Cis- and trans-Bis(1-phenyl-2,3,4,5-tetramethylphosphole)tetracarbonylmolybdenum(0), [Mo(CO)4(tmpPh)2]. Syntheses and structures

Article abstract of DOI:10.1016/S0022-328X(00)00874-3

1-Phenyl-2,3,4,5-tetramethylphosphole reacts with [Mo(CO)₆] to give the mono- and bis(phosphole) complexes [Mo(CO)₅L] and cis- and trans-[Mo(CO)₄L₂], where L=C₄Me₄PPh (tmpPh). The new complexes have been characterised by spectroscopic methods, supplemented by single-crystal X-ray analyses in the case of the bis(phosphole) isomers. The isomeric bis-tmpPh complexes show little evidence of the overcrowding which is thought to lengthen bonds and distort the metal coordination in the corresponding bis-PPh₃ and bis-PCy₃ isomers. The structural basis for the greater stability of the trans isomers is briefly considered: the cis→trans isomerisation typically involves little change in the mean Mo-CO distance, whereas there is a marked shortening of the Mo-P bonds.

Full text of DOI:10.1016/S0022-328X(00)00874-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 622 (2001) 297–301
Note
cis- and trans-Bis(1-phenyl-2,3,4,5-tetramethyl-
phosphole)tetracarbonylmolybdenum(0), [Mo(CO) (tmpPh) ].
4
2
Syntheses and structures
a,1
b,2
b
Kenneth W. Muir* , Fran c¸ ois Y. P e´ tillon* , Ren e´ Rumin ,
b
b
Philippe Schollhammer , Jean Talarmin
a
Chemistry Department, Uni6ersity of Glasgow, Glasgow, G12 8QQ, UK
b
UMR CNRS 6521, Chimie, Electrochimie Mol e´ culaires et Chimie Analytique, Facult e´ des Sciences, Uni6ersit e´ de Bretagne Occidentale,
BP 809, 29285 Brest-Cedex, France
Received 30 August 2000; received in revised form 23 October 2000; accepted 23 October 2000
Abstract
-Phenyl-2,3,4,5-tetramethylphosphole reacts with [Mo(CO) ] to give the mono- and bis(phosphole) complexes [Mo(CO) L] and
1
6
5
cis- and trans-[Mo(CO) L ], where L=C Me PPh (tmpPh). The new complexes have been characterised by spectroscopic
4
2
4
4
methods, supplemented by single-crystal X-ray analyses in the case of the bis(phosphole) isomers. The isomeric bis-tmpPh
complexes show little evidence of the overcrowding which is thought to lengthen bonds and distort the metal coordination in the
corresponding bis-PPh3 and bis-PCy3 isomers. The structural basis for the greater stability of the trans isomers is briefly
considered: the cis“trans isomerisation typically involves little change in the mean Mo–CO distance, whereas there is a marked
shortening of the Mo–P bonds. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Molybdenum; Carbonyl; Isomerisation; Phosphole; trans-Influence
1. Introduction
SMe)3} nucleus [4] by reacting 1-phenyl-2,3,4,5-
tetramethylphosphole with [Mo(CO) ]. However, even
6
We have recently shown that the reactivity of di-
at high temperature in refluxing diglyme, treatment of
the phosphole with hexacarbonylmolybdenum(0) did
not give rise to P–Ph bond cleavage, a reaction which
has been successfully used with other metals to generate
molybdenum thiolate complexes is changed when C H
5
5
is replaced by C Me [1]. Indeed, it is generally true that
5
5
the reactivity of such systems can be fine-tuned by
judicious choice of ligands: for example, six-electron
donor groups with widely differing steric and electronic
properties can replace the cyclopentadienyl ligand with
5
h -phospholyl complexes [5]. Instead, mono- and bis-
(
phosphole) complexes [Mo(CO) L] (1), and cis- and
5
trans-[Mo(CO) L ] (2) and (3) [L=C Me PPh
4
2
4
4
which they are isolobal [2]. In particular, the Me C P
4
4
(tmpPh)] were formed.
tetramethylphospholyl ring is almost the same size as
C Me but is a weaker electron-donor than C H [3].
