Reaction of spiro[2.4]hepta-4,6-diene with molybdenum(II) indenyl compounds: Effects of substitution in the indenyl ligand

Article abstract of DOI:10.1021/om100840r

The series of molybdenum indenyl compounds [(Ind′)Mo(CO) ₂(NCMe)₂][BF₄] was prepared, and their reactivity toward spiro[2.4]hepta-4,6-diene was studied. It was observed that the spiro[2.4]hepta-4,6-diene ring opening could be blocked through substitution in the indenyl ring. Hence, the 2-substituted compound [(η⁵- C₉H₆Me)Mo(CO)₂(NCMe)₂][BF ₄] and 1,3-disubstituted compound [(η⁵-C ₉H₅^tBu₂)Mo(CO)₂(NCMe) ₂][BF₄] do not produce the usual ansa-compounds but the compounds with η⁴-bonded spiro[2.4]hepta-4,6-diene [(Ind′)(η⁴-C₅H₄(CH₂) ₂)Mo(CO)₂][BF₄]. The use of 1-substituted compounds [(η⁵-C₉H₆R)Mo(CO) ₂(NCMe)₂][BF₄] (R = Ph, ^tBu) or compounds with less sterically demanding substituents in the 1,3-positions [(η⁵-C₉H₅Ph₂)Mo(CO) ₂(NCMe)₂][BF₄] does not block the ring-opening reaction. These compounds give ansa-molybdenocenes [(Ind′) (η⁵-C₅H₄CH₂-η¹- CH₂)Mo(CO)][BF₄] in a manner similar to that for the unsubstituted analogue. The reaction products were characterized by NMR and IR spectroscopy. Structures of [(η⁵-C₉H ₅Ph₂)Mo(η³-C₃H ₅)(CO)₂], [(η⁵-C₉H ₆Ph)( η⁵-C₅H₄CH ₂-η¹-CH₂)Mo(CO)][BF₄], and [(η⁵-C₉H₅Ph₂)(η⁵- C₅H₄CH₂-η¹-CH ₂)Mo(CO)][BF₄] were determined by single-crystal X-ray analysis.

Full text of DOI:10.1021/om100840r

Organometallics 2011, 30, 717–725 717
DOI: 10.1021/om100840r
Reaction of Spiro[2.4]hepta-4,6-diene with Molybdenum(II) Indenyl
Compounds: Effects of Substitution in the Indenyl Ligand
,†,‡
Jan Honzıcek,* Carlos C. Romao,* Maria J. Calhorda, Abhik Mukhopadhyay,
,†
§
ꢀ
~
ꢁ
‡
ꢀ
ꢀ
ꢁ‡
Jaromır Vinklarek, and Zdenka Padelkova
†
´
Instituto de Tecnologia Quımica e Biologica da Universidade Nova de Lisboa, Av. da Repuꢁblica, EAN, 2780-
ꢁ
157, Oeiras, Portugal, ‡Department of General and Inorganic Chemistry, Faculty of Chemical Technology,
§
University of Pardubice, Studentskaꢁ 573, 532 10 Pardubice, Czech Republic, Departamento de Quımica e
´
Bioquımica, CQB, Faculdade de Ciencias da Universidade de Lisboa, 1749-016 Lisboa, Portugal, and
´
REQUIMTE/CQFB, Departamento de Quımica, FCT-UNL, 2829-516 Monte de Caparica, Portugal
^
´
Received August 30, 2010
The series of molybdenum indenyl compounds [(Ind0)Mo(CO)2(NCMe)2][BF4] was prepared, and
their reactivity toward spiro[2.4]hepta-4,6-diene was studied. It was observed that the spiro-
[2.4]hepta-4,6-diene ring opening could be blocked through substitution in the indenyl ring. Hence,
the 2-substituted compound [(η5-C9H6Me)Mo(CO)2(NCMe)2][BF4] and 1,3-disubstituted com-
t
pound [(η5-C9H5 Bu2)Mo(CO)2(NCMe)2][BF4] do not produce the usual ansa-compounds but the
compounds with η4-bonded spiro[2.4]hepta-4,6-diene [(Ind0)(η4-C5H4(CH2)2)Mo(CO)2][BF4]. The
use of 1-substituted compounds [(η5-C9H6R)Mo(CO)2(NCMe)2][BF4] (R = Ph, tBu) or compounds
with less sterically demanding substituents in the 1,3-positions [(η5-C9H5Ph2)Mo(CO)2(NCMe)2]-
[BF4] does not block the ring-opening reaction. These compounds give ansa-molybdenocenes
[(Ind0)(η5-C5H4CH2-η1-CH2)Mo(CO)][BF4] in a manner similar to that for the unsubstituted
analogue. The reaction products were characterized by NMR and IR spectroscopy. Structures of
[(η5-C9H5Ph2)Mo(η3-C3H5)(CO)2], [(η5-C9H6Ph)(η5-C5H4CH2-η1-CH2)Mo(CO)][BF4], and [(η5-
C9H5Ph2)(η5-C5H4CH2-η1-CH2)Mo(CO)][BF4] were determined by single-crystal X-ray analysis.
Scheme 1. Reaction of [Cp0Mo(CO)2(NCMe)2][BF4] (1, Cp0 =
Introduction
Cp; 2, Cp0 = Ind) with Spiro[2.4]hepta-4,6-diene
Molybdenocene dichloride (Cp2MoCl2) has received great
attention, due to its antitumor1 and catalytic activity.2 Aque-
ous solutions of molybdenocene compounds catalyze var-
ious processes, including H/D exchange through C-H
activation,3 transfer hydrogenation,4 nitrile hydration,5
and hydrolysis of carboxylic acid esters,5 phosphate esters,5,6
*To whom correspondence should be addressed. E-mail: jan.
honzicek@upce.cz (J.H.); ccr@itqb.unl.pt (C.C.R.). Fax: þ420/46603
7068 (J.H.); þ351-21-441 12 77 (C.C.R.).
€
€
(1) (a) Kopf-Maier, P.; Leitner, M.; Voigtlander, R.; Kopf, H. Z.
Naturforsch., C 1979, 34, 1174–1176. (b) Abeysinghe, P. M.; Harding,
M. M. Dalton Trans. 2007, 3474–3482. (c) Waern, J. B.; Harding, M. M.
J. Organomet. Chem. 2004, 689, 4655–4668.
and thiophosphinates.7 A part of our research on molyb-
denocenes8,9 involves the quest for new ring-substituted com-
pounds with improved biological and catalytic properties.10
One of the specific synthetic routes giving molybdenum
cyclopentadienyl complexes uses C-C activation of 5,50-
disubstituted cyclopentadienes with molybdenum metal or
carbonyls. The transfer of the alkyl group is accompanied by
aromatization of the cyclopentadienyl ring and oxidation of
the metal center.11,12 This method was found to be suitable
(2) Breno, K. L.; Ahmed, T. J.; Pluth, M. D.; Balzarek, C.; Tyler,
D. R. Coord. Chem. Rev. 2006, 250, 1141–1151.
(3) (a) Balzarek, C.; Tyler, D. R. Angew. Chem., Int. Ed. 1999, 38,
2406–2408. (b) Balzarek, C.; Weakley, T. J. R.; Tyler, D. R. J. Am.
Chem. Soc. 2000, 122, 9427–9434.
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(8) Honzıcek, J.; Paz, F. A. A.; Romao, C. C. Eur. J. Inorg. Chem.
2007, 2827–2838.
(10) Ahmed, T. J.; Tyler, D. R. Organometallics 2008, 27, 2608–2613.
(11) Green, J. C.; Green, M. L. H.; Morley, C. P. J. Organomet.
Chem. 1982, 233, C4–C6.
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(9) Honzıcek, J.; Mukhopadhyay, A.; Silva, T. S.; Romao, M. J.;
~
Romao, C. C. Organometallics 2009, 28, 2871–2879.
(12) King, R. B.; Efraty, A. J. Am. Chem. Soc. 1971, 93, 4950–4952.
r
2011 American Chemical Society
Published on Web 02/03/2011
pubs.acs.org/Organometallics

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Honzıcek et al.
718 Organometallics, Vol. 30, No. 4, 2011
Scheme 2. Synthesis of the Ring-Substituted Indenyl Complexes [(Ind0)Mo(CO)2(NCMe)2][BF4] (10-14)
for synthesis of some Cp* (C5Me5-) metal complexes when
C5Me6 or C5Me5COOMe is used.11,13 However, most of the
attention has been given to reactions with spirocyclic cyclo-
pentadienes which produce ansa-compounds that are suita-
ble precursors for a variety of ring-functionalized compounds.14,15
In our laboratory, the reactivity of spiro[2.4]hepta-4,6-diene
toward the cationic molybdenum complexes [Cp0Mo(CO)2-
(NCMe)2][BF4] (1, Cp0 = Cp; 2, Cp0 = Ind) was inves-
tigated.8 It was observed that the cyclopentadienyl compound
[CpMo(CO)2(NCMe)2][BF4] (1) gives the stable η4-diene com-
plex [Cp(η4-C5H4(CH2)2)Mo(CO)2][BF4] (3), while the in-
denyl analogue [IndMo(CO)2(NCMe)2][BF4] (2) produces
the ring-opening product [Ind(η5-C5H4CH2-η1-CH2)Mo-
(CO)][BF4] (4) in high yield (see Scheme 1).
