Synthesis of acylphosphine complexes by controllable migration of acyl groups from molybdenum to phosphido ligands

Article abstract of DOI:10.1039/a703948d

The acyl complexes [Mo(COR¹)(CO)₂(PPh₂H)(η-C₅H ₅)] (R¹ = Me or Et) have been prepared in high yield by the reaction of [MoR¹(CO)₃(η-C₅H₅)] with PPh₂H. Deprotonation of the diphenylphosphine ligand with 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu) at -78°C produced a phosphorus-centred anion which can be alkylated by treatment with R²I (R² = Me or Et) to give the substituted phosphine acyl complexes [Mo(COR¹)(CO)₂(PPh₂R²)-(η-C ₅H₅)], or acylated with R²COCl to produce acylphosphine acyl complexes [Mo(COR¹)(CO)₂(PPh₂COR ²)-(η-C₅H₅)]. If the deprotonation is carried out at room temperature, however, migration of the metal acyl group to the phosphorus atom occurs to give the molybdenum-centred anion [Mo(CO)₂(PPh₂COR¹)(η-C₅H ₅)]^-, which can in turn be alkylated with R²I to give the acylphosphine alkyl complexes [MoR²(CO)₂(PPh₂COR¹)(η-C ₅H₅)]. The metal-centred anion also undergoes typical reactions with H⁺ and chlorinated solvents to give [MoX(CO)₂-(PPh₂COR¹)(η-C₅H ₅)] (X = H or Cl). Mechanistic studies showed that (i) on deprotonation of the related complex [MoMe(CO)₂(PPh₂H)(η-C₅H₅)] the methyl group does not undergo migration to phosphorus, and (ii) the reaction is largely intramolecular but with a measurable intermolecular component. A mechanism is therefore proposed involving nucleophilic attack on the acyl carbon atom by the anionic phosphido ligand. Full spectroscopic data for the new complexes are reported and interpreted, and the crystal structure of [Mo(COMe)(CO)₂(PPh₂COMe)(η-C₅H ₅)] has been, determined.

Full text of DOI:10.1039/a703948d

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Synthesis of acylphosphine complexes by controllable migration of
acyl groups from molybdenum to phosphido ligands†
Harry Adams, Neil A. Bailey, Peter Blenkiron and Michael J. Morris*
Department of Chemistry, University of Sheffield, Sheffield, UK S3 7HF
The acyl complexes [Mo(COR1)(CO)2(PPh2H)(η-C5H5)] (R1 = Me or Et) have been prepared in high yield by the
reaction of [MoR1(CO)3(η-C5H5)] with PPh2H. Deprotonation of the diphenylphosphine ligand with 1,8-
diazabicyclo[5.4.0]undec-7-ene (dbu) at Ϫ78 ЊC produced a phosphorus-centred anion which can be alkylated by
treatment with R2I (R2 = Me or Et) to give the substituted phosphine acyl complexes [Mo(COR1)(CO)2(PPh2R2)-
(η-C5H5)], or acylated with R2COCl to produce acylphosphine acyl complexes [Mo(COR1)(CO)2(PPh2COR2)-
(η-C5H5)]. If the deprotonation is carried out at room temperature, however, migration of the metal acyl group to
the phosphorus atom occurs to give the molybdenum-centred anion [Mo(CO)2(PPh2COR1)(η-C5H5)]–, which can
in turn be alkylated with R2I to give the acylphosphine alkyl complexes [MoR2(CO)2(PPh2COR1)(η-C5H5)]. The
metal-centred anion also undergoes typical reactions with Hϩ and chlorinated solvents to give [MoX(CO)2-
(PPh2COR1)(η-C5H5)] (X = H or Cl). Mechanistic studies showed that (i) on deprotonation of the related complex
[MoMe(CO)2(PPh2H)(η-C5H5)] the methyl group does not undergo migration to phosphorus, and (ii) the reaction
is largely intramolecular but with a measurable intermolecular component. A mechanism is therefore proposed
involving nucleophilic attack on the acyl carbon atom by the anionic phosphido ligand. Full spectroscopic data
for the new complexes are reported and interpreted, and the crystal structure of
[Mo(COMe)(CO)2(PPh2COMe)(η-C5H5)] has been determined.
1
The migratory insertion reaction of a metal-bound alkyl group
with a CO ligand to form a metal acyl is one of the fundamental
reactions of organometallic chemistry, and plays a major role
in important catalytic processes such as hydroformylation
and acetic acid carbonylation.1 On the other hand, further
migration reactions involving the acyl ligand itself, e.g. with CO
to give a ketoacyl ligand, are relatively rare, at least in part
because of the increased metal–carbon bond strength of
M᎐C(sp2) bonds. In this paper we report the unprecedented
migration of acyl ligands from a metal centre to a co-ordinated
phosphido group to form acylphosphine complexes. Part of
this work has previously appeared as a communication.2
P᎐H moiety present in their H NMR spectra. The complexes
exist, like the PPh3 analogues, exclusively as the trans isomers,
as shown by the intensities of the two peaks in the IR spectrum
and by the observation of one resonance for the two CO ligands
in the 13C NMR spectrum.7
Low-temperature deprotonation–alkylation reactions
Deprotonation of the phosphine ligand of complex 1 proceeds
smoothly with the organic base dbu (1,8-diazabicyclo[5.4.0]-
undec-7-ene) at Ϫ78 ЊC in tetrahydrofuran (thf) to give an
anionic species which is assumed to be the phosphido complex
[Mo(COR1)(CO)2(PPh2)(η-C5H5)]Ϫ. The choice of base is how-
ever quite important. Previous attempts to deprotonate the
acetyl ligand of [Mo(COMe)(CO)2(PPh3)(η-C5H5)] with LiBun
Results and Discussion
or the Wittig reagent PPh ᎐CH resulted only in loss of the acyl
᎐
3
2
We are interested in the processes of P᎐C bond cleavage and
formation in phosphido complexes because of their involve-
ment in the deactivation of industrially important catalyst sys-
tems, e.g. in hydroformylation.3 It has been known for a long
time that co-ordinated secondary phosphines can be readily
deprotonated to give anionic terminal phosphido species which
can subsequently be treated with a range of electrophiles.4 Dur-
ing our previous work, we showed that a simple deprotonation–
alkylation sequence could be successfully effected on the iron
acyl complexes [Fe(COR1)(CO)(PPh2H)(η-C5H5)] to give [Fe-
(COR1)(CO)(PPh2R2)(η-C5H5)] (R1, R2 = Me or Et).5 On exten-
sion of the study to the analogous molybdenum acyl complexes,
however, the unexpected results described below were obtained.
The appropriate starting materials [Mo(COR1)(CO)2-
(PPh2H)(η-C5H5)] ( R1 = Me 1a or Et 1b) were readily prepared
by stirring [MoR1(CO)3(η-C5H5)] with PPh2H at room tem-
perature in acetonitrile overnight, as already established for the
PPh3 analogues (Scheme 1).6 Their spectroscopic properties
(Tables 1–3) are in complete accord with the proposed struc-
tures, with the characteristic doublet (J = 360 Hz) due to the
ligand and formation of the [Mo(CO)2(PPh3)(η-C5H5)]Ϫ
anion.8,9 In contrast to [Fe(COMe)(CO)(PPh2H)(η-C5H5)],
which can be successfully deprotonated with either of these
reagents, their use in the current reaction led to mixtures of
products arising from competing phosphine deprotonation and
acyl loss in both cases.
Addition of R2I (R2 = Me or Et) to the anion solution at low
temperature produced excellent yields (>80%) of the alkyl-
phosphine acyl complexes [Mo(COR1
)(CO)2(PPh2R2)(η-C5H5)]
2a–2d (Scheme 1). This reaction therefore parallels the
deprotonation–alkylation sequence previously observed for the
iron acyl complexes. The products are known compounds, but
their full characterising data, including 13
C NMR spectra, have
not been previously reported and so are included here for ease
of comparison (Tables 1–3). The identities of 2a–2d were
also confirmed by independent synthesis from [MoR1(CO)3-
(η-C5
H )] and PPh R2 in MeCN.
5
2
Room-temperature deprotonation–alkylation reactions
When the deprotonation reaction was carried out at room tem-
perature (or if the low-temperature anion solution produced
above was stirred at room temperature for a while before alkyl-
ation) the addition of R2X (R2 = Me or Et) gave different
† Supplementary data available (No. SUP 57273,7 pp): characterisation
data for complexes 11–13. See Instructions for Authors, J. Chem. Soc.,
Dalton Trans., 1997, Issue 1.
