Protonation of the sulfonamido ligands in their Fe(CO)2Cp complexes

Article abstract of DOI:10.1135/cccc20070569

[Fe(CO)₂Cp(4-RC₆H₄SO₂NH)] complexes (R = Me, NO₂) undergo reversible protonation at the nitrogen atom bonded to the Iron centre. The molecular structure of the methyl complex was determined by single

Full text of DOI:10.1135/cccc20070569

Protonation of the Sulfonamido Ligands
569
PROTONATION OF THE SULFONAMIDO LIGANDS IN THEIR
Fe(CO) Cp COMPLEXES
2
Maria MAKOWSKA , Janusz ZAKRZEWSKIa1,* and Agnieszka RYBARCZYK-PIREKb
a
a
Department of Organic Chemistry, University of Łódź, Narutowicza 68, 90-136 Łódź, Poland;
e-mail: janzak@uni.lodz.pl
Department of Crystallography, University of Łódź, Pomorska 149/153, 90-136 Łódź, Poland;
1
b
e-mail: agnesr@uni.lodz.pl
Received Jan uary 30, 2007
Accepted April 18, 2007
Dedicated to Dr Karel Mach on the occasion of his 70th birthday in recognition of his outstanding
contribution to the area of organometallic synthesis and catalysis.
[
Fe(CO) Cp(4-RC H SO NH)] com plexes (R = Me, NO ) un dergo reversible proton ation at
2 6 4 2 2
th e n itrogen atom bon ded to th e iron cen tre. Th e m olecular structure of th e m eth yl com -
plex was determ in ed by sin gle crystal X-ray diffraction .
Keyw ord s: Cyclopen tadien yl ligan ds; Iron carbon yl com plexes; Sulfon am ides; Proton ation ;
X-ray diffraction ; Basicity.
+
+
Th e [Fe(CO) Cp] group (Fp ) form s with am in es (L) cation ic com plexes
2
+
–
Fp(L) an d with an ion ic n itrogen ligan ds L (an ion s of azoles, im ides, sulfon -
am ides, barbiturates etc.) n eutral com plexes FpL 1 . Som e of th e com plexes
h ave foun d application s in bioorgan om etallic ch em istry as IR-detectable
protein labellin g reagen ts an d h apten s in carbon ylm etalloim m un oassays or
,2
3
en zym e in h ibitors . Neutral com plexes FpL con tain a th ree-valen t n itrogen
atom bearin g lon e pair of electron s wh ich sh ould en dow th em with basic
properties. Herein we report th at n eutral Fp com plexes with sulfon am ido
ligan ds 1a, 1b un dergo proton ation at th e n itrogen atom to form cation ic
+
Fp(sulfon am ide) species 2a, 2b (Sch em e 1).
a) R = Me, b) R = NO2
SCHEME 1
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 4, pp. 569–578
©
2007 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc20070569

