Pyridylazole chelation of oxorhenium(V) and imidorhenium(V). Rates and trends of oxygen atom transfer from ReVO to tertiary phosphines

Article abstract of DOI:10.1021/ic011064t

The concerned azoles are 2-(2-pyridyl)benzoxazole (pbo) and 2-(2-pyridyl)benzthiazole (pbt). These react with ReOCI₃(PPh₃)₂ in benzene, affording Re^VOCI₃(pbo) and Re^VOCI₃(pbt), which undergo facile oxygen atom transfer to PPh₂R (R = Ph, Me) in dichloromethane solution, furnishing Re^III(OPPh₂R)CI₃(pbo) and Re^III(OPPh₂R)CI₃(pbt). The oxo species react with aniline in toluene solution, yielding the imido complexes Re^V(NPh)CI₃(pbo) and Re^V(NPh)CI₃(pbt). The X-ray structures of pbt, ReOCI₃(pbt), Re(OPPh₃)CI₃(pbt), and Re(NPh)CI₃(pbo) are reported. The lattice of pbt consists of stacked dimers. In all the complexes the azole ligand is N,N-chelated and the ReCI₃ moiety is meridionally disposed. In ReOCI₃(pbt) the metal-oxo bond length is 1.607(9) A. The second-order rates and the associated activation parameters of the oxygen atom transfer reactions of the Re^VO chelates with PPh₂R are reported. The large and negative entropy of activation (～ -24 eu) is consistent with an associative pathway involving nucleophilic phosphine attack. The rate increases with phosphine basicity (PPh₂Me > PPh₃) and azole heteroatom electronegativity (O(pbo) > S(pbt)). Logarithmic rate constants for ReOCI₃(pbo), ReOCI₃(pbt), and ReOCI₃-(pal) are found to correlate linearly with Re^VIO/Re^VO reduction potentials (pal is pyridine-2-(N-tolyl)aldimine). The relatively low rate constant of ReOCI₃(pbt) compared to that of ReOCI₃(pal) is consistent with the observed shortness of the metal-oxo bond in the former. Crystal data are as follows: (pbt) empirical formula -C₁₂H₈N₂S, crystal system orthorhombic, space group Pca2₁, a = 13.762(9) A, b = 12.952(8) A, c = 11.077(4) A, V = 1974(2) A³, Z = 8; (ReOCI₃(pbt)) empirical formula C₁₂H₈CI₃N₂OSRe, crystal system monoclinic, space group P2₁/c, a = 11.174(7) A, b = 16.403(10) A, c = 7.751(2) A, β = 99.35(4)°, V = 1401.8(13) A³, Z = 4; (Re(NPh)CI₃(pbo)) empirical formula C₁₈H₁₃CI₃N₃ORe, crystal system monoclinic, space group P2₁/c, a = 9.566(6) A, b = 16.082(8) A, c = 11.841(5) A, β = 94.03(4)°, V = 1817(2) A³, Z = 4.

Full text of DOI:10.1021/ic011064t

Inorg. Chem. 2002, 41, 2616−2622
Pyridylazole Chelation of Oxorhenium(V) and Imidorhenium(V). Rates
and Trends of Oxygen Atom Transfer from ReVO to Tertiary Phosphines
Jaydip Gangopadhyay,† Suman Sengupta,† Sibaprasad Bhattacharyya,† Indranil Chakraborty,† and
,†,‡
Animesh Chakravorty*
Department of Inorganic Chemistry, Indian Association for the CultiVation of Science,
Kolkata 700 032, India, and Jawaharlal Nehru Centre for AdVanced Scientific Research,
Bangalore 560 064, India
Received October 15, 2001
The concerned azoles are 2-(2-pyridyl)benzoxazole (pbo) and 2-(2-pyridyl)benzthiazole (pbt). These react with
ReOCl3(PPh3)2 in benzene, affording ReVOCl3(pbo) and ReVOCl3(pbt), which undergo facile oxygen atom transfer
III
III
to PPh2R (R ) Ph, Me) in dichloromethane solution, furnishing Re (OPPh2R)Cl3(pbo) and Re (OPPh2R)Cl3(pbt).
The oxo species react with aniline in toluene solution, yielding the imido complexes ReV(NPh)Cl3(pbo) and ReV-
(NPh)Cl3(pbt). The X-ray structures of pbt, ReOCl3(pbt), Re(OPPh3)Cl3(pbt), and Re(NPh)Cl3(pbo) are reported.
The lattice of pbt consists of stacked dimers. In all the complexes the azole ligand is N,N-chelated and the ReCl3
moiety is meridionally disposed. In ReOCl3(pbt) the metal−oxo bond length is 1.607(9) Å. The second-order rates
and the associated activation parameters of the oxygen atom transfer reactions of the ReVO chelates with PPh2R
are reported. The large and negative entropy of activation (∼ −24 eu) is consistent with an associative pathway
involving nucleophilic phosphine attack. The rate increases with phosphine basicity (PPh2Me > PPh3) and azole
heteroatom electronegativity (O(pbo) > S(pbt)). Logarithmic rate constants for ReOCl3(pbo), ReOCl3(pbt), and ReOCl3-
(pal) are found to correlate linearly with ReVIO/ReVO reduction potentials (pal is pyridine-2-(N-p-tolyl)aldimine). The
relatively low rate constant of ReOCl3(pbt) compared to that of ReOCl3(pal) is consistent with the observed shortness
of the metal−oxo bond in the former. Crystal data are as follows: (pbt) empirical formula C H N S, crystal system
12
8 2
3
orthorhombic, space group Pca21, a ) 13.762(9) Å, b ) 12.952(8) Å, c ) 11.077(4) Å, V ) 1974(2) Å , Z ) 8;
(ReOCl3(pbt)) empirical formula C H Cl3N OSRe, crystal system monoclinic, space group P21/c, a ) 11.174(7) Å,
12
8
2
3
b ) 16.403(10) Å, c ) 7.751(2) Å, â ) 99.35(4)°, V ) 1401.8(13) Å , Z ) 4; (Re(NPh)Cl3(pbo)) empirical
formula C H Cl3N ORe, crystal system monoclinic, space group P21/c, a ) 9.566(6) Å, b ) 16.082(8) Å, c )
18 13
3
3
11.841(5) Å, â ) 94.03(4)°, V ) 1817(2) Å , Z ) 4.