A theoretical investigation of these reactions has shown
that the discrepancy in the reactivity is a result of activation
through η5-η3 ring slippage that is favorable in the case of
indenyl compounds.16 However, this haptotropic reactivity
enhancement is kinetically controlled and requires a rather
subtle, nonobvious series of structural rearrangements of the
coordination sphere prior to ring opening. Since such re-
arrangements are likely to respond to the presence of sub-
stituents on the indenyl ring, the present study of the
reactivity of spiro[2.4]hepta-4,6-diene with ring-substituted
indenyl complexes [(Ind0)Mo(CO)2(NCMe)2][BF4] was de-
signed to provide a more detailed insight into the mechanism
of the spiro[2.4]hepta-4,6-diene ring-opening reaction.
Figure 1. ORTEP drawing of [(η5-C9H5Ph2)Mo(η3-C3H5)-
(CO)2] (8). The labeling scheme for all non-hydrogen atoms is
shown. Thermal ellipsoids are drawn at the 30% probability
level. Hydrogen atoms of the η3-allyl group have been omitted
for clarity. Selected bond lengths (A) and bond angles (deg):
Mo1-C1 = 1.955(3), Mo1-C2 = 1.943(3), Mo1-C6 =
2.373(2), Mo1-C7 = 2.300(2), Mo1-C8 = 2.326(2), Mo1-C9 =
˚
2.414(2), Mo1-C10
= 2.446(2), Mo1-Cg(C6-C10) =
Results
2.0341(10), C1-O1 = 1.155(3), C2-O2 = 1.152(3); C1-
Mo1-C2 = 80.57(10), Mo1-C2-O2 = 179.3(2), Mo1-C1-
O1 = 178.1(2).
Synthesis of Ring-Substituted Indenyl Complexes. The
cationic indenyl complexes [(Ind0)Mo(CO)2(NCMe)2][BF4]
(10-14) were prepared from [(η3-C3H5)Mo(CO)2(NCMe)2X]
(X = Cl, Br) and the lithium salt of the appropriate indene
using the route developed for the unsubstituted analogue
2 (Scheme 2).17,18
The allyl intermediates [(Ind0)Mo(η3-C3H5)(CO)2] (5, 6, 8,
and 9) were isolated and characterized by spectroscopic
methods. Infrared spectra of these compounds show two bands
in the region of CO stretching at ∼1940 and 1860 cm-1
.
Compounds 5, 6, 8, and 9 form mixtures of exo and endo
isomers in solution, as was evidenced by NMR spectroscopy.
At room temperature, the molar ratios between exo and endo
isomers were found to be 4:1 for 5, 3:1 for 6, 3.4:1 for 8, and 3:1
for 9. The structure of compound 8 was determined by X-ray
analysis (Figure 1).
(13) King, R. B.; Efraty, A. J. Am. Chem. Soc. 1972, 94, 3773–3779.
(14) (a) Raith, A.; Altmann, P.; Cokoja, M.; Herrmann, W. A.;
ꢁ
Kuhn, F. E. Coord. Chem. Rev. 2010, 254, 608–634. (b) Capape, A.;
Raith, A.; Herdtweck, E.; Cokoja, M.; Kuhn, F. E. Adv. Synth. Catal.
ꢁ
2010, 352, 547–556. (c) Capape, A.; Raith, A.; Kuhn, F. E. Adv. Synth.
Catal. 2009, 351, 66–70. (d) Zhao, J.; Jain, K. R.; Herdtweck, E.; Kuhn,
F. E. Dalton Trans. 2007, 5567–5571. (e) Zhao, J.; Herdtweck, E.;
Kuehn, F. E. J. Organomet. Chem. 2006, 691, 2199–2206. (f) Moriarty,
R. M.; Chen, K. M.; Churchill, M. R.; Chang, S. W. Y. J. Am. Chem.
Soc. 1974, 96, 3661–3663. (g) Eilbracht, P. Chem. Ber 1976, 109, 1429–
1435. (h) Eilbracht, P. Chem. Ber.-Recl. 1976, 109, 3136–3141. (i)
Eilbracht, P.; Dahler, P. J. Organomet. Chem. 1977, 127, C48–C50. (j)
Barretta, A.; Chong, K. S.; Cloke, F. G. N.; Feigenbaum, A.; Green,
M. L. H. J. Chem. Soc., Dalton Trans. 1983, 861–864. (k) Green,
M. L. H.; Ohare, D. J. Chem. Soc., Dalton Trans. 1985, 1585–1590. (l)
Chong, K. S.; Green, M. L. H. Organometallics 1982, 1, 1586–1590.
(15) Amor, F.; Royo, P.; Spaniol, T. P.; Okuda, J. J. Organomet.
Chem. 2000, 604, 126–131.
€
€
€
€
Protonation of [(Ind0)Mo(η3-C3H5)(CO)2] (5-9) with
HBF4 in the presence of acetonitrile gives the cationic
complexes [(Ind0)Mo(CO)2(NCMe)2][BF4] (10-14). NMR
measurements prove the coordination of two MeCN ligands
and the presence of the η5-coordinated substituted indenyl
ring. The infrared spectra show two bands in the region of
terminal carbonyls at ∼1960 (vs) and ∼1870 cm-1 (vs) and
two bands of the cyano groups at ∼2310 (m) and ∼2280 cm-1
(m). The broad band of the B-F stretching at ∼1055 cm-1
proves the presence of the BF4 anion. 1,3-Di-tert-butylin-
dene, necessary for the synthesis of 6, was prepared using the
fulvene protocol (see Scheme 3). Condensation of 3-tert-
butylindene with acetone in the presence of KOH gives
3-tert-butyl-1-isopropylideneindene. Subsequent reaction
ꢀ
~
(16) Veiros, L. F.; Honzıcek, J.; Romao, C. C.; Calhorda, M. J. Inorg.
Chim. Acta 2010, 363, 555–561.
(17) Faller, J. W.; Chen, C. C.; Mattina, M. J.; Jakubowski, A.
J. Organomet. Chem. 1973, 52, 361–386.
(18) Ascenso, J. R.; de Azevedo, C. G.; Gonc-alves, I. S.; Herdtweck,
~
E.; Moreno, D. S.; Pessanha, M.; Romao, C. C. Organometallics 1995,
14, 3901–3919.

Article
Organometallics, Vol. 30, No. 4, 2011 719
Scheme 3. Synthesis of 1,3-Di-tert-butylindene
Table 1. Chemical Shifts (ppm) of the CH2Mo Moiety in 1H NMR
Spectra of the ansa-Compounds [(Cp0)Mo(η5-C5H4CH2-η1-
CH2)(CO)][BF4]
Cp0
HA
HB
ref
η5-C5H5
-0.41
-0.07
-0.70
-0.09
-0.49
-0.32
-0.89
-3.21
-3.05
-3.75
-1.63
-2.50
8
8
η5-C9H7 (4)
η5-C9H6 Bu (15a)
t
η5-C9H6Ph (16a)
η5-C9H6Ph (16b)
η5-C9H5Ph2 (18)
Scheme 4. Reaction of Compounds 10 and 11 with
Spiro[2.4]hepta-4,6-diene
HB at much higher field than for its cyclopentadienyl
analogue [(Cp)(η5-C5H4CH2-η1-CH2)Mo(CO)][BF4] (3);
see Table 1. A similar effect was observed for isomers a
and b. The compounds 15a and 16a show the shift of HB
close to the value observed for the indenyl compound 4,
while the shift in compound 16b was found to be similar to
that of the cyclopentadienyl compound 3. These differ-
ences were assigned to the shielding effect of the benzene.
The steric effects cause the monosubstituted compounds
to prefer the conformation with the bulky substituent
in the position above the OC-Mo-CH2 moiety (see
Scheme 4). In this conformation, isomer a has the benzene
ring of the indenyl on the side of the CH2 group, while
isomer b has it on the side of the carbonyl ligand. This
behavior causes the isomers a to exhibit a much stronger effect
of the benzene ring than the isomer b.
with an excess of MeLi followed by hydrolysis produces the
1,3-di-tert-butylindene in 14% overall yield. An alternative
pathway giving 1,3-di-tert-butylindene uses the reaction of
tert-butyl chloride with the lithium salt of 3-tert-butylindene.
Use of this route is limited by very low yields (∼ 3%). Other
substituted indenes were prepared according to literature
procedures.19-22
Reaction of [(Ind0)Mo(CO)2(NCMe)2][BF4] (10-14) with
Spiro[2.4]hepta-4,6-diene. The replacement of MeCN ligands
by spiro[2.4]hepta-4,6-diene leads in most cases to the open-
ing of the cyclopropyl ring and oxidative addition of a C-C
bond to the Mo atom, as shown in the examples of Scheme 4.
The absence of a plane of symmetry in the 1-substituted
indenyl complexes [(Ind0)Mo(CO)2(NCMe)2][BF4] may re-
sult in the appearance of two diastereoisomeric products
(a and b) of the ring-opening reaction. However, in practice,
a good degree of selectivity is seen in the reaction of spiro-
[2.4]hepta-4,6-diene with the tert-butylindenyl compound
10 and the phenyl-substituted compound 11.
Compound 15a was found to be the sole product of the
reaction between 10 and spiro[2.4]hepta-4,6-diene. The phenyl-
substituted analogue 11 gives both possible products (16a,b).
The experiments in CD2Cl2 followed by NMR spectroscopy
have shown that 16a,b appear in the molar ratio 30:1. Multiple
recrystallizations from a CH2Cl2-hexane mixture give pure
isomer 16a.
