Molecular structure of diphenylbis(9,10-phenanthrenesemiquinonate)tin(IV), an organometallic diradical complex

Article abstract of DOI:10.1039/a608391i

The title compound, formed in the reaction between hexaphenylditin and 9,10-phenanthrenequinone, is shown to be an organotin(IV) diradical; its X-ray structure and EPR spectra are reported.

Full text of DOI:10.1039/a608391i

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Molecular structure of diphenylbis(9,10-phenanthrenesemiquinonate)tin(iv), an
organometallic diradical complex
Andrei S. Batsanov,a Judith A. K. Howard,a Martyn A. Brown,b Bruce R. McGarveyb and Dennis G. Tuck*b
a Department of Chemistry, University of Durham, South Road, Durham, UK DH1 3LE
b Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4
The title compound, formed in the reaction between
hexaphenylditin and 9,10-phenanthrenequinone, is shown
to be an organotin(IV) diradical; its X-ray structure and EPR
spectra are reported.
values of sI, 20.01 for Me and 0.12 for Ph.10 However, in both
polymorphs of 2, D is only 0.04 Å, probably due to electron-
poor character of the tropilium ring itself. It is noteworthy that
the shorter Sn–O bonds are invariably in trans-positions to the
less polar (Sn–C) ones, while exactly the opposite is observed in
psq complexes of transition metals,11 in accordance with the
view12 that in Sn complexes, less electronegative ligands
exercise cis-influence, rather than trans (as for d elements).
The EPR spectra of the solution obtained finally in the
reaction of Sn2Ph6 and pq show the presence of three species.
The room temperature solution spectrum which shows hyper-
fine structure is predominantly that of the primary reaction
product identified as the Ph3Sn(psq) monoradical, but the
frozen solution spectrum showed, in addition to the S = 1/2
resonance (g = 2.07), both a fine structure and a resonance at
half-field, indicating the presence of diradical species. The fine
structure of the central resonance showed the presence of two
such species, with D = 63 and 104 3 1024 cm21 respectively.
Substituted ortho-quinones can oxidize main-group elements or
their low-oxidation state compounds, yielding semiquinone or
catecholate complexes, characterised chemically and crystallo-
graphically.1 The oxidation has been shown to proceed via
successive one-electron transfer reactions,2 involving semi-
quinone derivatives as important intermediates, conveniently
detectable by electron paramagnetic resonance (EPR) spectro-
scopy. Some more unusual products were isolated, e.g. an
oxygen-bridged tetrachlorocatecholate derivative [(Cl4C6O2)-
TePh]2O from the reaction between Ph2Te and Cl4C6O2.3
The present work is a part of our study of reactions of Sn2Ph6
with various o-quinones and of Ph2SnCl2 or Ph3SnCl with
sodium semiquinonates,4 and of the redistribution processes
which follow these reactions. The resulting systems comprise
SnPh4 and various radical and diradical species, identified by
their EPR spectra. In particular, the reaction between equimolar
amounts of Sn2Ph6 and 9,10-phenanthrenequinone (pq) in
refluxing dichloromethane (1 h) yielded a brown solid,
identified as Ph3Sn(psq) (psq = 9,10-phenanthrenesemiqui-
none). The residual solution (strongly EPR active) after about 5
days at room temperature deposited dark brown shiny crystals
suitable for an X-ray diffraction study,† which proved them to
be Ph2Sn(psq)2 1.‡ On the available evidence we believe that
the primary reaction is given by eqn. (1), and the subsequent
The lower D value is very close to that of trans-
2
·
Cl2(dbsq)SnSn(dbsq)Cl2 (dbsq
=
3,5-di-tert-butylortho-
semiquinonate anion)1a and is presumably from the analogous
Ph2(psq)SnSn(psq)Ph2 compound with a Sn–Sn bond. The
higher D value can be assigned to 1. It is of the same order as
those observed for Cd(dbsq)2L (L = py, tmen, bipy) and related
·
Sn2Ph6 + pq ? Ph3Sn(psq) + Ph3Sn
(1)
processes include ligand redistribution to give the diradical.
The tin atom in 1 has a distorted cis-octahedral coordination
(Fig. 1). The sensitive indicators of the oxidation state of the
chelating ligand are known2,5 to be the lengths of the C–O bonds
(av. 1.23, 1.29 and 1.35 Å for the o-benzoquinone, o-semiqui-
none and catecholate) and the intervening C–C bond (1.53, 1.44
and 1.40 Å, respectively). Thus, the corresponding C–O and
C–C distances in 1 [mean 1.291(6) and 1.44(1) Å] characterise
it unequivocally as a semiquinone complex of tin(iv). The Sn–C
distances in 1 (2.16 Å) are essentially equal and within the range
(2.09–2.19 Å) observed in other R2Sn(O–O)2 complexes, viz.
R = Me, O–O = tropolonate (2);6,7 R = Me, O–O = kojate
C(210)
C(209)
O(4)
O(3)
O(2)
C(110)
C(21)
Sn
O(1)
C(109)
C(11)
(6-hydroxymethyl-4H-pyran-4-on-3-olate) (3);7
R = Me,
O–O = maltolate (3-hydroxy-2-methyl-4H-pyran-4-oate) (4)8
and R = Ph, O–O = maltolate (5).8 On the other hand, Sn–O
bonds formed by each semiquinone ligand show considerable
non-equivalence (D) in length. Formally, such a ligand forms
one covalent and one dative bond, and their unequal contribu-
tion can explain this difference. As Haaland9 pointed out, a
dative bond can have half the enthalpy of the corresponding
covalent one and be 0.2 Å (or more) longer. Its length is also
very sensitive to inductive effects of other ligands, increasing
with their electron donating ability. Indeed, D in diphenyl
complexes (0.08 Å in 1, 0.16 Å in 4) is much smaller than in
dimethyl ones (0.34 Å in 3, 0.28 Å in 5) in accordance with the
Fig. 1 Molecular structure of Ph2Sn(psq)2 1, showing 50% probability
ellipsoids. Selected bond distances (Å) and angles (°): Sn–O(1) 2.127(5),
Sn–O(2) 2.210(5), Sn–O(3) 2.137(5), Sn–O(4) 2.214(5), Sn–C(11)
2.160(9), Sn–C(21) 2.157(7), O(1)–C(109) 1.298(8), O(2)–C(110)
1.284(9), O(3)–C(209) 1.296(10), O(4)–C(210) 1.287(9), C(109)–C(110)
1.446(10), C(209)–C(210) 1.430(12); O(1)–Sn–O(2) 75.8(2), O(3)–Sn–
O(4) 76.0(2), C(11)–Sn–O(4) 164.7(3), C(21)–Sn–O(2) 163.8(3).
Chem. Commun., 1997
699

