Synthesis and Characterization of New Binuclear Co(0) Complexes with Diphosphinoamine Ligands. a Potential Approach for Asymmetric Pauson-Khand Reactions

Article abstract of DOI:10.1021/jo982245o

The synthesis of P-N-P bidentate ligands and the evaluation, based on IR and X-ray data, of their π-acceptor properties in the complexes derived from phenylacetylene-dicobalt hexacarbonyl have been carried out. In addition, the reactivity of these complexes in the Pauson-Khand reaction has been examined.

Full text of DOI:10.1021/jo982245o

3
492
J . Org. Chem. 1999, 64, 3492-3497
Syn th esis a n d Ch a r a cter iza tion of New Bin u clea r Co(0) Com p lexes
w ith Dip h osp h in oa m in e Liga n d s. A P oten tia l Ap p r oa ch for
Asym m etr ic P a u son -Kh a n d Rea ction s
†
†
‡
‡
†,§
Yves Gimbert, Fr e´ d e´ ric Robert, Andr e´ Durif, Marie-Th e´ r e` se Averbuch, Nina Kann, and
Andrew E. Greene*,
†
Universit e´ J oseph Fourier de Grenoble, Chimie Recherche et Service de Cristallographie (LEDSS),
3
8041 Grenoble Cedex, France
Received November 10, 1998
The synthesis of P-N-P bidentate ligands and the evaluation, based on IR and X-ray data, of
their π-acceptor properties in the complexes derived from phenylacetylene-dicobalt hexacarbonyl
have been carried out. In addition, the reactivity of these complexes in the Pauson-Khand reaction
has been examined.
In tr od u ction
Metal-mediated cyclization reactions have made sig-
1
nificant contributions in organic synthesis. One of the
earliest and most useful of these is the Pauson-Khand
reaction.2 In this reaction, promoted by Co
2 8
(CO) , a
cyclopentenone is formed through a formal [2 + 2 + 1]
cycloaddition that involves an alkyne, an alkene, and
carbon monoxide (eq 1).
which if appropriately chosen would give rise to unique
complexes, seemed to be of potential interest.
Considerable effort has been invested to develop asym-
3
metric variants of this novel reaction. Among the dif-
Diphosphorus compounds, having a single methylene
group or an amino group between the two phosphorus
atoms, have been used as chelating and bridging ligands
ferent approaches examined, one of the most interesting
appears to be that which involves complexes in which a
carbon monoxide ligand in the dicobalt hexacarbonyl
adducts is replaced by the chiral phosphine glyphos (eq
, L* ) glyphos). The purified phosphine complexes react
to afford the expected cyclopentenones with up to total
5
to transition-metal centers. However, examples of the
utilization of such ligands in the Pauson-Khand reaction
2
are rare. A complex involving bis(diphenylphosphino)-
6
methane (dppm) 2a (Chart 1) has been reported, but the
enantioselectivity.4
authors found that the ligand had a deleterious effect on
the yield of the Pauson-Khand reaction.
Nonetheless, the approach is not of preparative value
because of a major drawback, i.e., with this monodentate
ligand, the formation of two diastereomeric complexes in
roughly equimolar amounts results (except if R ) R′). To
The Pauson-Khand reaction is a multistep process,
but no definitive mechanistic pathway has been described
7
to date. Nevertheless, from various observations it
appears likely that before insertion the alkene coordi-
nates to a cobalt atom, with the displacement of a carbon
monoxide ligand. The ability of carbon monoxide, a
2
circumvent this problem, C bidentate ligands 2 (eq 3),
*
Tel: (33) 4-76-51-46-86. Fax: (33) 4-76-51-44-94. E-mail:
8
ubiquitous ligand in organometallic chemistry, to sta-
Andrew.Greene@ujf-grenoble.fr.
†
‡
§
bilize transition-metal centers in low oxidation states is
associated with its electron-withdrawing properties. The
replacement of carbon monoxide in various complexes
Chimie Recherche, LEDSS.
Service de Cristallographie, LEDSS.
Present address: Department of Chemistry, Chalmers University
of Technology, SE-412 96 Gothenborg, Sweden.
1) Noyori, R. Asymmetric Catalysis in Organic Synthesis; Wiley:
New York, 1994.
2) Khand, I. U.; Knox, G. R.; Pauson, P. L.; Watts, W. E. J . Chem.
Soc., Chem. Commun. 1971, 36.
3) For a recent review, see: Geis, O.; Schmaltz, H. G. Angew. Chem.,
Int. Ed. Engl. 1998, 37, 911.
4) (a) Hay, A. M.; Kerr, W. J .; Kirk, G. G.; Middlemiss, D.
(
(5) Chaudret, B.; Delavaux, B.; Poiblanc, R. Coord. Chem. Rev. 1988,
86, 191. Balakrishna, M. S.; Sreenivasa Reedy, V.; Krishnamurty, S.
S.; Nixon, J . F.; Burckett St. Laurent, J . C. T. R. Coord. Chem. Rev.