The diastereoisomers a and b were distinguished on the
basis of 1H NMR measurements. The methylene proton HB
from the group connected to molybdenum was found to be
suitable for this purpose (Scheme 1). Due to the shielding
effect of the benzene ring, the indenyl compound [(Ind)(η5-
C5H4CH2-η1-CH2)Mo(CO)][BF4] (4) shows the signal for
The molecular structure of the compound 16a obtained
from X-ray diffraction analysis (see Figure 2) supports the
NMR spectra assignment.
t
The η4-diene complex [(η5-C9H5 Bu2)(η4-C5H4(CH2)2)-
Mo(CO)2][BF4] (17) is formed upon reaction of the 1,3-di-
t
tert-butyl compound [(η5-C9H5 Bu2)Mo(CO)2(NCMe)2]-
[BF4] (12) with spiro[2.4]hepta-4,6-diene (Scheme 5).
The product is stable at room temperature. The reaction
of the 1,3-diphenyl analogue 13 gives the ansa-compounds
[(η5-C9H5Ph2)(η5-C5H4CH2-η1-CH2)Mo(CO)][BF4] (18) un-
der the same conditions.
Compounds 17 and 18 were characterized by spectro-
1
scopic methods. The H NMR spectrum of 17 shows two
triplets of the cyclopentadiene protons at 5.54 and 4.19 ppm
(3J(1H,1H) = 2.9 Hz) and two triplets of the methylene
groups at 1.36 and 0.67 ppm (3J(1H,1H) = 8.6 Hz). This
pattern is typical for η4-spiro[2.4]hepta-4,6-diene. The ansa-
compounds 18 shows four multiplets of the methylene pro-
tons at 2.62, 2.34, -0.32, and -2.50 ppm. The signals of the
methylene carbons were found at 18.8 and -36.7 ppm. The
presence of only one carbonyl group in compound 18 is
evident from the infrared spectrum. It shows only one band
in the CO stretching region at 2006 cm-1. The molecular
structure of compound 18 was determined by X-ray diffrac-
tion analysis (see Figure 3).
The compound [(η5-C9H6Me)Mo(CO)2(NCMe)2][BF4]
(14) reacts with spiro[2.4]hepta-4,6-diene, giving the η4-diene
complex [(η5-C9H6Me)(η4-C5H4(CH2)2)Mo(CO)2][BF4] (19)
(Scheme 6).
The coordinated spiro[2.4]hepta-4,6-diene gives two trip-
lets of cyclopentadiene at 5.28 and 4.70 ppm (3J(1H,1H) =
2.9 Hz) and two triplets of the methylene groups at 1.16 and
0.52 ppm (3J(1H,1H) = 8.4 Hz). These values are similar to
those observed for the cyclopentadienyl and 1,3-di-tert-buty-
lindenyl analogues [(η5-C5H5)(η4-C5H4(CH2)2)Mo(CO)2]-
(19) Ready, T. E.; Chien, J. C. W.; Rausch, M. D. J. Organomet.
Chem. 1996, 519, 21–28.
(20) Mills, N. S.; Llagostera, K. B.; Tirla, C.; Gordon, S. M.;
Carpenetti, D. J. Org. Chem. 2006, 71, 7940–7946.
(21) Bordwell, F. G.; Drucker, G. E. J. Org. Chem. 1980, 45, 3325–
3328.
t
[BF4] (3)8 and [(η5-C9H5 Bu2)(η4-C5H4(CH2)2)Mo(CO)2]-
(22) Schneider, N.; Huttenloch, M. E.; Stehling, U.; Kirsten, R.;
Schaper, F.; Brintzinger, H. H. Organometallics 1997, 16, 3413–3420.
[BF4] (17), respectively.

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Honzıcek et al.
720 Organometallics, Vol. 30, No. 4, 2011
Figure 2. ORTEP drawing of the two crystallographically independent molecules of [(η5-C9H6Ph)(η5-C5H4CH2-η1-CH2)Mo(CO)]þ
present in the crystal structure of 16a (S and R configurations). The labeling scheme for all non-hydrogen atoms is shown. Thermal
˚
ellipsoids are drawn at the 30% probability level. Selected bond lengths (A) and bond angles (deg): Mo1-C23 = 1.990(3), Mo1-C7 =
2.280(3), Mo1-Cg(C1-C5) = 1.9501(13), Mo1-Cg(C8-C16) = 2.0152(13), Mo1-C1 = 2.294(3), Mo1-C2 = 2.286(3), Mo1-
C3 = 2.290(3), Mo1-C4 = 2.307(3), Mo1-C5 = 2.292(3), Mo1-C8 = 2.369(3), Mo1-C13 = 2.476(3), Mo1-C14 = 2.373(3),
Mo1-C15 = 2.288(3), Mo1-C16 = 2.264(3), C23-O1 = 1.138(4), Mo2-C46 = 2.001(3), Mo2-C30 = 2.286(3), Mo2-Cg-
(C24-C28) = 1.9457(13), Mo2-Cg(C31-C35) = 2.0152(13), Mo2-C24 = 2.287(3), Mo2-C25 = 2.284(3), Mo2-C26 = 2.287(3),
Mo2-C27 = 2.289(3), Mo2-C28 = 2.306(3), Mo2-C31 = 2.382(3), Mo2-C32 = 2.276(3), Mo2-C33 = 2.282(3), Mo2-C34 =
2.332(3), Mo2-C35 = 2.464(3), C46-O2 = 1.136(4); C7-Mo1-C23 = 91.29(12), Cg(C1-C5)-Mo1-Cg(C8-C16) = 145.27(6),
Mo1-C7-C6 = 101.43(18), Mo1-C23-O1 = 177.3(3), C30-Mo2-C46 = 89.42(13), Cg(C24-C28)-Mo2-Cg(C31-C35) =
144.81(6), Mo2-C28-C29 = 101.49(19), Mo2-C46-O2 = 176.7(3).
Scheme 5. Reaction of 1,3-Disubstituted Compounds 12 and 13
with Spiro[2.4]hepta-4,6-diene
Figure 3. ORTEP drawing of the cation [(η5-C9H5Ph2)(η5-
C5H4CH2-η1-CH2)Mo(CO)]þ present in the crystal structure
of 18. The labeling scheme for all non-hydrogen atoms is shown.
Thermal ellipsoids are drawn at the 30% probability level.
Attempts to observe the intermediates of the reaction
˚
Selected bond lengths (A) and bond angles (deg): Mo1-C1 =
1.999(6), Mo1-C29 = 2.297(6), Mo-Cg(C23-C27) = 1.952(3),
Mo-Cg(C2-C10) = 2.009(2), Mo1-C23 = 2.306(6), Mo1-
C24 = 2.282(6), Mo1-C25 = 2.290(6), Mo1-C26 = 2.293(6),
Mo1-C27 = 2.294(6), Mo1-C2 = 2.305(5), Mo1-C3 =
2.295(5), Mo1-C4 = 2.337(5), Mo1-C5 = 2.439(5), Mo1-
C10 = 2.377(5), C1-O1 = 1.126(7); C1-Mo1-C29 = 89.2(3),
Cg(C23-C27)-Mo-Cg(C2-C10) = 143.59(12), Mo1-C29-
C28 = 101.2(4), Mo1-C1-O1 = 175.2(6).
between [(Ind0)Mo(CO)2(NCMe)2][BF4] (2, 10, 11, and 13)
and spiro[2.4]hepta-4,6-diene were unsuccessful. The appro-
priate ansa-compounds appear immediately after mixing the
starting compounds in CD2Cl2 and running the H NMR
spectra as fast as possible.
The compounds with coordinated spiro[2.4]hepta-4,6-
diene [(Ind0)(η4-C5H4(CH2)2)Mo(CO)2][BF4] (17 and 19)
are stable at room temperature. All attempts to force the
spiro[2.4]hepta-4,6-diene ring-opening reaction by heating
or by irradiating their solutions with a tungsten bulb led to
decomposition. None of the expected ansa-compounds were
obtained. Instead, a mixture of intractable products prob-
ably due to the polymerization of spiro[2.4]hepta-4,6-diene
was formed.
1
Crystal Structures. The structure of the allyl complex [(η5-
C9H5Ph2)Mo(η3-C3H5)(CO)2] (8) and the two ansa-com-
pounds [(Ind0)(η5-C5H4CH2-η1-CH2)Mo(CO)][BF4] (16a,
Ind0 = η5-C9H6Ph; 18, Ind0 = η5-C9H5Ph2) were determined

Article
Scheme 6. Reaction of Compound 14 with Spiro[2.4]hepta-
4,6-diene
Organometallics, Vol. 30, No. 4, 2011 721
addition of a C-C bond of the cyclopropyl ring to the Mo(II)
ion. Of course, one might expect some rate variations due to
the presence of the substituents. In fact, it is usually found
that the substitution in the indenyl ring only changes its
reactivity slightly, due to the small electronic effects of the
substituents.31 Surprisingly, though, the experimental data
presented above show that the reactions of spiro[2.4]hepta-
4,6-diene with methyl-, tert-butyl-, and phenyl-substituted
indenyl molybdenum(II) compounds (10-14) are quite sen-
sitive to the presence of substituents on the indenyl ring. The
mechanism of these ring-opening reactions in the absence of
such substituents has been studied in detail by DFT calcu-
lations.16 It was shown that the η5-η3 haptotropic rearran-
gement of the indenyl ligand lowers the barrier of the spiro-
[2.4]hepta-4,6-diene ring-opening reaction and enables the
formation of ansa-compounds. However, this haptotropic
shift is not a sufficient condition to enable the C-C bond
addition to the Mo(II) metal. In fact, the mechanism entails a
number of quite subtle structural rearrangements that are
responsible for the lowering of the energetic barriers of several
of the steps. Part of this mechanism is depicted in Scheme 7, in
accord with the DFT calculations already mentioned.16 Struc-
ture A is the most stable one for the indenyl spiro-diene com-
plexes. However, opening of the cyclopropyl ring from this
structure, even after an η5 f η3 shift of the indenyl ligand, is
hampered by very high activation energies. Several other struc-
tures are easily accessible from A at room temperature by
rotation of the π ligands. Central to this issue is structure B,
where the OC-Mo-CO group is above the condensed benzene
ring of the indenyl ligand and is no longer opposed to it, as in
the more stable conformation A. DFT calculations show that it
is structure B that leads to the lower energy pathway toward
ring opening. In the first step the η5 fη3 haptotropic shift of the
indenyl opens the coordination sphere of the Mo(II) ion and
allows for the oxidative addition of the C-C bond and for-
mation of the new H2C-Mo bond, leading to intermediate C.
