Reactivity of acryloyl chloride towards the anion [Cp2(CO)4Mo2(μ- PPhH)]-; synthesis of an unusual phosphaalkene

Article abstract of DOI:10.1039/a907915g

Deprotonation of the complex [Cp₂(CO)₄Mo₂(μ-PPhH)(μ-H)] by Bu(t)Li at -78 °C and subsequent addition of acryloyl chloride affords the metallophosphaalkene complex [Cp₂(CO)₄Mo₂(η¹

Full text of DOI:10.1039/a907915g

Reactivity of acryloyl chloride towards the anion [Cp2(CO)4Mo2(m-PPhH)]2;
synthesis of an unusual phosphaalkene
John E. Davies, Martin J. Mays,* Paul R. Raithby and Anthony D. Woods
Department of Chemistry, Lensfield Road, Cambridge, UK CB2 1EW. E-mail: mjm14@cus.cam.ac.uk
Received (in Basel, Switzerland) 25th September 1999, Accepted 1st November 1999
Deprotonation of the complex [Cp2(CO)4Mo2(m-PPhH)(m-
H)] by ButLi at 278 °C and subsequent addition of acryloyl
chloride affords the metallophosphaalkene complex
[Cp2(CO)4Mo2(h -h -PhPNCHMe)] in high yield; the com-
plex exhibits cis/trans isomerism, both isomers having been
crystallographically characterised.
tion of CO to give B and reductive elimination to give C. A 1,3
hydrogen shift within the bridging ligand then leads to 2. This
reaction sequence is supported by the isolation and structural
1
2
1
2
characterisation of [Cp2(CO)4(h –h -Ph2PCHNCH2)] 4, an
analogue of intermediate C. Complex 4 is obtained by treatment
of deprotonated [Cp2(CO)4Mo2(m-PPh2)(m-H)] with acryloyl
chloride. Presumably the final [1,3] sigmatropic shift which
converts intermediate C into the metallophosphaalkene 2 is
precluded in 4 by the absence in [Cp2(CO)4Mo2(m-PPh2)]2 of a
hydrogen atom on the bridging phosphido group. The vinyl
Metallophosphaalkenes have been shown to be important
synthons in the preparation of phosphorus-functionalised het-
erocycles owing to the highly polar PNC moiety present in such
complexes.1,2 A high yield route to the previously unknown
dinuclear Group 6 metallophosphaalkenes is now described.
We have previously demonstrated that the anion obtained
from deprotonation of [Cp2(CO)4Mo2(m-Ph2)(m-H)] with ButLi
1
2
phosphine moiety present in 4 acts as an h –h 4-electron
ligand; such a mode of coordination has only previously been
reported in Fe3 and Ru5 clusters as the result of alkyne insertion
into a P–M bond.8,9
2
at 278 °C reacts with ECl3 to give [Cp2(CO)4Mo2(m-h -PE)] (E
Thermolysis of the trans isomer 2 leads to the formation of
= P, As, Sb)3 and with organometallic halides to give
[Cp2(CO)4Mo2{m-P(R)MLn}(m-H)] [MLn = W(CO)3Cp, Fe-
(CO)2Cp, Mn(CO)5].4,5 We now report that reaction of
[Cp2(CO)4Mo2(m-PPhH)(m-H)] 1 with ButLi and acryloyl
chloride leads to the unusual metallophosphaalkene trans-
cis-[Cp2(CO)4Mo2(h –h -PhPNCHMe)] 3, in which the methyl
group of the phosphaalkene now lies cis to the PPh group and
points towards a cyclopentadienyl ring.† Presumably thermo-
lysis of 2 overcomes the barrier to rotation of the PNCHMe
moiety to yield 3 as the thermodynamically favoured product.