1994, 129, 1.
(6) Billington, D. C.; Helps, I. M.; Pauson, P. L.; Thomson, W.;
Willison, D. J . Organomet. Chem. 1988, 354, 233.
(7) Schore, N. E. Org. React. 1991, 40, 1.
(
(
(
Organometallics 1995, 14, 4986. (b) Brunner, H.; Niedernhuber, A.
Tetrahedron: Asymmetry 1990, 1, 711. (c) Bladon, P.; Pauson, P. L.;
Brunner, H.; Eder, R. J . Organomet. Chem. 1988, 355, 449.
(8) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th
ed; Wiley: New York, 1988.
1
0.1021/jo982245o CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/27/1999

Co(0) Complexes with Bis(phosphino)amine Ligands
J . Org. Chem., Vol. 64, No. 10, 1999 3493
Ch a r t 1
s
F igu r e 1. C2v and C conformers of diphosphinoamines.
9
with a ligand, in particular a C
2
bidentate ligand having
similar bonding characteristics, is potentially of consider-
able interest; unfortunately, however, the number of
ligands with nearly the π-acceptor ability of carbon
monoxide is rather small.10 K u¨ ndig and co-workers have
2
recently reported one such C ligand: two phosphorus
centers bearing electron-withdrawing fluoro groups and
linked by a trans-1,2-cyclopentanediol-derived bridge.9b
In this paper, we report the synthesis of new bidentate
ligands with the backbone P-N-P, evaluate their π-
acceptor properties in the complexes 3 (Chart 1), and
describe the reactivity of these complexes in the Pauson-
Khand reaction. We note in advance that the results
obtained in these initial systems are expected to help in
the design of effective chiral ligands for a new approach
to asymmetric Pauson-Khand reactions.
F igu r e 2. X-ray structure of ligand 2e (selected angles in deg).
Hydrogen atoms have been omitted for clarity.
on the basis of previously reported data.13a Diphosphino-
1
3
s
amines can also adopt a C conformation (Figure 1).
In each, the lone pairs on N and P are orthogonal. NMR
and electron and X-ray diffraction analyses14 show that
in general the C2v conformation is favored when the R
and R′ groups are relatively small, whereas the C
s
Resu lts a n d Discu ssion
conformation is preferred when the R and/or R′ substit-
uents are large. In 2b-e, R and R′ are rather small (R′
Liga n d Syn th esis. Ligand 2a is commercially avail-
)
CH
3
6 5 3 2
, R ) C H , F, pyrrolyl, (CF ) CHO), thus the C2v
able. Literature methods were used for the synthesis of
ligands 2b11 and 2c. The diphosphorus compounds 2d
12
conformation should in fact be preferred. X-ray diffraction
studies of 2b and 2e (Figure 2) (2d has not yet been
obtained in crystalline form) and an electron diffraction
study of 2c15 further support this conclusion. These
studies also indicate partial double-bond character for the
P-N bond in these ligands.1
and 2e were prepared (eq 4) through treatment of CH
3
N-
1
2
(PCl
2
)
2
with (CF ) CHOH in the presence of Et N and
3 2 3
with N-lithiated pyrrole, respectively, and were purified
by column chromatography on silica gel (2d , 50%, color-
less oil; 2e, 67%, colorless crystals).
3d
In general, the P-N bond lengths reported in the
literature16 for the diphosphinoamines lie in the 1.67-
1
.70 Å range (1.77 Å for a P-N single bond), and the
P-N-P angles are in the 110-123° range. The important
bond distances and angles in our ligands (Table 1) are
in agreement with the literature values. Note the differ-
ence, however, between the P-C-P and P-N-P angles,
which will be discussed below.
Crystallographic data for 2b and 2e are listed in Table
2
. In 2b and in 2e, and by extrapolation in 2d , the
geometry around the phosphorus and nitrogen atoms is,
respectively, pyramidal and almost planar.
The 31P NMR spectra of ligands 2b-e each exhibited
a singlet (apart from the P-F coupling in 2c). We have
assigned this resonance to the C2v conformer (Figure 1)
Coor d in a tion of Co(0) Com p lex 1 (R ) C
6 5
H , R′ )
H) w ith Liga n d s 2a -e To Give 3. Complexes 3a -e
(13) (a) Keat, R.; Manojlovic-Muir, L.; Muir, K. W.; Rycroft, D. S. J .
Chem. Soc., Dalton Trans. 1981, 2192. (b) Reed, A. E.; Schleyer, P.v.R.
Inorg. Chem. 1988, 27, 3969. (c) Browning, C. S.; Farrar, D. H.;
Peterson, M. R. J . Mol. Struct (THEOCHEM) 1991, 251, 153. (d)
Kremer, T.; Hampel, F.; Knoch, F. A.; Bauer, W.; Schmidt, A.; Gabold,
P.; Sch u¨ tz, M.; Ellermann, J .; Schleyer, P.v.R. Organometallics 1996,
15, 4776.