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molecules,13 but slightly smaller; the difference may be due to
the larger size of psq compared with dbsq
References
2
·
2
·
.
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This research was supported in part by grants from the
National Sciences and Engineering Research Council of
Canada (to B. R. M. and D. G. T.) and EPSRC of the UK
(to A. S. B.).
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Footnotes
5 R. M. Buchanan and C. G. Pierpont, Coord. Chem. Rev., 1981, 38, 45;
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L. Que Jr., Inorg. Chem., 1983, 22, 50.
* E-mail: dgtuck@uwindsor.ca
† The diffraction experiment at T = 150 K on a Siemens three-circle
diffractometer with a CCD area detector (graphite-monochromated Mo-Ka
–
radiation, l = 0.71073 Å, w scan mode, 2q @ 52°); structure solution by
Patterson method, refinement against F2 of all data (SHELXTL software).
The structure contains large cavities with highly disordered solvent of
crystallisation, approximated by arbitrary C atoms at electron density peaks;
no chemically sensible model could be found. Crystal data (neglecting the
solvent): C40H26O4Sn, M = 689.3, monoclinic, space group C2/c (no. 15),
a = 31.962(1), b = 12.402(1), c = 20.838(1) Å, b = 120.20(1)°,
U = 7138.9(7) Å3, Z = 8, Dc = 1.28 g cm23, m = 7.5 cm21, crystal size
0.35 3 0.2 3 0.2 mm, 15612 reflections total, 6026 unique, 4224 observed,
Rint = 0.068, 459 variables, final R(F, obs. data) = 0.066, R(F2, all
data) = 0.188, goodness-of-fit 1.14, max. residual Dr = 0.84 e Å23
.
12 Yu. A. Buslaev, E. A. Kravchenko, M. Yu. Burtev and L. A. Aslanov,
Coord. Chem. Rev., 1989, 93, 185.
13 A. Ozarowski, B. R. McGarvey, C. Peppe and D. G. Tuck, J. Am. Chem.
Soc., 1991, 113, 3288.
Atomic coordinates, bond lengths and angles, and thermal parameters have
been deposited at the Cambridge Crystallographic Data Centre (CCDC).
See Information for Authors, Issue No. 1. Any request to the CCDC for this
material should quote the full literature citation and the reference number
182/399.
Received in Cambridge, UK, on 13th December 1996; Com.
6/08391I
‡ Elemental analysis. Calc. for C40H26O4Sn, C 69.7, H 3.8. Found C 69.8,
H 4.0%. Yield ca. 9%.
700
Chem. Commun., 1997