Solvent-free organometallic migratory insertion reactions

Article abstract of DOI:10.1021/om0301738

Migratory insertion reactions of organometallic complexes have been shown to occur in the absence of solvent and, more significantly, between solid reagents. Reaction between (η⁵-C₅H₅)M(CO)₃Me (M = Mo, W) or (η⁵-C₅H₅)Fe(CO)₂ Me and PPh₃ (no solvent) took place at temperatures between 40 and 90°C and gave the products (η⁵-C₅H₅)M(CO)₂(PPh₃) COMe and (η⁵-C₅H₅)Fe(CO)(PPh₃)COMe in moderate to good yield (60-99%). The Mo and W complexes reacted in the solid state when T < 80°C. The decarbonylation of (η⁵-C₅H₅)- Mo(CO)₂(PPh₃)COMe to yield (η⁵-C₅H₅)Mo(CO)₂(PPh₃ )Me also occurred in the solid state (120°C). Reaction of (η⁵-C₅H₅)Mo(CO)₃Me with a range of ligands, L (L = PPh₃, P(p-MeOC₆H₄)₃, PCy₃, PEt₃, AsPh₃, POPh₃, P(OEt)₃; 1:1 reagent ratio, 90°C, 15 min), in the absence of solvent gave (η⁵-C₅H₅)Mo(CO)₂(L)COMe (7-100% yield) and, on extended reaction, (η⁵-C₅H₅)Mo(CO)₂(L)Me in varying yields. A kinetic study of the solid-state reaction between (η⁵-C₅H₅)Mo(CO)₃Me and PPh₃ yielded rate constants, e.g. κ = 5.18 × 10^-5 s^-1 (Mo:P = 1:10; 50°C), which compares with the literature solution data in toluene (κ = (0.8-2.5) × 10^-5 s^-1, 50°C) using similar metal to ligand ratios. The data are consistent with a pseudo-first-order reaction in the presence of PPh₃. Diffusional effects on the reaction rate are detected at low temperature and low PPh₃ ratios.

Full text of DOI:10.1021/om0301738

2284
Organometallics 2003, 22, 2284-2290
Solven t-F r ee Or ga n om eta llic Migr a tor y In ser tion
Rea ction s
Olalere G. Adeyemi and Neil J . Coville*
Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand,
J ohannesburg 2050, South Africa
Received March 10, 2003
Migratory insertion reactions of organometallic complexes have been shown to occur in
the absence of solvent and, more significantly, between solid reagents. Reaction between
(η5-C5H5)M(CO)3Me (M ) Mo, W) or (η5-C5H5)Fe(CO)2Me and PPh3 (no solvent) took place
at temperatures between 40 and 90 °C and gave the products (η5-C5H5)M(CO)2(PPh3)COMe
and (η5-C5H5)Fe(CO)(PPh3)COMe in moderate to good yield (60-99%). The Mo and W
complexes reacted in the solid state when T < 80 °C. The decarbonylation of (η5-C5H5)-
Mo(CO)2(PPh3)COMe to yield (η5-C5H5)Mo(CO)2(PPh3)Me also occurred in the solid state
(120 °C). Reaction of (η5-C5H5)Mo(CO)3Me with a range of ligands, L (L ) PPh3, P(p-
MeOC6H4)3, PCy3, PEt3, AsPh3, POPh3, P(OEt)3; 1:1 reagent ratio, 90 °C, 15 min), in the
absence of solvent gave (η5-C5H5)Mo(CO)2(L)COMe (7-100% yield) and, on extended reaction,
(η5-C5H5)Mo(CO)2(L)Me in varying yields. A kinetic study of the solid-state reaction between
(η5-C5H5)Mo(CO)3Me and PPh3 yielded rate constants, e.g. k ) 5.18 × 10-5 s-1 (Mo:P ) 1:10;
50 °C), which compares with the literature solution data in toluene (k ) (0.8-2.5) × 10-5
s-1, 50 °C) using similar metal to ligand ratios. The data are consistent with a pseudo-first-
order reaction in the presence of PPh3. Diffusional effects on the reaction rate are detected
at low temperature and low PPh3 ratios.
In tr od u ction
chemistry in the solid state, and the study interfaces
with investigations of surface organometallic chem-
istry7 and its relationship to catalysis.8 Further, recent
reports have indicated that the reaction of gases with
solid organometallic compounds can lead to gas up-
take (addition) reactions and that these studies may
lead to the use of organometallic complexes as gas
sensors.9
The reactions of (η5-C5H5)M(CO)3Me (M ) Mo, W) and
(η5-C5H5)Fe(CO)2Me with nucleophilic ligands, L, rep-
resent some of the earliest reactions reported in orga-
nometallic chemistry in the early 1950s.10 Initial studies
were dedicated to determining the mechanism of the
reaction between (η5-C5H5)M(CO)3Me (M ) Mo, W), (η5-
C5H5)Fe(CO)2Me, and other reactants with nucleophlilic
ligands, L.11 These reactions generated products of the
Environmental concerns in synthetic chemistry have
led to a reconsideration of reaction methodologies. This
has resulted in investigations into atom economy,1 the
use of supercritical CO2,2 ionic liquids,3 and other
procedures to reduce the disposal problems associated
with most chemical reactions. One obvious route to
reduce waste entails generation of chemicals from
reagents in the absence of solvents.4
While an obvious approach to chemical synthesis,
there are many problems associated with this ap-
proach, the chief of which is the role of diffusion/
interaction between reactants. Further, it is never clear
that the reactions in the solid state will generate the
same products as those found in the presence of sol-
vents.