J. Chem. Soc., Dalton Trans., 1997, Pages 3589–3598
3589

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2a R1 = R2 = Me
2b R1 = Me, R2 = Et
2c R1 = Et, R2 = Me
2d R1 = R2 = Et
(ii )
O
Mo
Mo
R1
CO
R2Ph2P
C
OC
R1
OC
OC
CO
R1 = Me, Et
Alkylphosphine acyl complexes
(i )
(iii )
Mo
R2
CO
(iv )
O
Ph2P
Mo
C
OC
HPh2P
O
C
R1
OC
CO
R1
(vi )
Mo
3a R1 = R2 = Me
H
Ph2P
1a R1 = Me
1b R1 = Et
Acylphosphine
alkyl complexes
3b R1 = Me, R2 = Et
3c R1 = Et, R2 = Me
3d R1 = R2 = Et
OC
CO
(v )
O
C
R1
(vii )
4a R1 = Me
4b R1 = Et
O
cis + trans isomers
Mo
Mo
6a R1 = R2 = Me
6b R1 = Me, R2 = Et
6c R1 = Et, R2 = Me
6d R1 = R2 = Et
CO
Ph2P
C
Ph2P
OC
R1
Cl
OC
CO
O
C
O
C
R1
R2
5a R1 = Me
5b R1 = Et
Acylphosphine acyl complexes
Scheme 1 Synthesis and deprotonation reactions of complexes 1a and 1b. Reagents and conditions: (i) PPh2H in MeCN, room temperature (r.t.),
18 h; (ii) PPh2R2 in MeCN, r.t., 18 h; (iii) dbu, thf, Ϫ78 ЊC, 30 min, then R2I, warm to r.t., stir for 18 h; (iv) dbu, thf, r.t., 30 min, then R2I, stir for 18 h;
(v) dbu, thf, Ϫ78 ЊC, 30 min, then R2COCl at Ϫ78 ЊC, stir cold for 2 h; (vi) dbu, thf, r.t., 30 min, then MeCO2H; (vii) CHCl3
ligands bound to molybdenum such as in 2 resonate at much
1
lower field, ca. δ 270. The H NMR spectra of the methyl
complexes 3a and 3c reveal the presence of small amounts
(<5%) of cis isomers, whereas in the ethyl complexes 3b and 3d
only the trans isomers could be distinguished.
From the exclusive formation of these products and the dis-
tribution of R1 and R2 in them, we concluded that at room
temperature a rapid migration of the acyl ligand to the phos-
phido group occurs, giving the molybdenum-centred anion
[Mo(CO)2(PPh2COR1)(η-C5H5)]Ϫ. Complexes containing acyl-
phosphine ligands are not common and have previously been
prepared by the reaction of suitably labile precursors with free
acylphosphines10 or by acetylation of anionic phosphido
ligands with acetyl chloride.11 There are no prior reports of
migration of an acyl ligand to a phosphido group, though it has
been reported that at 120 ЊC acylphosphines are decarbonylated
to alkylphosphines by Wilkinson’s catalyst, a reaction which
presumably involves the reverse process.12 There are, however,
examples of the attack of cyclopentadienylphosphine ligands
on η2-acyl groups bound to zirconium.13
Fig. 1 Proton NMR spectra of [MoH(CO)2(PPh2COR1)(η-C5H5)] in
[2H8]toluene at 25 ЊC and Ϫ50 ЊC: left, 4a (R1 = Me), right 4b (R1 = Et)
products, again in excellent yield. These four compounds 3a–3d
were identified as the novel acylphosphine alkyl complexes [Mo-
R2(CO)2(PPh2COR1)(η-C5H5)] on the basis of their spectro-
scopic data (Scheme 1). Examination of the data (Tables 1–3)
shows that the acylphosphine alkyl complexes 3 can be dis-
tinguished from their isomeric alkylphosphine acyl counter-
parts 2 in several ways. First, in the IR spectrum in CH2Cl2,
although there is little change in the two strong terminal CO
absorptions (indicative of a trans configuration of the CO lig-
ands), the rather weak ketonic carbonyl peak appears at ca.
1685 cmϪ1 for 3 compared to ca. 1600 cm–1 for 2. Secondly, the
31P NMR spectrum of 3 comprises a singlet at around δ 80, a
difference in chemical shift of approximately 30 ppm compared
to 2. Thirdly, the presence of the acylphosphine ligand is con-
firmed by the 13C NMR spectrum which contains a doublet at
about δ 212 (J = ca. 15 Hz) due to the acyl carbon, whereas acyl
The presence of [Mo(CO)2(PPh2COR1)(η-C5H5)]Ϫ is also
indicated by the fact that the solution undergoes the typical
reactions expected of such an anion (Scheme 1); thus proton-
ation with acetic acid afforded the hydride complexes [MoH-
(CO)2(PPh2COR1)(η-C5H5)] 4a, 4b and dissolution of these in
chlorinated solvents produced [MoCl(CO)2(PPh2COR1)-
(η-C5H5)] 5a, 5b, which were characterised spectroscopically.
All showed IR and NMR peaks for the acylphosphine ligand
similar to those observed for 3.
The hydride complexes 4a and 4b both give rise to asym-
metric doublets at δ Ϫ5.62 and Ϫ5.59 respectively in their
1
room-temperature H NMR spectra in [2H8]toluene because
they exist as rapidly interconverting cis and trans isomers.14 At
Ϫ50 ЊC this isomerisation can be frozen out (Fig. 1) and the
separate signals for the two isomers resolved. In keeping with
3590
J. Chem. Soc., Dalton Trans., 1997, Pages 3589–3598

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Table 1 Infrared, mass spectra and analytical data for the complexes
Compound
IR ν(CO)a/cmϪ1
Mass spectrum m/z
Microanalysis (%)b
1a
1b
2a
2b
2c
2d
3a
3b
3c
3d
4a
4b
5a
5b
6a
6b
6c
6d
7
[Mo(COMe)(CO)2(PPh2H)(η-C5H5)]
[Mo(COEt)(CO)2(PPh2H)(η-C5H5)]
[Mo(COMe)(CO)2(PPh2Me)(η-C5H5)]
[Mo(COMe)(CO)2(PPh2Et)(η-C5H5)]
[Mo(COEt)(CO)2(PPh2Me)(η-C5H5)]
[Mo(COEt)(CO)2(PPh2Et)(η-C5H5)]
[MoMe(CO)2(PPh2COMe)(η-C5H5)]
[MoEt(CO)2(PPh2COMe)(η-C5H5)]
[MoMe(CO)2(PPh2COEt)(η-C5H5)]
[MoEt(CO)2(PPh2COEt)(η-C5H5)]
[MoH(CO)2(PPh2COMe)(η-C5H5)]
[MoH(CO)2(PPh2COEt)(η-C5H5)]
[MoCl(CO)2(PPh2COMe)(η-C5H5)]
[MoCl(CO)2(PPh2COEt)(η-C5H5)]
[Mo(COMe)(CO)2(PPh2COMe)(η-C5H5)]
[Mo(COMe)(CO)2(PPh2COEt)(η-C5H5)]
[Mo(COEt)(CO)2(PPh2COMe)(η-C5H5)]
[Mo(COEt)(CO)2(PPh2COEt)(η-C5H5)]
[{Mo(CO)2(PPh2H)(η-C5H5)}2]
1940m, 1856s, 1618 (br)
1938m, 1853s, 1614mw
1934m, 1849s, 1601 (br)
1933m, 1847s, 1603 (br)
1931m, 1845s, 1610mw
1930m, 1845s, 1611w
1937m, 1855s, 1686vw
1931m, 1850s, 1686vw
1936m, 1854s, 1690w
1930m, 1849s, 1689w
1941s, 1861s, 1685w
1940s, 1860s, 1684w
1972s, 1881ms, 1686w
1971s, 1879ms, 1687w
1939m, 1858s, 1690vw, 1623w
1939m, 1857s, 1693w, 1622w
1937m, 1855s, 1690w, 1619mw
1936m, 1854s, 1692w, 1619m
1856m, 1835s
448 (Mϩ)
C 56.43 (56.52); H 4.14 (4.29)
C 57.36 (57.40); H 4.75 (4.60)
C 57.15 (57.40); H 4.35 (4.60)
C 58.18 (58.24); H 4.80 (4.89)
C 58.01 (58.24); H 4.72 (4.89)
C 58.87 (59.03); H 4.91 (5.16)
C 57.14 (57.40); H 4.74 (4.60)
C 58.10 (58.24); H 4.79 (4.89)
C 58.19 (58.24); H 4.78 (4.89)
C 58.83 (59.03); H 5.24 (5.16)
C 56.07 (56.52); H 4.18 (4.29)
C 57.54 (57.40); H 4.57 (4.60)
C 52.33 (52.47); H 3.81 (3.77)c
C 53.74 (53.41); H 4.22 (4.07)d
C 56.57 (56.57); H 4.15 (4.33)
C 57.13 (57.38); H 4.65 (4.62)
C 57.23 (57.38); H 4.88 (4.62)
C 57.90 (58.19); H 4.77 (4.88)
C 56.39 (56.59); H 4.20 (4.00)
C 57.90 (57.43); H 4.79 (4.58)
C 57.54 (57.57); H 4.53 (4.35)
C 58.18 (58.48); H 4.86 (4.67)
C 58.12 (58.34); H 4.95 (4.90)
C 58.74 (59.20); H 5.14 (5.19)
C 58.95 (59.20); H 5.00 (5.19)
C 59.91 (60.01); H 5.57 (5.57)
463 (M ϩ H)ϩ
462 (Mϩ)
477 (M ϩ H)ϩ
477 (M ϩ H)ϩ
491 (M ϩ H)ϩ
462 (Mϩ)
476 (Mϩ)
476 (Mϩ)
490 (Mϩ)
448 (Mϩ)
463 (M ϩ H)ϩ
484 (M ϩ H)ϩ
498 (M ϩ H)ϩ
491 (M ϩ H)ϩ
505 (M ϩ H)ϩ
504 (Mϩ)
519 (M ϩ H)ϩ
807 (M ϩ H)ϩ
420 (Mϩ)
8
[MoMe(CO)2(PPh2H)(η-C5H5)]
[{Mo(CO)2(PPh2Me)(η-C5H5)}2]
[{Mo(CO)2(PPh2Et)(η-C5H5)}2]
[MoMe(CO)2(PPh2Me)(η-C5H5)]
[MoEt(CO)2(PPh2Me)(η-C5H5)]
[MoMe(CO)2(PPh2Et)(η-C5H5)]
1935m, 1851s
1846m, 1825s
1844m, 1824s
1929m, 1842s
1924m, 1838s
1929m, 1842s
1923m, 1837s
9a
9b
10a
10b
10c
10d
834 (Mϩ)
863 (M ϩ H)ϩ
434 (Mϩ)
448 (Mϩ)
448 (Mϩ)
[MoEt(CO)2(PPh2Et)(η-C5H5)]
462 (Mϩ)
a
In CH2Cl2 solution. b Found (Calc.). c Cl 7.64 (7.37). d Cl 6.98 (7.17).
