Syntheses and structures of six and seven-coordinate diene complexes of molybdenum and tungsten(II). The crystal and molecular structures of [WBr2(CO)2(PMePh2)(norbornadiene)] and [WBr2(CO)(NCCH=CH2)(norbornadiene)]

Article abstract of DOI:10.1016/S0022-328X(99)00509-4

Reactions of [WI₂(CO)₃(NCMe)₂] with norbornadiene (NBD) and 1,5-cycloctadiene (COD) give six-coordinate dicarbonyls [WI₂(CO)₂(NBD)] and [WI₂(CO)₂(COD)], respectively. The related dibromo complex [WBr₂(CO)₂(NBD)] reacts with tertiary phosphines L to give unstable seven-coordinate adducts [WBr₂(CO)₂(L)(NBD)] (L=PPh₃, PMePh₂, PEt₃), which in the case of L=PMePh₂ was shown to undergo CO loss to give the six-coordinate derivative [WBr₂(CO)(PMePh₂)(NBD)]. X-ray diffraction studies of [WBr₂(CO)₂(PMePh₂)(NBD)] reveal a seven-coordinate structure (distorted pentagonal bipyramid) with the diene C=C bonds on the pentagonal plane lying approximately parallel to the W-CO axes. Reactions of [WBr₂(CO)₂(NBD)] with organonitriles NCR at room temperature afford CO substitution products (R=Me, Prⁱ, Ph, C₆H₄Me-4, CH=CH₂) directly with no evidence for seven-coordinate intermediates. [WBr₂(CO)₂(COD)] and acetonitrile similarly give [WBr₂(CO)(NCMe)(COD)]. X-ray diffraction studies of [WBr₂(CO)(NCCH=CH₂)(NBD)] confirmed a distorted octahedral structure where the carbonyl lies trans to the acrylonitrile ligand.

Full text of DOI:10.1016/S0022-328X(99)00509-4

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 592 (1999) 168–179
Syntheses and structures of six and seven-coordinate diene
complexes of molybdenum and tungsten(II). The crystal and
molecular structures of [WBr2(CO)2(PMePh2)(norbornadiene)] and
[WBr2(CO)(NꢀCCHꢁCH2)(norbornadiene)]
Jack L. Davidson *, Heiko Richtzenhein, Benedicte J.S. Thiebaut, Kai Landskron,
Georgina M. Rosair
Department of Chemistry, Heriot–Watt Uni6ersity, Riccarton, Edinburgh, EH14 4AS, UK
Received 6 July 1999; accepted 27 August 1999
Abstract
Reactions of [WI2(CO)3(NCMe)2] with norbornadiene (NBD) and 1,5-cycloctadiene (COD) give six-coordinate dicarbonyls
[WI2(CO)2(NBD)] and [WI2(CO)2(COD)], respectively. The related dibromo complex [WBr2(CO)2(NBD)] reacts with tertiary
phosphines L to give unstable seven-coordinate adducts [WBr2(CO)2(L)(NBD)] (L=PPh3, PMePh2, PEt3), which in the case of
L=PMePh2 was shown to undergo CO loss to give the six-coordinate derivative [WBr2(CO)(PMePh2)(NBD)]. X-ray diffraction
studies of [WBr2(CO)2(PMePh2)(NBD)] reveal a seven-coordinate structure (distorted pentagonal bipyramid) with the diene CꢁC
bonds on the pentagonal plane lying approximately parallel to the WꢂCO axes. Reactions of [WBr2(CO)2(NBD)] with
organonitriles NCR at room temperature afford CO substitution products (R=Me, Pri, Ph, C6H4Me-4, CHꢁCH2) directly with
no evidence for seven-coordinate intermediates. [WBr2(CO)2(COD)] and acetonitrile similarly give [WBr2(CO)(NCMe)(COD)].
X-ray diffraction studies of [WBr2(CO)(NCCHꢁCH2)(NBD)] confirmed a distorted octahedral structure where the carbonyl lies
trans to the acrylonitrile ligand. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Six coordination; Seven coordination; Tungsten; Norbornadiene; Synthesis; Crystal structures
e.g. halides or oxygen donor ligands. Previously we
1. Introduction
have reported evidence for sulphur“metal p donation
in thiolate complexes [MSC6F5(CO)(CF3CꢀCCF3)(h5-
An interesting feature of divalent molybdenum and
tungsten chemistry is the ability of the metal to form
C5H5)] [2], [M(SC6F5)4(h5-C5H5)]− and [W(SC6F5)3-
(CO)(h5-C5H5)]− [3]. This may be responsible for the
either seven-coordinate 18-electron complexes which
fact that pentafluorophenylthiolate norbornadiene com-
may be mono- or dinuclear or alternatively coordina-
tively unsaturated six-coordinate derivatives with a for-
plexes [WBr(SC6F5)(CO)2(NBD)] and [W(SC6F5)2-
(CO)2(NBD)] [4] (NBD=norbornadiene) prefer six co-
mal 16-electron configuration [1]. Although steric
ordination, even when two-electron donor ligands are
factors might be expected to play a significant role in
added. Related molybdenum and tungsten thiolate
determining the relative stability of six- and seven-coor-
dinate derivatives, in some cases electronic factors may
also be important. For example, formally electron defi-
cient six-coordinate complexes could, in principle, be
stabilised by p donation from certain anionic ligands,
complexes have also been reported [5–7] which provide
further support for this conclusion. However, substitu-
tion of one bromo ligand in [WBr2(CO)2(NBD)] (1a) [8]
by potentially bidentate ligands L–L=O(O)CMe and
O(S)CMe leads to 1:1 derivatives [WBr(L–L)(CO)2-
(NBD)] [4] which, according to spectroscopic data, are
probably seven coordinate. Seven coordination is also
preferred in related species such as [MoBr{O(X)CMe}-
(CO)2(PPh3)2] (X=O, S) [9].
* Corresponding author. Tel.:+44-131-451-3760; fax: +44-131-
451-3180.
E-mail address: j.l.davidson@hw.ac.uk (J.L. Davidson)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00509-4