The isomerisation of cis-[Mo(CO) L ] phosphine
4
2
5
5
5
5
complexes, such as 2, to the thermodynamically more
stable trans form has been much studied and attempts
have been made, notably by Cotton and co-workers, to
relate the reactivities of the cis complexes to their solid
state structures [6]. The trans-isomers formed as prod-
ucts of these reactions have only recently attracted
similar interest: structural comparisons of cis- and
5
Accordingly, we tried to make h -phospholyl analogues
5
of the known h -cyclopentadienyl thiolato-bridged di-
molybdenum complexes containing the {Cp Mo (m-
2
2
1
2
*
*
Corresponding author. Fax: +44-41-3304888
Corresponding author.
0
022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00874-3

2
98
K.W. Muir et al. / Journal of Organometallic Chemistry 622 (2001) 297–301
trans-[Mo(CO) L ] isomers have so far been limited to
4
2
the bis(tricyclohexylphosphine) (L=PCy ) complexes,
3
which are particularly crowded [7], and to the bis-PPh3
complexes [8]. In the latter example the trans-isomer
was co-crystallised with 1,4-bis(diphenylphosphino)-2,5-
difluorobenzene, while it has been suggested that the
cis-(PPh ) complex exhibits structural distortions not
3
2
found in other cis-[Mo(CO) L ] species [6,8b]. We
4
2
therefore now report the crystal structures of the iso-
mers 2 and 3. These are also of interest since phospho-
les, L, and [Mo(CO)6] are known to undergo
photochemical reactions to give [Mo(CO) L ] com-
4
2
plexes in which the phosphole ligands have undergone
Diels–Alder dimerisation, a reaction they do not show
in the absence of [Mo(CO) ] [9].
6
Fig. 1. Molecular drawings of (A) 2 and (B) 3 showing the atom
numbering and 20% probability ellipsoids for non-hydrogen atoms.
Symmetry code: (i ) −x, −y, −z.
2. Results and discussion
diffraction analyses (Fig. 1). Molecules of 3 lie on
crystallographic inversion centres.
The complexes 1–3 were obtained as products of the
The phosphole ligands in 2 and 3 are virtually identi-
cal. The CꢀC–CꢀC butadiene unit within each ring is
almost perfectly planar and displays bond lengths [CꢀC
reaction of [Mo(CO) ] with tmpPh. The respective IR
6
spectra show the expected set of w(CO) bands for
octahedral [Mo(CO) L] and cis- and trans-
1.335(5)–1.361(7), C– –C 1.459(8)–1.484(4) A
tent with little or no delocalisation. The endocyclic
P–C bonds [1.804(3)–1.816(3) A] are very slightly
shorter than the P–C(Ph) bonds [1.833(2)–1.837(2) A].
,
] consis-
5
31
1
13
[
Mo(CO) L ] species. Likewise, the P, H and
C
4
2
NMR spectra accord with the presence of one tmpPh
,
ligand in 1 and with two equivalent tmpPh ligands
,
1
3
which are cis in 2 and trans in 3. The C spectra of 2
and 3 are complicated because of the strong coupling
between the two phosphorus atoms: pseudo triplets are
observed instead of doublets of doublets; in the case of
The rings are slightly folded, by 9.0(2)° in 3 and by
5.0(2 and 6.4(2)° in 2, into shallow envelopes with the P
atom at the flap. The PC units are pyramidal, with
3
symmetrical Ph–P–C angles [101.6(1)–104.7(1)°] which
are rather more obtuse than the endocyclic C–P–C
angles [91.7(1)–92.9(2)°]. Similar structural features in
2
an isotope effect, for which there is a precedent [5a],
could explain the abnormal resonance pattern for the
carbon atoms linked to the phosphorus atoms: six such
resonances, suggesting the superposition of two dou-
blets of doublets, were observed. Mass spectroscopy
confirmed the mononuclear nature of the complexes
and indicated unambiguously the presence of five car-
bonyl ligands in 1 and four in 2 and 3. These conclu-
sions are confirmed for 2 and 3 by the results of
free and W(CO) -complexed 2,5-di(2-pyridyl)phos-
5
pholes have been interpreted in terms of a lack of
conjugation between the P atom and the dienic portion
of the phosphole ring [10]. We note that the C16–C11–
P1–C3 and –C6 angles in 3 [21.0(3) and −74.9(2)°]
agree to within 3° with corresponding angles for the
two phosphole ligands in 2. The similar conformations

K.W. Muir et al. / Journal of Organometallic Chemistry 622 (2001) 297–301
299
Table 1
Selected structural data (A
a
,
and °) for isomeric cis and trans-[Mo(CO) L ] complexes
4
2
Mo–P
D(Mo–P) Mo–CO
D(cis)
D(Mo–CO) P–Mo–P Ref.
