Solitaire and gemini metallocene porphyrazines

Article abstract of DOI:10.1021/ja003702x

We report the synthesis and physical characterization of a series of peripherally functionalized porphyrazines (pzs) of the forms H₂[pz(A;B₃)] and trans-H₂[pz(A₂;B₂)], where A is a dithiolene chelate of molybdocene or vanadocene and B is a solublizing group. The precursor pz's 8 and 9, of the form H₂[pz(A;B₃)], where A = (4-(butyloxycarbonyl)-S-benzyl)₂ and B = di-tert-butylphenyl (8) or di-n-propyl (9), have been prepared, deprotected, and peripherally metalated with molybdocene and vanadocene to form 1(Mo^IV) and 1(V^IV), prepared from 8, and 2(Mo^IV) from 9, respectively. Likewise, the protected trans-H₂[pz(A₂;B₂)], where A = (S-benzyl)₂ and B = 3,6-butyloxybenzene (12) or A = (S-benzyl)₂ and B = (tert-butylphenyl)2 (13), have been prepared and peripherally metalated with molybdocene and vanadocene to give the trans dinuclear complexes, 3(Mo^IV,mo^IV), 3(V^IV,V^IV) (from 12), and 4(V^IV,V^IV) (from 13). A crystal structure of the trans vanadocene pz 4(V^IV,V^IV) is presented; the distance between the two vanadium atoms is 14.5 A. The molybdocene-appended pz's are highly redox active and exhibit cyclic voltammograms that are more than just the sum of the metallocene and the parent pz's. Chemical oxidation with FcPF₆ gives the Mo^V species 1(Mo^V), 2(Mo^V), 3(Mo^V,Mo^IV), and 3(Mo^V,Mo^V). Their EPR spectra are indicative of extensive delocalization from the Mo^V into the dithiolato-pz. The EPR spectrum of the mononuclear paramagnetic vanadocene pz, 1(V^IV), shows an expected 8-line pattern for an S = 2 system with hyperfine coupling to a single ⁵¹V (I = 7/2) nucleus, but the dinuclear vanadocene pz's, 3(V^IV,V^IV) and 4(V^IVV^IV), exhibit a striking 15-line pattern of the same breadth from the S = 1 state formed by exchange coupling between the S = 2 vanadium centers of a dinuclear complex. Thus, the porphyrazine macrocycle is capable of mediating magnetic exchange interactions between metal ions bound to the periphery, separated by 14.5 A.

Full text of DOI:10.1021/ja003702x

J. Am. Chem. Soc. 2001, 123, 4741-4748
4741
Solitaire and Gemini Metallocene Porphyrazines
Sarah L. J. Michel,† David P. Goldberg,†,§ Charlotte Stern,† Anthony G. M. Barrett,*,‡ and
Brian M. Hoffman*,†
Contribution from the Departments of Chemistry, Northwestern UniVersity, EVanston, Illinois 60208, and
Imperial College of Science, Technology and Medicine, London, U.K. SW7 2AY
ReceiVed October 17, 2000
Abstract: We report the synthesis and physical characterization of a series of peripherally functionalized
porphyrazines (pzs) of the forms H2[pz(A;B3)] and trans-H2[pz(A2;B2)], where A is a dithiolene chelate of
molybdocene or vanadocene and B is a solublizing group. The precursor pz’s 8 and 9, of the form H2[pz-
(A;B3)], where A ) (4-(butyloxycarbonyl)-S-benzyl)2 and B ) di-tert-butylphenyl (8) or di-n-propyl (9), have
been prepared, deprotected, and peripherally metalated with molybdocene and vanadocene to form 1(MoIV)
and 1(VIV), prepared from 8, and 2(MoIV) from 9, respectively. Likewise, the protected trans-H2[pz(A2;B2)],
where A ) (S-benzyl)2 and B ) 3,6-butyloxybenzene (12) or A ) (S-benzyl)2 and B ) (tert-butylphenyl)2
(13), have been prepared and peripherally metalated with molybdocene and vanadocene to give the trans
dinuclear complexes, 3(MoIV,MoIV), 3(VIV,VIV) (from 12), and 4(VIV,VIV) (from 13). A crystal structure of
the trans vanadocene pz 4(VIV,VIV) is presented; the distance between the two vanadium atoms is 14.5 Å. The
molybdocene-appended pz’s are highly redox active and exhibit cyclic voltammograms that are more than just
the sum of the metallocene and the parent pz’s. Chemical oxidation with FcPF6 gives the MoV species 1(MoV),
2(MoV), 3(MoV,MoIV), and 3(MoV,MoV). Their EPR spectra are indicative of extensive delocalization from
the MoV into the dithiolato-pz. The EPR spectrum of the mononuclear paramagnetic vanadocene pz, 1(VIV),
shows an expected 8-line pattern for an S ) 2 system with hyperfine coupling to a single 51V (I ) 7/2) nucleus,
but the dinuclear vanadocene pz’s, 3(VIV,VIV) and 4(VIV,VIV), exhibit a striking 15-line pattern of the same
breadth from the S ) 1 state formed by exchange coupling between the S ) 2 vanadium centers of a dinuclear
complex. Thus, the porphyrazine macrocycle is capable of mediating magnetic exchange interactions between
metal ions bound to the periphery, separated by 14.5 Å.
Introduction
of the form H2[pz(A;B3)] and trans-H2[pz(A2;B2)], where the
A functionality is a dithiolene chelate used to bind redox-active
molybdocene and paramagnetic vanadocene units, and the B
functionality is designed to impart solubility in organic solvents
to the pz (Schemes 1 and 2). Macrocycles peripherally chelated
with molybdocene are highly redox active, and the oxidized
MoV forms exhibit EPR spectra indicative of extensive delo-
calization from the MoV into the dithiolato-pz. The H2[pz-
(A2;B2)], A ) S2VCp2 (Scheme 2, 3(VIV,VIV) and 4(VIV,VIV))
Porphyrazines (pzs), or tetraazaporphyrins, are porphyrin
variants in which the meso positions have nitrogens, not C-H.1
Not only does this difference give pz’s physiochemical proper-
ties intrinsically different from those of the porphyrins, but the
pz synthetic route also allows for the ready preparation of
macrocycles which have heteroatoms directly fused at the
â-position of the pyrroles.2 As part of an effort to prepare
heteroatom-functionalized pz’s, we have developed procedures
for the cocyclization of two different dinitriles to generate
porphyrazines of the form M[pz(An;B4-n)], n ) 1, 2, 4, where
A is a dithiolene moiety and B is a solubilizing group,3-6 and
have used them to bind metal ion “caps” to the periphery of
the pz.3-5,7
Recently, we reported the covalent attachment of a single
molybdocene to a dithiolene binding site on the pz periphery7
and discovered that this complex exhibited physical and
electrochemical properties that were more than just the sum of
the properties of the porphyrazine and molybdocene dithiolene
fragments. Here, we report the synthesis and physical charac-
terization of a series of metallocene-substituted porphyrazines
† Northwestern University.
‡ Imperial College of Science, Technology and Medicine.
§ Current address: Department of Chemistry, The Johns Hopkins
University, Baltimore, MD 21218.
(1) Linstead, R. P.; Whalley, M. J. Chem. Soc. (London) 1952, 4839-
4844.
