Regioselective electrophilic substitution and addition reactions at an N-coordinated pyrrolyl ligand in (PMe2Ph)3Cl2Re(NC4H4)

Article abstract of DOI:10.1021/om9900216

The reaction of excess pyrrolyllithium with mer-(PMe₂Ph)₃ReCl₃ leads to the formation of the air-stable product mer-(PMe₂Ph)₃Cl₂Re(NC₄H₄) (1), which has been characterized by spectroscopic techniques and by an X-ray diffraction study. Complex 1 reacts with electrophiles to form new Re(III) complexes with regioselectively substituted pyrrolyl ligands. For example, reaction with 1 equiv of N-chlorosuccinimide forms the complex with a 3-chloropyrrolyl ligand, while reaction with excess reagent produces the 3,4-dichloropyrrolyl and 2,3,4-trichloropyrrolyl complexes. The regiochemistry of the reactions has been established from the ¹H NMR data, and the structure of the dibrominated product (PMe₂-Ph)₃Cl₂Re(3,4-NC₄H ₂Br₂) (5) has been confirmed by X-ray diffraction. Reaction of 1 with methyl triflate produces after workup (PMe₂Ph)₃Cl₂Re(3-NC₄H₃Me) (6), and further reaction of 6 with methyl triflate yields (PMe₂Ph)₃Cl₂Re(3,4-NC₄H ₂(Me)₂) (7). In contrast, triflic acid protonates the pyrrolyl ligand of 1 at the α-carbon to form [(PMe₂Ph)₃Cl₂Re(NC₄H ₅)]OTf (8), which has been isolated and identified by an X-ray diffraction study. The Michael addition of dimethyl acetylenedicarboxylate to the β-carbon of the pyrrolyl ligand in 1 has also been characterized. Methods for the removal of the substituted pyrrolyl ligands from the rhenium center are described.

Full text of DOI:10.1021/om9900216

2230
Organometallics 1999, 18, 2230-2240
Regioselective Electr op h ilic Su bstitu tion a n d Ad d ition
Rea ction s a t a n N-Coor d in a ted P yr r olyl Liga n d in
(P Me2P h )3Cl2Re(NC4H4)
M. Rakowski DuBois,* Lisa D. Vasquez, L. Peslherbe, and B. C. Noll
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309
Received J anuary 19, 1999
The reaction of excess pyrrolyllithium with mer-(PMe2Ph)3ReCl3 leads to the formation of
the air-stable product mer-(PMe2Ph)3Cl2Re(NC4H4) (1), which has been characterized by
spectroscopic techniques and by an X-ray diffraction study. Complex 1 reacts with
electrophiles to form new Re(III) complexes with regioselectively substituted pyrrolyl ligands.
For example, reaction with 1 equiv of N-chlorosuccinimide forms the complex with a
3-chloropyrrolyl ligand, while reaction with excess reagent produces the 3,4-dichloropyrrolyl
and 2,3,4-trichloropyrrolyl complexes. The regiochemistry of the reactions has been
1
established from the H NMR data, and the structure of the dibrominated product (PMe2-
Ph)3Cl2Re(3,4-NC4H2Br2) (5) has been confirmed by X-ray diffraction. Reaction of 1 with
methyl triflate produces after workup (PMe2Ph)3Cl2Re(3-NC4H3Me) (6), and further reaction
of 6 with methyl triflate yields (PMe2Ph)3Cl2Re(3,4-NC4H2(Me)2) (7). In contrast, triflic acid
protonates the pyrrolyl ligand of 1 at the R-carbon to form [(PMe2Ph)3Cl2Re(NC4H5)]OTf
(8), which has been isolated and identified by an X-ray diffraction study. The Michael addition
of dimethyl acetylenedicarboxylate to the â-carbon of the pyrrolyl ligand in 1 has also been
characterized. Methods for the removal of the substituted pyrrolyl ligands from the rhenium
center are described.
In tr od u ction
Bu4NF is facile, providing an efficient route to selected
3- and 3,4-substituted pyrroles.
The pyrrole ring is incorporated into many biologically
active molecules,1 and various synthetic methods for the
substitution and derivatization of the heterocycle have
been studied. Electrophilic substitution reactions on the
π-electron-rich pyrrole molecule usually occur at the
R-positions of the ring.2 However, several methods have
been developed for enhancing and controlling an alter-
nate regioselectivity in the reactions of pyrrole with
electrophiles. For example, the use of N-(phenylsulfo-
nyl)pyrrole in electrophilic substitution reactions has led
to the selective substitution at the â-position of the ring
for certain reagents.3 The change in selectivity has been
attributed to an electronic effect of the electron-
withdrawing sulfonyl group. N-(triisopropylsilyl)pyrrole
has also been developed as a reagent that promotes
electrophilic substitution and metalation reactions of the
ring at the â-position, because of the large steric bulk
of the N-substituent.4 After substitution by certain
electrophiles, removal of the triisopropylsilyl group by
The activation of pyrrole toward regioselective elec-
trophilic attack has also been achieved by its interaction
with transition-metal systems. For example, unusual
activation of pyrrole has been characterized for the η2-
bonding mode of the ring to osmium(II) in [(NH3)5Os-
(η2-pyrrole)]2+.5 The η2 coordination disrupts the delo-
calization of π electrons in the pyrrole ligand and
induces enamine character for the heterocycle. The
back-bonding ability of the osmium center enhances the
electron-rich character of the ring, and regioselective
electrophilic substitution at the 3-position of the pyrrole
has been observed for a wide range of electrophiles.
Many synthetic elaborations on this reactivity have been
developed.6
Examples of transition-metal systems with a steri-
cally hindered N-substituent are the pyrrolylimido
(4) (a) Rucker, C. Chem. Rev. 1995, 95, 1009. (b) Bray, B. L.;
Mathies, P. H.; Naif, R.; Solas, D. R.; Tidwell, T. T.; Artis, D. R.;
Muchowski, J . M. J . Org. Chem. 1990, 55, 6317. (c) Shum, P. W.;
Kozikowski, A. P. Tetrahedron Lett. 1990, 31, 6785. (d) Kozikowski,
A. P.; Chen, X. M. J . Org. Chem. 1984, 49, 3239. (e) Muchowski, J .
M..; Naef, R. Helv. Chim. Acta 1984, 67, 1168. (f) Stefan, K. P.;
Schuhmann, W.; Parlar, H.; Korte, F. Chem. Ber. 1989, 122, 169.
(5) (a) Cordone, R.; Harman, W. D.; Taube, H. J . Am. Chem. Soc.
1989, 111, 5969. (b) Myers, W. H.; Sabat, M.; Harman, W. D. J . Am.
Chem. Soc. 1991, 113, 6682. (c) Myers, W. H.; Koontz, J . I.; Harman,
W. D. J . Am. Chem. Soc. 1992, 114, 5684. (d) Hodges, L. M.; Moody,
M. W.; Harman, W. D. J . Am. Chem. Soc. 1994, 116, 7931. (e) Hodges,
L. M.; Gonzalez, J .; Koontz, J . I.; Myers, W. H.; Harman, W. D. J . Org.
Chem. 1995, 60, 2125.
(1) Baxter, R. L.; Scott, A. I. In Comprehensive Heterocyclic Chem-
istry; Katritsky, A. R., Rees, C. W., Eds.; Pergamon Press: Oxford,
U.K., 1984; Vol. 1, pp 85-172. (b) Gribble, G. W. In Comprehensive
Heterocyclic Cemistry II; Katritzky, A. R., Rees, C. W., Scriven, E. F.
V., Eds; Pergamon Press: Oxford, U.K., 1996; Vol. 2, pp 207-258. (c)
J ones, R. A., Ed. Pyrroles: The Synthesis, Reactivity and Physical
Properties of Substituted Pyrroles; Wiley: New York, 1992.
(2) Black, D. St. C. Comprehensive Heterocyclic Chemistry II;
Katritzky, A. R., Rees, C. W., Scriven, E. F. V., Eds.; Pergamon Press:
Oxford, U.K., 1996; Vol. 2, pp 39-117.
(3) (a) Kakushima, M.; Hamel, P.; Frenette, R.; Rokach, J . J . Org.
Chem. 1983, 48, 3214. (b) Rokach, J .; Hamel, P.; Kakushima, M.
Tetrahedron Lett. 1981, 22, 4901. (c) Anderson, H. J .; Loader, C. E.;
Xu, R. X.; Le, N.; Gogan, N. J .; McDonald, R.; Edwards, L. G. Can J .
Chem. 1985, 63, 896.
(6) (a) Hodges, L. M.; Spera, M. L.; Moody, M. W.; Harman, W. D.
J . Am. Chem. Soc. 1996, 118, 7117. (b) Gonzalez, J .; Koontz, J . I.;
Hodges, L. M.; Nilsson, K. R.; Neely, L. K.; Myers, W. H.; Sabat, M.;
Harman, W. D. J . Am. Chem. Soc. 1995, 117, 3405.
