Intramolecular [4+2] Diels-Alder cycloaddition of a 2H-phosphole to coordinated unsaturated phosphines, phospholes, and an arsine

Article abstract of DOI:10.1021/ja9724654

Stereoselective [4+2] Dieis-Alder cycloadditions occur between unsaturated tertiary phosphine, phosphole, and arsine molybedenum carbonyl complexes, e.g., (Ph₂E-trans-CH₂CH=CHCH₃)Mo(CO)₅ [E = P, As] and 3,4- dim

Full text of DOI:10.1021/ja9724654

12560
J. Am. Chem. Soc. 1997, 119, 12560-12567
Intramolecular [4+2] Diels-Alder Cycloaddition of a
2H-Phosphole to Coordinated Unsaturated Phosphines,
Phospholes, and an Arsine
Kalyani Maitra, Vincent J. Catalano, and John H. Nelson*
Contribution from the Department of Chemistry/216, UniVersity of NeVadasReno,
Reno, NeVada 89557-0020
ReceiVed July 21, 1997X
Abstract: Stereoselective [4+2] Diels-Alder cycloadditions occur between unsaturated tertiary phosphine, phosphole,
and arsine molybedenum carbonyl complexes, e.g., (Ph2E-trans-CH2CHdCHCH3)Mo(CO)5 [E ) P, As] and 3,4-
dimethyl-1-phenylphosphole (DMPP). The coordinated DMPP undergoes a [1,5] phenyl migration at about 145 °C
prior to or concomitant with the [4+2] intramolecular cycloaddition reaction with the alkene moiety of the dienophile
to produce a new class of conformationally rigid bidentate ligands containing the 1-phosphanorbornene bicyclic ring
system. The characteristic 1H, 13C{1H}, and 31P{1H} NMR spectroscopic features of these compounds are described.
Crystal structures of most of the new compounds are reported.
Introduction
The highly efficient and diastereoselective [4+2] Diels-Alder
cycloaddition reactions of 1H-phospholes with various dieno-
philes is a classical approach that we have employed to prepare
rigid unsymmetrical diphosphines and triphosphines.1 In ad-
dition, asymmetric synthetic modifications of some of these
reactions have recently been reported.2 Mathey and co-workers
in the course of their extensive studies relating to the properties
and reactivities of phospholes have well established the existence
of an equilibrium between 1H-phospholes and 2H-phospholes
at elevated temperature.3
Rhodium complexes of a 2,2′-bis[1-phosphanorbornadienyl]
(BIPNOR) ligand have recently been shown5 to be excellent
catalysts for asymmetric hydrogenation of CdC and CdO
double bonds. The propensity of the 2H-phospholes to undergo
[4+2] cycloaddition reactions offers an excellent new synthetic
route for R,â-functionalization of 1-phosphanorbornenes and
1-phosphanorbornadienes.
In our laboratory the discovery that 2H-phospholes undergo
intramolecular [4+2] Diels-Alder cycloadditions within the
coordination sphere of a transition metal to form 1-phospha-
norbornene derivatives, which is unprecedented in the literature,
reveals a new aspect relating to the mechanistic pathway
involving the reactions of the 2H-phospholes. The general
question of whether [4+2] Diels-Alder cycloadditions are
concerted or stepwise processes is of considerable current
interest.6 In this context, we herein report the reactions of 2,4-
dimethyl-1-phenylphosphole (DMPP) at elevated temperatures
with trans-crotylphosphino and -arsino complexes, R2E-trans-
(CH2CHdCHCH3)Mo(CO)5 [E ) As, P], and analogous allyl
tertiary phosphine complexes to produce rigid unsymmetrical
chiral diphosphines and arsinophosphines having the generic
1-phosphanorbornene bicyclic ring system in their molecular
structures.
The 2H-phospholes appear to be very reactive dienes that
undergo facile Diels-Alder cycloaddition reactions with alkynes
and alkenes to produce bicyclic systems with phosphorus at the
bridgehead, commonly known as the 1-phosphanorbornadiene
and 1-phosphanorbornene systems, respectively.4
Results
X Abstract published in AdVance ACS Abstracts, December 1, 1997.
(1) (a) Solujic´, Lj.; Milosavljevic´, E. B.; Nelson, J. H.; Alcock, N. W.;
Fischer, J. Inorg. Chem. 1989, 28, 3453. (b) Affandi, S.; Nelson, J. H.;
Fischer, J. Inorg. Chem. 1989, 28, 4536. (c) Bhaduri, D.; Nelson, J. H.;
Day, C. L.; Jacobson, R. A.; Solujic´, Lj.; Milosavljevic´, E. B. Organome-
tallics 1992, 11, 4069. (d) Nelson, J. H. In Phosphorus-31 NMR Spectral
Properties in Compound Characterization and Structural Analysis, Quin,
L. D., Verkade, J. G., Eds.; VCH: Deerfield Beach, FL, 1994; pp 203-
214.
(2) Aw, B.-H.; Hor, T. S. A.; Selvaratnam, S.; Mok, K. F.; White, A. J.
P.; Williams, D. J.; Rees, N. H.; McFarlene, W.; Leung, P.-H. Inorg. Chem.
1997, 36, 2138 and references therein.
(3) (a) Mathey, F. Chem. ReV. 1988, 88, 429 and references cited therein.
(b) Holand, S.; Jeanjean, M.; Mathey, F. Angew. Chem., Int. Ed. Engl. 1997,
36, 98.
In order to explore the scope of these reactions we developed
a high-yield general synthesis of the crotyl tertiary phosphine
complexes (A and B).7 The synthesis of an analogous tertiary
(5) Robin, F.; Mercier, F.; Ricard, L.; Mathey, F.; Spagnol, M. Chem.
Eur. J. 1997, 3, 1365.
(6) (a) Houk, K. N.; Li, Y.; Evanseck, J. D. Angew. Chem., Int. Ed.
Engl. 1992, 31, 682. (b) Dewar, M. J. S.; Jie, C. Acc. Chem. Res. 1992, 25,
537. (c) Houk, K. N.; Gonzalez, J.; Li, Y. Acc. Chem. Res. 1995, 28, 81.
(d) Horn, B. A.; Herek, J. L.; Zewail, A. H. J. Am. Chem. Soc. 1996, 118,
8755. (e) Sustmann, R.; Tappanchai, S.; Bandmann, H. J. Am. Chem. Soc.
1996, 118, 12555.
(7) Maitra, K.; Wilson, W. L.; Jemin, M. M.; Yeung, C.; Rader, W. S.;
Redwine, K. D.; Striplin, D. P.; Catalano, V. J.; Nelson, J. H. Syn. React.
Inorg. Met.-Org. Chem. 1996, 26, 967.
(4) Le Goff, P.; Mathey, F.; Ricard, L. J. Org. Chem. 1989, 54, 4754.
S0002-7863(97)02465-7 CCC: $14.00 © 1997 American Chemical Society

Intramolecular [4+2] Diels-Alder Cycloadditions
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12561
Scheme 2a
Scheme 1a
a (i) refluxed in diglyme with complex D at ∼150 °C for 5 h; (ii)
refluxed in diglyme with complex E at ∼150 °C for 4.5 h.
Table 1. 121.6 MHz 31P{1H} NMR Data for the Complexes
complex
δ
31P (ppm)
2J(PP) (Hz)
a (i) refluxed in diglyme with complex A at ∼150 °C for 5 h; (ii)
refluxed in toluene at 110 °C with complex A for 8 h; (iii) refluxed in
diglyme at ∼150 °C for 4 h; (iv) refluxed in diglyme with complex B
at ∼150 °C for 4.5 h; (v) refluxed in toluene with complex B at 110
°C for 8 h; (vi) refluxed in diglyme at ∼150 °C for 4.5 h; (vii) refluxed
in diglyme with complex C at ∼150 °C for 5 h.
1a
1
2a
2
3a
3
4a
4
30.93, 28.55
64.14, 54.58
28.89, 26.12
66.74, 52.44
29.60
24.1
4.0
21.7
7.2
70.91
30.85, 27.25
72.74, 55.13
29.96, 25.34
75.13, 52.19
85.31, 70.70, 26.12
24.6
4.2
20.8
7.8
arsine complex (C) is also described here (see Experimental
Section). In this case the trans-crotyl complex was contaminated
with trace quantities of the cis isomer. The reactions of such
5a
5
6
178.9, 45.3, 20.5
{1H} NMR spectra (Table 1), one for each unique phosphorus.