(2) Michel, S. L. J.; Baum, S.; Barrett, A. G. M.; Hoffman, B. M. In
Progress in Inorganic Chemistry; Wiley: New York, 2001.
10.1021/ja003702x CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/25/2001

4742 J. Am. Chem. Soc., Vol. 123, No. 20, 2001
Michel et al.
Scheme 1. Preparation and Peripheral Metalation of Solitaire Porphyrazinesa
a Conditions: [i] (a) Mg(OBu)2, BuOH, reflux; (b) TFA, NH4OH. [ii] (a) Na, NH3(l), THF, -78 °C; (b) Cp2MCl2, M ) Mo, V. [iii] FcPF6,
CH2Cl2.
Scheme 2. Preparation and Peripheral Metalation of Solitaire Porphyrazinesa
a Conditions: [i] (a) Mg(OBu)2, BuOH, 100 °C; (b) TFA, NH4OH. [ii] (a) Na, NH3(l), THF, -78 °C; (b) Cp2MCl2, M ) Mo, V. [iii] FcPF6,
CH2Cl2/acetone.
compounds exhibit triplet EPR spectra, demonstrating the
presence of exchange coupling between two peripheral vana-
dium atoms separated by over 14.5 Å.
or dipropylmaleonitrile (6)9 (Scheme 1) under Linstead mag-
nesium ion template conditions.1,10 The use of the two reactants,
bis(4-tert-butylphenyl)pyrroline (5) and dipropylmaleonitrile (6)
was part of an effort to optimize the B solubilizing groups.
Previously, we had prepared norphthalocyanine pz’s, where the
B groups are fused benzene rings, but these pz’s have limited
solubility in organic solvents, and this hindered the preparation
of metallocene-substituted pz’s. The use of 5 and 6 led to
porphyrazines 8 (16%) and 9 (12%), which are fully soluble in
common organic solvents (CHCl3, CH2Cl2, etc.). In addition,
the desired cyclization products, 8 and 9, can be easily separated
from the other isomers by routine chromatographic methods
(silica gel, CH2Cl2, or CH2Cl2/MeOH eluant) because the
differences in polarity between the A and B groups imparts a
Results
Synthesis of the “Solitaire” Porphyrazines 1 and 2. The
preparation of the soluble solitaire porphyrazines, 1 and 2, which
are of the form H2[pz(A;B3)], begins with the mixed condensa-
tion of 4-(butyloxycarbonyl)benzyl-protected dithiomaleonitrile,
(BCB)2mnt (7),4 with either bis(4-tert-butylphenyl)pyrroline (5)8
(3) Baumann, T. F.; Sibert, J. W.; Olmstead, M. M.; Barrett, A. G. M.;
Hoffman, B. M. J. Am. Chem. Soc. 1994, 116, 2639-2640.
(4) Baumann, T. F.; Nasir, M. S.; Sibert, J. W.; White, A. J. P.; Olmstead,
M. M.; Williams, D. J.; Barrett, A. G. M.; Hoffman, B. M. J. Am. Chem.
Soc. 1996, 118, 10479-10486.
(5) Sibert, J. W.; Baumann, T. F.; Williams, D. J.; White, A. J. P.; Barrett,
A. G. M.; Hoffman, B. M. J. Am. Chem. Soc. 1996, 118, 10487-10493.
(6) Forsyth, T. P.; Williams, D. B. G.; Montalban, A. G.; Stern, C. L.;
Barrett, A. G. M.; Hoffman, B. M. J. Org. Chem. 1998, 63, 331-336.
(7) Goldberg, D. P.; Michel, S. L. J.; White, A. J. P.; Williams, D. J.;
Barrett, A. G. M.; Hoffman, B. M. Inorg. Chem. 1998, 37, 2100-2101.
(8) Baumann, T. F.; Barrett, A. G. M.; Hoffman, B. M. Inorg. Chem.
1997, 36, 5661-5665.
(9) Lange, S. J.; Nie, H.; Stern, C. L.; Barrett, A. G. M.; Hoffman, B.
M. Inorg. Chem. 1998, 37, 6435-6443.
(10) Greene, T. W.; Wuts, P. G. M. ProtectiVe Groups in Organic
Synthesis, 2nd ed.; John Wiley and Sons: New York, 1991.

Solitaire and Gemini Metallocene Porphyrazines
J. Am. Chem. Soc., Vol. 123, No. 20, 2001 4743
large difference in the polarity moments of the various cycliza-
tion products (Scheme 1).
Using Schlenck techniques, the BCB protecting group was
removed from either pz 8 or 9 using sodium and ammonia,10
and the resultant dithiolato pz, H2[pz(S22-;B3)], where B )
(4-tert-butylphenyl)2 (8a) or (n-propyl)2 (9a), was reacted, in
situ, with Cp2MCl2 (M ) Mo, V) to form 1(MoIV), 1(VIV), and
2(MoIV) (Scheme 1). Porphyrazines 1(MoIV) and 2(MoIV) are
air-stable and freely soluble in most organic solvents and were
purified by column chromatography; 1(VIV) is air-sensitive, so
purification by column chromatography was carried out in an
inert atmosphere glovebox.
Synthesis of the Trans “Gemini” Porphyrazines 3 and 4.
The soluble trans-H2[pz(S-benzyl)2;B2], where B ) 3,6-butyl-
oxybenzene (12), was prepared by cyclizing bis(benzylthio)-
maleonitrile (11) with 4,7-bis(butyloxy)-1,3-diiminoisoindoline
(10) (Scheme 2). The yield of 12 is a function of the ratio of
the two cyclization partners and the relative reactivity of the
two components. Bis(benzylthio)maleonitrile (11) is much more
reactive than the diiminoisoindoline, 10, and the latter reacts
only with the cocyclization partner under the conditions
employed, to give mainly 12, which was purified by column
chromatography. The S-benzyl protecting groups of 12 were
removed with sodium and ammonia, and the resultant bis-
dithiolato-pz, was reacted in situ with Cp2MCl2 (M ) Mo, V)
to give 3(MoIV,MoIV) and 3(VIV,VIV). The trans-H2[pz(S-
benzyl)2;B2], where B ) (4-tert-butylphenyl)2 (13), is a minor
product of the cocyclization of bis(benzylthio)maleonitrile (11)
with bis(4-tert-butylphenyl)pyrroline (5), and its yield could not
be improved appreciably. Nonetheless, 13 was deprotected and
peripherally chelated with vanadocene to form 4(VIV,VIV) via
the same route. Perversely, crystals were obtained only for
4(VIV,VIV) and not for 3(MoIV,MoIV) or 3(VIV,VIV).
X-ray Structure of 4(VIV,VIV). Dark green, platelike crystals
of 4(VIV,VIV) were grown from an acetone/MeOH solution.