10.1021/om9900216 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 05/06/1999

Substitution and Addition Reactions at a Pyrrolyl Ligand
Organometallics, Vol. 18, No. 11, 1999 2231
complexes of the formula [C4H4NdNM(dppe)2F]+ (M )
Mo, W), which were derived from the corresponding
dinitrogen complexes.7 The phenyl groups of the diphos-
phine ligands created a steric pocket which prevented
the electrophilic attack at the R-carbons of the pyr-
rolylimido ligand, and selective â-substitution was
observed with a range of strong electrophiles. Further
reaction of the substituted complex with hydride re-
agents in methanol produced a combination of substi-
tuted pyrroles and N-aminopyrroles.
In the complex CpRe(PPh3)(NO)(NC4H4), the σ-N-
coordinated pyrrolyl ligand was initially protonated by
strong acid at the R-carbon, but this derivative under-
went an isomerization to form products containing a
2-C-coordinated ring protonated at the 2′- or 3-position.8
Reactions of the parent rhenium pyrrolyl complex with
other electrophiles were not reported, and in general
the reactivity of σ-coordinated pyrrolyl ligands in metal
complexes has not been well-studied. The use of a metal
complex as an N-substituent of pyrrole has the potential
for providing not only a steric influence but also an
electronic control of the reactivity at the pyrrolyl ring,
and this control may be varied as the redox state and
auxiliary ligands of the metal complex are varied. To
extend the chemistry of σ-coordinated pyrrolyl ligands,
we have synthesized a new rhenium(III) N-bonded
pyrrolyl complex of the formula (PMe2Ph)3Cl2Re(NC4H4)
(1). We report here a study of the structure and
reactivity of this complex, which has proven to be a
versatile reagent for the activation of pyrrole to regi-
oselective reactions with electrophiles.
NMR spectra for these complexes show resonances with
narrow line widths and paramagnetic shifts.10-14
In the 1H NMR spectrum of 1, two methyl resonances
are observed for inequivalent sets of dimethylphen-
ylphosphine ligands at 1.38 and -3.65 ppm in a ratio
of 12:6. Phosphorus coupling is not observed, and the
resonances are sharp singlets. Two doublets for the
ortho hydrogens and four triplets (meta and para
hydrogens) are also observed for the phenyl rings in the
two types of phosphine ligands. These multiplets occur
in the range of 14-8 ppm (see assignments in Table 1).
Two additional singlets which are integrated for two
hydrogens each are observed at 10.56 and -2.53 ppm
and are assigned to the coordinated pyrrolyl ligand. The
upfield resonance is assigned to the R-hydrogens of the
ring, which are in closest proximity to the rhenium ion,
and the downfield resonance is assigned to the â-hy-
drogens. These assignments are supported by compari-
sons with spectra of substituted pyrrolyl derivatives of
1, which are described below. In previous NMR studies
of Tc(III) and Re(III) pyridine complexes,10,15 the ortho
and para protons of the ring have shown upfield shifts,
while the meta protons are shifted downfield. However,
this pattern of alternating upfield and downfield shifts
was not consistently observed in the Re(III) derivatives
with the five-membered imidazole ligand.10
In the 13C NMR spectrum of 1, weak resonances are
observed between 45 and 145 ppm. Because the para-
magnetic nature of the complex gives unusual chemical
shifts, the carbon resonances were assigned by two-
dimensional 1H-13C correlation techniques. Using a
heteronuclear multiple quantum coherence (HMQC)
experiment, we were able to correlate heteronuclei while
detecting high-sensitivity protons. Singlets at 49.5 and
86.2 ppm in the 13C spectrum were found to correspond
to the R- and â-hydrogens in the pyrrolyl ligand,
respectively. Broadened singlets at 93.3 and 72.6 ppm
in the carbon spectrum were assigned to the methyl
groups in the phosphine ligands that are trans and cis
to the pyrrolyl ligand, respectively. The resonances for
the phenyl groups in the phosphine ligands have also
been assigned, and data are included in Table 1.
Complex 1 is stable toward air and moisture and can
be stored on the benchtop without decomposition. The
cyclic voltammogram of 1 in 0.1 M n-Bu4NPF6/acetoni-
trile solution at a Pt electrode showed a quasi-reversible
oxidation at +0.016 V vs Fc (∆E ) 80 mV, ip,a/ip,c ) 1.6)
and a reversible reduction at -1.42 V (∆E ) 76 mV,
Resu lts a n d Discu ssion
Syn th esis of (P Me2P h )3Cl2Re(NC4H4) (1). The
reaction of (PMe2Ph)3ReCl3 with excess pyrrolyllithium
proceeded in diethyl ether at room temperature to form
the product (PMe2Ph)3Cl2Re(NC4H4) (1), which was
isolated in 94% yield as a brown crystalline solid after
hydrolysis of the excess lithium reagent (eq 1). The
formulation of 1 was confirmed by elemental analysis
and by the electrospray mass spectrum, which showed
a parent ion centered at m/z 738. The effective magnetic
moment for 1 was found to be 1.9 µB at 300 K. Similar
magnetic moments have been reported previously for
the starting Re complex and for related octahedral d4
Re(III) and Os(IV) complexes.9,10 The moments have
been explained on the basis of a second-order paramag-
netism of the octahedral d4 metal centers.11 The 1H
i
p,a/ip,c ) 1). These electron transfers are likely to
correspond to the Re(III)/Re(IV) and Re(III)/Re(II) couples,
respectively.
In an earlier metathesis reaction of (PMe2Ph)3ReCl3
with excess PhLi under conditions similar to those
employed here, all the chloride ligands were substituted
and the five-coordinate product (PMe2Ph)2RePh3 was
formed.16 However, using the present solvent and tem-
perature conditions, we were not able to identify prod-
(7) Seino, H.; Ishii, Y.; Sasagawa, T.; Hidai, M. J . Am. Chem. Soc.
1995, 117, 12181.
(8) J ohnson, T. J .; Arif, A. M.; Gladysz, J . A. Organometallics 1993,
12, 4728.
(9) Gunz, H. P.; Leigh, G. J . J . Chem. Soc. A 1971, 2229.
(10) (a) Pearson, C.; Beauchamp, A. L. Can. J . Chem. 1997, 75, 220.
(b) Pearson, C.; Beauchamp, A. L. Inorg. Chim. Acta 1995, 237, 13. (c)
Pearson, C.; Beauchamp, A. L. Inorg. Chem. 1998, 37, 1242.
(11) LaMar, G. N., Horrocks, W. D., J r., Holm, R. H., Eds. NMR of
Paramagnetic Molecules; Academic: New York, 1973.
(12) (a) Randall, E. W.; Shaw, D. J . Chem. Soc. A 1969, 2867. (b)
Shaw, D.; Randall, E. W. Chem. Commun. 1965, 82.
(13) Over, D. E.; Critchlow, S. C.; Mayer, J . M. Inorg. Chem. 1992,
31, 4643.
(14) J ohnson, M. F.; Pickford, M. E. L. J . Chem. Soc., Dalton Trans.
1976, 950.
(15) Breikss, A. I.; Davison, A.; J ones, A. G. Inorg. Chim. Acta 1990,
170, 75.
(16) Komiya, S.; Baba, A. Organometallics 1991, 10, 3105.

2232 Organometallics, Vol. 18, No. 11, 1999
Ta ble 1. 1H a n d 13C NMR Da ta for (P Me2P h )3Cl2Re-La
pyrrole PPh
DuBois et al.
