Coordination chemistry of Rh(III) porphyrins: Complexes with hydrazine, disulfide, and diselenide bridging ligands

Article abstract of DOI:10.1021/ic0011314

Rh(III) porphyrin complexes with bridging hydrazine and substituted hydrazine ligands were characterized in solution by ¹H NMR spectroscopy and in the solid state by X-ray diffraction. Addition of further ligand to these species afforded 1:1 complexes in which methylhydrazine and N,N-dimethylhydrazine preferentially bound to the Rh center through the substituted nitrogen atom, as evidenced by ¹H NMR chemical shifts. An alkylated Rh(III) porphyrin was isolated as a decomposition product of the reaction of N,N-dimethylhydrazine with Rh(III) porphyrin in the presence of light and oxygen. Me₂Se₂ and Me₂S₂ formed bridging and nonbridging complexes with Rh(III) porphyrin, analogous to that observed with N,N′-dimethylhydrazine.

Full text of DOI:10.1021/ic0011314

Inorg. Chem. 2001, 40, 3217-3221
3217
Coordination Chemistry of Rh(III) Porphyrins: Complexes with Hydrazine, Disulfide, and
Diselenide Bridging Ligands
James E. Redman,† Neil Feeder,† Simon J. Teat,‡ and Jeremy K. M. Sanders*,†
Cambridge Centre for Molecular Recognition, University Chemical Laboratory, Lensfield Road,
Cambridge, CB2 1EW, U.K., and CLRC Daresbury Laboratory, Daresbury,
Warrington, WA4 4AD, U.K.
ReceiVed October 13, 2000
Rh(III) porphyrin complexes with bridging hydrazine and substituted hydrazine ligands were characterized in
solution by 1H NMR spectroscopy and in the solid state by X-ray diffraction. Addition of further ligand to these
species afforded 1:1 complexes in which methylhydrazine and N,N-dimethylhydrazine preferentially bound to
1
the Rh center through the substituted nitrogen atom, as evidenced by H NMR chemical shifts. An alkylated
Rh(III) porphyrin was isolated as a decomposition product of the reaction of N,N-dimethylhydrazine with Rh(III)
porphyrin in the presence of light and oxygen. Me2Se2 and Me2S2 formed bridging and nonbridging complexes
with Rh(III) porphyrin, analogous to that observed with N,N′-dimethylhydrazine.
Introduction
paper, we describe the preparation of Rh(III) porphyrin com-
plexes with hydrazine ligands and demonstrate the formation
of analogous species with disulfide and diselenide ligands in
solution.
The crystal structure of a nitrogenase enzyme cofactor1
revealed an Fe-Mo sulfide cluster believed to be responsible
for the biological fixation of nitrogen. These findings renewed
interest in the coordination chemistry of dinitrogen with
transition metals with a view to both understanding the natural
system and developing artificial nitrogen fixation processes. Of
particular importance is the reduction of coordinated nitrogen
to hydrazine and ammonia or its incorporation into organic
molecules under mild conditions. Recent advances in this field
have included the formation of ammonia by reaction of a
tungsten-dinitrogen complex with an acidic Ru-η2-H2 com-
plex2 and reaction of a Zr2 (µ-η2:η2-N2) species with H2 to
form an N-H bond.3 The complexes of hydrazines with
metalloporphyrins have generated interest as models for inter-
mediates in the reduction of dinitrogen. Collman et al. have
reported the preparation and redox chemistry of covalently
linked Ru(II) porphyrin dimers in which hydrazine was bound
between the already cofacial porphyrins.4-6 We have previously
described hydrazine binding to steroid-capped Zn(II) por-
phyrins,7 and more recently, others have reported syntheses of
Ru(IV) and Ti(IV) porphyrin complexes with hydrazido ligands.8,9
Continuing our studies of rhodium porphyrins,10,11 in this
Experimental Section
Instrumentation. NMR spectra were recorded on Bruker DRX 500
(500.1 MHz for 1H, 125.7 MHz for 13C), AM 400 or DRX 400 (400.1
1
MHz for H, 100.6 MHz for 13C), and DPX 250 or AC 250 (250.1
MHz for 1H, 62.9 MHz for 13C) instruments. Chemical shifts are quoted
in parts per million with respect to tetramethylsilane (TMS). Infrared
spectra were recorded on a Perkin-Elmer Paragon 1000 FTIR spec-
trometer at 4 cm-1 resolution or better. UV-visible spectra were
recorded on a Hewlett-Packard 8452A diode array spectrophotometer.
X-ray Crystallography. Diffraction data were collected in Cam-
bridge on a Rigaku R-Axis IIc or Nonius Kappa CCD device, or for
small crystals, were collected at the Daresbury SRS (UK), Station 9.8,
using a Bruker AXS SMART CCD area detector.12-14 Structures were
solved with either SHELXS-97 or SIR92.15-17 Refinement was carried
out with SHELXL-97.18 Extensive disorder was often observed in the
solubilizing hexyl chains, typical of this kind of structure.19 The carbon
(9) Thorman, J. L.; Woo, L. K. Inorg. Chem. 2000, 39, 1301.
