The reactivity of a bis(μ-diphenylphosphido) dicyclopentadienyl dimolybdenum complex with an electron withdrawing ring substituent

Article abstract of DOI:10.1016/S0020-1693(97)05490-X

The synthesis of [(η⁵-C₅H₄CO₂Me) ₂Mo₂(CO)₆] (1), a bis(cyclopentadienyl) dimolybdenum complex with an electron withdrawing ring substituent, from the reaction of Mo(CO)₆ and [Na(C₅H₄CO₂Me)] is described. Complex 1 reacts thermally with P₂Ph₄ to form the bis(μ-diphenylphosphido) complex [(η⁵-C₅H₄CO₂Me) ₂Mo₂(μ-PPh₂)₂(CO)₂] (2). Air oxidation of 2 gives trans-[(η⁵-C₅H₄CO₂Me) ₂Mo₂(μ-PPh₂)₂(O)(CO)] (3a) and the corresponding cis-isomer 3b. The reactions of 3a and of the corresponding unsubstituted cyclopentadienyl complex [(η⁵-C₅H₅)₂Mo ₂(μ-PPh₂)₂(O)(CO)] (4) with [NO][BF₄], which yield respectively the nitrosyl substituted dimolybdenum complexes [(η⁵-C₅H₄CO₂Me) ₂Mo₂(μ-PPh₂)₂(O)(NO)][BF ₄] (5) and [(η⁵-C₅H₅)₂Mo ₂(μ-PPh₂)₂(O)(NO)][BF₄] (6), are described. Single crystal X-ray diffraction was used to determine the molecular structures of 1 (which crystallises in the monoclinic space group P2₁/c with a=9.811 (4), b=12.109 (2), c=9.919 (3) A, β=110.00 (3)° and Z=2), 2 (which crystallises in the triclinic space group P1, a=13.364 (4), b=14.535 (4), c=10.576 (2) A, α=91.33 (2), β=94.94 (2) γ=108.92 (2)° and Z=2) and 3a (which crystallises in the monoclinic space group P2₁/c with a=12.436 (2), b=15.300 (3), c=20.395 (4) A, β=111.59 (3)° and Z=4).

Full text of DOI:10.1016/S0020-1693(97)05490-X

Inorganica Chimica Acta 262 (1997) 9–20
The reactivity of a bis(m-diphenylphosphido) dicyclopentadienyl
dimolybdenum complex with an electron withdrawing ring substituent
Joanne C. Stichbury, Martin J. Mays U, John E. Davies, Paul R. Raithby, Gregory P. Shields,
Amanda G. Finch
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB3 1EW, UK
Received 17 September 1996; revised 23 October 1996; accepted 4 December 1996
Abstract
The synthesis of [(h5-C5H4CO2Me)2Mo2(CO)6] (1), a bis(cyclopentadienyl) dimolybdenum complex with an electron withdrawing
ring substituent, from the reaction of Mo(CO)6 and [Na(C5H4CO2Me)] is described. Complex 1 reacts thermally with P2Ph4 to form the
bis(m-diphenylphosphido) complex [(h5-C5H4CO2Me)2Mo2(m-PPh2)2(CO)2] (2). Air oxidation of 2 gives trans-[(h5-C5H4CO2Me)2-
Mo2(m-PPh2)2(O)(CO)] (3a) and the corresponding cis-isomer 3b. The reactions of 3a and of the corresponding unsubstituted cyclopen-
tadienyl complex [(h5-C5H5)2Mo2(m-PPh2)2(O)(CO)] (4) with [NO][BF4], which yield respectively the nitrosyl substituted dimolyb-
denum complexes [(h5-C5H4CO2Me)2Mo2(m-PPh2)2(O)(NO)][BF4] (5) and [(h5-C5H5)2Mo2(m-PPh2)2(O)(NO)][BF4] (6), are
described. Single crystal X-ray diffraction was used to determine the molecular structures of 1 (which crystallises in the monoclinic space
˚
group P21/c with as9.811 (4), bs12.109 (2), cs9.919 (3) A, bs110.00 (3)8 and Zs2), 2 (which crystallises in the triclinic space
#
˚
group P1, as13.364 (4), bs14.535 (4), cs10.576 (2) A, as91.33 (2), bs94.94 (2) gs108.92 (2)8 and Zs2) and 3a (which
˚
crystallises in the monoclinic space group P21/c with as12.436 (2), bs15.300 (3), cs20.395 (4) A, bs111.59 (3)8 and Zs4).
Keywords: Crystal structures; Molybdenum complexes; Oxo complexes; Nitrosyl complexes; Dinuclear complexes
1. Introduction
In the light of this result it was of interest to determine
whether or not the introduction of electron withdrawing sub-
stituent groups onto the cyclopentadienyl rings in the bis(m-
diphenylphosphido) complexes [(h5-C5H5)2Mo2(m-PPh2)2-
(CO)2] might similarly facilitate oxidation of the complexes
and perhaps lead to species in which both carbonyl groups
have been substituted by oxo ligands. To this end we have
now studied the reactivity of the complex [(h5-C5H4CO2-
Me)2Mo2(m-PPh2)2(CO)2] (2). The complex [(h5-C5H4-
CO2Me)2Mo2(CO)6] (1), required as a precursor to com-
pound 2, has not previously been reported and although
the analogous species [(h5-C5H4CO2Me)2M2(CO)6](Ms
Cr, W) [3,4] are known, their reactivity has not been
investigated.
We have previously reported that air oxidation of the
bis(m-diphenylphosphido) dicyclopentadienyl dimolyb-
denum complex [(h5-C5H5)2Mo2(m-PPh2)2(CO)2] leads
to replacement of onecarbonylligandbyaterminaloxogroup
to give a mixture of cis- and trans-[(h5-C5H5)2Mo2(m-
PPh2)2(CO)(O)] [1]. It was not possible by this means to
replace the remaining carbonyl group by a second oxo ligand.
More recently we have shown that air oxidation of the alkyne
bridged complexes [(h5-C5H5)2Mo2(CO)4(m-RCCR9)]
(RsR9sCO2Me or Ph; RsH, R9sPh and RsH,
R9sCO2Me) in the presence of trimethylamine N-oxide
leads to the new high oxidation state organometallic oxo
complexes [(h5-C5H5)2Mo2(O)2(m-O)(m-RCCR9)] in
which all the carbonyl ligands have been replaced by oxo
groups [2]. These latter reactions are facilitated when the
substituents on the bridging alkyne ligand are electron with-
drawing in character, the highest yield of product being
obtained when RsR9sCO2Me.
2. Results and discussion
2.1. Synthesis and X-ray characterisation of
[(h5-C5H4CO2Me)2Mo2(CO)6] (1)
The substituted sodium cyclopentadienide [Na(C5H4-
CO2Me)] was prepared according to the method of Rausch
and co-workers [5] and complex [CpU 2Mo2(CO)6]
U Corresponding author: Tel.: q44 1223-336 324; fax: q44 1223-336
362.
0020-1693/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved
PII S0020-1693(97)05490-X