R
â
PMe
unique
1H
93.32 8.17 t, m 133.40 8.95 t, m 136.10
trans
other
compd (L)
1H
-2.53
13C
1H
13C
1H
13C
13C
1H
13C
1H
13C
1
49.47 10.56
86.20 -3.65 (6H)
(C4H4N)
1.38 (12H) 72.61 10.14 t, p 121.75 10.02 t, p 124.58
9.98 d, o 133.22 13.67 d, o 140.26
2 (3-Cl-
pyr)
-2.70
-1.46
49.54 9.45
58.62
88.32 -3.51 (6H)
98.75 8.21 t, m 133.66 8.87 t, m 136.25
72.38 10.24 t, p 121.67 10.06 t, p 124.26
72.38 10.19 d, o 133.72 13.48 d, o 140.26
1.07 (6H)
1.14 (6H)
3 (3,4-
Cl2-pyr)
-1.86
51.71
-3.43 (6H) 104.64 8.23 t, m 134.07 8.78 t, m 136.18
0.74 (12H) 81.22 10.41 t, p 121.43 10.14 t, p 124.26
10.46 d, o 136.95 13.32 d, o 139.83
4 (2,3,4-
Cl3-pyr)
-6.49
-5.03 (6H)
0.71 (6H)
0.97 (6H)
-3.57 (6H)
1.00 (6H)
1.03 (6H)
-5.04 (6H)
0.88 (6H)
0.93 (6H)
8.45 t, m
10.94 t, p
12.49 d, o
8.16 t, m
10.16 d, o
10.22 t, p
8.85 t, m
10.30 t, p
13.89 d, o
8.81 t, m
10.02 t, p
13.42 d, o
(3-Br-
pyr)
-2.68
-1.40
9.75
(2,3,4-
Br3-pyr)
-6.88
-1.48
-3.24
196.86
14.67 8.50 t, m 134.94 8.82 t, m 137.25
78.20 11.00 t, p 121.32 10.28 t, p 124.56
75.09 12.69 d o 137.95 13.92 d, o 144.38
5 (3,4-
Br2-pyr)
63.29
-3.41 (6H) 105.30 8.26 t, m 134.95 8.79 t, m 136.78
0.73 (12H) 76.53 10.47 t, p 122.19 10.18 t, p 124.81
10.53 d, o 135.12 13.34 d, o 140.48
6 (3-
Me-pyr) -3.37
50.95 8.22
94.30 -3.78 (6H)
1.42 (12H) 73.50 9.63 d, o 133.40 10.00 t, p 125.25 (Me)
76.48 9.95 t, p 122.25 13.72 d, o 140.25
96.96 7.97 t, m 133.48 8.93 t, m 136.00
1.47 (12H) 77.81 9.77 t, p 122.35 9.97 t, p 125.09
9.19 d, o 133.06 13.80 d, o 140.18 2 Me)
0.65 (2H) 216.15 10.74 d (1H) 106.46 -2.26 (6H) 124.96 8.65 t, m 138.06 8.91 t, m 138.49
61.99 11.49 t, p 122.28 11.21 t, p 122.75
94.52 8.07 t, m 133.88 8.93 t, m 136.60
10.55 16.98
54.54
7 (3,4-
Me2-pyr)
-4.11 (2H) 41.88
-3.96 (6H)
11.98
(6H,
4.81
8 (C4H5-
N+)
6.05 (1H) 223.53 23.30 d (1H) 105.30 -1.70 (6H)
-0.21 (6H) 131.49 12.25 d, o 140.89 13.33 d, o 135.49
83.90 -3.46 (6H) 100.82 8.22 t, m 134.62 8.79 t, m 136.81
9 (3-C(C-
O2Me)-
CH(C-
-1.11
-1.21
42.30 12.29
6.53
(vinyl
H)
2.96
(CO2-
Me)
4.20
(CO2-
Me)
114.81
51.11
51.30
O2Me))
24.34
0.81 (6H)
0.93 (6H)
74.54 10.41 t, p 122.01 10.01 t, p 124.70
71.77 10.44 d, o 135.09 13.43 d, o 140.25
a
Spectra were recorded in CDCl3, except for 8, which was recorded in CD3CN. Resonances of quaternary carbons have not been assigned.
ucts containing more than one pyrrolyl ligand, even in
reactions with a 9-10-fold excess of pyrrolyllithium.
Other examples of Re(III) derivatives with amide ligands
are quite rare, but complexes with an anilide ligand
with the formulas [(PMe3)4Re(NHPh)(I)]I and [(PMe3)4-
Re(NHPh)(H)2 have been reported previously.17,18
X-r a y Diffr a ction Stu d y of 1. Single crystals of 1
were grown from an ether/hexane solution and were
characterized by an X-ray diffraction study. Two inde-
pendent molecules were identified in the unit cell, and
the Ortep plots for each of the structures are shown in
Figure 1. Selected bond distances and angles are given
in Table 2. The complex is an octahedral derivative with
a meridional arrangement of phosphine ligands and
with trans chloride ligands. The pyrrolyl ring is trans
to the unique phosphine, and the plane of the ring is
aligned with the Cl-Re-Cl vector. In one conformer the
phenyl rings in both trans phosphine ligands are
oriented away from the pyrrolyl ligand, while in the
second conformer, the phenyl ring of one phosphine is
directed toward and is roughly parallel with the pyrrolyl
ligand. The trans phosphine ligands, P1 and P2, are
displaced slightly away from the central phosphine and
toward the pyrrolyl ring, and this results in a P1-Re-
P2 angle of 166.17(6)°. Other angles about the rhenium
ion are closer to the expected octahedral values.
Related octahedral Re(III) complexes with nitrogen
donor ligands which have been structurally character-
ized19-22 include the nitrile complex (PPh3)2Cl3Re-
(NCMe),19 heterocyclic derivatives (PPh3)Cl3ReL2 (where
L ) pyridine, picoline or imidazole),10a and a complex
containing both ammonia and a protonated azo ligand,
[(PMe2Ph)2Cl2Re(NH3)(NdN(H)Ph)]Br.20 The Re-N dis-
tances reported for these derivatives were 2.05(3) Å for
the nitrile ligand, 2.178(12) Å for the pyridine ligand,
and 2.200(13) Å for the ammonia ligand, each trans to
a chloride. These distances appear to define a typical
range for a single Re(III)-N bond for neutral ligands.
(19) Drew, M. G. B.; Tilsey, D. G. J . Chem. Soc., Chem. Commun.
1970, 600.
(20) Mason, R.; Thomas, K. M.; Zubieta, J . A.; Douglas, P. G.;
Galbraith, A. R.; Shaw, B. L. J . Am. Chem. Soc. 1974, 96, 260.
(21) Hirsch-Kuchma, M.; Nicholson, T.; Davison, A.; Davis, W. M.;
J ones, A. G. Inorg. Chem. 1997, 36, 3237.
(22) Orth, S. D.; Barrera, J .; Sabat, M.; Harman, W. D. Inorg. Chem.
1993, 32, 594.
(17) Chiu, K. W.; Howard, C. G.; Rzepa, H. S.; Sheppard, R. N.;
Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. B. Polyhedron 1982,
1, 441.
(18) Chiu, K. W.; Wong, W. K.; Wilkinson, G.; Galas, A. M. R.;
Hursthouse, M. B. Polyhedron 1982, 1, 37.

Substitution and Addition Reactions at a Pyrrolyl Ligand
Organometallics, Vol. 18, No. 11, 1999 2233
the formal amide nitrogen of the pyrrolyl ring. This is
consistent with the electron-rich character of the pyr-
rolyl ligand, which is reflected in its reactivity with
electrophiles described below.
Rea ction s of 1 w ith Electr op h iles. Ha logen a tin g
Agen ts. The reactivity of the N-coordinated pyrrolyl
ligand in 1 toward electrophilic reagents has been
studied. The Re(III) -N bond has proven to be quite
kinetically inert, and new Re complexes with substi-
tuted pyrrolyl ligands have been isolated and character-
ized. The (PMe2Ph)3ReCl2 moiety coordinated to the
pyrrolyl nitrogen provides a steric, and perhaps an
electronic, influence which promotes electrophilic sub-
stitution at the â-carbons of the pyrrolyl ligand. For
example, the reaction of 1 with 1-2 equiv of N-
chlorosuccinimide in THF followed by hydrolysis with
an aqueous sodium bicarbonate solution gave a single
major product (88%). This was isolated after column
chromatography and identified as a derivative with a
monochloro-substituted pyrrolyl ligand, (PMe2Ph)3ReCl2-
(3-NC4H3Cl) (2) (eq 2). The synthesis of the 3-chloro-
F igu r e 1. Perspective drawing and numbering scheme for
conformers of (PMe2Ph)3Cl2Re(NC4H4) (1).
