Stereochemical control in metalloporphyrin chemistry: Synthesis and characterization of cis- and trans-Sn(porphyrin)Ph2

Full text of DOI:10.1021/ja961007c

6082
J. Am. Chem. Soc. 1996, 118, 6082-6083
Stereochemical Control in Metalloporphyrin
Chemistry: Synthesis and Characterization of cis-
and trans-Sn(porphyrin)Ph2
Ph Ph
Sn
CH2Cl2
–2 LiCl
Li2(Por)(OEt)2 +
Sn
(1)
Cl
Cl
Denisha Y. Dawson, Joan C. Sangalang, and John Arnold*
(por = TPP, TTP, TBPP, OEP)11
Department of Chemistry, UniVersity of California
Berkeley, California 94720-1460
of approximately 70-80% after recrystallization.12 These
compounds are light sensitive and thermally stable and can be
stored in a dry box (wrapped in foil) for months without
ReceiVed March 27, 1996
1
decomposition. In solution, H and 13C NMR spectroscopy
In metalloporphyrin chemistry, cis versus trans coordination
geometries are generally assumed to be controlled by the nature
of the metal ion, with the trans (or axial) arrangement being
indicated the absence of mirror symmetry in the porphyrin plane,
suggesting cis geometries, and in the solid state, X-ray crystal-
lography confirmed this stereochemistry for the TBPP derivative
(Figure 1).
L
L
L
M
For comparison, the trans isomers were readily prepared from
M
= (porphyrin dianion)
13
the known trans-Sn(por)Cl2 and diphenylmagnesium (eq 2).
L
cis
trans
by far the most common by virtue of the fact that most transition
and main group elements fit comfortably in the N4 plane of the
porphyrin ligand. Large ions, such as those early in the transition
series (e.g. Zr, Hf, Nb, Ta), sit out of the plane of the ring,
thereby directing additional ligands to cis coordination sites.1
Here we report an unusual example of stereochemical control
in Sn(IV) porphyrin chemistry exerted not by the metal ion but
by the choice of synthetic route.
In spite of the fact that the covalent radius of Sn is rather
large, being roughly in between that of Ti and Zr, all reported
derivatives of general formula Sn(por)L2 (L ) e.g. F, Cl, OMe,
OH) show trans geometries.2,3 Tin porphyrin dialkyls were first
reported by Pommier4-6 but could not be isolated because of
their photoactivity and O2 sensitivity. Kadish recently prepared
the first porphyrin complexes containing a stable tin-carbon
bond by oxidative addition of MeI to Sn(II)(Por).7 There are,
however, many organometallic derivatives of most of the other
metalloid porphyrins, including germanium, silicon, and all of
the Group 13 metals. The fact that there are so few tin(IV)
porphyrin organometallic complexes is surprising, particularly
in view of the potential biological interest (e.g. antitumor
activity) of such compounds.7-9
Cl
THF
–MgCl2
(2)
Ph2Mg +
Sn
Cl
Sn
Due to their high symmetry, the compounds are readily
identified as the trans derivatives by NMR spectroscopy. The
trans geometry of Sn(TPP)Ph2 was further confirmed by X-ray
crystallography (see Figure 2).
For the cis derivatives, the ortho H’s of the coordinated phenyl
group appear as a doublet, with 119Sn satellites (2JSn-H ) ca.
95 Hz) at between 3.0 and 3.4 ppm. This chemical shift is
almost identical to that seen in the diaryl zirconium porphyrin
Zr(OEP)(C6H4But)2.10 This resonance occurs at 0.8 ppm in the
trans species, suggesting a closer proximity of these H’s to the
center of the anisotropic porphyrin ring.14 The lack of mirror
symmetry in the porphyrin ring in the cis-ligated tin porphyrin
complexes is shown by the nonequivalence of the ortho protons
of the meso aryl on the ring, observed at room temperature as
two broad resonances, in contrast to the sharp doublet in the
analogous trans-diphenyl tin porphyrins. In the related OEP
derivative, the same phenomenon renders the methylene protons
diastereotopic. Both sets of isomers show normal-type UV-
vis spectra.15
We recently described a low-temperature route for the
preparation of cis-Zr(por)Cl2 using Li2(por) salts in combination
with ZrCl4(THF)2.10 Reasoning that if the reaction conditions
were mild enough to suppress ligand exchange we might be
able to isolate the unknown cis-ligated species, we investigated
the reaction of Li2(por) (as DME or OEt2 solvates) with SnCl2-
Ph2 in dichloromethane, as shown in eq 1. For each porphyrin
studied, the purple, crystalline cis isomer was obtained in yields
X-ray quality crystals of Sn(TBPP)Ph2(C6H5Cl)3.5 were
obtained from a mixture of chlorobenzene and hexanes.16 The
structure shows the tin atom to be well out of the plane of the
(1) Brand, H.; Arnold, J. Coord. Chem. ReV. 1995, 140, 137.