In each case the resonance corresponding to the bridgehead
phosphorus is downfield (64-75 ppm), typical for the phos-
phorus in a 1-phosphanorbornene ring.4,8 The other resonance
occurs in the region (52-55 ppm) typical of a phosphine
coordinated to Mo in a five-membered chelate ring.9 Formation
of the [4+2] Diels-Alder adduct from the cis mixed-ligand
complex is signaled by two significant changes in the 31P{1H}
NMR spectra. The two resonances for the Diels-Alder adduct
both appear downfield of those for the cis mixed-ligand complex
with ∆δ 31P being about 27 and 40 ppm, respectively. The
trans-crotyl complexes (A, B, and C) with DMPP were
conducted in refluxing diglyme. In all cases the changes in
the compostion of the reaction mixtures were monitored by 31P-
{1H} NMR spectroscopy. The first step involves the stereospe-
cific formation of the cis mixed-ligand complex (e.g., 1a, 2a)
followed by its conversion into the [4+2] Diels-Alder cy-
cloadduct of the 2H-phosphole of DMPP (Scheme 1). The latter
is evidenced by the gradual decay of the resonances for the cis
mixed-ligand complex followed by the growth of those for the
products in the 31P{1H} NMR spectra. The cis mixed-ligand
complexes 1a and 2a were also synthesized separately by
reaction of DMPP with A and B respectively, in refluxing
toluene. Complexes 1a and 2a could then be efficiently
converted to the 2H-phosphole Diels-Alder products (1 and
2) in diglyme at ∼150 °C. The reactions in refluxing diglyme
proceed to completion in a period of 4-5 h to give a single
diastereomer as the major product in high yield. To further
generalize these reactions, the allyl tertiary phoshine complexes
(D and E) were reacted with DMPP under the same reaction
conditions (Scheme 2). In both cases, the 2H-phosphole [4+2]
adducts were formed in high yield. For the reaction of the
dibenzophosphole- (DBP-) allyl complex E, a very minor
amount of a triphosphine complex (6) was also isolated and
was characterized only by 31P{1H} NMR spectroscopy and
X-ray structure analysis (Vide infra). The key step is the
addition of the phosphole to a refluxing solution of the
dienophile in diglyme at 145-150 °C.
2
magnitude of J(PP) decreases significantly from about 22 Hz
in the cis mixed-ligand complexes to about 6 Hz for the Diels-
Alder adducts. This is because the two contributions to J(PP)
(through the ligand backbone and through the metal) are similar
in magnitude and opposite in sign.10 In these reactions the
entering DMPP ligand occupies the site vacated by the departing
carbon monoxide, which is cis to the other phosphine or arsine
ligand already present within the metal coordination sphere.
Earlier studies11 have established the fact that this mutually cis
coordination geometry of the ligands is a necessary condition
for transition metal-promoted intramolecular [4+2] Diels-Alder
cycloaddition reactions, which produce chiral bidentate ligands.
In all cases when the reactions were monitored by 31P{1H} NMR
spectroscopy, the stereospecific formation of the cis mixed-
ligand complex was evident prior to the formation of the Diels-
Alder 2H-phosphole adduct. To verify this statement, in two
cases the cis mixed-ligand intermediates were isolated and/or
prepared separately, characterized, and then converted into the
(8) (a) Bevierre, M. O.; Mercier, F.; Ricard, L.; Mathey, F. Bull. Soc.
Chim. Fr. 1992, 129, 1. (b) Waschbu¨sch, K.; Le Floch, P.; Mathey, F. Bull.
Soc. Chim. Fr. 1995, 132, 910.
(9) Garrou, P. E. Chem. ReV. 1981, 81, 229.
(10) Crumbliss, A. L.; Topping, R. J. In Phosphorus-31 NMR Spectros-
copy in Stereochemical Analysis, Verkade, J. G., Quin, L. D., Eds.; VCH:
Deerfield Beach, FL, 1987; pp 531-557.
Discussion
(11) (a) Holt, M. S.; Nelson, J. H.; Savignac, P.; Alcock, N. W. J. Am.
Chem. Soc. 1985, 107, 6396. (b) Rahn, J. A.; Holt, M. S.; Gray, G. A.;
Alcock, N. W.; Nelson, J. H. Inorg. Chem. 1989, 28, 217.
Phosphorus NMR Spectroscopy. The Diels-Alder prod-
ucts of the 2H-phospholes display two resonances in their 31P-

12562 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Maitra et al.
cycloaddition products (Scheme 1). During the conversion
processes of 1a and 2a to products 1 and 2, respectively, no
resonances due to free phosphole were observed in the 31P-
{1H} NMR spectra. This indicates that there is no appreciable
ligand dissociation during the reaction period. It therefore
appears that after the formation of the cis mixed-ligand complex,
at an elevated temperature, the coordinated 1H-phosphole
rearranges to the 2H-phosphole within the metal coordination
sphere prior to the [4+2] cycloaddition to produce the highly
reactive hot diene. The fact that [1,5] sigmatropic shifts occur
for a P-coordinated phosphole has been demonstrated for
hydrogen.12 The reactive coordinated 2H-phosphole spontane-
ously adds to the crotyl unit acting as the dienophile to give
the Diels-Alder [4+2] cycloaddition product. So far we have
not been able to detect or isolate this short-lived, highly reactive
2H-phosphole cis mixed-ligand intermediate. The reactions of
other dienophiles, such as the allyl tertiary phosphine complexes
(D and E), with DMPP at high temperature led to the formation
of the same types of products (Scheme 2). 31P{1H} NMR
spectra of the crude reaction mixtures for each of these reactions
at first showed resonances indicating the formation of the cis
mixed-ligand complexes 4a and 5a, followed by their gradual
decay and appearance of the resonances for the [4+2] cyclo
adducts 4 and 5 (Table 1). For the reaction of E with DMPP,
another product 6 was isolated in a trace amount that resulted
from the further reaction of 5 with some unreacted DBP-allyl
complex present in the reaction mixture, following the substitu-
tion of the CO group trans to the 1-phosphaphosphorus in 5 by
the DBP-allyl unit. The 31P{1H} NMR spectrum of 6 showed
resonances for three inequivalent phosphorus nuclei at δ 80.31
(dd), 70.70 (dd), and 26.12 ppm (dd) coupled to each other,
with the most downfield resonance being for the nonchelated
phosphorus of the DBP allyl arm and the higher coupling
constant value being for the two mutually trans phosphorus
nuclei. This manifests the greater trans effect of the 1-phos-
phaphosphorus ligand, which labilizes the trans CO bond.
Figure 1. Structural drawing of 1 showing the atom numbering scheme
(40% probability ellipsoids). Hydrogen atoms have been omitted for
clarity.
Figure 2. Structural drawing of 2 showing the atom numbering scheme
(40% probability ellipsoids). Hydrogen atoms have been omitted for
clarity.
Proton and Carbon NMR Spectroscopy. Proton and
carbon chemical shift assignments (see Experimental Section)
were accomplished with the aid of a variety of decoupling
experiments, attached proton test (APT) spectra, along with
correlated (COSY) and heteronuclear correlation (HETCOR)
two-dimensional spectra. 1H nuclear Overhauser effect (NOE)
spectra confirmed that these molecules are very rigid and posses
the same structures in both the solution and solid states. The
1H resonance for H6 is distinct in the spectra of all compounds.
Its chemical shift is very sensitive to the substituent on E,
moving upfield by more than 1 ppm when Ph2P is replaced by
DBP, due to the diamagnetic sheilding of the DBP ring. The
for the carbonyls trans to phosphorus appear as doublets of
doublets with the larger 2J(PC) value being to the trans
phosphorus. The spectra for complexes 1, 2, 4, and 5 show
distinct resonances for each carbonyl carbon. For complex 3
all the carbonyl resonances appear as doublets with the larger
2J(PC) value for the carbonyl trans to the phosphorus atom.
The two phenyl groups derived from the dienophile phosphine
and arsine arm for complexes 1, 4, and 3, respectively, are
diastereotopic and give rise to distinct sets of resonances for
each carbon type in the phenyl rings. Similarly, the phenyl
group emanating from the 2H-phosphole, which is now bound
to an sp2-hybridized carbon atom in the 1-phosphanorbornene
ring of the product, gives rise to six distinct carbon resonances
due to restricted phenyl group rotation. Likewise for complexes
2 and 5 each carbon atom of the DBP ring gives rise to a distinct
resonance manifesting the complete lack of symmetry for these
compounds.
Crystal Structure Analysis. X-ray crystal structures of these
novel ligand complexes 1-6 were obtained to gain conclusive
support for their structures. These structures are shown in
Figures 1-6, respectively. Selected bond distances and angles
for 1-6 are listed in Table 2. All these complexes exist as
discrete molecules with no abnormal intermolecular contacts.