(10) Kim, H.-J.; Redman, J. E.; Nakash, M.; Feeder, N.; Teat, S. J.; Sanders,
J. K. M. Inorg. Chem. 1999, 38, 5178.
* Corresponding author e-mail: jkms@cam.ac.uk.
† Cambridge Centre for Molecular Recognition.
‡ CLRC Daresbury Laboratory.
(1) Kim, J.; Rees, D. C. Nature 1992, 360, 563.
(2) Nishibayashi, Y.; Iwai, S.; Hidai, M. Science 1998, 279, 540.
(3) Fryzuk, M. D.; Love, J. B.; Rettig, S. J.; Young, V. G. Science 1997,
275, 1445.
(4) Collman, J. P.; Hutchison, J. E.; Lopez, M. A.; Guilard, R.; Reed, R.
A. J. Am. Chem. Soc. 1991, 113, 2794.
(5) Collman, J. P.; Kim, K.; Leidner, C. R. Inorg. Chem. 1987, 26, 1152.
(6) Collman, J. P.; Hutchison, J. E.; Ennis, M. S.; Lopez, M. A.; Guilard,
R. J. Am. Chem. Soc. 1992, 114, 8074.
(11) Redman, J. E.; Feeder, N.; Teat, S. J.; Sanders, J. K. M. Inorg. Chem.
2001, 40, 2486.
(12) Cernik, R. J.; Clegg, W.; Catlow, C. R. A.; Bushnell-Wye, G.; Flaherty,
J. V.; Greaves, G. N.; Burrows, I.; Taylor, D. J.; Teat, S. J.; Hamichi,
M. J. Synchrotron Radiat. 1997, 4, 279.
(13) Clegg, W. J. Chem. Soc., Dalton Trans. 2000, 3223.
(14) SMART (control) and SAINT (integration) software, version 4; Bruker
AXS Inc.: Madison, WI, 1994.
(15) Sheldrick, G. M. SHELXS-97: Program for the Solution of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(16) Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo, C.; Polidori,
G.; Spagna, R.; Viterbo, D. J. Appl. Crystallogr. 1989, 22, 389.
(17) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1993, 26, 343.
(7) Bonar-Law, R. P.; Sanders, J. K. M. J. Chem. Soc., Perkin Trans. 1
1995, 3085.
(8) Sun, X.-R.; Huang, J.-S.; Cheung, K.-K.; Che, C.-M. Inorg. Chem.
2000, 39, 820.
(18) Sheldrick, G. M. SHELXL-97: Program for Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
10.1021/ic0011314 CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/24/2001

3218 Inorganic Chemistry, Vol. 40, No. 13, 2001
Redman et al.
Table 1. Crystallographic Data for 2, 4, 5, 7, and 9
2
4
5
7
9
empirical formula
fw
cryst size, mm
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C
120H156I2N10Rh2
C60H79IN5Rh
1100.09
0.07 × 0.06 × 0.02
P21/c
16.3158(13)
26.431(2)
12.7523(10)
90
100.830(2)
90
5401.5(8)
4
C123H162Cl2I2N10Rh2
2311.15
C123H162Cl2I2N10Rh2
2311.15
C122H160Cl2I2N10Rh2
2297.12
2198.17
0.09 × 0.04 × 0.02
P1h
0.16 × 0.14 × 0.03
0.20 × 0.04 × 0.04
0.12 × 0.06 × 0.06
P1h
P1h
P1h
16.2361(13)
18.6695(15)
20.6876(16)
72.554(2)
87.348(2)
67.114(2)
5493.8(8)
2
15.1170(4)
18.7980(8)
21.9870(9)
68.4040(14)
81.457(2)
79.604(2)
5691.0(4)
2
15.231(2)
18.438(3)
22.377(3)
65.943(5)
83.689(5)
81.358(5)
5664.8(14)
2
15.1665(9)
18.7297(11)
21.7848(12)
67.709(5)
81.345(5)
79.304(5)
5604.5(6)
2
Z
F
R
calc, mg/m3
1.329
0.0895
1.353
0.0632
1.349
0.0863
1.355
0.1544
1.361
0.0702
wR2
0.2170
1.065
0.1177
1.073
0.1988
1.032
0.3393
1.143
0.1891
0.997
GOF on F2
atoms in these disordered groups were refined with isotropic temperature
factors and restrained to give chains with a reasonable geometry. Even
with synchrotron radiation, crystals were found to be weakly diffracting,
resulting in a relatively high R1 value.
360, 408, 528, 558. IR (CCl4) νmax (cm-1): 3287 (w), 3231 (w), 3147
(w), 2957 (s), 2930 (s), 2858 (m), 1466 (m).
