Synthesis and Characterization of Isostructural Metalloporphyrin Chalconitrosyl Complexes Ru(TTP)(NE)Cl (E = O, S) and a Remarkable Thionitrosyl/Nitrite → Nitrosyl/Thiazate Transformation

Full text of DOI:10.1021/ic9614576

1992
Inorg. Chem. 1997, 36, 1992-1993
Synthesis and Characterization of Isostructural Metalloporphyrin Chalconitrosyl Complexes
Ru(TTP)(NE)Cl (E ) O, S) and a Remarkable Thionitrosyl/Nitrite f Nitrosyl/Thiazate Transformation
D. Scott Bohle,*,† Chen-Hsiung Hung,† Annie K. Powell,‡ Bryan D. Smith,† and Sigrid Wocadlo‡
Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071-3838, and School of Chemical Sciences,
University of East Anglia, Norwich NR4 7TJ, England
ReceiVed December 4, 1996
Although our understanding of the bonding in transition metal
chalcocarbonyls, LnMCtE (E ) O, S, Se, Te), is well grounded
in both experiment1 and theory,2 our knowledge of the bonding
in the related family of chalconitrosyls, LnMNtE, is much more
limited. For example, although numerous nitrosyl complexes
have been characterized, and frequently reviewed,3 the number
of isostructural LnMNtE complexes with E ) O and S remains
small, and there are no reported examples of stable isolable
complexes with either a bent thionitrosyl or linear selenonitrosyl
or telluronitrosyl ligand.4 A thorough analysis of the bonding
in CpCr(CO)2(NE) with Fenske-Hall calculations and vacuum
UV photoelectron spectroscopy5 indicates that for this metal
fragment the stronger σ-donation of the thionitrosyl is comple-
mented by stronger π interactions with both the filled high-
energy π(NS) orbital and the empty π*(NS). The net result is
that the thionitrosyl removes more electron density than nitric
oxide from the metal in the CpCr(CO)2 fragment. Similar
conclusions have been reached with CNDO/2 level calculations
for [LX4M(NE)] (M ) Ru, Os; E ) O, S; X ) Cl-, NR2-; L
) Cl-, OH2).6,7 However, recent electrochemical and structural
results for [Tc(phen)2X(NE)]n+ (phen ) 1,10-phenanthroline;
X ) Cl, E ) S, n ) 1; X ) NH3, E ) O, n ) 2) complexes
suggest that for this system there is stronger π-back-bonding
to the nitrosyl ligand,8 and there are similar trends for OsCl3-
(NE)(PPh3)2.9 These results suggest that when contrasting the
relative interactions of nitrosyl and thionitrosyl ligands with
transition metal centers, the fine balance of π-acceptance and
donation needs to be carefully considered. In this communica-
tion we describe the following: (1) the synthesis and charac-
terization by far-IR, UV-vis spectroscopy, differential scanning
calorimetry, and cyclic voltammetry of a new isostructural pair
of ruthenium porphyrin complexes Ru(TTP)(NE)Cl (E ) O,
S); (2) the remarkable transformation of a thionitrosyl/nitrite
complex to a nitrosyl/thiazate complex; (3) the crystal structures
of two of these derivatives. Together these results suggest that
for complexes with strong axially symmetric high-field donor
ligands, such as porphyrinato dianions, the nitrosyl ligand is
the better π-acceptor.
Scheme 1. Synthesis and Reactions of Ru(TTP)(NE)Cla
a Conditions: (i) CH2Cl2, 25 °C, 25 min; (ii) CH2Cl2, 1 h, 25 °C;
(iii) CH2Cl2, 25 °C, 30 min; (iv) CH2Cl2, 25 °C, 2 min.
monoxide and incorporation of both thionitrosyl and chloride
to give 1, Scheme 1, in 85% yield.10 An ORTEP view for the
structure of 1 as determined by X-ray diffraction is shown in
Figure 1.11 Important metrical parameters for this complex
include a significantly shorter nitrogen-sulfur bond length than
is found in most thionitrosyl complexes12 and a typically short
ruthenium-chloride bond length13 as is frequently found for
chloride ligands bound trans to nitric oxide. These data suggest
diminished Ru-NS interaction with relatively weak Ru(d)-
NS(π*) back-bonding. In addition, the porphyrin exhibits a very
slight S4-ruffling with the ruthenium displaced 0.101 Å toward
the thionitrosyl ligand.