Each asymmetric unit of 1 contains two crystallographically
inequivalent molecules, which are enantiomers. None of these
complexes contains any element of symmetry, and they are
therefore chiral. The five-membered chelate rings are rigid for
3
2
much larger magnitude J(PH) of about 38 Hz than J(PH) of
about 11 Hz for H6 was confirmed by selective phosphorus
decoupling experiments. Furthermore, this large coupling
constant is also observed for compound 3, which possesses only
the bridgehead phosphorus.
Assignment of the 13C{1H} NMR spectra was also aided by
the previous assignments for the P-oxo-substituted 1-phospha-
norbornene system.4 The 13C{1H} NMR spectra for all
complexes display distinct sets of resonances for all the carbonyl
carbons respectively trans to phosphorus and mutually trans to
each other. The chemical shifts for the latter carbonyls are
usually the more upfield. For the mixed-ligand complexes (1a
and 2a) the mutually trans carbonyl carbons have the same
magnitude for 2J(PC) to the two cis phosphorus atoms, and their
resonances therefore appear as apparent triplets. The resonances
(12) Holand, S.; Charrier, C.; Mathey, F.; Fischer, J.; Mitschler, A. J.
Am. Chem. Soc. 1984, 106, 826.

Intramolecular [4+2] Diels-Alder Cycloadditions
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12563
Figure 6. Structural drawing of 6 showing the atom numbering scheme
(40% probability ellipsoids). Hydrogen atoms have been omitted for
clarity.
Figure 3. Structural drawing of 3 showing the atom numbering scheme
(40% probability ellipsoids). Hydrogen atoms have been omitted for
clarity.
1H-phosphole of DMPP that results in the formation of the
7-phosphanorbornene ring with the phosphorus at the bridging
position, the values of these angles are smaller, ranging from
79° to 81°.1b Hence the ring strain in the 1-phosphanorbornene
systems is much reduced compared to the 7-phosphanorbornene
ring systems. This highly reduced angle strain in the 2H-
phosphole Diels-Alder adducts is in part responsible for the
extreme upfield shift for the 1-phosphaphosphorus resonance
in the 31P{1H} NMR spectra when compared to similar products
of the 1H-phosphole of DMPP. For each of these complexes
the coordination geometry at the metal center is a distorted
octahedron. The equatorial plane is formed by the two
phosphorus atoms and the two carbonyl groups trans to them
for 1-5, and by three phosphorus atoms for 6, two of which
are mutually trans and another phosphorus trans to a carbonyl.
For all the diphosphine complexes the P1-Mo1-P2 angles are
small due to the chelate effect and range between 78.49(4)°
and 79.21(3)°. In the triphosphine complex 6 for the same
reason the angle P1-Mo1-P2 [79.13(5)°] is smaller than the
angle P3-Mo1-P2 [90.49(5)°], as P3 is not involved in a
chelate ring. That the P1-Mo1-P3 angle is 169.04(5)° in 6
also suggests that P2 and P3 are in a trans orientation. The
Mo-P bond lengths for 1-6 are in very good agreement with
those reported for similar types of 7-phosphanorbornene-Mo-
(0) complexes.1b The Mo1-P1 bonds are shorter than the
Mo1-P2 bonds in complexes 1-6, signifying the better donor
ability of the 1-phosphanorbornene ligand. The Mo-CO bond
lengths are in the normal range. The CdC double bond of the
norbornene ring in 1-5 is localized between C9 and C10 as
expected and ranges between 1.337 ( 0.006 and 1.344 ( 0.005
Å. Similarly for 6 the bond distances of 1.341 ( 0.007 and
1.306 ( 0.001 Å between C8 and C9 and C44 and C45
respectively, suggest the presence of double bonds, the latter
being for the allyl unit.
Figure 4. Structural drawing of 4 showing the atom numbering scheme
(40% probability ellipsoids). Hydrogen atoms have been omitted for
clarity.
Finally, the structures of complexes 1, 2 and 3 reveal a very
important aspect about the mechanism involved for the [4+2]
cycloaddition reactions of the 2H-phosphole of DMPP toward
a dienophile. Conclusively, the cycloaddition reactions for all
the crotyl complexes leads to the formation of only one major
product with the -CH2 unit of the crotyl moiety substituted in
the exo position R to the bridgehead phosphorus. The dihedral
angles for C12-C7-C6-C5 are 107.4°, 104.8°, and 99.3° for
1, 2, and 3 respectively, and such deviations may be attributed
to the strain in the five-membered chelate ring due to ligand
variation. For these complexes their molecular structures show
that C5 and C12 are in the exo, endo configuration or rather
trans-oriented on the 1-phosphanorbornene ring moiety. This
Figure 5. Structural drawing of 5 showing the atom numbering scheme
(40% probability ellipsoids). Hydrogen atoms have been omitted for
clarity.
all the structures and are fused to the 1-phosphanorbornene ring
at P1 and C6 for 1-5 and at P1 and C5 for 6. The strain in the
norbornene ring can be best examined by considering the angles
made by the bridgehead carbon, the bridgehead phosphorus P1,
and at the bridging carbon C11 for complexes 1-5 and C10
for 6. These values are 97.3(2)°, 97.7(4)°, 97.0(3)°, 97.6(2)°,
97.0(3)°, and 98.1(4)° for complexes 1-6, respectively. For
the more commonly known [4+2] Diels-Alder adducts of the

12564 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Maitra et al.
Table 2. Bond Distances and Bond Angles for Complexes 1-6
complex
1
2
3
4
5
6
Bond Distances (Å)
2.000 (5)
Mo1-C1
Mo1-C2
Mo1-C3
Mo1-C4
Mo1-P1
Mo1-P2/As1
C9-C10
O1-C1
1.984 (4)
2.006 (4)
2.051 (5)
2.029 (5)
2.4768 (9)
2.5168 (9)
1.344 (5)
1.16 (2)
1.994 (7)
1.987 (7)
2.012 (7)
2.061 (7)
2.466 (2)
2.496 (2)
1.338 (8)
1.152 (7)
1.145 (7)
1.149 (7)
1.128 (7)
2.005 (4)
1.981 (3)
2.036 (4)
2.048 (4)
2.4532 (9)
2.5348 (8)
1.343 (5)
1.146 (4)
1.150 (4)
1.139 (4)
1.130 (4)
1.996 (6)
1.995 (6)
2.054 (6)
1.992 (6)
2.4795 (12)
2.4984 (13)
1.337 (6)
1.143 (6)
1.128 (6)
1.129 (6)
1.154 (7)
Mo1-C1
Mo1-C2
Mo1-C3
Mo1-P1
Mo1-P2
Mo1-P3
C8-C9
1.968 (7)
2.012 (6)
2.009 (7)
2.402 (2)
2.482 (2)
2.450 (2)
1.341 (7)
1.306 (10)
1.148 (6)
1.140 (6)
1.137 (7)
1.969 (4)
2.040 (4)
2.040 (4)
2.4607 (11)
2.6027 (6)
1.338 (5)
1.148 (5)
1.150 (5)
1.126 (5)
1.130 (5)
C44-C45
O1-C1
O2-C2
1.133 (5)
1.127 (6)
1.137 (5)
O3-C3
O4-C4
O2-C2
O3-C3
Bond Angles (deg)
C2-Mo1-C1
C2-Mo1-C3
C1-Mo1-C3
C2-Mo1-C4
C1-Mo1-C4
C3-Mo1-C4
P1-Mo1-P2/As1
C8-C11-P1
C12-C7-C6
89.9 (2)
89.2 (2)
90.9 (2)
88.3 (2)
92.1 (2)
176.1 (2)
79.21 (3)
97.3 (2)
112.6 (3)
93.0 (2)
89.1 (3)
89.9 (2)
89.0 (3)
88.9 (2)
177.7 (3)
79.13 (5)
97.7 (4)
112.7 (6)
90.6 (2)
91.8 (2)
90.0 (2)
91.4 (2)
87.6 (2)
176.0 (2)
79.00 (3)
97.0 (3)
111.9 (4)
90.07 (13)
92.16 (13)
86.00 (13)
90.84 (13)
90.05 (13)
175.04 (13)
78.69 (3)
92.1 (2)
90.0 (2)
89.5 (2)
91.5 (2)
84.2 (2)
173.6 (2)
78.49 (4)
97.0 (3)
C1-Mo1-C2
C1-Mo1-C3
C3-Mo1-C2
C1-Mo1-P1
C3-Mo1-P1
C2-Mo1-P1
C1-Mo1-P3
C3-Mo1-P3
C2-Mo1-P3
P1-Mo1-P3
C1-Mo1-P2
C3-Mo1-P2
C2-Mo1-P2
P1-Mo1-P2
P3-Mo1-P2
C7-C10-P1
88.9 (3)
87.0 (3)
175.7 (3)
93.2 (2)
93.4 (2)
85.7 (2)
97.1 (2)
90.7 (2)
90.9 (2)
169.04 (5)
172.4 (2)
93.3 (2)
90.7 (2)
79.13 (5)
90.49 (5)
98.1 (4)
97.6 (2)
to external PPh3 (δ31P ) -6.0 ppm); all shifts to low field (high
frequency) are positive.
clearly indicates that the stereochemistry of the crotyl units in
these molecules has been preserved during the [4+2] cycload-
dition reaction with the rearranged 2H-phosphole unit of DMPP.