5
70
Makowska, Zakrzewski, Rybarczyk-Pirek:
RESULTS AND DISCUSSION
Addition of HBF ·Et O to ben zen e solution s of 1a, 1b brin gs about in stan ta-
4
2
n eous precipitation of oran ge crystallin e water-soluble solids. Th e treat-
m en t of aqueous solution s of th ese products with potassium carbon ate
leads to precipitation of th e startin g com plexes 1a, 1b.
Th is m ean s th at th e 1a, 1b are reversibly proton ated by HBF . Th e spec-
4
troscopic data presen ted below reveal th at proton ation takes place at th e
n itrogen atom an d yields th e cation ic com plexes 2a, 2b. Th e IR spectrum of
2
a (Table I) sh ows two absorption ban ds in th e region of N–H stretch in g
vibration s attributable to th e an tisym m etric an d sym m etric vibration s of
th e NH2 group (accordin gly, com plex 1a sh ows in th is region on ly on e
absorption ban d). Furth er eviden ce for th e N-proton ation of 1a, 1b was
1
5
15
provided by N NMR spectra of com poun ds 1a an d 2a labelled with N.
1
5
In th e spectrum m easured with out proton decouplin g [ N]-1a displays a
doublet at δ 397 ppm (upfield from th e [ N]-n itrom eth an e sign al, J
3 Hz), wh ereas [ N]-2a a triplet at δ 337 ppm (J
1
5
=
5N-H
1
1
5
7
= 80 Hz), con firm in g
5N-H
1
th e presen ce of on e an d two h ydrogen s bon ded to n itrogen , respectively.
Th e observed down field sh ift (60 ppm ) due to th e proton ation of 1a is com -
1
5
parable with th at observed on proton ation of th e [ N]-ph th alim ide an ion
(
2
74 ppm , ch em ical sh ifts of th e an ion an d ph th alim ide bein g 302 an d
4
28 ppm , respectively) .
1
Closely sim ilar H NMR an d IR data were obtain ed for 2b (see Experim en -
tal) in dicatin g th at proton ation of 1b also occurs at th e m etal-boun d n itro-
1
gen atom . Th e H NMR spectra sh owed th at solution s of 2a in aceton e-d
6
are relatively stable wh ilst in solution s of 2b in th e sam e solven t a slow sub-
stitution of th e 4-n itroben zen e-1-sulfon am ide ligan d by th e solven t took
place. It is accom pan ied by appearan ce of doublets of arom atic proton s at
δ 8.43 (J = 9.4 Hz) an d 8.17 (J = 9.4 Hz) (2a itself sh ows doublets at δ 8.48
an d 8.21 ppm ) an d of th e n ew Cp sign al at δ 5.70 ppm (cf. th e correspon d-
in g sign al of 2b, 5.62 ppm ). Th e substitution was com plete with in 24 h .
4
-Nitroben zen e-1-sulfon am ide was isolated from such a solution an d iden -
tified by com parison with an auth en tic sam ple. We were un able to isolate
+
th e iron com plex form ed (presum ably [Fp(aceton e)] ) but wh en h alide
–
–
–
–
an ion s (X = Cl , Br or I ) were presen t in th e solution , th e correspon din g
h alides FpX were isolated. Th ese data in dicate th at th e 4-n itroben zen e-
1
-sulfon am ide ligan d can be readily substituted by oth er 2e don or ligan ds.
In con trast, n o reaction of 1b with h alide ligan ds was observed un der th e
sam e con dition s. Th is m ean s th at th e n eutral sulfon am ide ligan d is m ore
substitution -labile th at its correspon din g an ion .
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 4, pp. 569–578

Protonation of the Sulfonamido Ligands
571
Th e N–H acidities of 2a, 2b were determ in ed by m easurem en t of pH of
aqueous solution s of th ese com poun ds at kn own con cen tration . Th e pKa
values are 2.9 an d 2.7 for 2a an d 2b, respectively. Th erefore, coordin ation
of th e Fp+ m oiety to ben zen esulfon am ide an d 4-n itroben zen esulfon am ide
5
(
pK 9.41 an d 8.63, respectively) leads to an im portan t in crease (~6–7 pK
a
a
un its) of th eir N–H acidities.
1
Th e IR an d H NMR spectral data of com plexes 1a an d 1b alon g with th e
pertin en t data m easured for 4-m eth ylben zen e-1-sulfon am ide are collected
in Table I.
It is obvious th at frequen cies of asym m etric an d sym m etric stretch in g
vibration s of th e SO fragm en t an d th e ch em ical sh ifts of arom atic, m eth yl
2
an d NH proton s decrease in th e order: 2a > 4-m eth ylben zen e-1-sulfon -
am ide > 1a. Th is can be ration alized assum in g th at th e coordin ation of th e
+
Fp to th e sulfon am ide brin gs about a decrease in th e electron den sity at
th is ligan d, wh ereas substitution of on e of th e am ido h ydrogen s with th is
group causes an opposite effect due to repulsion between iron d electron s
an d th e lon e pair of electron s at n itrogen .
TABLE I
IR an d 1H NMR spectral data for com poun ds 1a, 2a an d 4-m eth ylben zen e-1-sulfon am ide
Spectral data
1a
2a
p-Toluen esulfon am ide
IR (KBr, cm –1
)
ν(NH), ν(NH2)
ν(SO2)
3295
3171, 3087
1373, 1179
2077, 2053
3251, 3133
1324, 1148
–
1290, 1132
2046, 1994
ν(C≡O)
1H NMR, aceton e-d
6
Substituted ph en yl
7.63, 7.25
5.14
7.83, 7.51
5.64
7.77, 7.36
Cp
–
NH (NH2)
Me
2.82
2.98
2.88
2.40
2.37
2.46
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5
72
X-ray Crystal Structure of 2a
Makowska, Zakrzewski, Rybarczyk-Pirek:
Th e crystals of 2a suitable for X-ray an alysis were grown from layered di-
ch lorom eth an e–eth er solution . Crystal data an d structure refin em en t de-
tails are collected in Table II. Selected bon d distan ces an d an gles are sh own
in Table III. Th e view of th e m olecule of 2a is sh own in Fig. 1.
+
Th e asym m etric un it of th e crystal of 2a con sists of on e (C H FeNO S)
1
4
14
4
–
cation an d on e (BF ) an ion . In th e crystal th ese ion s form in fin ite ch ain s
4
th rough NH···F h ydrogen bon ds (Fig. 2 an d Table IV).
Alth ough 2a crystallizes in a ch iral space group th e structure sh ow local
m irror plan e sym m etry. Th ere is a n on -crystallograph ic C sym m etry of cat-
s
ion with pseudo-m irror plan e passin g th rough C15, th e m idpoin t of th e
C12–C13 bon d, Fe1, N2, S2, C21 an d C24 observed. Th e bon d len gth s an d
an gles in th e cation are com parable with th ose of n eutral m olecule of th e
6
sim ilar structure except for th ose in volvin g th e N2 atom . In 2a, th e N2
bon ds are a little lon ger, 2.047(5) Å for N–Fe bon d an d 1.691(4) Å for N–S
bon d, in com parison with th e 4-th iocyan oben zen esulfon am ido derivative –
1
.965(4) an d 1.565 Å, respectively.
FIG. 1
View of th e cation an d an ion of 2a in asym m etric un it with atom n um berin g sch em e. Dis-
placem en t ellipsoids for n on -H atom s are drawn at 30% probability level. Hydrogen atom s are
sh own as sm all sph eres of arbitrary radii
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 4, pp. 569–578