Crystallographic characterization revealed that 4(VIV,VIV) stacks
in a typical herringbone fashion. Figure 1 shows an ORTEP
diagram of the complex; the pertinent parameters for the data
collection and structure determination are given in Table 1. As
expected, the Cp2V units are coordinated to two thiolates of a
pyrrole, like the analogous vanadium benzenedithiolate.11 The
macrocycle lies on an inversion center, and the imposed
symmetry causes the two S2VCp2 units to have identical bond
distances and angles. The average V-S bond distance of 2.438
Å matches the values reported for similar vanadium dithiolenes11
and is 0.036 Å shorter than the Mo-S bond distances for the
corresponding molybdenum porphyrazine complex 1(MoIV)7
because of the smaller ionic radius of vanadium. The average
V-Cp (centroid) distance of 2.299 Å is also similar to the values
reported for other vanadocene structures.11 The C-S distances,
1.725 Å, are consistent with single bonds, as for 1(MoIV).7
Likewise, the Câ-Câ-S average bond angle of 125(2)° matches
that found for 1(MoIV)7 as well as the analogous angles
previously reported for Ni, Pt, and Pt cis-diphosphine “star”
porphyrazines.12-14
Figure 1. Two perspectives of the molecular structure of the
divanadium pz 4(VIV,VIV). For clarity, the heteroatoms have been
labeled, and the hydrogen atoms have been omitted.
Table 1. Crystal Data and Structure Refinement for 4(VIV,VIV)
empirical formula
formula weight
crystal system
V2C86H88N8O6S4
1559.81
monoclinic
space group
P21/c (No. 14)
green, rectangles
0.177 × 0.17 × 0.20 mm
a ) 13.4103 Å
b ) 12.8078 Å
c ) 24.4431 Å
â ) 97.4744°
V ) 4162.58789(4) Å3
-120 ( 1 °C
2
crystal color, habit
crystal dimensions
lattice parameters
temperature
Z value
residuals: R1; wR2
goodness-of-fit indicator
0.143; 0.239
1.75
center, one of the vanadium atoms lies above the pz ring plane
while the other lies below. Such a tilt of the metallocene unit
in relation to the dithiolene ligand plane has been observed in
other 17-electron, d1 dithiolate MCp2 complexes.15 Fourmigue´
et al. suggested that this tilted orientation allows for better
overlap between the 17-electron metal center and the filled p
orbitals on the sulfur, which tends to make the metal center
less electron deficient.16 In support of this idea, the five-
membered chelate ring for 1(MoIV),7 which is an 18-electron
d2 system, is essentially planar.
Electrochemistry. The cyclic voltammograms of 8 and 9
show two reversible ring reductions, at E1/2 ) -1045 (Pz/Pz-)
and -1376 mV (Pz-/Pz2-) for 8 (Figure 2) and at E1/2 ) -1235
(Pz/Pz-) and -1597 mV (Pz-/Pz2-) for 9, plus an irreversible
The dihedral angle between the VS2 plane and the plane of
the porphyrazine is approximately 30°; because of the inversion
ring oxidation at E1/2 ) 839 mV for 8 (Pz+/Pz) and at E1/2
)
(11) Stephan, D. W. Inorg. Chem. 1992, 31, 4128-4223.
(12) Vela´zquez, C. S.; Baumann, T. F.; Olmstead, M. M.; Hope, H.;
Barrett, A. G. M.; Hoffman, B. M. J. Am. Chem. Soc. 1993, 115, 9997-
10003.
(13) Vela´zquez, C. S.; Fox, G. A.; Broderick, W. E.; Andersen, K. A.;
Anderson, O. P.; Barrett, A. G. M.; Hoffman, B. M. J. Am. Chem. Soc.
1992, 114, 7416-7424.
(14) Velazquez, C. S.; Broderick, W. E.; Sabat, M.; Barrett, A. G. M.;
Hoffman, B. M. J. Am. Chem. Soc. 1990, 112, 7408-7410.
722 mV for 9 (Pz+/Pz) (ref vs Fc+/Fc) (Table 2). The cyclic
voltammogram for the trans pz, 12, shows one reversible ring
reduction, at E1/2 ) -1018 mV (Pz/Pz-), and a quasi-reversible
(15) Fourmigue´, M. Coord. Chem. ReV. 1998, 178-180, 823-864.
(16) Fourmigue´, M.; Lenoir, C.; Coulon, C.; Guyon, F.; Amaudrut, J.
Inorg. Chem. 1995, 34, 4979-4985.

4744 J. Am. Chem. Soc., Vol. 123, No. 20, 2001
Michel et al.
Table 2. Comparison of Half-Wave Potentials (mV vs Fc+/Fc)
compound
Pz2+/Pz
Pz+/Pz
MoVI/MoV
MoV/MOIV
Pz/Pz-
Pz-/Pz2-
8
9
839 (irrev)
722 (irrev)
1060 (67)
1060 (194)
355 (110)
-1045 (122)
-1235 (106)
-1290 (68)
-1310 (76)
-1018 (96)
-1503 (74)
-1230
-1376 (186)
-1597 (118)
-1530 (68)
-1770 (102)
-1344 (228)
1(MoIV)
522 (116)
460 (108)
-132 (76)
-158 (80)
2(MoIV)
12
772 (88)
3(MoIV,MoIV)
1:3 Pc
-38 (76)
-1590
-1190
octa-S-benzyl-Pz
-850
E1/2 ) +1060 mV, by the addition of the metallocene unit, yet
has been made reversible. (Note: Although other physical data
show significant electronic delocalization between the metal-
locene fragment and the pz ring, the positive shift in the ring
oxidation (Pz+/Pz couple) must include charge effects resulting
from the fact that the ring is oxidized from the MoVIpz species,
which is a dication.) Thus, the molybdocene unit can act as
both an electron-accepting and an electron-donating partner
toward the porphyrazine. These same changes are observed for
2(MoIV), whose specific oxidation potentials are given in Table
2.
The peripheral metalation of the trans pz, 12, also results in
dramatically altered electrochemistry. The first oxidation of
3(MoIV,MoIV) (Figure 2), at E1/2 ) -38 mV, is attributed to
MoV/IV, and its height, 4.5 µA, is twice that of the ring reduction
at E1/2 ) -1503 mV (Pz/Pz-), 2.2 µA (and the internal ferrocene
standard), indicating that the two MoCp2 units undergo the
MoIV/V process at essentially the same potential.18 The peaks
have equal widths, ∆E, indicating that within the precision of
the measurements the redox processes for the two metal centers
at 14.5 Å separation are essentially independent. Only one ring
reduction is observed, centered at E1/2 ) -1503 mV (Pz/Pz-).
This is 485 mV more negative than the first ring reduction
observed for the parent pz, 12. This negative shift in potential
of the ring reduction is consistent with the Cp2Mo group acting
as an electron donor to the porphyrazine π-system. This shift
is almost double the one observed for 1(MoIV), consistent with
double the number of molybdocene units (2) chelated. In
addition, nonreversible redox processes occur beyond +600 mV,
which limits the potential range of the scan. No ring oxidations
are observed within the potential scanned (Figure 2).
Electronic Spectra. Figure 3 compares the optical spectra
of 8, 1(MoIV), 1(MoV), and 1(VIV). Pz 8 has idealized C2V
symmetry and a split Q-band, λ ) 608 and 678 nm. The
presence of MoCp2 in 1(MoIV) rather than the two thioethers
of 8 causes the Q-band to coalesce to a single peak, λ ) 620,
a phenomenon that we previously reported for the peripheral
metalation of norphthalocyanine-appended pz’s with Ni, Pt, and
Pd cis-diphosphine units,4 and which may be due to an extension
of the pz π-system into the peripheral metal chelate ring
mediated by the bridging sulfur atoms.
