ꢁ) (atoms defining
the angles were H(11), H(20), H(25), H(28), H(38) and
H(43) in 3 and H(6), H(9) and H(15) in complex 4). Exper-
imentally determined cone angles for the PPh3 ligand lie in
the region 130–170ꢁ (with the lower limit characteristic of
significant steric crowding) although values outside the
range 135–160ꢁ are uncommon. There is also an approxi-
mate correlation between the M–P distance and the PPh3
cone angle with the trend that cone angle decreases as the
M–P distance increases [25]. From the cone angles com-
puted for 3 and 4 above, it is clear that both complexes
have small values for the PPh3 cone angle consistent with
steric crowding. However, the values for 3 are not at the
extreme limit, nor is the decrease in cone angle between 4
and 3 particularly large especially in view of the trend for
cone angle to decrease with increase in the M–P distance.
We therefore conclude that although reduction of the
experimental PPh3 cone angle may be a minor response
of the system to accommodation of an additional PPh3
ligand, the increase in W–P distance remains the most sig-
nificant factor.
(PPh3)Cp] are in the range 2.32–2.34 A and that the effect
of replacement of Cp by Cp* is to increase the Ru–PPh3
bond length by 0.02–0.03 A. Therefore, at least in com-
˚
plexes of the Ru(PPh3)2Cp auxiliary, it is probable that
accommodation of the second PPh3 ligand results only in
a relatively small lengthening and weakening of the Ru–
PPh3 bond. The contrasting behaviour of the Ru(PPh3)2Cp
and W(PPh3)2(g-C7H7) systems in this respect may be
important in rationalising the relative stability of their
complexes.
3. Conclusions
The complexes [M(CO)(PPh3)2(g-C7H7)]+ (M = Mo or
W) are the first examples of derivatives of the sterically
crowded bis(triphenylphosphine) auxiliary M(PPh3)2-
(g-C7H7). An X-ray crystallographic structural comparison
of the tungsten complex [W(CO)(PPh3)2(g-C7H7)] [BF4] (3)
with its mono-phosphine counterpart, [W(CO)2-(PPh3)-
(g-C7H7)][BF4] Æ CH2Cl2 (4) reveals that the additional
PPh3 ligand is accommodated in the structure by a series
of modifications to the molecular geometry including an
increase in the sum of the angles between the tripodal
ligands, tilting of the cycloheptatrienyl ring and a small
decrease in the experimental cone angle of the PPh3ligands.
However, the most significant change appears to be an
elongation of the W–PPh3 bond lengths by approximately
Having established the structural changes in the
W(g-C7H7) system imposed to accommodate a second
PPh3 ligand, the remaining consideration is to examine
an equivalent pair of complexes of the Ru(g-C5R5) auxil-
iary. Two structural determinations are available for
[Ru(CO)(PPh3)2Cp]+ [26,27] and essential parameters are
˚
0.05 A. Although the W–PPh3 distances in complex 3
˚
(2.5360(6) and 2.5496(6) A) are not exceptionally long

E.C. Fitzgerald et al. / Journal of Organometallic Chemistry 691 (2006) 1879–1886
1885
{for example: [WBr2(CO)2(PPh3)2] (W–P = 2.481(9),
diethyl ether gave complex 2 as a lime green solid. Yield:
0.85 g (85%).
˚
2.486(9) A) [33]; [WCl(CO)2(PPh3)(g-C9H7)] (C9H7 =
˚
indenyl, W–P = 2.516(1) A) [34]; [W(CO)2(PPh3)2-
(g5-C7H9)]+ (C7H9 = cycloheptadienyl, W–P = 2.568(3),
4.4. Preparation of [W(CO)(PPh3)2(g-C7H7)][BF4] (3)
˚
2.522(3) A) [35]} they are towards the upper end of
observed values and moreover [W(CO)2(PPh3)2(g5-C7H9)]+
is also labile to PPh3 ligand dissociation. The chemistry
of the M(PPh3)2(g-C7H7) auxiliary should therefore be
dominated by PPh3 ligand dissociation with the prospect
of similar or enhanced reactivity compared to that of the
Ru(PPh3)2Cp* system.
Reaction of a stirred acetone solution (30 cm3) of
[WI(CO)(PPh3)(g-C7H7)]
(0.70 g,
1.01 mmol)
with
Ag[BF4] (0.20 g, 1.03 mmol) resulted in a colour change
from green to red then back to green. After 15 min the
reaction mixture was filtered and PPh3 (0.265 g,
1.01 mmol) added. The reaction mixture was gently
refluxed on a water bath for 2 h, then solvent removed
in vacuo. The resulting residue was redissolved in CH2Cl2
and gentle refluxing continued for 30 min. The resulting
green solution was filtered, reduced in volume and diethyl
ether added to precipitate the crude product. Recrystalli-
sation from CH2Cl2-diethyl ether gave 3 as a green-brown
solid as the first precipitated fraction. Yield: 0.14 g (14%).
This sample gave microanalytical data indicative of
CH2Cl2 solvent of crystallisation (C, 54.8%, H, 3.9%,
Cl, 5.60%; required for C44H37OP2-WBF4CH2Cl2: C,
54.1%, H, 3.9%, Cl, 7.1%); the microanalytical data given
in Table 1 were obtained by further recrystallisation of
the complex from acetone-diethyl ether.