Protonation of the Sulfonamido Ligands
573
TABLE II
Crystal data for 2a an d structure refin em en t details
Em pirical form ula
C14H14BF FeNO S
4 4
Form ula weigh t
434.98
orth orh om bic, P2 2 2 (No. 19)
Crystal system , space group
Un it cell dim en sion s, Å
1
1 1
a = 11.373(1)
b = 16.060(1)
c = 9.740(1)
1779.0(3)
4
V, Å3
Z
ρcalc, g cm –3
1.624
Absorption coefficien t, m m –1
8.468
Tm in /Tm ax
0.0951/0.3343
880
F(000)
Crystal h abit
oran ge prism
0.3 × 0.25 × 0.2
Crystal size, m m
T, K
293(2)
Radiation type; wavelen gth , Å
θ ran ge for data collection , °
Lim itin g in dices
CuKα; 1.54178
4.76–68.45
–13 ≤ h ≤ 13
–
–
12 ≤ k ≤ 19
8 ≤ l ≤ 11
Reflection s collected/un ique
3477/3174 [Rin t = 0.043]
Data/restrain ts/param eters
GOF on F2
3174/24/215
0.907
a
b
b
Fin al R in dices [I > 2σ(I)]
R in dices (all data)
R = 0.0365 , wR = 0.0600
a
R = 0.0699 , wR = 0.1162
Largest diff. peak an d h ole, e Å–3
0.236 an d –0.249
–0.015(6)
Flack param eter
Extin ction coefficien t
0.0042(2)
a
R(F) = ∑(|F – F |)/∑|F |; wR(F ) = [∑w(|F – F |) /∑|F | ] ; w = 3[(sin θ)/λ]/[σ (F 2) +
b
2
2
2
1/2
2
o
c
o
o
c
o
o
0.0097P) ], wh ere P = [(Fo2) + 2(F )]/3.
2
2
(
c
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 4, pp. 569–578

5
74
Makowska, Zakrzewski, Rybarczyk-Pirek:
TABLE III
Selected geom etric param eters for 2a
Bon d, Å
An gle, °
Fe1–C30
Fe1–C40
Fe1–N2
1.751(6)
1.780(5)
2.044(4)
2.102(3)
2.071(3)
2.070(3)
2.073(2)
2.108(2)
1.416(3)
1.425(3)
1.691(4)
1.752(5)
1.168(5)
1.145(5)
C30–Fe1–C40
94.0(3)
98.1(2)
C30–Fe1–N2
C40–Fe1–N2
96.5(2)
Fe1–C11
Fe1–C12
Fe1–C13
Fe1–C14
Fe1–C15
S2–O22
S2–O21
S2–N2
O22–S2–O21
121.2(3)
105.0(2)
104.6(2)
110.6(3)
109.0(2)
104.9(2)
120.0(2)
174.7(5)
172.8(6)
175.8(3)
–67.6(3)
61.0(3)
O22–S2–N2
O21–S2–N2
O22–S2–C21
O21–S2–C21
N2–S2–C21
S2–N2–Fe1
O31–C30–Fe1
O41–C40–Fe1
Fe1–N2–S2–C21
Fe1–N2–S2–O22
Fe1–N2–S2–O21
N2–S2–C21–C22
N2–S2–C21–C26
O21–S2–C21–C22
O21–S2–C21–C26
O22–S2–C21–C22
O22–S2–C21–C26
S2–C21
C30–O31
C40–O41
94.4(5)
–85.5(5)
–154.0(4)
26.1(5)
161.8(5)
–18.4(5)
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 4, pp. 569–578