Figure 2. Cyclic voltammograms for 8, 1(MoIV), 3(MoIV,MoIV), and
12 in CH2Cl2 with 0.1 M TBAPF6, referenced versus Fc+/Fc.
couple at E1/2 ) -1344 mV (Pz-/Pz2-), but also two fully
reversible ring oxidations, at E1/2 ) 335 (Pz+/Pz) and 772 mV
(Pz2+/Pz+) (Figure 2). Although the number of A and B groups
and the nature of the B groups differ for these three porphyra-
zines, these differences do not appear to affect the ring
reductions, which are observed at approximately the same
potentials. In contrast, 8 and 9, which are of the form H2[pz-
(A;B3)], show only a single, irreversible ring oxidation, while
the trans pz, 12, exhibits both a reversible and a quasi-reversible
ring oxidation; this suggests that the oxidation potentials are
more sensitive to changes at the periphery, although correlations
are not obvious.
The peripheral metalation of 8 with molybdocene to form
1(MoIV) produces a dramatically altered cyclic voltammogram
in which five reversible waves are observed, two reductions
The electrochemical data indicate that 1(MoIV) can be
oxidized to 1(MoV)PF6 (E1/2 ) -132) by addition of ferroce-
nium hexafluorophophate (E1/2 ) 0). This oxidation causes the
single Q-band of 1(MoIV) at λ ) 620 to split into two peaks,
Qy ) 622 nm and Qx ) 672 nm for 1(MoV). Similarly, for
2(MoIV) (E1/2 ) -158), the single Q-band at λ ) 637 nm splits
into two peaks at Qy ) 601 nm and Qx ) 627 nm upon oxidation
to 2(MoV). These oxidations are fully reversible: addition of
cobaltocene to 1(MoV) and 2(MoV) regenerates 1(MoIV) and
2(MoIV). The vanadocene pz, 1(VIV), which is isoelectronic with
the one-electron oxidized molybdocene pz, 1(MoV), also exhibits
and three oxidations (Figure 2). The first oxidation, at E1/2
)
-132 mV, is typical of a MoV/MoIV couple,15,17 but the
reversible MoVI/MoV couple, seen as the second oxidation at
E1/2 ) 522 mV, is a rarity for this coordination environment.15
The two ring reductions are shifted negative by as much as 250
mV to E1/2 ) -1290 and -1530 mV, consistent with the Cp2-
Mo group acting as an electron-donating unit which changes
the redox properties of the entire porphyrazine π-system. In
contrast, the Pz+/Pz couple is shifted positive by ∼300 mV, to
(17) Hsu, J. K.; Bonangelino, C. J.; Kaiwar, S. P.; Boggs, C. M.;
(18) Bard, A. J.; Faulkner, L. R. Electrochemical Methods; Wiley: New
Fettinger, J. C.; Pilato, R. S. Inorg. Chem. 1996, 35, 4743-4751.
York, 1980.

Solitaire and Gemini Metallocene Porphyrazines
J. Am. Chem. Soc., Vol. 123, No. 20, 2001 4745
Figure 5. X-band, 77 K, EPR spectrum of 1(MoV) in CHCl3/toluene
(50:50), mod. amp. ) 2.5 G. Inset: X-band, 298 K, EPR spectrum of
1(MoV), mod. amp. ) 5.0 G.
Table 3. Comparison of EPR Parameters for Molybdocene
Dithiolene Systems
compound
g
Aiso (MHz)
reference
21
[Cp2MoCl2]+
[Cp2Mo(O2CPh)2]+
[Cp2MoMeTDT]+ a
1(MOV)+
1.999
1.982
2.009
2.010
2.010
105
111
50
22
22
this work
this work
2(MOV)+
Figure 3. Absorption spectra of complexes 8, 1(MoIV), 1(MoV), and
1(VIV) (CH2Cl2).
a TDT ) [MeC6H4S2]2-
.
(E1/2 ) -38 mV) sharpen the absorbance peaks, although again
they appear to occur at essentially the same wavelengths as for
the trans pz, 12.
Electron Paramagnetic Resonance Spectroscopy.
(i) Molybdocene pz’s. The room-temperature and frozen-
solution X-band EPR spectra of 1(MoV) in CH2Cl2/i-PrOH are
shown in Figure 5. The room-temperature spectrum (inset)
shows a singlet centered at g ) 2.012 attributable to the
molybdenum species with spinless Mo (I ) 0, 74.5%). In
addition, the spectrum shows the four outer peaks of a lower
intensity sextet created by hyperfine coupling of the S ) 2 spin
5
to 95,97Mo (I ) /2, 25.5% total). 2(MoV) also was chemically
oxidized with FcPF6 and gave spectra identical to those
measured for 1(MoV). The g values for 1(MoV) and for 2(MoV)
(Table 3) are larger than those for [Cp2MoVCl2]+ and [Cp2MoV-
(O2CPh)2]+, which can be ascribed to the effect of delocalization
onto the sulfurs. The 77 K spectrum of 1(MoV) shows a typical
rhombic signal with g1 ) 2.026, g2 ) 2.019, g3 ) 1.993, with
an average value of g ) 2.013, which, within experimental
error, is equal to the giso from the room-temperature spectrum.
The measured 95,96Mo hyperfine coupling constant, A ) 22
MHz for 1(MoV) and for 2(MoV), is about one-fifth that for
the simple complexes, [Cp2MoVCl2]+ and [Cp2MoV(O2CPh)2]+,
and more striking, less than half the value for [Cp2Mo(tdt)]+ 21
(Table 3). The diminished coupling constants for 1(MoV) and
for 2(MoV) indicate that the dithiolatoporphyrazine delocalizes
spin from the molybdocene moiety even better than the
apparently similar [Cp2Mo(tdt)]+.
Figure 4. Absorption spectra of complexes 12 (top), 3(MoIV,MoIV),
3(MoV,MoIV), and 3(MoV,MoV) (CH2Cl2).
a split Q-band, with measured absorbances of λ ) 609 and 684
nm.
The two 3,6-butyloxybenzene groups of the trans porphyra-
zine, 12, enhance the Q-band red-shift and splitting: Qx ) 796
nm and Qy ) 656 nm, as reported previously (Figure 4).6,19,20
In addition, a small peak is observed at 720 nm, which we
tentatively assign as a Qx(“0 f 1”) transition, corresponding to
a vibrational frequency of 1326 cm-1 and likely attributable to
ring vibrational modes. Peripheral metalation with molybdocene
drastically alters the breadth and intensity of features in the
Q-band region, although the Qx and Qy features and their
vibrational partners still can be discerned. The one-electron and
two-electron oxidations to 3(MoV,MoIV) and 3(MoV,MoV)
3(MoIV,MoIV) can be titrated with ferrocenium hexafluoro-
phosphate, to form first 3(MoV,MoIV) and then 3(MoV,MoV).
The 77 K EPR spectra of frozen solutions of both the singly
and doubly oxidized species are given in Figure 6, which also
shows the 77 K EPR spectra of 1(MoV) for comparison. As
expected, 3(MoV,MoIV), which has one MoV ion, gives a
spectrum identical to that measured for 1(MoV). The spectrum
(19) Ehrlich, L. A.; Skrdla, P. J.; Jarrell, W.; Sibert, J. W.; Armstrong,
N. R.; Saavedra, S. S.; Barrett, A. G. M.; Hoffman, B. M. Inorg. Chem.
2000, 39, 3963-3969.