J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
169
although seven-coordinate species appeared to be
formed initially. It subsequently proved possible to
isolate the initial product in each case by slow addition
of a diethylether solution of the phosphine to a di-
ethylether solution of [WBr2(CO)2(NBD)] at 0°C when
the adducts 2a–c were obtained as yellow solids.
Elemental analysis of all three products isolated
confirmed the stoichiometry [WBr2(CO)2(L)(NBD)]
(L=PPh3 2a, PMePh2 2b, and PEt3 2c). Spectroscopic
data are similar to those of the previously isolated
adduct [WBr2(CO)2(PMe2Ph)(NBD)] vide infra but
these did not allow unambiguous structure assignment.
Consequently a single-crystal X-ray diffraction study of
the PMePh2 complex 2b was carried out. Single crystals
of 2b suitable for X-ray crystallography were obtained
from dichloromethane/60–80 petroleum ether solution.
The molecular structure is shown in Fig. 1 and selected
bond lengths and angles are given in Table 1.
The tungsten atom in 2b is seven coordinate and can
be described as having a distorted pentagonal bipyrami-
dal geometry. The two trans carbonyls occupy the two
axial sites and the two alkene bonds, bromides and the
phosphine the pentagonal plane. To a first approxima-
tion the structure is derived from [W(CO)2Br2(NBD)]
by opening out of the BrꢂWꢂBr angle from 105.86(9)°
in 1a to 146.43(4)° in 2b thus generating a seventh
coordination site which allows the phosphine to bond
to tungsten. The metal therefore achieves coordinative
saturation and attainment of the favoured 18-electron
configuration. The effect of phosphine coordination on
most of the molecular parameters is slight. Most signifi-
cant are the increases in the OCꢂWꢂCO angle from
172.9(4) to 176.6(4)° and in the tungsten to bromine
It has so far proved difficult to rationalise the differ-
ent structural preferences exhibited by d4 complexes in
this area of chemistry. However, there is some con-
straint on the structure and isomeric forms adopted by
d4 diene carbonyl derivatives such as [WBr2(CO)2-
(NBD)] since, to achieve maximum p back donation to
the CꢁC p* orbitals, the diene is constrained to lie cis to
the carbonyl ligand(s) with the CꢁC axes approximately
parallel to the MꢂCꢂO bonds [10]. This led us to extend
our initial studies of seven-coordinate diene carbonyl
complexes derived from the six-coordinate derivatives
[WBr2(CO)2(NBD)] [8] in order to assess the possible
influence of diene ligands on structural preferences for
six and seven coordination in W(II) derivatives.
Papers describing the reactions of [MoX2(CO)2-
(NBD)] (X=I, Br) with N-donor ligands [11], the
structure of the terpyridine (Terp) complex [WBr-
(Terp)(CO)2(NBD)]+ [12] and the tin complex
[WCl(SnCl3)(CO)3(NBD)] [13] prompt us to report
some of our results in this area of chemistry.
2. Results and discussion
,
distances from 2.489(1) and 2.493(1) A to 2.6452(12)
Previously we reported that two electron donors L
(L=PMe2Ph, P(OMe)3 and CNBut) react with
[WBr2(CO)2(NBD)] (1a) to give related six-coordinate
complexes [WBr2(CO)(L)(NBD)] (2) via seven-coordi-
nate intermediates [WBr2(CO)2(L)(NBD)] (3) [8]. With
a view to characterising the role of seven-coordinate
intermediates in CO substitution reactions of
[WBr2(CO)2(NBD)] reactions with other phosphines
PPh3, PMePh2 and PEt3 were carried out. Reactions
carried out at room temperature proved to be complex
,
and 2.6508(12) A. The last may reflect the possibility of
reduced opportunities for Br“W p bonding in the
seven-coordinate complex or alternatively the effect of
increased steric congestion in the pentagonal plane. We
also draw attention to two intramolecular contacts
between Br2 and a phenyl H atom, H22A, [2.592(12) A]
and between Br1 and another phenyl H atom, H21A,
,
,
[3.036(12) A].
The most significant feature of this complex is the
fact that the pentagonal bipyramidal structure is pre-
ferred to the two main alternatives, the capped trigonal
prism and the capped octahedron. Structural and theo-
retical studies suggest that the energy surface linking
these three idealised seven-coordinate geometries is rel-
atively flat [14,15]. The capped octahedron is usually
preferred by halocarbonyl complexes of Mo(II) and
W(II) [1b] but some examples of pentagonal bipyrami-
dal geometry have been found e.g. [WI2(CO)3-
{P(OPh)2}2NPh] and [WI2(CO)3(PPh2CH2PPh2)] [16].
Interestingly, the structure of the related seven-coordi-
nate norbornadiene derivative [WCl(SnCl3)(CO)3-
(NBD)] has been described as a distorted capped trigo-

170
J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
nal prism [13]. However, we note that the coordination
geometry is almost identical to that of [WBr2(CO)2-
(PMePh2)(NBD)] (2b) which we prefer to describe as a
distorted pentagonal bipyramid. To compare [WCl-
(SnCl3)(CO)3(NBD)] with 2b, the trans carbonyl ligands
were considered axial and the pentagonal plane consist-
ing of tungsten, the two midpoints of the NBD ligands,
chloride, carbonyl and the tin ligand. The mean devia-
ometry whereas with b\1.11 capped octahedral or
capped trigonal prismatic structures are preferred [14].
In the case of [WBr2(CO)2(PMePh2)(NBD)] (2b) a nor-
malised bite value b=1.04 was determined for the
norbornadiene ligand, similarly for [WCl(SnCl3)-
(CO)3(NBD)] [13], b=1.05, consistent with the ob-
served isomeric form. For this purpose the position of
the ‘donor atoms’ of the diene were taken as the mid
points of the CꢁC bonds. We note that in related
complexes where the diene has a larger b value e.g.
1,5-cyclooctadiene, six rather than seven coordination
is preferred e.g. in [WBr(SC5H4N)(CO)(NBD)] b ca.
1.28 [18]. Interestingly, the two equatorial halogens in
,
tion from the pentagonal plane is 0.024 and 0.0934 A
for the former and 2b, respectively, with the axial
carbonyl carbon atoms no less than 82° from the
pentagonal plane in both complexes. This similarity
was confirmed by molecular modelling studies [17],
which revealed a close correlation between the two
structures. This apparent conflict in structure descrip-
tion merely illustrates that with seven-coordinate spe-
cies, relating actual geometries of compounds to those
of idealised polyhedra can be fraught with difficulties
when distortions from idealised forms occur.
pentagonal
bipyramidal
derivatives
[WI2(CO)3-
{P(OPh)2}2NPh] and [WI2(CO)3(PPh2CH2PPh2)] [16]
and the Cl and SnCl3 ligands in [WCl(SnCl3)-
(CO)3(NBD)] occupy adjacent sites, whereas the more
symmetric structure in which the two equatorial halo
ligands are separated by the phosphine ligand is pre-
ferred in [WBr2(CO)2(PMePh2)(NBD)]. This difference
may reflect thermodynamic preferences perhaps due to
the effect of having different numbers of strong p
acceptor carbonyl ligands coordinated to the metal.
Alternatively, kinetic factors may be involved as a
Kepert has shown that complexes of this type i.e.
[MX2(CO)3L–L] containing a bidentate ligand L–L
with a ‘normalised bite’ (distance between donor atoms
of the chelate ring divided by the metal–ligand dis-
tance) bB1.11 exhibit the pentagonal bipyramidal ge-
Fig. 1. Molecular structure of [WBr2(CO)2(PMePh2)(NBD)] (2b).
Table 1
Selected bond lengths and angles for 2b
,
Bond lengths (A)
W(1)ꢂC(2)
W(1)ꢂC(8)
W(1)ꢂP(1)
2.013(11)
2.325(10)
2.641(3)
W(1)ꢂC(1)
W(1)ꢂC(9)
W(1)ꢂBr(1)
2.042(10)
2.333(11)
2.6452(12)
W(1)ꢂC(5)
W(1)ꢂC(4)
W(1)ꢂBr(2)
2.325(11)
2.339(11)
2.6508(12)
Bond angles (°)
C(2)ꢂW(1)ꢂC(1)
P(1)ꢂW(1)ꢂBr(1)
176.6(4)
74.33(6)
Br(1)ꢂW(1)ꢂBr(2)
C(2)ꢂW(1)ꢂBr(2)
146.43(4)
94.4(3)
P(1)ꢂW(1)ꢂBr(2)
C(1)ꢂW(1)ꢂBr(2)
73.30(7)
83.0(3)