10
J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
eters listed in Table 2. The structure is similar to that of the
unsubstituted analogue [1] with an anti disposition of the
CpU ligands, the molecule lying on a crystallographic inver-
˚
sion centre. The Mo–Mo bond length (3.2135(12) A) in 1
shows a slight shortening relative to the metal–metaldistance
in the unsubstituted cyclopentadienyl complex (3.235(1)
˚
A). Complex 1 is crystallographically isomorphous with the
published tungsten analogue [4b], for which one metal–
˚
metal bond length was reported as 3.216(1) A.
2.2. Synthesis and X-ray characterisation of
[(h5-C5H4CO2Me)2Mo2(m-PPh2)2(CO)2] (2)
The reaction of equimolar quantities of 1 and P2Ph4 in
refluxing toluene, according to the procedure used for the
analogous unsubstituted complex [1], gave on cooling a high
yield of a greenish brown crystallinesolid(Scheme 2).Spec-
troscopic characterisation of this complex, described in detail
in Section 3, was consistent with the formulation [(h5-
C5H4CO2Me)2Mo2(m-PPh2)2(CO)2] (2); this was subse-
quently confirmed by X-ray analysis. Unlike the un-
substituted analogue which showed appreciable solubility
only in dichloromethane, complex 2 is moderately soluble in
most organic solvents. The electron withdrawing nature of
the ring substituent is revealed by the IR spectrum of 2 in
which a carbonyl absorption at 1875 cmy1 is observed, as
compared to the reported value of 1855 cmy1 for the unsub-
stituted complex [(h5-Cp)2Mo2(m-PPh2)2(CO)2].
Fig. 2 shows the molecular structure of 2 which consists
of two crystallographically independent centrosymmetric
molecules. The two molecules are shown in the same orien-
tation to demonstrate that they are essentially the same, the
sole difference between them being the configuration of the
carbomethoxy cyclopentadienyl ring substituents. Selected
bond lengths and angles are listed in Table 3, final fractional
Scheme 1. Reagents and conditions: (i) CO3(CH3)2 (1.5 equiv.), THF,
678C, 6 h; (ii) Mo(CO)6 (1 equiv.), THF, 678C, 12 h; (iii) Fe(III),
CH3COOH, H2O.
(CpUs(h5-C5H4CO2Me)) (1) then synthesised by oxida-
tion of the sodium salt Na[CpUMo(CO)3] (Scheme 1) [6].
The IR spectrum of 1 in chloroform shows carbonyl absorp-
tions at 2021, 1970 and 1924 cmy1, with an additional
absorption at 1724 cmy1 due to the substituent group on the
cyclopentadienyl ring. In comparison, the carbonyl absorp-
tions of the unsubstituted cyclopentadienyl complex
[Cp2Mo2(CO)6] (Cps(h5-C5H5)) are at significantly
lower wavenumbers (1959, 1916, 1905 cmy1) [6] clearly
demonstrating the electron withdrawing properties of the
cyclopentadienyl ring substituent. The1Hand13CNMRspec-
tra, FAB mass spectrum and microanalysis of 1 are in accord
with the proposed formulation of the complex and are
described in Section 3.
The molecular structure of 1 is shown in Fig. 1 with
selected bond lengths and angles listed in Table 1 and final
fractional atomic coordinates and equivalent thermal param-
Fig. 1. ORTEP plot of the molecular structure of [(h5-C5H4CO2Me)2Mo2(CO)6] (1) with thermal ellipsoids at 40% probability level. The atom numbering
scheme used in Table 1 is defined.

J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
11
Table 1
5
˚
Selected bond lengths (A) and angles (8) for [(h -C5H4CO2Me)2Mo2(CO)6] (1)
Mo(1)–Mo(1A)
Mo(1)–C(8)
Mo(1)–C(9)
Mo(1)–C(10)
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1)–C(3)
Mo(1)–C(4)
Mo(1)–C(5)
C(1)–C(2)
3.2135(12)
1.972(6)
1.988(5)
1.989(6)
2.366(5)
2.401(5)
2.368(5)
2.321(6)
2.301(5)
1.417(7)
1.409(8)
C(3)–C(4)
C(4)–C(5)
C(1)–C(5)
C(8)–O(8)
C(9)–O(9)
C(10)–O(10)
C(5)–C(6)
C(6)–O(1)
C(6)–O(2)
C(7)–O(2)
1.418(8)
1.435(7)
1.417(7)
1.141(7)
1.149(6)
1.150(7)
1.488(7)
1.200(7)
1.335(7)
1.455(7)
C(2)–C(3)
C(8)–Mo(1)–Mo(1A)
C(9)–Mo(1)–Mo(1A)
C(10)–Mo(1)–Mo(1A)
C(1)–Mo(1)–Mo(1A)
C(2)–Mo(1)–Mo(1A)
C(3)–Mo(1)–Mo(1A)
C(4)–Mo(1)–Mo(1A)
C(5)–Mo(1)–Mo(1A)
C(1)–C(5)–C(6)
C(4)–C(5)–C(6)
C(5)–C(6)–O(1)
C(5)–C(6)–O(2)
C(6)–O(2)–C(7)
C(6)–C(5)–Mo(1)
C(5)–C(1)–Mo(1)
C(2)–C(1)–Mo(1)
C(3)–C(2)–Mo(1)
C(4)–C(3)–Mo(1)
C(4)–C(5)–Mo(1)
C(8)–Mo(1)–C(9)
C(8)–Mo(1)–C(10)
C(9)–Mo(1)–C(10)
127.6(2)
71.4(2)
71.3(2)
C(8)–Mo(1)–C(1)
C(8)–Mo(1)–C(2)
C(8)–Mo(1)–C(3)
C(8)–Mo(1)–C(4)
C(8)–Mo(1)–C(5)
C(9)–Mo(1)–C(1)
C(9)–Mo(1)–C(2)
C(9)–Mo(1)–C(3)
C(9)–Mo(1)–C(4)
C(9)–Mo(1)–C(5)
C(10)–Mo(1)–C(1)
C(10)–Mo(1)–C(2)
C(10)–Mo(1)–C(3)
C(10)–Mo(1)–C(4)
C(10)–Mo(1)–C(5)
O(8)–C(8)–Mo(1)
O(9)–C(9)–Mo(1)
O(10)–C(10)–Mo(1)
122.1(2)
144.7(3)
118.7(3)
87.8(3)
103.82(13)
87.57(14)
105.75(14)
140.9(2)
139.14(14)
127.6(5)
123.8(5)
124.6(5)
110.8(5)
116.4(5)
121.2(4)
69.8(3)
74.1(3)
71.6(3)
70.6(3)
72.7(3)
78.0(2)
78.7(2)
106.9(2)
89.7(2)
151.4(2)
117.3(2)
95.3(2)
106.1(2)
141.4(2)
97.5(2)
121.2(2)
154.6(2)
140.5(2)
106.2(2)
179.0(6)
173.6(5)
174.0(5)
The atoms denoted ‘A’ are related to the equivalently numbered atoms by the symmetry operation yx, yy, yz.
Table 2
atomic coordinates and equivalent thermal parameters are
Atomic coordinates (=104) and equivalent isotropic displacement param-
listed in Table 4. The Mo2P2 core is planar, with the pairs of
cyclopentadienylligandsandcarbonylligandslyinginatrans
configuration with respect to the plane. The molybdenum–
molybdenum bond is symmetrically bridged by the PPh2
groups, the separation between the metal atoms (2.7239(12)
3
5
˚
eters (A=10 ) for [(h -C5H4CO2Me)2Mo2(CO)6] (1)
x
y
z
Ueq
37(1)
Mo(1)
O(1)
C(1)
O(2)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
O(8)
C(9)
O(9)
C(10)
O(10)
1417(1)
5288(6)
3356(5)
5295(5)
2525(6)
2541(6)
3399(6)
3894(6)
4880(6)
6323(9)
1671(7)
1838(8)
y243(6)
751(1)
2125(4)
256(1)
2084(5)
1003(5)
3384(4)
y426(6)
76(1)
43(1)
62(1)
48(1)
50(1)
51(1)
45(1)
50(1)
85(2)
58(2)
101(2)
47(1)
69(1)
46(1)
71(1)
˚
˚
A in molecule 1, Fig. 2 (a) and 2.7317(10) A in molecule
2, Fig. 2 (b)) being consistent withthepresenceoftheformal
double bond required to satisfy the 18-electron rule. In com-
parison, the analogous unsubstituted complex [(h5-
Cp)2Mo2(m-PPh2)2(CO)2] displays a slightly shorter bond
y526(4)
607(4)
y820(4)
66(5)
y1340(6)
y499(6)
962(6)
927(5)
554(4)
˚
length, 2.716(1) A, the lengthening in 2 perhaps being a
1204(5)
1128(7)
2323(5)
3228(4)
1451(4)
1916(4)
742(4)
2180(6)
4644(8)
809(6)
consequence of electron withdrawal from a metal–metal
bonding orbital by the substituted cyclopentadienyl ligands.
1140(6)
y1257(6)
y2160(5)
2045(6)
3139(5)
2.3. Synthesis of trans- and cis-[(h5-CpU)2Mo2(m-PPh2)2-
(CO)(O)] ((3a) and (3b)). X-ray characterisation of the
trans-isomer 3a
y1109(5)
929(6)
766(6)
778(4)
Air oxidation of [(h5-Cp)2Mo2(m-PPh2)2(CO)2] for 4
days at room temperature leads to replacement of a carbonyl
ligand by a terminal oxo ligand and formation of the oxo
complex [(h5-Cp)2Mo2(m-PPh2)2(CO)(O)] [1]. Under
the same conditions, it was found to be impossible to replace
even one of the carbonyl ligands of 2, but air purging of a
solution of 2 in refluxing toluene for 8 h resulted in a good