(20) Lee, S.; White, A. J. P.; Williams, D. J.; Barrett, A. G. M.; Hoffman,
B. M. J. Org. Chem., 2001, 66, 461-465.
(21) Lindsell, W. E. J. Chem. Soc., Dalton Trans. 1975, 23, 2548-2552.

4746 J. Am. Chem. Soc., Vol. 123, No. 20, 2001
Michel et al.
lines “interpolated” between them, as shown in the figure.23 This
pattern indicates that exchange coupling between the vanadium
centers24 creates an S ) 1 state. The n ) 2 interacting vanadium
7
nuclei (I ) /2) give 2nI + 1 ) 15 hyperfine lines, but the
breadth of the pattern is preserved because each electron spin
is hyperfine-coupled only to its own nucleus by Aiso. As a result
of this,24 the effective dinuclear isotropic hyperfine coupling
constant of 3(VIV,VIV) and 4(VIV,VIV), Adiiso ) 30 G (84 MHz),
is exactly half the hyperfine coupling found for the mononuclear
compound, 1(VIV) (Aiso ) 60 G ) 169 MHz). Spectra of frozen
solutions of 3(VIV,VIV) and 4(VIV,VIV) show a strong “powder”
signal that also displays splittings from n ) 2 equivalent
vanadium nuclei. As with the solution spectra, the hyperfine
couplings are half those seen for 1(VIV), and thus the 77 K signal
also is associated with the triplet state. The fluid solution data
do not show whether exchange is ferromagnetic, with the triplet
as ground state, or is antiferromagnetic with thermal population
of the triplet, while the observation of a strong signal from the
triplet state at 77 K is compatible with ferromagnetic coupling.
However, only helium temperature experiments would be
conclusive on this point. Regardless, these EPR results dem-
onstrate that the porphyrazine macrocycle is capable of mediat-
ing exchange interactions between metals bound to the periphery
of 4(VIV,VIV) at a V-V separation of 14.5 Å.
Figure 6. X-band, 77 K, EPR spectra of 3(MoV,MoIV), 3(MoV,MoV),
and 1(MoV) modulation amplitude ) 5.0 G.
Conclusion
We have prepared and characterized a series of novel soluble
molybdocene and vanadocene porphyrazines and obtained the
X-ray structure of the trans divanadium pz, 4(VIV, VIV). The
molybdocene pz’s are highly redox-actiVe, and the MoV states
show substantial delocalization by the pz ring. The electron spins
of the two vanadium atoms of 3(VIV,VIV) and of 4(VIV,VIV)
exhibit through-bond exchange coupling, though the vanadium
atoms are separated by a metal-metal distance of 14.5 Å. The
coupling will be far stronger when mediated by a metal ion
incorporated within the pz core, and thus these results suggest
that dithiolene-appended porphyrazines may be useful precursors
for the preparation of redox-switchable, magnetically coupled
supermolecular arrays.
Figure 7. X-band, 298 K, EPR spectra of (A) 1(VIV) and (B)
3(VIV,VIV) and 4(VIV,VIV). The dashed lines are included to facilitate
comparison between spectra A and B, which is hampered by the extreme
line width variations in B. Outer dashed lines indicate fields from MI
) -7/2 and +7/2 for 1(VIV); dashed lines b and b′ indicate the mI )
(1/2 lines. They are seen to correlate with two lines, mIt ) mI(1) +
mI(2) ) (1, for B. Dashed line a corresponds to no line in A but to
the mIt ) 0 line in B.
for the doubly oxidized species, 3(MoV,MoV), is much broader,
presumably due to dipole-dipole interactions between the two
MoV centers.
Materials and Methods
Procedures. All starting materials were purchased from Aldrich
Chemical and used as received, with the exception of the metallocene
dichlorides (MoCp2Cl2 and VCp2Cl2), which were purchased from Strem
Chemicals and used as received. THF was distilled from sodium/
benzophenone ketyl, acetone was distilled from CaSO4, and MeOH
was distilled from CaH2. All other solvents were used as purchased
without additional purification. Anhydrous NH3 (Linde Specialty Gases)
was ultra-high-purity grade. Silica gel used for chromatography was
Baxter silica gel 60 Å (230-400 mesh). Sodium metal was freshly cut
under hexanes prior to use.
Bis(4-tert-butylphenyl)pyrroline (5),8 2,3-dipropylmaleonitrile (6),9
[(4-((butyloxy)carbonyl)benzyl)thio]maleonitrile ((BCB)2mnt, 7),3,4 bis-
(benzylthio)maleonitrile (11),13 and 8 and 138 were prepared as
previously reported. Schlenk-line manipulations were performed on an
apparatus purchased from Chemglass with all PTFE valves and with
dry nitrogen (CaSO4).
(ii) Vanadocene pz’s. The room-temperature X-band EPR
spectrum for the solitaire vanadocene pz, 1(VIV) (Figure 7),
exhibits the expected 8-line pattern for an S ) 2 system with
hyperfine coupling to a single 51V (I ) 7/2) nucleus. The
hyperfine splitting constant of 60 G (169 MHz) matches values
reported for other vanadocene dithiolene compounds.15 The
peaks do not have equal intensity because they are differentially
broadened by motional effects; the high-molecular-weight pz
has a relatively slow tumbling rate in solution (large τc). In this
tumbling regime, the line widths (lw) follow the well-known
relation, lw ) A + BmI + CmI2, where mI represents the nuclear
spin subcomponent of the transitions.22
The room-temperature X-band EPR spectra for the dinuclear
pz’s, 3(VIV,VIV) and 4(VIV,VIV) (Figure 7), do not exhibit the
simple 8-line pattern for monomeric vanadium(IV) that is seen
for 1(VIV) and that is expected if the two vanadocene units of
a dinuclear complex are independent. Instead, 3(VIV,VIV) and
4(VIV,VIV) exhibit a striking 15-line pattern, which has the same
breadth as the 8-line pattern seen for 1(VIV), but with additional
1H and 13C NMR spectra were obtained using either a Gemini 300
MHz, Mercury 400 MHz, or Inova 500 MHz spectrometer. Electronic
absorption spectra were recorded using a Hewlett-Packard HP8452A
diode array spectrophotometer. Cyclic voltammetry experiments were
done at room temperature in methylene chloride with 0.1 M tetrabu-
(23) Toward the edge of the pattern, this is somewhat obscured by
differential broadening.
(24) Pilbrow, J. R. Transition Ion Electron Paramagnetic Resonance;
Clarendon Press: Oxford, 1990.
(22) Weil, J. A.; Bolton, J. R.; Wertz, J. E. Electron Paramagnetic
Resonance: Elementary Theory and Practical Applications; John Wiley
& Sons: New York, 1994.