Isomer
cis
trans
cis
trans
trans to CO trans to CO
cis
cis
trans to P
L=tmpPh 2.550(1)
.537(1)
2.576(2)
.577(2)
2.649(4)
.659(4)
2.480(1)
2.500(1)
2.544(1)
−0.064
−0.076
−0.111
1.981(2)
1.982(2)
1.972(8)
1.973(9)
1.97(2)
2.031(2)
2.033(2)
2.059(9)
2.022(9)
2.01(2)
2.025(3)
2.024(3)
2.016(5)
2.005(5)
2.020(4)
2.028(3)
−0.051 0.018
−0.067 0.004
101.7(1)
104.6(1)
105.1
This work
2
L=PPh3
L=PCy3
[8]
[7]
2
−0.05
0.03
2
1.97(2)
2.02(2)
CSD b
2.532
2.491
−0.041
1.980(2)
2.026(3)
2.020(3)
−0.046 0.017
a
D(Mo–P) and D(Mo–CO) are the increases in the mean Mo–P and Mo–CO bond lengths on going from the cis to the trans isomer. D(cis) is
the difference between the mean lengths of the Mo–CO bonds trans to P and trans to CO in cis complexes.
b
Database means: a search of the Cambridge Structural Database for [Mo(CO) L ] structures (L=tertiary phosphine) yielded 87 hits for cis
4
2
complexes and six for trans complexes. Three atypical cis structures (NEGNIW, POGMIW, TOGNAE) were excluded from the mean calculations.
of the phospholes in 2 and 3 and the absence of specific
intramolecular contacts between the phosphole ligands
of 2 suggest that steric crowding is not particularly
significant in either molecule. Moreover, it is apparent
from Fig. 1(A) that the structure of 2 is not conducive
to reaction between the coordinated phosphole rings
which are not close to one another, lending weight to
the suggestion that a seven-coordinate M(CO) L spe-
the steric bulk of L though Cotton [8b] has emphasised
the difficulties of assessing steric effects in these com-
plexes through ‘crude arguments based on purely geo-
metric criteria’. As an illustration of this it is worth
noting that the mean molecular volume for the trans-
3
tmpPh complex is 22 A less than for the cis-isomer; for
,
the PCy complexes there is a slightly greater decrease
3
3
5
2
of 32 A
,
in molecular volume on going from the cis to
cies rather than 2 may be involved in the Diels–Alder
phosphole dimerisation reaction [9b].
the trans isomer. This contributes relatively little, 1–2 J
−1
mol
in free energy, to the stabilisation of the trans
Structural data for 2 and 3 are compared with corre-
sponding values for the isomeric PPh and PCy com-
isomer but it is unexpected given that the cis isomer is
normally considered to be more overcrowded than its
trans counterpart.