For a stepwise process such complete retention of orientation
of the -CH3 and the -CH2 unit of the crotyl moiety would not
be likely, and the other diastereomers (exo, exo/endo, endo)
would have been detected in the product mixture. We may
therefore conclude that for all the above discussed complexes
1-6, the metal-promoted [4+2] Diels-Alder cycloaddition of
2H-phospholes to the dienophile is most likely a concerted
process. The concertedness of the [4+2] cycloadditions of 2H-
phospholes with acetylene as the dienophile has been established
on the basis of theoretical calculations.13 Moreover, since only
one diastereomer was obtained as the major isolated product in
all cases, these reactions are highly stereoselective.
Synthesis of Ph2As-trans-(CH2CHdCHCH3)Mo(CO)5. To a solu-
tion of 5.0 g (16.33 mmol) of AsPh3 in 15 mL of freshly distilled
tetrahydrofuran was added 1.0 g (144.1 mmol) of lithium (cut into small
flat pieces) under a nitrogen atmosphere with stirring. After 15-20
min, when the solution became deep red, 240 mL of freshly distilled
THF was added and the reaction mixture was stirred at ambient
temperature for 4 h. During this period, the color of the reaction
mixture intensified to a deep orange-brown. The excess lithium was
removed under a N2 purge and disposed of by cautiously reacting it
with approximately 300 mL of 95% ethanol. Then 0.73 g (5.44 mmol)
of anhydrous AlCl3 was added to the reaction mixture.15 (Caution:
the reaction of the AlCl3 with phenyllithium is vigorous; white fumes
may result.) The reaction mixture was stirred for 15 min and then 4.32
g (16.36 mmol) of Mo(CO)6 was added under a N2 purge. Ef-
fervescence was detected and the solution turned bright red-orange.
The reaction mixture was stirred at ambient temperature for 1-2 h
until the effervescence ceased, followed by the addition of 1.5 molar
equiv of trans-crotyl chloride. The reaction mixture immediately paled
in color. The mixture was allowed to stir at ambient temperature for
about 30 min, followed by the addition of 100 mL of 1 M HCl and
100 mL of hexane. The contents of the reaction flask were then
transferred to a 1 L separatory funnel and the aqueous layer was
removed and discarded. To the organic phase was added 50 mL of
ether, and the solution was washed with two 100 mL portions of 1 M
HCl followed by two 100 mL portions of H2O. The organic phase
was dried with anhydrous magnesium sulfate and filtered by suction
through 80 mL of silica gel covered with 2 cm of Celite in a 200 mL
fritted glass funnel. The silica gel was washed with 200 mL of ether
and the combined solvents were removed from the filtrate by rotary
evaporation using a water bath that was initially at ambient temperature
and gradually heated to 95-100 °C; the flask containing the product
was left on the rotary evaporator until the unreacted Mo(CO)6 had
sublimed. The flask was allowed to cool and was removed from the
rotary evaporator. The crude product was a viscous oil that solified to
a gray-white solid when left at -20 °C for 6-8 h. The crude product
was purified by column chromatography on silica gel with hexane as
Experimental Section
Reagents and Physical Measurements. Commercially available,
reagent-grade chemicals were used unless otherwise indicated. All
experiments were performed under a dry nitrogen atmosphere using
7
standard Schlenk line techniques. (RPh2P)Mo(CO)5 and (RDBP)-
Mo(CO)5,7 where R ) -CH2CHdCH2 or -(trans)CH2CHdCHCH3, and
3,4-dimethyl-1-phenylphosphole (DMPP)14 were prepared by literature
methods. Tetrahydrofuran was distilled under nitrogen from sodium
benzophenone ketyl, and diglyme was distilled under nitrogen over
sodium. Silica gel for column chromatography (grade 12, 28-200
mesh) was obtained from Aldrich. Melting points were determined
on a Mel-Temp apparatus and are uncorrected. Elemental analyses
were performed by Galibraith Laboratories, Knoxville, TN. Solution
infrared spectra were obtained on a Perkin-Elmer Paragon 1000 PC
FT spectrometer in sealed CaF2 cells. 31P{1H}, 13C{1H}, and 1H NMR
spectra were recorded at 121.66 (202.35), 75 (125.71), and 300 (499.86)
MHz, respectively, on either a General Electric GN-300 or a Varian
Unity Plus-500 spectrometer. Proton and carbon chemical shifts are
relative to internal Me4Si, and phosphorus chemical shifts are relative
(13) Bachrach, S. M. J. Org. Chem. 1994, 59, 5027.
(14) Bre`que, A.; Mathey, F.; Savignac, P. Synthesis 1981, 983.
(15) Holand, S.; Mathey, F.; Fischer, J. Polyhedron 1986, 5, 1413.

Intramolecular [4+2] Diels-Alder Cycloadditions
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12565
eluant. Several attempts were made to separate the cis and trans
isomers by column chromatography or fractional crystallization without
any success. Product was obtained (6.92 g, 13.30 mmol, 81.4%) that
was shown by H NMR spectroscopy to be a 3.33:1 mixture of the
trans and cis isomers.
obtain 0.66 g (0.103 mmol, 73.5%) of pale yellow crystals of 1. Mp
> 166-168 °C (decomp). IR (CH
2Cl2) νCO (cm-1) 2022 (w), 1922
(sh), 1908 (s, b), 1886 (sh). 31P{1H} NMR (CDCl3, 121.66 MHz) δ
1
2
2
64.14 [d, J(PP) ) 4.0 Hz, PA], 54.58 [d, J(PP) ) 4.0 Hz, Px). 1H
NMR (CDCl3, 500 MHz) δ 7.64-7.06 (m, 15 H, Ph), 3.33 [dddd,
2
2
3
3J(PH) ) 38.5 Hz, J(PH) ) 11.0 Hz, J(H5H6) ) 11.0 Hz, J(H4H6)
2
Ha
CH3
Hb
) 3.5 Hz, 1 H, H6], 2.03 [d, J(H1H2) ) 11.50 Hz, 1 H, H2], 1.87 [d,
C
C
4J(PH) ) 1.5 Hz, 3 H, CH3(c)], 1.78 [qd, 3J(CH3(a)H3) ) 7.0 Hz, 3J(PH)
C
2
2
) 5.0 Hz, 1 H, H3], 1.63 [dd, J(H2H1) ) 11.5 Hz, J(PH) ) 4.0 Hz,
1 H, H1], 1.43 (s, 3 H, CH3(b)), 1.42-1.34 (m, 2 H, H4 and H5), 1.14
[d, 3J(H3CH3(a)) ) 7.0 Hz, 3 H, CH3(a)]. 13C{1H} NMR (CDCl3, 125.70
MHz) δ 217.05 [dd, 2J(PC) ) 25.5 Hz, 2J(PC) ) 8.0 Hz, COeq], 216.85
[dd, 2J(PC) ) 27.4 Hz, 2J(PC) ) 9.1 Hz, COeq], 209.79 [dd, 2J(PC) )
10.0 Hz, 2J(PC) ) 8.1 Hz, COax], 207.13 [dd, 2J(PC) ) 10.1 Hz, 2J(PC)
) 8.8 Hz, COax], 152.84 [d, 2J(PC) ) 3.5 Hz, Ci′], 139.49 [dd, 1J(PC)
H2
C (trans): Gray-white solid. 1H NMR (CDCl3, 500 MHz) δ 7.3-
3
3
7.5 (m, 10 H, Ph), 5.45 [dqt, J(HbHa) ) 15.50 Hz, J(HbCH3) ) 6.5
4
3
Hz, J(HbCH2) ) 1.00 Hz, 1 H, Hb], 5.25 [apparent dt, J(HaHb) )
15.50 Hz, 3J(HaCH2) ) 7.75 Hz, 4J(HaCH3) ) 1.50 Hz, 1 H, Ha], 3.06
3
4
5
[ddq, J(CH2Ha) ) 7.75 Hz, J(CH2Hb) ) J(CH2CH3) ) 1.00 Hz, 2
H, CH2), 1.60 [ddt, 3J(CH3Hb) ) 6.5 Hz, 4J(CH3Ha) ) 1.5 Hz, 5J(CH3-
CH2) ) 1.0 Hz, 3 H, CH3]. 13C{1H} NMR (CDCl3, 125.71 MHz) δ
210.58 (s, COtrans), 205.56 (s, 4COcis), 136.92 (s, Ci), 131.87 (s, Co),
131.45 (s, CdCCH3), 129.76 (s, Cp), 128.9 (s, Cm), 122.43 (s,
CdCCH2), 34.83 (s, CH2), 17.97 (s, CH3).