J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
171
trans to the diene. Since this would give the observed
product 2b directly it is conceivable that this reaction is
indeed frontier orbital controlled.
It is interesting to compare our results with those of
Templeton [19] who measured equilibrium constants for
a series of ligand additions to [Mo(S2CNR2)2(CO)2]
(R=Me, Et) including L=PPh3 and P(OPh)3 Eq. (1).
[Mo(S2CNR2)2(CO)2]+L X [Mo(S2CNR2)2(CO)2L]
(1)
The six-coordinate derivative [Mo(S2CNR2)2(CO)2] (i)
(see Scheme 1) exhibits an unusual trigonal prismatic
structure rather than the distorted octahedron found
for [WBr2(CO)2(NBD)]. A frontier orbital approach to
the reactivity of [Mo(S2CNR2)2(CO)2] predicts ligand
attack on the LUMO in the cavity defined by the
dihedral angle between the two chelating ligands. Sig-
nificantly, the weakly coordinating ligand tetrahydroth-
iophene (tht) was found to form such an adduct
[Mo(S2CNEt2)2(CO)2(tht)] (ii) whereas CO and PPh3
form 1:1 complexes which exhibit structure (iii) with a
mutually cis-MoL(CO)2 fragment. However, this does
not preclude frontier orbital control in the last two
cases since, as mentioned previously, facile structural
rearrangements are well known in seven-coordinate sys-
tems of this type. It would seem that initial attack on (i)
occurs at the predicted site giving (ii) but in some cases
rearrangement can occur to give the thermodynamically
favoured structure (iii).
The spectroscopic data for [WBr2(CO)2(PMePh2)-
(NBD)] (2b) are in accord with the solid state structure
with two wCO modes at 2037(vw) and 1944 (s) cm−1
reflecting the slight distortion of the OCꢂWꢂCO group-
ing from 180° and the consequent activation, albeit
weakly, of the higher frequency asymmetric stretch.
The 1H-NMR spectrum shows phenyl and methyl
group signals due to a single PMePh2 and, more signifi-
cantly, three norbornadiene peaks at l 4.08 (4H), 3.68
(2H) and 1.40 (2H) with chemical shifts and intensities
similar to those of the previously reported derivative
[WBr2(CO)2(PMe2Ph)(NBD)].
Fig. 2. The LUMO of [WBr2(CO)2(NBD)] (1a) according to EHMO
calculations.
consequence of the fact that the diphosphazane and tin
complexes result from ligand displacement from seven-
coordinate complexes, whereas [WBr2(CO)2(PMePh2)-
(NBD)] was obtained by addition of the seventh ligand,
PMePh2 to a six-coordinate precursor.
In this connection we note that the formal 16-elec-
tron configuration of the metal in 1a implies the exis-
tence of a low lying metal-based orbital which could
function as the site of attack by the phosphine. Conse-
quently extended Hu¨ckel calculations [17] were carried
out on the precursor [WBr2(CO)2(NBD)] based on the
geometry found in the solid state but with the NBD
and CO positions adjusted to generate C26 symmetry.
These gave similar results to Fenske–Hall calculations
on the idealised complex [MoBr2(CO)2(H2CꢁCH2)2] re-
ported by Cotton [10] with the octahedral t2g set of dp
orbitals split into a high-energy empty orbital the
LUMO (primarily dxz in Cotton’s coordinate system)
and two lower energy filled orbitals. The significant
HOMO–LUMO gap, which is sufficient to produce
spin pairing in the lower set of dp orbitals, results from
strong p bonding between dxy, dyz and the CO and
diene p* orbitals. If addition of a seventh ligand is
frontier orbital controlled there are three possible direc-
tions for attack of a nucleophile such as a phosphine on
the LUMO, see Fig. 2, all involving approach in the
pentagonal plane. Two (equivalent) situations involve
attack between a diene CꢁC bond and a bromide
ligand. However, these are sterically less favourable
than from a direction between the two bromides and
Previously we observed that seven-coordinate com-
plexes [WBr2(CO)2(L)(NBD)] (L=PMe2Ph, P(OMe)3,
CNBut), undergo CO loss at room temperature to give
dark
blue/black
six-coordinate
monocarbonyls
Scheme 1. Mechanism of ligand addition to [Mo(S2CNR2)2(CO)2].

172
J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
Scheme 2. Mechanism of CO substitution in [WBr2(CO)2(NBD)] (1a).
terised nitrile derivatives [WBr2(CO)(NCR)(NBD)] re-
ported later in this paper.
[WBr2(CO)(L)(NBD)] (3). These give blue solutions
similar to those observed in the formation of complexes
2. A blue/black derivative 3a was subsequently ob-
tained on allowing a dichloromethane solution of
[WBr2(CO)2(PMePh2)(NBD)] to sit at room tempera-
ture for 15 h. Analytical data suggest the stoichiometry
[WBr2(CO)(PMePh2)(NBD)] whilst the IR spectrum
shows a single wCO mode at 1964 cm−1 in accord with
this formulation. This compares with 1974 cm−1 for
[WBr2(CO)(PMe2Ph)(NBD)] (3b). The presence of a
single peak in the 31P{1H}-NMR spectrum at l −4.76
with tungsten satellites JPꢂW=171.5 Hz confirms the
presence of a metal-coordinated phosphine and accord-
These findings unequivocally establish the mechanism
of CO substitution in [WBr2(CO)2(NBD)] in reactions
with phosphines. The incoming nucleophile attacks the
metal trans to the diene in a symmetrical fashion lead-
ing to a seven-coordinate pentagonal bipyramidal
derivative [WBr2(CO)2(L)(NBD)]. This is followed by
slow CO expulsion and transfer of the incoming ligand
to the site vacated by the leaving CO, i.e. trans to the
remaining carbonyl. The exact mechanism by which the
latter process occurs is not known but the simplest
involves CO dissociation followed by non-dissociative
phosphine migration to the site trans to CO, i.e.
Scheme 2 path (i).
1
ingly the H-NMR spectrum shows phenyl and methyl
group signals due to a single PMePh2. More signifi-
cantly, five norbornadiene peaks are observed at l 4.63
(2H), 3.84 (1H), 3.33 (1H), 3.22 (2H) and 0.41 (2H)
with chemical shifts and intensities similar to those of
[WBr2(CO)(PMe2Ph)(NBD)] (3b) {l 4.69 (2H), 3.84
(1H), 3.46 (1H), 3.23 (2H) and 0.43 (2H)}. These data
suggest an octahedral structure similar to that of
[WBr2(CO)2(NBD)] but with one of the carbonyls re-
placed by PMePh2. Direct substitution of the CO by a
phosphine would give the illustrated structure which
would give rise to the observed 1H-NMR spectrum with
five norbornadiene peaks. Further support for this con-
clusion is derived from the fact that the spectroscopic
data are very similar to those of the structurally charac-
An alternative, path (ii), involves prior structural
rearrangement in which the CO and PMePh2 undergo
site exchange and this is then followed by CO dissocia-
tion. This is suggested by our recent observations of