The structures of 2 and 3 have been determined by X-ray
diffraction analysis, confirming the trans and cis assignments
(Fig. 1). The two molecules exhibit several significant differ-
ences.‡
1
2
1
2
[Cp2(CO)4Mo2(h -h -PhPNCHMe)] 2 in high (70–80%) yield
rather than to the formation of a complex containing an acyl-
substituted bridging phosphido group as would have been
predicted on the basis of earlier work.4 Previously only
mononuclear Group 6 metal complexes containing phosphaalk-
enes have been characterised; these involve coordination of the
ligand via the phosphorus atom only.6 To the authors’
knowledge there exists only one other group of complexes
Thus complex 3 shows a significantly shorter Mo–Mo bond
length of 3.220(1) Å as compared to 3.240(1) Å in 2 and the P–
Mo separations are both significantly shorter in the former
1
2
containing a phosphaalkene bonding in an h –h fashion to a
bimetallic fragment. These were formed in low yield by the
reaction
HP(SiMe3)2.7
A possible reaction pathway for the formation of trans-
of
[Cp2(CO)2(m-CO)Fe2(m-CSMe)]+
with
1
2
[Cp2(CO)4Mo2(h –h -PhPNCHMe)] 2 is shown in Scheme 1. It
is proposed that electrophilic attack of the acryloyl chloride on
deprotonated 1 to give intermediate A is followed by deinser-
Fig. 1 Molecular structure of 2 and 3. Selected bond lengths (Å) and angles
(°): 2: Mo(1)–Mo(2) 3.240(1), Mo(1)–P(1) 2.435(2), Mo(1)–C(21)
2.382(7), Mo(2)–P(1) 2.346(2), P(1)–C(21) 1.754(7); C(1)–P(1)–C(21)
107.3(4), P(1)–C(21)–C(22) 121.2(6), P(1)–C(21)–Mo(1) 70.3(2), P(1)–
C(21)–Mo(2) 121.0(3), P(1)–Mo(1)–Mo(2) 46.19(5), C(21)–Mo(1)–Mo(2)
77.46(5), Mo(1)–C(9)–O(9) 166.6(6). 3: Mo(1)–Mo(2) 3.220(1), Mo(1)–
C(21) 2.392(3), Mo(1)–P(1) 2.418(1), Mo(2)–P(1) 2.334(1), P(1)–C(21)
1.749(3); C(1)–P(1)–C(21) 114.6(2), P(1)–C(21)–C(22) 127.4(3), P(1)–
C(21)–Mo(1) 69.5(1), P(1)–Mo(1)–Mo(2) 46.27(2), C(21)–Mo(1)–Mo(2)
74.96(8), Mo(1)–C(9)–O(9) 167.2(3).
Scheme 1 Possible reaction pathway for formation of 2 and 4.
Chem. Commun., 1999, 2455–2456
This journal is © The Royal Society of Chemistry 1999
2455

For 3: nCO 1951m, 1921vs, 1880s, 1847m; NMR: 1H, d 7.69–7.45 (m,
5H, Ph), 5.04 (s, 5H, Cp), 5.03 (s, 5H, Cp), 1.80 (dd, 3JPH 13.03, 3JHH 7.04,
2
3
3H, PNCCH3), 1.48 (dq, JPH 20.84, JHH 7.04, 1H, PNCH); 31P{1H}, d
164.81; 13C, d 229.71 (Mo–CO), 134.88–128.54 (m, phenyl region), 93.17
1
2
(s, Cp), 91.39 (s, Cp), 49.14 (d, JPC 22.82, PNC), 24.05 (d, JPC 12.68,
PNCCH3); FAB MS: m/z 572 (M+), 544 (M+ 2 CO). C22H19MoO4P
requires C, 46.34; H, 3.36; P, 5.43. Found: C, 46.10; H, 3.29; P, 5.42%.
For 4: nCO 1938m, 1888vs, 1868s; NMR: 1H, d 7.79–7.17 (m, 10H, Ph),
2
3
3
4.75 (s, Cp), 4.72 (s, Cp), 3.32 (ddd, JPH 29.2, JHH 9.1, JHH 2.3, 1H,
3
3
3
Ph2PCHNCH2), 1.96 (ddd, JPH 21.8, JHH 12.4, JHH 2.3, 1H, cis-
3
3
3
Ph2PCHNCHH), 1.61 (ddd, JHH 12.4, JHH 9.1, JPH 2.1, 1H, trans-
CHNCHH); 31P{1H}, d 35.93; 13C, d 238 (CO), 228 (CO), 137.37–128.10
2
(m, phenyl groups), 91.71 (s, Cp), 91.16 (s, Cp), 50.84 (d, JPC 14.17,
Ph2PCNC), 10.64 (d, JPC 41.70, Ph2PCNC); FAB MS: m/z 650 (M+).
1
C
28H23Mo2O4P requires C, 52.03; H, 3.59; P 4.79. Found: C, 52.29; H,
3.66; P, 4.68%.
‡ Crystal data: Data in common: graphite monochromated Mo-Ka
radiation; l
= 0.71069; data collected at 180(2) K using an Oxford
Cryostream cooling apparatus. Solution by direct methods (SIR 9)13 and
subsequent Fourier syntheses, anisotropic full-matrix least-squares refine-
ment on F2 (SHELXL 93),14 hydrogen atoms included using a riding
model.