Upon loss of the CO which is trans to the new H2C-Mo bond
the 18e count is restored by the η3 f η5 indenyl shift. The
corresponding structure D is only idealized because the whole
process following CO loss takes place simultaneously with the
structural relaxation toward the metallocene-like structure of
the final product E. As depicted in Scheme 8, which is a top-
down view of intermediate B, the cyclopropyl ring must present
itself to the Mo atom from a direction either between the
indenyl substituents R1 and R2 or between the other substitu-
ents R2 and R3.
by X-ray diffraction analysis. Their crystallographic data are
summarized in Table 2. Compound 16a has two crystal-
lographically independent complexes in the unit cell that are
essentially the same. They are shown in Figure 2.
The molecule of compound 8 has distorted-tetrahedral
coordination around Mo(II) with η3-allyl, η5-bonded sub-
stituted indenyl and two carbonyl ligands (Figure 1). The
˚
Mo-C(CO) bond lengths are 1.943(3) and 1.955(3) A. The
C(CO)-Mo-C(CO) bond angle was found to be 80.57(10)°.
The distance between the molybdenum atom and the cen-
5
˚
troid of the η -bonded indenyl is 2.0341(10) A. The Mo-C-
(Ind) distances vary between 2.300(2) and 2.446(2) A. The
˚
phenyl groups are not coplanar with the indenyl framework.
The interplanar angles between phenyl groups and the five-
membered ring of the indenyl group are 39.36(12) and
40.16(13)°.
The cations of compounds 16a and 18 have a bent-
metallocene structure with the ligands η5:η1-cyclopentadie-
nidoethyl, η5-bonded substituted indenyl, and one carbonyl.
They make a distorted tetrahedron around Mo(IV). The
angle Cg(Cp)-Mo-Cg(Ind) was found to be 145.27(6)° for
16a(A), 144.81(6)° for 16a(B), and 143.59(12)° for 18. The
bond angle C(CO)-Mo-C(CH2) is 91.29(12)° for 16a(A),
89.42(13)° for 16a(B), and 89.2(3)° for 18. These parameters
are similar to those previously obtained for the unsubstituted
analogue [(Ind)(η5-C5H4CH2-η1-CH2)Mo(CO)][BF4] (Cg-
(Ind)-Mo-Cg(Cp) = 145.43(2), 145.43(2)°; C(CO)-Mo-
C(CH2) = 88.5(2), 92.4(2)°).8 The distance between the moly-
bdenum atom and the centroid of the cyclopentadienyl ligand
˚
(1.946(1)-1.952(3) A) and the bond lengths Mo-C(CH2)
˚
(2.280(3)-2.297(6) A) are in line with those for other moly-
bdenum(IV) compounds containing an η5:η1-cyclopentadieni-
˚
doethyl ligand (Mo-Cg(Cp) = 1.934-1.983(4) A, Mo-
C(CH2) = 2.268(5)-2.281(7) A).8,23 The bond lengths Mo-
˚
˚
C(CO) were found to be 1.990(3) A for 16a(A), 2.001(3) A for
˚
˚
16a(B), and 1.999(6) A for 18. The distances between moly-
bdenum and the five-membered ring of indenyl are 2.0152(13)
Both corresponding conformers B1 and B3 are equally
accessible and reactive when R1 = R2 = R3 = H. However,
when bulkier groups are introduced at these positions, dif-
ferences may arise. When position R1 is occupied by a bulky
group such as tBu, conformer B1 is disfavored and only one
product can be formed: that arising from conformer B3. Fol-
lowing the expulsion of the CO trans to the new H2C-Mo bond
and the rotation of the new Cp0 ligand (counterclockwise in this
case) to form the E bent-metallocene-like structure, it is clear
that the new Mo-CH2 bond will be on the same side as R1.This
is exactly what is observed in the formation of 15a (Scheme 4).
In the case where R1 = Ph, a much less bulky substituent than
tBu, both conformers B1 and B3 can react. However, the pro-
duct resulting from conformer B3 will obviously be favored
over that resulting from the more hindered B1. This is experi-
mentally observed and summarized in Scheme 4 and Figure 2.
The product resulting from conformer B3 (16a, with the new
H2C-Mo bond on the same side as the Ph substituent) is
˚
˚
˚
A for 16a(A), 2.0063(12) A for 16a(B), and 2.009(2) A for 18.
The phenyl groups are not coplanar with the indenyl frame-
work. The interplanar angles between phenyl groups and the
five-membered ring of indenyl vary between 19.4(3) and
44.7(3)°.
Discussion
In light of our previous studies, one would tend to expect
that the reactions described here, between the substituted-
indenyl complexes [(Ind0)Mo(CO)2(NCMe)2][BF4] and spir-
o[2.4]hepta-4,6-diene, would all end in the corresponding
ansa-metallocenes as a result of the intramolecular oxidative
(23) (a) Barretta, A.; Cloke, F. G. N.; Feigenbaum, A.; Green,
M. L. H.; Gourdon, A.; Prout, K. J. Chem. Soc., Chem. Commun.
1981, 156–158. (b) Kreiter, C. G.; Wenz, M.; Bell, P. J. Organomet.
Chem. 1990, 394, 195–211.

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Honzıcek et al.
722 Organometallics, Vol. 30, No. 4, 2011
Table 2. Crystallographic Data of Molybdenum Compounds
9
16a
18
formula
C
460.36
296(2)
monoclinic
P21/n
12.6539(3)
11.5810(3)
14.7388(3)
111.286(1)
2012.55(8)
4
1.519
0.671
936
26H20MoO2
C23H19BF4MoO
494.14
296(2)
monoclinic
P21/c
10.6558(4)
18.9207(8)
19.6544(8)
92.642 (1)
3958.4(3)
C29H23BF4MoO
570.22
150(1)
monoclinic
P21/c
9.6430(8)
11.9781(6)
22.1769(17)
110.86(1)
2393.6(3)
4
1.582
formula wt
temp (K)
cryst syst
space group
˚
a (A)
˚
b (A)
˚
c (A)
β (deg)
3
V (A )
˚
Z
8
1.658
0.712
1984
Dc (g cm-3
)
μ (mm-1
F(000)
)
0.600
1152
cryst size (mm)
θ range (deg)
index ranges
0.18 ꢀ 0.16 ꢀ 0.06
1.82-30.54
-18 e h e 18
-15 e k e 16
-21 e l e 21
36 519
0.30 ꢀ 0.18 ꢀ 0.04
1.49-25.00
-12 e h e 10
-22 e k e 22
-23 e l e 23
47 438
0.59 ꢀ 0.52 ꢀ 0.30
1.96-26.6
-11 e h e 12
-14 e k e 15
-28 e l e 27
15 334
no. of rflns collected
no. of indep rflns
no. of params
5223 (Rint = 0.0312)
272
6096 (Rint = 0.0292)
536
3474 (Rint = 0.0714)
325
final R indices (I > 2σ(I)) a,b
R1 = 0.0276
wR2 = 0.0657
R1 = 0.0393
wR2 = 0.0702
0.540, -0.712
P
R1 = 0.0264
wR2 = 0.0659
R1 = 0.0305
wR2 = 0.0754
1.181, -0.481
R1 = 0.0565
wR2 = 0.1210
R1 = 0.0968
wR2 = 0.1479
1.037, -0.922
final R indices (all data) a,b
-3
˚
largest diff peak and hole (e A
)
P
P
P
a R1 = |||Fo| - |Fc||/ |Fo|. b wR2 = ( [w(Fo2 - Fc2)2]/ [w(Fo2)2])1/2
.
Scheme 7. Mechanism of the Spiro[2.4]hepta-4,6-diene
Ring-Opening Reaction According to Ref 16a
Scheme 8. Top-Down View of Intermediate Ba
a The spiro-diene is on top with the cyclopropyl ring on a plane per-
pendicular to the paper projecting from the sp3 carbon. Immediately
below the diene plane lies the plane formed by the OC-Mo-CO atoms.
The indenyl ring with substituents R1-R3 forms the lower, bottom
plane. The BF4- counterion is omitted.
an intermediate such as B hinders the approach of the C3 ring to
the Mo and blocks the reaction. This explains the stability of 19
to ring opening and formation of the corresponding ansa-
metallocene. This explanation may be corroborated by DFT
calculations using indenyl substituted in the R2 position.