(14) From the data in the literature for the diphosphinoamines, it
can be expected that no major conformational differences will exist
between the solid and solution states. See ref 13a.
(15) Hedberg, E.; Hedberg, L.; Hedberg, K. J . Am. Chem. Soc. 1974,
96, 4417.
(
9) (a) J ohnson, J . B.; Klemperer, W. G. J . Am. Chem. Soc. 1977,
9, 7132. (b) K u¨ ndig, E. P.; Dupr e´ , C.; Bourdin, B.; Cunningham, A.;
Pons, D. Helv. Chim. Acta 1994, 77, 421 and references therein.
10) Moloy, K. G.; Petersen, J . L. J . Am. Chem. Soc. 1995, 117, 7696.
9
(
Schnabel, R. C.; Roddick, D. M. Inorg. Chem. 1993, 32, 1513. Koola, J .
D.; Roddick, D. M. J . Am. Chem. Soc. 1991, 113, 1450.
(11) Ewart, G.; Lane, A. P.; McKechnie, J .; Payne, D. S. J . Chem.
Soc. 1964, 1543. Wang, F. T.; Najdzionek, J .; Leneker, K. L.; Wasser-
man, H.; Braitsch, D. M. Synth. React. Inorg. Met.-Org. Chem. 1978,
8
, 119.
12) King, R. B.; Gimeno, J . Inorg. Chem. 1978, 17, 2390. Nixon, J .
F. J . Chem. Soc. A 1968, 2689.
(
(16) Kamalesh Babu, R. P.; Krishnamurty, S. S.; Nethaji, M.
Heteroat. Chem. 1991, 2, 477.

3
494 J . Org. Chem., Vol. 64, No. 10, 1999
Gimbert et al.
Ta ble 1. Selected Bon d Dista n ces a n d An gles for
a
Liga n d s 2a -c,e
P-E-P
(deg)
sym-
P‚‚‚P(Å) metry
ligand
P-E(Å)
ref
2
2
2
2
a
b
c
e
1.858
106.2
2.970
C
C
C
C
2v
2v
2v
2v
17
1.701(1), 1.704(1) 114.86(4) 2.8699(5)
1.680 116.1 2.850
1.6991(9), 1.685(1) 110.89(5) 2.7874(7)
this work
14
this work
b
a
The esd’s are given in parentheses. b By electron diffraction.
Ta ble 2. Cr ysta l Da ta , Da ta Collection P a r a m eter s a n d
Refin em en t Con d ition s, a n d Resu lts for Com p ou n d s 2b
a n d 2e
formula
fw, g/mol
color/habit
dimensions, mm
a, Å
compound 2b
399.41
colorless
compound 2e
355.32
colorless
0.48 × 0.48 × 0.45 0.45 × 0.42 × 0.42
10.091(6)
10.002(2)
11.524(3)
90.00
7.594(3)
17.346(4)
14.106(2)
90.00
98.74(2)
90.00
1836.5(8); 4
P21/a
1.28
b, Å
c, Å
R, deg
â, deg
105.06(4)
90.00
1123.2(7); 2
P21
1.181
2.032
γ, deg
3
V, Å ; Z
space group
3
dcalc, g/cm
-
1
µ(Mo KR), cm
scan type
2.45
ω
59.9
ω
59.9
2
θ max, deg
reflections:
measd/unique
3596/3461
no
5717/5533
0.5
4034 (n ) 2)
293
0.033/0.046
0.035
none
decay, %
with Fo > nσ(Fo2) 3084 (n ) 1)
2
no. of variables
253
0.032/0.039
0.030
0.261 × 10
a
R/Rw
fudge factor
extinction coeff
-
5
a
See Experimental Section.
Ta ble 3. IR CO F r equ en cies for Com p lexes 3a -e
complex
υCO (cm-1)a
3
3
3
3
3
a
b
c
d
e
2020
2020
2065
2061
2042
a
Only highest CO stretch frequency is given.
were prepared by stirring 1 with 2a -e in dry toluene at
0-80 °C until the starting complex 1 was consumed
1-3 h, TLC), followed by evaporation of the toluene
7
(
under reduced pressure and purification of the residue
by flash chromatography. All of the complexes are dark
red, crystalline compounds, which can be easily recrys-
tallized from ethanol and stored at -30 °C for several
weeks. Despite the decreased nucleophilicity of the
phosphorus atoms in the ligands 2c-e in comparison
with 2a ,b, the complexation yields were uniformly good:
F igu r e 3. X-ray structure of complexes 3b (a) and 3c (b)
(selected bond lengths in Å and angles in deg). Hydrogen atoms
have been omitted for clarity.