Some years ago we discovered that organometallic
complexes, of the type CpML4, undergo cis-trans ligand
isomerization reactions in the solid state.5 Little is
known about reactivity patterns of organometallic com-
plexes in the solid state, and we have now com-
menced a systematic examination of this type of reac-
tion.6 Our emphasis is on synthetic organometallic
(7) (a) Basset, J . M.; Lefebvre, F.; Santini, C. Coord. Chem. Rev.
1998, 178/ 180, 1703. (b) Roberto, D.; D’Alfonso, G.; Ugo, R.; Vailati,
M. Organometallics 2001, 20, 4307.
(8) Gates, B. C. Chem. Rev. 1995, 95, 111.
(9) (a) Albrecht, M.; Gossage, R. A.; Lutz, M.; Spek, A. L.; van Koten,
G. Chem. Eur. J . 2000, 6, 1431. (b) Braga, D.; Cojazzi, G.; Emiliani,
D.; Maini, L.; Grepioni, F. Organometallics 2002, 21, 1315. (c) Burger,
P. Angew. Chem., Int. Ed. 2001, 40, 1917. (d) Kovalensky, A. Y.; Bagley,
K. A.; Coppens, P. J . Am. Chem. Soc. 2002, 124, 9241. (e) Tokitch, N.;
Arai, Y.; Sasamori, T.; Okazaki, R.; Nagase, S.; Uekusa, H.; Ohashi,
Y. J . Am. Chem. Soc. 1998, 120, 433.
(10) Piper, T. S.; Wilkinson, G. J . Inorg. Nucl. Chem. 1956, 3, 104.
(11) (a) Butler, I. S.; Basolo, F.; Pearson, R. G. Inorg. Chem. 1967,
6, 2074. (b) Cotton, J . D.; Crisp, G. T.; Daly, V. A. Inorg. Chim. Acta
1981, 47, 165. (c) Barnett, K. W.; Beach, D. L.; Gaydos, S. P.; Pollmann,
T. G. J . Organomet. Chem. 1974, 69, 121. (d) Barnett, K. W.; Treichel,
P. M. Inorg. Chem. 1967, 6, 294. (e) Wax, M. J .; Bergman, R. G. J .
Am. Chem. Soc. 1981, 103, 7028. (f) Craig, M. P.; Green, M. J . Chem.
Soc. A 1969, 157. (g) Churchill, M. R.; Fennessey, M. P. Inorg. Chem.
1968, 7, 953. (h) Cotton, J . D.; Kroes, M. M.; Markwell, R. D.; Miles,
E. A. J . Organomet. Chem. 1990, 388, 133. (i) Craig, P. J .; Green, M.
J . Chem. Soc. A 1968, 1978.
* To whom correspondence should be addressed: E-mail: ncoville@
aurum.chem.wits.ac.za. Fax: +27 11 717 6749. Tel: +27 11 717 6738.
(1) Trost, B. M. Acc. Chem. Res. 2002, 35, 386.
(2) Wells, S.; DiSimone, J . M. Angew. Chem., Int. Ed. 2001, 40, 519.
(3) Seddon, K. R. J . Chem. Technol. Biotechnol. 1997, 68, 351.
(4) (a) Tanaka, K.; Toda, F. Chem. Rev. 2000, 100, 1025. (b) Bradley,
D. Chem. Br. 2002, 42 (Sept).
(5) Cheng, L.; Coville, N. J . Organometallics 1996, 15, 867.
(6) (a) Coville, N. J .; Cheng, L. J . Organomet. Chem. 1998, 571, 149.
(b) Coville, N. J .; Levendis, D. C. Eur. J . Inorg. Chem. 2002, 3067.
Bogadi, R.; Levendis, D. C.; Coville, N. J . J . Am. Chem. Soc. 2002,
124, 1004.
10.1021/om0301738 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 04/26/2003

Solvent-Free Migratory Insertion Reactions
Organometallics, Vol. 22, No. 11, 2003 2285
dures.10 (η5-C5H5)Fe(CO)2Cl, prepared by a literature proce-
dure,10,16 was reacted with MeMgI to give (η5-C5H5)Fe(CO)2Me.
The complexes were characterized by IR and NMR spectros-
copy (Table 1).
Sch em e 1. Migr a tor y In ser tion a n d
Deca r bon yla tion Rea ction
IR spectra were recorded on a Bruker Vector FTIR spec-
trometer, typically in CH2Cl2 (KBr cells), and NMR spectra
on a Bruker AC 200 spectrometer (CDCl3). High-pressure
reactions were performed in a home-built autoclave (100 mL
capacity).
Solven t less R ea ct ion of (η5-C5H 5)Mo(CO)3Me a n d L
(L ) P P h 3, P (p -C6H 4OMe)3, P Cy3, P E t 3, AsP h 3, P OP h 3,
P (OEt)3). Reaction of a range of ligands, L, with (η5-C5H5)-
Mo(CO)3Me was performed in the absence of solvent. The lig-
and, L (L ) PPh3, P(p-MeOC6H4)3, PCy3, PEt3, AsPh3, POPh3,
P(OEt)3; 0.08 mM), and (η5-C5H5)Mo(CO)3Me (0.08 mM) were
dissolved in dry CH2Cl2 (5 mL). The solvent was then removed
in vacuo to give a bright yellow solid (or liquid). NMR spectra
revealed no conversion to the insertion product by this
procedure. About 14 mg of the mixture was loaded, under
nitrogen, into an NMR tube and placed in an oil bath (90 °C).