3
1
) 22.9 Hz, J(PC) ) 3.1 Hz, C6], 136.98 [d, J(PC) ) 29.7 Hz, Ci],
136.76 [dd, 1J(PC) ) 33.2 Hz, 3J(PC) ) 3.7 Hz, Ci], [135.55 [d, 2J(PC)
2
2
) 15.5 Hz, C5], 132.39 [d, J(PC) ) 12.8 Hz, Co], 130.59 [d, J(PC)
) 12.3 Hz, Co], 129.92 [d, 4J(PC) ) 2.0 Hz, Cp], 129.55 (s, Cm′), 129.25
(s, Cm′), 129.38 [d, 4J(PC) ) 1.6 Hz, Cp], 128.51 [d, 3J(PC) ) 9.6 Hz,
Cm], 128.49 [d, 3J(PC) ) 8.9 Hz, Cm], 128.30 (s, Co′), 128.24 (s, Co′),
128.23 (s, Co′), 127.09 [d, J(PC) ) 1.8 Hz, Cp′], 61.09 [d, J(PC) )
1.1 Hz, C4], 50.72 [d, 1J(PC) ) 25.4 Hz, C7], 48.75 [apparent t, 1J(PC)
) 2J(PC) ) 17.2 Hz, C2], 47.84 [dd, 2J(PC) ) 14.7 Hz, 3J(PC) ) 2.3
Hz, C3], 35.53 [dd, J(PC) ) 22.3 Hz, J(PC) ) 14.6 Hz, C1], 19.90
[d, 3J(PC) ) 7.9 Hz, CH3(c)], 17.61 [d, 3J(PC) ) 3.5 Hz, CH3(b)], 16.13
[dd, 3J(PC) ) 5.9 Hz, 4J(PC) ) 1.1 Hz, CH3(a)]. Anal. Calcd for
C32H30MoO4P2:, C, 60.41; H, 4.72. Found: C, 60.47; H, 4.82.
5
2
Ha
Hb
C
C
C
H2
CH3
1
2
C (cis): Gray-white solid. 1H NMR (CDCl3, 500 MHz) δ 7.3-7.5
3
3
(m, 10 H, Ph), 5.58 [dqt, J(HbHa) ) 11.0 Hz, J(HbCH3) ) 7.0 Hz,
4J(HbCH2) ) 1.5 Hz, 1 H, Hb], 5.42 [dtq, J(HaHb) ) 11.0 Hz, J(Ha-
CH2) ) 8.0 Hz, 4J(HaCH3) ) 1.5 Hz, 1 H, Ha], 3.12 [apparent dt,
3J(CH2Ha) ) 8.0 Hz, 4J(CH2Hb) ) 5J(CH2CH3) ) 1.00 Hz, 2 H, CH2],
1.28 [ddt, J(CH3Hb) ) 7.0 Hz, J(CH3Ha) ) 1.5 Hz, J(CH3CH2) )
1.0 Hz, 3 H, CH3). 13C{1H} NMR (CDCl3, 125.71 MHz) δ 210.54 (s,
COtrans), 205.52 (s, 4COcis), 136.83 (s, Ci), 133.07 (s, CH3CdC), 131.92
(s, Co), 129.78 (s, Cp), 128.9 (s, Cm), 121.48 (s, CdCCH2), 29.63 (s,
CH2), 12.65 (s, CH3).
3
3
[2-Phenyl-3,4,5-trimethyl-6-methylene(dibenzophosphole)-1-
phosphabicyclo[2.2.1]hept-2-ene]tetracarbonylmolybdenum(0) (Com-
plex 2). (Method a) A solution of 5.39 g (11.37 mmol) of B in 200
mL of freshly distilled diglyme maintained at 135 °C was reacted with
2.14 g (11.37 mmol) of DMPP under the same reaction conditions as
mentioned for complex 1, method a. The reddish-brown oily residue
that was left after removal of the solvent was column-chromatographed
on silica gel with benzene-hexane (10:90). The concentration of
benzene in the eluant was gradually increased. The first few fractions
eluted the oxides of the ligands and some unreacted pentacarbonyl
complex followed by the elution of the 2H-phosphole Diels-Alder
product 2. Crystallization from hot hexane gave 5.75 g (9.06 mmol,
79.7%) of pale yellow crystals of pure 2.
3
4
5
(Method b) (1.00 g, 1.58 mmol) Complex 2a was reacted in the
same way as described in method b for complex 1. Purification of the
crude product and crystallization following the same strategy gave 0.58
g ( 0.92 mmol, 57.8%) of pure pale yellow crystals of 2. Mp > 210-
212 °C (decomp). IR (CH2Cl2) νCO (cm-1) 2023 (w), 1931 (sh), 1907
Syntheses and Characterization of [4+2] Cycloadducts: (A)
[2-Phenyl-3,4,5-trimethyl-6-methylene(diphenylphosphino)-1-
phosphabicyclo[2.2.1]hept-2-ene]tetracarbonylmolybdenum(0) (Com-
plex 1). (Method a) To a solution of 2.50 g (5.25 mmol) of A in 200
mL of freshly distilled diglyme maintained at 135 °C, was added 0.99
g (5.25 mmol) of DMPP under a nitrogen atmosphere with stirring.
The temperature of the resulting reaction mixture was then maintained
between 145 and 150 °C for a period of 4-5 h. This was followed by
the removal of the solvent by vacuum distillation by heating the reaction
vessel on a water bath. The reddish-brown oily residue was column-
chromatographed on silica gel with benzene-hexane (10:90). The first
few fractions eluted the oxides of the ligands and some unreacted
starting materials. The concentration of the benzene in the eluant was
gradually increased. The cis mixed-ligand tetracarbonyl complex 1a
(0.83 g, 1.57 mmol, 29.9%) was eluted next, followed by the
2H-phosphole Diels-Alder adduct 1 (1.5 g, 2.36 mmol, 45.0%). The
latter was further purified by recrystallization from hot hexane.