pyrrolyl ligand appeared to be quite regioselective. In
contrast, the reaction of N-chlorosuccinimide with pre-
viously studied N-substituted pyrrole systems resulted
in the formation of primarily R-substituted products.4b,7
The electrospray mass spectrum of 2 showed a parent
ion at m/z 772 and fragments at m/z 666 and 628 which
corresponded to the stepwise loss of chloropyrrolyl and
dimethylphenylphosphine ligands. In the 1H NMR
spectrum of 2, three singlets for the pyrrolyl hydrogens
were observed at -2.70, -1.46, and 9.45 ppm. The two
upfield resonances are assigned to inequivalent R-hy-
drogens, and the chloro substituent is assigned to a
â-position on the ring. (These chemical shift assign-
ments are consistent with those of a related structure
identified by an X-ray diffraction study, which is dis-
cussed below.) In the HMQC spectrum the R-hydrogens
(-2.70 and -1.46 ppm) on the pyrrolyl ligand are
correlated with carbon resonances at 49.54 and 58.62
ppm, respectively, while the unsubstituted â-carbon is
assigned to a resonance at 88.32 ppm. Other 13C data
are given in Table 1.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for (P Me2P h )3Cl2Re(NC4H4) (1)
Bond Lengths
Re(1)-N(1)
Re(1)-Cl(1)
Re(1)-Cl(2)
Re(1)-P(1)
Re(1)-P(2)
Re(1)-P(3)
N(1)-C(1)
N(1)-C(4)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
2.171(6)
Re(2)-N(2)
Re(2)-Cl(3)
Re(2)-Cl(4)
Re(2)-P(4)
Re(2)-P(5)
Re(2)-P(6)
N(2)-C(29)
N(2)-C(32)
C(29)-C(30)
C(30)-C(31)
C(31)-C(32)
2.168(5)
2.3546(16)
2.3511(16)
2.4656(18)
2.4659(18)
2.4383(18)
1.385(8)
2.3406(16)
2.3551(16)
2.4323(17)
2.4608(18)
2.4677(18)
1.360(9)
1.376(9)
1.373(8)
1.392(10)
1.401(10)
1.383(10)
1.385(10)
1.399(12)
1.387(10)
Bond Angles
N(1)-Re(1)-P(1)
N(1)-Re(1)-P(2)
N(1)-Re(1)-P(3)
P(1)-Re(1)-P(2)
83.75(16) N(2)-Re(2)-P(6)
82.70(16) N(2)-Re(2)-P(5)
175.98(15) N(2)-Re(2)-P(4)
166.17(6) P(5)-Re(2)-P(6)
82.91(15)
87.63 (15)
175.65(14)
170.19(6)
Cl(1)-Re(1)-Cl(2) 176.53(6) Cl(3)-Re(2)-Cl(4) 177.36(6)
Re(1)-N(1)-C(1) 127.4(5)
Re(1)-N(1)-C(4) 126.4(4)
C(1)-N(1)-C(4)
Re(2)-N(2)-C(27) 126.5(5)
Re(2)-N(2)-C(30) 126.2(4)
C(27)-N(2)-C(30) 107.1(6)
106.3(6)
Three phosphine methyl singlets (6 H each) were
1
In contrast, the protonated azo ligand in the above
complex, for which multiple Re-N bond character was
proposed, had a Re-N distance of 1.750(12) Å. The
mean Re-N bond distance for the conformers of 1 of
2.170(6) Å appears to be consistent with a single-bond
distance of an anionic ligand, and suggests there is little
multiple-bond character arising from π donation from
observed in the H NMR spectrum of 2 at -3.51, 1.07,
and 1.14 ppm, suggesting a restricted rotation about the
Re-N bond of the pyrrolyl ligand. Although the trans
phosphine ligands are related by a plane of symmetry,
the two methyls on each trans phosphine ligand are
diastereotopic and are resolved with slow rotation of the
monosubstituted ligand. A high-temperature NMR study

2234 Organometallics, Vol. 18, No. 11, 1999
DuBois et al.
of 2 showed coalescence of the two methyl singlets near
1 ppm at 52 °C.23 The restricted rotation appears to
arise primarily from steric effects rather than from
multiple-bond character in the Re-N bond.
The reaction of 1 with 2-3 equiv of N-chlorosuccin-
imide gave a mixture of products which could be
partially separated by column chromatography and
which were identified as the derivatives with dichloro-
and trichloro-substituted pyrrolyl ligands, (PMe2Ph)3-
ReCl2(3,4-NC4H2Cl2) (3) and (PMe2Ph)3ReCl2(2,3,4-NC4-
HCl3) (4) (eq 3). The relative yields of these products
F igu r e 2. Perspective drawing and numbering scheme for
(PMe2Ph)3Cl2Re(3,4-NC4H2Br2) (5).
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for (P Me2P h )3Cl2Re(NC4H2Br 2) (5)
Bond Lengths
varied depending on reaction conditions (see Experi-
mental Section). When 3 equiv of the chlorinating
reagent was used, 4 was the major product (52%), but
some displacement of the pyrrolyl ligand was also
observed to form (PMe2Ph)3ReCl3. No evidence was
observed in the NMR spectra for the formation of the
tetrachloropyrrole product.
Re-N
2.170(4)
N-C(1)
1.367(6)
1.370(6)
1.375(7)
1.377(7)
1.371(7)
1.867(5)
Re-Cl(1)
Re-Cl(2)
Re-P(1)
Re-P(2)
Re-P(3)
C(3)-Br(1)
2.3381(12)
2.3524(11)
2.4662(12)
2.4734(12)
2.4338(12)
1.892(5)
N-C(4)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(2)-Br(2)
Bond Angles
The electrospray mass spectra showed the expected
parent ions for 3 and 4, and the formulation of 4 was
also supported by elemental analyses. The 1H NMR
spectrum of 3 indicates that the complex maintains
planes of symmetry along the Cl-Re-Cl axis as well
as along the P1-Re-P2 axis. Two phosphine methyl
signals (12:6 ratio) are observed at 0.74 and -3.43 ppm,
and a single resonance for the equivalent pyrrolyl
hydrogens is present at -1.86 ppm. This upfield reso-
nance is assigned to the R-hydrogens on the ring, and 3
is formulated as the 3,4-dichloropyrrolyl derivative. This
assignment is confirmed by an X-ray diffraction study
of the analogous dibromopyrrolyl derivative, which is
discussed below.
N-Re-P(1)
N-Re-P(2)
N-Re-P(3)
P(1)-Re-P(2)
N-Re-Cl(1)
86.75(11)
83.45(11)
176.04(10)
170.06(4)
90.60(11)
Cl(1)-Re-Cl(2)
177.75(4)
126.1(3)
127.3(3)
106.4(4)
90.85(11)
Re-N-C(1)
Re-N-C(4)
C(1)-N-C(4)
N-Re-Cl (2)
addition products were deprotonated with aqueous
sodium bicarbonate solution and then separated by
column chromatography. Derivatives with 3-bromo-, 3,4-
dibromo-, and 2,3,4-tribromo-substituted pyrrolyl ligands
were isolated and characterized by spectroscopic data
and in some cases by elemental analyses. The electro-
spray mass spectra show the expected parent ions for
the mono and disubstituted products, and the NMR data
for all three products are very similar to those described
for the chloro analogues.
X-r a y Diffr a ction Stu d y of (P Me2P h )3ReCl2(3,4-
NC4H2Br 2) (5). To confirm the NMR assignments for
the pyrrolyl hydrogens in these halogenated derivatives,
an X-ray diffraction study was carried out. Single
crystals of (PMe2Ph)3ReCl2(3,4-NC4H2Br2) (5) were
obtained by slow evaporation of an ether/hexane solu-
tion. The structure determined by X-ray diffraction is
shown in Figure 2. Selected bond distances and angles
are shown in Table 3. The structure shows that the
rhenium complex maintains an octahedral geometry
with the same stereochemistry of the ligands as ob-
served in the parent pyrrolyl complex 1. The structure
also confirms that the bromo substitution of the pyrrolyl
ligand occurs at the 3- and 4-positions of the ring. A
disorder was observed in the bromine positions with
bromines observed at the 2-, 3-, and 4-positions of the
ring. This was modeled as partial contamination by the
The spectroscopic data and elemental analyses for 4
are consistent with the formulation (PMe2Ph)3ReCl2-
1
(2,3,4-NC4HCl3). In the H NMR spectrum a resonance
for a single pyrrolyl R-hydrogen is observed in the
spectrum at -6.49 ppm. Three singlets for inequivalent
phosphine methyls are observed, and, as was discussed
for the monochloropyrrolyl derivative, this indicates a
restricted rotation about the Re-N bond. Coalescence
of the two Me signals on the trans phosphine ligands
was not observed in NMR spectra in d8-toluene at
temperatures up to 100 °C. There appears to be a
significant activation energy for rotation of the bulky
trisubstituted ligand.
The reactions of 1 with N-bromosuccinimide in vary-
ing ratios were also carried out. The electrophilic
(23) In the low-temperature spectra of these rhenium complexes,
we observed that the chemical shift difference between the two trans
Me resonances continued to increase and a limiting value for δν was
not observed. As a result, values for ∆Gq were not calculated.

Substitution and Addition Reactions at a Pyrrolyl Ligand
Organometallics, Vol. 18, No. 11, 1999 2235
triply brominated product, which was observed in the
NMR spectrum of the crystallized dibromo product in
trace amounts (<5%). In the final structure solution the
tribromo derivative had a site occupancy of 0.033(2). All
of the rhenium ligand distances in 5 as well as the C-N
and C-C distances within the pyrrolyl ligand are very
similar to those of 1. The P1-Re-P2 angle in this
complex was 170.06(4)°, slightly larger than the corre-
sponding angle of 1.