At this temperature the (η5-C5H5)Mo(CO)3Me is a liquid (mp
81 °C) and the reaction thus takes place in the liquid phase.
The mixture was allowed to react for 15 min, the tube removed
from the oil bath, CDCl3 added to the product, and the solution
analyzed by solution IR and 1H NMR spectroscopy. The results
are shown in Table 2. Reactions were performed in the
presence of ambient light and in the dark (foil-enclosed tubes),
and no difference in the degree of reaction was noted.
Solven tless Reaction of (η5-C5H5)Mo(CO)3Me an d P P h 3.
(η5-C5H5)Mo(CO)3Me (27.4 mg, 0.11 mM) and PPh3 (1× to 25×
excess; see Table 2) was completely dissolved in dry CH2Cl2
(3 mL). A bright yellow solid was collected after the removal
of the CH2Cl2 in vacuo. About 15 mg of the mixture was loaded,
under nitrogen, into an NMR tube and placed into an oil bath
at a preset temperature (40-70 °C). The reaction, which occurs
in the solid state, was then monitored with time. At the end
of a requisite time period, the NMR tube was removed from
the oil bath, CDCl3 was added to the tube, and the NMR
spectrum was recorded. At the end of a reaction (typically
100% conversion) the product was isolated and characterized
by IR as well as 1H and, in some instances, 31P NMR spec-
troscopy. Both (η5-C5H5)Mo(CO)2(PPh3)COMe and (η5-C5H5)-
Mo(CO)2 (PPh3)Me were detected, the relative amounts vary-
ing with the reaction conditions.
type (η5-C5H5)M(CO)2(L)COMe and (η5-C5H5)Fe(CO)(L)-
COMe (L ) wide range of two-electron-donor ligands).
A secondary reaction, decarbonylation of CO from the
acyl product, was sometimes observed. The reaction (for
the case of Mo and W) is summarized in Scheme 1.
Remarkably, no attempt appears to have been made
to systematically investigate the reaction sequence of
Scheme 1 in the absence of solvents. Only odd reports
of reactions performed in the absence of solvent,11f,12 e.g.
that of (η5-C5H5)Mo(CO)3Et with CO to give (η5-
C5H5)Mo(CO)3COEt and [(η5-C5H4Et)Mo(CO)3]2, have
appeared in the literature.12a A reported reaction on the
influence of Lewis acids (e.g. AlBr3) on the insertion
reaction of (η5-C5H5)M(CO)3Me to give (η5-C5H5)Mo-
[C(OAlBrBr2)Me](CO)2 (Br attached to CO also bonds
to Mo) has been attempted in the solid state. While a
related reaction between Mn(CO)5Me and AlBr3 in the
solid state was successful, extensive decomposition was
noted for the Mo complex.13
Herein we report on a solid-state investigation of the
migratory insertion reaction.14 In particular we report
on the CO insertion/methyl migration reaction of (η5-
C5H5)M(CO)3Me (M ) Mo, W) and (η5-C5H5)Fe(CO)2Me
with phosphines, phosphites, AsPh3, and CO in the
absence of solvents. While reactions in neat PPh3 (i.e.
in the molten state) are known,15 reactions with solid
PPh3 have not previously been described.
When the reaction was performed at T > 80 °C, the PPh3
and (η5-C5H5)Mo(CO)3Me both melted and a yellow liquid
formed that solidified rapidly at the reaction temperature (5
min) as product formed.
Solven tless Rea ction of (η5-C5H5)W(CO)3Me a n d P P h 3.
(η5-C5H5)W(CO)3Me (34.8 mg, 0.1 mM) and PPh3 (1:1 and 1:10
ratios) were completely dissolved in dry CH2Cl2 (3 mL). A
bright yellow solid was collected after the removal of the CH2-
Cl2 in vacuo. The procedure used to study the solid-state
reaction is the same as that described for the Mo reaction
above.
Exp er im en ta l Section
The starting materials (η5-C5H5)M(CO)3Me (M ) Mo, W)
were synthesized by minor variations of literature proce-
R ea ct ion of (η5-C5H 5)Mo(CO)3Me w it h CO. (η5-C5H5)-
Mo(CO)3Me (20 mg) was loaded into a sample vial and placed
in a steel autoclave. The autoclave was purged with argon,
after which a CO pressure of 10 bar was introduced. The
autoclave was then placed into an oil bath at 70 °C (and 80
°C) and the reaction allowed to proceed for 15 h. A brown solid
was collected at the end of the reaction and characterized as
(η5-C5H5)Mo(CO)3COMe (Table 1). A trace amount of decom-
position product was observed. This result is to be contrasted
with the high-pressure reactions in solution that gave mainly
Mo(CO)6.17
(12) (a) McCleverty, J . A.; Wilkinson, G. J . Chem. Soc. 1963, 4096.
(b) Closson, R. D.; Coffield, T. H.; Kozikowski, J . Int. Conf. Coord.