(Method b) Complex 1a (0.895 g, 1.41 mmol) was dissolved in 100
mL of freshly distilled diglyme and refluxed at 150 °C for 4 h under
a nitrogen atmosphere. The solvent was then removed by vacuum
distillation while the reaction vessel was warmed in a water bath. The
residue left behind was dark brown in color and was flash-chromato-
graphed through a bed of silica covered with Celite, using 50% benzene
in hexane as the eluant. Removal of the solvent by rotary evaporation
afforded an orange oil that was further purified by column chroma-
tography on silica gel, with 20% benzene in hexane solution as the
eluant. The recovered yellow oil was crystallized from hot hexane to
3
(s). 31P{1H} NMR (CDCl3, 121.66 MHz) δ 66.74 [d, J(PP) ) 7.2
Hz, PA], 52.44 [d, 3J(PP) ) 7.2 Hz, PX]. 1H NMR (CDCl3, 500 MHz)
δ 7.9-7.1 (m, 13 H, DBP, Ph), 2.24 [dddd, 3J(PH) ) 38.5 Hz, 2J(PH)
) 11.5 Hz, 2J(H5H6) ) 11.5 Hz, 3J(H4H6) ) 4.3 Hz, 1 H, H6], 2.13 [d,
2J(H1H2) ) 11.6 Hz, 1 H, H2], 1.94 [d, 4J(PH) ) 1.5 Hz, 3 H, CH3(c)],
2
2
1.75 [dd, J(H2H1) ) 11.6 Hz, J(PH) ) 3.8 Hz, 1 H, H1], 1.68 (qd,
3J(CH3(a)H3) ) 6.6 Hz, 3J(PH) ) 5.0 Hz, 1 H, H3], 1.46 (s, 3 H, CH3(b)),
3
1.40-1.35 (m, 2 H, H4 and H5), 1.02 [d, J(H3CH3(a)) ) 6.6 Hz, 3 H,
CH3(a)]. 13C{1H} NMR (CDCl3, 125.71 MHz) δ 216.63 [dd, 2J(PC) )
24.9 Hz, 2J(PC) ) 8.8 Hz, COeq], 215.16 [dd, 2J(PC) ) 27.2 Hz, 2J(PC)
2
2
) 8.0 Hz, COeq], 209.72 [dd, J(PC) ) 10.4 Hz, J(PC) ) 8.2 Hz,
2
2
COax], 207.62 [apparent t, J(PC) ) J(PC) ) 9.3 Hz, COax], 152.64
[d, 2J(PC) ) 3.8 Hz, Ci′), 142.18 [d, 2J(PC) ) 6.4 Hz, Câ], 141.84 [d,
2J(PC) ) 6.3 Hz, Câ], 140.16 [d, J(PC) ) 33.6 Hz, CR], 139.78 [dd,
1
1J(PC) ) 25.6 Hz, J(PC) ) 3.3 Hz, C6], 139.52 [dd, J(PC) ) 39.5
3
1
3
2
Hz, J(PC) ) 4.3 Hz, CR], 135.58 [d, J(PC) ) 15.0 Hz, C5], 130.53
[d, 4J(PC) ) 1.6 Hz, C2′], 130.31 [d, 4J(PC) ) 1.1 Hz, C2′], 129.77 [d,
2J(PC) ) 15.5 Hz, C4′], 129.75 (s, Cm′), 129.71 (s, Cm′), 129.68 [d,
2J(PC) ) 16.0 Hz, C4′], 128.63 [d, J(PC) ) 10.1 Hz, C3′], 128.54 (s,
3
3
5
Co′), 127.83 [d, J(PC) ) 9.7 Hz, C3′], 127.41 [d, J(PC) ) 1.5 Hz,
3
3
Cp′], 121.59 [d, J(PC) ) 4.3 Hz, C1′], 121.13 [d, J(PC) ) 4.8 Hz,
C1′], 61.33 [d, 2J(PC) ) 1.0 Hz, C4], 50.80 [d, 1J(PC) ) 26.2 Hz, C7],
48.44 [apparent t, 1J(PC) ) 2J(PC) ) 17.7 Hz, C2], 47.39 [dd, 2J(PC)
) 15.5 Hz, 3J(PC) ) 1.6 Hz, C3], 38.33 [dd, 1J(PC) ) 19.7 Hz, 2J(PC)
3
3
) 14.5 Hz, C1], 19.91 [d, J(PC) ) 7.5 Hz, CH3(c)], 17.49 [d, J(PC)

12566 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Maitra et al.
3
) 3.8 Hz, CH3(b)], 16.20 [d, J(PC) ) 5.9 Hz, CH3(a)]. Anal. Calcd
manner using the same solvent system. The first few fractions eluted
oxides of the ligand and a trace quantity of unreacted starting material
E. With increasing benzene concentration in the eluant, 5 was eluted
next, followed by a trace amount of the triphosphine complex 6. The
latter was crystallized from hot hexane to give only a few platelike
yellow crystals. Complex 5 was recrystallized from hot hexane to give
1.00 g (1.61 mmol, 33%) of pale yellow crystals of the pure product.
Mp >220 °C (decomp). IR (CH2Cl2) νCO (cm-1) 2022 (w), 1930 (sh),
1906 (s, b), 1894 (sh). 31P{1H} NMR (CDCl3, 121.66 MHz) δ 75.13
for C32H28MoO4P2: C, 60.60; H, 4.41. Found: C, 60.46; H, 4.27.
[2-Phenyl-3,4,5-trimethyl-6-methylene(diphenylarsino)-1-
phosphabicyclo[2.2.1]hept-2-ene]tetracarbonylmolybdenum(0) (Com-
plex 3). Compound C (2.43 g, 4.67 mmol) was reacted with 0.88 g
(4.67 mmol) of DMPP following the same reaction conditions and
procedure as mentioned earlier in method a. The crude product was
purified by column chromatography on silica gel with a 10:90 benzene-
hexane mixture. Oxides of the ligands and unreacted pentacarbonyl
complexes were eluted first. On increasing the concentration of benzene
in the eluant gradually to 20-25%, complex 3 was eluted and was
obtained as a pale yellow oil on removal of the solvents. Crystallization
from hot hexane gave 1.96 g (2.88 mmol, 61.7%) of pale yellow crystals
of 3. Mp >184-185 °C (decomp). IR (CH2Cl2) νCO (cm-1) 2024
(w), 1924 (sh), 1911 (s, b), 1886 (sh). 31P{1H} NMR (CDCl3, 121.66
MHz) δ 70.91. 1H NMR (CDCl3, 500 MHz) δ 7.6-7.1 (m, 15 H,
2
2
[d, J(PP) ) 7.8 Hz, PA], 52.19 [d, J(PP) ) 7.8 Hz, Px]. 1H NMR
(CDCl3, 500 MHz) δ 7.9-7.18 (m, 13 H, DBP and Ph), 2.16 [dddd,
2
2
3
3J(PH) ) 39.5 Hz, J(H5H6) ) 14.0 Hz, J(PH) ) 12.0 Hz, J(H4H6)
2
) 5.8 Hz, 1 H, H6], 2.02 [d, J(H1H2) ) 12.0 Hz, 1 H, H2], 1.88 [d,
4J(PH) ) 1.5 Hz, 3 H, CH3(c)], 1.86-1.80 (m, 2 H, H3 and H4), 1.63
2
2
[dd, J(H2H1) ) 12.0 Hz, J(PH) ) 3.5 Hz, 1 H, H1], 1.49 (s, 3 H,
CH3(b)), 1.42-1.34 (m, 2 H, H5 and H7). 13C{1H} NMR (CDCl3, 125.71
MHz) δ 216.49 [dd, 2J(PC) ) 24.9 Hz, 2J(PC) ) 8.80 Hz, COeq], 215.13
[dd, 2J(PC) ) 27.3 Hz, 2J(PC) ) 8.2 Hz, COeq], 209.70 [dd, 2J(PC) )
10.3 Hz, 2J(PC) ) 8.0 Hz, COax], 207.69 [apparent t, 2J(PC) ) 2J(PC)
) 9.5 Hz, COax], 153.81 [d, J(PC) ) 3.6 Hz, Ci′], 142.21 [d, J(PC)
) 6.4 Hz, Câ], 141.84 [d, J(PC) ) 6.4 Hz, Câ], 140.25 [d, J(PC) )
3
2
3
Ph), 3.28 [ddd, J(PH) ) 38.0 Hz, J(H5H6) ) 12.0 Hz, J(H4H6) )
6.0 Hz, 1 H, H6], 2.03 [dd, 2J(H1H2) ) 12.0 Hz, 2J(PH) ) 1.0 Hz, 1 H,
4
3
H2], 1.85 [d, J(PH) ) 1.0 Hz, 3 H, CH3(c)), 1.74 [qd, J(CH3(a)H3) )
2
2
4
2
6.8 Hz, J(PH) ) 5.0 Hz, 1 H, H3], 1.61 [dd, J(H1H2) ) 12.0 Hz,
2
1
2J(PH) ) 3.8 Hz, 1 H, H1], 1.43 (s, 3 H, CH3(b)), 1.36-1.20 (m, 2 H,
1
3
H4 and H5), 1.12 [d, J(H3CH3(a)) ) 6.8 Hz, 3 H, CH3(a)). 13C{1H}
3
33.9 Hz, CR], 139.51 [dd, J(PC) ) 39.6 Hz, J(PC) ) 4.4 Hz, CR],
138.82 [dd, 1J(PC) ) 21.9 Hz, 3J(PC) ) 3.1 Hz, C6], 135.52 [d, 2J(PC)
) 15.3 Hz, C5], 130.54 [d, 4J(PC) ) 1.8 Hz, C2′], 130.33 [d, 4J(PC) )
2
NMR (CDCl3, 125.70 MHz) δ 217.64 [d, J(PC) ) 8.8 Hz, COeq],
2
2
216.63 [d, J(PC) ) 27.5 Hz, COeq], 209.05 [d, J(PC) ) 10.1 Hz,
2
2
2
2
1.15 Hz, C2′], 129.72 [d, J(PC) ) 15.7 Hz, C4′], 129.70 [d, J(PC) )
COax], 207.46 [d, J(PC) ) 10.1 Hz, COax], 153.08 [d, J(PC) ) 3.6
3
1
3
16.2 Hz, C4′], 129.53 (s, Cm′), 129.49 (s, Cm′), 128.64 [d, J(PC) )
Hz, Ci′], 139.78 [d, J(PC) ) 23.1 Hz, C6], 137.61 [d, J(PC) ) 4.9
3
2
10.3 Hz, C3′], 128.51 (s, Co′), 128.50 (s, Co′), 127.77 [d, J(PC) ) 9.6
Hz, Ci], 137.24 (s, Ci), 135.75 [d, J(PC) ) 15.5 Hz, C5], 132.06 (s,
5
3
Hz, C3′], 127.39 [d, J(PC) ) 1.8 Hz, Cp′], 121.60 [d, J(PC) ) 4.4
Co), 130.98 (s, Co), 129.72 (s, Cp), 129.60 (s, Cm′), 129.57 (s, Cm′),
129.47 (s, Cp), 128.90 (s, Cm), 128.82 (s, Cm), 128.30 (s, 2Co′), 127.16
Hz, C1′], 121.34 [d, 3J(PC) ) 4.8 Hz, C1′], 58.87 [d, 2J(PC) ) 1.3 Hz,
1
1
5
2
C4], 48.58 [d, J(PC) ) 25.0 Hz, C7], 41.58 [dd, J(PC) ) 19.3 Hz,
[d, J(PC) ) 1.8 Hz, Cp′], 61.13 [d, J(PC) ) 0.8 Hz, C4], 50.72 [d,
2J(PC) ) 16.8 Hz, C2], 39.28 [dd, J(PC) ) 20.0 Hz, J(PC) ) 14.0
1
2
1J(PC) ) 25.4 Hz, C7], 48.27 (s, C3), 47.50 [d, 1J(PC) ) 16.1 Hz, C2],
Hz, C1], 39.15 [dd, 2J(PC) ) 16.2 Hz, 3J(PC) ) 2.2 Hz, C3], 21.22 [d,
2
3
33.27 [d, J(PC) ) 15.0 Hz, C1], 19.91 [d, J(PC) ) 7.8 Hz, CH3(c)],
17.57 [d, 3J(PC) ) 3.8 Hz, CH3(b)], 16.17 [d, 3J(PC) ) 6.0 Hz, CH3(a)].