J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
173
fluxional behaviour in related seven-coordinate com-
plexes [WBr(S2PMe2)(CO)(PMe2Ph)(NBD)] and
plex,
the
molybdenum
adduct
[MoBr2(CO)-
(bipy)(NBD)] [11]. The spectroscopic features of the
two complexes are very similar in addition to which
they are isomorphous. The crystallographic unit cell for
4 is 8.349(2), 14.277(3) and 14.615 A, i=93.78(2)°,
V=1738.3(7) A , whilst for the molybdenum species it
[W(S2PR2)2(CO)(NBD)] (R=Me, OMe) containing
bidentate ligands [18] in addition to which ligand site
exchange in seven-coordinate compounds is a well
known phenomenon, sometimes with very low energy
barriers [1b].
,
3
,
,
is: 8.3808, 14.2490, 14.6530 A, i=94.43°, V=1745.
Since the structural features of the two derivatives are
very similar no further details of [WBr2(CO)-
(bipy)(NBD)] (4) will be reported here but crystallo-
graphic data are available from the Cambridge Crystal-
lographic Data centre. Interestingly these reactions
contrast with those of [MoBr2(CO)2(NBD)] with ter-
pyridines (terpy) which give ionic complexes [Mo-
Br(CO)(terpy)(NBD)]+ one of which was shown to
adopt an unusual structure in which the norbornadiene
and Br form a triangle perpendicular to the plane of the
terpyridine and CO ligands [12]. The reaction of 2,2%-
bipyridyl with the related bis-alkyne derivative
[WClI(CO)(NCMe)MeCꢀCMe)2] also yields a cationic
derivative [WCl(CO)(bipy)MeCꢀCMe)2]I, in this case
by iodine displacement [22]. Other cationic alkyne
derivatives have been reported by Baker et al. in which
halide displacement results from phosphine addition
[23]. This again reflects the preference of alkyne deriva-
tives for six coordination where both sets of alkyne p
orbitals are involved in bonding with the metal. Diene
complexes such as 1 where this is not possible, resort to
seven coordination when an 18-electron configuration is
required. So far we have not observed the formation of
cationic derivatives in reactions of these complexes
despite the fact that simple Mo(II) and W(II) ionic
derivatives have been known for many years [1,24].
Nakamura also reported the synthesis of
[MoBr2(CO)2(NBD)]n=1 which exists in two forms, one
The observation that seven-coordinate species are
intermediates in CO substitution reactions of
[WBr2(CO)2(NBD)] is not entirely surprising taking
into account the formal 16-electron configuration of the
complex. A wide range of seven-coordinate Mo(II) and
W(II) carbonyl complexes is known, many of which
undergo CO loss to give six-coordinate derivatives
[1a,1d]. This contrasts with related six-coordinate
alkyne complexes of Mo(II) and W(II) where stabilisa-
tion of the apparent 16-electron configuration has been
ascribed to additional p donation from the alkyne
ligands [20]. In the case of mono- and bis-alkyne com-
plexes up to four electrons can formally be considered
to be donated from the CꢀC triple bond(s) to the d4
metal center. In other cases oxo and sulphur based
ligands are considered to function as p donors and thus
contribute to reducing the electron deficiency at the
metal. Perhaps not suprisingly, seven-coordinate inter-
mediates have never been reported in substitution reac-
tions of six-coordinate mono and bis alkyne d4
complexes since this would require the alkyne(s) to
revert to two-electron donation.
Previously we reported that [WBr2(CO)2(NBD)] re-
acts with the bidentate ligand 2,2%-bipyridyl (bipy) to
give a seven-coordinate complex, the monocarbonyl
[WBr2(CO)(bipy)(NBD)] [8]. In view of the pentagonal
bipyramidal structure established for [WBr2(CO)2-
(PMePh2)(NBD)] an X-ray diffraction study of
[WBr2(CO)(bipy)(NBD)] was carried out [21]. This re-
vealed a seven-coordinate structure 4 similar to that of
[WBr2(CO)2(PMePh2)(NBD)] with one nitrogen in the
phosphine position in the pentagonal plane and the
other trans to the remaining carbonyl and with a
BrꢂWꢂBr angle, 144.81(4)° slightly less than that ob-
served in the phosphine derivative 2b, 146.43(4)°.
a
monomer (n=1) structurally analogous to
[WBr2(CO)2(NBD)], the other di- or polymeric, n\1
[11]. This reacts with acetonitrile to give an unstable, ill
defined complex formulated as the seven-coordinate
derivative [MoBr2(CO)2(NCMe)(NBD)]. In principle
this species should exhibit some similarities to phos-
phine adducts [WBr2(CO)2(PR3)(NBD)] (2). Since
Baker has made extensive use of the nitrile derivatives
[MI2(CO)3(NCMe)2] (M=Mo, W) in developing the
chemistry of Mo(II) and W(II) [1d,25] we decided to
explore the use of these reagents in the synthesis of
diene complexes with the possibility in mind that car-
bonyl nitrile derivatives similar to that reported by
Nakamura might be obtained. While this work was
being carried out a report of the synthesis of the
aforementioned tin derivative [WCl(SnCl3)(CO)3-
(NBD)] from the reaction of [WCl(SnCl3)(CO)3-
(NCMe)2] with norbornadiene was published [13].
Complexes [MI2(CO)3(NCMe)2] (M=Mo, W) were
prepared as described previously by iodine oxidation of
an acetonitrile solution of [M(CO)3(NCMe)3] (M=Mo,
However, during the course of this work Nakamura
reported structural studies of an almost identical com-