Chem., Chem. Soc. Spec. Pub. 1959, 13, 126. (c) Capron-Cotigny, G.;
Poilblanc, R. C. R. Acad. Sci. Paris, Ser. C 1966, 266, 285. (d) Barnett,
K. W.; Slocum, D. W. J . Organomet. Chem. 1972, 44, 1.
(13) (a) Butts, S. B.; Holt, E. M.; Strauss, S. H.; Alcock, N. W.;
Stimson, R. E.; Shriver, D. F. J . Am. Chem. Soc. 1979, 101, 5864. (b)
Butts, S. B.; Strauss, S. H.; Holt, E. M.; Stimson, R. E.; Alcock, N. W.;
Shriver, D. F. J . Am. Chem. Soc. 1980, 102, 5093.
(14) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry, 2nd
ed.; University Science Books: Mill Valley, CA, 1987; pp 355-375. (b)
Kuhlman, E. J .; Alexander, J . J . Coord. Chem. Rev. 1980, 33, 195. (c)
Wojcicki, A. Adv. Organomet. Chem. 1973, 11, 87. (d) Calderazzo, F.
Angew. Chem., Int. Ed. Engl. 1977, 16, 299.
(15) (a) Masters, C. Homogeneous Transition-Metal Catalysis; Chap-
man and Hall: London, 1981. (b) Chaudhari, R. V.; Bhattacharya, B.;
Bhanage, B. M. Catal. Today 1995, 24, 123.
(16) Komiya, S. Synthesis of Organometallic Compounds; Wiley:
New York, 1998; pp 177-178.
(17) King, R. B.; King, A. D.; Iqbal, M. Z.; Frazier, C. C. J . Am. Chem.
Soc. 1978, 100, 1687.

2286 Organometallics, Vol. 22, No. 11, 2003
Ta ble 1. Sp ectr oscop ic Da ta for th e Rea cta n ts a n d P r od u cts
Adeyemi and Coville
IRa
1H NMRb
complex
ν
CO/cm-1
ν
CO(acetyl)/cm-1 C5H5
Me
CH3CO
other
ref
(η5-C5H5)Mo(CO)3Me
2018 (s), 1927 (s)
2018 (s), 1927 (s)
2006 (s), 1945 (s)
1938 (s), 1852 (vs)
1930 (s), 1844 (vs)
1928 (s), 1835 (s)
1949 (s), 1876 (s)
1946 (s), 1862 (vs)
5.30
5.30
4.75
0.37 (s)
0.37 (s)
0.16 (s)
10
10
10
11c
(η5-C5H5)W(CO)3Me
(η5-C5H5)Fe(CO)2Me
(η5-C5H5)Mo(CO)2(PPh3)COMe
(η5-C5H5)Mo(CO)2(PEt3)COMe
(η5-C5H5)Mo(CO)2(PCy3)COMe
(η5-C5H5)Mo(CO)2[P(OPh)3]COMe
(η5-C5H5)Mo(CO)2(P(OEt)3)COMe
1597 (w)
1598 (m)
1600 (w)
1593 (s)
1609 (m)
1594 (m)
1580 (w)
1665 (s)
1600 (w)
1601 (s)
5.00
5.14
5.18
4.82
5.22
5.00
5.05
5.29
5.00c
4.74
4.75
2.61
2.56
2.58
2.36
2.56
2.61
2.65
2.17
2.61
2.32
7.43 (m)
1.13 (m), 1.84 (m) 12c
1.26-2.03 (m)
7.29 (m)
1.30 (t), 3.94 (q)
6.89-7.25 (m)
7.39 (m)
18
11i
11i
18
(η5-C5H5)Mo(CO)2 (P(p-MeOPh)3)COMe 1936 (s), 1841 (vs)
(η5-C5H5)Mo(CO)2(AsPh3)COMe
(η5-C5H5)Mo(CO)3COMe
1937 (s), 1851 (vs)
2006 (s), 1946 (s)
1938 (s), 1853 (vs)
1913 (vs)
1934 (s), 1896 (s),
1848 (vs)
(η5-C5H5)W(CO)2(PPh3)COMe
(η5-C5H5)Fe(CO)(PPh3)COMe
(η5-C5H5)Mo(CO)2(PPh3)Me
7.43 (m)
7.3-7.6 (m)
7.40 (m)
11c
13
11d
0.40 (d)
(η5-C5H5)Mo(CO)2[P(OPh)3]Me
(η5-C5H5)Fe(CO)2COMe
4.79d 0.30
4.55e 0.31
4.52
7.31-7.34 (m)
16
1994 (s), 1951 (s)
1770 (s)
-
2.02
11a
a
b
In CH2Cl2. In CDCl3, relative to TMS. Abbreviations: s ) singlet, d ) doublet, q ) quintet, m ) multiplet. c Occurs as doublet.
Cis isomer. e Trans isomer.