Rea ction s of 1 w ith Ca r bon Electr op h iles. The
reactions of 1 with alkylating agents have also led to
the formation of new substituted pyrrole products. For
example, reaction with methyl triflate followed by
deprotonation with base resulted in the formation of a
complex with a â-substituted methylpyrrolyl ligand,
(PMe2Ph)3ReCl2(3-NC4H3Me) (6), which was isolated in
pure form by column chromatography (eq 4). The 1H
reported to react directly with carbocations. However,
3,4-dimethylpyrrole has been synthesized previously by
the monolithiation of i-Pr3Si-NC4H2Br2 and its reaction
with methyl iodide, followed by a second lithiation/
alkylation step.4c
Rea ction of 1 w ith P r otic Acid . The reactions of 1
with electrophiles studied so far involved regioselective
attack on the â-carbons of the heterocycle. We were
interested in the regiochemistry displayed for the reac-
tion of 1 with protic acid, since this is the least sterically
demanding electrophile. Although 1 did not react with
acetic acid, the reaction with triflic acid proceeded at
room temperature to form a ring-protonated product
which was isolated as a crystalline yellow solid. Both
elemental analyses and FAB mass spectral data con-
firmed the formulation of the product as [(PhMe2P)3-
Cl2Re(NC4H5]OTf (8) (eq 5). The addition of sodium
carbonate to a solution of 8 resulted in deprotonation
of the ligand and regeneration of the pyrrolyl complex
1. The NMR spectrum of 8 in CD3CN solution indicated
that only one isomer was present over a period of 24-
48 h, and within this time frame there was no evidence
for a tautomerization of the ligand such as that reported
previously for [CpRe(NO)(PPh3)(NC4H5)]+.8
1
The H NMR spectrum of 8 in CD2Cl2 was invariant
over a temperature range of -60 to +20 °C.24 Two new
doublets (each with intensity for 1 H) were observed at
23.30 and 10.74 ppm (J ) 6.3 Hz), and additional
singlets assigned to the protonated pyrrole ligand were
observed at 6.05 (1 H) and 0.65 ppm (2 H). Three
singlets for inequivalent phosphine methyls were also
present, as well as the usual multiplets for the phenyl
hydrogens. On the basis of the integration value of 2
for the upfield pyrrole resonance, the site of protonation
was tentatively assigned to the R-position of the ring,
and the two doublets were assigned to the â-protons. A
similar coupling between â-hydrogens has been ob-
NMR spectrum for this product shows the characteristic
pattern of one low-field (8.22 ppm) and two high-field
(-3.24 and -3.37 ppm) resonances for the pyrrolyl
hydrogens. A singlet at 10.55 ppm (3 H) is assigned to
the methyl group on the pyrrole ring. In the room-
1
temperature H spectrum, only two phosphine methyl
singlets are observed at δ 1.42 (12 H) and δ -3.78 (6
H), but the former resonance is broadened. In the low-
temperature spectra of 6, evidence for restricted rotation
about the Re-N bond was observed with the splitting
of the resonance at δ 1.42 into two singlets (Tc ) 11
°C). The splitting (δν) for these signals continued to
increase as the temperature was decreased to -60 °C,
and a limiting value was not established. Other spec-
troscopic characterization data for 6 are included in the
Experimental Section.
Complex 6 reacted readily with an additional 1 equiv
of methyl triflate to form a complex with a 3,4-dimeth-
ylpyrrolyl ligand, (PMe2Ph)3ReCl2(3,4-NC4H2Me2) (7),
which was also isolated and characterized by spectro-
scopic data (see Experimental data). Further reactions
to free the substituted pyrrole rings from the rhenium
center can be achieved with certain acidic reagents and
are described below. The alkylation of a â-carbon of the
N-methylpyrrole ring with MeOTf has been accom-
plished previously with the Os-η2-N-methylpyrrole
complex,5 but this system was not useful for the
synthesis of the NH analogue or of the dialkylated rings.
Other reagents designed to promote the electrophilic
substitution of pyrrole in the â-positions have not been
1
served in the H NMR spectrum of free pyrrole proto-
nated at the R-position.25 In the HMQC spectrum of 8,
the low-field proton doublets at 10.74 and 23.30 ppm
were correlated with carbon resonances at 106.49 and
105.30 ppm, respectively, while the R-hydrogen reso-
nance at 6.05 ppm was correlated with a carbon signal
at 223.53 ppm. The 13C resonance of the protonated
R-carbon was also found to have a very large downfield
shift of 216.15 ppm.
To confirm the site of the pyrrolyl ring protonation,
single crystals of 8 were grown by vapor diffusion of
diethyl ether into a concentrated CH2Cl2 solution of the
(24) The pattern of the spectrum did not change at lower temper-
atures, but changes in chemical shifts were observed and these were
found to be proportional to temperature. Similar direct proportionali-
ties have been observed for spectra of other octahedral Re(III)
derivatives.
(25) Chiang, Y.; Whipple, E. B. J . Am. Chem. Soc. 1963, 85, 2763.
Whipple, E. B.; Chiang, Y.; Hinman, R. L. J . Am. Chem. Soc. 1963,
85, 26.

2236 Organometallics, Vol. 18, No. 11, 1999
DuBois et al.
was observed, and 1 was regenerated in high yield (eq
6). Partial deprotonation of 8 was also observed in the
F igu r e 3. Perspective drawing and numbering scheme for
[(PMe2Ph)3Cl2Re(NC4H5)]OTf (8).
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [(P Me2P h )3Cl2Re(NC4H5)]OTf (8)
Bond Lengths
Re-N
2.20(2)
N-C(1)
1.348(4)
1.436(4)
1.465(5)
1.332(5)
1.475(4)
reaction with Bu3SnH, while no reaction was observed
when the nonbasic hydride donor Et3SiH was used.
The addition of HCl/AlCl3 to 1, 6, or 7 resulted in the
dissociation of the pyrrole ligands and the quantitative
formation of (PMe2Ph)3ReCl3. When the reactions of 6
and 7 with excess HCl/AlCl3 were monitored by NMR
spectroscopy, the corresponding rhenium complexes
with R-protonated pyrrolyl ligands were observed as the
initial products, which underwent pyrrole ligand dis-
sociation (see Experimental for NMR data). It was not
necessary to use an isolated sample of 6 for the
preparation of methylpyrrole. For example, 1 was
reacted with MeOTf to form the cationic addition
product. When this cation was stirred at room temper-
ature with LiCl/AlCl3 in acetonitrile solution, free
3-methylpyrrole was displaced (eq 7). The free pyrrole
was vacuum-transferred and identified by NMR and
mass spectroscopy.
Re-Cl(1)
Re-Cl(2)
Re-P(1)
Re-P(2)
Re-P(3)
2.3537(6)
2.33638(6)
2.4847(7)
2.4860(6)
2.4435(7)
N-C(4)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
Bond Angles
N-Re-P(1)
87.26(6)
87.36(6)
175.88(6)
171.27(2)
88.85(6)
Cl(1)-Re-Cl(2)
179.21(2)
128.8(2)
125.17(19)
106.1(2)
90.46(6)
N(1)-Re-P(2)
N(1)-Re-P(3)
P(1)-Re-P(2)
N-Re-Cl(1)
Re-N-C(1)
Re-N-C(4)
C(1)-N-C(4)
N-Re-Cl (2)
compound, and a structural study was carried out. The
complex crystallized with eight formula units per unit
cell in the orthorhombic space group Pbca. A perspective
drawing of the cation is shown in Figure 3, and selected
bond distances and angles are given in Table 4. The
structure confirmed that the protonation occurs on an
R-carbon (C4) of the pyrrolyl ligand. The N-C4 distance
is 1.436(4) Å, while the N-C1 distance is 1.348(4) Å.
Alternating C-C lengths in the ring are also observed
with the C4-C3 distance of 1.475(4) Å, the C3-C2
distance of 1.332(5) Å, and the C2-C1 distance of 1.465-
(5) Å. The ring retains its planar structure with the
plane parallel to the Cl-Re-Cl vector. The Re-N bond
distance for the protonated ligand is lengthened slightly
relative to that of the pyrrolyl complex to a value of
2.201 Å, and the Re-P distances in 7 are found to be
about 0.02 Å longer than those of the starting pyrrolyl
derivative.
Mich a el Ad d ition Rea ction s. Free pyrrole has been
found to react with the activated alkyne dimethyl
acetylenedicarboxylate (DMAD) to give several products
that result either from Michael addition at the 2-posi-
tion or from cycloaddition of one or two molecules of
DMAD.27 The η2-pyrrole complex [(NH3)5Os(η2-pyr-
role)]2+ has been found to undergo Michael addition
Although larger electrophiles preferentially attacked
the 3- and 4-positions of the pyrrolyl ligand in 1, the
protonation product indicates that the coordinated ring
retains significant electron density at the R-carbon
atoms. The alternate regioselectivity for the larger
electrophiles therefore appears to be driven primarily
by steric factors. Several attempts were made to further
reduce the ligand in 8 to an N-coordinated pyrrolinyl
ring by the addition of NaBH4 or other hydride donors.
In a previous report, stepwise diastereoselective addi-
tions of electrophiles and nucleophiles to σ(N)-indole
ligands in chiral complexes of rhenium have been
carried out to form indoline derivatives.26 However, in
the reactions of 8 with NaBH4 as well as with other
nucleophilic reagents, the deprotonation of the ligand
(26) (a) J ohnson, T. J .; Arif, A. M.; Gladysz, J . A. Organometallics
1994, 13, 3182. For related stepwise additions of nucleophiles and then
electrophiles to σ(N)-quinoline and σ(N)-isoquinoline complexes of Re,
see: (b) Stark, G. A.; Arif, A. M.; Gladysz, J . A. Organometallics 1994,
13, 4523. (c) Richter-Addo, G. B.; Knight, A. D.; Dewey, M. A.; Arif, A.
M.; Gladysz, J . A. J . Am. Chem. Soc. 1993, 115, 11863.
(27) (a) Kotsuki, H.; Mori, Y.; Nishizawa, H.; Ochi, M.; Matsuoka,
K. Heterocycles 1982, 19, 1915. (b) Lee, C. K.; Hahn, C. S.; Noland, W.
E. J . Org. Chem. 1978, 43, 3727. (c) Acheson, R. M.; Vernon, J . M. J .
Chem. Soc. 1962, 1148.