The usefulness of the carbon monoxide infrared fre-
quency to evaluate ligand electronic properties in com-
8
plexes of this type has been recognized. The frequency
is sensitive to changes in the electron density at the metal
and reflects the extent of π-back-bonding into the carbon
monoxide π* orbital. The infrared spectra of complexes
6
for 3a , 3b, 3c, 3d , and 3e, 70% (lit. 67% ), 75%, 72%,
7
2%, and 58%, respectively. Furthermore, with the
diphosphinoamines, complexes in which the ligand che-
lated one metal center were found, if at all, in only trace
amounts. It is known that replacing the methylene group
in dppm with a small amino group increases the ligand’s
propensity to bridge two metal centers. This has been
interpreted in terms of the ring-strain energy associated
with the difference between the P-C-P and P-N-P
angles in the free ligand and in the ligand coordinated
to one metal center versus two.18
3
c-e indicate, as expected, that the substituents on
phosphorus act as electron-withdrawing groups. As shown
in Table 3, the carbonyl frequencies are significantly
higher than that with the phenyl substituent (3b) but
(
17) Schimdbaur, H.; Reber, G.; Schier, A.; Wagner, F. E.; Muller,
G. Inorg. Chim. Acta 1988, 147, 143.
18) Browning, C. S.; Farrar, D. H. J . Chem. Soc., Dalton Trans.
995, 521. Browning, C. S.; Borrow, R. A.; Farrar, D. H.; Mirza, H. A.
Inorg. Chim. Acta 1998, 271, 112.
(
1

Co(0) Complexes with Bis(phosphino)amine Ligands
J . Org. Chem., Vol. 64, No. 10, 1999 3495
Ta ble 4. Cr ysta l Da ta , Da ta Collection P a r a m eter s a n d
Refin em en t Con d ition s, a n d Resu lts for Com p ou n d s
parameters that may influence the efficiency of the
complexation process (apart from nucleophilicity).
3
a -c
1
. Effect of th e Electr on ic P r op er ties of th e
formula
fw, g/mol
compound 3a compound 3b compound 3c
Liga n d . Bond lengths involving cobalt are of particular
interest. Indeed, complexes 3c-e have Co-P bonds
lengths that are shorter than in 3b . The shift toward
shorter Co-P bonds is fully consistent with the IR data
for these electron-deficient phosphorus-containing com-
plexes. Although phosphorus in these complexes is a poor
σ-donor, the shortened Co-P distance indicates that
there is enhanced π-back-bonding from cobalt to phos-
phorus. As might be expected, 3c-e possess Co-C(CO)
bonds that are longer than those in 3b, carbon monoxide
now being more seriously challenged by the diphosphino-
amine ligands as the π-acceptor.
716.44
731.45
499.03
color/habit
dark red
dark red
dark red
dimensions, mm
0.35 × 0.33 × 0.45 × 0.45 × 0.30 × 0.26 ×
0
.30
0.32
0.25
7.166(2)
9.205(3)
28.231(9)
90.0
a, Å
b, Å
c, Å
40.127(6)
12.434(3)
14.716(2)
90.0
14.128(5)
14.927(6)
17.277(9)
90.00
R, deg
â, deg
γ, deg
92.87(2)
90.0
110.70(4)
90.00
90.0
90.0
3
V, Å ; Z
7333(2); 8
C2/c
3408(3); 4
1862.2(9); 4
space group
P2
1
/a
P2
1
2
1
2
1
d
calc, g/cm3
1.30
10.27
ω
1.425
11.07
ω
1.78
20.09
ω
-
1
µ(Mo KR), cm
2. Effect of Str u ctu r a l P a r a m eter s on th e Ef-
ficien cy of th e Com p lexa tion . From the crystal-
lographic data, it is possible to evaluate the distortion
from their normal geometries the ligands experience on
bridging the two cobalt atoms. The amount of distortion
determines, at least in part, the difficulty of complex-
scan type
2
θ max, deg
51.9
60.0
59.9
reflections:
measd/unique
7112/6810
0
2853 (n ) 3)
406
0.034/0.043
0.030
none
10 957/10 304 3114/3114
decay, %
7.085
0.0
2
> nσ(F 2
with F
o
o
)
6338 (n ) 1)
532
2671 (n ) 1)
236
no. of variables
R/R
18
ation and thus should roughly correlate with the
w
0.046/0.037
0.020
0.040/0.048
0.035
0.131 × 10
efficiency of the latter process (for invariable nucleo-
philicity). It can be assumed that the smaller the differ-
ence between the P-E-P angle in the free ligand and in
the bridged complex, as with the P‚‚‚P distance, the more
favorable the complexation. The differences in the meas-
ured values are reported in Table 7.