1H NMR Titrations. CDCl3 for use in titrations was stored over
anhydrous K2CO3 in a refrigerator. Typically, a solution of Rh(III)
porphyrin (1)‚MeOH (4 mg) in CDCl3 (600 µL) was titrated with 5-µL
aliquots of a solution of ligand in CDCl3 at a concentration of 72 mM.
1H spectra (400 MHz) were acquired at room temperature. Me2Se2 was
filtered through neutral alumina before use.
UV-Visible Titrations. A 3.0-mL aliquot of a 4 µM solution
of 1‚MeOH in CH2Cl2/MeOH (200 µL MeOH/100 mL of solvent)
was titrated at 25 °C with 10-µL aliquots of a 75 µM solution of
ligand in the same solvent mixture. The cuvette was magnetically stirred
for ∼30 s prior to recording each spectrum. Spectra were processed
by factor analysis followed by least-squares fitting using the program
Specfit.20
Materials. 1 was prepared as previously described10 and recrystal-
lized from CHCl3 layered with MeOH. Other chemicals were obtained
from Aldrich and used without further purification. Merck 60 mesh
silica gel was used for column chromatography.
1‚NH3 Complex (4). A solution of 1 (5 mg, 4.6 µmol) in CH2Cl2 (1
mL) was treated with vapor from aqueous NH3 solution for 30 min at
room temperature. The solvent was evaporated by blowing with N2,
and the product was obtained quantitatively after being dried in vacuo.
Crystals for structure determination were obtained from a toluene
solution layered with MeOH.
Synthesis. 12‚NH2NH2 (2). Hydrazine monohydrate (0.5 µL, 10
µmol) in water (10 mL) was added to a mixture of a solution of 1 (10
mg, 9.2 µmol) in CH2Cl2 (1 mL) and water (5 mL). After 150 min at
room temperature, an additional portion of CH2Cl2 (20 mL) was added,
and the organic layer was separated, washed with water (2 × 30 mL),
and dried (MgSO4). Evaporation of the solvent afforded the product as
an orange solid (5 mg, 49%).
For structure determination, crystals of 2 were obtained from a
solution of 2 and 3 (prepared by adding > 0.5 equiv of N2H4‚H2O to
1) in toluene layered with MeOH (see Table 1).
1H NMR (400 MHz, CDCl3): δ 9.37 (s, 4H, meso), 7.84 (m, 8H,
Ar), 7.55 (m, 8H, Ar), 7.25 (m, Ar), 3.72 (m, 16H, hex H1), 2.24 (s,
24H, CH3), 2.04 (m, 16H, hex H2), 1.84 (m, 16H, hex H3), 1.63 (m,
16H, hex H4), 1.52 (m, 16H, hex H5), 1.05 (t, J ) 7 Hz, 24H, hex H6),
-11.03 (s, 4H, NH2). 13C NMR (100.6 MHz, CDCl3): δ 143.5, 141.6,
138.6, 138.0, 137.8, 133.0, 132.9, 128.5, 127.6, 127.3, 118.3, 96.8,
33.4, 31.9, 30.5, 27.0, 22.9, 15.1, 14.2. UV-vis (CH2Cl2) λmax, nm:
1H NMR (400 MHz, CDCl3): δ 10.23 (s, 2H, meso), 8.14 (d, J )
7 Hz, 2H, Ar), 7.98 (d, J ) 7 Hz, 2H, Ar), 7.78-7.68 (m, 6H, Ar),
4.00 (m, 4H, hex H1), 3.89 (m, 4H, hex H1), 2.45 (s, 12H, CH3), 2.22
(m, 8H, hex H2), 1.80 (m, 8H, hex H3), 1.55 (m, 8H, hex H4), 1.43 (m,
8H, hex H5), 0.95 (t, J ) 7 Hz, 12H, hex H6), -5.77 (s, 3H, NH3). 13
C
NMR (100.6 MHz, CDCl3): δ 144.1, 142.8, 140.5, 140.1, 138.6, 134.0,
132.8, 128.3, 127.8, 127.2, 119.3, 98.8, 33.4, 32.0, 30.3, 27.1, 22.8,
15.6, 14.2. UV-vis (CH2Cl2) λmax (nm): 360, 420, 532, 562. MALDI
MS m/z: [M - NH3]+ 1084. IR (CCl4) νmax (cm-1): 3381 (w), 2957
(s), 2930 (s), 2858 (m). Anal. Calcd for C60H79IN5Rh: C, 65.51; H,
7.24; N, 6.37. Found: C, 65.70; H, 7.43; N, 6.03.
12‚NHMeNHMe (5). A solution of 1‚NHMeNHMe (6) (10 mg, 8.7
µmol) in CH2Cl2/hexane (1:1) was passed through a silica column. The
solvent was evaporated to afford the product as an orange solid (7.1
mg, 73%). Crystals for structure determination were obtained from a
CH2Cl2 solution layered with MeOH.