Introduction
an element in the periodic group next to that of molybdenum
and tungsten, transfer reactions involving ReVO are of value
as potential models.3
In the pyridyl ligands used so far (pyridine-2-aldimines
are representative examples), N,N-chelation of ReVO is
completed by the pyridine nitrogen along with a nitrogen
site present in an acyclic substituent pendent from the
This work stems from our interest in the design of new
oxorhenium(V) reagents based on pyridyl ligands and in the
chemical transformations thereof providing access to other
rhenium systems.1-3 A notable reaction of ReVO species is
oxygen atom transfer to oxophilic substrates.1-7 Transfer
reactions promoted by enzymatic oxo sites based on iron,
molybdenum, and tungsten are important in the chemistry
of life.8 Rhenium is not a biometal in the same sense, but as
(2) (a) Chakraborty, I.; Bhattacharyya, S.; Banerjee, S.; Dirghangi, B. K.;
Chakravorty, A. J. Chem. Soc., Dalton Trans. 1999, 3747. (b)
Bhattacharyya, S.; Chakraborty, I.; Dirghangi, B. K.; Chakravorty,
A. Inorg. Chem. 2001, 40, 286. (c) Bhattacharyya, S.; Chakraborty,
I.; Dirghangi, B. K.; Chakravorty, A. J. Chem. Soc., Chem. Commun.
2000, 1813. (d) Menon, M.; Pramanik, A.; Das, S.; Bag, N.;
Chakravorty, A. Inorg. Chem. 1994, 33, 403. (e) Menon, M.;
Chowdhury, S.; Pramanik, A.; Deb, A. K.; Chandra, S. K.; Bag, N.;
Goswami, S.; Chakravorty, A. J. Chem. Soc., Chem. Commun. 1994,
57.
* To whom correspondence should be addressed at the Indian Association
for the Cultivation of Science. Fax: +91-33-473-2805. E-mail: icac@
mahendra.iacs.res.in.
† Indian Association for the Cultivation of Science.
‡ Jawaharlal Nehru Centre for Advanced Scientific Research.
(1) Banerjee, S.; Bhattacharyya, S.; Dirghangi, B. K.; Menon, M.;
Chakravorty, A. Inorg. Chem. 2000, 39, 6 and references therein.
2616 Inorganic Chemistry, Vol. 41, No. 9, 2002
10.1021/ic011064t CCC: $22.00 © 2002 American Chemical Society
Published on Web 04/11/2002

Chelation of Oxorhenium(V) and Imidorhenium(V)
2-position of the pyridine ring.1-3 The use of heterocyclic
substituents instead would add a new dimension to pyridyl-
ReVO chemistry. A familiar example of such a ligand is 2,2′-
bipyridine, but the oxygen transfer behavior of its monooxo
of dichloromethane as the solvent (in which 1 is soluble) in
the above synthesis leads to further reaction, eq 2, furnishing
violet-colored complexes of type 2 (R ) Ph) which can also
be synthesized from preisolated 1 and PPh3. The type 2 (R
) Me) species were prepared from 1 and PPh2Me. The blue-
colored imide complexes of type 3 were synthesized by
reacting 1 with excess aniline in toluene, eq 3.
9c
complexes such as ReOCl3(bpy)5,9 and ReOMe2(bpy)Cl3
have not been documented. This has prompted us to explore
other heterocyclic systems as possible ligands. Herein we
report the synthesis and characterization of ReVO complexes
incorporating chelation by 2-(2-pyridyl)azoles. Structure
determination in one case has revealed the presence of a
relatively short metal-oxo bond. The oxo chelates react with
tertiary phosphines, furnishing stable phosphine oxide spe-
cies. The rates and activation parameters of oxygen atom
transfer are reported, and reactivity trends are scrutinized in
terms of ligand variation, reduction potentials, and bond
parameters. The ReVNPh species derived from the ReVO
complexes are also reported, and the chelation mode of a
hitherto unreported pyridyloxazole is authenticated by struc-
ture determination in one case.
ReOCl3(PPh3)2 + pbo/pbt f 1 + 2PPh3
1 + PPh2R f 2
(1)
(2)
(3)
1 + PhNH2 f 3 + H2O
Selected characterization data for the ligands and com-
plexes are given in the Experimental Section. The electronic
spectra of the complexes are of diagnostic value and have
been employed in rate studies (see below). The complexes
of types 1 and 3 are diamagnetic (5dxy2) and give rise to
normal H NMR spectra. The type 2 complexes (t2g4) have
1
magnetic moments near 2 µB as in some other rhenium(III)
species, and their H NMR spectra are paramagnetically
shifted.1,2,12
1
Results and Discussion
Syntheses of Ligands and Complexes. The concerned
ligands are 2-(2-pyridyl)benzoxazole (pbo) and 2-(2-pyridyl)-
benzthiazole (pbt). To our knowledge pbo is a hitherto
unreported oxazole. It has been synthesized in excellent
yields by extending a procedure10 based on the oxidation of
Schiff bases by Ag2O. A synthesis of pbt simpler than those
reported11 is described.
Upon reaction of ReOCl3(PPh3)2 with the azoles in equi-
molar proportions in benzene at room temperature, the oxo
complexes of type 1 are obtained as yellow solids, eq 1. Use
Structures. The following compounds afforded single
crystals and were subjected to X-ray crystallography: pbt,
ReOCl3(pbt), Re(OPPh3)Cl3(pbt), and Re(NPh)Cl3(pbo).
Satisfactory refinement could not be achieved in the case of
Re(OPPh3)Cl3(pbt) due to crystallographic complications (see
the Experimental Section). However, the results demonstrate
beyond doubt that the overall connectivity is as in 2.
A molecular view of pbt and selected bond parameters
therein are shown in Figure 1. The asymmetric unit consists
of two approximately planar (mean deviation ∼0.05 Å)
molecules lying parallel to each other in an eclipsed
configuration. The distance between the centroids of the two
molecules is 3.838(3) Å. Aromatic stacking is a general
feature of all the structures reported here. The relative
orientations of the azole molecules in the stacks, however,
vary from one case to another.
(3) Dirghangi, B. K.; Menon, M.; Pramanik, A.; Chakravorty, A. Inorg.
Chem. 1997, 36, 1095.
(4) Rowbottom, J. F.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1972,
826.
(5) Bryan, J. C.; Stenkamp, R. E.; Tulip, T. H.; Mayer, J. M. Inorg. Chem.
1987, 26, 2283.
(6) Fontaine, X. L. R.; Fowles, E. H.; Layzell, T. P.; Shaw, B. L.;
Thornton-Pett, M. J. Chem. Soc., Dalton Trans. 1991, 1519.