other complexes of this type, the hydride signal of the cis
isomer occurs at slightly higher field and has a much larger
J(PH) value (ca. 65 Hz) than the trans isomer (ca. 20 Hz).15 The
ratio of the cis:trans isomers at this temperature was approx-
imately 57:43 for both compounds.
The chloride complexes 5a and 5b could be obtained either
by treatment of the hydrides 4 with chloroform, or directly from
the anion by dissolution in CH2Cl2 or CHCl3. They exist
exclusively as the cis isomers, as shown by the IR spectrum and
the appearance of two terminal CO resonances in the 13C NMR
spectrum. In a seminal study of the cis:trans ratios in com-
plexes of the type [MoR(CO)2L(η-C5H5)], Faller and Ander-
son 14 showed that the steric and electronic properties of R
and L were both important factors, but for a constant L the
cis:trans ratio increased in the order R = CH2Ph < Me < H < I
< Br < Cl. The observation of small amounts of cis isomers
for the methyl complexes 3a and 3c, an approximate 6:4
ratio for the hydride complexes 4a and 4b, and exclusively cis
for the chlorides 5a and 5b is entirely consistent with these
findings.
Fig. 2 Molecular structure of [Mo(COMe)(CO)2(PPh2COMe)(η-
C5H5)] 6a in the crystal
the bond angles around the basal ligands except for a very slight
opening up of the C(21)᎐Mo᎐P angle.16 The two acetyl groups
are orientated almost perpendicular to each other; the C(3)᎐
O(3) distance in the acylphosphine unit is slightly shorter
than the C(21)᎐O(4) length of the metal acyl, but not signifi-
cantly so.
Deprotonation–acylation reactions
The phosphorus-centred anions derived from low-temperature
deprotonation of complex 1 reacted cleanly with the acyl chlor-
ides R2COCl to give the acylphosphine acyl complexes [Mo-
(COR1)(CO)2(PPh2COR2)(η-C5H5)] 6a–6d in yields of over
80% (Scheme 1). Attempts to obtain the same products from
the molybdenum-centred anions derived by room-temperature
deprotonation of 1 led instead to a mixture of products, includ-
ing the hydride complexes 4. As expected these four compounds
show NMR signals characteristics of both molybdenum–acyl
and phosphorus–acyl functionalities which can be readily
assigned by comparison with the spectra of 2 and 3.
The structure of complex 6a was determined by X-ray dif-
fraction and is shown in Fig. 2. Selected bond lengths and
angles are given in Table 4. As expected the acylphosphine
and acyl ligands occupy the trans positions in a typical four-
legged piano-stool structure. The Mo᎐P and Mo᎐C(21) dis-
tances are virtually identical to those found in the triphenyl-
phosphine analogue [Mo(COMe)(CO)2(PPh3)(η-C5H5)], as are
Synthesis of alkylphosphine alkyl complexes
In order to study the mechanism of the migration reaction (see
below) we required a route to the complex [MoMe(CO)2-
(PPh2H)(η-C5H5)]. Attempts to prepare it by thermal decarb-
onylation of the acyl complex 1a led instead to loss of the
phosphine ligand and formation of [MoMe(CO)3(η-C5H5)]
among other products. A different method was therefore
employed (Scheme 2). The substituted dimer [{Mo(CO)2-
(PPh2H)(η-C5H5)}2] 7 was prepared by the reaction of [Mo2-
(CO)4(η-C5H5)2] with 2 equivalents of PPh2H. Cleavage of this
dimer with sodium amalgam and alkylation of the resulting
anion with MeI gave the desired complex 8 in moderate yield
1
(46%). The H NMR spectrum of the product showed that it
exists mainly as the cis isomer (cis:trans ratio 1.66:1).
J. Chem. Soc., Dalton Trans., 1997, Pages 3589–3598
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Table 2 Proton and 31P NMR spectra of the complexes
1H NMR a
31P NMR a
Compound
(δ)
(δ)
1a
1b
7.75–7.30 (m, 10 H, Ph), 7.08 (d, JPH 361, 1 H, PH), 5.08 (d, JPH 1.6, 5 H, η-C5H5), 2.60 (s, 3 H, Me)
7.61–7.37 (m, 10 H, Ph), 7.07 (d, JPH 360, 1 H, PH), 5.07 (d, JPH 1.2, 5 H, η-C5H5), 2.98 (q, JH H 7.4, 2 H, CH2),
0.88 (t, JH H 7.4, 3 H, CH3)
41.3
42.3
2a
2b
7.58–7.42 (m, 10 H, Ph), 5.00 (d, JPH 1.0, 5 H, η-C5H5), 2.59 (s, 3 H, COMe), 2.20 (d, JPH 8.5, 3 H, PMe)
7.51–7.41 (m, 10 H, Ph), 4.92 (d, JPH 1.0, 5 H, η-C5H5), 2.67 (dq, JPH 8.5, JH H 7.8, 2 H, CH2 of Et), 2.61 (s, 3 H,
COMe), 1.16 (dt, JPH 19, JH H 7.8, 3 H, CH3 of Et)
49.5
60.2
2c
2d
3a
7.56–7.41 (m, 10 H, Ph), 4.99 (d, JPH 1.2, 5 H, η-C5H5), 3.00 (q, JH H 7.1, 2 H, CH2 of Et), 2.19 (d, JPH 8.1, 3 H,
PMe), 0.89 (t, JH H 7.1, 3 H, CH3 of Et)
7.53–7.38 (m, 10 H, Ph), 4.92 (d, JPH 1.5, 5 H, η-C5H5), 3.07 (q, JH H 7.0, 2 H, CH2 of COEt), 2.67 (dq, JH H 7.5,
JPH 0.5, 2 H, CH2 of PEt), 1.16 (dt, JPH 18.0, JH H 7.5, 3 H, CH3 of PEt), 0.92 (t, JH H 7.0, 3 H, CH3 of COEt)