The chemistry just described can be readily explained by
the previously published computational predictions on the
mechanism of C-C activation of spiro-heptadienes coordi-
nated to [IndMo(CO)2]þ fragments. Interestingly, the stereo-
selectivity of the reactions performed with substituents on
the indenyl ring was shown to be fully compatible with the
structural characteristics of the reaction intermediates that
are required by the computational results in order to obtain a
reaction pathway with feasible activation energies.
a Structure D is idealized and is only added to help identify the
haptotropic shifts accompanying the reaction. The BF4- counterion is
omitted.
formed in great excess (30:1) over the product resulting from
conformer B1 (16b), which would have the Mo-CO bond over
Conclusions
t
t
the R1 = Bu substituent. When R1 = R3 = Bu, both
conformers are hindered and the reaction does not proceed
because the C3 ring is in a position unfavorable to approach the
Mo ion (see Scheme 5: 17 is stable). Of course, when R1 = R3 =
Ph the reaction takes place and only one product (18) is formed,
since there is no energetic difference between B1 and B3 (see
Scheme 5). We propose that the occupation of the R2 position in
The reaction of several ring-substituted Mo(II) cationic
complexes of formula [(Ind0)Mo(CO)2(NCMe)2][BF4] with
spiro[2.4]hepta-4,6-diene led to a number of different out-
comes, depending on the nature and position of those sub-
stituents. In the cases where the oxidative addition of the
C-C bond of the cyclopropyl ring to the Mo(II) central ion

Article
Organometallics, Vol. 30, No. 4, 2011 723
takes place, the reactions occur within the time of mixing and
no intermediates could be detected. When the substituent is
in the 1-position (Schemes 4 and 8), two diastereoisomers are
produced (a and b; see Scheme 4) but the formation of the
isomer a is highly preferred and becomes exclusive when the
bulk of the substituent increases to that of tBu. When posi-
tions 1 and 3 are occupied simultaneously by bulky tBu sub-
stituents, the oxidative addition of the cyclopropyl ring
is sterically hindered and the very stable η4-diene complex
17 (Scheme 5) is obtained. Similar substitution using Ph
instead of tBu already allows ready oxidative addition
and formation of only one compound (18). The presence of
one Me group in the 2-position again prevents oxidative
addition and leads to the stable η4-diene complex 19. This
unexpectedly strong reaction discrimination can be easily
accommodated by the structural requirements of the C-C
oxidative addition reaction that have been previously
reported and are elicited by the fluxionality oþf the cationic
[(Ind0)Mo(η4-spiro[2.4]hepta-4,6-diene)(CO)2] .
7.12 (t, 3J(1H,1H) = 7.5 Hz, 1H, C9H6), 6.19 (s, 1H, C9H6), 3.14
t
t
(s, 1H, C9H6), 1.37 (s, 9H, Bu), 1.00 (s, 9H, Bu). 13C NMR
(CDCl3; 101 MHz): δ 152.7, 148.0, 144.7 (3Cipso), 130.3, 125.9,
125.2, 123.7, 122.1 (5C, C9H6), 58.8 (1C, C9H6), 34.5, 33.2
(2Cipso, tBu), 29.7, 28.7 (2 ꢀ 3C, tBu).
t
Synthesis of [(η3-C3H5)(η5-C9H6 Bu)Mo(CO)2] (5). 3-tert-
Butylindene (0.86 g, 5 mmol) was diluted with 30 mL of THF,
cooled to 0 °C, and treated dropwise with 3.1 mL of nBuLi
(1.6 mol L-1). The reaction mixture was stirred overnight and
then added dropwise to a THF solution of [(η3-C3H5)Mo(CO)2-
(NCMe)2Cl] (1.55 g, 5 mmol) precooled to -80 °C. The reaction
mixture was stirred at room temperature overnight and then
vacuum-evaporated to dryness. The solid residue was extracted
with hexane at 60 °C. The yellow extract was evaporated to dry-
ness in vacuo. The crude product was recrystallized from hexane
at -100 °C and dried in vacuo, giving a yellow powder. Yield:
1.42 g (3.9 mmol, 78%). Anal. Calcd for C18H20MoO2: C, 59.34;
H, 5.53. Found: C, 59.23; H, 5.75. 1H NMR (CDCl3; 400 MHz;
4:1 mixture of 5a (exo-C3H5) and 5b (endo-C3H5)): δ 7.60
3
(m, 1H, C9H6), 7.35-7.20 (m, 3H, C9H6), 6.13 (d, J(1H,1H)
= 2.8 Hz, 1H of a, C9H6), 6.03 (d, 3J(1H,1H) = 2.9 Hz, 1H of b,
C9H6), 5.81 (d, 3J(1H,1H) = 2.8 Hz, 1H of a, C9H6), 5.77
(d, 3J(1H,1H) = 2.9 Hz, 1H of b, C9H6), 3.73 (dd, J(1H,1H) =
6.5 Hz, J(1H,1H) = 2.7 Hz, 1H of b, syn of C3H5), 3.65
(dd, J(1H,1H) = 6.5 Hz, J(1H,1H) = 2.7 Hz, 1H of b, syn of
C3H5), 3.54 (m, 1H of b, meso of C3H5), 2.61 (d, J(1H,1H) =
7.3 Hz, 1H of a, syn of C3H5), 2.48 (d, J(1H,1H) = 7.3 Hz, 1H of
a, syn of C3H5), 1.76 (s, 9H, tBu), 1.24 (d, J(1H,1H) = 11.3 Hz,
1H of a, anti of C3H5), 1.11 (d, J(1H,1H) = 11.3 Hz, 1H of a, anti
of C3H5), 0.01 (m, 1H of a, meso of C3H5), -0.22 (d, J(1H,1H) =
11.0 Hz, 1H of b, anti of C3H5), -0.89 (d, J(1H,1H) = 11.0 Hz,
1H of b, anti of C3H5). FTIR (KBr, cm-1): 1940 vs (νa(CO)),
1860 vs (νs(CO)).
Experimental Section
Methods and Materials. All operations were performed under
nitrogen using conventional Schlenk-line techniques. The sol-
vents were purified and dried by standard methods.24 Spiro-
[2.4]hepta-4,6-diene,15 3-tert-butylindene,19 3-phenylindene,20
1,3-diphenylindene,21 [(η3-C3H5)Mo(CO)2(NCMe)2Cl],17 [(η3-
C3H5)Mo(CO)2(NCMe)2Br],25 and [IndMo(CO)2(NCMe)2][B-
F4] (2)18 were prepared according to literature procedures.
Positive-ion electrospray ionization (ESI) mass spectra were
recorded on an API-ION TRAP instrument (PO 03 MS). Sam-
ples were measured in CH2Cl2 solution. The molybdenum-
containing ions had a clearly visible metal isotope pattern,
arising from the distribution 92Mo 14.84%, 94Mo 9.25%, 95Mo
15.92%, 96Mo 16.68%, 97Mo 9.55%, 98Mo 24.13%, and 100Mo
9.63%.26 Spectra obtained were computer-simulated (WSearch32
2005). Mass peaks listed refer to fragments with the isotopes 1H,
11B, 12C, 14N, 16O, 19F, and 98Mo. 1H and 13C{1H} NMR spectra
were measured in CDCl3 solutions on a Bruker Avance 400 spec-
trometer at room temperature. Chemical shifts are given in ppm
relative to TMS. IR spectra were recorded in the 4000-440 cm-1
region (step 2 cm-1) on a Mattson 7000 FT-IR spectrometer using
KBr pellets.
Synthesis of [(η3-C3H5)(η5-C9H6Ph)Mo(CO)2] (6). The reac-
tion was carried out as was described for compound 5, but with
3-phenylindene (0.96 g, 5 mmol). The orange oil of the crude
product was used for the next reaction without further purifica-
tion. Yield: 1.52 g (3.9 mmol, 79%). 1H NMR (CDCl3; 400 MHz;
3:1 mixture of 6a (exo-C3H5) and 6b (endo-C3H5)): δ 7.72-6.95
(m, 5H of C6H5 and 4H of C9H6), 6.04 (d, 3J(1H,1H) = 2.8 Hz, 1H
3
of a, C9H6), 6.01 (d, J(1H,1H) = 2.8 Hz, 1H of a, C9H6), 5.95
(s, 2H of b, C9H6), 3.50-3.30 (m, 3H of b, C3H5), 2.34 (d,
J(1H,1H) = 7.2 Hz, 1H of a, syn of C3H5), 2.07 (d, J(1H,1H) =
7.2 Hz, 1H of a, syn of C3H5), 0.94(d, J(1H,1H) = 11.1 Hz, 1H of a,
anti of C3H5), 0.84 (d, J(1H,1H) = 11.1 Hz, 1H of a, anti of C3H5),
0.68 (m, 1H of a, meso of C3H5), -0.42 (d, J(1H,1H) = 10.7 Hz, 1H
of b, anti of C3H5), -0.72 (d, J(1H,1H) = 10.7 Hz, 1H of b, anti of
C3H5). FTIR (KBr, cm-1): 1940 vs (νa(CO)), 1856 vs (νs(CO)).