(7) Seymore, S. B.; Brown, S. N. Inorg. Chem. 2000, 39, 325.
(8) (a) Hille, R. Chem. ReV. 1996, 96, 2757. (b) Holm, R. H. Kennepohl,
P.; Solomon, E. I. Chem. ReV. 1996, 96, 2239.
(9) (a) Chakravorti, M. C. J. Inorg. Nucl. Chem. 1975, 37, 1991. (b) Fortin,
S.; Beauchamp, A. L. Inorg. Chem. 2000, 39, 4886. (c) Jung, J. H.;
Albright, T. A.; Hoffman, D. M.; Lee, T. R. J. Chem. Soc., Dalton.
Trans. 1999, 4487. (d) Ram, M. S.; Johnson, C. S.; Blackbourn, R.
L.; Hupp, J. T. Inorg. Chem. 1990, 29, 238. (e) Fergusson, J. E. Coord.
Chem. ReV. 1966, 459 and references therein.
(10) Yoshifuji, M.; Nagase, R.; Kawashima, T.; Inamoto, N. Heterocycles
1978, 10, 57.
(11) (a) Miller, P. E.; Oliver, G. L.; Dann, J. R.; Gates, J. W. J. Org. Chem.
1957, 22, 664. (b) Lindoy, L. F.; Livingstone, S. E. Inorg. Chim. Acta
1967, 365.
(12) (a) Bhattacharyya, S.; Banerjee, S.; Dirghangi, B. K.; Menon, M.;
Chakravorty, A. J. Chem. Soc., Dalton Trans. 1999, 155. (b) Gunz,
H. P.; Leigh, G. J. J. Chem. Soc. A 1971, 2229. (c) Tisato, F.; Refosco,
F.; Bolzati, C.; Cagnolini, A.; Galto, S.; Bandoli, G. J. Chem. Soc.,
Dalton Trans. 1997, 1421.
Inorganic Chemistry, Vol. 41, No. 9, 2002 2617

Gangopadhyay et al.
Figure 1. Molecular view and atom-labeling scheme for free pbt, 1. All
non-hydrogen atoms are represented by 30% thermal probability ellipsoids.
Selected bond distances (Å) and angles (deg): C(18)-S(2) 1.728(6), S(2)-
C(24) 1.719(6), C(24)-C(19) 1.399(8), C(19)-N(4) 1.365(7), N(4)-C(18)
1.282(7), C(6)-S(1) 1.728(8), S(1)-C(12) 1.733(7), C(12)-C(7) 1.371-
(11), C(7)-N(2) 1.402(9), N(2)-C(6) 1.269(9); C(6)-S(1)-C(12) 89.1-
(4), N(2)-C(6)-S(1) 116.8(6), S(1)-C(12)-C(7) 108.6(6), C(12)-C(7)-
N(2) 115.8(7), C(7)-N(2)-C(6) 109.7(6), C(18)-S(2)-C(24) 88.6(3),
N(4)-C(18)-S(2) 116.3(4), S(2)-C(24)-C(19) 109.4(4), C(24)-C(19)-
N(4) 114.6(5), C(19)-N(4)-C(18) 111.0(5).
Figure 3. Molecular view and atom-labeling scheme for Re(NPh)Cl3-
(pbo). All non-hydrogen atoms are represented by 30% thermal probability
ellipsoids.
The Re(pbt) fragment in ReOCl3(pbt) is planar with a
mean deviation of 0.05 Å, and the oxo oxygen atom also
lies in this plane. There is a relatively short nonbonded C8‚
‚‚O contact, 2.980(3) Å. In the lattice the Re(pbt) fragments
align nearly parallel to one another in an infinite array, and
this stacking leads to nonbonded Cl‚‚‚S contacts (3.475(2)
and 3.421(2) Å) involving two trans chloride ligands and
the thiazole S atoms.
In the distorted octahedral ReOCl3N2 coordination sphere
of the complex, the chloride ligands are meridionally
disposed. These together with the N(2) atom constitute a
plane (mean deviation 0.01 Å) from which the metal atom
is displaced 0.27 Å toward the oxo oxygen atom. At 1.607-
(9) Å, the Re-O distance is relatively short. In reported
ReVO species the Re-O distances generally lie within the
range 1.68 ( 0.03 Å, and shorter lengths are uncommon.14
The Re-N(1) bond is subject to the trans influence of the
oxo oxygen atom and is accordingly longer than the Re-
N(2) bond (trans ligand Cl(1)) by ∼0.15 Å.
Figure 2. Molecular view and atom-labeling scheme for ReOCl3(pbt).
All non-hydrogen atoms are represented by 30% thermal probability
ellipsoids.
The structure of Re(NPh)Cl3(pbo), shown in Figure 3,
authenticates N,N-chelation of the new pbo ligand in the
planar Re(pbo) fragment. Selected bond parameters are listed
in Table 2. In the meridional ReCl3N3 coordination sphere
the metal atom is displaced by 0.36 Å toward the imide
nitrogen, N(3), from the plane defined by Cl(1), Cl(2), Cl-
(3), and N(2). The observed Re-N(3) length, 1.698(9) Å,
corresponds to triple bonding.15
Table 1. Selected Bond Distances (Å) and Angles (deg) for
ReOCl3(pbt)
Distances
Re-O
Re-N(1)
Re-N(2)
1.607(9)
2.270(13)
2.118(12)
Re-Cl(1)
Re-Cl(2)
Re-Cl(3)
2.291(5)
2.312(5)
2.330(5)
Angles
O-Re-N(2)
92.8(5)
73.3(5)
162.3(4)
101.2(5)
82.9(4)
96.3(5)
80.1(4)
162.4(2)
O-Re-N(1)
165.3(5)
Rates and Activation Parameters of Oxygen Atom
Transfer. The variable-temperature rates of the reaction of
eq 2 (R ) Ph) have been studied spectrophotometrically in
N(2)-Re-N(1)
N(2)-Re-Cl(1)
O-Re-Cl(2)
O-Re-Cl(1)
104.7(4)
89.4(4)
86.4(4)
87.4(2)
92.9(4)
88.1(2)
N(1)-Re-Cl(1)
N(2)-Re-Cl(2)
Cl(1)-Re-Cl(2)
N(2)-Re-Cl(3)
Cl(1)-Re-Cl(3)
N(1)-Re-Cl(2)
O-Re-Cl(3)
N(1)-Re-Cl(3)
Cl(2)-Re-Cl(3)
(13) (a) Chia P. S. K.; Livingstone, S. E. Inorg. Chim. Acta 1968, 2, 427.