trans isomer: 7.58–7.42 (m, 10 H, Ph), 4.77 (d, JPH 1.5, 5 H, η-C5H5), 2.27 (d, JPH 4.0, 3 H, COMe), 0.44 (d, JPH
2.5, 3 H, MoMe)
50.0
60.6
trans 83.0,
cis 77.9
cis isomer: 5.12 (s, η-C5H5), 2.18 (d, JPH 3.1, COMe), Ϫ0.20 (d, JPH 11.8, MoMe)
7.55–7.41 (m, 10 H, Ph), 4.75 (d, JPH 1.5, 5 H, η-C5H5), 2.27 (d, JPH 4.5, 3 H, COMe), 1.73 (m, 2 H, CH2 of Et),
1.53 (dt, JH H 7.5, JPH 1.0, 3 H, CH3 of Et)
trans isomer: 7.56–7.38 (m, 10 H, Ph), 4.76 (d, JPH 1.5, 5 H, η-C5H5), 2.58 (q, JH H 7.0, JPH 0.8, 2 H, CH2 of Et),
1.02 (dt, JH H 7.0, JPH 0.5, 3 H, CH3 of Et), 0.42 (d, JPH 2.1, 3 H, MoMe)
3b
3c
84.1
trans 81.0,
cis 76.8
cis isomer: 5.10 (s, η-C5H5), 2.43 (m, CH2 of Et), 0.88 (m, CH3 of Et), Ϫ0.21 (d, JPH 11.5, MoMe)
7.54–7.37 (m, 10 H, Ph), 4.73 (d, JPH 1.4, 5 H, η-C5H5), 2.59 (dq, JH H 7.5, JPH 0.8, 2 H, CH2 of COEt), 1.71 (m,
2 H, CH2 of MoEt), 1.53 (t, JH H 7.5, CH3 of MoEt), 1.01 (dt, JH H 7.0, JPH 0.8, 3 H, CH3 of COEt)
ϩ25 ЊC:b 7.58–6.92 (m, 10 H, Ph), 4.66 (d, JPH 0.8, 5 H, η-C5H5), 2.01 (d, JPH 4.3, 3 H, Me), Ϫ5.62 (d, JPH 50.4,
1 H, MoH)
3d
4a
82.1
81.5
cis isomer, Ϫ50 ЊC:b 7.48–6.85 (m, 10 H, Ph), 4.54 (s, 5 H, η-C5H5), 2.02 (m, 3 H, Me), Ϫ5.65 (d, JPH 65.1, MoH)
trans isomer, Ϫ50 ЊC:b 7.48–6.85 (m, 10 H, Ph), 4.43 (s br, 5 H, η-C5H5), 1.81 (d, JPH 6.0, 3 H, Me), Ϫ5.42 (d, JPH
20.7, MoH)
4b
ϩ25 ЊC:b 7.52–6.92 (m, 10 H, Ph), 4.65 (s, 5 H, η-C5H5), 2.44 (q, JH H 6.8, 2 H, CH2), 0.87 (t, JPH 6.8, 3 H, CH3),
Ϫ5.59 (d, JPH 50.5, 1 H, MoH)
79.6
cis isomer, Ϫ50 ЊC:b 7.51–6.89 (m, 10 H, Ph), 4.56 (s, 5 H, η-C5H5), 2.45 (m, 2 H, CH2), 0.86 (m, 3 H, CH3),
Ϫ5.63 (d, JPH 65.5, MoH)
trans isomer, Ϫ50 ЊC:b 7.51–6.89 (m, 10 H, Ph), 4.45 (s br, 5 H, η-C5H5), 2.45 (m, 2 H, CH2), 0.86 (m, 3 H, CH3),
Ϫ5.42 (d, JPH 20.8, MoH)
5a
5b
7.66–7.38 (m, 10 H, Ph), 5.44 (s, η-C5H5), 2.24 (d, JPH 2.7, 3 H, Me)
7.67–7.36 (m, 10 H, Ph), 5.39 (s, η-C5H5), 2.44 (ddq, JH H 7.0, JPH 2.1, 2 H, CH2), 0.95 (dt, JH H 7.0, JPH 1.0, 3 H,
CH3)
59.1
58.0
6a
6b
7.55–7.45 (m, 10 H, Ph), 5.00 (d, JPH 1.3, 5 H, η-C5H5), 2.66 (s, 3 H, MoCOMe), 2.43 (d, JPH 4.5, 3 H, PCOMe)
7.51–7.41 (m, 10 H, Ph), 4.97 (d, JPH 1.5, 5 H, η-C5H5), 2.72 (dq, JH H 7.0, JPH 1.0, 2 H, CH2 of Et), 2.64 (s, 3 H,
COMe), 1.09 (dt, JH H 7.0, JPH 0.8, 3 H, CH3 of Et)
77.0
75.0
6c
6d
7.51–7.41 (m, 10 H, Ph), 4.98 (d, JPH 1.1, 5 H, η-C5H5), 3.05 (q, JH H 7.2, 2 H, CH2 of Et), 2.41 (d, JPH 4.0, 3 H,
COMe), 0.92 (t, JH H 7.2, 3 H, CH3 of Et)
7.62–7.40 (m, 10 H, Ph), 4.99 (d, JPH 1.2, 5 H, η-C5H5), 3.06 (q, JH H 7.0, 2 H, CH2 of MoCOEt), 2.73 (dq, JH H
7.0, JPH 1.2, 2 H, CH2 of PCOEt), 1.10 (dt, JH H 7.0, JPH 0.8, 3 H, CH3 of PCOEt), 0.94 (t, JH H 7.0, 3 H, CH3 of
MoCOEt)
77.4
75.5
7
8
7.71–7.28 (m, 20 H, Ph), 7.26 (d, JPH 353, 2 H, PH), 4.61 (d, JPH 2.2, 10 H, η-C5H5)
cis isomer: 7.59–7.30 (m, 10 H, Ph), 6.36 (d, JPH 346, 1 H, PH), 5.06 (s, 5 H, η-C5H5), Ϫ0.08 (d, JPH 15.0, 3 H, Me)
trans isomer: 7.10 (d, JPH 355, 1 H, PH), 4.84 (d, JPH 1.9, 5 H, η-C5H5), 0.34 (d, JPH 2.5, 3 H, Me)
trans isomer: 7.64–7.38 (m, 20 H, Ph), 4.63 (d, JPH 1.8, 10 H, η-C5H5), 2.16 (d, JPH 8.3, 6 H, Me)
cis isomer: 4.81 (d, JPH 1.4, 10 H, η-C5H5), 2.17 (m, 6 H, Me)
57.8
cis 58.4,
trans 45.7
trans 60.7,
cis 62.7
trans 70.8,
cis 71.2
9a
9b
trans isomer: 7.77–7.38 (m, 20 H, Ph), 4.66 (d, JPH 1.8, 10 H, η-C5H5), 2.58 (dq, JPH 7.0, JH H 7.0, 4 H, CH2), 1.10
(m, 6 H, CH3)
cis isomer: 4.72 (d, JPH 1.5, 10 H, η-C5H5), 2.68 (dq, JPH 7.0, JH H 7.0, 4 H, CH2), 1.10 (m, 6 H, CH3)
trans isomer: 7.59–7.30 (m, 10 H, Ph), 4.74 (d, JPH 1.5, 5 H, η-C5H5), 2.11 (d, JPH 8.0, 3 H, PMe), 0.34 (d, JPH 2.6, 3
H, MoMe)
10a
trans 53.7,
cis 49.8
cis isomer: 5.08 (s, 5 H, η-C5H5), 1.95 (d, JPH 8.0, 3 H, PMe), Ϫ0.20 (d, JPH 11.5, 3 H, MoMe)
7.58–7.38 (m, 10 H, Ph), 4.72 (d, JPH 1.5, 5 H, η-C5H5), 2.15 (d, JPH 8.0, 3 H, PMe), 1.69–1.58 (m, 2 H, CH2 of Et),
1.54–1.47 (m, 3 H, CH3 of Et)
trans isomer: 7.56–7.36 (m, 10 H, Ph), 4.66 (d, JPH 1.5, 5 H, η-C5H5), 2.70 (dq, JH H 7.0, JPH 7.5, 2 H, CH2 of Et),
1.00 (dt, JH H 7.0, JPH 17.5, 3 H, CH3 of Et), 0.37 (d, JPH 2.5, 3 H, MoMe)
cis isomer: 5.10 (s, 5 H, η-C5H5), 2.33 (m, 2 H, CH2 of Et), 0.98 (dt, JH H 7.5, JPH 16.5, 3 H, CH3 of Et), Ϫ0.2 (d, JPH
1.5, MoMe)
10b
10c
54.9
trans 65.3,
cis 60.5
10d
7.56–7.30 (m, 10 H, Ph), 4.65 (d, JPH 1.5, 5 H, η-C5H5), 2.58 (dq, JH H 7.5, JPH 7.5, 2 H, CH2 of PEt), 1.66–1.59 (m, 2
H, CH2 of MoEt), 1.55–1.48 (m, 3 H, CH3 of MoEt), 1.00 (dt, JH H 7.5, JPH 18.0, 3 H, CH3 of PEt)
65.9
a
In CDCl3 solution unless otherwise stated; J in Hz. b In [2H8]toluene solution.