(19) Nakash, M.; Clyde-Watson, Z.; Feeder, N.; Teat, S. J.; Sanders, J. K.
M. Chem.sEur. J. 2000, 6, 2112.
(20) Specfit, version 2.09X; Spectrum Software Associates: Chapel Hill,
NC.
1H NMR (400 MHz, CDCl3): δ 9.64 (s, 4H, meso), 7.79 (m, 12H,
Ar), 7.53 (m, 8H, Ar), 4.17 (m, 4H, hex H1), 4.05 (m, 4H, hex H1),

Coordination Chemistry Rh(III) Porphyrins
Inorganic Chemistry, Vol. 40, No. 13, 2001 3219
3.79 (m, 8H, hex H1), 2.32 (s, 12H, CH3), 2.29 (s, 12H, CH3), 1.96
(m, 4H, hex H2), 1.85 (m, 12H, hex H2), 1.65 (m, 16H, hex H3), 1.47-
1.33 (m, 32H, hex H4,5), 0.93, 0.90 (2 × t, J ) 7 Hz, 24H, hex H6),
-7.32 (d, J ) 6 Hz, 6H, NHCH3), -9.40 (t, J ) 6 Hz, 2H, NHCH3).
1‚NHMeNHMe (6). To a solution of 1‚MeOH (12.2 mg, 11 µmol)
in CH2Cl2 (20 mL) was added N,N′-dimethylhydrazine dihydrochloride
(17.3 mg, 0.13 mmol) in water (20 mL). NaOH (10%, 2 drops) was
added, and the mixture was shaken. The organic phase was separated,
dried (MgSO4), and evaporated to an orange solid (10.6 mg, 85%).
1H NMR (400 MHz, CDCl3): δ 10.28 (s, 2H, meso), 8.10 (m, 2H,
Ar), 8.04 (m, 2H, Ar), 7.76 (m, 6H, Ar), 4.03 (m, 4H, hex H1), 3.91
(m, 4H, hex H1), 2 × 2.48 (s, 12H, CH3), 2.21 (m, 8H, hex H2), 1.77
(m, 8H, hex H3), 1.52 (m, 8H, hex H4), 1.41 (m, 8H, hex H5), 2 ×
0.92 (t, J ) 7 Hz, hex H6), -0.66 (s, 3H, NHCH3), -3.27 (d, J ) 6
Hz, 3H, RhNHCH3), -4.09 (s, 1H, NHCH3), -4.90 (m, 1H, RhNHCH3).
13C NMR (100.6 MHz, CDCl3): δ 2 × 144.3, 142.7, 140.5, 140.4,
140.1, 140.0, 138.8, 138.7, 133.8, 133.0, 128.3, 127.7, 127.3, 119.5,
98.9, 34.3, 33.8, 2 × 33.3, 32.0, 2 × 30.1, 2 × 27.0, 22.7, 15.5, 14.1.
12‚NH2NMe2 (7). 7 was prepared by titration of a solution of 1‚
MeOH (4.0 mg, 3.6 µmol) with N,N-dimethylhydrazine in CDCl3.
Material for crystal growth was prepared by passing a solution of 1
(5.2 mg, 4.8 µmol) and N,N-dimethylhydrazine (1 µL, 13 µmol) in
CH2Cl2 (0.5 mL) and hexane (0.5 mL) through a silica column.
Porphyrin was washed from the column with CH2Cl2/hexane (1:1), and
the solvent was evaporated. X-ray quality crystals were obtained from
a CH2Cl2 solution layered with MeOH.
Figure 1. Molecular structure of 2. Hydrogen atoms and porphyrin â
substituents have been omitted for clarity.
1H NMR (400 MHz, CDCl3): δ 9.77 (s, 2H, meso), 0.37 (s, 2H,
meso), 7.80 (m, 12H, Ar), 7.62 (m, 6H, Ar), 7.37 (d, J ) 7 Hz, 2H,
Ar), 4.04 (m, 8H, hex H1), 3.76 (m, 8H, hex H1), 2.38 (s, 12H, CH3),
2.29 (s, 12H, CH3), 1.85 (m, 16H, hex H2), 1.63 (m, 16H, hex H3),
1.50-1.30 (m, 32H, hex H4,5), 0.93 (t, J ) 7 Hz, 12H, hex H6), 0.88
(t, J ) 7 Hz, 12H, hex H6), -7.83 (s, 6H, NCH3), -10.24 (s, 2H,
NH2).
12‚NHMeNH2 (9). 9 was prepared by titration of a solution of 1‚
MeOH (4.2 mg, 3.8 µmol) with methylhydrazine in CDCl3. After the
titration, the sample was eluted through a silica column with hexane/
CH2Cl2 (1:1) and evaporated to an orange solid. This was dissolved in
CH2Cl2 and layered with MeOH to obtain crystals for structure
determination.