Synthesis of [(η3-C3H5)(η5-C9H5Ph2)Mo(CO)2] (8). The reac-
tion was carried out as was described for compound 5, but with
1,3-diphenylindene (1.34 g, 5 mmol). The crude product was
recrystallized from hexane and dried in vacuo, giving a yellow
powder. Yield: 1.54 g (3.3 mmol, 67%). Anal. Calcd for C26H20-
Synthesis of 3-tert-Butyl-1-isopropylideneindene. A solution of
3-tert-butylindene (8.61 g, 50 mmol) and acetone (8 mL, 110 mmol)
in 100 mL of methanol was treated with crushed KOH pellets (5 g,
90 mmol). The mixture was refluxed overnight, giving an orange oil
after workup. Vacuum distillation of the crude product gave a
yellow oil (bp 120 °C; 100 Pa). Yield: 8.07 g (38 mmol, 76%). 1H
3
NMR (CDCl3; 400 MHz): δ 7.72 (d, J(1H,1H) = 7.4 Hz, 1H,
3
C9H5), 7.56 (d, J(1H,1H) = 7.5 Hz, 1H, C9H5), 7.16 (m, 2H,
C9H5), 6.52 (s, 1H, C9H5), 2.34, 2.21 (2 ꢀ s, CH3), 1.39 (s, 9H, tBu).
1
MoO2: C, 67.83; H, 4.38. Found: C, 67.94; H, 4.21. H NMR
13C NMR (CDCl3; 101 MHz): δ 150.4, 142.7, 140.1, 137.8, 135.2
(CDCl3; 400 MHz; 3.4:1 mixture of 8a (exo-C3H5) and 8b (endo-
C3H5)): δ 7.78-7.05 (m, 10H of C6H5 and 4H of C9H5), 6.37
(s, 1H of a, C9H5), 6.35 (s, 1H of b, C9H5), 3.40 (d, J(1H,1H) =
6.3 Hz, 2H of b, syn of C3H5), 3.33 (m, 1H of b, meso of C3H5),
2.17 (d, J(1H,1H) = 7.2 Hz, 2H of a, syn of C3H5), 1.11 (m, 1H of
a, meso of C3H5), 0.88 (d, J(1H,1H) = 10.9 Hz, 2H of a, anti of
C3H5), -0.32 (d, J(1H,1H) = 10.7 Hz, 2H of b, anti of C3H5).
FTIR (KBr, cm-1): 1946 vs (νa(CO)), 1854 vs (νs(CO)). Crystals
suitable for X-ray analysis were obtained upon cooling of the
saturated hexane solution from room temperature to -10 °C.
Synthesis of [(η3-C3H5)(η5-C9H6Me)Mo(CO)2] (9). The reac-
tion was carried out as was described for compound 5, but with
2-methylindene (0.65 g, 5 mmol). The crude product was recrys-
tallized from Et2O/hexane at low temperature and dried in
vacuo, giving a yellow powder. Yield: 0.95 g (2.9 g, 59%). Anal.
Calcd for C15H14MoO2: C, 55.91; H, 4.38. Found: C, 55.81;
(5Cipso), 125.5, 124.2, 123.7, 122.0, 121.5 (5C, C9H5), 33.2 (Cipso
tBu), 29.8 (3C, tBu), 24.9, 23.0 (2C, CH3).
,
Synthesis of 1,3-Di-tert-butylindene. A solution of 3-tert-
butyl-1-isopropylideneindene (8.07 g, 38 mmol) in THF was
treated with methyllithium (60 mmol) and refluxed overnight.
The reaction mixture was treated with water and extracted with
hexane, giving a yellow oil after workup. Vacuum distillation of
the crude product gave a pale yellow oil (bp 100 °C; 100 Pa).
1
Yield: 1.62 g (7 mmol, 18%). H NMR (CDCl3; 400 MHz):
δ 7.55 (m, 2H, C9H6), 7.25 (t, 3J(1H,1H) = 7.4 Hz, 1H, C9H6),
(24) Armarego, W. L. F.; Perrin, D. D. In Purification of Laboratory
Chemicals; Butterworth-Heinemann: Oxford, U.K., 1996.
(25) Dieck, H. T.; Friedel, H. J. Organomet. Chem. 1968, 14, 375–385.
(26) Vocke, R. D. Pure Appl. Chem. 1999, 71, 1593–1607.

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Honzıcek et al.
724 Organometallics, Vol. 30, No. 4, 2011
1
H, 4.56. H NMR (CDCl3; 400 MHz; 3:1 mixture of 9a (exo-
giving an orange powder. Yield: 1.47 g (2.7 mmol, 54%). Anal.
Calcd for C23H29BF4MoN2O2: C, 50.39; H, 5.33; N, 5.11. Found:
C, 50.24; H, 5.21; N, 5.39. Positive-ion MS: m/z 422 [M -
C3H5) and 9b (endo-C3H5)): δ 7.05-6.85 (m, 4H of C9H6), 5.92
(s, 1H of a, C9H6), 3.43 (d, J(1H,1H) = 6.4 Hz, 2H of b, syn of
C3H5), 3.27 (m, 1H of b, meso of C3H5), 2.36 (3H, CH3), 2.27
(d, J(1H,1H) = 7.3 Hz, 2H of a, syn of C3H5), 0.88 (d,
J(1H,1H) = 11.1 Hz, 2H of a, anti of C3H5), 0.19 (m, 1H of a,
meso of C3H5), -0.88 (d, J(1H,1H) = 11.0 Hz, 2H of b, anti of
C3H5). FTIR (KBr, cm-1): 1945 vs (νa(CO))], 1858 vs (νs(CO)).
1
MeCN]þ. Negative-ion MS: m/z 87 [BF4]-. H NMR (CDCl3;
400 MHz): δ 7.80 (m, 2H, C9H5), 7.58 (m, 2H, C9H5), 4.75 (s, 1H,
C9H5), 2.41(s, 6H, CH3CN), 2.41 (s, 18H, tBu). 13CNMR(CDCl3;
101 MHz): δ 252.1 (2C, CO), 138.8 (2C, CH3CN), 130.8, 127.7
(2C, C9H5), 118.9 (2Cipso, C9H5), 110.4 (2Cipso, C9H5), 87.1
(1C, C9H5), 33.1 (2Cipso, tBu), 31.6 (6C, tBu), 4.3 (2C, CH3CN).
FTIR (KBr, cm-1): 2315 m [νa(CN)], 2289 m [νs(CN)], 1960 vs
[νa(CO)], 1882 vs [νs(CO)], 1056 vs-br [νs(BF)].
Synthesis of [(η5-C9H6 Bu)Mo(CO)2(NCMe)2][BF4] (10). [(η3-
t
t
C3H5)(η5-C9H6 Bu)Mo(CO)2] (5; 1.30 g, 3.6 mmol) was dis-
solved in a CH2Cl2/MeCN (1/10) mixture, cooled to 0 °C, and
treated with 1 equiv of HBF4 Et2O. The solution immediately
Synthesis of [(η5-C9H5Ph2)Mo(CO)2(NCMe)2][BF4] (13). The
reaction was carried out as was described for compound 10, but
with [(η3-C3H5)(η5-C9H5Ph2)Mo(CO)2] (8; 1.45 g, 3.1 mmol).
The crude product was recrystallized from CH2Cl2/hexane,
washed with hexane, and dried in vacuo, giving an orange powder.
Yield: 1.63 g (2.8 mmol, 88%). Anal. Calcd for C27H21BF4Mo-
N2O2: C, 55.13; H, 3.60; N, 4.76. Found: C, 54.96; H, 3.23; N, 4.57.
Positive-ion MS: m/z462 [M - MeCN]þ. Negative-ion MS: m/z 87
[BF4]-. 1H NMR (CDCl3; 400 MHz): δ 7.89 (m, 2H, C9H5), 7.69
(m, 2H, C9H5), 7.63 (d, J(1H,1H) = 7.4 Hz, 4H, C6H5), 7.52-7.40
(m, 6H, C6H5), 5.75 (s, 1H, C9H5), 2.51 (s, 6H, CH3CN). FTIR
(KBr, cm-1): 2319 m (νa(CN)), 2286 m (νs(CN)), 1972 vs (νa(CO)),
1903 vs (νs(CO)), 1056 vs-br (νs(BF)).
3
changed color from yellow to dark red. After 10 min the reaction
mixture was warmed to room temperature and stirred for an
additional 1 h. The reaction mixture was concentrated in vacuo
to ∼3 mL, and Et2O was added to precipitate the red powder.
The crude product was recrystallized from CH2Cl2/hexane,
washed with hexane, and dried in vacuo, giving an orange
powder. Yield: 1.60 g (3.3 mmol, 91%). Anal. Calcd for
C19H21BF4MoN2O2: C, 46.37; H, 4.30; N, 5.69. Found: C,
46.25; H, 4.31; N, 5.88. Positive-ion MS: m/z 366 [M - MeCN]þ.
Negative-ion MS: m/z 87 [BF4]-. 1H NMR (CDCl3; 400 MHz):
3
δ 7.80 (d, J(1H,1H) = 8.6 Hz, 1H, C9H6), 7.63-7.52 (m, 3H,
3
C9H6), 5.87 (d, 3J(1H,1H) = 2.6 Hz, 1H, C9H6), 4.85(d,
Synthesis of [(η5-C9H6Me)Mo(CO)2(NCMe)2][BF4] (14). The
reaction was carried out as was described for compound 10, but
with [(η3-C3H5)(η5-C9H6Me)Mo(CO)2] (9; 0.80 g, 2.5 mmol).
The crude product was recrystallized from CH2Cl2/hexane,
washed with hexane, and dried in vacuo, giving an orange powder.
Yield: 1.02 g (2.3 mmol, 91%). Anal. Calcd for C16H15BF4Mo-
N2O2: C, 42.70; H, 3.36; N, 6.22. Found: C, 42.51; H, 3.14; N, 6.01.