(2) Smith, G.; Arnold, D. P.; Kennard, C. H. L.; Mak, T. C. W.
Polyhedron 1991, 10, 509.
(12) Selected characterization data for new compounds. cis-(TTP)-
SnPh2: 1H NMR (300 MHz, CDCl3) 2.71 (s, 12), 3.36 (d, 4), 6.00 (m,
4), 6.22 (t, 2), 7.19 (d, tol), 7.24 (d, tol), 7.45 (d, 8), 8.03 (d, 8), 8.89 (s, 8).
UV/vis (C6H6) 340, 442, 516, 552, 582, 632 nm. cis-(TBPP)SnPh2: 1H
NMR (300 MHz, CDCl3) 1.60 (s, 36), 2.52 (s, 3, tol), 3.41 (d, 4), 6.06
(m 4), 6.23 (t, 2), 7.20 (d, 2, tol), 7.24 (d, 2, tol), 7.72 (m, 8), 7.8-8.2 (br
m, 8), 9.01 (s, 8). UV/vis (CH2Cl2) 340, 440, 486, 546, 579, 631 nm.
trans-(TTP)SnPh2: 1H NMR (300 MHz, CDCl3) 0.84 (d, 4), 2.71 (s,
12), 5.06 (m, 4), 5.48 (t, 2), 7.19 (d, tol), 7.57 (d, 8), 8.03 (d, 8), 8.11 (d,
8), 9.06 (s, 8). UV/vis (C6H6) 356, 450, 600, 646 nm. trans-(TPP)SnPh2:
1H NMR (300 MHz, CDCl3) 0.85 (d, 4), 5.03 (m, 4), 5.29 (s, 2, CH2Cl2),
5.50 (t, 2), 7.79 (m, 12), 8.22 (d, 8), 8.99 (s, 8). UV/vis (C6H6): 350, 448,
602, 646 nm. trans-(TTP)Sn(Ph)Cl: 1H NMR (300 MHz, CDCl3) 1.42
(d, 2), 2.73 (s, 12), 5.30 (m, 2), 5.73 (t, 1), 7.60 (m, 8), 8.09 (dd, 4), 8.2 6
(dd, 4), 9.13 (s, 8). UV/vis (C6H6) 354, 420, 442, 570, 622 nm. Full details
are provided as supporting information.
(3) Arnold, D. P.; Tiekink, E. R. T. Polyhedron 1995, 14, 1785.
(4) Cloutour, C.; Lafargue, D.; Richards, J. A.; Pommier, J.-C. J.
Organomet. Chem. 1977, 137, 157.
(5) Cloutour, C.; Lafargue, D.; Pommier, J.-C. J. Organomet. Chem.
1978, 161, 327.
(6) Cloutour, C.; Lafargue, D.; Pommier, J.-C. J. Organomet. Chem.
1980, 190, 35.
(7) Kadish, K. M.; Dubois, D.; Koeller, S.; Barbe, J.-M.; Guilard, R.
Inorg. Chem. 1992, 31, 3292.
(8) Drummond, G. S.; Galbraith, R. A.; Sardana, M. K.; Kappas, A. Arch.
Biochem. Biophys. 1987, 255, 64.
(9) Miyamoto, T. K.; Sugita, N.; Matsumoto, Y.; Saski, Y.; Konno, M.
Chem. Lett. 1983, 1695.
(10) Brand, H.; Arnold, J. Organometallics 1993, 12, 3655.
(11) Abbreviations: TPP is the dianion of meso-tetraphenylporphyrin;
TTP is the dianion of meso-tetra-p-tolylporphyrin; TBPP is the dianion of
meso-tetra(p-tert-butylphenyl)porphyrin; OEP is the dianion of 2,3,7,8,
12,13,17,18-octaethylporphyrin.
(13) Rothemund, P.; Menotti, A. R. J. Am. Chem. Soc. 1948, 70, 1808.
(14) Jenson, T. R.; Katz, J. J. In The Porphyrins; Dolphin, D., Ed.;
Academic: New York, 1978; Vol. 4, Chapter 5.
(15) Gouterman, M. In The Porphyrins; Dolphin, D., Ed.; Academic:
New York, 1978; Vol. 3, p 1.
S0002-7863(96)01007-4 CCC: $12.00 © 1996 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 118, No. 25, 1996 6083
a methylene chloride solution of the compound.17 The core of
the porphyrin macrocycle is slightly expanded, with the Sn-N
bonds being somewhat longer than in previously reported tin(IV)
porphyrin derivatives.