Anal. Calcd for C32H30AsMoO4P: C, 56.51; H, 4.41. Found: C, 56.38;
H, 4.53.
3J(PC) ) 7.5 Hz, CH3(c)], 13.03 [d, J(PC) ) 6.2 Hz, CH3(b)]. Anal.
3
Calcd for C31H26MoO4P2: C, 60.03; H, 4.19. Found: C, 59.87; H,
4.03.
Syntheses and Characterization of Complexes 1a and 2a: cis-
(trans-crotyldiphenylphosphine)(1-phenyl-3,4-dimethylphosphole)-
tetracarbonylmolybdenum(0) (Complex 1a). To a solution of 5.20
g (10.92 mmol) of A in 200 mL of freshly distilled toluene was added
2.1 g (10.92 mmol) of DMPP under a nitrogen atmosphere with stirring.
The resulting reaction mixture was refluxed at 110 °C for 8 h. It was
cooled to ambient temperature and the solvent was removed by vacuum
distillation. The resulting oily brown-yellow residue was column-
chromatographed on silica gel with benzene-hexane (5:95). The oxide
of DMPP was eluted first followed by some of the unreacted
pentacarbonyl complex. The cis-mixed-ligand tetracarbonyl complex
was eluted next and obtained as a yellow oil after removal of the solvent.
It was further purified by recrystallization from a mixture of 1:1
methylene chloride and methanol to give 4.00 g (6.30 mmol, 57.7%)
of pale yellow crystals of 1a.
[2-Phenyl-3,4-dimethyl-6-methylene(diphenylphosphino)-1-
phosphabicyclo[2.2.1]hept-2-ene]tetracarbonylmolybdenum(0) (Com-
plex 4). Compound D (2.19 g, 4.74 mmol) was reacted with 0.89 g
(4.74 mmol) of DMPP under the same reaction conditions as mentioned
in method a earlier. By employing the same purification and crystal-
lization techniques, 1.30 g (2.09 mmol, 44.10%) of pale yellow crystals
of 4 was obtained. Mp > 164-166 °C (decomp). IR (CH2Cl2) νCO
(cm-1) 2022 (w), 1924 (sh), 1909 (s, b), 1886 (sh). 31P{1H} NMR
(CDCl3, 121.66 MHz) δ 72.74 [d, 2J(PP) ) 4.2 Hz, PA], 55.13 [d, 2J(PP)
) 4.2 Hz, Px]. 1H NMR (CDCl3, 500 MHz) δ 7.64-7.10 (m, 15H,
3
2
2
Ph), 3.27 [dddd, J(PH) ) 39.0 Hz, J(H5H6) ) 14.0 Hz, J(PH) )
11.0 Hz, 3J(H4H6) ) 4.5 Hz, 1 H, H6], 1.92 (m, 2 H, H3 and H4), 1.91
2
4
[d, J(H1H2) ) 11.5 Hz, 1 H, H2], 1.81 [d, J(PH) ) 2.0 Hz, 3 H,
2
2
CH3(c)], 1.51 [dd, J(H2H1) ) 11.5 Hz, J(PH) ) 3.5 Hz, 1 H, H1],
1.49 (m, 1 H, H7), 1.47 (s, 3 H, CH3(b)), 1.39 (m, 1 H, H5). 13C{1H}
2
2
NMR (CDCl3, 125.70 MHz) δ 216.92 [dd, J(PC) ) 25.6 Hz, J(PC)
2
2
) 8.8 Hz, COeq], 216.84 [dd, J(PC) ) 27.3 Hz, J(PC) ) 8.9 Hz,
COeq], 209.76 [dd, 2J(PC) ) 10.1 Hz, 2J(PC) ) 8.0 Hz, COax], 207.73
2
2
2
[dd, J(PC) ) 9.9 Hz, J(PC) ) 8.9 Hz, COax], 154.04 [d, J(PC) )
1
3
3.6 Hz, Ci′], 138.60 [dd, J(PC) ) 22.2 Hz, J(PC) ) 3.4 Hz, C6],
137.04 [d, 1J(PC) ) 29.7 Hz, Ci], 136.75 [dd, 1J(PC) ) 33.3 Hz, 3J(PC)
) 3.6 Hz, Ci], 135.52 [d, 2J(PC) ) 15.3 Hz, C5], 132.37 [d, 2J(PC) )
2
4
12.9 Hz, Co], 130.66 [d, J(PC) ) 12.3 Hz, Co, 129.92 [d, J(PC) )
4
2.0 Hz, Cp], 129.39 [d, J(PC) ) 1.8 Hz, Cp], 129.29 (s, Cm′), 129.26
(s, Cm′), 128.48 [d, 3J(PC) ) 9.6 Hz, Cm], 128.46 [d, 3J(PC) ) 9.1 Hz,
5
Cm], 128.21 (s, Co′), 128.20 (s, Co′), 127.06 [d, J(PC) ) 1.9 Hz, Cp′],
58.60 [d, 2J(PC) ) 1.4 Hz, C4], 48.45 [d, 1J(PC) ) 24.6 Hz, C7], 41.80
Mp >145-147 °C (decomp). IR (CH2Cl2) νCO (cm-1) 2020 (w), 1912
(s, b), 1876 (sh). 31P{1H} NMR (CDCl3, 121.66 MHz) δ 30.93 [d,
1
2
2
[dd, J(PC) ) 18.3 Hz, J(PC) ) 4.2 Hz, C2], 39.60 [dd, J(PC) )
15.2 Hz, J(PC) ) 2.6 Hz, C3], 36.45 [dd, J(PC) ) 22.9 Hz, J(PC)
) 14.3 Hz, C1], 21.20 [d, J(PC) ) 7.5 Hz, CH3(c)], 12.93 [d, J(PC)
) 6.0 Hz, CH3(b)]. Anal. Calcd for C31H28MoO4P2: C, 59.84; H, 4.50.
Found: C, 59.71; H, 4.63.