174
J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
W) [26]. Although these were previously obtained in
quantitative yield without the requirement for purifica-
tion, in our hands this method gave impure products
according to IR studies and a minor modification to the
procedure was required. This involved filtration fol-
lowed by two recrystallisations from CH2Cl2–
petroleum ether to give brown (M=Mo) or red–brown
(M=W) crystals of [MI2(CO)3(NCMe)2] (M=Mo, W)
in good yield (M=Mo, 68%; M=W, 76%). The reac-
tion of [MoI2(CO)3(NCMe)2] with norbornadiene in
CH2Cl2 was followed by IR spectroscopy which indi-
cated that initially the nitrile free species
[MoI2(CO)2(NBD)]n, previously reported by Nakamura
[11], is formed but when the reaction was allowed to
proceed further an additional broad band near 1990
cm−1 appeared, close to that reported for
[MoI2(CO)2(NCMe)(NBD)] (5). Unfortunately neither
of these two species could be isolated in a pure form
also by refluxing in petroleum ether. However, all of
these attempts were unsuccessful. The tungsten complex
[WBr2(CO)2(COD)] has been obtained previously [8] by
the same route which affords the norbornadiene com-
pound i.e. refluxing a solution of the diene and
[WBr2(CO)4]2 in 60–80 petroleum ether. In contrast to
the reactions involving the molybdenum derivative,
refluxing a suspension of [WI2(CO)3(NCMe)2] and nor-
bornadiene in 60–80 petroleum ether for 3 h gave a
red-wine coloured solution which, on work up gave
dark-green crystals of the dicarbonyl derivative
[WI2(CO)2(NBD)] (1b) (42% yield) analogous to
[WBr2(CO)2(NBD)] (1a). This formulation is based on
elemental analysis and mass spectrometry which shows
a molecular ion at m/z=584 [M]+. The IR spectrum
contains two bands at 2058 (w) and 1992 (s) cm−1
indicating trans carbonyls but no trace of the wCꢀN
mode of coordinated acetonitrile. This, and the fact
that all other data are similar to that of the analogous
bromide complex 1a, indicates that [WI2(CO)2(NBD)]
1
but H-NMR data for the impure product compares
well with those reported by Nakamura for the above
species. We note that Nakamura suggested a seven-co-
ordinate structure for the nitrile complex 5 but did not
propose a definite structure. As illustrated seven-coordi-
nate pentagonal bipyramidal structures based on that
of the phosphine adduct 2b and the tin complex
[WCl(SnCl3)(CO)3(NBD)] [13] would not give rise to
the spectrum reported for 5 since 5(i) has only three sets
of non-equivalent protons Ha, Hb and Hc, ratio 4:2:2
and the less symmetrical 5(ii) five sets Ha, Hb, Hc, Hd
and He, ratio 2:2:2:1:1. A third isomeric form 5(iii) is
consistent with the NMR data but this structure with
cis carbonyls should give rise to two strong peaks in the
IR spectrum and must therefore be excluded. Interest-
ingly however, we note that the six-coordinate form
5(iv) should give rise to the observed NMR and IR
spectra.
has
a
distorted octahedral structure where the
OCꢂWꢂCO angle is slightly less than 180° as revealed
in [WBr2(CO)2(NBD)] by single-crystal X-ray diffrac-
tion studies. Two norbornadiene resonances are ob-
1
served in the H-NMR spectrum at l 4.56 (4H) and
3.99 ppm. This, and a simple triplet for the two
methylene protons, underlines the high symmetry of the
norbornadiene ligand as found in the free hydrocarbon.
Subsequently, the corresponding cyclooctadiene com-
plex [WI2(CO)2COD] (1c) was obtained as dark-green
crystals in 31% yield using the synthetic methodology
employed for the norbornadiene complex 1b. The IR
and NMR spectra are almost identical to those of the
previously reported bromo complex [WBr2(CO)2COD]
[8] suggesting a similar structure. These findings con-
trast with the fact that the aforementioned seven-coor-
dinate tricarbonyl [WCl(SnCl3)(CO)3(NBD)] was
obtained from the reaction of [WCl(SnCl3)(CO)3-
(NCMe)2] with norbornadiene [13]. It would therefore
appear that, as with complexes 2 and 3, the stability of
the seven-coordinate species with respect to CO loss to
give a six-coordinate derivative depends on a subtle
combination of donor and acceptor properties of the
various ligands.
In view of these findings, reactions of [WBr2(CO)2-
(NBD)] (1a) with nitriles RCꢀN (R=Me, Pri, Ph,
C6H4Me-4, CHꢁCH2) were carried out and followed by
IR spectroscopy. In each case little change in colour
was observed over several hours but IR spectroscopy
indicated the formation of a new carbonyl containing
species. Work up from dichloromethane–light
petroleum gave, in each case, a dark blue/black crys-
talline complex which analysed as the carbonyl substi-
tution product [WBr2(CO)(NCR)(NBD)] 6. The
complexes are reasonably stable in the solid state for
lengthy periods if kept at low (−15°C) temperature
In view of this anomaly we attempted synthesis of an
analogous complex by reacting [MoI2(CO)3(NCMe)2]
with 1,5-cyclooctadiene in CH2Cl2, THF or Et2O and

J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
175
OCꢂWꢂCO angle in the latter, 172.9(4)° is similarly
close to the equivalent NꢂWꢂC angle of 169.9(7)° in 6e.
Interestingly the replacement of a p acceptor, carbon
monoxide, by a | donor nitrile also has little effect on
the bond distances. For example the remaining CO has
Fig. 3. Molecular structure of [WBr2(CO)(NCCHꢁCH2)(NBD)] (6e).
,
a CꢂW distance of 1.98(2) A, which compares with an
,
average of 2.04 (1) A in the precursor 1a, probably
under nitrogen. However, they become unstable in solu-
tion at room temperature but addition of free nitrile
significantly inhibits the decomposition process. This
may suggest that initial nitrile dissociation is occurring.
In view of the contrast with Nakamura’s report that
[MoI2(CO)2(NBD)]n and acetonitrile reversibly give a
seven-coordinate 1:1 dicarbonyl adduct 5 a single-crys-
tal X-ray diffraction study of the acrylonitrile complex
[WBr2(CO)(NCCHꢁCH2)(NBD)] (6e) was carried out.
reflecting the expected increase in p back donation to
the remaining carbonyl. However, the tungsten to car-
bon distances of the diene ligand W(1)ꢂC(5) 2.26(2),
W(1)ꢂC(6) 2.31(2), W(1)ꢂC(8) 2.27(2) and W(1)ꢂC(9)
2.26(2) are very similar to those of the precursor, i.e.
,
2.29 (1), 2.30 (1), 2.26 (1) and 2.26 (1) A implying that
tungsten–alkene bonding is little affected by CO substi-
tution. This is a little unexpected since with this struc-
ture the diene p* orbitals effectively interact with the
same metal dp orbitals as the CO ligands. The only
other features of note are the short CꢁC bond in the
Single crystals of 6e were obtained from
a
dichloromethane–light petrolium mixture at −15°C.
The molecular structure is shown in Fig. 3 and selected
bond lengths and angles are given in Table 2.
,
nitrile ligand, 1.21(3) A, which may simply be a conse-
quence of libration and the intermolecular contact be-
The structure of [WBr2(CO)(NCCHꢁCH2)(NBD)]
(6e) is based on distorted octahedral coordination
about the metal centre and is therefore closely related
to that of the precursor [WBr2(CO)2(NBD)] (1a). The
nitrile lies trans to the remaining CO whilst the NBD
ligand is cis to the CO and in the same plane as the two
Br ligands. Direct substitution of one of the carbonyl
ligands in 1a by the nitrile ligand appears to have little
overall effect on the geometry of the molecule. For
example the largest distortion from octahedral geome-
try, Br(1)ꢂW(1)ꢂBr(2), is 107.15(9)°, which compares
with 105.86(5)° in the parent dicarbonyl 1a. The
,
tween Br(2) and a NBD H atom, H8A, of 2.88(2) A.
The structure of [WBr2(CO)(NCCHꢁCH2)(NBD)]
(6e) can also be compared with that of bis alkyne
complexes [WI2(CO)(NCR)(R%CꢀCR%)2] (W, R=Me,
But, R=Me, R=Me, R%=Ph) reported by Baker et al
[27,28].
The
structure
of
[WI2(CO)(NCMe)-
(MeCꢀCMe)2] is similar to that of 6e but with two cis
alkynes occupying the donor sites in place of the nor-
,
bornadiene. The WꢂCO distance 1.937(14) A is some-
,
what shorter and the WꢂN distance, 2.132(14) A,
slightly longer than those of 6e. However the most
Table 2
Selected bond lengths and angles for 6e
,
Bond lengths (A)
W(1)ꢂC(1)
W(1)ꢂBr(1)
1.98(2)
2.512(2)
W(1)ꢂN(1)
W(1)ꢂBr(2)
2.228(13)
2.516(2)
C(3)ꢂC(4)
N(1)ꢂC(2)
1.21(3)
1.07(2)
Bond angles (°)
C(1)ꢂW(1)ꢂN(1)
169.9(7)
Br(1)ꢂW(1)ꢂBr(2)
107.15(9)
N(1)ꢂW(1)ꢂC(9)
78.6(6)