(b) Lindoy, L. F.; Livingstone, S. E. Inorg. Chim. Acta 1968, 2, 119.
(c) Hossain, M.; Chattopadhyay, S. K.; Ghosh, S. Polyhedron 1997,
16, 143. (d) Maji, M.; Sengupta, P.; Chattopadhyay, S. K.; Mostafa,
G.; Schwalbe, C. H.; Ghosh, S. J. Coord. Chem. 2001, 54, 13.
(14) (a) Mayer, J. M. Inorg. Chem. 1988, 27, 3899. (b) Edwards, L. F.;
Griffith, W. P.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton
Trans. 1992, 957.
(15) (a) Dirghangi, B. K.; Menon, M.; Banerjee, S.; Chakravorty, A. Inorg.
Chem. 1997, 36, 3595. (b) Banerjee, S.; Dirghangi, B. K.; Menon,
M.; Pramanik, A.; Chakravorty, A. J. Chem. Soc., Dalton. Trans.
1997, 2149. (c) Goeden, G. V.; Haymore, B. L. Inorg. Chem. 1983,
22, 157. (d) Nugent, W. A.; Haymore, B. L. Coord. Chem. ReV. 1980,
31, 123.
A molecular view of ReOCl3(pbt) is shown in Figure 2,
and selected bond parameters are listed in Table 1. On going
from the free ligand (Figure 1) to the complex, the con-
formation of pbt has changed corresponding to a ∼180°
rotation around the C-C bond linking the pyridyl and
thiazole rings. With this change the ligand achieves N,N-
chelation as in 1. The coordination chemistry of pbt has
received some previous attention.13
2618 Inorganic Chemistry, Vol. 41, No. 9, 2002

Chelation of Oxorhenium(V) and Imidorhenium(V)
Table 4. Rate Constants and Activation Parametersa for the Reaction
ReOCl3(pbt) + PPh2R f Re(OPPh2R)Cl3(pbt) in Dichloromethaneb,c
R
T, K
102[PPh2R]
105kobsd, s-1
103k, M-1 s-1
Ph
299
0.63
1.06
1.40
2.00
0.63
1.06
1.40
2.00
0.63
1.06
1.40
2.00
0.63
1.06
1.40
2.00
0.61
1.15
1.60
2.00
0.96
1.82
2.18
2.95
1.22
2.15
2.77
3.87
1.51
2.71
3.67
5.07
2.03
3.43
4.72
6.63
6.70
13.30
17.15
21.91
1.68(0.03)
302
305
308
302
2.00(0.06)
2.58(0.05)
3.35(0.04)
10.65(0.03)
Me
Figure 4. Time evolution spectra for the reaction between ReOCl3(pbo)
and PPh3 in dichloromethane solution at 302 K (At is absorbance).
a For R ) Ph, ∆Hq ) 14.31(0.56) kcal mol-1 and ∆Sq ) -23.32(1.8)
eu. b The initial concentration of ReOCl3(pbt) is 1.25 × 10-4 M. c Least-
squares deviations are given in parentheses.
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Re(NPh)Cl3(pbo)
Under pseudo-first-order conditions (excess PPh3), the
rates are proportional to the concentration of the oxo complex
and the observed rate constant, kobsd, is proportional to the
concentration of PPh3. The reaction law is thus second order,
eq 4
Distances
Re-N(1)
Re-N(2)
Re-N(3)
2.266(9)
2.075(10)
1.698(9)
Re-Cl(1)
Re-Cl(2)
Re-Cl(3)
2.324(3)
2.365(3)
2.324(3)
Angles
N(3)-Re-N(2)
N(2)-Re-N(1)
N(2)-Re-Cl(1)
N(3)-Re-Cl(3)
N(1)-Re-Cl(3)
N(3)-Re-Cl(2)
N(1)-Re-Cl(2)
Cl(3)-Re-Cl(2)
98.4(4)
73.4(3)
161.7(3)
102.3(3)
82.5(3)
N(3)-Re-N(1)
N(3)-Re-Cl(1)
N(1)-Re-Cl(1)
N(2)-Re-Cl(3)
Cl(1)-Re-Cl(3)
N(2)-Re-Cl(2)
Cl(1)-Re-Cl(2)
170.7(4)
99.7(3)
88.3(2)
90.0(3)
88.31(12)
87.7(3)
88.39(12)
rate ) kobsd[ReOCl3(L)]
) k[ReOCl3(L)][PPh3]
(4)
95.5(3)
80.0(3)
(L ) pbo/pbt). The rate constant k follows the Eyring
equation. Rate data and activation parameters are listed in
Tables 3 and 4. The large and negative entropy of activation
implies close association of ReOCl3(L) and PPh3 in the
transition state. The probable mode of this association and
subsequent events are stylized in 4 in light of previous work3
162.23(11)
Table 3. Rate Constants and Activation Parametersa for the Reaction
ReOCl3(pbo) + PPh2R f Re(OPPh2R)Cl3(pbo) in Dichloromethaneb,c
R
T, K
102[PPh2R]
105kobsd, s-1
103k, M-1 s-1
Ph
299
0.63
1.06
1.40
2.00
0.63
1.06
1.40
2.00
0.63
1.06
1.40
2.00
0.63
1.06
1.40
2.00
0.61
1.15
1.60
2.00
1.95
3.42
4.47
6.70
2.40
4.33
5.60
8.17
3.00
5.78
7.32
10.53
3.73
6.95
3.45(0.02)
302
305
308
302
4.18(0.02)
5.42(0.02)
7.12(0.02)
24.80(0.05)
9.55
13.47
15.78
25.37
34.52
49.62
and the findings on oxygen atom transfer reactions of MoVIO2
and WVIO2 species.16 In 4 the full and broken lines,
respectively, represent coordinate covalent bonds and weak
links. Following attack on π*(ReO) orbitals by the phosphine
lone pair (4a), the π-bonds are weakened and a O‚‚‚P link
is established (4b, transition state). In the end, the PdO bond
remains coordinated to the metal (4c). In Re(OPPh3)Cl3(pbt),
Me
a For R ) Ph, ∆Hq ) 13.49 (0.81) kcal mol-1 and ∆Sq ) -24.15(2.5)
eu. b The initial concentration of ReOCl3(pbo) is 1.25 × 10-4 M. c Least-
squares deviations are given in parentheses.