Exposure of either isomer to light in CHCl3 results in
formation of trans-Sn(Por)Ph(Cl) (eq 3). This reaction is clean
Cl
CHCl3 + hν
CHCl3 + hν
Sn
Sn
(3)
Sn
Figure 1. Shown is an ORTEP view of (TBPP)SnPh2, with ellipsoids
drawn at 50% probability and the hydrogens and tert-butyl groups
omitted for clarity. Sn-N bond distances: 2.367(6), 2.171(5), 2.341(6),
and 2.183(6) Å. Sn-C bond distances: 2.210(7) and 2.193(7)Å.
C-Sn-C angle: 89.7(3)°.
1
for the trans derivative; however, for the cis the H NMR
spectrum indicates the formation of additional products in which
the porphyrin ring symmetry is disrupted. Decomposition
products of this type are also observed in the light sensitive
dialkyl zirconium and trialkyl tantalum porphyrins, but we have
been unable to isolate or characterize any of these species.18
Facile cleavage of one M-R bond is common in Group 14
metalloporphyrins,4,6,19-21 and analogous chemistry of diphenyl
germanium porphyrin has been reported.20,21
In summary, using a new low-temperature synthetic route,
we have been able to prepare novel cis-Sn(Por)Ph2 isomers, in
which the resulting stereochemistry is controlled not by the
nature of the central metal ion, but by choice of synthetic
method. This is an unusual system in that both cis and trans
metalloporphyrin geometries are accessible and stable.
Acknowledgment. We thank the donors of the Petroleum Research
Fund administered by the American Chemical Society for partial
funding, the Sloan Foundation for the award of a fellowship to J.A.,
and the National Physical Sciences Consortium for a fellowship to
D.Y.D.
Figure 2. Shown is an ORTEP view (TPP)SnPh2‚(CH2Cl2) (molecule
1) with ellipsoids drawn at 50% probability and hydrogens omitted for
clarity. Sn-N bond distance (av): 2.134(4) Å. Sn-C bond distances:
2.196(4) and 2.212(4) Å.
Supporting Information Available: Experimental details and
characterization data for new compounds and details of structure
determinations, including tables of crystal and data collection param-
eters, anisotropic thermal parameters, positional parameters, and ORTEP
representations (22 pages). See any current masthead page for ordering
and Internet access instructions.
porphyrin (1.11 Å out of the mean plane of the porphyrin), with
a phenyl-tin-phenyl angle of 89.7°. The porphyrin ring is
highly distorted (both ruffled and domed), and the Sn-N bond
distances show two short and two long interactions, perhaps
due to steric repulsion between the phenyl rings and the pyrrole
rings closest to them.
The typical, in-plane, octahedral coordination geometry of
the trans derivatives was confirmed by the crystal structure of
trans-Sn(TPP)Ph2(CH2Cl2), obtained from diffusion of ether into
JA961007C
(17) Crystal data for (TPP)SnPh2(CH2Cl2): C57H40N4Cl2Sn, mw )
970.57, space group P1h (No. 2) with a ) 10.0503(3) Å, b ) 12.5071(4) Å,
c ) 18.6408(7) Å, R ) 75.239(1)°, )85.026(1)°, ) 81.483(1) °, V )
2237.9(1) Å3, dcalc ) 1.440 g cm-3, and Z ) 2. Data were collected on a
Siemens SMART diffractometer at -105 °C with Mo KR ( ) 0.71069
Å). A 2 range from 3-46.5° gave 6204 unique reflections. The structure
was solved by direct methods and refined by least squares and Fourier
techniques using 588 variables against 5143 data for which I > 3 (I), to
give R ) 0.040, Rw ) 0.052, and GOF ) 2.51.
(16) Crystal data for (TBPP)SnPh2(PhCl)3.5: C97H100.5N4Cl3.5Sn, mw )
1565.16, space group P21/n (No. 14) with a ) 17.0864(4) Å, b ) 17.9988(4)
Å, c ) 25.6002(4) Å, ) 93.599(1)°, V ) 7857.4(2) Å3, dcalc ) 1.323 g
cm-3, and Z ) 4. Data were collected on a Siemens SMART diffractometer
at -130 °C with Mo KR ( ) 0.71069 Å). A 2 range from 3-46.5° gave
11 589 unique reflections. The structure was solved by direct methods and
refined by least squares and Fourier techniques using 870 variables against
7058 data for which I > 3 (I), to give R ) 0.064, Rw ) 0.071, and GOF
) 2.63.
(18) Dawson, D. Y.; Brand, H.; Arnold, J. J. Am. Chem. Soc. 1994, 116,
9797.
(19) Kadish, K. M.; Xu, Q. Y.; Barbe, J.-M.; Guilard, R. Inorg. Chem.
1988, 27, 1191.
(20) Kadish, K. M.; Xu, Q. Y.; Barbe, J.-M.; Anderson, J. E.; Wang, E.;
Guilard, R. J. Am. Chem. Soc. 1987, 109, 7705.
(21) Maiya, G. B.; Barbe, J.-M.; Kadish, K. M. Inorg. Chem. 1989, 28,
2524.