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J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
significant differences lie in the distortion from octahe-
dral geometry, which is much more significant in the
alkyne complex. This is exemplified by the IꢂWꢂI bond
angle, which at 83.51(4) is much more acute {cf. 6e,
BrꢂWꢂBr, 107.15(9)°}, as is the NꢂWꢂCO angle of
163.3(6)°, cf. 169.9(7)° in 6e. This may reflect: (a) the
steric effects of the bulky iodine ligands; (b) the effect
of the geometrically constrained diene with limited
chelate bite; and (c) the presence of pÞ orbitals on the
alkynes which enables additional electron donation (a
total of six electrons from the two alkynes) giving, in
effect, a coordinatively saturated 18-electron complex.
The spectroscopic features of the nitrile derivatives 6
are in full accord with the solid-state structure of 6e
with one weak wCꢀN and a strong wCO band in the IR
spectra. The spectra were recorded in KBr to minimise
decomposition which was occasionally significant in
solution. In all cases peaks due to the precursor
[WBr2(CO)2(NBD)] (1a) were observed. Even in the
solid state additional weak peaks were observed and
these increased in intensity with time. The decomposi-
tion process was also followed by 1H-NMR spec-
troscopy which confirmed the formation of 1a. For this
2:2:1:1:2 in the 1H-NMR spectrum. The possibility
therefore exists that Nakamura’s complex is a six-coor-
dinate derivative [MoI2(CO)(NCMe)(NBD)] with struc-
ture 5(iv) similar to complexes 6. Although this is not
consistent with Nakamura’s observation that prolonged
drying of the complex in vacuo regenerates the dicar-
bonyl [MoI2(CO)2(NBD)] we note that all of the tung-
sten complexes [WBr2(CO)(NCR)(NBD)] reported
herein undergo decomposition in solution generating
peaks in the IR and NMR spectra due to
[WBr2(CO)2(NBD)]. This presumably results from ni-
trile dissociation and intermolecular CO transfer. The
process appears to be inhibited by addition of excess
organonitrile suggesting that decomposition proceeds
via nitrile dissociation. This may raise some doubts as
to the exact composition of the molybdenum derivative
5 or alternatively that the structure is totally unrelated
to that exhibited by the phosphine adducts 2.
3. Experimental
NMR spectra were recorded on Bruker AM 400 and
WP 200SY spectrometers at 400 and 200.13 MHz (1H,
13C) and 80.13 MHz (31P). Coupling constants are in
Hertz and chemical shifts are referenced to Me4Si (1H,
13C) and H3PO4 (31P), (l=0 ppm). IR spectra were
recorded on a Nicolet Impact 400 FT–IR machine and
mass spectra (FAB, EI) on an Vacuum Generators
updated A.E.I. MS 11. Reactions were carried out
under dry oxygen-free nitrogen using standard Schlenk
techniques. Solvents were dried by refluxing over P2O5
(CH2Cl2), sodium/benzophenone (petroleum ether (60–
80), Et2O, THF, MeCN) and distilled just before use.
[WBr2(CO)2(NBD)] was synthesised as described previ-
ously [8] as were [MI2(CO)3(NCMe)2, (M=Mo, W)
[26] although some modifications to the published pro-
cedure were employed as described in Section 2.
1
reason H-NMR spectra were recorded at low tempera-
1
tures, ca. −20°C. The H-NMR spectra of the major-
ity of the complexes are initially confusing since only
three non-methylene norbornadiene proton signals are
observed, with an integrated ratio of 2:2:2, suggesting a
higher symmetry structure. However, the NCC6H4Me-4
derivative 6d shows the expected five signals ratio
2:1:1:2 suggesting accidental degeneracy of two of the
peaks in the spectra of the other nitrile derivatives.
Further support for this conclusion was provided by
synthesis
of
the
cyclooctadiene
derivative
[WBr2(CO)(NCMe)(COD)] (6f) from the reaction of
MeCN and [WBr2(CO)2(COD)] (1c). The green crys-
talline product has the expected single wCO mode at
1927 cm−1 but, more significantly, six well resolved
equal intensity cyclooctadiene multiplets (a–f) between
l 2.7 and 5.7 consistent with the illustrated six-coordi-
nate structure.
3.1. Reaction of [WI2(CO)3(NCMe)2] with
norbornadiene
Norbornadiene (0.25 ml, 2.46 mmol) was added to a
suspension of [WI2(CO)3(NCMe)2] (1.24 g, 2.05 mmol)
in petroleum ether (100 ml) and the solution was
refluxed gently for 3 h until an intense red-wine
coloured solution was obtained. The hot solution was
filtered, concentrated in vacuo and crystallised from
petroleum ether. The crystalline solid was recrystallised
from CH2Cl2/petroleum ether to give dark-green crys-
tals of [WI2(CO)2(NBD)] (1b) (0.51 g, 42%). (Found: C,
17.7; H, 1.0. C9H8I2O2W requires: C, 18.44; H, 1.38%).
(m/z)=584 [M]+). IR (CH2Cl2): w(CO) 2058(w), 1992(s)
cm−1. 1H-NMR (CDCl3): l 4.56 (m, 4H), 3.99 (m, 2H),
0.52 (t, 2H).
Interestingly the norbornadiene complexes 6a–e have
very similar spectroscopic features to the purported
seven-coordinate derivative [MoI2(CO)2(NCMe)(NBD)]
(5) which has five norbornadiene peaks in the ratio