CH2Cl2 solution for both ReOCl3(pbo) and ReOCl3(pbt).
Time evolution spectra are characterized by multiple isos-
bestic points, and a representative case is shown in Figure
4.
(16) (a) Tucci, G. C.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 1998, 37,
1602 and references therein. (b) Pietsch, M. A.; Hall, M. B. Inorg.
Chem. 1996, 35, 1273. (c) Enemark, J. H.; Young, C. G. AdV. Inorg.
Chem. 1993, 43, 1.
Inorganic Chemistry, Vol. 41, No. 9, 2002 2619

Gangopadhyay et al.
the P atom lies ∼2.8 Å away from the centroids of the two
OCl2 faces. The distances from the OClN centroids are ∼3.3
Å. Thus, phosphine attack may have occurred from the side
away from the chelate ring.
Reactivity Trends. In reaction model 4, an increase of
the phosphine basicity should make the reaction more facile.
In agreement with this, PPh2Me reacts faster than PPh3, the
ratio k(PPh2Me)/k(PPh3) being 5.93 (L ) pbo) and 5.33 (L
) pbt) at 302 K (Tables 3 and 4). The data of Tables 3 and
4 also reveal that ReOCl3(pbo) is a more potent transfer
reagent than ReOCl3(pbt), the rate constant for the former
complex at any given temperature being approximately
double that of the latter complex. This is qualitatively
consistent with the heteroatom electronegativity order O >
S, resulting in larger electron withdrawl from the oxometal
moiety in the pbo complex. Significantly, for protonated
azoles the pKa trend is oxazole < thiazole.17
In similarly constituted molecules, the metal reduction
potential is a qualitative index of the effective electron
density at the metal site (the higher the E1/2, the lower the
electron density). In acetonitrile solution the ReVO complexes
display a quasireversible (peak-to-peak separation ∼100 mV)
one-electron response assigned to the ReVIO/ReVO couple.
The E1/2 values are 1.64 and 1.54 V vs SCE at 298 K for the
pbo and pbt complexes, respectively. Significantly, the ReVI-
NPh/ReVNPh couple in 3 also displays a similar trend: 0.85
V (pbo) and 0.81 V (pbt). Oxygen atom transfer rate and
E1/2 data for a ReVO pyridylaldimine system, viz., ReOCl3-
(pal), 5, are also available.3 Complex 5 (k ) 7.96 × 10-3
Figure 5. ReVIO/ReVO reduction potential versus logarithmic rate constant
for oxygen atom transfer to PPh3 at 299 K.
ReVOCl3(pbt) from which the corresponding ReIII(OPPh2R)
and ReV(NPh) species have been prepared. The reactions are
stereoretentive, the ReCl3 moeity being uniformly meridional
in geometry. The azole ligands are N,N-chelated, and in the
case of pbt, chelation is attended with a conformational
change.
The associative oxygen atom transfer reactions of ReOCl3-
(pbo), ReOCl3(pbt), and ReOCl3(pal)3 with tertiary phos-
phines are consistent with reaction model 4. The rate
constants increase with phosphine basicity (PPh3 < PPh2-
Me), azole heteroatom electronegativity (S(pbt) < O(pbo)),
metal reduction potential (1 (X ) S) < 1 (X ) O) < 5),
and metal-oxo bond length (1 (X ) S) < 5). A linear
correlation between metal reduction potentials and the
logarithmic rate constants is noted.
M-1 s-1 at 299 K) reacts with PPh3 more than twice as fast
as ReOCl3(pbo). The ReVIO/ReVO reduction potential of 5
is also relatively high, 1.72 V.3 Indeed the E1/2 and ln k values
of the three complexes are linearly related with a correlation
constant of 0.999 (Figure 5).
Last, we note that the Re-O distance in ReOCl3(pbt) is
0.06 Å shorter than that in ReOCl3(pal).3 The superior
strength of the metal-oxo bond (less stable π*(ReO)
orbitals) in the pbt complex would hinder transfer of the
oxygen atom by weakening the association in the activated
state. Indeed the ∆Hq value of ReOCl3(pbt) is more positive
and the ∆Sq value is less negative (Table 4) than those of
ReOCl3(pal) (∆Hq ) 8.91 kcal M-1 s-1 and ∆Sq ) -38.69
eu).3 Thus, the relatively higher electron density of the Re-O
bond in the pbt complex as reflected in the smaller E1/2 value
(see above) is also expressed as a shortening of the Re-O
bond with the consequent sluggishness of the oxygen atom
transfer reaction.
Experimental Section
Materials. The ReOCl3(PPh3)2 complex was prepared by a
reported method.18 The purification and drying of dichloromethane
and acetonitrile for synthesis as well as electrochemical and spectral
work were done as before.19 Benzene was distilled over sodium
before use. All other chemicals and solvents were of reagent grade
and were used as received.
Physical Measurements. All UV-vis spectral measurements
were carried out with a Shimadzu UVPC 1601 spectrometer fitted
with thermostated cell compartments. Proton NMR spectra were
recorded on a Bruker FT 300 MHz spectrometer. The atom
1
numbering scheme used for H NMR is the same as in crystal-
lography. Spin-spin structures are abbreviated as follows: s, singlet;
d, doublet; t, triplet; i, ill-resolved. Electrochemical measurements
were performed on a PAR model 370-4 electrochemistry system
as described elsewhere20 using a platinum working electrode under
a nitrogen atmosphere. The supporting electrolyte was tetraethy-
Concluding Remarks
(18) Chatt, J.; Rowe, G. A. J. Chem. Soc. 1962, 4019.
(19) (a) Lahiri, G. K.; Bhattacharya, S.; Ghosh, B. K.; Chakravorty, A.
Inorg. Chem. 1987, 26, 4324. (b) Sawyer, D. T.; Roberts, J. L., Jr.
Experimental Electrochemistry for Chemists; Wiley: New York, 1974;
p 167.
Oxorhenium(V) complexes of two pyridyl heterocyclic
ligands have been isolated in the form of ReVOCl3(pbo) and
(17) Katritzsky, A. R.; Rees, C. W. ComprehensiVe Heterocyclic Chemistry,
(20) Pramanik, A.; Bag, N.; Lahiri, G. K.; Chakravorty, A. Inorg. Chem.
1991, 30, 410.
1st ed.; Pergamon Press: New York, 1984; Vol. 6, p 184.