Positive-ion MS: m/z324 [M - MeCN]þ. Negative-ion MS: m/z 87
[BF4]-. 1H NMR (CDCl3; 400 MHz): δ 7.51 (m, 4H, C9H6), 5.90
(s, 2H, C9H6), 2.43 (s, 6H, CH3CN), 1.88 (s, 3H, CH3). 13C NMR
(CDCl3; 101 MHz): δ 249.7 (2C, CO), 139.9 (2C, CH3CN), 131.3
(2C, C9H6), 126.2 (2C, C9H6), 118.4 (2Cipso, C9H6), 78.6 (2C,
C9H6), 110.4 (2Cipso, C9H5), 108.7 (1Cipso, C9H6), 15.5 (1C, CH3),
4.5 (2C, CH3CN). FTIR (KBr, cm-1): 2293 m (νa(CN)), 2253 m
(νs(CN)), 1948 vs (νa(CO)), 1875 vs (νs(CO)), 1060 vs-br (νs(BF)).
J(1H,1H) = 2.7 Hz, 1H, C9H6), 2.42, 2.41 (2 ꢀ s, 6H, CH3CN),
1.42 (s, 9H, Bu). 13C NMR (CDCl3; 101 MHz): δ 250.3,
248.6 (2C, CO), 139.6, 138.3 (2C, CH3CN), 131.9, 130.6,
t
127.6, 126.7 (4C, C9H6), 119.0 (2Cipso, C9H6), 113.0 (Cipso
,
t
t
C9H6), 87.6, 74.4 (2C, C9H6), 33.2 (Cipso, Bu), 31.5 (3C, Bu),
4.4, 4.2 (2C, CH3CN). FTIR (KBr, cm-1): 2287 m (νa(CN)),
2252 m (νs(CN)), 1959 vs (νa(CO)), 1865 vs (νs(CO)), 1055 vs-br
(νs(BF)).
Synthesis of [(η5-C9H6Ph)Mo(CO)2(NCMe)2][BF4] (11). The
reaction was carried out as was described for compound 10, but
with [(η3-C3H5)(η5-C9H6Ph)Mo(CO)2] (6; 1.40 g, 3.6 mmol).
The crude product was recrystallized from CH2Cl2/hexane,
washed with hexane, and dried in vacuo, giving an orange
powder. Yield: 1.62 g (3.2 mmol, 87%). Anal. Calcd for
C21H17BF4MoN2O2: C, 49.25; H, 3.35; N, 5.47. Found: C,
49.34; H, 3.58; N, 5.22. Positive-ion MS: m/z 386 [M - MeCN]þ.
Negative-ion MS: m/z 87 [BF4]-. 1H NMR (CDCl3; 400 MHz):
δ 7.87 (d, 3J(1H,1H) = 8.4 Hz, 1H, C9H6), 7.67-7.37 (m, 3H of
C9H6 and 5H of C6H5), 6.04 (d, 3J(1H,1H) = 2.6 Hz, 1H, C9H6),
5.37 (d, 3J(1H,1H) = 2.7 Hz, 1H, C9H6), 2.47, 2.46 (2 ꢀ s, 6H,
CH3CN). 13C NMR (CDCl3; 101 MHz): δ 248.1, 247.0 (2C,
CO), 140.2, 139.4 (2C, CH3CN), 132.9 (Cipso, C6H5), 131.9,
131.4 (2C, C9H6), 129.4 (2C, C6H5), 129.3 (1C, C6H5), 128.6 (2C,
C6H5), 127.1, 125.5 (2C, C9H6), 117.7 (2Cipso, C9H6), 101.5
(Cipso, C9H6), 88.8, 76.3 (2C, C9H6), 4.6, 4.5 (2C, CH3CN).
FTIR (KBr, cm-1): 2310 m (νa(CN)), 2279 m (νs(CN)), 1962 vs
(νa(CO)), 1874 vs (νs(CO)), 1060 vs-br (νs(BF)).
t
Synthesis of [(η5-C9H6 Bu)(η5-C5H4CH2-η1-CH2)Mo(CO)]-
t
[BF4] (15). A solution of [(η5-C9H6 Bu)Mo(CO)2(NCMe)2][BF4]
(10; 0.20 g, 0.4 mmol) in CH2Cl2 (20 mL) was treated with an
excess of spiro[2.4]hepta-4,6-diene (0.1 g, 1.1 mmol). After it was
stirred for 15 min, the reaction mixture was concentrated in
vacuo to ca. 3 mL. Addition of Et2O precipitated an orange
powder that was recrystallized from CH2Cl2/Et2O. Yield: 0.18 g
(0.38 mmol, 93%). Anal. Calcd for C21H23BF4MoO: C, 53.19;
H, 4.89. Found: C, 53.36; H, 4.73. Positive-ion MS: m/z 389
[M]þ. Negative-ion MS: m/z 87 [BF4]-. 1H NMR (CDCl3;
3
400 MHz): δ 7.67 (d, J(1H,1H) = 8.5 Hz, 1H, C9H6), 7.50-
7.42 (m, 2H, C9H6), 7.32 (m, 1H, C9H6), 6.50 (m, 1H, C5H4),
6.38 (d, 3J(1H,1H) = 3.5 Hz, 1H, C9H6), 5.63 (d, 3J(1H,1H) =
3.5 Hz, 1H, C9H6), 5.56, 4.90, 4.73 (3 ꢀ m, 3H, C5H4), 2.54
(m, 6 lines, 1H, CH2CH2Mo), 2.31 (m, 6 lines, 1H, CH2CH2-
t
Synthesis of [(η5-C9H5 Bu2)Mo(CO)2(NCMe)2][BF4] (12).
1,3-Di-tert-butylindene (1.14 g, 5 mmol) was diluted with 30 mL
of THF, cooled to 0 °C, and treated dropwise with 3.1 mL of nBuLi
(1.6 mol L-1). The reaction mixture was stirred overnight and then
added dropwise to a THF solution of [(η3-C3H5)Mo(CO)2-
(NCMe)2Cl] (1.55 g, 5 mmol) precooled to -80 °C. The reaction
mixture was stirred at room temperature overnight and then
vacuum-evaporated to dryness. The solid residue was extracted
with hexane at 60 °C. The yellow extract was evaporated to dryness
in vacuo, recrystallized from Et2O/hexane at -60 °C, and dried
in vacuo, giving a yellow powder. The crude [(η3-C3H5)(η5-C9H5-
tBu2)Mo(CO)2] (7; 1.5 g, 3.5 mmol) was dissolved in a CH2Cl2/
MeCN (1/10) mixture, cooled to 0 °C, and treated with 1 equiv of
t
Mo), 1.44 (s, 9H, Bu), -0.70 (m, 5 lines, 1H, CH2CH2Mo),
-3.05 (m, 7 lines, 1H, CH2CH2Mo). 13C NMR (CDCl3;
101 MHz): δ 228.5 (1C, CO), 131.6, 130.0, 127.5, 124.3 (4C,
C9H6), 117.2, 112.5, 110.5 (3Cipso, C9H6), 97.1, 92.7, 90.1 (3C,
C5H4), 84.9 (1C, C9H6), 81.6 (1C, C5H4), 81.4 (1C, C9H6), 80.6
t
t
(Cipso, C5H4), 33.8 (Cipso, Bu), 31.5 (3C, Bu), 18.6 (1C, CH2-
CH2Mo), -38.5 (1C, CH2CH2Mo). FTIR (KBr, cm-1): 1999 vs
(ν(CO)), 1056 vs-br (νs(BF)).
Synthesis of [(η5-C9H6Ph)(η5-C5H4CH2-η1-CH2)Mo(CO)]-
[BF4] (16). The reaction was carried out as was described for
compound 15, but with [(η5-C9H6Ph)Mo(CO)2(NCMe)2][BF4]
(11; 0.20 g, 0.4 mmol). The product recrystallized from CH2Cl2/
Et2O contains a 30:1 mixture of 16a and 16b. Repeated recrys-
tallization from a CH2Cl2/hexane mixture gives a pure sample of
16a. Yield: 0.17 g (0.34 mmol, 88%). Anal. Calcd for C23H19-
BF4MoO: C, 55.90; H, 3.88. Found: C, 55.61; H, 3.72. Positive-ion
HBF4 Et2O. The solution immediately changed color from yellow
3
to dark red. After 10 min the reaction mixture was warmed to room
temperature and stirred for an additional 1 h. The reaction mixture
was concentrated in vacuo to ∼3 mL, and Et2O was added to
precipitate the red powder. The crude product was recrystallized
from CH2Cl2/hexane, washed with hexane, and dried in vacuo,

Article
Organometallics, Vol. 30, No. 4, 2011 725
MS: m/z 409 [M]þ. Negative-ion MS: m/z 87 [BF4]-. 1H
Table 2. Programs used: data collection, Smart (Bruker 2003);
data reduction, Saint (Bruker version 6); absorption correction,
SADABS version 2.10 (Bruker AXS 2001). Structure solution
and refinement was done using SHELXTL (Bruker 2003). The
structure was solved by direct methods and refined by full-
matrix least-squares methods on F2. The non-hydrogen atoms
were refined anisotropically. There is a disordered carbon atom
of the C-H fragment originating from the allyl moiety. This
disorder was solved by standard constraint and restraint proce-
dures in the SHELXL97 software.27 The allyl ligand of com-
pound 8 has positional disorder. It was refined in exo and endo
orientations with 60% and 40% occupancy, respectively. The
hydrogen atoms of the η3-allyl were refined only for the major
isomer.