3
3
plexes and with database mean values in Table 1. In the
cis complexes D(cis), the mean difference in length
between Mo–CO bonds trans to P and those trans to
CO, is virtually constant and is negative, indicating that
CO has a greater trans influence than the P-donor
ligands. However, D(Mo–CO), the increase in mean
Mo–CO bond length on cis“trans isomerisation, is
The structures of 2 and 3 display bond lengths which
are close to the average values for Mo(CO) L com-
4
2
plexes. When L is the bulky PPh ligand, or the even
3
more demanding PCy species, more distortion of the
3
Mo coordination and longer Mo–P bonds are ob-
served, especially in the cis series.
small, except for the PCy complexes where the mean
3
Mo-CO distance may be significantly greater in the
trans isomer. By contrast, the negative D(Mo–P) values
indicate that on average the Mo–P bonds shrink when
the configuration at the metal atom changes from cis to
trans. This may be partly ascribed to trans influence
3
. Experimental
Reactions were performed under nitrogen using stan-
dard Schlenk techniques and solvents were deoxy-
genated and dried by standard methods. A mixture of
(CO\phosphine), but the steric bulk of the phosphine
may also be a factor since ꢀD(Mo–P)ꢀ increases along
[Mo(CO) ] (2 g, 7.6 mmol) and C Me PPh (1.65 g, 7.6
the series tmpPhBPPh BPCy , as indeed do the Mo–
6 4 4
3
3
mmol) was stirred under reflux in THF or diglyme for
h. The colorless solution became yellow-orange dur-
P distances themselves in the cis and trans series of
complexes. Whatever the explanation, the structural
results indicate that Mo–P bonds are shorter and
stronger in the trans isomer while the average length of
the Mo–CO is little different in the two isomers; they
are therefore consistent with the trans isomer having
the greater thermodynamic stability. The P–Mo–P an-
gles in the cis complexes also show some dependence on
2
ing this time. The solvent was removed under vacuum.
Recrystallisation from dichloromethane and pentane
gave separately 1, 2 and 3 as colorless crystals; yield
25% 1, 20% 2, 10% 3. Compound 3 has low solubility in
dichloromethane and pentane and 2 has low solubility
in pentane.

3
00
K.W. Muir et al. / Journal of Organometallic Chemistry 622 (2001) 297–301
3.1. Analysis of 1
3.5. Crystal data
Found C, 50.7; H, 3.9; P, 7.5; C H PMoO re-
C H MoO P , M=640.47. Compound 2: mono-
19
17
5
32 34
4 2
1
quires: C, 50.4; H, 3.8; P, 6.9%. NMR (CDCl ): H l:
clinic, a=9.9097(4), b=21.3320(17), c=14.9143(9) A
,
,
3
3
7
(
.40, 7.37 (5H, m, C H ), 2.00 (6H, s, 2×C CH ), 1.97
i=99.012(4)°, V=3113.9(3) A
,
, T=293 K, space
6
5
3
3
13
1
−1
d, JPH=12.0Hz, 6H, 2×C CH ). C{ H} l: 209.5 (d,
group P2 /n, Z=4, v(Mo–K ) 0.557 mm , 11 522
2
3
1 a
JPC=19.5 Hz, COtrans), 205.7 (d, JPC=8.6 Hz, CO ),
reflections (qB30°) measured, 9019 unique (R =
cis
int
1
43.7 (d, JPC=14.6 Hz, C ), 136.5 (d, JPC=39.9 Hz,
0.010) used in refining 352 parameters. R (all data)=
3
1
−
3
C ), 132.1 (d, JPC=12.5 Hz, Cortho),130.5 (d, JPC=2.0
Hz, Cpara), 129.4 (d, JPC=31.3 Hz, Cipso), 128.9 (d,
JPC=9.8 Hz, Cmeta), 13.5 (d, J =8.6 Hz, C CH ),
0.0497, wR (all data)=0.100, ꢀDzꢀB0.54 e A
.
2
2
Compound 3: triclinic, a=8.8904(5), b=9.0712(5), c=
11.2077(6)
112.398(4)°, V=756.63(7) A
P1, Z=1, v(Mo–K ) 0.573 mm , 3937 reflections
A, h=103.372(4), i=103.947(4), k=
,
PC
1
3
3
3
3
11.8 (d, J =17.5 Hz, C CH ). P l: 51.7.IR (CH Cl ,
,
, T=293 K, space group
PC
2
3
2
2
−
1
+
−1
cm ), (w ): 2070(s), 1935(s). MS (m/z):452 [M] , 424
(
CO
+
a
+
+
[M–CO] , 396 [M–2CO] , 368 [M–3CO] , 340 [M–
(qB27°) measured, 3291 unique (R =0.017) used in
int
+
+
4CO] , 312 [M–5CO] .
refining 178 parameters. R (all data)=0.040, wR (all
1
2
−
3
data)=0.077, ꢀDzꢀB0.35 e A
.