1H NMR (400 MHz, CDCl3): δ 9.47 (s, 2H, meso), 9.43 (s, 2H,
meso), 7.93 (d, J ) 7 Hz, 2H, Ar), 7.82 (m, 8H, Ar), 7.52 (m, 8H, Ar),
7.33 (d, J ) 4 Hz, 2H, Ar), 4.03 (m, 4H, hex H1), 3.89 (m, 4H, hex
H1), 3.75 (m, 4H, hex H1), 3.66 (m, 4H, hex H1), 2.33 (s, 6H, CH3), 2
× 2.27 (2 × s, 18H, CH3), 2.17-1.34 (m, 64H, hex H2-5), 0.96 (m,
24H, hex H6), -7.79 (d, J ) 6 Hz, 3H, NHCH3), -10.00 (m, 2H,
NHMeNHH), -10.34 (m, 1H, NHH).
can be attributed to exchange of the latter protons catalyzed by
traces of acidic impurity. In support of this hypothesis, exposure
of the sample to trifluoroacetic acid vapor further broadened
the RhNH2NH2 resonance without affecting the width of the
RhNH2NH2 peak.
Passage of a solution of 2 and 3 through a silica gel column
eluted with CH2Cl2/hexane (1:1) retained hydrazine on the silica
and converted 3 to 2. In this way, a mixture with initial meso
resonances in the intensity ratio of 1:0.77 (3:2) was converted
to a mixture in which this ratio was 1:9.6. Starting from 10 mg
of 1‚MeOH, a total of 8.0 mg of material was recovered after
this treatment, confirming that there is a true conversion of 3
to 2 on the silica gel and that this filtration does not simply
remove 3 to leave a mixture enriched in 2. An alternative route
to 2 was extraction of an aqueous solution of hydrazine with a
solution of 1 in CH2Cl2 followed by a standard aqueous workup.
The infrared spectrum of 2 in CCl4 solution showed a band at
3231 cm-1 and a further pair of very weak bands in the same
spectral region, which may be assigned to the NH stretches of
the hydrazine.21
Results and Discussion
1 was prepared as a methanol complex according to the
literature.10 A solution of 1‚MeOH in CDCl3 was titrated with
hydrazine monohydrate, and the product distribution was
Crystallization of a mixture of 3 and 2 from a toluene solution
layered with methanol resulted in preferential crystallization of
2, most likely because of the poor solubility of this complex in
methanol. A single-crystal X-ray diffraction study revealed that
in the solid state the hydrazine adopts a trans geometry with a
Rh-N-N-Rh torsion angle of 178.5(1)° (Figure 1). The N-N
bond length of 1.47(1) Å is in the range typically reported for
bridging hydrazine complexes.22 The two inequivalent Rh-Naxial
bond lengths are 2.030(9) and 2.089(9) Å. The porphyrins are
oriented with almost parallel planes but with the axes joining
the opposite meso positions twisted slightly, apparently to avoid
steric clash of the peripheral substituents. The deviation of the
porphyrins from planarity is irregular and not easily classified
into one of the commonly observed distortion modes.23
1
monitored by H NMR spectroscopy. Hydrazine displaced the
coordinated methanol and initially formed a 2:1 complex (2)
with a bridging hydrazine ligand as evidenced by a highly
shielded resonance at -11.03 ppm and an upfield shifted
porphyrin meso resonance at 9.37 ppm. Collman et al. observed
a similarly upfield shifted resonance at -10.15 ppm, corre-
sponding to hydrazine bound within a Ru(II) cofacial dipor-
phyrin.6 Addition of >0.5 equiv of hydrazine resulted in the
breakup of the dimeric complex to afford the 1:1 complex 3,
which displayed a pair of shielded NH2 resonances at -3.77
and -3.28 ppm and a porphyrin meso resonance at 10.25 ppm.
2 and 3 were in slow exchange on the NMR chemical shift
time scale, although equilibration occurred too rapidly to readily
For comparison with 2 and 3, the complex of 1 with ammonia,
4, was prepared by exposure of a CH2Cl2 solution of 1 to
1
monitor the kinetics of this process by H NMR. The more
upfield NH2 resonance, assigned to RhNH2NH2, remained sharp
throughout the titration, whereas the peak at -3.28 ppm,
assigned to RhNH2NH2, progressively broadened. Broadening
(21) Sacconi, L.; Sabatini, A. J. Inorg. Nucl. Chem. 1963, 25, 1389.
(22) Heaton, B. T.; Jacob, C.; Page, P. Coord. Chem. ReV. 1996, 154, 193.
(23) Scheidt, W. R.; Lee, Y. J. Struct. Bonding 1987, 64, 1.

3220 Inorganic Chemistry, Vol. 40, No. 13, 2001
Redman et al.