12
J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
Scheme 2. Reagents and conditions: (i) P2Ph4 (1 equiv.), toluene, 1118C, 4 h; (ii) air, toluene, 1118C, 8 h.
combined yield of the trans- and cis-isomers of the carbonyl–
oxo complex [(h5-CpU)2Mo2(m-PPh2)2(CO)(O)] (3a)
and (3b) (Scheme 2). The two non-interconverting isomers
were easily separated by column chromatography, 3a having
a higher RF value than 3b. As in the case of the analogous
unsubstituted cyclopentadienyl species, 3a is formed in a
much higher yield than 3b, the ratio of 3a:3b being approx-
imately 30:1. Upon repeating the oxidation reaction of 2 in
the presence of trimethylamine N-oxide it was found that 3a
and 3b were formed in the same ratio but in considerably
lower yield. Prolonged reflux of 3a in toluene while purging
with air, did not, as had been hoped, lead to replacement of
the remaining CO group by a second oxo ligand and, in the
presence of trimethylamine N-oxide, resulted in complete
decomposition.
The IR spectra of 3a and 3b each show a single carbonyl
ligand absorption (1842 and 1870 cmy1, respectively) and
two separate peaksfortheestergrouponthecyclopentadienyl
ligand (1722, 1712 and 1718, 1711 cmy1, respectively). The
molecular ions of 3a and 3b were identical, as determined
by FAB mass spectroscopy, and corresponded to [(h5-
C5H4CO2Me)2Mo2(m-PPh2)2(CO)(O)]q at m/z 853 with
a fragment ion peak at 28 mass units lower, arising from loss
of the single carbonyl ligand. The 1H NMR spectra of 3a and
3b showed the cyclopentadienyl rings to be inequivalent,
each ring giving rise to two distinct resonances in the cyclo-
pentadienyl region. Multiplet peaks characteristic of the
phenyl protons on the phosphido bridges were also observed.
The 31P{1H} spectra each showed a single peak, for 3a at
27.9 ppm and for 3b at 23.0 ppm (relative to P(OMe)3 (0.0
Table 3
5
˚
Selected bond lengths (A) and angles (8) for [(h -C5H4CO2Me)2Mo2(m-PPh2)2(CO)2] (2)
Mo(1)–Mo(1A)
Mo(1)–P(1)
Mo(1)–P(1A)
Mo(1) C(1)
Mo(1)–C(2)
Mo(1)–C(3)
Mo(1)–C(4)
Mo(1)–C(5)
Mo(1)–C(6)
P(1)–C(9)
2.7239(12) Mo(2)–Mo(2A)
2.7317(10) C(2)–C(3)
1.419(10) C(22)–C(23)
1.402(11) C(23)–C(24)
1.410(10) C(24)–C(25)
1.431(9) C(25)–C(26)
1.425(9) C(22)–C(26)
1.469(9) C(26)–C(27)
1.197(8) C(27)–O(5)
1.155(7) C(21)–O(4)
1.410(9)
1.394(10)
1.393(10)
1.427(9)
1.422(9)
1.487(9)
1.183(9)
1.164(7)
2.406(2)
2.399(2)
1.935(6)
2.345(6)
2.380(6)
2.366(7)
2.290(7)
2.282(6)
1.839(5)
1.833(6)
Mo(2)–P(2)
Mo(2)–P(2A)
Mo(2)–C(21)
Mo(2)–C(22)
Mo(2)–C(23)
Mo(2)–C(24)
Mo(2)–C(25)
Mo(2)–C(26)
P(2)–C(29)
2.401(2)
2.402(2)
1.928(6)
2.306(6)
2.342(6)
2.349(6)
2.340(6)
2.304(5)
1.837(6)
1.838(6)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(2)–C(6)
C(6)–C(7)
C(7)–O(2)
C(1)–O(1)
P(1)–C(15)
P(2)–C(35)
P(1)–Mo(1)–P(1A)
P(1)–Mo(1)–C(2)
P(1)–Mo(1)–C(3)
P(1)–Mo(1)–C(4)
P(1)–Mo(1)–C(5)
P(1)–Mo(1)–C(6)
P(1)–Mo(1)–C(1)
110.94
P(2)–Mo(2)–P(2A)
P(2)–Mo(2)–C(22)
P(2)–Mo(2)–C(23)
P(2)–Mo(2)–C(24)
P(2)–Mo(2)–C(25)
P(2)–Mo(2)–C(26)
P(2)–Mo(2)–C(21)
110.68(4) Mo(1)–P(1)–Mo(1A) 69.06(5) Mo(2)–P(2)–Mo(2A) 69.32(4)
145.3(2)
110.3(2)
91.8(2)
107.2(2)
143.6(2)
85.0(2)
141.1(2)
149.4(2)
115.1(2)
93.2(2)
Mo(1)–P(1)–C(9)
Mo(1)–P(1)–C(15)
Mo(1)–C(1)–O(1)
C(9)–P(1)–C(15)
C(2)–C(6)–C(7)
C(6)–C(7)–O(2)
123.5(2) Mo(2)–P(2)–C(29)
117.7(2) Mo(2)–P(2)–C(35)
174.8(6) Mo(2)–C(21)–O(4)
122.3(2)
119.1(2)
173.6(5)
103.5(3)
102.5
C(29)–P(2)–C(35)
105.6(2)
85.8(2)
124.0(6) C(22)–C(26)–C(27) 122.6(6)
123.6(7) C(26)–C(27)–O(5) 124.2(6)
P(1)–Mo(1)–Mo(1A) 55.35(4) P(2)–Mo(2)–Mo(2A)
C(1)–Mo(1)–Mo(1A) 79.1(2)
C(1)–Mo(1)–P(1A) 82.7(2)
55.36(4)
C(21)–Mo(2)–Mo(2A) 81.7(2)
C(21)–Mo(2)–P(2A) 84.8(2)
The atoms denoted ‘A’ are related to the equivalently numbered atoms by the symmetry operation yx, yyq1, yzq1 in molecule 1 and yxq1, yy, yz in
molecule 2.