3
1
2
2
2J(PP) ) 24.1 Hz, PA], 28.55 [d, J(PP) ) 24.1 Hz, Px]. 1H NMR
3
3
2
(CDCl3, 500 MHz) δ 7.42-7.28 (m, 15 H, Ph), 6.10 [d, J(PH) )
35.5 Hz, 2 H, HR], 5.16 (m, 2 H, Ha and Hb), 2.98 (m, 2 H, CH2), 1.97
(s, 6 H, CH3 of DMPP), 1.49 (m, 3 H, CH3). 13C{1H} NMR (CDCl3,
125.70 MHz) δ 215.02 [dd, 2J(PC) ) 17.0 Hz, 2J(PC) ) 8.7 Hz, COeq],
214.82 [dd, 2J(PC) ) 21.9 Hz, 2J(PC) ) 8.7 Hz, COeq], 209.24 [apparent
[2-Phenyl-3,4-dimethyl-6-methylene(dibenzophosphole)-1-
phosphabicyclo[2.2.1]hept-2-ene]tetracarbonylmolybdenum(0) (Com-
plex 5). Compound E (2.64 g, 4.92 mmol) was reacted with an
equimolar amount of DMPP under the same reaction conditions as
mentioned above. The crude product mixture was purified in the same
2
2
t, J(PC) ) 9.1 Hz, 2COax], 148.53 [d, J(PC) ) 7.9 Hz, Câ], 137.14
1
3
1
[dd, J(PC) ) 28.7 Hz, J(PC) ) 1.1 Hz, Ci], 133.12 [dd, J(PC) )
32.4 Hz, 3J(PC) ) 1.1 Hz, Ci], 132.43 [d, 2J(PC) ) 6.2 Hz, Co], 131.29

Intramolecular [4+2] Diels-Alder Cycloadditions
Table 3. Crystallographic Data for Complexes 1-6
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12567
complex
1
2
3
4
5
6
chemical formula
formula weight
crystal system
space group
a (Å)
b (Å)
c (Å)
C64H60Mo2O8P4
1272.88
triclinic
C32H28MoO4P2
634.42
monoclinic
P21/c
17.341 (3)
9.347 (2)
18.195 (4)
90
91.866 (9)
90
C32H30AsMoO4P
680.39
triclinic
C31H28MoO4P2
622.41
triclinic
C31H26MoO4P2
620.40
monoclinic
P21/c
9.2723 (9)
23.242 (2)
13.2746 (12)
90
92.848 (7)
90
C45H39MoO3P3
816.61
monoclinic
P21/n
11.8832 (13)
16.924 (2)
20.059 (2)
90
94.108 (9)
90
P1h
P1h
P1h
10.0576 (14)
14.316 (2)
22.726 (3)
79.692 (12)
85.132 (10)
71.609 (11)
3053.4 (8)
2
10.132 (2)
10.946 (2)
13.985 (2)
91.289 (10)
93.890 (10)
91.586 (13)
1546.4 (5)
2
9.757 (2)
10.9580 (10)
13.7321 (12)
92.740 (6)
91.883 (9)
92.047 (10)
1464.7 (3)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
2947.6 (10)
4
1.430
2857.3 (4)
4
1.442
4023.8 (8)
4
1.348
Z
F
calcd (g cm-3
)
1.384
0.568
1.461
1.571
1.411
0.590
µ (mm-1
)
0.588
0.605
0.484
min and max trans
data/restrnt/params
GOF(F2)a
0.9558, 0.8561
13909/0/721
1.052
0.0496
0.1422
0.9309, 0.6189
5392/0/361
1.037
0.0367
0.0883
0.7993, 0.7349
3826/0/343
1.028
0.0281
0.0749
0.8758, 0.8444
5016/0/352
1.052
0.0493
0.1065
0.7697, 0.7297
5247/0/469
1.030
0.0488
0.0961
3849/0/352
1.016
0.0478
R1(F)b
wR2(F2)c
0.0916
2
2
2
a GOF ) S ) [∑[w(Fo - Fc2)2]/(n - p)]0.5
.
b R1(F) ) ∑||Fo| - |Fc||/∑|Fo|. c wR2(F2) ) [∑[w(Fo - Fc2)2]/∑[w(Fo )]2]0.5
.
2
1
[d, J(PC) ) 11.7 Hz, Co], 130.69 [d, J(PC) ) 35.1 Hz, CR], 130.62
[d, 3J(PC) ) 10.8 Hz, CdCCH3], 129.25 (s, Cp), 129.24 (s, Cp), 128.34
[d, 3J(PC) ) 9.3 Hz, Cm], 128.03 [d, 3J(PC) ) 8.5 Hz, Cm], 122.47 [d,
33.7 Hz, 2J(PC) ) 2.5 Hz, CR], 128.85 [d, 4J(PC) ) 2.0 Hz, Cp], 128.06
[d, 3J(PC) ) 9.4 Hz, Cm], 127.78 [d, 3J(PC) ) 9.7 Hz, C3], 122.25 [d,
3
2J(PC) ) 6.9 Hz, CdCCH2), 120.96 [d, J(PC) ) 4.2 Hz, C1], 39.37
2J(PC) ) 3.0 Hz, CdCCH2), 37.41 [dd, J(PC) ) 19.4 Hz, J(PC) )
[dd, 1J(PC) ) 17.0 Hz, 3J(PC) ) 4.2 Hz, CH2], 17.70 [d, 4J(PC) ) 2.6
1
3
4
3
2.0 Hz, CH2], 17.97 [d, J(PC) ) 0.9 Hz, CH3 of crotyl], 17.19 [dd,
Hz, CH3 of crotyl], 17.07 [d, J(PC) ) 10.1 Hz, CH3 of DMPP].
3J(PC) ) 9.9 Hz, J(PC) ) 1.4 Hz, CH3 of DMPP].
X-ray Data Collection and Processing. Pale yellow crystals of
1-6 were grown by slow cooling of saturated solutions of the
complexes from hot hexane. Suitable crystals were mounted on glass
fibers and placed on a Siemens P4 diffractometer. Crystal data and
details of data collection for complexes 1-6 are given in Table 3.
Intensity data were taken in the ω-mode at 298K with Mo-KR graphite
monochromated radiation (λ ) 0.710 73 Å). Three check reflections
monitored every 100 reflections showed random (<2%) variation during
the data collections. The data were corrected for Lorentz, polarization
effects, and absorption (using an empirical model derived from
azimuthal data collections), except for 2, where no absorption correction
was applied. Scattering factors and corrections for anomalous disper-
sion were taken from a standard source.16 Calculations were performed
with the Siemens SHELXTL PLUS version 5.03 software package on
a personal computer. The structures were solved by direct methods.
Anisotropic thermal parameters were assigned to all non-hydrogen
atoms. Hydrogen atoms were refined at calculated positions with a
riding model in which the C-H vector was fixed at 0.96 Å.
5
cis-(trans-Crotyldibenzophosphole)(1-phenyl-3,4-dimethylphos-
phole)tetracarbonylmolybdenum(0) (Complex 2a). To a solution of
2.60 g (5.65 mmol) of B in 150 mL of freshly distilled toluene was
added 1.06 g (5.65 mmol) of DMPP under a nitrogen atmosphere; the
mixture was reacted under the same reaction conditions as described
above. Purification of the crude product by the above method gave
2.8 g (4.41 mmol, 78.1%) of 2a as a pale yellow viscous oil.
Acknowledgment. We are grateful to the donors of the
Petroleum Research Fund, administered by the American
Chemical Society, for financial support.
IR (CH2Cl2) νCO (cm-1) 2020 (w), 1920 (sh), 1908 (s, b), 1882 (sh).
2
31P{1H} NMR (CDCl3, 121.66 MHz) δ 29.89 [d, J(PP) ) 21.7 Hz,
2
PA], 26.12 [d, J(PP) ) 21.7 Hz, Px]. 1H NMR (CDCl3, 500 MHz) δ
7.8-6.9 (m, 13 H, DBP and Ph), 5.74 [d, 2J(PH) ) 36.5 Hz, 2 H, HR′],
5.07 (m, 2 H, Ha and Hb), 2.67 (m, 2 H, CH2), 1.68 (s, 6 H, CH3 of
DMPP), 1.43 (m, 3 H, CH3). 13C{1H} NMR (CDCl3, 125.70 MHz) δ
Supporting Information Available: X-ray characterization
data for complexes 1-6, including tables of experimental details,
atomic coordinates, thermal parameters, bond distances and bond
angles, anisotropic displacement parameters, and hydrogen
coordinates (42 pages). See any current masthead page for
ordering and Internet access instructions.
2
2
214.84 [dd, J(PC) ) 20.6 Hz, J(PC) ) 8.9 Hz, COeq], 213.53 [dd,
2J(PC) ) 24.8 Hz, 2J(PC) ) 8.4 Hz, COeq], 209.23 [apparent t, 2J(PC)
2
2
) J(PC) ) 9.4 Hz, 2COax], 148.38 [d, J(PC) ) 8.0 Hz, Câ], 142.37
2
1
[d, J(PC) ) 5.2 Hz, Câ′], 140.32 [d, J(PC) ) 34.2 Hz, CR′], 132.88
[dd, 1J(PC) ) 33.9 Hz, 3J(PC) ) 2.1 Hz, Ci], 130.70 [d, 2J(PC) ) 11.6
JA9724654
2
3
Hz, Co], 130.30 [d, J(PC) ) 15.2 Hz, C4], 130.01 [d, J(PC) ) 10.2
Hz, CdCCH3], 129.73 [d, 4J(PC) ) 1.3 Hz, C2], 129.39 [dd, 1J(PC) )
(16) International Tables For X-ray Crystallography, D. Reidel Publish-
ing Co., Boston, MA, 1992; Vol. C.