d
Ta ble 2. Exp er im en ta l Da ta for th e Rea ction betw een (η5-C5H5)M(CO)n Me a n d Liga n d (M ) F e, n ) 2; M )
Mo, W, n ) 3)
reactants
reaction conditions
major product
yielda,b
(η5-C5H5)Mo(CO)3Me + PPh3
solid-solid, 40 °C, 36 h
solid-solid, 50 °C, 5 h
solid-solid, 60 °C, 1 h
solid-solid, 70 °C, 30 min
solvent free, 80 °C, 30 min
solvent free, 80 °C, 2 h
solvent free, 90 °C, 15 min
solvent free, 90 °C, 15 min
solvent free, 90 °C, 2 min
solvent free, 90 °C, 15 min
solvent free, 90 °C, 15 min
solvent free, 90 °C, 15 min
solvent free, 90 °C, 15 min
solvent free, 80 °C, 15 h,
10 bar of CO
solid-solid, 40 °C, 48 h
solid-solid, 50 °C, 5 h
solid-solid, 60 °C, 1 h
solid-solid, 70 °C, 30 min
solid-solid, 70 °C, 1 h
solvent free, 80 °C, 1 h
solvent free, 80 °C, 15 h
solvent free, 80 °C, 24 h,
10 bar of CO
(η5-C5H5)Mo(CO)2PPh3COMe
99
92
92
98
99
83:7
90:10
25:25
100
80:5
80:5
80:10:10c
10:2
100
(η5-C5H5)Mo(CO)3Me + PCy3
(η5-C5H5)Mo(CO)3Me + PEt3
(η5-C5H5)Mo(CO)3Me + P(OEt)3
(η5-C5H5)Mo(CO)3Me + P(p-MeOPh)3
(η5-C5H5)Mo(CO)3Me + P(OPh)3
(η5-C5H5)Mo(CO)3Me + AsPh3
(η5-C5H5)Mo(CO)3Me + CO
(η5-C5H5)Mo(CO)2(PCy3)COMe
(η5-C5H5)Mo(CO)2(PEt3)COMe
(η5-C5H5)Mo(CO)2P(OEt)3COMe
(η5-C5H5)Mo(CO)2[P(p-MeOPh)3]COMe
(η5-C5H5)Mo(CO)2(P(OPh)3)COMe
η5-C5H5)Mo(CO)2(AsPh3)COMe
(η5-C5H5)Mo(CO)3COMe
(η5-C5H5)W(CO)3Me + PPh3
(η5-C5H5)W(CO)2(PPh3)COMe
60
72
75
78
100
30
80
d
(η5-C5H5)W(CO)3Me + PPh3 (1:10)
(η5-C5H5)Fe(CO)2Me + PPh3
(η5-C5H5)Fe(CO)2Me + PPh3
(η5-C5H5)Fe(CO)2Me + CO
(η5-C5H5)Fe(CO)(PPh3)COMe
(η5-C5H5)Fe(CO)2COMe
(η5-C5H5)Fe(CO)2COMe
(η5-C5H5)Fe(CO)2Me + CO
solid-gas, 40 °C, 24 h, 5 bar
tracee
As determined from 1H NMR spectra. Ratio of acetyl and decarbonylation products. c Cis and trans isomers were both observed
a
b
(10%), see text. Sublimed product collected in the autoclave. e As determined by IR spectroscopy.
d
Rea ction of (η5-C5H5)F e(CO)2Me w ith CO. The proce-
dure used is the same as that described for (η5-C5H5)Mo-
(CO)3Me above. The mixture was allowed to react for 24 h
(80 °C, 10 bar of CO). A product was collected from the lid
of the autoclave. TLC and IR and 1H NMR spectral analy-
ses confirmed the formation of (η5-C5H5)Fe(CO)2COMe (Table
1). Under milder conditions (40 or 50 °C; 5 bar of CO, 24 h)
only trace amounts of the product was detected by IR spec-
troscopy.
Solven tless Reaction between (η5-C5H5)Fe(CO)2Me an d
P P h 3. The reaction was performed as for the Mo complexes
(80 °C) above to yield an orange-yellow product that was
characterized as (η5-C5H5)Fe(CO)(PPh3)COMe (1 h, 30% yield;
15 h, 80% yield; Table 1).
tive yield) was recrystallized from 1:10 CH2Cl2-hexane.
(η5-C5H5)Mo(CO)2(PPh3)COMe (100 mg, 0.19 mmol) was loaded
into a flask and heated at 120 °C for 14 h to give 75%
conversion to the decarbonylated product. The reaction was
terminated and the product isolated by column chromatogra-
phy (silica gel; 1:10 CH2Cl2-hexane). At 80 °C, <5% conversion
was noted, even after 16 h. A reaction was also performed
using a 0.25:1 mixture of (η5-C5H5)Mo(CO)2(PPh3)COMe and
(η5-C5H5)Mo(CO)3Me (90 °C, 2 h) to give (η5-C5H5)Mo(CO)2-
(PPh3)Me (5% yield; reaction products characterized by IR and
NMR spectroscopy).
Resu lts a n d Discu ssion
Rea ction betw een (η5-C5H5)M(CO)3Me a n d L (L
) P P h 3, P (p-C6H4OMe)3, P Cy3, P Et3, AsP h 3, P OP h 3,
P (OEt)3). Initially, reactions using 1:1 reactant ratios
were performed at 90 °C (i) to evaluate the generality
Decar bon ylation Reaction s of (η5-C5H5)Mo(CO)2(P P h 3)-
COMe. (η5-C5H5)Mo(CO)3Me (0.274 g; 1.1 mmol) and PPh3
(0.264 g, 1.0 mmol) were reacted at 90 °C for 30 min, and the
product (η5-C5H5)Mo(CO)2(PPh3)COMe (obtained in quantita-

Solvent-Free Migratory Insertion Reactions
Organometallics, Vol. 22, No. 11, 2003 2287
F igu r e 1. Plot of conversion against time for the reaction of (η5-C5H5)Mo(CO)3Me with PPh3 at different Mo:P ratios
(40 °C).
of the reaction and (ii) to limit the extent of the re-
action. At this temperature reaction is expected to occur
in the liquid/molten phase, as many of the ligands are
liquids at T > 90 °C and the starting material is a liquid
at this temperature (mp 81 °C). The data reveal conver-
sion of (η5-C5H5)Mo(CO)3Me to (η5-C5H5)Mo(CO)2(L)-
COMe with the conversion dependent on L (Table 2).