2: trans-C22H19Mo2O4P, M = 570.22, red plate, 0.20 3 0.15 3 0.10 mm,
monoclinic, space group P21/n, a
= 8.278(3), b = 14.908(6), c =
16.694(6) Å, b = 92.97(3)°, U = 2057.4(13) Å3, Z = 4, Dc = 1.841 Mg
m23, m(Mo-Ka) 1.323 mm21, F(000)
1128, 5467 reflections
Fig. 2 Molecular structure of 4. Selected bond lengths (Å) and angles (°):
Mo(1)–Mo(2) 3.288(1), Mo(1)–P(1) 2.408(1), Mo(2)–C(16) 2.295(3),
Mo(2)–C(15) 2.339(3), C(16)–C(15) 1.409(4); C(23)–P(1)–C(16) 101.9(2),
P(1)–C(16)–Mo(2) 97.3(2), C(15)–C(16)–Mo(2) 74.0(2), Mo(1)–Mo(2)–
C(16) 74.6(2).
=
=
measured using w–2q method on a Rigaku AFC7R diffractometer, 3631
unique (Rint = 0.059) used in all calculations. Data collection range 2.69 <
q < 25.03. R1 = 0.0538, wR2 = 0.1540 for 2960 observed reflections [I >
2s(I)] and 262 parameters.
3: cis-C22H19Mo2O4P, M = 570.22, red plate, 0.15 3 0.12 3 0.12 mm,
orthorhombic, space group P212121, a = 9.615(3), b = 14.568(4), c =
15.191(3) Å, U = 2127.8(1) Å3, Z = 4, Dc = 1.780 Mg m23, m(Mo-Ka)
= 1.279 mm21, F(000) = 1128. 8608 reflections measured on a Nonius
Kappa CCD diffractometer, 4896 unique (Rint = 0.0031). Data collection
range 1.94 < q < 27.48. R1 = 0.025, wR2 = 0.0735 for 4648 observed
reflections [I > 2s(I)] and 263 parameters.
complex (see Figs. 1 and 2). The P(1)–C(21)–C(22) bond angle
increases from 121.2(6) to 127.4(3) on conversion of 2 to 3.
The PNC bond lengths of 1.754(7) and 1.749(3) Å for 2 and
3, respectively, are significantly shorter than the 1.812(9) Å
recorded by Weber et al. for their related complex [Cp2-
1
2
(CO)2Fe2{h –h -(Cp(CO)2Fe)PNCHSMe}].7 However, they do
fall within the range recorded by Williams et al. for their series
of cluster-stabilised phosphaalkenes.10 Both 2 and 3 contain a
semi-bridging carbonyl group linking to the second molybde-
num atom.
4: C28H23Mo2O4P, M = 646.31, red plate, 0.10 3 0.05 3 0.03 mm,
¯
triclinic, space group P1, a = 8.304(1), b = 9.978(1), c = 16.024(1) Å, a
= 94.19(1), b = 102.92(1), g = 106.26(1)°, U = 1229.2(2) Å3, Z = 4, Dc
= 1.746 Mg m23, m(Mo-Ka) = 1.119 mm21, F(000) = 644, 8421
reflections measured on a Nonius Kappa CCD diffractometer, 5589 unique
(Rint = 0.037). Data collection range 1.32 < q < 27.46. R1 = 0.0398, wR2
= 0.0732 for 5582 observed reflections [I > 2s(I)] and 316 parameters.
CCDC 182/1469. See http://www.rsc.org/suppdata/cc/1999/2455/ for
crystallographic files in .cif format.
The molecular structure of 4 shows a Mo–Mo bond length of
3.288(1) Å, which is slightly longer than that present in 2 and 3
(Fig. 2). The C(15)–C(16) bond length of 1.409(4) Å is typical
1
2
of that in other complexes containing a h –h vinyl phos-
phine.11,12
1 R. Appel, in Multiple Bonds and Low Coordination in Phosphorus
Chemistry, M. Regitz and O. J. Scherer, Thieme, Stuttgart, 1990 and
references therein; J. F. Nixon, Chem. Rev., 1988, 88, 1327.
2 L. Weber, O. Kaminski, H.-G. Stammler, B. Neumann and V. D.
Romanenko, Z. Naturforsch., Teil B, 1993, 48, 1784.