1
Figure 3. Upfield region of the 500 MHz H NMR spectrum of 9
showing the NH resonances.
centrosymmetric with a molecule of each enantiomer in the unit
cell. The porphyrin planes are not parallel but are tilted by
28.31(5)° to accommodate the methyl groups of the ligand. The
axes joining the opposite substituted meso positions of each
porphyrin are rotated by approximately 90° with respect to each
other to avoid steric clash. The Rh-Naxial bond lengths of
2.195(7) and 2.199(7) Å are comparable to the value of
Figure 2. Molecular structure of 5. Hydrogen atoms have been omitted.
2.216(8)
Å reported for the Rh-N distance of the
Table 2. Selected Bond Lengths (Å), Angles (deg), and Torsions
for 2, 4, and 5
[RhCl4(PPh3)(NHMeNHMe)]- anion.25
Titrations of 1‚MeOH in CDCl3 with methylhydrazine and
N,N-dimethylhydrazine were carried out. On addition of <0.5
equiv of these substituted hydrazines, the expected bridging
complexes 7 and 9 were observed, as evidenced by highly
shielded NH and methyl resonances. The resonances of methyl-
hydrazine in 9 all appear as multiplets (Figure 3). The methyl
2
4
5
Rh-Naxial
2.030(9), 2.089(9) 2.113(5) 2.195(7), 2.199(7)
2.622(1), 2.620(1) 2.6447(6) 2.6261(8), 2.6261(9)
177.7(3), 179.5(3) 178.0(1) 176.4(2), 175.9(2)
Rh-Iaxial
Iaxial-Rh-Naxial
Naxial-Naxial
Rh-Naxial-Naxial
1.47(1)
1.479(9)
120.1(6), 115.8(6)
Rh-Naxial-Naxial-Rh 178.5(5)
C-Naxial-Naxial-C
118.2(5), 117.3(5)
151.4(3)
3
resonance is assigned to a doublet at -7.79 ppm with JHNCH
58.2(9)
3
) 6 Hz. JHNCH for free methylhydrazine has been reported as
Rh-Naxial-C
114.5(5), 114.6(5)
6.25 Hz.26 A COSY spectrum revealed a cross-peak between
this resonance and a multiplet at -10.00 ppm that integrated to
two protons. This peak is assigned to the overlapping resonances
of the NHCH3 proton and a single proton of the diastereotopic
NH2 group. The resonance of the other proton of this group
resembles a triplet at -10.34 ppm. In contrast to 9, the 1H NMR
spectrum of 7 is simple with singlets at -7.83 and -10.24 ppm
assigned to the N(CH3)2 and NH2 resonances, respectively.
Addition of >0.5 equiv of the hydrazines dissociated the dimers
to afford the 1:1 complexes 8 and 10. Here, the situation is
complicated by the possibility of isomeric forms in which the
hydrazine coordinates through different nitrogen atoms. Al-
though theoretical and NMR studies27 have supported the belief
that the substituted nitrogen of alkyl hydrazines is the more
basic, in reported crystal structures of methylhydrazine and N,N-
dimethylhydrazine, these ligands bound through the unsubsti-
tuted and less sterically hindered nitrogen atom.28-33 The ability
of the Rh(III) porphyrin to act as a shift reagent for bound
ligands has now permitted the elucidation of the binding mode
of these substituted hydrazines. We propose that the N,N-
dimethylhydrazine ligand of 8 is bound through the substituted
nitrogen atom on the basis of the chemical shifts of the methyl
groups (-3.31 ppm) and by comparison with the spectrum of
ammonia vapor. The 1H NMR spectrum of 4 displays a singlet
at -5.77 ppm, arising from the ammonia ligand. We have been
unable to observe any coupling between the NH3 protons and
103Rh. The X-ray structure of 4 revealed a Rh-Naxial bond length
of 2.113(5) Å, comparable with the corresponding bond lengths
of 2 (see Table 2).
Treatment of 1 in dichloromethane with an aqueous solution
of N,N′-dimethylhydrazine dihydrochloride basified by addition
of NaOH afforded the 1:1 complex 6. Both the 13C and 1H NMR
spectra of this compound are complicated by the formation
of a chiral center at the bound nitrogen atom of the dimethyl-
hydrazine. This removes mirror symmetry from the porphyrin,
leaving only average C2 symmetry, assuming free rotation about
the Rh-Naxial bond. Splittings are observed in the hexyl and
â-methyl resonances but not the meso and aryl resonances.
Coupling is observed between the proton of the coordinated
nitrogen atom at -4.90 ppm and its methyl group at -3.27
3
ppm with J ) 6 Hz. The value of JHNCH in N,N′-dimethyl-
hydrazine has been reported as 6.1 Hz.24 The other methyl group
of the ligand appears as a singlet at -0.66 ppm while the NH
resonance at -4.09 ppm is broad, presumably because of proton
exchange. Passage of this sample through silica gel and
recrystallization from a chloroform/methanol mixture afforded
the 2:1 complex 5. Although this could exist as a mixture of
(25) Hursthouse, M. B.; Newton, J.; Page, R. P.; Villax, I. Polyhedron 1988,
7, 2087.