2620 Inorganic Chemistry, Vol. 41, No. 9, 2002

Chelation of Oxorhenium(V) and Imidorhenium(V)
lammonium perchlorate (TEAP), and potentials are referred to the
saturated calomel electrode (SCE) without junction correction.
Room-temperature magnetic susceptibilities of powders were
measured with a model 155 PAR vibrating sample magnetometer.
Microanalyses (C, H, N) were performed using a Perkin-Elmer 2400
series II elemental analyzer.
c. Re(OPPh3)Cl3(pbo). To a solution of ReOCl3(pbo) (65 mg,
0.13 mmol) in 25 mL of dichloromethane was added 68 mg (0.28
mmol) of PPh3. The resulting solution was magnetically stirred for
3.5 h at room temperature, and during this time the solution color
changed from yellow to violet. The solution was subjected to
chromatography on a silica gel column (25 × 1 cm, 60-120 mesh).
Excess PPh3 was eluted with benzene. The violet band that followed
was eluted with a benzene-acetonitrile (50:3) mixture. Solvent
removal from the eluate under reduced pressure afforded Re-
(OPPh3)Cl3(pbo) as a violet solid. Yield: 70 mg (71%). Anal. Calcd
for C30H23Cl3N2O2PRe: C, 46.95; H, 3.02; N, 3.65. Found: C, 46.95;
H, 3.03; N, 3.67. UV-vis (λmax, nm (ꢀ, M-1 cm-1), CH2Cl2
Preparation of Ligands. a. 2-(2-Pyridyl)benzoxazole, pbo.
Pyridine-2-carboxaldehyde (1.07 g, 10 mmol) and 2-aminophenol
(1.09 g, 10 mmol) were mixed thoroughly to make a paste which
was then extracted thrice (3 × 15 mL) with diethyl ether. The Schiff
base was isolated as a red-yellow solid by removing the solvent
from the extract. To a solution of the Schiff base (0.99 g, 5 mmol)
in 50 mL of dichloromethane was added silver oxide (1.74 g, 7.5
mmol), and the mass was magnetically stirred for 10 h in the air
and then filtered through a Celite bed. The filtrate was then
subjected to chromatography on an active alumina column (30 ×
1 cm). A pale-yellow band was eluted by benzene, and solvent
removal from the eluate under reduced pressure afforded pbo as a
pale-yellow solid which was dried in vacuo over fused CaCl2. The
solid was recrystallized from hot methanol, furnishing pale-yellow
needles. Yield: 0.75 g (77% based on the Schiff base). Mp: 102
°C. Anal. Calcd for C12H8N2O: C, 73.46; H, 4.11; N, 14.28. Found:
C, 73.44; H, 4.08; N, 14.30. UV-vis (λmax, nm (ꢀ, M-1 cm-1),
CH2Cl2 solution): 250 (28500); 305 (22950). 1H NMR (δ (J, Hz),
CDCl3): 8.74 (H(1), d, 4.7); 7.59 (H(2), t, 4.6); 7.76 (H(3), t, 6.8);
7.82 (H(4), d, 6.2); 8.28 (H(8), d, 7.9); 7.33 (H(9), t, 5.6); 7.30
(H(10), t, 5.2); 7.38 (H(11), d, 5.9).
1
solution): 733 (2420); 580 (1710); 513 (1950); 319 (11330). H
NMR (δ (J, Hz), CDCl3): 25.85 (H(1), d, 7.8); 7.94 (H(2), t, 8.3);
10.99 (H(3), t, 7.6); 8.37 (H(4), d, 7.8); 20.75(H(8), d, 7.7); 10.36
(H(9), t, 7.6); 6.98 (H(10), t, 6.9); 22.96 (H(11), d, i). 1H NMR (δ
(J, Hz), PPh3): 7.45 (H(o), d, 5.1); 7.40 (H(m), t, i); 7.07 (H(p), t,
i). µ (in powder): 1.95 µB (298 K).
The complex could also be prepared directly from a solution of
ReOCl3(PPh3)2 (50 mg, 0.06 mmol) in 25 mL of dichloromethane
containing pbo (12 mg, 0.06 mmol). Magnetic stirring at room
temperature for 3.5 h afforded a violet solution which was subjected
to chromatography on a silica gel column as described above.
d. Re(OPPh3)Cl3(pbt). A similar procedure was used to prepare
this and the following phosphine oxide complexes. Yield: 79 mg
(75%). Anal. Calcd for C30H23Cl3N2SOPRe: C, 45.99; H, 2.96; N,
3.58. Found: C, 45.95; H, 2.89; N, 3.61. UV-vis (λmax, nm (ꢀ,
M-1 cm-1), CH2Cl2 solution): 737 (4200); 585 (3050); 518 (2940);
b. 2-(2-Pyridyl)benzthiazole, pbt. To a solution of pyridine-2-
carboxaldehyde (1.07 g, 10 mmol) in 20 mL of methanol was added
2-aminothiophenol (1.25 g, 10 mmol). The solution was refluxed
for 6 h in the air. Upon cooling of the solution to room temperature,
a light-yellow solid precipitated. The solid was collected by filtration
and washed several times with hexane and then with diethyl ether.
It was finally dried in vacuo over fused CaCl2. The solid was
recrystallized from hot methanol, affording pale-yellow needles.
Yield: 1.76 g (82%). Mp: 132 °C. Anal. Calcd for C12H8N2S: C,
67.90; H, 3.80; N, 13.20. Found: C, 67.86; H, 3.76; N, 13.23. UV-
vis (λmax, nm (ꢀ, M-1 cm-1), CH2Cl2 solution): 312 (35105); 234
1
328 (21340). H NMR (δ (J, Hz), CDCl3): 28.24 (H(1), d, 7.8);
8.32 (H(2), t, 7.5); 22.54 (H(3), t, i); 7.83 (H(4), d, 7.5); 23.74
(H(8), d, i); 10.69 (H(9), t, 7.5); 8.35 (H(10), t, 7.8); 12.15 (H(11),
d, 7.8). 1H NMR (δ (J, Hz), PPh3): 7.19 (H(o), d, 6.9); 6.44 (H(m),
t, 7.8); 7.04 (H(p), t, 7.2). µ (in powder): 2.02 µB (298 K).
e. Re(OPPh2Me)Cl3(pbo). Yield: 67 mg (74%). Anal. Calcd
for C25H21Cl3N2O2PRe: C, 42.57; H, 3.00; N, 3.97. Found: C, 42.60;
H, 2.97; N, 3.95. UV-vis (λmax, nm (ꢀ, M-1 cm-1), CH2Cl2
1
solution): 733 (2720); 578 (1870); 503 (2180); 316 (11120). H
NMR (δ (J, Hz), CDCl3): 25.45 (H(1), d, 7.2); 2.32 (H(2), t, i);
10.57 (H(3), t, 7.0); -3.53 (H(4), d, 11.6); 10.78 (H(11), d, 6.6);
1
(29030). H NMR (δ (J, Hz), CDCl3): 8.68 (H(1), d, 4.6); 7.51
1
(H(2), t, 7.5); 7.85 (H(3), t, 7.5); 8.10 (H(4), d, 8.1); 8.37 (H(8), d,
7.8); 7.42 (H(9), t, 7.9); 7.38 (H(10), t, 6.2); 7.96 (H(11), d, 7.7).