Protonation of the Sulfonamido Ligands
575
Moreover, som e differen ces in m olecular con form ation aroun d n itrogen
atom wh en com pared n eutral an d ion ic structure are n oticeable. For exam -
ple in like to tetrah edral geom etry aroun d N atom of ion ic structure Fe–N–S
an gle is equal 120.0(2)°, wh ile in pyram idal geom etry of th e n eutral m ole-
cule in creasin g value of 129.8(2)° is observed.
TABLE IV
Hydrogen bon din g geom etry (in Å an d °)
D–H
A
d(D–H)
d(H···A)
d(D···A)
⊄ DHA
N2–H2A···F53i
N2–H2B···F52ii
0.90
0.90
1.93
1.96
2.816(4)
2.857(4)
167
174
Sym m etry codes: i x – 1/2, 1/2 – y, –z; ii x, y, z.
FIG. 2
Th e sch em e of in term olecular h ydrogen bon din g ch ain s in th e crystal of 2a. N–H···F in terac-
tion s form in g in fin ite ch ain s of m olecules aroun d th e 21 screw axis parallel to th e [100] crys-
tallograph ic direction are sh own with dotted lin es
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 4, pp. 569–578

5
76
Conclusion
Makowska, Zakrzewski, Rybarczyk-Pirek:
We h ave foun d th at th e Fp(ben zen esulfon am ido) com plexes un dergo in a
stron gly acidic m edium (HBF ), proton ation at th e n itrogen atom to afford
4
+
th e Fp(ben zen esulfon am ide) species. Th e proton ation is reversible an d
proton ated cation ic com plexes are m ore substitution -labile th an th eir n eu-
tral coun terparts. In th e con text to th ese results it is worth y n otin g th at re-
versible proton ation of a tetrazolate ligan d in an Fp com plex was observed
1
c
by Palazzi et al. but in th is case it occurred at a n itrogen atom th at was
n ot directly boun d to th e iron atom .
EXPERIMENTAL
Reaction s usin g organ oiron com plexes were carried out un der argon . 1H an d 15N NMR
1
spectra (δ, ppm ; J, Hz) were recorded on a Varian 200BB spectrom eter (200 MHz for H an d
15
2
0 MHz for 15N) usin g in tern al TMS an d extern al [ N]-n itrom eth an e referen ce, respectively.
–
1
IR spectra (ν, cm ) were run on a Bio-Rad FTS-175C apparatus. Com poun ds 1a, 1b were
prepared accordin g to th e earlier publish ed procedure . Ben zen e was distilled over Na-
7
ben zoph en on e im m ediately before use. All reagen ts were com m ercially available (Sigm a–
Aldrich ) an d were used with out furth er purification . Kieselgel 60 (Merck, 230–400 m esh
ASTM) was used for colum n ch rom atograph y.
Preparation of 4-Meth yl[15N]ben zen e-1-sulfon am ide
To 2 m l of 6 M aqueous solution of 15NH , tosyl ch loride (3 m m ol) was added at 60 °C.
3
Th e resultin g m ixture was refluxed for 3 h , cooled to room tem perature an d th e solid fil-
1
5
tered off an d recrystallized from m eth an ol–water. Yield 82%. N NMR (DMSO-d ): 284 t,
6
J15N-H = 84. IR (CHCl ): 3435, 3341 (NH ); 1349, 1164 (SO ).
3
2
2
Preparation of [15N]-1a
Th is com plex was syn th esized from an d th e 4-m eth yl[15N]ben zen e-1-sulfon am ide accordin g
1
5
to th e earlier publish ed procedure. N NMR (DMSO-d ): 397 d, J
= 73. IR (CHCl ):
3
6
15N-H
2
053, 2004 (CO); 3362 (NH); 1297, 1135 (SO ).
2
Preparation of Proton ated Com plexes 2a an d 2b
Com plexes 1a an d 1b (0.2 m m ol) were dissolved in ben zen e (30 m l) an d treated with
HBF ·Et O (0.3 m l) with vigorous stirrin g. Th e oran ge-red solution s turn ed im m ediately yel-
4
2
low an d oran ge solids precipitated. Th e solids were filtered off, wash ed with ben zen e an d di-
eth yl eth er an d dried in vacuo.
1
2
a (yield 75%): H NMR (aceton e-d ): 7.83 d, J = 8.0, 2 H (arom . H); 7.51 d, J = 8.0, 2 H,
6
(
arom . H); 5.64 s, 5 H (Cp); 2.98 s, 2 H (NH ); 2.46 s, 3 H (Me). IR (KBr): 2077, 2053 (CO);
2
3
111, 3079 (NH ); 1296, 1166 (SO ); 1048 (BF ). For C14H14BF FeNO S·0.5H O (435.0) calcu-
2 2 4 4 4 2
lated: 37.87% C, 3.41% H, 3.15% N, 7.22% S; foun d: 37.87% C, 3.44% H, 3.46% N, 7.51% S.
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 4, pp. 569–578