Solitaire and Gemini Metallocene Porphyrazines
J. Am. Chem. Soc., Vol. 123, No. 20, 2001 4747
tylammonium hexafluorophosphate as the supporting electrolyte using
a Cypress Systems 2000 electroanalytical system. A platinum working
electrode, a Ag/AgCl reference electrode, and an Ag wire counter
electrode were used, with ferrocene added to the cell at the end of the
experiment as an internal reference, unless otherwise noted. All E1/2
values were calculated from (Epa + Epc)/2 at a scan rate of 110 mV s-1
and no correction for junction potentials. Elemental analyses were
preformed by Onieda Research Services (Whiteboro, NY). Fast atom
bombardment mass spectra (FAB-MS), atmospheric phase chemical
ionization mass spectra (APCI-MS), and electrospray mass spectra
(ES-MS) were recorded locally by Dr. Doris Hung and Dr. Fenghe
Qiu using a VG-70-250SE (FAB-MS) and a Micromass Quattro II
RCMS triple-quadrupole (APCI-MS) instrument. Electron paramagnetic
resonance (EPR) spectra were measured by using a modified Varian
E-4 X-band spectrometer, with the field calibrated using diphenylpi-
cryhydrazyl (dpph) as a standard.
Synthesis of H2[Pz(SBCB)2;B3], B ) (n-propyl)2 (9). Magnesium
metal (0.230 g, 9.46 mmol) and n-BuOH (90 mL) were heated to reflux
under N2. At reflux, a small chip of iodine was added to facilitate the
formation of magnesium butoxide. After 12 h at reflux, 4.00 g (25
mmol) of 2,3-dipropylmaleonitrile (6)9 and 1.84 g (3.5 mmol) of [(4-
((butyloxy)carbonyl)benzyl)thio]maleonitrile ((BCB)2mnt, 7) were added
to the butoxide mixture; the solution immediately turned a bright green
color which developed into a dark blue color over the course of the
reaction. After 24 h, the reaction was stopped and the BuOH was
removed under reduced pressure; the remaining dark blue residue was
dissolved in excess CF3COOH (∼50 mL).The solution was stirred for
15 min in the dark and then poured onto crushed ice and neutralized
with concentrated NH4OH. The dark blue solid was filtered and washed
copiously with MeOH until the washings were colorless. The solid was
filtered through a slurry of silica gel in chloroform. The filtrate was
then purified by column chromatography (100% CHCl3 eluant) (430
mg, 0.425 mmol, 12%): 1H NMR (300 MHz, CDCl3) δ 7.81 (d, J )
8 Hz, 4H), 7.42 (d, J ) 8 Hz, 4H), 5.28 (s, 4H), 4.20 (t, J ) 7 Hz,
4H), 3.93 (m, 8H), 3.78 (m, 4H), 2.28 (m, 12H), 1.63 (m, 4H), 1.28
(m, 4H), 1.24 (m, 18H), 0.88 (m, 6H); 13C NMR (125 MHz, CDCl3)
δ 13.9, 15.2, 19.4, 25.6, 26.1, 28.4, 29.9, 30.9, 40.0, 62.6, 129.3, 129.5,
130.0, 141.2, 142.2, 142.3, 143.8, 146.2, 147.6, 158.2, 162.5, 162.8;
UV-vis (CHCl3) λmax (log ꢀ) 346 (4.63), 596 (4.48), 634 (4.50); HRMS
(FAB-MS) m/z 1011.543 (M + H+), calcd for C58H75N8S2O4 1011.535
Anal. Calcd for C59H75N8Cl3O4S4 (9 + CHCl3): C, 62.67; H, 6.68;
N,9.91. Found: C, 63.28; H, 7.03; N, 10.16.
to isolate the product. The reaction residue containing 4b was dissolved
in deaerated acetone (40 mL). In a separate 100 mL Schlenck flask,
Cp2MoCl2 and Cs2CO3 were suspended in deaerated acetone (40 mL).
The pz2- was transferred dropwise, via cannula, to the Cp2MoCl2
suspension and stirred for 12 h. The solvent was removed, and the pz
was chromatographed on silica gel using CHCl3 as the eluant. The major
azure blue-green band was collected (0.60 g, 36% yield based on 9):
1H NMR (300 MHz, CDCl3) δ 5.64 (s, 10H), 3.88 (m, 12H), 2.30 (M,
12H), 1.22 (m, 18H); UV-vis (CHCl3) λmax 346, 576, 637; HRMS
(MALDI-TOF) m/z 856.298 (M+), calcd for C44H54N8S2Mo 856.297.
H2[Pz(S2MoCp2;B3)], B ) (tert-butylphenyl)2, 1(VIV). Macrocycle
8 (0.100 g, 0.065 mmol) was deprotected by the method described above
for the preparation of 1(MoIV). The dithiolate was not isolated, due its
air sensitivity. The reaction residue was dissolved in deaerated acetone
(20 mL). In a separate 50 mL Schlenck flask, Cp2VCl2 was suspended
in deaerated acetone (20 mL). The pz2- was transferred dropwise, via
cannula, to the Cp2VCl2 suspension and stirred for 12 h. The solvent
was removed under vacuum, and the crude pz was taken into the
glovebox and chromatographed on silica gel using toluene as the eluant.
The major blue-green band was collected (0.30 g, 30% yield based on
8): UV-vis (CHCl3) λmax 371, 459, 609, 684; FAB-MS m/z 1349 (M+),
calcd for C86H90N8S2V 1349; EPR (X-band, 9.132 GHz), G rt ) 2.014,
8-line pattern, Aiso ) 60 G (168 MHz).
H2[Pz(S2MoVCp2;B3)]+[PF6]-, B ) (tert-butylphenyl)2, 1(MoV).
Macrocycle 1(MoIV) (0.040 g, 0.029 mmol) was dissolved in ca. 10
mL of deaerated CH2Cl2. Ferrocenium hexafluorophosphate (FcPF6)
(0.020 g, 0.054 mmol) was dissolved in ca. 20 mL of deaerated CH2-
Cl2 and added, via a syringe, to the teal green pz solution, which
changed to a dark green color, which was used without further
purification: UV-vis (CH2Cl2) λmax 371, 481, 622, 672; APCI-MS
m/z 1397.7 (M + H+), calcd for C86H90N8S2Mo 1396.6; EPR (X-band,
9.132 GHz), 95,97Mo, I ) 5/2, 25.5%, G rt ) 2.010, 6-line pattern, Aiso
) 8 G (22 MHz), G
- g1 ) 2.024, g2 ) 2.018, g3 ) 1.998.
77 K
H2[Pz(S2MoVCp2;B3)]+[PF6]-, B ) (n-propyl)2, 2(MoV). Macro-
cycle 2(MoIV) (0.030 g, 0.035 mmol) was dissolved in ca. 10 mL of
deaerated CH2Cl2. Ferrocenium hexafluorophosphate (FcPF6) (0.026
g, 0.070 mmol) was dissolved in ca. 20 mL of deaerated CH2Cl2 and
added, via a syringe, to the teal green pz solution, which changed to a
dark green color, which was used without further purification: UV-
vis (CH2Cl2) λmax 352, 601, 627; EPR (X-band, 9.132 GHz), 95,97Mo,
5
I ) /2, 25.5%, G ) 2.009, 6-line pattern, Aiso ) 8 G (22 MHz),
rt
G
- g1 ) 2.026, g2 ) 2.019, g3 ) 1.993.