The spectroscopic results for Ru(TTP)(NE)Cl in Table 1 allow
for a comparison of the bonding of a thionitrosyl versus a
nitrosyl group in an isosteric and isoelectronic environment. In
(10) All new compounds give satisfactory elemental analysis for C, H, and
N. Additional characteristic data for 1-3 are as follows. 1H NMR (δ
in ppm and coupling constants in Hz): 1 (in CDCl3), 8.92 (s, 8H,
Hâ), 8.10 (d, 3JHH ) 6.8, 4H, Hm), 8.05 (d, 3JHH ) 6.8, 4H, Hm′), 7.48
3
(t, JHH ) 7.7, 8H, Ho, Ho′), 2.63 (s, 12H, p-CH3); 2 (in C6D6), 9.16
3
3
(s, 8H, Hâ), 8.11 (d, JHH ) 7.1, 4H, Hm), 7.91 (d, JHH ) 7.7, 4H,
H
m′), 7.16 (Ho, Ho′ obscured by solvent), 2.39 (s, 12H, p-CH3); 3 (in
CDCl3), 8.90 (s, 8H, Hâ), 8.07 (d, 3JHH ) 7.7, 4H, Hm), 8.00 (d, 3JHH
) 8.6, 4H, Hm′), 7.48 (t, 3JHH ) 9.0, 8H, Ho, Ho′), 2.62 (s, 12H, p-CH3).
15N NMR (CDCl3, δ in ppm referenced to nitric acid): 1, 111.95 (s,
NS).
When Ru(TTP)(CO)(HOMe) is treated with trithiazyl trichlo-
ride at room temperature, there is rapid displacement of carbon
† University of Wyoming.
(11) Crystal data for 1: Ru(TTP)(NS)Cl, C48H36ClN5RuS, M ) 851.43,
monoclinic, space group P21/n, a ) 11.309(2) Å, b ) 27.633(6) Å, c
) 19.404(4) Å, â ) 92.56(3)°, V ) 6058(2) Å3, Z ) 6, Dc ) 1.400
Mg m-3, λ ) 0.710 73 Å, µ ) 0.547 mm-1, F(000) ) 2616, T ) 293
K. Data were collected on a Siemens P4 diffractometer for 2 < θ <
24°. The structure was solved by direct and Fourier methods and
refined by least squares against F2 to R1 ) 0.0509 (wR2 ) 0.1002)
and Sgoof ) 1.123 for 9476 unique intensity data with I > 2σ(I). There
are two independent molecules in the unit cell with a nondisordered
molecule lying on a general position, shown in Figure 1, and the second
disordered molecule lying on an inversion center. For molecule B axial
ligand NS/Cl disorder prevents meaningful interpretation of the metric
parameters for these ligands, but the final least-squares refinement of
this fragment was unconstrained and included half-occupancies of
nitrogen, sulfur, and chlorine on both sides of the porphyrin.
(12) Typical range of MN-S bond lengths is 1.49(2)-1.592(11) Å.
(13) For example the average Ru-Cl bond length in octahedral complexes
of 102 structures is 2.409(40) Å.14
‡ University of East Anglia.
(1) Clark, G. R.; Marsden, K.; Rickard, C. E. F.; Roper, W. R. Wright,
L. J. J. Organomet. Chem. 1988, 338, 393.
(2) Lichtenberger, D. L.; Fenske, R. F. Inorg. Chem. 1976, 15, 2015.
(3) Richter-Addo, G. B.; Legzdins, P. Chem. ReV. 1988, 88, 991. Richter-
Addo, G. B.; Legzdins, P. Metal Nitrosyls; Oxford University Press:
Oxford, U.K., 1992.
(4) For possible intermediary bent thionitrosyl and selenonitrosyl ligands
see: Demant, U.; Willing, W.; Mu¨ller, U.; Dehnicke, K. Z. Anorg.
Allg. Chem. 1986, 532, 175. Vogler, S.; Massa, W.; Dehnicke, K. Z.
Naturforsch., B 1991, 46, 1625.
(5) Lichtenberger, D. L.; Hubbard, J. L. Inorg. Chem. 1985, 24, 3835.