From these values, it is possible to understand why
2c despite its low nucleophilicity in comparison with 2a ,b
is, in fact, a good bridging ligand and 2e, which exhibits
the largest ∆(P-E-P), is a relatively poor one.
fudge factor
extinction coeff
0.231 × 10-
6
-4
Ta ble 5. Cr ysta l Da ta , Da ta Collection P a r a m eter s a n d
Refin em en t Con d ition s, a n d Resu lts for Com p ou n d s 3d
a n d 3e
formula
fw, g/mol
color/habit
dimensions, mm
a, Å
compound 3d
1091.16
dark red
compound 3e
691.39
dark red
0.35 × 0.30 × 0.25 0.35 × 0.30 × 0.30
10.611(2)
12.401(6)
15.960(4)
111.07(4)
98.14(2)
76.85(3)
1904.2(1.2); 2
P1h
14.148(4)
13.928(4)
17.126(3)
90.0
111.54(2)
90.0
3139(1); 4
P21/a
1.45
Rea ctivity of Com p lexes 3 in th e In ter m olecu la r
P a u son -Kh a n d Rea ction . Norbornene was used to
evaluate the reactivity of the complexes 3c-e (eq 5). A
stirred solution of the complex and norbornene (5 equiv)
in dry toluene was heated at 80 °C for 3-5 days
b, Å
c, Å
R, deg
â, deg
γ, deg
3
V, Å ; Z
(disappearance of 3 monitored by TLC). After evaporation
space group
3
of the solvent under reduced pressure, the crude product
was purified by flash chromatography to give the ex-
pected adduct, 3a,4,5,6,7,7a-hexahydro-4,7-methano-2-
phenyl-1H-inden-1-one (4), in 24% from 3a , 65% from 3b,
dcalc, g/cm
1.90
11.19
ω
59.9
-
1
µ(Mo KR), cm
scan type
12.00
ω
49.9
2
θ max, deg
reflections:
9
2% from 3c, >98% from 3d , and 90% from 3e.
measd/unique
9738/9210
5.4
5515/5515
0.0
3051 (n ) 2)
380
0.034/0.021
0.000
0.996 × 10
decay, %
with Fo > nσ(Fo2) 5632 (n ) 2)
2
no. of variables
R/Rw
fudge factor
extinction coeff
406
0.039/0.043
0.025
-
7
none
lower than in the parent hexacarbonyl complex (2098
-
1
cm ). Most notable is the carbon monoxide stretch in
3
c, which is 45 cm-1 higher than in 3b. These shifts to
Our results show that complexes 3c-e are highly
higher frequency clearly indicate reduced electron density
donation from cobalt to the carbonyl ligands.
effective in the Pauson-Khand reaction, giving excellent
yields of the cyclopentenone product 4 in comparison with
the reaction of the dicobalt hexacarbonyl complex under
Str u ctu r a l Stu d ies of Com p lexes 3. To explore
further the steric and electronic properties of these
ligands, X-ray crystallographic determinations have been
carried out. Views of the complexes 3b and 3c are shown
in Figure 3. Crystallographic data for 3a -c and 3d ,e are
listed in Tables 4 and 5, respectively. Relevant bond
lengths and angles are listed in Table 6. The electronic
effects of the ligands can be evaluated through examina-
tion of the structural parameters of the complexes in the
solid state. Furthermore, by comparison of the structures
of free ligands 2 with the structures of the same ligands
in the complexes 3, it is possible to gain insight into the
4c
purely thermal conditions (toluene, 110 °C, 58%). The
complex 3c has also been treated with the less reactive
alkene indene (toluene, 110 °C, 5 days) to give the
expected product in 72% yield, which compares favorably
19
with the best literature yield for this reaction (52%,
toluene, 110 °C, 5 h).
The relatively long reaction times with complexes 3c-e
may reflect the strengthening of the Co-CO bonds in the
(19) Khand, I. U.; Pauson, P. L.; Habib, M. J . A. J . Chem. Res. (M)
1978, 4401.

3
496 J . Org. Chem., Vol. 64, No. 10, 1999
Ta ble 6. Selected Bon d Dista n ces a n d An gles for Com p lexes 3a -ea
Gimbert et al.
complex
P-Co
Co-C(CO)
C-O(CO)
Co-Co
P‚‚‚P
E-P-Co
P-E-P
3
3
3
3
3
a
b
c
d
e
2.225(1)
1.759(6)
1.781(6)
1.138(6)
1.125(6)
1.131(6)
1.134(6)
1.137(2)
1.144(3)
1.141(3)
1.136(3)
1.134(5)
1.129(5)
1.129(5)
1.129(5)
1.135(4)
1.125(4)
1.127(4)
1.131(3)
1.139(4)
1.138(3)
1.126(4)
1.145(3)
2.4776(9)
3.012(2)
108.4(1)
108.9(1)
110.9(2)
2
.227(1)
1
1
.788(6)
.762(5)
2.2018(7)
.1958(9)
1.759(2)
1.777(2)
2.4451(4)
2.4397(6)
2.4434(5)
2.4287(6)
2.9280(8)
2.799(1)
2.8545(9)
2.856(1)
112.00(6)
113.71(6)
118.7(1)
115.6(2)
118.0(1)
116.7(1)
2
1
1
.754(2)
.792(3)
2.104(1)
.109(1)
1.802(4)
1.763(4)
116.9(1)
117.6(1)
2
1
1
.794(4)
.789(4)
2.1301(7)
.1498(7)
1.783(3)
1.787(3)
114.02(8)
115.87(7)
2
1
1
.804(3)
.779(3)
2.154(1)
.152(1)
1.776(3)
1.755(3)
113.68(9)
115.49(8)
2
1
1
.792(3)
.743(3)
a
Bond lengths X-Y are given in Å and angles X-Y-Z in degrees. The esd’s are in parentheses.