77 K
H2[Pz(S2MoCp2;B3)], B ) (tert-butylphenyl)2, 1(MoIV). Macrocycle
8 (0.200 g, 0.129 mmol) was put in a 50 mL three-neck round-bottomed
flask, equipped with a coldfinger. The pz was cooled to -78 °C in an
acetone/CO2 bath, and ca. 30 mL of liquid NH3 was added via the
coldfinger. Sodium metal (0.030 g, 1.30 mmol), freshly cut under
hexanes, was added followed by ca. 20 mL of THF to solubilize the
mixture. The solution immediately turned a red-orange color, which
progressed to a purple-cranberry color. After 1 h, the acetone/CO2 bath
was removed, and the solution was allowed to reflux through the
coldfinger for 30 min. NH4Cl (0.041 g, 0.774 mmol) was added to
quench the excess sodium and sodium amide. The NH3 and THF were
vented off under a stream of N2, yielding a dark green powder
containing the disodium salt of the porphyrazine and NaCl. The
dithiolate was not isolated, due its air sensitivity. The reaction residue
was dissolved in deaerated acetone (40 mL). In a separate 100 mL
Schlenck flask, Cp2MoCl2 and Cs2CO3 were suspended in deaerated
acetone (40 mL). The pz2- was transferred dropwise, via cannula, to
the Cp2MoCl2 suspension and stirred for 12 h. The solvent was removed,
and the pz was chromatographed on silica gel using CH2Cl2/hexane
(80:20) as the eluant. The major teal green band was collected (0.80 g,
44% yield based on 8): 1H NMR (300 MHz, CDCl3) δ 8.48 (m. 4H),
8.29 (m, 8H), 5.69 (s, 10H), 1.49 (s, 18H), 1.482 (s, 18H), 1.476 (s,
18H); UV-vis (CHCl3) λmax (log ꢀ) 368 (4.85), 462 (4.35), 622 (4.95),
672 (sh) (4.44); HRMS (FAB-MS) m/z 1396.29 (M+), calcd for C86H90-
MoN8S2 1396.58. Anal. Calcd for C86H90MoN8S2: C, 74.00; H, 6.50;
N, 8.03. Found C, 73.66; H, 6.10; N, 8.05.
4,7-Bis(butyloxy)-1,3-diiminoisoindoline (10). Commercially avail-
able 3,6-dibutoxy-1,2-benzene dicarbonitrile (9.0 g, 33.1 mmol) was
suspended in ethylene glycol (450 mL) in a 1 L three-necked round-
bottom flask. Freshly cut Na (0.145 g) was added, and NH3(g) was
bubbled through the solution for ca. 1 h, after which time the mixture
was heated to 150 °C under a positive pressure of N2 for 5 h. During
the course of the reaction, the solution turned from colorless to a yellow
color. The hot solution was then poured into ice-water (1 L), and the
precipitate which formed was filtered and recrystallized from MeOH
to yield 8 (9.17 g, 31.7 mmol, 96% yield): 1H NMR (300 MHz, CDCl3)
δ 0.97 (t, J ) 8 Hz, 6H), 1.49 (m, 4H), 1.82 (m, 4H), 4.06 (t, J ) 6
Hz, 4H), 6.91 (s, 2H), 8.1 (vbr, s, 3H); 13C NMR (100 MHz, CDCl3)
δ 14.2, 19.6, 31.5, 68.9, 77.0, 77.3, 77.6, 116.3, 120.8, 149.4, 167.7;
IR APCI-MS m/z 290.4 (M + H+), calcd for C16H23N3O2 289.2.
trans-H2[Pz(S-benzyl2)2;B2)], B ) 3,6-dibutoxybenzene (12).
Magnesium metal (0.110 g, 4.53 mmol) and n-BuOH (35 mL) were
heated to reflux under N2. At reflux, a small chip of iodine was added
to facilitate the formation of magnesium butoxide. After 12 h at reflux,
the temperature was lowered to 100 °C, 2.40 g (8.3 mmol) of 4,7-bis-
(butyloxy)-1,3-diiminoisoindoline (8) and 2.25 g (6.99 mmol) of bis-
(benzylthio)maleonitrile (9) were added to the butoxide mixture, and
the solution immediately turned a yellow-orange color which developed
into a green color over the course of the reaction. After 5 h, the reaction
was stopped, and the BuOH was removed under reduced pressure; the
remaining green residue was dissolved in excess CF3COOH (∼50
mL).The solution was stirred for 15 min, in the dark, and then poured
onto crushed ice and neutralized with concentrated NH4OH. The green
pz was extracted into CH2Cl2, dried over Na2SO4, and then purified by
column chromatography (80:20 CH2Cl2/hexane) (0.157 g, 0.131 mmol,
H2[Pz(S2MoCp2;B3)], B ) (n-propyl)2, 2(MoIV). Macrocycle 9
(0.200 g, 0.198 mmol) was deprotected by the method described above
for 8. Due to the air sensitivity of the dithiolate, no attempt was made

4748 J. Am. Chem. Soc., Vol. 123, No. 20, 2001
Michel et al.
8.3%): 1H NMR (300 MHz, CDCl3) δ 1.05 (t, J ) 7 Hz, 12H), 1.75
(m, 8H), 2.18 (m, 8H), 4.58 (t, J ) 7.04 Hz, 8H), 5.40 (s, 8H), 7.01
(m, 12H), 7.27 (m, 8H), 7.54 (s, 4H); 13C NMR (125 MHz, CD2Cl3) δ
12.4, 19.8, 32.2, 39.8, 72.8, 118.3, 128.7, 129.2, 129.3, 131.6, 138.1,
139.4, 139.5, 151.2. 151.5; UV-vis (CH2Cl2) λmax (log ꢀ) 342 (5.37),
434 (4.99), 656 (5.42), 720 (5.10), 796 (5.34); APCI-MS m/z 1191.5
(M + H+), calcd for C68H70N8O4S4 1190.4.
solution initially turned from a teal green color to a dark green color,
and then a dark green solid precipitated out. The solid was filtered and
redissolved in 60:40 CH2Cl2/acetone and was used without further
purification: UV-vis (CH2Cl2) λ 368, 418, 642, 708, 808; EPR (X-
band, 9.132 GHz), 95,97Mo, I ) 5/2, 25.5%, G 77 K - g1 ) 2.032, g2 )
2.013, g3 ) 1.997.
X-ray Structure Determination. Platelike crystals of 4(VIV,VIV)
were grown from acetone/MeOH in a nitrogen-filled NMR tube.
Immediately prior to the X-ray experiment, these crystals were
transferred to Paratone-N oil, and one crystal (0.17 × 0.17 × 0.20
mm) was mounted on a glass fiber. Data were collected on an Enraf
Nonius CAD4 diffractometer with graphite-monochromated Mo KR
radiation at a temperature of -120 ( 1 °C using the ω-2θ scan
technique to a maximum 2θ value of 46.9°. The structure was solved
by direct methods25 and expanded using Fourier techniques26 in the
space group P21/c (No. 14). Out of 6633 reflections collected, only
2143 were greater than 3σ, and considered “observed”. Owing to the
paucity of data, the vanadium and sulfur atoms were refined anisotro-
pically, while the rest were refined isotropically. Hydrogen atoms were
included in idealized positions, except those on the solvent molecules,
but not refined. The final cycle of full-matrix least squares refinement
(least-squares function minimized: ∑w(Fo2 - Fc2)2, where w ) 1/[σ2-
H2[Pz(S2MoCp2)2;B2)], B ) (3,6-dibutoxybenzene), 3(MoIV,MoIV).