Sequential addition of dbu and EtI to a thf solution of com-
plex 8 at room temperature afforded a single product which was
characterised as [MoMe(CO)2(PPh2Et)(η-C5H5)] 10c. It is
therefore possible to say that there is no migration of the methyl
ligand to the phosphido group in the intermediate anion, and
this remained so even when the reaction was repeated in reflux-
ing thf.
we then prepared the alkylphosphine alkyl species [MoR2-
(CO)2(PPh2R1)(η-C5H5)] 10a–10d by the same synthetic route
as used for 8 (Scheme 2). The substituted dimers 9a and 9b were
made from [Mo2(CO)4(η-C5H5)2] and PPh2Me or PPh2Et; they
display similar spectroscopic properties to those of the PPh3
analogue, though their relative insolubility prevented the acquis-
ition of useful 13C NMR spectra.17 Reduction with Na/Hg and
alkylation with R2X gave good yields of 10a–10d. Of these, 10a
has been previously made by the thermal decarbonylation of
To complete a series of related complexes and provide a
sample of complex 10c independently for comparison purposes,
3592
J. Chem. Soc., Dalton Trans., 1997, Pages 3589–3598

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Table 3 Carbon-13 NMR data for the complexes
Compound
δ (J/Hz)a
1a
1b
265.6 (d, J 11, COMe), 235.8 (d, J 25, CO), 133.5 (d, J 40, Cipso), 133.8–128.4 (m, Ph), 95.8 (s, η-C5H5), 51.4 (s, Me)
267.3 (d, J 12, COEt), 236.2 (d, J 16, CO), 133.2 (apparent s, Cipso), 132.3–128.9 (m, Ph), 95.7 (s, η-C5H5), 58.2 (s, CH2), 9.9 (s,
CH3)
2a
2b
2c
2d
3a
266.7 (d, J 11, COMe), 237.5 (d, J 24, CO), 137.1 (d, J 44, Cipso), 131.4–128.4 (m, Ph), 96.0 (s, η-C5H5), 51.3 (s, COMe), 20.5
(d, J 34, PMe)
265.9 (d, J 11, COMe), 238.3 (d, J 23, CO), 135.8 (d, J 40, Cipso), 131.9–128.5 (m, Ph), 96.3 (s, η-C5H5), 50.7 (s, COMe), 26.3 (d,
J 32, CH2 of Et), 8.8 (s, CH3 of Et)
268.2 (d, J 11, COEt), 237.9 (d, J 24, CO), 137.4 (d, J 40, Cipso), 131.4–128.5 (m, Ph), 96.1 (s, η-C5H5), 57.9 (s, CH2 of Et), 20.3 (d,
J 34, PMe), 9.9 (s, CH3 of Et)
267.9 (d, J 11, COEt), 238.5 (d, J 23, CO), 135.8 (d, J 40, Cipso), 131.9–128.5 (m, Ph), 96.2 (s, η-C5H5), 57.4 (s, CH2 of COEt), 26.1
(d, J 32, CH2 of PEt), 10.0 (s, CH3 of COEt), 8.8 (s, CH3 of PEt)
trans isomer: 235.5 (d, J 21, CO), 212.9 (d, J 15, COMe), 133.6 (d, J 40, Cipso), 133.7–128.5 (m, Ph), 92.3 (s, η-C5H5), 30.3 (d, J 43,
COMe), Ϫ18.8 (d, J 9, MoMe)
cis isomer: 92.2 (s, η-C5H5)
3b
3c
236.0 (d, J 21, CO), 213.0 (d, J 15, COMe), 133.3 (apparent s, Cipso), 133.7–128.5 (m, Ph), 92.6 (s, η-C5H5), 30.2 (d, J 44, COMe),
19.6 (s, CH3 of Et), Ϫ2.5 (d, J 9, CH2 of Et)
trans isomer: 234.7 (d, J 21, CO), 215.9 (d, J 13, COMe), 133.7 (d, J 39, Cipso), 133.7–128.5 (m, Ph), 92.3 (s, η-C5H5), 36.1 (d, J 41,
CH2 of Et), 8.3 (d, J 2, CH3 of Et), Ϫ18.8 (d, J 9, MoMe)
cis isomer: 92.2 (s, η-C5H5)
3d
236.2 (d, J 21, CO), 216.0 (d, J 13, COMe), 133.7 (d, J 39, Cipso), 133.7–128.4 (m, Ph), 92.6 (s, η-C5H5), 36.0 (d, J 40, CH2 of
COEt), 19.55 (s, CH3 of MoEt), 8.2 (d, J 2, CH3 of COEt), Ϫ2.3 (d, J 9, CH2 of MoEt)
236.1 (s br, CO), 213.5 (d, J 16, COMe), 135.4 (d, J 42, Cipso), 133.9–128.5 (m, Ph), 89.9 (s, η-C5H5), 29.5 (d, J 46, COMe)b
236.5 (s br, CO), 216.7 (d, J 13, COEt), 135.4 (d, J 40, Cipso), 133.9–128.6 (m, Ph), 89.9 (s, η-C5H5), 35.8 (d, J 43, CH2 of Et), 8.3 (d,
J 2, CH3 of Et)b
4a
4b
5a
5b
6a
6b
6c
6d
8
255.4 (d, J 28, cis CO), 242.6 (d, J 6, trans CO), 218.5 (d, J 11, COMe), 135.4–128.7 (m, Ph), 132.6 (d, J 38, Cipso), 129.3 (d, J 38,
Cipso), 95.0 (s, η-C5H5), 36.9 (d, J 35, COMe)
255.9 (d, J 29, cis CO), 242.9 (d, J 6, trans CO), 220.9 (d, J 9, COEt), 135.5–128.7 (m, Ph), 132.8 (d, J 37, Cipso), 129.4 (d, J 36, Cipso),
95.0 (s, η-C5H5), 43.0 (d, J 32, CH2), 6.9 (s, CH3)
263.3 (d, J 10, MoCOMe), 236.6 (d, J 22, CO), 212.0 (d, J 15, PCOMe), 133.6–128.8 (m, Ph), 132.0 (d, J 41, Cipso), 96.5 (s,
η-C5H5), 51.3 (s, MoCOMe), 30.9 (d, J 44, PCOMe)
263.5 (d, J 9, COMe), 236.8 (d, J 22, CO), 215.3 (d, J 12, COEt), 133.6–128.7 (m, Ph), 132.2 (d, J 40, Cipso), 96.5 (s, η-C5H5), 51.2 (s,
COMe), 37.1 (d, J 41, CH2 of Et), 8.0 (d, J 3, CH3 of Et)
264.6 (d, J 10, COEt), 236.8 (d, J 22, CO), 212.1 (d, J 15, COMe), 133.6–128.8 (m, Ph), 132.2 (d, J 41, Cipso), 96.4 (s, η-C5H5), 58.2
(s, CH2 of Et), 30.9 (d, J 44, COMe), 10.1 (s, CH3 of Et)
265.2 (d, J 10, MoCOEt), 236.9 (d, J 22, CO), 215.3 (d, J 12, PCOEt), 133.5–128.7 (m, Ph), 132.1 (d, J 41, Cipso), 96.3 (s, η-C5H5),
58.1 (s, CH2 of MoCOEt), 36.9 (d, J 41, CH2 of PCOEt), 10.1 (s, CH3 of MoCOEt), 8.0 (d, J 3, CH3 of PCOEt)
cis isomer: 253.5 (d, J 28, cis CO), 239.7 (s, trans CO), 137.5 (d, J 41, Cipso), 134.7 (d, J 43, Cipso), 133.7–128.5 (m, Ph), 92.0 (s,
η-C5H5), Ϫ16.6 (d, J 20, Me),
trans isomer: 233.9 (d, J 23, CO), 91.6 (s, η-C5H5), 20.0 (d, J 10, Me)
10a
trans isomer: 235.5 (d, J 23, CO), 139.2 (d, J 40, Cipso), 132.4–128.1 (m, Ph), 92.0 (s, η-C5H5), 21.5 (d, J 34, PMe), Ϫ19.6 (d, J 10,
MoMe)
cis isomer: 91.9 (s, η-C5H5)
10b
10c
236.6 (apparent s, CO), 139.3 (d, J 40, Cipso), 133.0–127.8 (m, Ph), 92.3 (s, η-C5H5), 21.5 (d, J 33, PMe), 20.0 (s, CH3 of Et), Ϫ3.4 (d,
J 11, CH2 of Et)
trans isomer: 236.4 (d, J 22, CO), 137.7 (d, J 37, Cipso), 132.1–128.3 (m, Ph), 92.0 (s, η-C5H5), 27.1 (d, J 33, CH2 of Et), 8.7 (s, CH3 of
Et), Ϫ18.8 (d, J 11, MoMe)
cis isomer: 91.7 (s, η-C5H5)
10d
237.9 (d, J 22, CO), 137.8 (d, J 37, Cipso), 132.2–128.2 (m, Ph), 92.4 (s, η-C5H5), 26.7 (d, J 33, CH2 of PEt), 19.6 (s, CH3 of MoEt),
8.7 (s, CH3 of PEt), Ϫ2.9 (d, J 10, CH2 of MoEt)
a
In CDCl3 solution unless otherwise stated, all couplings are JPC.
b In C6D6 with added [Cr(acac)3] (acac = acetylacetonate).
2a, but the others appear to be new compounds.6 Their spectro-
scopic data are as expected; in the cases where R2 = Me, signi-
complex 8 exists predominantly as the cis isomer and so is cor-
rectly aligned for migration to occur. We therefore propose that
the migration occurs by nucleophilic attack of the phosphido
group on the acyl carbon as shown in Scheme 3. This pathway
would not be available to the alkyl complex 8.
1
ficant amounts of cis isomers were observed in the H NMR
spectra whereas the signals for a cis isomer could not be
unambiguously identified for 10b and 10d.