Substitution and Addition Reactions at a Pyrrolyl Ligand
Organometallics, Vol. 18, No. 11, 1999 2237
reactions at the 3-position of the ring,5 but this type of
reactivity has not been observed previously for N-
bonded pyrrolyl complexes. The reaction of 1 with
DMAD proceeds at room temperature in the presence
of a catalytic amount of acetic acid to form the addition
product (PMe2Ph)3Cl2Re(NC4H3C(CO2Me)CH(CO2Me))
(9) (eq 8). After 3 days the NMR spectrum of the crude
collected on a Varian Inova 500 MHz instrument. All chemical
shifts are reported in ppm relative to tetramethylsilane. Mass
spectra were obtained on a HB5989A mass spectrometer with
ES ionization, on a VG Analytical 7070 EQ-HF mass spec-
trometer, or on a Finnigan MATR LCQ ion-trap mass spec-
trometer. Elemental analyses were performed by Desert
Analytical Laboratory, Tucson, AZ. The complex (PMe2-
Ph)3ReCl3 was prepared according to the literature proce-
dure.13,28 KReO4 and PMe2Ph were obtained from Strem
Chemicals. Dimethyl acetylenedicarboxylate was obtained
from Aldrich and vacuum-distilled prior to use.
Syn th esis of m er -(P Me2P h )3Cl2Re(NC4H4) (1). Diethyl
ether (40 mL) was added to a flask containing mer-(PMe2-
Ph)3ReCl3 (0.938 g, 1.33 mmol) and pyrrolyllithium (0.891 g,
8.03 mmol). The yellow solution immediately turned green and
then slowly changed to brown. After the reaction mixture was
stirred for 21 h at room remperature, the diethyl ether was
removed in vacuo. Dichloromethane was then added to the
reaction flask, and salts were extracted with a saturated
aqueous solution of NaCl. The organic layer was dried over
Na2SO4, filtered, and dried in vacuo to give a brown solid.
Yield: 0.978 g (94.5%). The complex could be recrystallized
from ether/hexanes or chloroform/hexanes solvent mixtures.
Mp: 150-151 °C. See Table 1 for 1H and 13C NMR data. MS
reaction mixture indicated a mixture of 9 and 1 in a
85/15% ratio. The cycloaddition product was not identi-
fied in this reaction. After chromatography on a neutral
alumina column the product ratio decreased to about
50/50, and significant amounts of 1 were recovered
under these conditions. The factors that promoted the
loss of the substituent were not studied further.
(ESI): m/z 738 (P+); 671 (P+ - C4H4N). Anal. Calcd for C28H37
-
Cl2NP3Re: C, 45.59; H, 5.06; N, 1.90. Found: C, 45.58; H, 5.10;
N, 2.20.
The product 9 has been isolated in pure form after
column chromatography and recrystallization. The elec-
trospray mass spectrum, which shows a parent ion at
m/e 880, confirms the formulation of the addition
X-r a y Diffr a ction Stu d y of 1. A suitable crystal was
selected and mounted with silicone grease into the 153 K N2
cold stream of a Siemens SMART three-circle goniometer.
Indexing was determined after collection of 3 sets of 20 0.3°
(ω) scans. Least-squares refinement of final cell dimensions
was performed using all reflections harvested during data
collection. An arbitrary sphere of data was collected. Equiva-
lent reflections were merged, and all data were corrected for
Lorentz and polarization effects as well as for absorption.
Friedel opposites were merged.
Structure solution by direct methods in the centrosymmetric
space group P1h revealed the complete non-hydrogen structure.
All other hydrogens were placed at calculated positions and
then refined using a riding model. Hydrogen thermal motion
was modeled as isotropic; thermal parameters for hydrogen
were calculated as 1.2 times the Ueq value for the parent
atom.
The asymmetric unit contains two crystallographically inde-
pendent molecules. The space group choice was verified using
LePage’s MISSYM algorithm as incorporated in Spek’s Platon
package.29 No disorder is present. The largest peak in the final
difference map is 5.13 e/Å3, located 0.95 Å from Re(2). Details
of data collection and refinement are given in Table 5.
Rea ction s of 1 With Ha logen a tin g Agen ts. Syn th esis
of (P Me2P h )3ReCl2(3-NC4H3Cl) (2). Complex 1 (0.190 g,
0.257 mmol) and N-chlorosuccinimide (NCS; 0.0566 g, 0.424
mmol) were dissolved in 70 mL of tetrahydrofuran. The yellow
solution was stirred for 20 h at room temperature. The
tetrahydrofuran was removed, and the product was redissolved
in dichloromethane and extracted with a saturated aqueous
solution of NaHCO3. The organic layer was dried over MgSO4,
filtered, and dried in vacuo. The 1H NMR spectrum showed
one major product in about 88% yield. The crude product
mixture was dissolved in dichloromethane and loaded on an
alumina/toluene chromatography column. A yellow fraction
was eluted with dichloromethane. Evaporation of solvent gave
the desired product, which could be recrystallized by vapor
diffusion of hexanes into a concentrated dichoromethane
solution. Mp: 167-169 °C. See Table 1 for 1H and 13C NMR
data. MS (ESI): m/z 772 (P). Anal. Calcd for C28H37Cl3NP3Re:
C, 43.49; H, 4.79; N, 1.81. Found: C, 43.40; H, 4.56; N, 1.73.
1
product. Once again the H NMR data indicate that the
addition reaction occurs at the 3-position of the hetero-
cycle. The resonance for the unique â-hydrogen of the
ring is observed at 12.29 ppm, while the inequivalent
R-hydrogens occur as singlets at -1.11 and -1.21 ppm.
As is noted for other â-substituted ligands in this
system, three singlets are observed for the methyls in
the phosphine ligands. The methyls of the dicarboxylate
groups occur as singlets at 2.96 and 4.20 ppm, and the
vinyl hydrogen is assigned to a singlet at 6.53 ppm.
We were unable to isolate Michael addition products
from reactions of 1 with other less activated reagents
such as methyl propionate and dimethyl fumarate. Nor
did 1 undergo a Diels-Alder reaction with malonic
anhydride. These observations indicate that the η1-
pyrrole ligand in 1 is significantly less activated toward
electrophilic attack than the η2-ligand in [(NH3)5Os(η2-
pyrrole)]2+, which reacted readily with all of the above
reagents.5 In general, the range of reactivity of the
heterocycle in 1 is similar to that of free pyrrole, and
the (PMe2Ph)3Cl2ReIII substituent on the pyrrole nitro-
gen appears to exert primarily a steric rather than an
electronic effect on the ring. It will be interesting to
determine to what extent a change in auxiliary ligands
and/or in metal oxidation state might alter the electronic
influence of the σ-metal complex on the pyrrolyl ligand,
and further studies are in progress to address this
question.
Exp er im en ta l Section
Gen er a l P r oced u r es. Reactions were carried out under
nitrogen using Schlenk-line and vacuum-line techniques.
Dichloromethane and acetonitrile were distilled from CaH2
prior to use. Tetrahydrofuran, toluene, and diethyl ether were
distilled from sodium/benzophenone. 1H NMR spectra were
recorded at 300 and 400.13 MHz on Varian VXR-300 and
Bruker AM-400 spectrometers, respectively. HMQC data were
(28) Parshall, G. W. Inorg. Synth. 1977, 17, 110.
(29) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 1995.

2238 Organometallics, Vol. 18, No. 11, 1999
Ta ble 5. Cr ysta l Da ta for Com p ou n d s 1, 5, a n d 8
DuBois et al.
1
5
8
formula
fw
C
28H37Cl2NP3Re
C28H35Br2Cl2NP3Re
895.40
C29H38Cl2F3NO3P3SRe
887.67
737.60
cryst syst
unit cell dimens
a (Å)
b (Å)
c (Å)
triclinic
monoclinic
orthorhombic
13.5873(5)
14.9088(6)
15.2916(6)
83.5610(10)
86.5230(10)
80.6980(10)
3034.8(2)
P1h
12.0709(2)
20.6838(3)
14.0166(1)
90
104.7220(10)
90
3384.66(8)
P21/c
4
21.6796(1)
14.3429(2)
23.2750(3)
90
90
90
7237.32(14)
Pbca
8
R (deg)
â (deg)
γ (deg)
V (Å3)
space group
Z
4
calcd density (g/cm3)
λ(Mo KR) (Å)
temp (K)
scan type
θ range (deg)
no. of unique rflns
no. of rflns obsd
1.614
0.710 73
153(2)
1.757
0.710 73
297(2)
ω scans
1.97-28.29
8110 (R(int) ) 0.0435)
6239
6.269
0.0577
0.0915
1.009
1.629
0.710 73
171(2)
ω scans
1.75-30.00
ω scans
1.34-25.00
10 382 (R(int) ) 0.0312)
8719
10 534 (R(int) ) 0.0768)
8152
abs coeff (mm-1
)
4.356
0.0583
0.1304
1.039
empirical from equivalentsd
Ra
0.0283
0.0549
1.047
1.002 and -0.776
b
Rw
GOFc
largest peak in final diff map (e/Å3)
5.133 and -2.528
1.201 and -1.994
R ) R1 ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
.
c GOF ) S ) [∑[w(Fo - Fc2)2]/(M - N)]1/2 where M is the
a
b
2
2
d
number of reflections and N is the number of parameters refined. Blessing, R. H. Acta Crystallogr., Sect. A 1995, A51, 33-38.