Macrocycle 12 (0.099 g, 0.083 mmol) was deprotected via the method
described above for the preparation of 3(MoIV,MoIV). The tetrathiolate
was not isolated, due its air sensitivity. The reaction residue was
dissolved in deaerated MeOH (40 mL). In a separate 100 mL Schlenck
flask, Cp2MoCl2 and Cs2CO3 were suspended in deaerated MeOH (40
mL). The pz4- was transferred dropwise, via cannula, to the Cp2MoCl2
suspension and stirred for 12 h. The solvent was removed, and the pz
was chromatographed on silica gel using CH2Cl2/MeOH (90:10) as the
eluant. The major azure blue-green band was collected (0.54 g, 51%
yield based on 12): 1H NMR (300 MHz, CD2Cl ) δ 0.880 (t, J ) 7
2
Hz, 12H), 2.025 (m, 8H), 2.043 (m, 8H), 4.619 (t, J ) 6, 8H), 5.670
(s, 20H), 7.430 (s, 4H); UV-vis (CH2Cl2) λmax (log ꢀ) 312 (5.50), 344
(5.56), 622 (5.79), 670 sh (5.23); (FAB-MS) m/z 1282.0 (M+), calcd
for C60H62N8O4S4Mo2 1282.2.
3,6-dibutoxybenzene, 3(VIV,VIV).
(Fo)] ) [σ2 (Fo)] ) [σ2 (Fo) + p2Fo /4]-1; σc(Fo) is the esd based on
2
H2[Pz(S2VCp2)2;B2)],
B
)
c
c
Macrocycle 12 (0.131 g, 0.110 mmol) was deprotected by the method
described above for 3(MoIV,MoIV). The tetrathiolate was not isolated,
due its air sensitivity. The reaction residue was dissolved in deaerated
acetone (40 mL). In a separate 100 mL Schlenck flask, Cp2VCl2 (0.045
g, 0.179 mmol) was suspended in deaerated acetone (40 mL) The pz4-
was transferred dropwise, via cannula, to the Cp2VCl2 suspension and
stirred for 12 h. The solvent was removed under vacuum, and the crude
pz was taken into the glovebox and chromatographed on silica gel using
toluene/acetone (90:10) as the eluant. The major blue band was collected
(0.025 g, 19% yield based on 0.131 g of 12): UV-vis λmax 399, 610,
667, 742 (very broad); (FAB-MS) m/z 1189 (M + H+), calcd for
C60H62N8O4S4V2 1188.3; X-band EPR spectrum (298 K, toluene) g )
2.00, 15 lines, aiso ) 30 G.
counting statistics and p is the p-factor) on F2 was based on 2143
observed reflections and 228 variable parameters and converged (largest
parameter shift was 0.01 times its esd) with unweighted and weighted
agreement factors of R1 ) 0.143 and wR2 ) 0.239. The standard
deviation of an observation of unit weight was 1.75. The weighting
scheme was based on counting statistics. The maximum and minimum
peaks on the final difference Fourier map corresponded to 1.18 and
-0.74 e-/Å3, respectively, and were located in the tert-butyl and
vanadium positions. Neutral atom scattering factors were taken from
Cromer and Waber.27 Anomalous dispersion effects were included in
Fcalc; the values for ∆f 1 and ∆f 11 were those of Creagh and McAuley.28
The values for the mass attenuation coefficients are those of Creagh
and Hubbell.29 All calculations were performed using the teXsan for
Windows version 1.05 crystallographic software packages from
Molecular Structure Corp.
H2[Pz(S2VCp2)2;B2)],
B )
(tert-butylphenyl)2, 4(VIV,VIV).
Macrocycle 13 (0.075 g, 0.043 mmol) was deprotected via the method
described above for the preparation of 3(MoIV,MoIV). The tetrathiolate
was not isolated, due its air sensitivity. The reaction residue was
dissolved in deaerated acetone (40 mL). In a separate 100 mL Schlenck
flask, Cp2VCl2 (0.022 g. 0.087 mmol) was suspended in deaerated
acetone (40 mL). The pz4- was transferred dropwise, via cannula, to
the Cp2VCl2 suspension and stirred for 12 h. The solvent was removed
under vacuum, and the crude pz was taken into the glovebox and
chromatographed on silica gel using toluene/acetone (90:10) as the
eluant. The major blue band was collected (0.014 g, 23% yield based
on 13): UV-vis λmax 399, 610, 667, 742 (very broad); (FAB-MS) m/z
1329 (M + H+), calcd for C76H74N8S4V2 1328; X-band EPR spectrum
(298 K, toluene) g ) 2.00, 15 lines, aiso ) 30 G.
Acknowledgment. This work has been supported by the
NSF (Grant CHE-9729590) and the Materials Research Center
of Northwestern University. We thank Dr. Peter Doan for help
with some of the EPR experiments and for helpful discussions.
Supporting Information Available: Crystal data, structure
refinement, and tables of positional parameters, bond distances,
bond angles, and anisotropic displacement parameters (PDF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
JA003702X
H2[Pz(S2MoVCp2;S2MoIVCp2;B2)]+[PF6]-, B ) 3,6-dibutoxy-
benzene, 3(MoV,MoIV). 3(MoIV,MoIV) (0.015 g, 0.018 mmol) was
dissolved in ca. 10 mL of deaerated CH2Cl2. One milliliter of a 9.0
mM solution of ferrocenium hexafluorophosphate in 80:20 CH2Cl2/
acetone was added to the pz. The solution, which turned from a teal
green color to a dark green color, was used without further purifica-
tion: UV-vis (CH2Cl2) λ 420, 625, 709, 809; EPR (X-band, 9.132
GHz), 95,97Mo, I ) 5/2, 25.5%, G 77 K - g1 ) 2.024, g2 ) 2.018, g3 )
1.998.
(25) Sheldrick, G. M. In Crystallographic Computing 3; Sheldrick, G.
M., Kru¨ger, C., Goddard, R., Eds.; Oxford University Press: London, 1985;
pp 175-189.
(26) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-94 Program System;
Technical Report of the Crystallography Laboratory; University of
Nijmegen: The Netherlands, 1994.
(27) Cromer, D. T.; Waber, J. T. In International Tables for X-ray
Crystallography; Ibers, J. A., Hamilton, W. C., Eds.; Kynoch Press:
Birmingham, England, 1974; Vol. IV, pp 72-98.
(28) Creagh, D. C.; McAuley, W. J. In Table 4.2.6.8; Wilson, A. J. C.,
Ed.; Kluwer Academic Publishers: Boston, 1992; pp 219-222.
(29) Creagh, D. C.; Hubbell, J. H. In Table 4.2.4.3; Wilson, A. J. C.,
Ed.; Kluwer Academic Publishers: Boston, 1992; pp 200-206.
H2[Pz(S2MoVCp2)2;B2)]2+[PF6]22-, B ) 3,6-dibutoxybenzene, 3-
(MoV,MoV). 17 (0.015 g, 0.018 mmol) was dissolved in ca. 10 mL of
deaerated CH2Cl2. One milliliter of an 18.0 mM solution of ferrocenium
hexafluorophosphate in 80:20 CH2Cl2/acetone was added to the pz. The