This mechanism has precedent in the deprotonation of
[Fe(COMe)(CO)(PPh2H)(η-C5H5)], which afforded [Fe(CO)-
The mechanism
{PPh2CMe(OSiMe3)}(η-C5H5)] on addition of SiMe3Cl;18
a
At low temperature the complexes 1 undergo a standard
deprotonation–alkylation sequence at the secondary phosphine
ligand to produce 2, whereas at room temperature migration of
the acyl group to phosphorus leads to the acylphosphine alkyl
complexes 3. The migration must occur from a cis position,
whereas both reagent and product exist almost exclusively in
the trans conformation. On the other hand the methyl complex
8 does not undergo any rearrangement on deprotonation, even
when heated. If the rearrangement was a simple migratory
insertion reaction the methyl group of 8 would be expected to
migrate more readily than the acyl group of 1 because (i) Me
has a much higher migratory aptitude than COMe and (ii)
similar complex, [Mn(CO)4{PPh2CMe(OSiMe3)}], was pre-
pared by addition of a silylphosphine ligand to a manganese
acyl.19 Both of these contain the silylated form of the ligand
present in our postulated intermediate, but we were unable to
intercept it in this form by conducting the deprotonation of 1a
in the presence of SiMe3Cl. The formation of a three-
membered MoPC ring during this mechanism is a known pro-
cess; for example, we have recently observed that addition of
᎐
PPh2H to [Mo(CO) (C᎐CR)(η-C H )] affords [Mo(PPh2-
᎐
3
5
5
C=CHR)(CO)2(η-C5H5)], which contains a similar MoPC ring
with an exocyclic double bond,20 and several other examples are
known.21
J. Chem. Soc., Dalton Trans., 1997, Pages 3589–3598
3593

View Article Online
O
C
O
C
O
C
O
C
PPh2R1
(i)
(iii)
[Mo2(CO)6(η-C5H5)2]
Mo
Mo
Mo
Mo
R1Ph2P
C
O
C
O
C
O
C
O
9a R1 = Me
9b R1 = Et
(iv)
(iii)
O
C
O
C
PPh2H
(v)
Mo
Mo
Mo
Me
Mo
R2
CO
R1Ph2P
HPh2P
HPh2P
OC
CO
OC
C
O
C
O
10a R1 = R2 = Me
10b R1 = Me, R2 = Et
10c R1 = Et, R2 = Me
10d R1 = R2 = Et
8
7
Alkylphosphine alkyl complexes
Scheme 2 Synthesis of the alkylmolybdenum phosphine complexes 8 and 10. Reagents and conditions: (i) refluxing toluene, argon purge, 24 h;
(ii) PPh2R1, r.t.; (iii) Na/Hg, then R2I; (iv) PPh2H, r.t.; (v) Na/Hg, MeI
Table 4 Selected bond lengths (Å) and angles (Њ) for [Mo(COMe)-
(CO)2(PPh2COMe)(η-C5H5)] 6a
O
O
Mo
Mo
–
C
C
Ph2P
OC
–
Mo᎐P
2.446(2)
1.956(4)
2.314(5)
2.322(5)
2.259(6)
1.817(4)
1.154(4)
1.185(5)
1.487(7)
Mo᎐C(1)
Mo᎐C(4)
Mo᎐C(6)
Mo᎐C(8)
P᎐C(3)
1.963(3)
2.371(4)
2.303(4)
2.347(5)
1.890(4)
1.821(4)
1.149(5)
1.203(7)
1.506(7)
R1
R1
OC
OC
CO
PPh2
Mo᎐C(2)
Mo᎐C(5)
Mo᎐C(7)
Mo᎐C(21)
P᎐C(9)
O(1)᎐C(1)
O(3)᎐C(3)
C(3)᎐C(23)
P᎐C(15)
O(2)᎐C(2)
O(4)᎐C(21)
C(21)᎐C(22)
–
O
C
O
–
Mo
Mo
C
OC
OC
P᎐Mo᎐C(1)
80.5(1)
106.4(2)
136.3(1)
112.6(2)
103.0(2)
175.8(3)
116.6(3)
P᎐Mo᎐C(2)
80.3(2)
74.8(2)
73.1(2)
104.5(2)
101.2(2)
175.4(3)
120.5(3)
123.6(4)
R1
R1
OC
OC
C(1)᎐Mo᎐C(2)
P᎐Mo᎐C(21)
Mo᎐P᎐C(3)
C(3)᎐P᎐C(9)
Mo᎐C(2)᎐O(2)
P᎐C(3)᎐C(23)
C(1)᎐Mo᎐C(21)
C(2)᎐Mo᎐C(21)
C(9)᎐P᎐C(15)
C(3)᎐P᎐C(15)
Mo᎐C(1)᎐O(1)
P᎐C(3)᎐O(3)
PPh2
PPh2
Scheme 3 Intramolecular mechanism for the acyl migration reaction
(η-C5H4Me)] 11a with dbu at –78 ЊC followed by addition of
MeI gave exclusively [Mo(COEt)(CO)2(PPh2Me)(η-C5H5)] 2c
and [Mo(COMe)(CO)2(PPh2Me)(η-C5H4Me)] 12, showing that
the low-temperature reaction is, as expected, wholly intra-
molecular.
O(3)᎐C(3)᎐C(23) 122.8(4)
Mo᎐C(21)᎐O(4) 119.6(4)
Mo᎐C(21)᎐C(22)
O(4)᎐C(21)᎐C(22) 116.8(5)
Parallels can also be drawn between the anionic rearrange-
ment observed here and that reported by Heah and Gladysz
in [Re(COMe)(NO)(PPh3)(η-C5H5)]. Deprotonation of this
complex occurs at the C5H5 ligand and is followed by rapid
intramolecular migration of the acyl group to the ring, whereas
in the analogous methyl complex [ReMe(NO)(PPh3)(η-C5H5)]
no migration occurs.22
Although the intramolecular pathway shown in Scheme 3
accounts perfectly for the products observed, we realised that a
second possibility existed: that the reaction could be inter-
molecular, as shown in Scheme 4 (upper pathway), with the
phosphido group of one molecule attacking the acyl group of
another. We therefore prepared and characterised complexes
11a, 11b, 12, 13a and 13b, the η-C5H4Me analogues of 1a, 1b,
2a, 3a and 3c respectively, and carried out some crossover reac-
tions (the spectroscopic data for these compounds have been
deposited as SUP 57273).
Deprotonation of a mixture of the same two complexes at
room temperature followed by addition of MeI gave a some-
what different result. The 31P NMR spectrum of the mixture
of products obtained after chromatography is shown in Fig. 3.
The two major products are those formed by intramolecular
reaction, i.e. [MoMe(CO)2(PPh2COEt)(η-C5H5)] 3c and [Mo-
Me(CO)2(PPh2COMe)(η-C5H4Me)] 13a. However significant
(and equal) amounts of the two crossover products arising from
intermolecular reaction, i.e. [MoMe(CO)2(PPh2COMe)-
(η-C5H5)] 3a and [MoMe(CO)2(PPh2COEt)(η-C5H4Me)] 13b
are also present (identified by comparison with authentic
samples). Separate experiments established that stirring a mix-
ture of the starting complexes 1b and 11a in thf for 24 h did not
result in ligand exchange; similarly a mixture of the major
products remained intact under these conditions. Hence any
crossover products must arise during the reaction. A second
crossover reaction starting from [Mo(COMe)(CO)2(PPh2H)-
(η-C5H5)] 1a and [Mo(COEt)(CO)2(PPh2H)(η-C5H4Me)] 11b
produced a similar proportion of intramolecular (3a and 13b)
Deprotonation of an equimolar mixture of [Mo(COEt)-
(CO)2(PPh2H)(η-C5H5)] 1b and [Mo(COMe)(CO)2(PPh2H)-
3594
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O
C
O
–
Mo
Mo
C
–
OC
OC
O
C
–
R1
R1
OC
P
Ph2
R2
MeI
OC
PPh2
Mo
Mo
P
Ph2
crossover products
observed
+
OC
+
CO
CO
Ph2P
OC
C
R2
O
O
C
–
–
O
Mo
Mo
C
–
PPh2
OC
CO
R2
OC
R1
OC
P
Ph2
–
O
C
Ph2
P
MeI
O
–
Mo
Mo
Mo
O
Mo
C
Ph2P
C
Ph2P
Me
R1
MePh2P
R2
R2
OC
CO
OC
CO
OC
CO
OC
CO
O
C
R1
not observed
Scheme 4 Possible intermolecular mechanism for the acyl migration reaction
phine alkyl complexes and the acylphosphine acyl complexes,
none of which is observed at all.
There are two possible reasons why the migration reaction
does not occur at low temperature; first there might be a signif-
icant activation energy for the process, presumably associated
with the Mo᎐C bond cleavage, or secondly the complex might
be frozen into the trans configuration at low temperature,
thus preventing migration by stopping the nucleophilic attack
on the acyl ligand. In any event it seems likely that the
phosphorus-centred anion is the kinetic product of deproton-
ation whereas the molybdenum-centred anion is the thermo-
dynamic product.