(26) Yunda, N. G.; Lagodzinskaya, G. V.; Manelis, G. B. Bull. Acad. Sci.
USSR, DiV. Chem. Sci. 1975, 24, 2330.
(27) Bagno, A.; Menna, E.; Mezzina, E.; Scorrano, G.; Spinelli, D. J. Phys.
Chem. A 1998, 102, 2888.
(28) Le Floc’h, C.; Henderson, R. A.; Hitchcock, P. B.; Hughes, D. L.;
Janas, Z.; Richards, R. L.; Sobota, P.; Szafert, S. J. Chem. Soc., Dalton
Trans. 1996, 2755.
(29) Ashworth, T. V.; Nolte, M. J.; Singleton, E. J. Organomet. Chem.
1977, 139, C73.
(30) Goedkin, V. L.; Peng, S.-M. J. Chem. Soc., Chem. Commun. 1975,
258.
(31) Ashworth, T. V.; Nolte, M. J.; Singleton, E. J. Chem. Soc., Dalton
Trans. 1978, 1040.
1
diastereomers, H NMR spectroscopy suggested that only one
was present or that interconversion was rapid on the NMR time
scale. A single meso resonance and doubled hexyl and â-methyl
resonances were observed, consistent with the presence of a
chiral center at the nitrogen atom of the bound ligand but with
rapid rotation about the Rh-Naxial bond. The methyl groups of
the ligand at -7.32 ppm are split into a doublet with 3JHNCH
)
6 Hz, and a corresponding splitting is observed in the NH
resonance at -9.40 ppm. In the solid-state structure (Figure 2),
the ligand is ordered, and the chirality of each of the nitrogen
atoms in a molecule is the same, but overall, the crystal is
(32) Davies, C. J.; Dodd, I. M.; Harding, M. M.; Heaton, B. T.; Jacob, C.;
Ratnam, J. J. Chem. Soc., Dalton Trans. 1994, 787.
(33) Sellman, D.; Waeber, M. Z. Naturforsch., B: Chem. Sci. 1986, 41,
877.
(24) Yunda, N. G.; Lagodzinskaya, G. V.; Fel’dman, E. B.; Manelis, G.
B. Bull. Acad. Sci. USSR, DiV. Chem. Sci. 1977, 26, 1181.

Coordination Chemistry Rh(III) Porphyrins
Inorganic Chemistry, Vol. 40, No. 13, 2001 3221
6. The situation for 10 is not so clear-cut, although the
observation of a doublet at -3.24 ppm with J ) 6 Hz, assigned
to the hydrazine methyl group, suggests that the hydrazine is
bound through the substituted nitrogen atom in the major species
in solution. However, a minor singlet at -0.79 ppm can be
tentatively assigned to the methyl group of the isomeric complex
in which the unsubstituted nitrogen is bound to the rhodium
center. In support of this assignment was the observation of a
cross-peak in the NOESY spectrum, acquired at 40 °C, between
the peaks at -0.79 and -3.24 ppm. At room temperature, this
cross-peak was extremely weak, consistent with an increasing
rate of exchange of the methylhydrazine between the two
binding modes as the temperature was increased. The NH
protons of the minor species cannot be located with confidence,
although the peak at -3.91 ppm assigned to the NHCH3
resonance of the major isomer appears to be overlapping with
another minor resonance.
Passage of samples of 8 and 10 through silica gel, eluted
with dichloromethane/hexane (1:1), converted them into 7 and
9, respectively. The solid-state structures of 7 and 9 were found
to resemble that of 5, except the ligands were disordered. As in
5, the porphyrins are canted to accommodate the methyl groups.
The angles between the best fit planes of 7 and 9 are 25.49(9)
and 25.94(3)°, respectively.
Me2S2 led to broadening of the porphyrin resonances and an
upfield shift of the meso resonance to 9.8 ppm. Evidence for a
bridged dimer was the observation of a broad peak at -5.6 ppm
assigned to the methyl groups of the bridging ligand. On addition
of >0.5 equiv of Me2S2, this peak progressively disappeared,
to be replaced by peaks at 0.1 and -2.7 ppm assigned to the
inequivalent methyl groups of a 1:1 complex in which a single
sulfur atom binds to the rhodium center. This was accompanied
by a sharpening and downfield shift of the meso resonance to
10.22 ppm. Likewise, a titration of 1 in CDCl3 with Me2Se2
afforded a bridged dimer with a meso resonance at 9.62 ppm
and ligand-methyl resonance at -5.21 ppm. The 1:1 complex
displayed a meso resonance at 10.21 ppm and methyl groups
at 0.58 and -2.30 ppm. In this case, peaks were sharper, and
the meso resonances were in slow exchange on the 400 MHz
1H NMR chemical shift time scale, indicating that the diselenide
ligand has a lower exchange rate than the disulfide ligand.