Protonation of the Sulfonamido Ligands
577
2
b (yield 68%): 1H NMR (aceton e-d ): 8.48 d, J = 9.0, 2 H (arom . H’s); 8.21 d, J = 9.0, 2 H
6
(
(
arom . H’s); 5.62 s, 5 H (Cp); 2.88 s, 2 H (NH ). IR (KBr): 2066, 2020 (CO); 3142, 3070
2
NH ); 1534, 1380 (NO ); 1363, 1187 (SO ); 1039 (BF ). For C13H11BF FeN O S (465.2) calcu-
2
2
2
4
4
2
6
lated: 33.57% C, 2.38% H, 6.02% N, 6.89% S; foun d: 33.51% C, 2.63% H, 5.62% N, 6.42% S.
Reaction of 2b with Halide Ion s
Th e com plex 2b (8.5 m g, 0.018 m m ol) was dissolved in aceton e (1 m l) con tain in g LiCl, LiBr
or KI (0.06 m m ol). After 2.5 h at room tem perature th e solven t was evaporated to dryn ess
an d th e residue triturated with ch loroform (3 m l). Th e in soluble solid was filtered off,
wash ed with water an d dried. Th is m aterial was iden tified, by spectral com parison with an
auth en tic sam ple as 4-n itroben zen e-1-sulfon am ide. Th e filtrate was ch rom atograph ed (SiO2,
ch loroform ) to afford th e correspon din g Fp h alide (iden tified by com parison with an au-
th en tic sam ple) in practically quan titative yield.
X-ray Structure Determ in ation
X-ray data were collected on a Rigaku AFC5S diffractom eter8 usin g CuKα X-ray source an d a
graph ite m on och rom ator. Th e un it cell dim en tion s were obtain ed from a least-squares fit to
9
settin g an gles of 25 reflection s. An alytical absorption correction was applied . Th e structure
1
0
was solved by direct m eth od usin g program Crystal Structure an d refin ed by th e full-
1
1
m atrix least-square m eth od usin g SHELXL97 . Th e fluoride atom s sh ow large an isotropic
–
displacem en t param eters, wh ich can m ask som e kin d of disorder in th e BF4 an ion . Th e
h ydrogen atom s were in troduced in calculated position s with idealized geom etry except for
H2A an d H2B atom s wh ich were foun d in th e Fourier differen ce m ap. In th e fin al step of
th e refin em en t procedure, all n on -h ydrogen atom s were refin ed with an isotropic displace-
m en t param eters an d all th e h ydrogen atom s were refin ed usin g a rigid body m odel. Th e
1
2
13
m olecular geom etry was calculated by PARST
an d Win GX . Selected bon d distan ces an d
1
4
an gles are sum m arized in Table II. Th e drawin gs were m ade by program PLATON . A sum -
m ary of crystallograph ic data is given in Table I.
CCDC 299656 (2a) con tain s th e supplem en tary crystallograph ic data for th is paper. Th ese
data can be obtain ed free of ch arge via www.ccdc.cam .ac.uk/con ts/retrievin g.h tm l (or from
th e Cam bridge Crystallograph ic Data Cen tre, 12, Un ion Road, Cam bridge, CB2 1EZ, UK;
fax: +44 1223 336033; or deposit@ccdc.cam .ac.uk).
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