J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
177
3.2. Reaction of [WI2(CO)3(NCMe)2] with
1,5-cyclooctadiene
vacuo to ca. 4 ml when yellow crystals formed. The
remaining solvent was removed by syringe and the
crystals washed with petroleum ether and dried in
vacuo to give [WBr2(CO)2(PEt3)(NBD)] (2c) (75 mg,
41%). (Found: C, 29.52; H, 3.76. C15H23Br2O2PW re-
quires: C, 29.54; H 3.80%). IR (Nujol/pet. ether) wCO
Cyclooctadiene (0.13 ml, 1.03 mmol) was added to a
suspension of [WI2(CO)3(NCMe)2] (0.52 g, 0.86 mmol)
in petroleum ether (80 ml) and the solution gently
refluxed for 3 h until an intense dark-green solution was
obtained. The hot solution was filtered and worked up
as for complex 1b to give dark-green crystals of
[WI2(CO)2COD] (1c) (0.16 g, 31%). (Found: C, 20.1; H,
1.7. C10H12I2O2W requires: C, 19.96; H, 2.01%). MS:
(m/z)=601 [M]+). IR(CH2Cl2): w(CO) 2056(w), 1992(s)
cm−1. 1H-NMR (CDCl3): l 4.52 (m, 4H), 3.73 (m, 4H),
3.05 (m, 4H).
1
2035(w), 1950(s) cm−1. NMR (CDCl3): H l 4.08 (m,
4H), 3.68 (m, 2H), 2.35 (m, 6H, CH2CH3), 1.45 (m,
2H), 1.22 (m, 9H, CH2CH3).
3.6. Synthesis of [WBr2(CO)(PMePh2)(NBD)]
[WBr2(CO)2(PMePh2)(NBD)] (2b) (0.200 g, mmol)
was dissolved in 20 ml CH2Cl2 at room temperature to
give a yellow solution. Within 1 h the solution turned
blue, and after 15 h the reaction reached completion
according to IR studies. The resulting blue solution was
reduced in volume and petroleum ether was added to
give a green powder. This was recrystallised from
Et2O–petroleum ether at −15°C to give green crystals
of [WBr2(CO)(PMePh2)(NBD)] (3a) (33 mg, 17%)
(Found: C, 37.64; H, 3.01. C21H21Br2OPW requires: C,
3.3. Reaction of [WBr2(CO)2(NBD)] with PPh3
A total of 300 mg (0.61 mmol) of [WBr2(CO)2(NBD)]
were dissolved in 20 cm3 diethylether and cooled to
0°C. A solution of 159 mg (0.61 mmol) PPh3 was added
slowly to the stirred mixture upon which a yellow
precipitate immediately formed. The solid was allowed
to settle and the remaining blue solution syringed off.
The yellow precipitate was washed with 20 ml
petroleum ether and dried in vacuo to give
[WBr2(CO)2(PPh3)(NBD)] (2a) (410 mg, 90%). (Found:
C, 42.5; H, 2.99. C27H23Br2O2PW requires: C, 43.00; H
37.98; H, 3.19%). IR (CH2Cl2): w(CO) 1964(s) cm−1
.
1H-NMR (CDCl3, 25°C): l 7.78–7.35 (m, 10H, Ph),
4.63 (m, 2H, NBD), 3.84 (M, 1H, NBD), 3.33 (m, 1H,
NBD), 3.22 (m, 2 H, NBD), 2.26 (d, 3H, Me), 0.41 (br
s, 2H, NBD). 31P{1H}-NMR (CDCl3, 25°C) l −4.76
(t, JPꢂW=171.5 Hz).
3.07%). IR (KBr): wCO 2039(w), 1934(s), 1926(s) cm−1
.
1H-NMR (CDCl3, −40°C): l 7.3–7.7 (m, 15H), 4.12
(m, 4H), 3.70 (br s, 2H), 1.40 (br s, 2H).
3.7. Reaction of [WBr2(CO)2(NBD)] with NCMe
3.4. Reaction of [WBr2(CO)2(NBD)] with PMePh2 at
0°C
The complex [WBr2(CO)2(NBD)] (0.133 g, 0.27
mmol) was dissolved in 20 ml Et2O and cooled down to
0°C. A solution of NCMe (0.016 ml, 0.28 mmol) was
slowly added to the previous purple solution. The solu-
tion was allowed to warm up to room temperature to
react for 5 h. At this stage of the reaction another mole
equivalent of the ligand was added to the mixture and
1 h at room temperature was required to complete the
reaction. The resulting blue solution was concentrated
in vacuo and a layer of petroleum ether added. Slow
recrystallisation at −15°C afforded green crystals of
[WBr2(CO)(NCMe)(NBD)] (6a) (0.058g, 43%). (Found
C, 23.62; H, 2.10; N, 2.65. C10H11Br2NOW requires: C,
23.79, H, 2.20; N, 2.77%). IR (KBr): w(CꢀN) 2311(w),
A total of 150 mg (0.31 mmol) of [WBr2(CO)2(NBD)]
were dissolved in 10 ml ether, stirred and cooled down
to 0°C. A solution of ten drops PPh2Me in 20 ml ether
was added very slowly until the formation of a yellow
precipitate was complete. The blue solution was sy-
ringed off and the precipitate washed with 10 ml
petroleum ether and dried in vacuo to give yellow
crystals of [WBr2(CO)2(PMePh2)(NBD)] (2b) (178 mg,
86%). (Found: C, 38.5; H, 3.0. C23H21Br2OPW requires:
C, 39.24; H 3.01%). IR (CH2Cl2): wCO 2037(w), 1944(s)
1
cm−1. H-NMR (CDCl3, −55°C): l 7.4–7.7 (m, 10H),
1
4.08 (br s, 4H), 3.68 (br s, 2H), 2.55 (d, 3H PMePh2),
2284(w), w(CO) 2028(w), 1929(s) cm−1. H-NMR (400
1.40 (br s, 2H).
MHz, CDCl3, −20°C): l 5.29 (tm, 2H, NBD), 3.99 (m,
2H, NBD), 3.78 (tm, 2H, NBD), 2.86 (s, 3H, NCMe),
0.77 (s, 2H, NBD).
3.5. Reaction of [WBr2(CO)2(NBD)] with PEt3
A total of 150 mg (0.31 mmol) of [WBr2(CO)2(NBD)]
were dissolved in 10 ml ether, stirred and cooled down
to 0°C. A solution of 0.22 ml PEt3 in 20 ml diethylether
was added slowly over a period of about 1 min to give
a yellow solution. The solution was filtered off, 10 ml
petroleum ether added and the solution reduced in
3.8. Reaction of [WBr2(CO)2(NBD)]with NCPri
The complex [WBr2(CO)2(NBD)] (0.179 g, 0.36
mmol) was dissolved in 20 ml Et2O and a solution of
NCPri (0.033 ml, 0.37 mmol) was slowly added. The
reaction was allowed to proceed at room temperature