J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
13
Fig. 2. ORTEP plot of the molecular structures of the two crystallographically independent molecules of [(h5-C5H4CO2Me)2Mo2(m-PPh2)2(CO)2] (2) with
thermal ellipsoids at 40% probability level, (a) molecule 1 and (b) molecule 2. The atom numbering scheme used in Table 3 is defined.
ppm)). From the spectroscopic data alone it was not possible
to determine which isomer was which, although comparison
with the data for the unsubstituted cyclopentadienyl ana-
logues suggested that 3a was trans-[(h5-CpU)2Mo2(m-
PPh2)2(CO)(O)] and 3b the corresponding cis-isomer. An
X-ray diffraction study of 3a was undertaken in order to

14
J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
Table 4
confirm its configuration and to compare its structure with
that of complex 2 and the unsubstituted analogue [(h5-
Cp)2Mo2(m-PPh2)2(CO)(O)].
Atomic coordinates (=104) and equivalent isotropic displacement param-
3
5
˚
eters (A=10 ) for [(h -C5H4CO2Me)2Mo2(m-PPh2)2(CO)2] (2)
Ueq
34(1)
The molecular structure of 3a is shown in Fig. 3 with
selected bond lengths and angles listed in Table 5 and final
fractional atomic coordinates and equivalent thermal param-
eters listed in Table 6. The structure is similar to that of the
unsubstituted analogue possessing a trans arrangement of h5-
cyclopentadienyl ligands as predicted [1]. The oxo ligand is
bonded to Mo(1), which is formally in oxidation state IV,
while Mo(2), bonded to the carbonyl ligand, is formally in
oxidation state II. The metal–metal bond is asymmetrically
bridged by the two m-PPh2 groups, with Mo(1)–P distances
x
y
z
Mo(1)
Mo(2)
P(1)
P(2)
O(1)
C(1)
C(2)
O(2)
C(3)
O(3)
C(4)
O(4)
C(5)
O(5)
C(6)
O(6)
C(7)
274(1)
5178(1)
1430(1)
3640(1)
y699(4)
y331(5)
143(6)
y1694(4)
1199(6)
y916(4)
1718(5)
6311(4)
992(5)
5989(1)
y18(1)
5112(1)
225(1)
5092(1)
1289(1)
4511(1)
196(1)
32(1)
36(1)
35(1)
75(2)
49(2)
55(2)
77(2)
67(2)
80(2)
65(2)
61(1)
57(2)
79(2)
50(2)
72(1)
58(2)
123(4)
39(1)
52(2)
62(2)
63(2)
72(2)
55(2)
45(1)
64(2)
84(3)
88(3)
71(2)
56(2)
40(1)
49(1)
57(2)
60(2)
54(2)
43(1)
54(2)
94(3)
42(1)
56(2)
69(2)
83(3)
86(3)
64(2)
41(1)
55(2)
70(2)
88(3)
78(3)
59(2)
160(11)
167(9)
147(7)
209(8)
123(4)
5619(4)
5714(5)
7295(5)
7612(4)
7289(5)
7608(5)
7455(5)
2191(3)
7554(5)
1990(4)
7463(4)
1231(4)
7569(5)
7617(10)
5123(4)
5714(5)
5683(6)
5086(6)
4492(6)
4525(5)
5268(4)
5868(5)
6023(6)
5569(7)
4957(6)
4784(5)
1356(4)
213(5)
2296(4)
3339(6)
6333(6)
4914(6)
6605(7)
3129(5)
5494(8)
1152(4)
4499(7)
4223(5)
5016(6)
3951(5)
4371(7)
2368(10)
5510(5)
6624(6)
7377(6)
7062(7)
5952(8)
5178(7)
2924(5)
2716(7)
1489(9)
467(8)
˚
of 2.455(2) and 2.454(2) A compared to the correspond-
ingly shorter Mo(2)–P distances of 2.341(2) and 2.336(2)
˚
A. The bridging phosphido ligands may be positioned more
closely to Mo(2) because the p back-donation from Mo(2)
to the empty phosphorus d orbitals is enhanced relative
to that from Mo(1) which is in a higher oxidation state.
The separation between the molybdenum atoms in 3a
5787(5)
12(5)
4047(4)
y960(6)
y1877(9)
2631(4)
2983(5)
3858(5)
4414(5)
4067(6)
3187(5)
1893(5)
2881(6)
3159(8)
2456(9)
1479(8)
1193(6)
5871(4)
6113(5)
5914(6)
4816(6)
4311(6)
5123(5)
5045(6)
3951(8)
2307(4)
2158(5)
1162(6)
298(6)
˚
(2.9265(11) A) has increased with respect to 2(2.7243(13)
C(8)
C(9)
˚
A), but is slightly shorter than that observed for the unsub-
5
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
C(40)
C(01)
Cl(1)
Cl(2)
Cl(19)
Cl(29)
˚
stituted analogue (2.942(1) A). The (h -C5H4CO2Me)
ring attached to Mo(1), the metal atom bonded to oxygen,
is coordinated asymmetrically. Three of the Mo(1)–C
˚
distances (Mo(1)–C(10) 2.369(8) A, Mo(1)–C(11)
˚
˚
2.369(8) A, Mo(1)–C(14) 2.382(8) A) are significantly
shorter than the remaining two distances (Mo(1)–C(12)
3
2
˚
˚
2.450(8) A, Mo(1)–C(13) 2.470(8) A). This (h ,h )
mode of coordination has previously been observed in com-
plexes of similar structure [1,7]. The distortion is attributed
to the electronic effects of the strongly p-donating oxo ligand
which lies trans to C(12)–C(13) and exerts a labilisingtrans
effect [8].
651(6)
1869(5)
1127(5)
3272(5)
2879(6)
2784(6)
3097(5)
3406(5)
3890(6)
4413(8)
145(5)
640(6)
565(8)
y11(9)
y519(9)
y449(7)
466(5)
y84(6)
179(8)
994(10)
1570(9)
1314(7)
4509(11)
3093(17)
5658(18)
3593(18)
5984(10)
y770(5)
y1224(5)
y560(5)
356(4)
2.4. Synthesis of [(h5-CpU)2Mo2(m-PPh2)2(NO)(O)][BF4]
(5) and [(h5-Cp)2Mo2(m-PPh2)2(NO)(O)][BF4] (6)
1296(6)
2157(7)
It was of interest to determine whether it was possible to
replace the remaining carbonyl group in complex 3 by any
other ligand. The trans complex 3a was investigated because
the yield of the cis complex 3b was very low. Forcomparative
purposes, the reactions were also carried out on trans-[(h5-
Cp)2Mo2(m-PPh2)2(CO)(O)] (4) since the possibility of
replacing the CO group in 4 with other ligands was not
explored in the original investigation [1]. Separate toluene
solutions of 3a were refluxed in the presence of each of the
two-electron donor ligands P(OMe)3, PPh3, ButNC for sev-
eral days, but the IR and NMR spectra of the reaction
solutions showed only unreacted 3a to be present. Under the
same reaction conditions 4 behaved in an identical manner,
yielding only starting material and insoluble decomposition
products. The IR carbonyl absorptions of 3a and 4 (1842 and
1826 cmy1, respectively) indicate a strong degree of p back-
donation to the sole carbonyl group in each case, this presum-
ably accounting for the resistance to substitution. It appears
y686(4)
y1589(5)
y2277(6)
y2095(7)
y1203(7)
y506(6)
1386(4)
2213(5)
3095(5)
3163(7)
2345(7)
1465(5)
134(22)
y377(16)
y61(15)
120(15)
433(6)
1430(5)
3400(4)
3967(5)
3822(6)
3115(8)
2537(6)
2687(5)
1285(23)
918(18)
514(16)
222(14)
1123(11)
y114(9)
Site occupancy factors: C(01)s0.50; Cl(1), Cl(2)s0.20; Cl(19),
Cl(29)s0.30.