Syn th esis of (P Me2P h )3ReCl2(3,4-NC4H2Cl2) (3). Com-
plex 1 (0.062 g, 0.083 mmol) and NCS (0.025 g, 0.19 mmol)
were dissolved in 50 mL of tetrahydrofuran. The solution was
stirred at room temperature for 19.5 h before the solvent was
evaporated. The residue was redissolved in dichloromethane,
extracted with saturated aqueous NaHCO3, dried over MgSO4,
filtered over Celite, and dried in vacuo. The 1H NMR spectrum
of the crude reaction mixture showed that complexes 3, 4, and
(PMe2Ph)3ReCl3 were present in approximately 27%, 35%, and
37% yield, respectively. The mixture was eluted on a silica gel
column with dichloromethane. The second fraction was en-
riched in 3 but still contaminated with 4. See Table 1 for 1H
and 13C NMR data for 3. MS (ESI): m/z 807 (M); 671 (M -
Cl2pyrr).
for C28H35Br2Cl2NP3Re: C, 37.67; H, 3.92; N, 1.56. Found: C,
37.49; H, 3.69; N, 1.27.
Further elution of the silica gel column with dichlo-
romethane gave a second yellow-green band that was then
eluted on a neutral alumina column with CH2Cl2. The result-
ing band contained (PMe2Ph)3ReCl2(3-NC4H3Br) and some
starting material. Yield: 19%. See Table 1 for 1H NMR data.
MS (ESI): m/z 818 (P+); 671 (P - Br - pyrr); 533 (P - Br -
pyrr - PMe2Ph). Relative yields are as follows. When 1.3 equiv
of NBS was added in portions at room temperature and the
reaction mixture was stirred for 1 or 2 days, about 50% mono-
Br and 25% di-Br products were formed. When 2.3 equiv of
NBS was added at room temperatue and the reaction mixture
was stirred for 3 h, 10% mono-Br and 40% di-Br products were
formed.
Syn th esis of (P Me2P h )3ReCl2(2,3,4-NC4HCl3) (4). Com-
plex 1 (0.089 g, 0.121 mmol) and NCS (0.0470 g, 0.352 mmol)
were dissolved in 20 mL of tetrahydrofuran. The solution was
stirred at room temperature for appoximately 1 day. After a
A similar reaction with 1 (0.045 g, 0.061 mmol) and NBS
(0.034 g, 0.189 mmol) was carried out at room temperature
for 1 day. The workup procedure was similar to that described
above. The NMR spectrum of the resulting product showed
that the major product was (PMe2Ph)3ReCl2(2,3,4-NC4HBr3).
The product was further purified by recrystallization from CH2-
1
similar workup procedure, the H NMR spectrum of the crude
product mixture showed approximately 52% 4, 27% (PMe2-
Ph)3ReCl3, and 21% 3. The brown residue was dissolved in
dichoromethane and the solution eluted on a silica gel column.
Complex 4 was eluted with dichloromethane and isolated in
the first yellow fraction. The product was recrystallized by
vapor diffusion of hexanes into a dichloromethane solution of
4. See Table 1 for 1H NMR data. MS (ESI): m/z 841 (P); 807
(P - Cl); 671 (P - Cl3pyrr). Anal. Calcd for C28H34Cl5NP3Re:
C, 39.99; H, 4.08; N, 1.67. Found: C, 40.02, H, 4.34; N, 1.69.
Syn th esis of (P Me2P h )3ReCl2(3,4-NC4H2Br 2) (5) a n d
Oth er Br om in a ted P r od u cts. Complex 1 (0.233 g, 0.316
mmol) and N-bromosuccinimide (NBS) (0.119 g, 0.668 mmol)
were combined in 20 mL of tetrahydrofuran, and the solution
was stirred at room temperature. After 1 day the reaction was
quenched with a saturated aqueous solution of NaHCO3 (30
mL) and extracted with CH2Cl2 (40 mL). The extract was
washed with NaHCO3 solution, dried over MgSO4, and evapo-
rated to give a brown solid. This solid was eluted on a silica
gel column with CH2Cl2 to give an orange-brown band which
was evaporated and identified as (PMe2Ph)3ReCl2(3,4-NC4H2-
Br2) (5). Yield: 0.012 g, 19%. Mp: 147-150 °C. See Table 1
1
Cl2/hexane. Mp: 138-142 °C. See Table 1 for H and 13C NMR
data.
X-r a y Diffr a ction Stu d y of 5. A suitable crystal was
selected and mounted with 5-min epoxy into a Siemens
SMART three-circle goniometer. Indexing was determined
after collection of 3 sets of 20 0.3° (ω) scans. Least-squares
refinement of final cell dimensions was performed using all
reflections harvested during data collection. A hemisphere of
data was collected. Equivalent reflections were merged, and
all data were corrected for Lorentz and polarization effects.
Friedel opposites were merged.
Structure solution by direct methods in the centrosymmetric
space group P21/c revealed the complete non-hydrogen struc-
ture. All hydrogens were placed at calculated positions and
then refined using a riding model. Hydrogen thermal motion
was modeled as isotropic; thermal parameters for hydrogen
were calculated as 1.2 times the Ueq value for the parent atom.
The largest feature in the final difference map is 1.2 e/Å3,
located 1.10 Å from Re, and likely is an artifact of absorp-
tion.
1
for H NMR data. MS (ESI): m/z 896 (P+); 757 (P - PMe2Ph);
671 (P - PMe2Ph - Br2pyrr); 619 (P - 2 PMe2Ph). Anal. Calcd
Disorder was observed in phenyl ring C(5)-C(10) as well

Substitution and Addition Reactions at a Pyrrolyl Ligand
Organometallics, Vol. 18, No. 11, 1999 2239
as in the bromine positions. The phenyl ring is slipped across
two positions. The site occupancy of each group was refined
dependent upon the other. Final refined occupancies were 0.31-
(3)/0.69(3). Three positions were observed for Br. This was
modeled as partial contamination by the triply brominated
product, consistent with NMR data. This triply brominated
species has a site occupancy of 0.033(2). Details of data
collection and refinement are given in Table 5.
Syn th esis of (P Me2P h )3ReCl2(3-NC4H3Me) (6). Complex
1 (0.200 g, 0.271 mmol) was dissolved in 20 mL of diethyl ether,
and methyl triflate (100 µL, 0.88 mmol) was syringed into the
solution. Within hours, a yellow precipitate had formed. After
it was stirred at room temperature for 3 days, the green
solution was removed by cannula. The solvent was removed
from this portion, and the remaining complex was identified
as 1 (0.030 g). The yellow-brown precitipate was redissolved
in dichloromethane and extracted with a saturated aqueous
solution of NaHCO3. The solution was then dried over Na2-
SO4, filtered, and dried in vacuo to give a dark yellow-brown
of the SO3 group of the triflate anion. Each group was
successfully refined without restraints. A partial site oc-
cupancy factor was refined for each group such that the total
would sum to full occupancy. The ratio of this occupancy is
0.6(2)/0.4(2). All non-hydrogen atoms were refined with aniso-
tropic parameters for thermal motion. Hydrogens were intially
placed at calculated positions and freely refined in subsequent
cycles of least-squares refinement. Isotropic thermal param-
eters for hydrogen were also refined. The largest peak in the
final difference map, 1.002 e/Å3, is located near Re and is likely
an artifact of absorption. Details of data collection and refine-
ment are given in Table 5.
Attem p ted Rea ction of 1 w ith HOAc. To a solution of 1
(0.0536 g, 0.0727 mmol) in dichloromethane was added acetic
acid (8.0 µL, 0.14 mmol). The mixture was stirred at room
temperature for approximately 4 days. The solvent was
removed in vacuo, and the brown residue was characterized
by 1H NMR spectroscopy. Complex 1 and (PMe2Ph)3ReCl3 were
the major components of the mixture. No evidence for the
complex containing a protonated pyrrolyl ligand was observed.
P r oton a tion of (P Me2P h )3ReCl2(3,4-NC4H2Me2) (7). To
a CDCl3 solution of 7 (0.010 g, 0.013 mmol) and AlCl3 (0.0013
g, 0.01 mmol) was added 1.8 µL of CDCl3 saturated with
gaseous HCl in an NMR tube. The tube was flame-sealed
solid. Chromatography on
a neutral Al2O3 column, with
dichloromethane as eluent, gave a yellow band which was
evaporated to give 6. Yield: 0.088 g, 51%. See Table 1 for NMR
data. MS (ESI): m/z 752 (P); 671 (P - Mepyrr); 614 (P - PMe2-
Ph). The analytical data were calculated for 1 mol of H2O
included with the complex. Evidence for the water molecule
was observed in the NMR spectrum (s, 2 H, 1.51 ppm). Anal.