(6) Pandey, K. K.; Sharma, R. B.; Pandit, P. K. Inorg. Chim. Acta 1990,
169, 207. Pandey, K. K. J. Coord. Chem. 1991, 22, 307.
(7) Pandey, K. K.; Massoudipour, M.; Paleria, V. Ind. J. Chem. 1990,
29A, 260.
(8) Lu, J.; Clarke, M. J. J. Chem. Soc., Dalton Trans. 1992, 1243.
(9) Roesky, H. W.; Pandey, K. K.; Clegg, W.; Noltemeyer, M.; Sheldrick,
G. M. J. Chem. Soc., Dalton Trans. 1984, 719.
(14) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1.
S0020-1669(96)01457-7 CCC: $14.00 © 1997 American Chemical Society

Communications
Inorganic Chemistry, Vol. 36, No. 10, 1997 1993
Table 1. Summary of Characteristic Data for Ru(TTP)(NE)X Complexes
thermochemistry:e
electrochemistry, E1/2d (mV)
Tmin (°C),
compd
X
UV-vis (nm (log ꢀ))c
Soret Q-bands
1271 (1235), ν(NS); 298 m, ν(RuCl) 424 (5.44) 514 (4.26), 538 sh 658 (3.32) 940 (178), 1410(174) -655
a
E
S
no.
IR (cm-1
)
MLCT
oxidn
redn ∆H (kcal mol-1
)
Cl
O Cl
O NSO
1
2
3
384, -5.25
stable to 480
356, -25.28
1845 (1830), ν(NO);b 323 m, ν(RuCl) 414 (5.28) 562 (3.94), 600 sh
1021 (126), 1489 (120) -789
1829 (1793), ν(NO); 1255 (1232),
ν(NSO)a; 1075 (1073) w, ν(NSO)s;
515 (509) w, δ(NSO)s
416 (5.40) 572 (3.96), 606 sh
a Recorded in KBr pellets with 15N labeled bands given in parentheses. All bands are strong unless otherwise noted. b Solid-state splitting as
confirmed by solution IR. c Measured in dichloromethane. d Potentials listed in mV Vs Ag+/Ag in dichloromethane solution with 0.1 M [N(n-
butyl)4][PF6] as supporting electrolyte on a platinum button working electrode. Peak separation at a 100 mV s-1 scan speed in the cyclic voltammetric
experiment given in parentheses for reversible processes; all other potentials are for quasi-reversible processes. e As determined by differential
scanning calorimetry with a 10 °C/min scan rate under a flow of nitrogen.
Figure 2. Molecular structure of Ru(TTP)(NO)(NSO) with view as
Figure 1. Molecular structure of Ru(TTP)(NS)Cl for the nondisordered
molecule A. Hydrogen atoms are omitted for clarity. Important bond
lengths (Å) and angles (deg): Ru(1)-N(1-4) 2.046-2.050(4); Ru-
per Figure 1: Ru(1)-N(1,3,5,7) 2.052-2.064(5); Ru(1)-N(2) 1.737-
(5); N(2)-O(1) 1.164(6); Ru(1)-N(4) 2.022(5); N(4)-S(1) 1.467(5);
S(1)-O(2) 1.458(6); Ru(1)-N(4)-S(1) 140.8(3); N(4)-S(1)-O(2)
(1)-N(5) 1.768(4); N(5)-S(1) 1.489(5); Ru(1)-Cl(1) 2.356(2); Ru-
122.8(3); Ru(1)-N(2)-O(1) 170.2(5).
(1)-N(5)-S(1) 169.1(3); N(5)-Ru(1)-Cl(1) 174.3(1).
2,16 resulted in the formation of a nitrosyl thiazate complex,
the far-IR, the ν(Ru-Cl) is ca. 25 cm-1 lower in energy for
Ru(TTP)(NO)(NSO), 3. The identity of this complex has been
the thionitrosyl complex 1, and this is consistent with a stronger
confirmed by X-ray crystallography,18 Figure 2, by IR spec-
trans influence due to better σ-donation by the NS ligand. Both
troscopy, and an independent synthesis by treating 2 with
the UV-vis and electrochemical results in Table 1 suggest that
there is greater electron density on the Ru(TTP) moiety in 1;
the oxidation potentials are significantly lower and the separation
of the Soret and Q-bands is less for 1 than for 2. An unusual
relatively weak and broad band at 658 nm is observed in the
UV-vis spectrum of 1. On this basis, we have assigned this
band as resulting from an MLCT transition from the ruthenium
to the low-lying π*(NS) and note that we have not observed a
similar band for any of the series Ru(TTP)(NO)X.15,16
Most notably though, the reactions of 1 are indicative of a
markedly more labile thionitrosyl ligand than is the nitric oxide
ligand in 2. For example, when 1 is treated with trimethylphos-
phine at room temperature, there is rapid loss of both the NS
and Cl ligands; Ru(TTP)(PMe3)2 is formed quantitatively.