Ta ble 7. Differ en ces of An gles (P -E-P ) a n d P ‚‚‚P
Dista n ces in F r ee a n d Com p lexed Liga n d s 2a -c,e
Exp er im en ta l Section
Toluene and diethyl ether were distilled from sodium-
benzophenone, and triethylamine and pyrrole were distilled
liganda
∆(P-E-P) (deg)
∆(P‚‚‚P) (Å)
a (67%)
b (75%)
c (72%)
e (58%)
4.9
3.8
0.3
5.4
0.04
0.05
0.05
0.07
from CaH
by the Service Central d’Analyse du CNRS. Melting points are
uncorrected. CH N(PF , CH N(P(C , and CH N(PCl
were prepared according to literature procedures.
2
prior to use. Elemental analyses were performed
3
2
)
2
3
6
H
5
)
2
)
2
3
2 2
)
11,12
Bis-
a
(diphenylphosphino)methane (dppm, Aldrich) and dicobalt
octacarbonyl (Fluka) were used as received.
Yields of complexation given in parentheses.
N ,N -Bis[d i(1,1,1,3,3,3-h e xa flu or oisop r op oxy)p h os-
p h in o]-N-m eth yla m in e (2d ). To a solution of 1,1,1,3,3,3-
hexafluoropropanol (2.1 mL, 20 mmol) and triethylamine (2.8
mL, 20 mmol) in 30 mL of ether at 0 °C was added a solution
complexes as the result of decreased back-bonding to the
phosphorus ligands compared with carbon monoxide in
the parent complex.20 Steric and electronic factors though
appear to combine to extend the effective lifetimes of the
3 2 2
of CH N(PCl ) (932 mg, 4.0 mmol) in 5 mL of ether. After
being allowed to warm to 20 °C, the mixture was refluxed for
4 h. The precipitate was filtered and washed with ether. After
removal of the solvent under reduced pressure, the product
was isolated by dry column chromatography with silica gel
pretreated with 2.5% (v/v) of triethylamine (ethyl acetate/
complexes by reducing their tendency toward clusteriza-
tion21 and thereby allow the significantly improved yields
to be attained.
In conclusion, in this study new bidentate P-N-P
ligands have been designed so as to provide efficiently
bridged complexes with dicobalt hexacarbonyl-acetylene.
The derived complexes, as expected, manifest useful
levels of reactivity, between that of the uncomplexed but
reactive dicobalt hexacarbonyl intermediate and the
complexed but unreactive bis(diphenylphosphino)methane
derivative. This provides an excellent opportunity for
asymmetric synthesis, and our preliminary results ap-
pear to bear this out: (+)-R-methylbenzylamine in place
of methylamine in the ligand 2b22 affords the norbornene
adduct in 54% yield and with a small, but encouraging,
1
hexane, 5/95) to yield 1.48 g (49%) of colorless liquid: H NMR
3
(
J
1
200 MHz, CDCl
3
) δ 2.80 (t, J H-P ) 3.8 Hz, 3 H), 4.55 (hept,
3
31
H-F ) 5.5 Hz, 4 H); P NMR (81 MHz, CDCl
3
) δ 153; IR
373, 1297, 1202, 1109, 690 cm . Anal. Calcd for C13
: C, 20.56; H, 0.92; N, 1.84. Found: C, 20.66; H, 1.21;
N, 2.00.
-
1
7 24
H F -
4 2
NO P
N,N-Bis(d ip yr r olylp h osp h in o)-N-m eth yla m in e (2e). To
a solution of pyrrole (1.4 mL, 20 mmol) in 20 mL of ether cooled
to -78 °C under argon was added 8.7 mL of n-butyllithium
(
2.3 M/hexane, 20 mmol) dropwise. After the addition was
complete, the solution was stirred at -78 °C for 1 h, whereupon
CH N(PCl (932 mg, 4.0 mmol) in 4 mL of ether was added
3
2 2
)
dropwise. The reaction mixture was then allowed to warm to
20 °C and stirred for an additional 12 h. The greenish
precipitate was filtered, and the filtrate was concentrated
under reduced pressure to leave the crude product, which was
1
6% enantiomeric excess. Efforts to attain a practical
induction level and yield through the use of other chiral
amines and electron-withdrawing groups on phos-
phorus, as well as the study of other potential approaches
to this important reaction (e.g., placing chiral groups on
phosphorus), are being actively pursued in our labora-
tory.
recrystallized from hexane to yield 950 mg (67%) of white
1
solid: mp 116-119 °C; H NMR (200 MHz, CDCl
3
) δ 2.74 (t,
3
3
3
J
H-P ) 3.4 Hz, 3 H), 6.38 (t, J H-H ) 2 Hz, 8 H), 6.75 (t, J H-H
31
)
2 Hz, 8 H); P NMR (81 MHz, CDCl
3
) δ 92.5; IR 1457, 1240,
-1
1
5
184, 1067, 815, 736 cm . Anal. Calcd for C17 : C,
7.47; H, 5.39; N, 19.71. Found: C, 57.46; H, 5.33; N, 19.98.