Only the trans isomer appears to have been formed.11g
The crude rate data (total conversion after 15 min)
reveals that the reaction rate decreases in the order
PEt3 > P(OPh)3 > PPh3 ≈ P(p-C6H4OMe)3 ≈ P(OEt)3)
> PCy3 > AsPh3, in keeping with results obtained from
solution studies.
Products derived from the decarbonylation reaction
were generally observed in the reaction product
F igu r e 2. Reaction mechanism for the interaction of (η5-
(2-20%). They are formed in secondary reactions. Thus,
C5H5)Mo(CO)3Me with PPh3 (based on ref 11a).
reaction with AsPh3 after 15 min gave 10% (η5-C5H5)-
Mo(CO)2(AsPh3)COMe and 2% (η5-C5H5)Mo(CO)2(AsPh3)-
36 h), indicating that no equilibrium is set up between
the reactants and products.
Me, while after 30 min about 12% of both products were
observed. However, the reaction is not a straightforward
The rate of reaction as a function of PPh3 molar ratio
(40 °C) is shown in Figure 1. The reaction rate is clearly
dependent on [PPh3].
one, as noted for the reactions with PPh3 (see below).
As yet, no information is available on the stereochem-
istry of the reaction, although in general only the trans
decarbonylated products are observed. Even in the case
where cis and trans isomers are observed (for (η5-C5H5)-
Mo(CO)2(P(OPh)3)Me) the isomer ratio (1:1) generated
could relate to isomerization during the NMR charac-
terization procedure, since the ratio is the same as that
reported in solution.18
Reaction between (η5-C5H5)Mo(CO)3Me an d P P h 3.
At T < 70 °C the reaction with PPh3 was found to occur
in the solid state (PPh3 melts at ca. 80 °C). This reaction
thus provides a facile system to investigate a solid-state
organometallic migratory insertion reaction. To limit
diffusional factors, thorough mixing of the reactants was
achieved prior to reaction. Kinetic data were generated
(i) by varying the molar reactant ratios (0.1:(0.1-2.5))
and (ii) by varying the reaction temperature (40-70 °C).
The reaction was found to go to completion at 40 °C (ca.
The mechanism of the migratory insertion reaction
for the reaction in solution has been well studied,11 and
a comprehensive mechanism to explain most of the
experimental data accumulated to date is shown in
Figure 2. It will be noted that the proposed general
mechanism allows for the formation of an intermediate,
(η5-C5H5)Mo(CO)2(sol)COMe (sol ) solvent molecule),
prior to addition of a ligand.11a The reaction has been
found to depend on both L and the solvent (tetrahydro-
furan, substituted tetrahydrofurans, toluene etc.11a,e).
Depending on the values of the rate constants, both
first-order and second-order kinetics have been mea-
sured. For example, reaction with PPh3 (in toluene)
gives the rate equation11a
(18) Faller, J . W.; Anderson, A. S. J . Am. Chem. Soc. 1970, 92, 5852.

2288 Organometallics, Vol. 22, No. 11, 2003
d[(η5-C5H5)Mo(CO)3Me]/dt )
Adeyemi and Coville
(k1 + k5[PPh3])[(η5-C5H5)Mo(CO)3Me]
and kobs ) k1 + k5[L] with k1 ) 0.
If [(η5-C5H5)Mo(CO)3Me] is kept constant, then
d[(η5-C5H5)Mo(CO)3Me]/dt ) k′[PPh3]
An attempt was made to evaluate the solid-state kinetic
data assuming first-order kinetics. A typical plot is
shown in Figure 3 (1:10 ratio, correlation factor 0.998).
Similar plots were observed at the other Mo to P ratios
(even the 1:1 ratio!), and k values are given in Table 3.
Attempts to fit the data to other reaction orders were
not successful.
The reaction was also carried out at different tem-
peratures, at both the 1:1 and 1:10 ratios. Data for the
reaction at a 1:10 ratio is shown in Figure 4, and the k
values are listed in Table 3. The study in the solid state
yielded rate constants, e.g. k′ ) 5.18 × 10-5 s-1 (Mo:P
) 1:10; 50 °C), which can be compared with the
literature data in toluene (k ) 0.8-2.5 × 10-5 s-1, 50
°C)11a under similar reaction conditions. (Note: the
amount of ligand used has different units in the solid
and solution states.)
F igu r e 3. First-order plot of the reaction between
(η5-C5H5)Mo(CO)3Me with PPh3 (1:10 ratio, 40 °C).
The evaluation of solid-state rate data is fraught with
difficulties,19 and in this reaction diffusional issues are
expected to dominate the rates of reactions. This is
revealed by the attempts to extract activation energy
data from the Arrhenius plots (Figure 5). Curvature can
be seen suggesting two activation energies, one energy
relating to diffusion and the other to the chemical
reaction. At the higher PPh3 ratio the curvature de-
creases (especially in the low-temperature regime).
Clearly as either the Mo:P ratio or the tempera-
ture increases, diffusional constraints will be re-
stricted, as observed in Figure 5. Attempts to extract
activation energies (Ea) from the data give limiting
values: Ea(reaction) < 75 kJ mol-1 and Ea(diffusion) >
F igu r e 4. Plot of conversion against time for the reaction
of (η5-C5H5)Mo(CO)3Me with PPh3 at different tempera-
tures (1:10 reactant ratio).
120 kJ mol-1
.