178
J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
for 14 h with addition of a mole equivalent of
NCCH(CH3)2 after ca. 6 h. The resulting blue solution
3.11. Reaction of [WBr2(CO)2(NBD)]with NCCHꢁCH2
was slightly concentrated before addition of
a
The complex [WBr2(CO)2(NBD)] (0.197 g, 0.40
mmol) was dissolved in 20 ml Et2O and a solution of
NCCHꢁCH2 (0.027 ml, 0.41 mmol) was slowly added.
Another two mole equivalents were added every 3 h
and the reaction was allowed to completion for an extra
6 h after the last addition. The resulting blue solution
was concentrated to 10 ml and a layer of petroleum
ether was added. Slow recrystallisation at −15°C af-
forded green crystals of [WBr2(CO)(NCCHꢁCH2)-
(NBD)] (6e) (0.128 g, 62%). (Found C, 25.32; H, 1.88;
N, 2.59. C11H11Br2ONW requires: C, 25.56; H, 2.15; N,
2.71%). IR (KBr): w(CꢀN) 2258(w); w(CO) 2033(w),
1992(w), 1942(s). 1H-NMR (400 MHz, CDCl3, −
20°C): l 6.70 (d, 1H, CHꢁCH2), 6.49 (d, 2H, CHꢁCH2),
6.34 (dd, 1H, CHꢁCH2), 5.30 (t, 2H, NBD), 4.00 (m,
2H, NBD), 3.83 (t, 2H, NBD), 0.78 (br s, 2H, NBD).
petroleum ether layer. Slow recrystallisation at −15°C
afforded dark-green crystals of [WBr2(CO)(NCPri)-
(NBD)] (6b) (0.121 g, 63%). (Found C, 26.72; H, 2.70;
N, 2.57. C12H15Br2ONW requires: C, 27.05; H, 2.84; N,
2.63%). IR (KBr): w(CꢀN) 2282(w), w(CO) 2029(w), 1934(s)
1
cm−1. H-NMR (400 MHz, CDCl3, −20°C): l 5.28 (t,
2H, NBD), 3.93 (m, 2H, NBD), 3.72 (t, 2H, NBD),
3.41 (sept, 1H, CH(CH3)2), 1.63 (d, 6H, CH(CH3)2),
0.76 (br s, 2H, NBD).
3.9. Reaction of [WBr2(CO)2(NBD)] with NCPh
The complex [WBr2(CO)2(NBD)] (0.143 g, 0.29
mmol) was dissolved in 20 ml Et2O and cooled down to
0°C. A solution of NCPh (0.030 ml, 0.30 mmol) was
slowly added to the previous purple solution. The solu-
tion was allowed to warm up to room temperature to
react for 4 h. At the stage of the reaction another mole
equivalent of the ligand was added to mixture and left
to react for 7 h. Half of a mole equivalent was finally
added and another 7 h were allowed to complete the
reaction. The resulting blue solution was slightly con-
centrated before addition of a petroleum ether layer.
Slow recrystallisation at −15°C afforded dark-green
crystals of [WBr2(CO)(NCPh)(NBD)] (6c) (0.093 g,
57%). (Found: C, 31.46; H, 2.16; N, 2.38.
C15H13Br2ONW requires: C, 31.78; H, 2.31; N, 2.47%).
IR (KBr): w(CꢀN) 2266(w), w(CO) 1992(w), 1929(s)
3.12. Reaction of [WBr2(CO)2(COD)]with NCMe
The complex WBr2(CO)2COD (0.098 g, 0.19 mmol)
was dissolved in 20 ml CH2Cl2 at room temperature.
NCMe (0.030 ml, 0.58 mmol) was added to the green
solution. After 3 h an extra three mole equivalents of
NCMe were added to the solution and 26 h at room
temperature were required to complete the reaction.
The resulting blue solution was concentrated to ca. 10
ml and a layer of petroleum ether was added. Slow
recrystallisation at −15°C afforded dark-green crystals
of [WBr2(CO)(NCMe)(COD)] (6f) (0.057 g, 58%)
(Found C, 24.69; H, 2.72; N, 2.59. C11H15Br2NOW
requires: C, 25.36; H, 2.90; N, 2.69%). IR (KBr): w(CꢀN)
1
cm−1. H-NMR (400 MHz, CDCl3, −20°C): l 7.98
(m, 2H, Ph), 7.79 (tt, 1H, Ph), 7.67 (m, 2H, Ph), 5.33 (t,
2H, NBD), 4.06 (m, 1H, NBD), 4.00 (m, 1H, NBD),
3.89 (t, 2H NBD), 0.79 (br s, 2H, NBD).
1
2318(w), 2291(w), w(CO) 1927(s) cm−1. H-NMR (400
MHz, CDCl3, −19°C): l 5.65 (m, 2H, COD), 4.06 (m,
2H, COD), 3.83 (m, 2H, COD), 3.54 (m, 2H, COD),
3.02 (m, 2H, COD), 2.95 (s, 3H, NCMe), 2.80 (m, 2H,
COD).
3.10. Reaction of [WBr2(CO)2(NBD)] with
NCC6H4Me-4
The complex [WBr2(CO)2(NBD)] (0.197 g, 0.40
mmol) was dissolved in 20 ml Et2O and a solution of
NCC6H4Me-4 (0.027 ml, 0.41 mmol) was slowly added.
The mixture was allowed to react at room temperature
for 20 h with addition of another two mole equivalents
of the ligand during the course of the reaction. The
resulting blue solution was concentrated to 10 ml and a
layer of petroleum ether was added. Slow recrystallisa-
tion at −15°C over several days afforded dark-green
crystals of [WBr2(CO)(NCC6H4Me-4)(NBD)] (6d)
(0.139 g, 60%). (Found: C, 32.92; H, 2.38; N, 2.38.
C16H15Br2ONW requires: C, 33.08; H, 2.60; N, 2.41%).
4. Crystallographic studies
Crystals of 6e and 2b were both grown by solvent
diffusion from CH2Cl2/60–80 petroleum ether in an N2
atmosphere. Intensity measurements on 6e and 2b were
carried out at room temperature on a Siemens P4
diffractometer [29] with graphite-monochromated
,
MoꢂKa radiation (u=0.71069 A) using ꢀ scans. Table
3 lists details of unit cell data, intensity data collection
and structure refinement. Data were corrected for ab-
sorption by psi scans (for 2b) and integration via index-
ing of crystal faces for 6e. Both structures were solved
by direct and difference Fourier methods and refined
[30] by full-matrix least squares against F2. All H atom
positions were calculated and treated as riding models.
IR (KBr): w(CꢀN) 2255(m), w(CO) 2045(w), 1951(s) cm−1
.
1H-NMR (400 MHz, CDCl3, −20°C): l 7.5–7.3 (m,
5H, Ph), 5.25 (tm, 2H, NBD), 4.00 (br m, 2H, NBD),
3.84 (tm, 2H, NBD), 2.81 (s, 3H, CH3).

J.L. Da6idson et al. / Journal of Organometallic Chemistry 592 (1999) 168–179
179
Table 3
Crystallographic data for complexes 2b and 6e
References
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2b
6e
Crystal colour, habit
Crystal size (mm)
Formula
M
System
Yellow needle
0.5×0.3×0.2
Green block
0.58×0.25×0.21
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C22H21Br2O2PW C11H11Br2NOW
692.03
Monoclinic
P21/c
8.7487(8)
15.6411(15)
16.043(2)
96.174(12)
2182.5(4)
4
516.88
Monoclinic
P21/c
8.2867(9)
12.1208(12)
13.315(2)
91.103(12)
1337.1(3)
4
Space group
,
a (A)
,
b (A)
,
c (A)
i (°)
3
,
U (A )
Z
v(MoꢂKa) mm−1
qdata collection (°)
Completeness
(%, q=25)
Data measured
(% decay)
9.043
1.82–25.0
99.3
14.60
2.27–25.00
100
5004(10)
3174(3.4)
Unique data
R, wR2 (all data)
Rint
Observed data
[I\2|(I)]
3832
0.0738, 0.1059
0.0812
2359
0.0990, 0.1570
0.0379
2768
1626
R, wR2 (observed data) 0.0429, 0.0876
0.0599, 0.1343
1.047
145
S
1.022
253
1.54, −0.976
Variables
Emax, Emin (e A
−3
,
)
2.44, −2.88, near W
[16] (a) M.S. Balakrishna, S.S. Krishnamurthy, H. Manohar,
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Phenyl, norbornadiene, nitrile ligand and methyl H
atom displacement parameters were treated as riding
models with Uij 1.2, 1.2, 1.2, and 1.5 times the bound
carbon atom Uij, respectively.
1
[21] J.L. Davidson, G. Rosair, B.J.S. Thiebaut, unpublished work.
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5. Supplementary material
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data centre, CCDC No’s CCDC 127758 for 2b, CCDC
133547 for 4 and CCDC 127759 for 6e. Copies of this
information may be obtained free of charge from: The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (Fax: +44-1223-336033; email: de-
posit@ccdc.cam.ac.uk
www.ccdc.cam.ac.uk).
or
www:
http://
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(1988) 319.
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[29] XSCANS, X-ray Single Crystal Analysis System, Version 2.2,
Siemens Analytical X-ray Instruments Inc., Madison, WI, USA,
1994.
Acknowledgements
.
We thank Heriot–Watt University (B.J.S.T., GR)
and the European Union (H.R., K.L.) for studentships
and financial support.
[30] G.M. Sheldrick, SHELXTL/PC, Siemens Analytical X-ray Instru-
ments, Madison, WI, 1994.