Preparation of Complexes. a. ReOCl3(pbo). To a suspension
of ReOCl3(PPh3)2 (100 mg, 0.12 mmol) in 50 mL of benzene was
added 24 mg (0.12 mmol) of pbo. The resulting mass was stirred
magnetically for 4.5 h at room temperature, affording a turbid
yellow solution which was kept undisturbed overnight at 0 °C, to
ensure complete precipitation. The yellow solid was collected by
filtration, washed thoroughly with benzene, and finally dried in
vacuo over fused CaCl2. Yield: 36 mg (58%). Anal. Calcd for C12H8-
Cl3N2O2Re: C, 28.53; H, 1.60; N, 5.54. Found: C, 28.51; H, 1.62;
N, 5.56. UV-vis (λmax, nm (ꢀ, M-1 cm-1), CH2Cl2 solution): 764
8.17 (H(9), t, 7.2); 8.59 (H(10), t, 9.4); 21.94 (H(8), d, 7.5). H
NMR (δ (J, Hz), PPh2Me): 6.09 (H(o), d, i); 7.33 (H(m), t, 7.4);
7.88 (H(p), t, 8.1); -4.45 (Me, s). µ (in powder): 2.08 µB (298 K).
f. Re(OPPh2Me)Cl3(pbt). Yield: 68 mg (73%). Anal. Calcd for
C25H21Cl3N2SOPRe: C, 41.64; H, 2.94; N, 3.89. Found: C, 41.58;
H, 2.91; N, 3.96. UV-vis (λmax, nm (ꢀ, M-1 cm-1), CH2Cl2
1
solution): 741 (4600); 584 (2800); 515 (2650); 328 (18700). H
NMR (δ (J, Hz), CDCl3): 29.15 (H(1), d, 8.0); 9.02 (H(2), t, 7.7);
22.16 (H(3), t, i); 8.47 (H(4), d, 7.8); 22.69 (H(8), d, i); 11.18 (H(9),
1
t, 7.4); 8.72 (H(10), t, 8.7); 13.87 (H(11), d, 7.4). H NMR (δ (J,
Hz), PPh2Me): 8.01 (H(o), d, 8.2); 7.84 (H(m), t, 8.2); 7.49 (H(p),
t, 6.8); -3.43 (Me, s). µ (in powder): 2.05 µB (298 K).
1
(120); 475 (2350); 318 (16060). H NMR (δ (J, Hz), DMSO-d6):
g. Re(NC6H5)Cl3(pbo). To a solution of ReOCl3(pbo) (60 mg,
0.12 mmol) in dichloromethane (15 mL) was added aniline (56
mg, 0.60 mmol) in toluene (50 mL), and the mixture was heated
to reflux for 1.5 h, affording a blue solution. The solvent was then
removed under reduced pressure, and the mass thus obtained was
subjected to chromatography on a silica gel column (20 × 1 cm,
60-120 mesh). Excess aniline was eluted with benzene. A blue
band was then eluted with a benzene-acetonitrile (25:1) mixture.
Solvent removal from the eluate under reduced pressure afforded
Re(NC6H5)Cl3(pbo) as a blue solid. Yield: 56 mg (81%). Anal.
Calcd for C18H13Cl3N3ORe: C, 37.26; H, 2.26; N, 7.24. Found: C,
37.30; H, 2.28; N, 7.22. UV-vis (λmax, nm (ꢀ, M-1 cm-1), CH2Cl2
9.55 (H(1), d, 5.4); 7.56 (H(2), t, 6.6); 8.46 (H(3), t, 7.7); 8.20
(H(4), d, 8.7); 8.89 (H(8), d, 7.8); 8.07 (H(9), t, 7.4); 7.94 (H(10),
t, 8.4); 8.55 (H(11), d, 6.3).
b. ReOCl3(pbt). This complex was prepared by a similar
procedure. Yield: 32 mg (51%). Anal. Calcd for C12H8Cl3N2SORe:
C, 27.65; H, 1.55; N, 5.37. Found: C, 27.68; H, 1.60; N, 5.31. UV-
vis (λmax, nm (ꢀ, M-1 cm-1), CH2Cl2 solution): 766 (240); 493
(2700); 323 (11290). 1H NMR (δ (J, Hz), DMSO-d6): 8.75 (H(1),
d, 5.4); 7.57 (H(2), t, 6.4); 8.41 (H(3), t, 7.5); 8.10 (H(4), d, 8.1);
8.55 (H(8), d, 7.8); 7.94 (H(9), t, 7.8); 7.88 (H(10), t, 8.1); 8.50
(H(11), d, 7.5).
Inorganic Chemistry, Vol. 41, No. 9, 2002 2621

Gangopadhyay et al.
Table 5. Crystallographic Data for pbt, ReOCl3(pbt), and
Re(NPh)Cl3(pbo)
and Re(NPh)Cl3(pbo), slow diffusion of hexane into dichlo-
romethane solution afforded single crystals. Cell parameters were
determined by a least-squares fit of 30 machine-centered reflections
(14° e 2θ e 28°). Data were collected by the ω scan technique in
the 2θ range 3-50° for pbt, ReOCl3(pbt), and Re(OPPh3)Cl3(pbt)
and in the 2θ range 3-47° for Re(NPh)Cl3(pbo) on a Siemens
R3m/V four-circle diffractometer with graphite-monochromated Mo
KR (λ ) 0.71073 Å) radiation at 298 K. Two check reflections
after each 198 reflections showed no significant intensity reduction
for any of the crystals. Data were corrected for Lorentz-polarization
effects and in the case of complexes for absorption.21
The structure of pbt was generated by direct methods and those
of ReOCl3(pbt), Re(OPPh3)Cl3(pbt), and Re(NPh)Cl3(pbo) by using
Patterson maps followed by successive Fourier synthesis. The
structures of pbt, ReOCl3(pbt), and Re(NPh)Cl3(pbo) were refined
by full-matrix least-squares procedures on F2. All non-hydrogen
atoms were made anisotropic, and the hydrogen atoms were added
at the calculated positions. Calculations were performed using the
SHELXTL V5.0322 program package. The crystal data for pbt,
ReOCl3(pbt), and Re(NPh)Cl3(pbo) are given in Table 5.