19 5 2
H N P
Gen er a l P r oced u r es for th e P r ep a r a tion of th e Coba lt
(
20) 13CO exchange experiments and theoretical studies are planned
Com p lexes 3. To a solution of 188 mg (0.55 mmol) of dicobalt
octacarbonyl in 4 mL of hexane at 20 °C was added 55 µL (51
mg, 0.5 mmol) of phenylacetylene. The resulting mixture was
stirred for 1 h, whereupon the solvent was removed under
reduced pressure and the resulting crude product was purified
by silica gel chromatography with pentane to yield 179 mg
to examine this and other possible interpretations. We thank a referee
for having suggested exchange experiments.
(21) Reduced tendency toward clusterization could eventually permit
a catalytic version of the above chemistry; see: Lee, B. Y.; Chung, Y.
K.; J eong, N.; Lee, Y.; Hwang, S. H. J . Am. Chem. Soc. 1994, 116,
8
793. Lee, N. Y.; Chung, Y. K. Tetrahedron Lett. 1996, 37, 3145.
22) A known, easily available chiral PNP ligand; see: Kamalesh
Babu, R. P.; Krishnamurthy S. S.; Nethaji, M. Tetrahedron: Asymmetry
995, 6, 427.
(
(92%) of the brown phenylacetylene-dicobalt hexacarbonyl
1
complex.

Co(0) Complexes with Bis(phosphino)amine Ligands
J . Org. Chem., Vol. 64, No. 10, 1999 3497
Complexes 3 were prepared by warming (70-80 °C) a
toluene solution (4 mL) of the phenylacetylene-dicobalt hexa-
carbonyl complex (0.5 mmol) with the appropriate ligand (0.45
mmol) until TLC indicated disappearance of the initial complex
gel chromatography (ethyl acetate/hexane, 5/95) to yield
3a,4,5,6,7,7a-hexahydro-4,7-methano-2-phenyl-1H-inden-1-
one (4).23
Cr ysta llogr a p h ic Stu d ies. Sin gle-Cr ysta l X-r a y Dif-
fr a ct ion . The main crystallographic features for the seven
compounds examined are gathered in Tables 2, 4, and 5. All
of the X-ray single-crystal data reported in the present study
were collected on an Enraf-Nonius CAD4 four-circle diffrac-
tometer operating with Mo KR radiation, monochromated with
a graphite plate. All measurements were run at room tem-
perature. In all cases, the accurate unit-cell dimensions were
obtained by least-squares refinements of angular data of 25
reflections centered in a range of 20-24° (2θ). The stability of
the experimental setup and crystal integrity were monitored
by measuring two standard orientation reflections every 400
measurements and two standard intensity reflections every 2
h. Eventual intensity decays are reported. No absorption
correction was made. All structures were solved by using the
(1-3 h). After removal of the solvent, the crude product was
purified by dry column silica gel chromatography (ethyl
acetate/hexane, 5/95).
µ-[N,N-Bis(d ip h en ylp h osp h in o)-N-m eth yla m in e]tetr a -
2
2
1
ca r bon yl-µ-[η :η -p h en yla cetylen e]d icoba lt (3b): H NMR
3
3
(
200 MHz, CDCl
8.6 Hz, 1 H), 7.1-8.0 (m, 25 H); P NMR (81 MHz, CDCl )
δ 114.6; IR 2020, 1991, 1969 cm ; MS (FAB ) m/z 704 (3.7%,
- CO), 663 (13%), 648 (24%, M - 3CO), 620 (18.7%, M
4CO), 432 (100%). Anal. Calcd for C37 NO : C, 60.75;
H, 3.99; N, 1.91. Found: C, 60.89; H, 4.12; N, 2.04.
3
) δ 2.25 (t, J H-P ) 4.8 Hz, 3 H), 5.37 (t, J H-P
31
)
3
-
1
+
+
+
+
M
-
H
29Co
2
4 2
P
µ-[N,N-Bis(d iflu or op h osp h in o)-N-m eth yla m in e]tetr a -
2
2
1
ca r bon yl-µ-[η :η -p h en yla cetylen e]d icoba lt (3c): H NMR
) δ 2.88 (t, J H-P ) 6.1 Hz, 3 H), 6.07 (t, J 3H-P
3
24
(
)
200 MHz, CDCl
3
direct methods of the teXsan software package. When pos-
10.6 Hz, 1 H), 7.25-7.40 (m, 3 H), 7.50-7.65 (m, 2 H); 1P
3
sible, the secondary extinction was taken into account and the
various values of the coefficients are given. All non-hydrogen
atoms were refined anisotropically. The complete data-collec-
tion parameters and details of the structure solution and
refinement for all compounds are given in Tables 2, 4, and 5.