J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
15
Fig. 3. ORTEP plot of the molecular structure of trans-[(h5-C5H4CO2Me)2Mo2(m-PPh2)2(CO)(O)] (3a) with thermal ellipsoids at 40% probability level.
The atom numbering scheme used in Table 5 is defined.
Table 5
5
˚
Selected bond lengths (A) and angles (8) for trans-[(h -C5H4CO2Me)2Mo2(m-PPh2)2(CO)(O)] (3a)
Mo(1)–C(13)
Mo(1)–C(14)
Mo(1)–O(5)
Mo(1)–Mo(2)
2.470(8)
2.382(8)
1.702(5)
Mo(2)–C(6)
Mo(2)–C(7)
Mo(2)–C(39)
2.359(9)
2.314(8)
1.954(9)
1.165(10) C(12)–C(13)
C(13)–C(14)
P(1)–C(21)
C(10)–C(11)
C(11)–C(12)
1.829(7)
P(2)–C(33)
1.838(8)
1.419(12) C(3)–C(4)
1.416(12) C(4)–C(5)
1.404(13) C(5)–C(6)
1.424(12) C(6)–C(7)
1.440(12) C(3)–C(7)
1.441(12)
1.400(13)
1.411(14)
1.389(13)
1.400(13)
2.9265(11) C(39)–O(6)
C(10)–C(14)
P(1)–Mo(1)–Mo(2)
P(1)–Mo(2)–Mo(1)
P(1)–Mo(1)–P(2)
Mo(1)–P(1)–Mo(2)
O(5)–Mo(1)–P(1)
O(5)–Mo(1)–P(2)
O(5)–Mo(1)–Mo(2)
C(10)–Mo(1)–Mo(2) 153.6(2)
C(11)–Mo(1)–Mo(2) 128.5(2)
C(12)–Mo(1)–Mo(2)
C(13)–Mo(1)–Mo(2)
50.64(5)
54.19(6)
100.39(8)
75.17(7)
101.0(2)
101.9(2)
115.4(2)
P(2)–Mo(1)–Mo(2)
50.53(5) C(10)–Mo(1)–O(5)
91.0(3)
O(6)–C(39)–Mo(2) 175.7(8)
C(15)–P(1)–Mo(1) 116.5(3)
C(15)–P(1)–Mo(2) 126.7(3)
C(21)–P(1)–Mo(1) 117.5(3)
C(21)–P(1)–Mo(2) 117.8(3)
P(2)–Mo(2)–Mo(1)
P(2)–Mo(2)–P(1)
Mo(1)–P(2)–Mo(2)
C(39)–Mo(2)–P(1)
C(39)–Mo(2)–P(2)
C(39)–Mo(2)–Mo(1)
C(3)–Mo(2)–Mo(1)
C(4)–Mo(2)–Mo(1)
C(5)–Mo(2)–Mo(1)
C(6)–Mo(2)–Mo(1)
C(7)–Mo(2)–Mo(1)
C(3)–Mo(2)–P(1)
C(4)–Mo(2)–P(1)
C(5)–Mo(2)–P(1)
C(6)–Mo(2)–P(1)
C(7)–Mo(2)–P(1)
C(3)–Mo(2)–P(2)
C(4)–Mo(2)–P(2)
C(5)–Mo(2)–P(2)
C(6)–Mo(2)–P(2)
C(7)–Mo(2)–P(2)
54.19(6) C(11)–Mo(1)–O(5) 107.3(3)
107.50(8) C(12)–Mo(1)–O(5) 141.4(3)
75.28(7) C(13)–Mo(1)–O(5) 144.2(3)
92.2(3)
94.0(2)
86.9(2)
C(14)–Mo(1)–O(5) 110.4(3)
C(4)–C(3)–C(2)
C(7)–C(3)–C(2)
C(3)–C(2)–O(1)
C(3)–C(2)–O(2)
C(2)–O(2)–C(1)
O(1)–C(2)–O(2)
C(11)–C(10)–C(9)
C(14)–C(10)–C(9)
C(10)–C(9)–O(3)
C(10)–C(9)–O(4)
128.0(9)
125.1(8)
C(15)–P(1)–C(21)
102.4(4)
C(27)–P(2)–Mo(1) 117.5(3)
164.3(2)
133.9(2)
121.8(2)
132.3(3)
160.2(3)
141.3(2)
140.1(3)
105.5(3)
88.1(3)
123.8(10) C(27)–P(2)–Mo(2) 127.8(3)
114.3(9)
116.8(9)
C(33)–P(2)–Mo(1) 115.7(3)
C(33)–P(2)–Mo(2) 116.6(3)
98.9(2)
97.1(2)
122.0(10) C(27)–P(2)–C(33)
102.9(4)
116.8(9)
125.2(9)
C(14)–Mo(1)–Mo(2) 124.7(2)
129.0(8)
123.5(8)
124.4(9)
110.3(8)
C(9)–O(4)–C(8)
O(3)–C(9)–O(4)
C(10)–Mo(1)–P(1)
C(11)–Mo(1)–P(1)
C(12)–Mo(1)–P(1)
C(13)–Mo(1)–P(1)
C(14)–Mo(1)–P(1)
C(10)–Mo(1)–P(2)
C(11)–Mo(1)–P(2)
C(12)–Mo(1)–P(2)
C(13)–Mo(1)–P(2)
C(14)–Mo(1)–P(2)
129.1(2)
95.1(2)
87.0(2)
111.5(2)
143.2(2)
125.3(2)
143.5(2)
113.8(2)
87.0(2)
91.7(2)
106.1(3)
110.2(2)
87.5(2)
101.8(3)
136.3(3)
144.5(3)

16
J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
Table 6
that the electron withdrawing substituent on the cyclopenta-
dienyl rings does not significantly increase the ease of sub-
stitution of the carbonyl group of complex 3a as compared
to the unsubstituted analogue 4.
Atomic coordinates (=104) and equivalent isotropic displacement param-
3
5
˚
eters (A=10 ) for trans-[(h -C5H4CO2Me)2Mo2(m-PPh2)2(CO)(O)]
(3a)
x
y
z
Ueq
29(1)
However, when 3a and 4 were treated with [NO][BF4]
at room temperature, a substitution reaction occurred almost
instantaneously in each case, with the CO ligand being
replaced by NOq to give a near quantitative yield of
[(h5-CpU)2Mo2(m-PPh2)2(NO)(O)][BF4] (5) and [(h5-
Cp)2Mo2(m-PPh2)2(NO)(O)][BF4] (6), respectively
(Scheme 3). There are relatively few known examples of
dimolybdenum nitrosyl complexes [9] and, to our knowl-
edge, the recently reported complexes [Mo2(m-H)(m-
Ph2P(CH2)nPPh2)(CO)7(NO)] (ns1–4) [10] are the
only other dimolybdenum nitrosyls to be prepared by the use
of [NO][BF4]. The oxo- and nitrido-bridged species [(h5-
C5Me5)Mo(NO)(CH2SiMe3)]2(m-O) [11] and [(h5-
C5Me5)Mo(NO)(CH2SiMe3)](m-N)[(h5-C5Me5)Mo(O)-
(CH2SiMe3)] [12] are the only other reported dimolyb-
denum complexes containing both nitrosyl and oxo ligands.
Complexes 5 and 6 were fully characterised spectroscop-
ically, as described in Section 3 and a single crystal of 6 was
grown in an attempt to determine the molecular structure of
6 by X-ray diffraction. The crystallographic data obtained
could not be fully refined due to the disorder within the
structure but confirmed the proposedatomarrangement[13].
Complex 5 displays no carbonyl ligand absorptions in its
IR spectrum, although there is a peak at 1730 cmy1 due to
the ester group of the substituted cyclopentadienyl ligand,
and a single NO stretching frequency at 1701 cmy1. Complex
6 displays a single nitrosyl absorption at 1692 cmy1. The 1H
NMR spectrum of each complex reveals the inequivalence of
the cyclopentadienyl ligands, while the 31P{1H} spectra for
5 and 6 each show a single peak at 37.1 and 36.0 ppm,
respectively, due to the equivalent diphenylphosphido
bridges. The 19F NMR of each complex shows a broad single
peak at y152.8 ppm which confirms the presence of the
[BF4]y anion, while the FAB mass spectra, run in positive
ion mode, display molecular ion signals for the cations only,
at m/z 855 and 739 for 5 and 6, respectively.
Mo(1)
Mo(2)
P(1)
P(2)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
9485(1)
8129(1)
2345(1)
2514(1)
2480(1)
2132(1)
3972(6)
3098(5)
1894(5)
2144(5)
1313(4)
4520(4)
3803(9)
3281(7)
2578(5)
1727(6)
1281(6)
1838(7)
2623(6)
1490(9)
2250(6)
2892(5)
3322(5)
3877(5)
3783(6)
3154(6)
3381(5)
3372(7)
4068(8)
4767(8)
4790(7)
4103(5)
1542(5)
704(5)
9855(1)
10756(1)
11143(1)
9563(1)
11249(5)
10380(4)
8192(4)
9101(4)
9772(3)
10471(4)
10092(8)
10946(6)
11179(5)
10867(5)
11278(5)
11826(5)
11761(5)
8833(7)
8732(5)
9075(4)
9732(5)
9841(5)
9272(5)
8800(4)
11542(4)
11611(5)
11896(6)
12150(6)
12110(5)
11802(5)
11671(4)
11411(5)
11855(6)
12555(6)
12831(5)
12392(5)
8819(4)
8128(5)
7572(5)
7708(6)
8385(6)
8946(5)
9351(4)
9584(5)
9502(5)
9168(5)
8945(6)
9025(5)
10567(4)
29(1)
31(1)
31(1)
99(3)
70(2)
74(2)
67(2)
42(1)
59(2)
97(4)
54(3)
42(2)
48(2)
52(3)
59(3)
52(2)
101(5)
46(2)
39(2)
42(2)
48(2)
50(2)
45(2)
41(2)
56(3)
76(4)
86(5)
70(3)
52(3)
34(2)
53(3)
76(4)
68(3)
68(3)
55(3)
38(2)
52(2)
63(3)
66(3)
60(3)
47(2)
33(2)
52(2)
56(3)
55(3)
62(3)
50(2)
39(2)
10149(2)
7404(2)
5881(7)
4896(6)
10301(7)
11959(6)
9932(5)
7997(6)
4040(10)
5790(9)
6648(7)
6606(8)
7611(9)
8283(10)
7690(9)
12573(12)
10831(8)
10341(8)
10877(8)
10046(9)
8989(9)
9145(8)
11141(8)
12296(8)
13036(10)
12605(13)
11502(12)
10742(9)
10898(7)
10725(9)
11187(11)
11796(10)
11938(10)
11527(8)
6408(7)
6176(8)
5393(9)
4835(9)
5090(9)
5859(8)
6879(7)
7618(9)
7176(9)
6012(9)
5283(9)
5704(8)
8082(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
y8(6)
116(7)
940(7)
1650(6)
2760(6)
2507(6)
2977(8)
3689(7)
3953(6)
3484(6)
1005(5)
289(6)
In conclusion, the above reactions show that the introduc-
tion of electron withdrawing substituents onto the cyclopen-
tadienyl rings in 2 does not facilitate the displacement of the
carbonyl groups by other ligands. Indeed, the presence of the
carbomethoxy groups as ring substituents renders the dis-
placement of a carbonyl group by an oxo ligand more diffi-
cult. The exchange of carbonyl ligands in [Co2(CO)6-
y561(6)
y703(6)
y10(7)
830(6)
3768(6)
Scheme 3. Reagents and conditions: (i) NOBF4 (excess), CH2Cl2, r.t.