In conclusion the reactions described in this paper demon-
strate the unprecedented migration of an acyl ligand from a
metal centre to a co-ordinated phosphido group, and serve as
a further example of anionic rearrangement similar to those
involving migration of acyl groups to deprotonated cyclo-
pentadienyl rings.8,22 The fact that this migration can easily
be controlled provides a versatile and convenient method for
the selective synthesis of a wide range of alkyl- and acyl-
phosphine complexes, and we are currently exploring the
scope of the reaction both with molybdenum and other
metals.
Experimental
General experimental techniques were as detailed in recent
papers from this laboratory.23 Infrared spectra were recorded in
CH2Cl2 solution on a Perkin-Elmer 1600 FT-IR machine using
0.5 mm NaCl cells, H, 13C and 31P NMR spectra in CDCl3
1
Fig. 3 The 31P NMR spectrum of the mixture of products obtained
from the reaction of equimolar quantities of complexes 1b and 11a with
dbu and MeI at room temperature (see text)
solution on a Bruker AC250 machine with automated sample-
changer or on AM250 (1H, 13C) or WP80SY (31P) spectro-
meters. Chemical shifts are given on the δ scale relative to
SiMe4 (δ 0.0). The 13C-{1H} NMR spectra were recorded using
an attached proton test technique (JMOD pulse sequence). The
31P-{1H} NMR spectra were referenced to 85% H3PO4 (δ 0.0)
with downfield shifts reported as positive. Mass spectra were
recorded on a Kratos MS 80 instrument operating in fast atom
bombardment mode with 3-nitrobenzyl alcohol as matrix.
Elemental analyses were carried out by the Microanalytical
Service of the Department of Chemistry.
and intermolecular (3c and 13a) reaction products. It therefore
appears that the reaction proceeds predominantly intramolec-
ularly, as in Scheme 3, but with a measurable intermolecular
component arising from the mechanism in Scheme 4. The fact
that the two crossover products appear in approximately equal
amounts supports the pairwise acyl exchange mechanism of the
upper pathway of Scheme 4. If a random acyl transfer mechan-
ism, such as that shown in the lower pathway of Scheme 4, were
operating, additional products would include the alkylphos-
Literature methods were used to prepare [Mo2(CO)6(η-C5-
H5)2] and [MoR1(CO)3(η-C5H5)].24 Acyl halides were distilled
J. Chem. Soc., Dalton Trans., 1997, Pages 3589–3598
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and stored under argon before use. The phosphine ligands,
alkyl and acyl halides and dbu were all obtained from
Aldrich. Light petroleum refers to the fraction boiling in the
range 60–80 ЊC.
the alkylating agent provided a yellow oil which was recrystal-
lised from light petroleum to produce orange crystals of 3b
(200 mg, 38%). M.p. 104 ЊC.
Starting from 1b, the complexes 3c (85%, m.p. 134 ЊC) and 3d
(61%, m.p. 134 ЊC) were prepared in the same way.
Syntheses
[MoH(CO)2(PPh2COR1)(ç-C5H5)] (R1 = Me 4a or Et 4b).
A solution of complex 1a (500 mg, 1.12 mmol) in thf (30 cm3)
was deprotonated at room temperature with dbu (0.18 cm3,
1.20 mmol). After 30 min of stirring the ruby-red solution was
treated with 2 equivalents of glacial acetic acid (0.12 cm3, 2.1
mmol). After 1 h a change to orange-red had occurred. Evapor-
ation to dryness gave a red oil which was dissolved in the min-
imum volume of CH2Cl2 and chromatographed. The major
product was eluted as a yellow band with light petroleum–
CH2Cl2 (4:1) and identified as 4a (100 mg, 20%). M.p. 88 ЊC.
An improved yield of 60% was obtained by using a four-fold
excess of acetic acid.
The same method was followed for complex 1b (500 mg,
1.09 mmol) except that a five-fold excess of MeCO2H (0.30
cm3, 5.24 mmol) was used. Chromatography gave a bright
yellow band which was eluted as above. On removal of the
solvent complex 4b (230 mg, 46%) was obtained as an orange-
brown powder by triturating with light petroleum. M.p. 106 ЊC.
[Mo(COR1)(CO)2(PPh2H)(ç-C5H5)] (R = Me 1a or Et 1b). A
solution of [MoMe(CO)3(η-C5H5)] (3.00 g, 11.54 mmol) and
PPh2H (2.1 cm3, 12.07 mmol) in MeCN (170 cm3) was stirred
for 17 h. On removal of the solvent an orange oil was obtained
which was dissolved in the minimum volume of CH2Cl2 and
chromatographed on a silica column. A single yellow band was
eluted with CH2Cl2 which gave complex 1a as a yellow powder
after washing with light petroleum. Yield 4.50 g, 87%. In an
alternative work-up the orange oil was dissolved in a small vol-
ume of diethyl ether to which a large amount of light petroleum
was then added. Decanting the supernatant, washing the
residual solid with light petroleum and drying afforded 1a as a
yellow powder. M.p. 70 ЊC.
In a similar reaction, [MoEt(CO)3(η-C5H5)] (1.00 g, 3.65
mmol) and PPh2H (0.7 cm3, 4.02 mmol) produced complex 1b
as a yellow solid (1.03 g, 58%). M.p. 135 ЊC.
Low-temperature deprotonation–alkylation of complexes 1a,
1b: synthesis of [Mo(COR1)(CO)2(PPh2R2)(ç-C5H5)] (R1 =
R2 = Me 2a; R1 = Me, R2 = Et 2b; R1 = Et, R2 = Me 2c;
R1 = R2 = Et 2d). The complex 1a (300 mg, 0.67 mmol) was
dissolved in thf (20 cm3) and cooled to Ϫ78 ЊC. Addition of
dbu (0.11 cm3, 0.73 mmol) caused a slight darkening of the
solution to orange-red which was complete after 20 min of stir-
ring. Methyl iodide (0.10 cm3, 1.62 mmol) was added and the
solution was allowed to warm to room temperature. Filtration
of the yellow solution, removal of the solvent and washing with
light petroleum yielded yellow solid 2a (0.28 g, 91%). M.p.
108 ЊC.
Using the same method, complex 1a (500 mg, 1.12 mmol)
was deprotonated and quenched with EtI (0.09 cm3, 1.13
mmol). Column chromatography gave 433 mg (81%) of 2b as a
yellow powdery solid on elution with CH2Cl2. M.p. 128 ЊC. The
complexes 2c (89%, m.p. 114 ЊC) and 2d (90%, m.p. 157 ЊC)
were prepared in the same way from complex 1b.
[MoCl(CO)2(PPh2COR1)(ç-C5H5)] (R1 = Me 5a or Et 5b).
A solution of complex 1a (500 mg, 1.12 mmol) in thf (30 cm3)
was deprotonated with dbu (0.18 cm3, 1.20 mmol) at room
temperature as above. The addition of a four-fold excess of
glacial acetic acid (0.25 cm3, 4.36 mmol) gave a bright yellow
solution which was left to stir for 2 min before removing the
solvent under reduced pressure. The resulting yellow oil was
redissolved in CHCl3 (30 cm3) which gave an orange-red solu-
tion. The reaction was complete after 10 min (IR monitoring) at
which point the solution was evaporated to dryness. The oily
residue was then dissolved in the minimum volume of CH2Cl2
and chromatographed. A minor red zone was observed before
elution of the major product as an orange-red band with light
petroleum–CH2Cl2 (1:1). Removal of the solvent produced
bright red powdery solid 5a (300 mg, 56%). M.p. 170 ЊC.
Analogous treatment of complex 1b gave a 74% yield of 5b as
an orange powder. M.p. 140 ЊC.
Low-temperature deprotonation–acylation of complexes 1a,
1b: synthesis of [Mo(COR1)(CO)2(PPh2COR2)(ç-C5H5)] (R1 =
R2 = Me 6a; R1 = Me, R2 = Et 6b; R1 = Et, R2 = Me 6c; R1 =
R2 = Et 6d). A solution of complex 1a (500 mg, 1.12 mmol) in
thf (30 cm3) was cooled to Ϫ78 ЊC and treated with a slight
excess of dbu (0.18 cm3, 1.20 mmol), effecting a change to
orange-red. After stirring for 30 min, acetyl chloride (0.09 cm3,
1.27 mmol) was added. Stirring was continued for a further 10
min before removing the solvent under reduced pressure and
chromatographing the resulting yellow solid. Eluting with
CH2Cl2 afforded a bright yellow band which gave a yellow
powdery solid of 6a (430 mg, 79%) on triturating with light
petroleum. M.p. 125 ЊC. Recrystallisation from toluene at
Ϫ25 ЊC provided yellow crystals suitable for X-ray diffraction.
Following the same method with EtCOCl (0.10 cm3, 1.15
mmol) as the acylating agent led to the isolation of complex 6b
(460 mg, 82%) as a yellow powder. M.p. 132 ЊC.