Con ver sion of (η5-C5H5)Mo(CO)2(P P h 3)COMe to
(η5-C5H5)Mo(CO)2(P P h 3)Me. A competing reaction in
the solution state that occurs after migratory insertion
is the CO decarbonylation reaction. In the solid state
this reaction also occurs after the insertion migration
reaction. The decarbonylation of purified (i.e. crystal-
lized) (η5-C5H5)Mo(CO)2(PPh3)COMe in the solid state
was monitored by carrying out the reaction in NMR
tubes. Surprisingly, no product is formed when the
reaction is carried out at 80 °C. This finding is at
variance with the formation of insertion product (≈10%)
during the ligand migratory insertion reaction, at 90 °C,
described above. Further, the reaction in solution (ac-
etonitrile) is also reported to be rapid.20One possibility
is that the decarbonylation actually occurs in the
molten/liquid phase at 90 °C.
Ta ble 3. Ra te Con sta n t Da ta for th e Rea ction s of
(η5-C5H5)M(CO)3Me w ith P P h 3
M
temp/°C
40
concn/mM
k/s-1
Mo
0.10:0.10
0.10:0.25
0.10:0.50
0.10:1.00
0.10:2.50
0.10:0.10
0.10:0.10
0.10:0.10
0.10:1.00
0.10:1.00
0.10:1.00
0.10:0.10
1.81 × 105
2.49 × 105
3.89 × 105
5.18 × 105
9.28 × 105
2.60 × 104
1.30 × 103
2.14 × 103
5.18 × 104
1.52 × 103
2.61 × 103
1.11 × 103
50
60
70
50
60
70
60
W
reacted at 90 °C, a temperature at which (η5-C5H5)-
Mo(CO)3Me has melted. In this instance the reaction
did generate (η5-C5H5)Mo(CO)2(PPh3)Me (5%, 30 min),
consistent with the proposal.
To test this possibility, a 0.25:1 mixture of (η5-C5H5)-
Mo(CO)2(PPh3)COMe and (η5-C5H5)Mo(CO)3Me was
(19) (a) Galwey, A. K.; Brown, M. E. Thermochim. Acta 2002, 386,
91. (b) Bezjak, A.; Kurajica, S.; Sipusic, J . Thermochim. Acta 2002,
386, 81.
(20) (a) Barnett, K. W.; Pollmann, T. G.; Solomon, T. W. J .
Organomet. Chem. 1972, 36, C23. (b) Barnett, K. W. Inorg. Chem. 1969,
8, 2009.
At higher temperatures (120 °C) a solid-state decar-
bonylation reaction does occur and (η5-C5H5)M(CO)2-
(PPh3)Me is formed (45%, 4 h; 75%, 14 h). This is
expected to be a first-order reaction.

Solvent-Free Migratory Insertion Reactions
Organometallics, Vol. 22, No. 11, 2003 2289
F igu r e 6. Comparison of reaction rates for (η5-C5H5)-
M(CO)3Me (M ) Mo, W) with PPh3 (1:1 ratio; 60 °C).
F igu r e 5. Arrhenius plot for the reaction of (η5-C5H5)-
Mo(CO)3Me with PPh3 (1:10 and 1:1 reactant ratios).
conditions (Table 2). Earlier reports suggest that this
is a difficult reaction to induce in a solvent.17
This large temperature difference between the solid
state and solution reactions suggests strong solvent
effects on the decarbonylation reaction, a result not
apparent from earlier studies.20
(b) Rea ction betw een (η5-C5H5)F e(CO)2Me a n d L
(L ) P P h 3, CO). Reactions between (η5-C5H5)Fe(CO)2-
Me and L in the solution state have been investigated
by numerous workers over the years.13,17 The solid-state
reaction between (η5-C5H5)Fe(CO)2Me and PPh3 occurs
more slowly than that between (η5-C5H5)Mo(CO)3Me
and PPh3 (80 °C; 80%, 15 h versus 99%, 30 min; Table
2), in line with solution data. The reaction between CO
and (η5-C5H5)Fe(CO)2Me, in an autoclave, was also
attempted.17 As the reactant is a waxy solid, it is
assumed that the reaction takes place in the molten
state in the autoclave. The reaction was performed at
temperatures between 40 and 80 °C (24 h, 5-10 bar of
CO). While the reaction occurred to give (η5-C5H5)-
Fe(CO)2COMe, difficulty was experienced in evaluating
the reaction conversion because of product/reactant
sublimation. The reaction has not been pursued further
at this time.
Rea ction betw een (η5-C5H5)W(CO)3Me a n d P P h 3.
This reaction occurred at 40 °C to give the required
product, (η5-C5H5)W(CO)2(PPh3)COMe, in good yield (1:1
reactant ratio; 60%; 48 h). The reported reaction in
solution gives poor conversions over extended time
periods (refluxing acetonitrile, 48 h). Reactions (1:1
ratio) were also carried out at higher temperatures
(Table 2), and the data reveal that the reaction does not
go to completion (ca. 72-78% yield). No (η5-C5H5)-
W(CO)2 (PPh3)Me was formed under the reaction condi-
tions. Not unexpectedly, reaction with a mixture of
(η5-C5H5)W(CO)3Me and PPh3 in a 1:10 ratio (70 °C, 1
h) gave 100% conversion, and under these conditions a
small amount (5%) of (η5-C5H5)W(CO)2(PPh3)Me was
also formed.