J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
17
(RCCR9)] has previously been shown to be slowed when R
is an electron withdrawing substituent [14]. This was attrib-
uted to the strengthening of the metal–alkyne bond with
cleavage of this bond being involved in the rate determining
step. It may be that the metal–cyclopentadienyl bond is sim-
ilarly strengthened by the electron withdrawing substituent
on the ring and that this slows the oxidation of 2 to 3a and
3b, relative to the unsubstituted analogue described previ-
ously [1]. Alternatively, the increased steric bulk of the ring
may adversely influence the rate of reaction.
C5H4CO2Me), 96.3 (2C, s, C5H4CO2Me), 94.9 (4C, s,
C5H4CO2Me), 52.3 (2C, s, C5H4CO2CH3). FAB-MS: m/z
607 [(Mq)q1], 578 [(Mq)yCO], 550 [(Mq)y2CO],
522 [(Mq)y3CO], 494 [(Mq)y4CO], 466 [(Mq)y
5CO] and 438 [(Mq)y6CO].
3.2. Synthesis of [(h5-C5H4CO2Me)2Mo2(m-PPh2)2(CO)2]
(2)
P2Ph4 was prepared in situ from PPh2H (1.8 ml, 10.3
mmol) and PPh2Cl (1.85 ml, 10.3 mmol). In order to ensure
a slight excess of the ligand in the subsequent reaction, ayield
of 80% was assumed, although in practice it is essentially
quantitative. To the solution of P2Ph4 in toluene (150 ml)
was added 1 (5 g, 8.25 mmol) and the mixture refluxed for
4 h. On cooling to room temperature a greenish brown solid
was precipitated, collected by filtration and washed with hex-
ane (50 ml). The solvent was removed from the combined
filtrate and washings and redissolved in the minimum
of dichloromethane. Silica was added (10 g), the dichloro-
methane removed in vacuo, and the silica loaded onto a silica
chromatography column. Elution with hexane–dichlorome-
thane (2:1) gave an orange band dueto[(h5-C5H4CO2Me)2-
Mo2(m-PPh2)(m-H)(CO)4] (0.29 g, 5%) and then a green–
brown band due to 2. The latter band was collected, the
solvent removed, and the solid added to that already obtained
by filtration, yielding [(h5-C5H4CO2Me)2Mo2(m-PPh2)2-
(CO)2] (2) (4.5 g, 63%). Analytically pure samples were
prepared by recrystallisation from hexane–dichloromethane
1:1 at y48C. Anal. Found: C, 55.45; H, 3.9; P, 7.8. Calc. for
C40H34Mo2O6P2: C, 55.6; H, 4.0; P, 7.9%. IR (nmax(CHCl3)
cmy1): (CO) 1875(vs) and 1717(s). 1H NMR (400 MHz):
d 3.19 (6H, s, CO2CH3), 5.65 (4H, t, J(PH)s1.9 Hz,
C5H4CO2Me), 5.84 (4H, t, J(PH)s2.2 Hz, C5H4CO2Me),
7.55–7.23 (20H, m, C6H5). 13C NMR (400 MHz): d 208.8
(2C, s, CO), 165.9 (2C, s, C5H4CO2Me), 143.5 (4C, d,
J(PC)s42.7 Hz, C6H5), 133.2–127.5 (20C, m, C6H5), 94.9
(4C, s, C5H4CO2Me) 89.8 (4C, s, C5H4CO2Me), 89.4 (2C,
s, C5H4CO2Me), 52.3 (2C, s, C5H4CO2CH3). 31P NMR(250
MHz): d y50.1 (2P, s, m-PPh2). FAB-MS: m/z 865
[(Mq)q1], 836 [(Mq)yCO] and 808 [(Mq)y2CO].
3. Experimental
Except where stated, all reactions were carried out under a
nitrogen atmosphere, usingstandardSchlenktechniques.Sol-
vents were distilled under nitrogen, from appropriate drying
agents, and degassed prior to use. All reagents were obtained
from commercial suppliers and used without further purifi-
cation. The compounds trans-[(h5-C5H5)2Mo2(m-PPh2)2-
(CO)(O)] (4) and P2Ph4 were prepared by literature meth-
ods [1,15]. Column chromatography was performed on
Kieselgel 60 (70–230 or 230–400 mesh). Products are given
in order of decreasing RF values.
The instrumentation used to obtain spectroscopic data has
been described previously [16]. 1H, 13C and 31P NMR were
recorded in CDCl3 at 293 K. The solvent resonance was used
as internal standard, except for 31P where chemical shifts are
given relative to P(OMe)3 with upfield shifts negative and
19F where chemical shifts are given relative to CFCl3. The
13C and 31P spectra were 1H gated decoupled.
3.1. Synthesis of [(h5-C5H4CO2Me)2Mo2(CO)6] (1) by a
modification of literature procedures [5,6]
Freshly cracked cyclopentadiene (18 ml, 210 mmol,
excess) was added to sodium sand (1.75 g, 76 mmol) in
THF, and stirred for 1 h until complete reaction had occurred.
Dimethyl carbonate (9.45 ml, 115 mmol) was added to the
solution, which was then refluxed for 6 h. Mo(CO)6 (20 g,
76 mmol) was added, and refluxing continued for further 12
h. The reaction mixture was then cooled to room temperature
and a solution of Fe2(SO4)3P9H2O (17 g, 30 mmol) and
acetic acid (10 ml) in water (250 ml) added dropwise with
stirring. The purple–red precipitate was filtered and washed
succesively with water (200 ml), cold methanol (20 ml) and
hexane (20 ml), then dried overnight in vacuo to yield [(h5-
C5H4CO2Me)2Mo2(CO)6] (1) (17.6 g, 77%). Analytically
pure samples were prepared by recrystallisation from di-
chloromethane at y48C. Anal. Found: C, 39.4; H, 2.2. Calc.
for C20H14Mo2O10: C, 39.6; H, 2.3%. IR (nmax(CHCl3)
cmy1): (CO) 2021(sh), 1970(vs), 1924(vs) and 1724(s).
1H NMR (400 MHz): d 3.76 (6H, s, CO2CH3), 5.26
(4H, s, C5H4CO2Me), 5.83 (4H, s, C5H4CO2Me). 13C NMR
(400 MHz): d 231.3 (2C, s, CO), 224.9 (2C, s, CO), 201.0
(2C, s, CO), 165.1 (2C, s, C5H4CO2Me), 97.3 (4C, s,
3.3. Synthesis of [(h5-CpU)2Mo2(m-PPh2)2(CO)(O)] (3a)
and (3b)
Complex 2 (1 g, 1.3 mmol) was dissolved in toluene (150
ml) and refluxed for 8 h whilst purging gently with com-
pressed air. Solvent was removed, the residue dissolved in
the minimum of dichloromethane, and silica added (2 g).
The dichloromethane was evaporated in vacuo and the silica
loaded onto a chromatography column. Elution with hexane–
dichloromethane (2:1) gave trace quantities of startingmate-
rial 2, then a purple band which was collected. The solvent
was removed in vacuo, yielding crystalline trans-[(h5-
CpU)2Mo2(m-PPh2)2(CO)(O)] (3a) (0.69 g, 71%). Anal.
Found: C, 55.7; H, 3.95; P, 7.2. Calc. for C39H34Mo2O6P2:

18
J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
C, 54.9; H, 4.0; P, 7.3%. IR (nmax(CHCl3) cmy1): (CO)
1842(vs), 1722(s) and 1712(s). H NMR (400 MHz): d
3.5. Further thermolysis reactions of trans-[(h5-CpU)2-
Mo2(m-PPh2)2(CO)(O)] (3a) with O2, P(OMe)3, PPh3 and
ButNC
1
3.01 (2H, s, C5H4CO2Me), 3.71 (3H, s, CO2CH3), 3.79(3H,
s, CO2CH3), 4.41 (2H, s, C5H4CO2Me), 5.45 (2H, s,
C5H4CO2Me), 6.93 (2H, s, C5H4CO2Me), 7.16–8.10 (20H,
m, C6H5). 13C NMR (400 MHz): d 235.6 (1C, s, CO), 167.5
(1C, s, C5H4CO2Me), 162.0 (1C, s, C5H4CO2Me), 147.2
(2C, d, J(PC)s34.1 Hz, C6H5), 141.1 (2C, d, J(PC)s43.0
Hz, C6H5), 134.9–127.6 (20C, m, C6H5), 110.4 (1C, s,
C5H4CO2Me) 100.1(1C, s, C5H4CO2Me), 94.85 (2C, s,
C5H4CO2Me), 92.4 (2C, s, C5H4CO2Me), 91.0 (2C, s,
C5H4CO2Me), 89.8 (2C, s, C5H4CO2Me), 52.4 (1C, s,
C5H4CO2CH3), 51.3 (1C, s, C5H4CO2CH3). 31P NMR (250
MHz): d 27.9 (2P, s, m-PPh2). FAB-MS: m/z 853
[(Mq)q1] and 824 [(Mq)yCO]. Further elution with
ethyl acetate–hexane (1:1) gave another purple band which,
on removal of solvent, afforded cis-[(h5-CpU)2Mo2(m-
PPh2)2(CO)(O)] (3b) (0.025 g, 2.5%). Anal. Found: C,
55.65; H, 4.0; P, 7.3. Calc. for C39H34Mo2O6P2: C, 54.9; H,
4.0; P, 7.3%. IR (nmax(CHCl3) cmy1): (CO) 1870(vs),
3a (0.29 g, 0.33 mmol) was dissolved in toluene (50 ml)
and refluxed for 18 h (1118C) while purging gently with
compressed air. Spot TLC throughout the reaction showed
that no new products were formed, and that the starting mate-
rial was gradually decomposing. The procedure was repeated
separately, under nitrogen, with trimethyl phosphite (0.11
ml, 1 mmol, excess); triphenyl phosphine (0.26 g, 1 mmol,
excess) and tert-butyl isocyanide (0.11ml, 1 mmol, excess)
refluxing each solution for several days. A little decomposi-
tion of 3a was observed by spot TLC but no new products
were formed. The reflux of 3a (0.25 g, 0.3 mmol) in toluene
(50 ml) was repeated in the presence of excess trimethylam-
ine N-oxide (0.068 g, 0.9 mmol) whilst purging gently with
compressed air. Spot TLC throughout the reaction showed
that no new products were formed and after 2 h, complex 3a
had completely decomposed to an intractable blue solid.
1
1718(s) and 1711(s) (CHCl3). H NMR (400 MHz): d
3.6. Thermolysis reactions of trans-[(h5-Cp)2Mo2(m-PPh2)2-
(CO)(O)] (4) with O2, P(OMe)3, PPh3 and ButNC
3.25 (2H, s, C5H4CO2Me), 3.76 (3H, s, CO2CH3), 3.80(3H,
s, CO2CH3), 4.72 (2H, s, C5H4CO2Me), 5.67 (2H, s,
C5H4CO2Me), 6.64 (2H, s, C5H4CO2Me), 7.0–7.78 (20H,
m, C6H5). 13C NMR (400 MHz): d 232.6 (1C, s, CO), 166.3
(1C, s, C5H4CO2Me), 161.2 (1C, s, C5H4CO2Me), 146.1
(2C, d, J(PC)s30.9 Hz, C6H5), 139.8 (2C, d, J(PC)s41.2
Hz, C6H5), 132.0–127.3 (20C, m, C6H5), 108.4 (1C, s,
C5H4CO2Me) 97.8 (1C, s, C5H4CO2Me), 93.2 (2C, s,
C5H4CO2Me), 91.1 (2C, s, C5H4CO2Me), 90.5 (2C, s,
C5H4CO2Me), 88.8 (2C, s, C5H4CO2Me), 50.7 (1C, s,
C5H4CO2CH3), 49.1 (1C, s, C5H4CO2CH3). 31P NMR (250
MHz): d 23.0 (2P, s, m-PPh2). FAB-MS: m/z 853
[(Mq)q1] and 824 [(Mq)yCO].
Following a similar procedure to Section 3.5 using 4 (0.24
g, 0.33 mmol), each reaction mixture was refluxed for 24 h.
Spot TLC throughout the reaction time showed that no new
products had formed.
3.7. Synthesis of [(h5-CpU)2Mo2(m-PPh2)2(NO)(O)][BF4]
(5)
To a solution of 3a (0.5 g, 0.66 mmol) in dichloromethane
(100 ml) was added [NO][BF4] (0.16 g, 1.37 mmol). The
solution was stirred for 10 min, during which time the colour
was observed to change from purple–red to orange. Hexane
(20 ml) was added, and the solution concentrated in vacuo
until a precipitate was observed. The precipitatewascollected
by filtration, dissolved in the minimum of diethyl ether–
dichloromethane (1:1) and recrystallised at y48C to afford
orange crystals of [(h5-CpU)2Mo2(m-PPh2)2(NO)(O)]-
[BF4] (5) (0.47 g, 94%). Anal. Found: C, 48.35; H, 3.5; N,
1.4; P, 6.65. Calc. for [C38H34Mo2NO6P2][BF4]: C, 48.5;
H, 3.6; N, 1.5; P, 6.6%. IR (nmax(CHCl3) cmy1): (CO)
3.4. Synthesis of [(h5-CpU)2Mo2(m-PPh2)2(CO)(O)] ((3a)
and (3b)) by air oxidation of 2 in the presence of
trimethylamine N-oxide
Complex 2 (1 g, 1.3 mmol) was dissolved in toluene (150
ml), excess trimethylamine N-oxide (0.26 g, 3.9 mmol)
added and the mixture refluxed for 1 h whilst purging gently
with compressed air. After this time the reaction mixture had
turned blue in colour indicating that considerable decompo-
sition had occurred. Solvent was removed, the residue dis-
solved in the minimum of dichloromethane, and silica added
(2 g). The dichloromethane was evaporated in vacuo and the
silica loaded onto a chromatography column. Elution with
hexane–dichloromethane (2:1) gave a purple band which
was collected and identified as trans-[(h5-CpU)2Mo2(m-
PPh2)2(CO)(O)] (3a) (0.26 g, 26%) by comparison with
the fully characterised products from Section 3.3. Further
elution with ethyl acetate–hexane (1:1) gave a trace of a
purple band which, on removal of solvent, afforded cis-[(h5-
CpU)2Mo2(m-PPh2)2(CO)(O)] (3b) (0.009 g, 0.9%),
identified by comparison with the products from Section 3.3.
1
1730(s) and (NO) 1701. H NMR (400 MHz): d 3.77
(3H, s, CO2CH3), 3.90 (3H, s, CO2CH3), 4.74 (2H, s,
C5H4CO2Me), 5.92 (2H, s, C5H4CO2Me), 6.57 (2H, s,
C5H4CO2Me), 6.59 (2H, s, C5H4CO2Me), 6.86–7.87 (20H,
m, C6H5). 31P NMR (250 MHz): d 37.1 (2P, s, m-PPh2).
19F NMR (250 MHz): d y152.8 (4F, BF4). FAB-MS: m/z
855 [(Mq)q1].
3.8. Synthesis of [(h5-Cp)2Mo2(m-PPh2)2(NO)(O)][BF4]
(6)
Following a similar procedure to Section 3.7, a dichloro-
methane solution of [(h5-Cp)2Mo2(m-PPh2)2(CO)(O)]