When 1 is treated with a stream of nitric oxide at room
temperature and atmospheric pressure, there is rapid substitution
of the thionitrosyl to give 2. In contrast, 15NO exchange in
Ru(TTP)(NO)Cl is slow and requires forcing conditions of
temperature and pressure,16 and prolonged exposure of 2 to
excess tertiary phosphines results in little appreciable loss of
nitric oxide.
The best comparison of the relative bonding of NO versus
NS would be their presence mutually trans in a single complex
with identical steric effects. However, a mutually trans
arrangement of two nitrosyl ligands is very rare, with Os(OEP)-
(NO)2 being the only reported stable example;17 a similar
complex with trans NO/NS ligands has not been described. In
an attempt to prepare such a complex, 1 was treated with silver
nitrite, which instead of returning the anticipated methathesis
product, Ru(TTP)(NS)(ONO), as is known for its reaction with
potassium thiazate, Scheme 1.19 Although a similar thionitrosyl
f thiazate transformation has been observed for the oxygenation
of IrCl2(NS)(PPh3)2,20 the transformation of the most likely
intermediate, Ru(TTP)(NS)(NO2) to 3 represents a remarkable
case of an oxo transfer reaction to give a thiazate/nitrosyl
complex and illustrates the propensity for the formation of
ruthenium nitrosyl complexes.21 We are currently using
Fenske-Hall level theory to dissect the relative Ru-NE bonding
interactions and will describe these results in the future.
Acknowledgment. We gratefully acknowledge support from
the DOE (Grant DE-FCO2-91ER), the National Institutes of
Health, (Grant GM-RO1-53828), the American Heart Associa-
tion, the Camille and Henry Dreyfus Foundation for a teacher
scholar award (D.S.B.), the BBSRC, and the Wellcome Trust
(U.K.) for their generous support of this research. We also thank
Professor Suzanne Harris of this department for numerous
valuable discussions.
Supporting Information Available: Listings of crystallographic
and structural data and ORTEP diagrams for 1 and 3 (23 pages).
Ordering information is given on any current masthead page.
IC9614576
(18) Crystal data for 3: Ru(TTP)(NO)(NSO), C48H36N6O2RuS‚2C6H6, M
) 1018.17, monoclinic, space group C2/c, a ) 40.918(16) Å, b )
9.012(4) Å, c ) 24.965(11) Å, â ) 96.666(4)°, V ) 9144(7) Å3, Z )
8, Dc ) 1.479 Mg m-3, λ ) 0.710 69 Å, µ ) 0.428 mm-1, F(000) )
3472, T ) 293 K. Data were collected on a Molecular Structure Corp.
rotating anode diffractometer for 1.64 < θ < 23°. The structure was
solved by direct and Fourier methods and refined by least squares
against F2 to R1 ) 0.0450 (wR2 ) 0.1155) and Sgoof ) 1.029 for
6352 unique intensity data with I > 2σ(I). In the latter stages of
refinement two benzene solvate molecules were located, one disordered
and the other not.
(15) The UV and near-IR spectra for all reported complexes have been
measured between 200 and 1700 nm.
(16) Bohle, D. S.; Goodson, P. A.; Smith, B. D. Polyhedron 1996, 15,
3147.
(19) Armitage, D. A.; Brand, J. C. J. Chem. Soc., Chem. Commun. 1979,
1078.
(20) Pandey, K. K.; Agarwala, U. C. Indian J. Chem. 1981, 20, 906.
(21) Griffith, W. P. The Chemistry of the Rarer Platinum Metals; Wiley-
Interscience: New York, 1967; p 174.
(17) Buchler, J. W.; Smith, P. D. Chem. Ber. 1976, 109, 1465.