Additional support for these complexes was obtained from UV-
visible titrations of 1 with Me2S2 and Me2Se2 in dichloromethane
with methanol added as a competitive ligand. On addition of
the chalcogenide, the Soret band of 1 at 412 nm was replaced
by a red-shifted Soret band, observed at 422 nm in the case of
Me2S2 and 428 nm for Me2Se2. In the former instance, we have
been able to account for the observed spectral changes during
the course of the titration using a model consisting solely of 1,
Me2S2, and 1‚Me2S2 with a binding constant of log(K) ) 5.7.
The concentration of 2:1 complex is likely to be negligible at
the porphyrin concentration employed for the titration experi-
ment. However, the data for Me2Se2 cannot be satisfactorily
modeled without inclusion of the species 12‚Me2Se2 with a broad
Soret band centered at 426 nm. In this case, we calculate log-
(K) ) 6.6 for the binding of a single porphyrin to Me2Se2, and
log(K) ) 5.4 for the binding of a second porphyrin unit,
implying weakly anticooperative behavior.
Initial attempts to obtain crystals of 7 by diffusion of methanol
into a solution of 8 and excess N,N-dimethylhydrazine afforded
a mixture of crystals from which could be identified the
organometallic derivative 11 by X-ray diffraction and 1H NMR,
in comparison with an authentic sample.10 By integration of the
In summary, we have prepared complexes of Rh(III) por-
phyrins with bridging hydrazine and substituted hydrazine
ligands and characterized these in solution by 1H NMR
spectroscopy and in the solid state by X-ray diffraction. Addition
of further hydrazine to these species afforded 1:1 complexes.
1
meso resonances in the H NMR spectrum, 11 was estimated
to comprise 6% of the porphyrinic material in this sample, with
the remainder largely attributed to 7. Further experiments, in
which samples of 8 and excess N,N-dimethylhydrazine in CDCl3
were exposed to combinations of air and light, revealed that a
combination of both accelerates the formation of 11 and other
unidentified products. Similarly, others have reported the
formation of metal alkyls from decomposition of alkyl hydrazine
complexes.34-38 The IR spectrum of 7 showed a sharp but weak
peak at 3216 cm-1, whereas 9 gave a group of peaks at 3224
cm-1, which are attributed to NH stretches by analogy with 2.
As Me2S2 and Me2Se2 are also known to act as bridging
ligands,39-43 we predicted that they would form complexes with
1
On the basis of H NMR chemical shift evidence, we propose
that methylhydrazine and N,N-dimethylhydrazine preferentially
bind to the Rh center through the substituted nitrogen atom. A
methylated Rh(III) porphyrin was obtained as a decomposition
product of the reaction of N,N-dimethylhydrazine with Rh(III)
porphyrin in a process accelerated by oxygen and light. Me2Se2
and Me2S2 behaved analogously to N,N′-dimethylhydrazine and
formed bridging and nonbridging complexes with Rh(III)
porphyrin.
1
1 analogous to 5. An H NMR titration of 1 in CDCl3 with
Acknowledgment. We thank EPSRC and Avecia for finan-
cial support and Dr. N. Bampos for helpful discussions.
(34) Samsel, E. G.; Kochi, J. K. Inorg. Chem. 1986, 25, 2450.
(35) Goedken, V. L.; Peng, S.-M.; Park, Y. J. Am. Chem. Soc. 1974, 96,
284.
(36) Dey, K.; De, R. L. J. Inorg. Nucl. Chem. 1977, 39, 153.
(37) Kunze, K. L.; Ortiz de Montellano, P. R. J. Am. Chem. Soc. 1983,
105, 1380.
(38) Braunstein, P. J. Chem. Soc., Chem. Commun. 1973, 851.
(39) Boorman, P. M.; Merrit, C. L.; Nandana, W. A. S.; Richardson, J. F.
J. Chem. Soc., Dalton Trans. 1986, 1251.
Supporting Information Available: 1H NMR spectra of 1-10 and
titrations of 1 with Me2S2 and Me2Se2. Crystallographic data of 2, 4,
5, 7, and 9 in CIF format. Equations of least-squares planes and
deviations from them. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC0011314
(40) Bernal, I.; Atwood, J. L.; Calderazzo, F.; Vitali, D. Isr. J. Chem. 1977,
15, 153.
(41) Lewkebandara, T. S.; McKarns, P. J.; Haggerty, B. S.; Yap, G. P. A.;
Rheingold, A. L.; Winter, C. H. Polyhedron 1998, 17, 1.
(42) Abel, E. W.; Khan, A. R.; Kite, K.; Hursthouse, M. B.; Malik, K. M.
A.; Mazid, M. A. J. Organomet. Chem. 1982, 235, 121.
(43) Abel, E. W.; Khan, A. R.; Kite, K.; Orrell, K. G.; Sik, V.; Cameron,
T. S.; Cordes, R. J. Chem. Soc., Chem. Commun. 1979, 713.