All non-hydrogen atoms were refined with an-
isotropic displacement tensors. H-atom positions were
determined from stereochemical considerations (phenyl
H) or difference maps (methyl H) and subsequently
rode on parent C atoms [12]. The carbon atoms of the
3.2. Analysis of 2
Found: C, 59.7; H, 5.4; P, 10.0; C H P MoO re-
32
34
2
4
1
quires: C, 60.0; H, 5.3; P, 9.7%. NMR (CDCl ): H l:
3
7
.30 (10H, m, C H ), 1.86 (12H, s, 4×C CH ), 1.83 (d,
P2 phosphole ring in 3 show very anisotropic displace-
6
5
3
3
1
3
1
2
JPH=11.1Hz, 12H, 4×C CH ). C{ H} l: 214.0 (m,
COtrans), 210.5 (ps t, JPC=9.2 Hz, CO ), 142.9 (m,
ment tensors (Umax=0.61 A
,
) which may indicate
2
3
disorder.
cis
C ), 136.3 (m, C ), 132.4 (m, Cipso),132.0 (ps t, JPC=5.8
3
2
Hz, Cortho), 128.7 (s, Cpara), 128.4 (ps t, JPC=4.5 Hz,
Cmeta), 13.9 (ps t, JPC=4.0 Hz, C CH ), 12.2 (ps t,
3
3
4. Supplementary material
31
−1
JPC=8.7 Hz, C CH ). P l: 52.3. IR (CH Cl , cm ),
2
3
2
2
(
wCO): 2010(s), 1905(sh), 1890(s), 1870(sh). MS (m/
Crystallographic data for the structures reported in
this paper have been deposited with the Cambridge
Crystallographic Data Centre, CCDC no. 149038 for
compound 2 and CCDC no. 149037 for compound 3.
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;
e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.
cam.ac.uk).
+
+
+
z):640 [M] , 618 [M–CO] , 584 [M–2CO] , 556 [M–
+
+
3
3
6
CO] , 528 [M–4CO] .
.3. Analysis of 3
Found: C, 59.1; H, 5.4%; C H P MoO requires: C,
3
2
34
2
4
1
0.0; H, 5.3%. NMR (CDCl ): H l: 7.50, 7.37 (10H,
3
m, C H ), 1.99 (12H, s, 4×C CH ), 1.98 (d, JPH=
1
6
5
3
3
1
3
1
0.4Hz, 12H, 4×C CH ). C{ H} l: 210.9 (ps t,
2 3
JPC=8.5 Hz, CO), 141.2 (ps t, JPC=7.4 Hz, C ), 138.9
3
Acknowledgements
(
dd, JPC=19.0Hz, C ), 132.4 (dd, partially obscured by
2
Cortho signal, JPC=14.1 Hz, Cipso), 132.1 (ps t, JPC=6.5
Hz, Cortho), 129.5 (s, Cpara), 128.4 (ps t, JPC=4.7 Hz,
Cmeta), 13.4 (ps t, JPC=4.3 Hz, C CH ), 12.0 (ps t,
We thank the CRNS (France), EPSRC (UK), and
the Universities of Brest and Glasgow.
3
3
31
−1
JPC=8.7 Hz, C CH ). P l: 64.5. IR (CH Cl , cm ),
2
3
2
2
+
+
(
[
wCO): 1880(s). MS (m/z):640 [M] , 618 [M–CO] , 584
M–2CO] , 556 [M–3CO] , 528 [M–4CO] .
+
+
+
References
Chemical analyses were performed by the Centre de
Microanalyses du CNRS, Vernaison.
[
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