In all cases, the following formulae were used for refinements:
1
NMR (81 MHz, CDCl
3
) δ 170 (t broad, J P-F ) 1100 Hz); IR
-
1
+
+
2
(
065, 2031, 2011 cm ; MS (FAB ) m/z 499 (8.7%, M ), 471
100%, M - CO). Anal. Calcd for C13H Co F NO P : C, 31.29;
9 2 4 4 2
H, 1.81; N, 2.80. Found: C, 31.31; H, 1.71; N, 2.71.
+
µ-{N,N-Bis[d i(1,1,1,3,3,3-h exa flu or oisop r op oxy)p h os-
2
2
ph in o]-N-m eth ylam in e}tetr acar bon yl-µ-[η :η -ph en ylacet-
R ) Σ(|F | - |F |)/Σ|F |
o
c
o
1
ylen e]d icoba lt (3d ): H NMR (200 MHz, CDCl
3
) δ 2.81 (t,
3
3
2
2 1/2
J
(
H-P )6.1 Hz, 3 H), 4.70 (hept, J H-F ) 5.5 Hz, 2 H), 4.89
R ) [Σw(|F | - |F |) /Σw|F |) ]
w
o
c
o
3
3
hept, J H-F ) 5.5 Hz, 2 H), 5.70 (t, J H-P ) 12 Hz, 1 H), 7.38
2
2
2 -1
31
with w ) [σ (F ) + p /4|F | ]
(
2
1
m, 3 H), 7.64 (m, 2 H); P NMR (81 MHz, CDCl
3
) δ 181.5; IR
o
o
-1
+
+
061, 2037, 2015 cm ; MS (FAB ) m/z 1063 (6.5%, M - CO),
The final atomic coordinates, temperature factors, and their
estimated standard deviations are deposited as Supporting
Information.
+
+
035 (11.6%, M - 2CO), 1007 (2%, M - 3CO), 979 (14%,
+
M
2 8 2
- 4CO), 586 (100%). Anal. Calcd for C25H13Co F24NO P :
C, 27.51; H, 1.20; N, 1.28. Found: C, 27.61; H, 1.18; N, 1.48.
µ-[N,N-Bis(d ip yr r olylp h osp h in o)-N-m eth yla m in e]tet-
r acar bon yl-µ-[η :η -ph en ylacetylen e]dicobalt (3e): H NMR
Ackn owledgm en t. Financial support from the CNRS
UMR 5616) and fellowship awards from M.R.E.S. to
F. R. and from the Swedish Natural Sciences Research
Council to N. K. are gratefully acknowledged.
2
2
1
(
3
3
(
)
200 MHz, CDCl
3
) δ 2.50 (t, J H-P ) 5.8 Hz, 3 H), 5.51 (t, J H-P
3 3
11 Hz, 1 H), 6.42 (t, J H-H ) 2 Hz, 4 H), 6.45 (t, J H-H ) 2
3
3
Hz, 4 H), 6.87 (q, J H-H ) 2 Hz, 4 H), 6.98 (q, J H-H ) 2 Hz, 4
3
1
H), 7.22-7.34 (m, 3 H), 7.50-7.60 (m, 2 H); P NMR (81 MHz,
Su p p or tin g In for m a tion Ava ila ble: Listings of atomic
positional and thermal parameters, bond lengths, bond angles,
and anisotropic thermal parameters. This material is available
free of charge via the Internet at http://pubs.acs.org.
-1
+
CDCl ) δ 132.1; IR 2042, 2016, 1998 cm ; MS (FAB ) m/z 687
3
+
+
+
(
M
1%, M ), 659 (13%, M - CO), 631 (2%, M - 2CO), 603 (32%,
+
+
- 3CO), 575 (100%, M - 4CO). Anal. Calcd for C29
: C, 50.67; H, 3.66; N, 10.18. Found: C, 50.74; H,
.91; N, 9.96.
Gen er a l P r oced u r e for th e P a u son -Kh a n d Rea ction .
25
H -
2 5 4 2
Co N O P
J O982245O
3
(
23) Reg. No. [122986-92-9]; see: Khand, I. U.; Knox, G. R.; Pauson,
P. L.; Watts, W. E.; Foreman, M. I. J . Chem. Soc., Perkin Trans. 1
973, 977.
24) teXsan: Single-Crystal Structure Analysis Software, Version 1.7;
Molecular Structure Corporation: The Woodlands, TX, 1995.
A solution of the complex 3 (0.2 mmol) and norbornene (1
mmol) in 4 mL of toluene was heated at 80 °C for 3-5 days
until no starting complex remained). After removal of the
1
(
(
solvent, the crude mixture was purified by dry column silica