J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
19
(0.3 g, 0.41 mmol) was treated with [NO][BF4] (0.095 g,
0.82 mmol). The precipitate that resulted from addition of
hexane (20 ml) was collected by filtration and recrystallised
from the minimum of diethyl ether–dichloromethane (1:1)
to afford red–orange crystals of [(h5-Cp)2Mo2(m-PPh2)2-
(NO)(O)][BF4] (6) (0.29 g, 97%). Anal. Found: C, 49.35;
H, 3.5; N, 1.6; P, 7.35. Calc. for [C34H30Mo2NO2P2][BF4]:
C, 49.5; H, 3.7; N, 1.7; P, 7.5%. IR (nmax(CHCl3) cmy1):
1692. 1H NMR (400 MHz): d 5.90 (5H, s, C5H5), 5.62 (5H,
s, C5H5), 6.82–7.93 (20H, m, C6H5). 31P NMR (250 MHz):
d 36.0 (2P, s, m-PPh2). 19F NMR (250 MHz): d y152.8
(4F, BF4). FAB-MS: m/z 739 [(Mq)q1].
four-circle diffractometer. In each case, three standard reflec-
tions measured at intervals of 100 reflections showed no
significant variation in intensity. Cell parameters were
obtained by least-squaresrefinementondiffractometerangles
from 25 centred reflections (30F2uF408).
A semi-empirical absorption correction based on c-scan
data was applied (teXsan) [17]. The structures were solved
by direct methods (SHELXTL PLUS) [18] and subsequent
Fourier difference syntheses, and refined anisotropically
(non-H atoms) by full-matrix least-squares on F2 (SHELXL
93) [19]. Hydrogen atoms were placed in geometrically
idealised positions and refined using a riding model or as
rigid methyl groups.
Two half-molecules of CH2Cl2 are associated with the
inversion centre at 0, 0, 0.5. Each was disordered over two
positions with a common C atom and was modelled with
restraints applied to the atomic distances and isotropic ther-
mal parameters (site occupation factors given in Table 4).
Details of the data collection and structure refinements are
given in Table 7.
3.9. Crystal structure determination for complexes 1, 2
and 3a
The crystals were mounted on a glass fibre with epoxy
resin at room temperature. Data were collected by the v/2u
scan method on a Rigaku AFC5R [1,3a] and AFC7R [2]
Table 7
Details of data collection and structure refinements for complexes 1, 2 and 3a a
Complex
1
2
3a
Molecular formula
M
C20H14Mo2O10
606.19
C40H34Mo2O6P2P0.5(CH2Cl2)
906.96
C39H34Mo2O6P2
852.48
Crystal system
monoclinic
P21/c
9.811(4)
12.109(2)
9.919(3)
90
110.00(3)
90
1107.3(4)
2
triclinic
P 1
monoclinic
P21/c
12.436(2)
15.300(3)
20.395(4)
90
111.59(3)
90
3608.3(12)
4
#
Space group
˚
a (A)
13.364(4)
14.535(4)
10.576(2)
91.33(2)
94.94(2)
108.92(2)
1933.3(9)
2
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
U (A )
Z
Dc (g cmy3
)
1.818
1.558
1.569
Crystal size (mm)
Crystal habit
F(000)
0.2=0.2=0.04
red plate
596
0.3=0.2=0.15
green prism
914
0.2=0.2=0.05
purple plate
1720
m (mmy1
)
1.186
0.846
0.83
Relative transmission max., min.
Data collection range (8)
Index ranges
1.000, 0.894
4.5F2uF55
0FhF12
0FkF15
y12FlF12
2682
2538 (Rints0.018)
145, 0
0.1437
1.000, 0.938
5.0F2uF50
0FhF15
y17FkF16
y12FlF12
7113
6721 (Rints0.041)
472, 9
0.1357
1.000, 0.861
5.0F2uF50
y14FhF13
y18FkF0
0FlF24
6583
6329 (Rints0.048)
442, 0
0.1834
Reflections measured
Independent reflections
Parameters, restraints
wR2 (all data) b
x, y b
0.0848, 2.82
0.0458
0.0474, 4.60
0.0442
0.1000, 0.00
0.0523
R1 (I)2s(I)) b
Observed reflections
Goodness-of-fit on F2 (all data) b
Maximum shift/s
2152
1.030
0.001
1.394, y1.181
5304
1.074
y0.003
0.923, y0.653
3770
0.956
y0.008
1.262, y0.974
y3
˚
Peak, hole in final difference map (e A
)
a
˚
Data in common: graphite-monochromated Mo Ka radiation, ls0.71073 A, Ts293(2) K.
b R1s8NNFoNyNFcNN/8NFoN and wR2s[8w(Fo yFc 2)2/8wFo
]
1/2, ws1/[s2(Fo2)q(xP)2qyP], Ps(Fo q2Fc )/3 where x and y are constants
2
4
2
2
adjusted by the program. Goodness-of-fits{8[w(Fo yFc )2]/(nyp)}1/2 where n is the number of reflections and p is the number of parameters.
2
2

20
J.C. Stichbury et al. / Inorganica Chimica Acta 262 (1997) 9–20
[6]
[7]
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4. Supplementary material
Hydrogen atom coordinates, full tables of atomic coordi-
nates, thermal parameters and bond lengths and angles have
been deposited at the Cambridge Crystallographic Data Cen-
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[9]
(a) P. Legzdins, S.J. Rettig and J.E. Veltheer, J. Am. Chem. Soc., 114
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Acknowledgements
We wish to thank the EPSRC for financial support (J.E.D.,
G.P.S. and J.C.S.). We are grateful to the Cambridge Crys-
tallographic Data Centre for a CASE award (G.P.S.).
[10]
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[12]
J.T. Lin, Y.C. Lee, H.M. Kao, T.-Y. Dong and Y.S. Wen, J.
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J.C. Stichbury, M.J. Mays, G. Conole, unpublished work.
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Chem., 6 (1967) 1225.
W. Kuchen and H. Buchwald, Chem. Ber., 91 (1958) 2871.
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teXsan, single crystal structure analysis software, Version 1.7-1,
Molecular Structure Corporation, The Woodlands, TX, 1993, p. 77381.
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