A comparison of rate data between Mo and W com-
plexes (1:10 ratio with PPh3) at 60 °C is shown in Figure
6. The Mo complex reacts faster than the W complex at
all temperatures studied, and although consistent with
solution studies,11c the rates in the solid state are more
similar than the rates obtained from solution studies.
The remarkably low reaction temperatures required
to achieve the substitution reactions at W in the solid
state suggests that solvent effects must be responsible
for the poor reactions reported in the solution phase.
The solid-state data are in keeping with reaction rates
that are related to the Mo-C and W-C bond strengths
in the complexes.21 Could this methodology provide a
general approach to overcoming the sluggish behavior
of third-row transition metals?
Oth er Exa m p les. The generality of the reaction type
has briefly been explored, and the preliminary results
indicate that the reaction is quite general.
(a ) Rea ction betw een (η5-C5H5)Mo(CO)3Me a n d
CO. This reaction took place in an autoclave at 70 and
80 °C (15 h, 10 bar of CO), and (η5-C5H5)Mo(CO)3COMe
was produced in quantitative yield under mild thermal
Rea ction Mech a n ism . As mentioned above, the
extraction of thermodynamic and mechanistic informa-
tion from kinetic data obtained in solid-state reactions
is nontrivial.19 The migratory insertion has similarities
to inorganic addition reactions of the type A + B f C,
and analyses of a variant of this reaction type (spinel
formation) has revealed the importance of diffusion in
these reactions.22
Reaction is initiated when reactants are in contact
with each other. In the ideal situation reactants A and
B (in our case A ) PPh3 and B ) (η5-C5H5)Mo(CO)3-
Me)), would be precipitated in pairs, viz. ABABABAB...
More likely, however, the precipitation will yield do-
mains of A and B, viz. AAABBABBBBBAAAA... Reac-
tion between A and B molecules in close proximity will
be determined by the migratory insertion chemical
reaction. However, as the reaction proceeds, product
formation creates a barrier to further reaction, leading
to a decrease in reaction rate, viz. AAABBABBBB-
(22) (a) Brown, W. E.; Dollimore, D.; Galwey, A. K. In Comprehensive
Chemical Kinetics; Bamford, C. H., Tipper, C. F. H., Eds.; Elsevier:
Amsterdam, 1980; Vol. 22, Chapter 5. (b) Tolkatchev, V. A. Reactivity
of Molecular Solids; Boldyreva, E., Boldyrev, V., Eds.; Wiley: Chich-
ester, U.K., 1999; Chapter 5.
(21) Mancuso, C.; Halpern, J . J . Organomet. Chem. 1992, 428, C8.

2290 Organometallics, Vol. 22, No. 11, 2003
Adeyemi and Coville
BAAAA... f AA(AB)(BA)BBBB(BA)AAA..., where (AB)
) (BA) ) (η5-C5H5)M(CO)2(PPh3)COMe.
Only if A and/or B are mobile will further reaction
occur. The kinetic analysis must thus describe both the
chemical reaction and diffusional components of the
reaction.
In the migratory insertion reaction, premixing of
reactants is expected to lead to a reasonably good
contact between reagents. Our studies to date have
entailed reaction with amorphous materials, and par-
ticle size effects are not expected to be a dominant effect
in the reaction. However, the premixing is not expected
to remove domain effects. Since grinding of reactants
leads to reaction, reactions carried out by merely mixing
reagents have given limited data and thus to date we
have not been able to separate out the diffusional effects
from the chemical reaction.
In the studies reported above, the products are the
same as those found in solution studies. The rates of
reaction are similar in the solid and solution phases,
and this would suggest that the mechanisms (involving
reactant interaction) are similar in the different phases.
Single-crystal studies on some of the above reactions
may provide further detail to generate more precise
stereochemical information, especially on the decarbo-
nylation reactions.
Reaction between a solid and a liquid ligand is more
facile than between two solids, and indeed the reaction
between (η5-C5H5)Mo(CO)3Me and PPh3 (70-90 °C;
PPh3 is a solid at the lower temperature and a liquid
at the higher temperature) shows this. It is possible that
the reaction at the lower temperatures actually occurs
at the microscopic level in a “liquid” phase, but this
possibility needs further study.
It is not clear at this stage whether the Mo complex
and/or the ligand are mobile. Both are bulky, and both
have similar melting points. The reaction also requires
the correct orientation of the reagents. Since reaction
with the 1:1 mixture of PPh3 and (η5-C5H5)Mo(CO)3Me
occurs at 40 °C, it is apparent that the diffusional and
orientational barriers for the reaction cannot be large.
When the two solid reagents are in close proximity
to each other, reaction can occur. The actual manner in
which this interaction occurs is still not known and will
require further study. The reactions between (η5-
C5H5)Mo(CO)3Me or (η5-C5H5)Fe(CO)2Me and CO most
certainly also occur in the solid phase. Modification of
the ligands attached to the metals will provide for a
variation of channel widths in the solid and, conse-
quently, on the ability to control CO diffusion to the
metal center. Experiments to evaluate this possibility
are in progress.
Con clu sion
This study reveals that migratory insertion of orga-
nometallic compounds can occur between a solid orga-
nometallic complex and a ligand that exists in the solid,
liquid, or gas phase without the intervention of a solvent.
Well-known examples have been chosen to highlight this
reaction type and, where possible, to compare data with
equivalent solution state studies.
Ack n ow led gm en t. We wish to thank the NRF
(Project #2053379), THRIP, and the University of the
Witwatersrand for financial support.
OM0301738