3
NMR (CDCl3; 400 MHz) of 16a: δ 7.93 (d, J(1H,1H) = 8.8
Hz, 1H, C9H6), 7.62 (m, 1H, C9H6), 7.56-7.39 (m, 2H of C9H6,
and 5H of C6H5), 6.77 (m, 1H, C5H4), 6.65 (d, 3J(1H,1H) = 3.5
Hz, 1H, C9H6), 6.02 (d, 3J(1H,1H) = 3.5 Hz, 1H, C9H6), 5.67,
4.73, 4.58 (3 ꢀ m, 3H, C5H4), 2.46 (m, 6 lines, 1H, CH2CH2Mo),
2.36 (m, 6 lines, 1H, CH2CH2Mo), -0.09 (m, 5 lines, 1H, CH2-
CH2Mo), -3.75 (m, 7 lines, 1H, CH2CH2Mo). 13C NMR
(CDCl3; 101 MHz) of 16a: δ 226.5 (1C, CO), 133.1, 130.7,
130.3, 128.1 (3C of C9H6 and 1C of C6H5), 131.1 (Cipso, C6H5),
129.7, 128.3 (2 ꢀ 2C, C6H5), 122.5 (1C, C9H6), 114.4, 106.4,
105.7 (3Cipso, C9H6), 98.1, 95.6, 89.8 (3C, C5H4), 83.2 (1C,
C9H6), 82.7 (1C, C5H4), 82.1 (1C, C9H6), 81.3 (Cipso, C5H4),
18.7 (1C, CH2CH2Mo), -36.0 (1C, CH2CH2Mo). FTIR (KBr,
cm-1): 2002 vs (ν(CO))], 1059 vs-br (νs(BF)). 1H NMR (CDCl3;
400 MHz) of 16b (selected signals): δ -0.49 (m, 5 lines, 1H,
CH2CH2Mo), -1.63 (m, 5 lines, 1H, CH2CH2Mo). Single crys-
tals of 16a suitable for X-ray analysis were prepared by slow
evaporation of the CDCl3 solution.
The X-ray data (Table 2) for crystals of 18 were obtained at
150 K using an Oxford Cryostream low-temperature device on a
Nonius KappaCCD diffractometer with Mo KR radiation (λ =
˚
0.710 73 A) and a graphite monochromator. Data reductions
were performed with DENZO-SMN.28 The absorption was
corrected by integration methods.29 Structures were solved by
direct methods (Sir92)30 and refined by full-matrix least squares
based on F2 (SHELXL97).27 Hydrogen atoms were mostly
localized on a difference Fourier map; however, to ensure
uniformity of the treatment of the crystal, all hydrogen atoms
were recalculated into idealized positions (riding model) and
assigned temperature factors Uiso(H) = 1.2[Ueq(pivot atom)] or
t
Synthesis of [(η5-C9H5 Bu2)(η4-C5H4(CH2)2)Mo(CO)2][BF4]
(17). The reaction was carried out as was described for com-
t
pound 15, but with [(η5-C9H5 Bu2)Mo(CO)2(NCMe)2][BF4]
(12; 0.22 g, 0.4 mmol). Yield: 0.14 g (0.24 mmol, 59%). Anal.
Calcd for C26H31BF4MoO2: C, 55.94; H, 5.60. Found: C, 56.29;
H, 5.83. 1H NMR (CDCl3; 400 MHz): 7.79 (m, 2H, C9H5), 7.63
(m, 2H, C9H5), 5.54 (t, J(1H,1H) = 2.9 Hz, 2H, C5H4), 5.20
(s, 1H, C9H5), 4.19 (t, J(1H,1H) = 2.9 Hz, 2H, C5H4), 2.42 (s,
˚
1.5Ueq for the methyl moiety with C-H = 0.96, 0.97, and 0.93 A
t
18H, Bu), 1.36 (t, 3J(1H,1H) = 8.6 Hz, 2H, CH2), 0.67 (t,
for methyl, methylene, and hydrogen atoms in aromatic rings or
the allyl moiety, respectively.
3J(1H,1H) = 8.6 Hz, 2H, CH2).
Synthesis of [(η5-C9H5Ph2)(η5-C5H4CH2-η1-CH2)Mo(CO)]-
[BF4] (18). The reaction was carried out as was described for
compound 15, but with [(η5-C9H5Ph2)Mo(CO)2(NCMe)2][BF4]
(13; 0.24 g, 0.4 mmol). Yield: 0.22 g (0.39 mmol, 94%). Anal.
Calcd for C29H23BF4MoO: C, 61.08; H, 4.07. Found: C, 60.86;
H, 3.92. Positive-ion MS: m/z 485 [M]þ. Negative-ion MS: m/z
87 [BF4]-. 1H NMR (CDCl3; 400 MHz): δ 8.02 (m, 1H, C9H5),
7.71 (m, 1H, C9H5), 7.62 (m, 6H, C9H5 and C6H5), 7.53 (m, 4H,
C6H5), 7.41 (m, 2H, C6H5), 6.39 (s, 1H, C9H5), 5.53 (m, 1H,
C5H4), 4.74 (m, 2H, C5H4), 4.40 (m, 1H, C5H4), 2.62 (m, 6 lines,
1H, CH2CH2Mo), 2.34 (m, 8 lines, 1H, CH2CH2Mo), -0.32
(m, 6 lines, 1H, CH2CH2Mo), -2.50 (m, 7 lines, 1H, CH2-
CH2Mo). 13C NMR (CDCl3; 101 MHz): δ 225.3 (1C, CO),
131.8, 131.6, 130.4, 130.3 (2C of C6H5 and 2C of C9H5), 131.4,
130.9 (2Cipso, C6H5), 130.2, 129.9, 128.2, 127.8 (4 ꢀ 2C, C6H5),
Crystallographic data for structural analysis have been de-
posited with the Cambridge Crystallographic Data Centre.
Copies of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2 1EY,
U.K. (fax, þ44-1223-336033; e-mail, deposit@ccdc.cam.ac.uk;
web, http://www.ccdc.cam.ac.uk).
Acknowledgment. We are grateful to the Czech Science
Foundation (GACR, Czech Republic) and Ministry of
Education of the Czech Republic (MSM, Czech Repub-
lic) for support through projects GACR/203/09/P100 and
MSM 0021627501, respectively. J.H. thanks the FCT for
the postdoctoral research grant SFRH/BPD/24889/2005.
A.M. thanks the FCT for the postdoctoral research grant
ꢁ
SFRH/BPD/30142/2006. We thank Cecilia Bonifacio from
the FCT-UNL and Paula Brandao from the Universidade
124.8, 124.6 (2C, C9H5), 110.6, 106.7, 103.6, 102.8 (4Cipso
,
~
C9H5), 105.4, 97.3, 90.3, 85.9, 84.4 (4C of C5H4 and 1C of
C9H5), 80.0 (Cipso, C5H4), 18.8 (1C, CH2CH2Mo), -36.7 (1C,
CH2CH2Mo). FTIR (KBr, cm-1): 2006 vs (ν(CO)), 1054 vs-br
(νs(BF)). Single crystals suitable for X-ray analysis were pre-
pared by careful overlayering of the CH2Cl2 solution with
hexane.
de Aveiro for crystal mounting and data collection. We
thank the FCT (Portugal) for the funding of the single-
crystal diffractometer. The NMR spectrometers are part of
the National NMR Network and were acquired with funds
from the FCT and FEDER.
Synthesis of [(η5-C9H6Me)(η4-C5H4(CH2)2)Mo(CO)2][BF4]
(19). The reaction was carried out as was described for com-
pound 15, but with [(η5-C9H6Me)Mo(CO)2(NCMe)2][BF4] (14;
0.18 g, 0.4 mmol). Yield: 0.10 g (0.22 mmol, 54%). Anal. Calcd
for C19H17BF4MoO2: C, 49.60; H, 3.72. Found: C, 49.88; H,
4.03. 1H NMR (CDCl3; 400 MHz): 7.67 (m, 2H, C9H6), 7.38 (m,
2H, C9H6), 6.20 (s, 2H, C9H6), 5.28 (t, J(1H,1H) = 2.9 Hz, 2H,
C5H4), 4.70 (t, J(1H,1H) = 2.9 Hz, 2H, C5H4), 2.26 (s, 3H, CH3),
1.16 (t, 3J(1H,1H) = 8.4 Hz, 2H, CH2), 0.52 (t, 3J(1H,1H) = 8.4
Hz, 2H, CH2).
Supporting Information Available: CIF files giving crystal-
lographic data for 9, 16a, and 18. This material is available free
of charge via the Internet at http://pubs.acs.org.
€
(27) Sheldrick, G. M. SHELXL97; University of Gottingen, Gottingen,
€
Germany, 1997.
(28) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307–
326.
(29) Coppens, P. In Crystallographic Computing; Munksgaard:
Copenhagen, 1970; pp 255-270.
(30) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.
J. Appl. Crystallogr. 1993, 26, 343–350.
(31) (a) King, R. B.; Bisnette, M. B. Inorg. Chem. 1965, 4, 475–481.
(b) Green, M.; McGrath, T. D.; Thomas, R. L.; Walker, A. P.
J. Organomet. Chem. 1997, 532, 61–70.
X-ray Structure Determination. The measurements of struc-
tures 9 and 16a were carried out on a Bruker SMART APEX
CCD diffractometer using graphite-monochromated Mo KR
˚
radiation (λ = 0.710 73 A) from an X-ray tube. Details of the
crystallographic data and refinement parameters are given in