[Mo(COR1)(CO)2(PPh2R2)(ç-C5H5)] 2a–2d from [MoR1-
(CO)3(ç-C5H5)] and PPh2R2. Following the same method as
used for complex 1, a solution of [MoMe(CO)3(η-C5H5)] (2.95
g, 11.35 mmol) in MeCN (150 cm3) was treated with a slight
excess of PPh2Me (2.2 cm3, 11.82 mmol) and stirred for 17 h.
Removal of the solvent yielded a yellow oil which was chrom-
atographed to give a single yellow band on eluting with CH2Cl2.
Trituration with light petroleum gave a pale yellow powder
of 2a (4.70 g, 90%). Complexes 2b (88), 2c (77) and 2d (95%)
were prepared in the same way from the appropriate starting
materials.
Room-temperature deprotonation-alkylation of complexes 1a,
1b: synthesis of [MoR2(CO)2(PPh2COR1)(ç-C5H5)] (R1 = R2 =
Me 3a; R1 = Me, R2 = Et 3b; R1 = Et, R2 = Me 3c; R1 = R2 = Et
3d). A solution of 1a (300 mg, 0.67 mmol) in thf (40 cm3) was
treated with dbu (0.11 cm3, 0.74 mmol) at room temperature.
A rapid change from yellow to deep red ensued. After stirring
for 30 min, methyl iodide (0.05 cm3, 0.80 mmol) was added,
causing an instantaneous change to yellow-orange. After stir-
ring for 17 h to ensure complete reaction, the solvent was
removed and the resulting oil dissolved in a little diethyl ether.
The yellow solution was decanted from a white precipitate (pre-
sumably the iodide salt of protonated dbu) to yield orange 3a
(270 mg, 87%) on removal of the solvent. M.p. 118 ЊC. A simi-
lar reaction in which EtBr (0.09 cm3, 0.12 mmol) was used as
Starting from 1b, the complexes 6c (82%, m.p. 148 ЊC) and 6d
(81%, m.p. 122 ЊC) were prepared in the same way.
[{Mo(CO)2(PPh2H)(ç-C5H5)}2] 7. A solution of [Mo2(CO)6-
(η-C5H5)2] (1.3 g, 3.06 mmol) in toluene (150 cm3) was heated to
reflux with an argon purge for 24 h to produce a solution of
[Mo2(CO)4(η-C5H5)2]. The solution was allowed to cool to
room temperature before dropwise addition of 2 equivalents of
PPh2H (1.10 cm3, 6.32 mmol). The solution was stirred for 2 h.
Column chromatography gave a weak orange band of [Mo2-
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J. Chem. Soc., Dalton Trans., 1997, Pages 3589–3598

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(µ-H)(µ-PPh2)(CO)4(η-C5H5)2],25 eluted with light petroleum–
CH2Cl2 (3:7) followed by a dark purple band of complex 7
(1.85 g, 75%), which was eluted with a 2:3 mixture of the same
solvents. M.p. 146 ЊC. Like 9a and 9b (see below) the complex
was found to have limited solubility.
γ = 86.41(4)Њ , U = 1055.5(9) Å3, Z = 2, Dc = 1.53 g cmϪ3, Mo-Kα
radiation (λ = 0.710 69 Å), µ(Mo-Kα) = 7.05 cmϪ1, F(000) =
495.87.
Three-dimensional, room-temperature X-ray data were col-
lected in the range 3.5 < 2θ < 50Њ on a Nicolet R3 diffract-
ometer by the ω-scan method. The 3271 independent reflections
(of 3762 measured) for which |F |/σ(|F |) > 3.0 were corrected for
Lorentz-polarisation effects, and for absorption by analysis
of eight azimuthal scans (minimum and maximum trans-
mission coefficients 0.733 and 0.820). The structure was solved
by Patterson and Fourier techniques and refined by blocked-
cascade least-squares methods. Hydrogen atoms were included
in calculated positions and refined in riding mode. Refinement
on F 2 converged at a final R = 0.0389 (RЈ = 0.0386, 262 par-
ameters, mean and maximum δ/σ 0.002, 0.007), with allowance
for the thermal anisotropy of all non-hydrogen atoms. Min-
[MoMe(CO)2(PPh2H)(ç-C5H5)] 8. A solution of the dimeric
complex [{Mo(CO)2(PPh2H)(η-C5H5)}2] (500 mg, 0.62 mmol)
in thf (40 cm3) was shaken with sodium amalgam (29 mg, 1.26
mmol of Na in 0.5 cm3 Hg) for 10 min causing the initially
purple solution to turn olive green. The solution was trans-
ferred to a separate Schlenk tube by syringe and treated with
MeI (0.08 cm3, 1.29 mmol). After stirring overnight the green
solution was evaporated to dryness, dissolved in the minimum
volume of CH2Cl2 and chromatographed. A single yellow band
was eluted with light petroleum–CH2Cl2 (9:1). Crystallisation
of the resulting yellow oil from light petroleum at Ϫ25 ЊC gave
240 mg (46%) of complex 8 as yellow crystals. M.p. 99 ЊC. Ratio
of cis:trans = 1.66:1.
imum and maximum final electron density –0.86 and 0.34 e ÅϪ3
.
A weighting scheme wϪ1 = σ2(F) ϩ 0.000 46F 2 was used in the
latter stages of refinement. Complex scattering factors were
taken from the program package SHELXTL26 as implemented
on the Data General DG30 computer.
Room-temperature deprotonation–alkylation of [MoMe-
(CO)2(PPh2H)(ç-C5H5)] 8. A solution of complex 8 (50 mg,
0.12 mmol) in thf (20 cm3) was treated with a small excess of
dbu (0.02 cm3, 0.13 mmol) at room temperature and stirred for
30 min, darkening slightly during this time. No colour change
was observed on the addition of EtI (0.02 cm3, 0.25 mmol).
After 1 h the solvent was removed and the resulting yellow oil
chromatographed. Elution with CH2Cl2 produced a yellow
band of the PPh2Et complex 10c.
CCDC reference number 186/665. Tables of structure factors
are available from the authors.
Acknowledgements
We thank the SERC for the award of a Research Studentship
(to P. B.) and the University of Sheffield for support.
[{Mo(CO)2(PPh2R1)(ç-C5H5)}2] (R1 = Me 9a or Et 9b). The
method used was the same as for complex 7. A solution of
[Mo2(CO)4(η-C5H5)2] was generated from [Mo2(CO)6(η-C5H5)2]
(3.0 g, 6.12 mmol) and treated at room temperature with
PPh2Me (2.30 cm3, 12.36 mmol) for 2 h. Column chrom-
atography, eluting with light petroleum–CH2Cl2 (1:1), gave a
broad red-purple band of 9a (3.41 g, 66%). M.p. 160 ЊC. It was
shown by NMR spectroscopy to exist as a mixture of trans and
cis isomers in a ratio of 5:1.
References
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A similar reaction with PPh2Et (2.60 cm3, 12.72 mmol)
afforded a purple powder of complex 9b (4.0 g, 76%) as a
mixture of trans and cis isomers (2:1). M.p. 174 ЊC. Both
compounds were only sparingly soluble in most solvents.
[MoR2(CO)2(PPh2R1)(ç-C5H5)] (R1 = R2 = Me 10a; R1 = Me,
R2 = Et 10b; R1 = Et, R2 = Me 10c; R1 = R2 = Et 10d). The
method used was the same as that for complex 8. A solution of
[{Mo(CO)2(PPh2Me)(η-C5H5)}2] (1.00 g, 1.19 mmol) in thf
(100 cm3) was shaken with an excess of sodium amalgam (0.45
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insoluble purple powder had dissolved to give a green solution
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molar equivalents of MeI (0.15 cm3, 2.41 mmol). After stirring
for 17 h the thf was removed under reduced pressure and the
residue chromatographed. Elution with diethyl ether led to 0.70
g (71%) of [MoMe(CO)2(PPh2Me)(η-C5H5)] 10a as a yellow-
orange powder. M.p. 138 ЊC. By the same method, reduction of
9a (1.00 g, 1.19 mmol) followed by alkylation with EtBr (0.18
cm3, 2.41 mmol) gave orange powdery [MoEt(CO)2(PPh2Me)-
(η-C5H5)] 10b (0.700 g, 65%). M.p. 82 ЊC.
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Starting from 9b, the compounds 10c (74%, m.p. 110 ЊC) and
10d (66%, m.p. 86 ЊC) were prepared in the same way.
Crystallography
Crystal data for [Mo(COMe)(CO)2(PPh2COMe)(ç-C5H5)]
6a. C23H21Mo2O4P M = 488.22, crystallises from toluene as
yellow oblongs, crystal dimensions 0.60 × 0.50 × 0.40 mm,
1
¯
triclinic, space group P1 (Ci , no. 2), a = 8.148(4), b =
11.628(7), c = 12.697(6) Å, α = 63.43(4), β = 78.91(4),
J. Chem. Soc., Dalton Trans., 1997, Pages 3589–3598
3597

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Received 6th June 1997; Paper 7/03948D
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J. Chem. Soc., Dalton Trans., 1997, Pages 3589–3598