3 J. E. Davies, L. C. Kerr, M. J. Mays, P. R. Raithby, P. K. Tompkin and
A. D. Woods, Angew. Chem., Int. Ed. Engl., 1998, 37, 1428.
4 J. E. Davies, M. J. Mays, E. J. Pook, P. R. Raithby and P. K. Tompkin,
J. Chem. Soc., Dalton Trans., 1997, 3283.
5 P. K. Tompkin, PhD Dissertation, University of Cambridge, 1997.
6 D. Gudat, E. Niecke, W. Malisch, U. Hofmockel, S. Quashie, A. H.
Cowley, A. M. Arif, B. Krebs and M. Dartmann, J. Chem. Soc., Chem.
Commun., 1985, 1687; S. Holand, C. Charrier, F. Mathey, J. Fischer and
A. Mitschler, J. Am. Chem. Soc., 1984, 106, 826; D. Gudat, E. Niecke,
B. Krebs and M. Dartmann, Chimia, 1985, 39, 277; L. Weber, Angew.
Chem. Chem., Int. Ed. Engl., 1996, 35, 271.
1
The H NMR spectra of 2 and 3 highlight the different
environments of the vinylic proton. In 2 the proton resonates as
a doublet of quartets at d 4.14, whereas the analogous resonance
in 3 occurs as a broad peak at d 1.48; this latter value is in good
agreement with that recorded by Weber et al. for their
compound.7
Bimetallic Group 6 metal complexes coordinated to phos-
1
2
phaalkenes have not been reported previously, and an h –h
bonding mode for a phosphaalkenes is extremely rare. Addi-
tionally, the described method represents the first high yield
route to metallophosphaalkenes that contain no other heteroa-
tom substituents.
We thank the EPSRC for a quota award to A. D. W. and ICI
for a CASE award to A. D. W. EPSRC support for the purchase
of the Nonius Kappa CCD diffractometer is also gratefully
acknowledged.
7 L. Weber, I. Schumann, H.-G. Stammler and B. Neumann, Organome-
tallics, 1995, 14, 1626.
8 K. Knoll, G. Huttner, L. Zsolani and O. Orami, Angew. Chem., Int. Ed.
Engl., 1986, 25, 1119.
Notes and references
9 C. J. Adams, M. I. Bruce, B. W. Skelton and A. H. White, J. Organomet.
Chem., 1996, 506, 191.
10 G. D. Williams, G. L. Geoffrey, R. R. Whittle and A. L. Rheingold,
J. Am. Chem. Soc., 1985, 107, 729.
11 J. Lunniss, S. A. MacLaughlin, N. J. Taylor, A. J. Carty and E. Sappa,
Organometallics, 1985, 4, 2066.
12 D. Buchholz, G. Huttner and L. Zsolani, J. Organomet. Chem., 1990,
381, 97.
† Selected spectroscopic data: [IR (nCO/cm21) measured in hexane; 1H
NMR and 31P {1H} NMR spectra were recorded in CDCl3 solution relative
to TMS and 85% H3PO4(aq) respectively, with upfield shifts negative; J in
Hz].
For 2: nCO 1955m, 1927.6vs, 1822s, 1851m; NMR: 1H d 7.8–7.3 (m, 5H,
Ph), 5.24 (s, 5H, Cp), 4.82 (s, 5H, Cp), 4.14 (dq, 2JPH 14.1, 3JHH 7.1, 1H,
PNCH), 1.42 (dd, 3JPH 17.82, 3JHH 7.1, 3H, PNCCH3); 31P{1H}, d 158.32;
13 A. Altomare, G. Cascarano, C. Giacavazzo, A. Guagliardi, M. C. Byrla,
G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27, 435.
14 G. M. Sheldrick, SHELXL 93, University of Go¨ttingen, 1993.
2
2
13C, d 242.31 (d, JPC 22.96, Mo–CO), 235.32 (d, JPC 7.55, Mo–CO),
230.02 (s, Mo–CO), 141.03–128.27 (m, PPh), 92.90 (s, Cp), 91.39 (s, Cp),
42.29 (d, 1JPC 12.4, PNC), 18.62 (d, 2JPC 7.23, PNCCH3) FAB MS: m/z 572
(M+), 544 (M+ 2 CO); C22H19MoO4P requires C, 46.34; H, 3.36; P 5.43.
Found: C, 46.21; H, 3.38; P 5.42%.
Communication 9/07915G
2456
Chem. Commun., 1999, 2455–2456