Calcd for C31H39Cl2NOP3Re: C, 45.25; H, 5.37; N, 1.82.
Found: C, 45.21; H, 4.99; N, 1.88.
Syn th esis of (P Me2P h )3ReCl2(3,4-NC4H2Me2) (7). To a
solution of 6 (0.041 g, 0.055 mmol) in 10 mL of dichlo-
romethane was added methyl triflate (6 µL, 0.05 mmol). After
20 h, the solvent was removed in vacuo. The brown residue
was redissolved in dichloromethane and the solution eluted
on a neutral Al2O3 column with dichloromethane. The first
yellow fraction contained ReCl3(PMe2Ph)3, and the second
yellow fraction contained a mixture of 1 and ReCl3(PMe2Ph)3.
The last fraction, which contained 7, eluted as a red-brown
band with a 10:1 mixture of dichloromethane and tetrahydro-
furan. See Table 1 for NMR data. MS (ESI): m/z 766 (M); 671
1
under vacuum and monitored by H NMR spectroscopy. The
solution immediately turned yellow, and the 1H NMR spectrum
indicated that the pyrrolyl ligand had been protonated at an
R-carbon. After a period of 2-3 days, the spectrum indicated
the quantitative formation of mer-(PMe2Ph)3ReCl3. The free
pyrrole was not isolated in this experiment. 1H NMR of
protonated complex (CDCl3): δ -2.33, -1.86, -0.14 (s, 6 H
each, PMe); 1.64 (s, 2H, NCH2); 4.49, 5.95 (s, 3 H each, Me
pyrr); 4.81 (s, 1 H, R-H, pyrr); 8.64 (t, 2 H J ) 6.9 Hz, m-H,
unique PPh); 8.91 (t, J ) 6.9 Hz, 4 H, m-H, trans-PPh); 11.25
(t, J ) 7.9 Hz, 2 H, p-H, trans-PPh); 11.45 (t, J ) 7.9 Hz, 1 H,
p-H, unique PPh); 12.29 (d, 2 H, J ) 6.9 Hz, o-H, unique PPh);
13.29 (d, 4 H, J ) 6.9 Hz, o-H, trans-PPh). 13C NMR (CDCl3):
δ 122.39, 48.63, 154.39 (PMe); 27.93 (R-C, pyrr); 3.66 (R-CH2,
pyrr): 34.69, 13.80 (Me2 pyrr); 122.45 (p-C, trans PPh); 122.47
(p-C, unique PPh); 134.95 (o-C, trans PPh); 138.41 (m-C, trans
+ unique PPh); 140.95 (o-C, unique PPh).
(M - Me2 - pyrr); 628 (M - PMe2Ph). Anal. Calcd for C30H41
-
Cl2NP3Re: C, 47.06; H, 5.40; N, 1.83. Found: C, 46.98, H, 5.28;
N, 1.55.
Isola tion of 3-Meth ylp yr r ole. Complex 1 (0.11 g, 0. 15
mmol) was dissolved in diethyl ether, and methyl triflate (0.70
µL, 0.62 mmol) was added by syringe. The solution was stirred
overnight. The resulting yellow precipitate was filtered under
nitrogen and washed with diethyl ether. A portion of this
cationic product was redissolved in CD3CN, and LiCl (4 equiv)
and AlCl3 (2 equiv) were added. The salts did not completely
dissolve, but the solution was stirred at room temperature for
4 days. The acetonitrile was removed under vacuum at room
temperature, the residue was dissolved in CDCl3, and the
volatiles were vacuum-transferred while the solution was
heated at 45 °C. The resulting pyrrole products were identified
by NMR and GC/mass spectroscopy as 3-methylpyrrole (ca.
Syn th esis of [(P Me2P h )3ReCl2(NC4H5)]OTf (8). Complex
1 (0.134 g, 0.182 mmol) was dissolved in 30 mL of Et2O, and
triflic acid (19 µL, 0.24 mmol) was added by syringe. A bright
yellow precipitate formed immediately. The solution was
stirred for 2 h at room temperature, and then the precipitate
was allowed to settle, the solution was decanted, and the
yellow solid was washed with diethyl ether. Yield: 0.155 g,
95%. The product was recrystallized by vapor diffusion of
diethyl ether into a dichloromethane solution of the compound.
See Table 1 for NMR data. Anal. Calcd for C29H38Cl2F3NO3P3-
SRe: C, 39.28; H, 4.28; N, 1.58. Found: C, 38.84; H, 4.02; N,
1.69.
X-r a y Diffr a ction Stu d y of 8. The crystal was mounted
to a thin glass fiber on a tapered copper mounting pin. This
assembly was aligned on a Siemens SMART CCD diffracto-
meter equipped with an LT-2A low-temperature apparatus
operating at 171 K. Data collection to 0.68 Å covered slightly
more than a hemisphere of arbitrary orientation. Each 0.3° ω
scan was exposed for 30 s. The initial orientation matrix was
determined from 3 approximately orthogonal sets of 20 0.3° ω
scans, each with a total exposure of 10 s. Standard uncertain-
ties of the final cell parameters were refined from 8192
reflections of 49 568 with I > 10σ(I) harvested from the data
collection. Data collection was complete to 0.75 Å and 91.9%
complete to 0.70 Å.
1
65%), 2-methylpyrrole (ca. 15%), and pyrrole (20%). H NMR
(CDCl3: 3-methylpyrrole, δ 2.09 (s, Me), multiplets at 6.80,
6.55, 6.04; 2-methylpyrrole, δ 2.26 (s, Me), multiplets at 6.63,
6.06, and 5.88; pyrrole, multiplets at δ 6.68 and 6.23. The NMR
spectrum of the remaining residue confirmed that no Re-
pyrrole complexes remained. Resonances were observed for
(PMe2Ph)3ReCl3 and a second unidentified pyrrole-free Re
complex.
Syn th esis of (P Me2P h )3Cl2Re[3-NC4H3-C(CO2Me)CH-
(CO2Me)] (9). Complex 1 (0.105 g, 0.142 mmol) was dissolved
in 40 mL of toluene. To the yellow-brown solution was added
dimethyl acetylenedicarboxylate (DMAD) (0.0208 g, 18.0 µL,
0.146 mmol) and glacial acetic acid (8.0 µL). The solution was
stirred for 3 days at room temperature; then the solvent was
removed in vacuo to give a brown oil. The NMR spectrum of
the crude product showed a mixture of 15% 1 and 85% 9. The
brown oil was redissolved in dichloromethane and loaded onto
Structure solution via direct methods in the centrosymmet-
ric space group Pbca revealed the non-hydrogen structure. No
crystallographically imposed symmetry is present in either the
cation or the anion. Disorder is manifest in two orientations

2240 Organometallics, Vol. 18, No. 11, 1999
DuBois et al.
a neutral alumina chromatography column. Complex 1 was
eluted with dichloromethane in the first yellow band in
approximately 51% yield. Complex 9 was eluted in the last
yellow band. See Table 1 for NMR data. MS (ESI): m/z 880
(M). Anal. Calcd for C34H43Cl2NO4P3Re‚2H2O: C, 44.59; H,
4.73; N, 1.53. Found: C, 44.61; H, 4.87; N, 1.55.
Attem p ted Rea ction of 1 w ith Dim eth yl F u m a r a te.
Complex 1 (0.115 g, 0.156 mmol) and dimethyl fumarate
(0.0224 g, 0.155 mmol) were dissolved in 20 mL of toluene.
Glacial acetic acid (1.0 µL) was added and the reaction mixture
stirred at room temperature for 5 days. No reaction was
observed by 1H NMR spectroscopy. Additional fumarate (0.0241
g, 0.167 mmol) and HOAc (5 mL) were added, and the reaction
mixture was stirred at room temperature for another 7 days.
No reaction was observed by NMR spectroscopy.
µL) and HOAc (3.5 µL). The solution was stirred at room
temperature for 4 days, and solvent was then removed in vacuo
1
to give a red oil. The H NMR spectrum of the crude product
showed a mixture of 6, (PMe2Ph)3ReCl3, and a new Re(III)
product. Attempts were made to separate the mixture by
elution with dichloromethane on a neutral alumina column,
but a new product was not successfully isolated.
Ack n ow led gm en t. Financial support by the Divi-
sion of Chemical Sciences, Office of Basic Energy
Sciences, Office of Energy Research, U.S. Department
of Energy, is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tal data, positional and thermal parameters, bond distances,
and bond angles for 1, 5, and 8. This material is available free
of charge via the Internet at http://pubs.acs.org.
At t em p t ed R ea ct ion of (P Me2P h )3R eCl2(3-NC4H 3Me)
(6) w ith Meth yl P r op iola te. To a solution of 6 (0.015 g, 0.020
mmol) in dichloromethane was added methyl propriolate (3.0
OM9900216