4. Experimental
4.1. General procedures
The preparation, purification and reactions of the com-
plexes described were carried out under dry nitrogen. All
solvents were dried by standard methods, distilled and
deoxygenated before use. The compounds [MX(CO)-
(PPh3)(g-C7H7)] (M = Mo, X = Br [11]; M = W, X = I
[10]), [MoMe(CO)(PPh3)(g-C7H7)] [11], [Mo(NCMe)(CO)-
(PPh3)(g-C7H7)][BF4] [13] and [W(CO)2(PPh3)(g-C7H7)]
[BF4] [36] were prepared by published procedures.
300 MHz 1H and 75 MHz 13C{1H} NMR spectra were
recorded on Varian Inova 300 or Varian Inova 400 spec-
trometers. Infrared spectra were obtained on a Perkin–
Elmer FT 1710 spectrometer and mass spectra were
recorded using Kratos Concept 1S (FAB spectra), Micro-
mass Platform II (ES spectra) or Micromass/Waters Tof
Spec 2E (MALDI spectra) instruments. Microanalyses
were by the staff of the Microanalytical Service of the
School of Chemistry, University of Manchester.
4.5. X-ray crystal structures of [W(CO)(PPh3)2(g-C7H7)]
[BF4] (3) and [W(CO)2(PPh3)(g-C7H7)][BF4] Æ
CH2Cl2 (4)
The majority of details of the structure analyses car-
ried out on complexes 3 and 4 are given in Table 4. Data
collection, cell refinement and data reduction were car-
ried out with Bruker SMART and Bruker SAINT software;
4.2. Preparation of [Mo(CO)(PPh3)2(g-C7H7)][PF6] Æ
CH2Cl2 (1)
Table 4
Crystal data and refinement parameters for [W(CO)(PPh3)2(g-C7H7)][BF4]
(3) and [W(CO)2(PPh3)(g-C7H7)][BF4] Æ CH2Cl2 (4)
A green, stirred solution of [Mo(CH3)(CO)(PPh3)-
(g-C7H7)] (0.132 g, 0.27 mmol) in thf (30 cm3) was cooled
to ꢀ78 ꢁC, then treated with [Ph3C][PF6] (0.110 g,
0.28 mmol) immediately followed by PPh3 (0.079 g,
0.30 mmol). On warming slowly to room temperature the
colour changed first to yellow-brown, then green brown.
The reaction mixture was then reduced to dryness in vacuo
and the residue recrystallised from thf-diethyl ether then
CH2Cl2-diethyl ether to give 1 as a green brown solid.
Yield: 0.13 g (50%, as CH2Cl2 solvate).
Complex
Formula
3
4
WC44H37P2OBF4 WC27H22PO2BF4 Æ
CH2Cl2 Æ O
914.34
100(2)
0.71073 (Mo Ka) 0.71073 (Mo Ka)
Monoclinic
P21/c
15.4445(19)
13.4246(13)
17.891(3)
97.721(13)
3675.8(8); 4
32.86
Mass
781.00
100(2)
Temperature (K)
˚
k (A)
Crystal System
Space group
Monoclinic
P21/c
˚
a (A)
10.9042(7)
18.6959(11)
14.3821(9)
92.6390(10)
2928.9(3); 4
42.35
˚
b (A)
˚
c (A)
b (ꢁ)
V (A ); Z
3
˚
4.3. Preparation of [W(NCMe)(CO)(PPh3)(g-C7H7)]
[BF4] (2)
Absorption coefficient (cmꢀ1
)
h Range (ꢁ)
Limiting indices (hkl)
1.90–26.39
19; 16; 22
1.79–28.27
ꢀ14/14; ꢀ23/24;
ꢀ18/19
Addition of Ag[BF4] (0.35 g, 1.79 mmol) to a green,
stirred solution of [WI(CO)(PPh3)(g-C7H7)] (1.00 g,
1.45 mmol) in NCMe (40 cm3) rapidly produced a precipi-
tate of AgI. Reaction was continued for 1 h then the reac-
tion mixture was filtered and solvent removed from the
filtrate. Recrystallisation of the residue from CH2Cl2-
Total reflections
Independent reflections, I > 2r(I) 7506
R1
wR2
28,680
25,089
6930
0.0392
0.1081
0.0173
0.0417
99.6
Completeness to theta (%)
95.3

1886
E.C. Fitzgerald et al. / Journal of Organometallic Chemistry 691 (2006) 1879–1886
SHELXS-97 [37] was employed for the computing of struc-
ture solution and SHELXL-97 [38] for the computing of
structure refinement. In each case an absorption correc-
tion was applied with the aid of the SADABS programme
[39]. Both structures were solved by direct methods with
refinement by full-matrix least-squares based on F2
and all non-hydrogen atoms were refined anisotropi-
cally; hydrogen atoms were included in calculated
positions.
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4 Æ CH2Cl2 were obtained as red blocks by vapour diffusion
of diethyl ether into a CH2Cl2 solution of the complex. A
crystal of dimensions 0.20 · 0.10 · 0.05 mm was selected
for analysis. The asymmetric unit of complex 4 contains
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Acknowledgement
We are grateful to the EPSRC for the award of a Re-
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Appendix A. Supplementary data
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic Data
Centre. CCDC 288657 contains the supplementary crystal-
lographic data for complex 3 and CCDC 288658 the data
for complex 4. These may be obtained free of charge from
the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033. Supple-
mentary data associated with this article can be found,
in the online version, at doi:10.1016/j.jorganchem.
2006.01.013.
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