The complex Re(OPPh3)Cl3(pbt) crystallized in the chiral space
group P1 with Z ) 2, and the asymmetric unit generated from
Patterson maps and successive Fourier synthesis consisted of two
molecules making a nearly centrosymmetric pair. This vitiated least-
squares refinement. Only the coordination sphere could be refined
anisotropically, the benzene rings having been affixed as idealized
hexagons. With these constraints the refinement did not proceed
normally, but the gross structure was revealed with certainty. Crystal
data are as follows: empirical formula C30H23Cl3N2OPSRe, formula
weight 783.08, crystal system triclinic, space group P1, a ) 10.369-
(8) Å, b ) 11.459(6) Å, c ) 13.787(5) Å, r ) 91.08(4)°, â )
89.92(5)°, γ ) 106.98(5)°, V ) 1566(2) Å3, Z ) 2, R1[I > 2σ(I)]
) 0.1070, wR2[I > 2σ(I)] ) 0.2527. Selected bond lengths
probably good to within (0.05 Å are Re-O 2.08 Å, Re-Cl 2.31
Å, and O ) P 1.50 Å, which are not incompatible with those in
other ReIII-OP systems.1-3 All other results are deposited.
pbt
empirical formula C12H8N2S
ReOCl3(pbt)
Re(NPh)Cl3(pbo)
C12H8Cl3N2OSRe C18H13Cl3N3ORe
fw
212.28
520.81 579.86
cryst size, mm
cryst syst
space group
a, Å
b, Å
c, Å
0.40 × 0.40 × 0.30 0.35 × 0.30 × 0.30 0.40 × 0.35 × 0.30
orthorhombic
Pca21
monoclinic
P21/c
monoclinic
P21/c
13.762(9)
12.952(8)
11.077(4)
11.174(7)
16.403(10)
7.751(2)
9.566(6)
16.082(8)
11.841(5)
R, deg
â, deg
γ, deg
V, Å
99.35(4)
94.03(4)
1974(2)
8
1.428
0.289
0.0543, 0.1354
1401.8(13)
4
2.468
9.382
0.0553, 0.1308
1817(2)
4
2.120
7.141
0.0581, 0.1497
Z
F
calcd, mg m-3
µ, mm-1
R1,a wR2b
[I > 2σ(I)]
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo - Fc )2/∑w(Fo )2]1/2
.
2
2
2
solution): 735 (330); 563 (1900); 320 (10600). 1H NMR (δ (J, Hz),
CDCl3): 9.48 (H(1), d, 5.2); 7.16 (H(2), t, 8.0); 8.12 (H(3), t, 6.6);
8.47 (H(4), d, 7.9); 8.58 (H(8), d, 4.8); 7.90 (H(9), t, 4.7); 7.85
1
(H(10), t, 6.5); 7.38 (H(11), d, 8.4). H NMR (δ (J, Hz), NC6H5):
7.74 (H(o), d, 8.2); 7.51 (H(m), t, 4.0); 7.65 (H(p), t, 4.6).
h. Re(NC6H5)Cl3(pbt). A procedure similar to the above was
used. Yield: 63 mg (79%). Anal. Calcd for C18H13Cl3N3SRe: C,
36.25; H, 2.20; N, 7.05. Found: C, 36.31; H, 2.18; N, 7.07. UV-
vis (λmax, nm (ꢀ, M-1 cm-1), CH2Cl2 solution): 738 (270); 566
1
(1840); 321 (10730). H NMR (δ (J, Hz), CDCl3): 9.43 (H(1), d,
5.4); 7.22 (H(2), t, 6.6); 8.07 (H(3), t, 7.8); 7.96 (H(4), d, 8.1);
7.89 (H(8), d, 7.8); 7.81 (H(9), t, i); 7.78 (H(10), t, 4.3); 7.63 (H(11),
1
d, 6.8). H NMR (δ (J, Hz), NC6H5): 7.71 (H(o), d, 7.4); 7.42
(H(m), t, 8.2); 7.50 (H(p), t, 7.6).
Rate Measurements. The representative case of the reaction of
ReOCl3(pbo) with PPh3 will be described. A known excess of PPh3
was added to a solution of ReOCl3(pbo) (1.25 × 10-4 M) in
dichloromethane at the desired temperature, and the thermostated
reaction was followed spectrophotometrically (quartz cell path
length 1 cm) by measuring the absorbance (At) of the peak at 737
nm as a function of time (t). The absorbance (AR) at the end of the
reaction (24 h) was also measured. Values of kobsd and k were
obtained from the slopes of the linear plots of -[ln(AR-At)] versus
t and kobsd versus [PPh3], respectively. The activation enthalpy and
entropy parameters were determined from the linear plot of -(ln
kh)/KBT vs T-1 using the Eyring equation (eq 5).
Acknowledgment. We thank the Department of Science
and Technology and Council of Scientific and Industrial
Research, New Delhi, for financial support.
Supporting Information Available: For pbt, ReOCl3(pbt), Re-
(OPPh3)Cl3(pbt), and Re(NPh)Cl3(pbo), crystallographic data (atomic
coordinates and equivalent isotropic coefficients, complete bond
distances and angles, anisotropic thermal parameters, and hydrogen
atom positional parameters) and crystallographic files in CIF format.
This material is available free of charge via the Internet at
http://www.pubs.acs.org.
k ) (KBT/h)[exp(-∆Hq/RT) exp(∆Sq/R)]
(5)
IC011064T
(21) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr. 1968,
24A, 351.
(22) Sheldrich, G. M. SHELXTL V5.03; Bruker Analytical X-ray Systems:
Madison, WI, 1994; Part Number 269-015900.
X-ray Structure Determination. Crystals of pbt and ReOCl3-
(pbt) were grown by slow evaporation of methanol and dichlo-
romethane solutions, respectively. In the case of Re(OPPh3)Cl3(pbt)
2622 Inorganic Chemistry, Vol. 41, No. 9, 2002