Synthesis of cationic rhenium(VII) oxo imido complexes and their tunability towards oxygen atom transfer

Article abstract of DOI:10.1021/ja065551p

A facile method is described for the synthesis of cationic Re(VII) cis oxo imido complexes of the form [Re(O)(NAr)(salpd)⁺] (salpd = N,N′-propane-1,3-diylbis(salicylideneimine)), 4, [Re(O)(NAr)(saldach) ⁺] (saldach = N,N′-cyclohexane-1,3-diylbis(salicylideneimine)), 5, and [Re(O)(NAr)(hoz)₂⁺] (hoz = 2-(2′- hydroxyphenyl)-2-oxazoline) (Ar = 2,4,6,-(Me)C₆H₂; 4-(CF₃)C₆H₄; 4-(Me)C₆H₄; 4-(CF₃)C₆H₄; 4-MeC₆H ₄SO₂), 6, from the reaction of oxorhenium(V) [(L)Re(O)(Solv)⁺] (1-3) and aryl azides under ambient conditions. Unlike previously reported cationic Re(VII) dioxo complexes, these cationic oxo imido complexes can be obtained on a preparative scale, and an X-ray crystal structure of [Re(O)(NMes)(saldach)⁺], 5a, has been obtained. Despite the multiple stereoisomers that could arise from tetradentate ligation of salen ligands to rhenium, one major isomer is observed and isolated in each instant. The electronic rationalization for stereoselectivity is discussed. Investigation of the mechanism suggests that the reactions of Re(V) with aryl azides proceed through an azido adduct similar to the group 5 complexes of Bergman and Cummins. Treatment of the cationic oxo imido complexes with a reductant (PAr ₃, PhSMe, or PhSH) results in oxygen atom transfer (OAT) and the formation of cationic Re(V) imido complexes. [(salpd)Re(NMes)(PPh ₃)⁺] (7) and [(hoz)₂Re(NAr)(PPh ₃)⁺] (Ar = m-OMe phenyl) (9) have been isolated on a preparative scale and fully characterized including an X-ray single-crystal structure of 7. The kinetics of OAT, monitored by stopped-flow spectroscopy, has revealed rate saturation for substrate dependences. The different plateau values for different oxygen acceptors (Y) provide direct support for a previously suggested mechanism in which the reductant forms a prior-equilibrium adduct with the rhenium oxo (Re^VII = O←Y). The second-order rate constants of OAT, which span more than 3 orders of magnitude for a given substrate, are significantly affected by the electronics of the imido ancillary ligand with electron-withdrawing imidos being most effective. However, the rate constant for the most active oxo imido rhenium(VII) is 2 orders of magnitude slower than that observed for the known cationic dioxo Re(VII) [(hoz) ₂Re(O)₂⁺].

Full text of DOI:10.1021/ja065551p

Published on Web 01/17/2007
Synthesis of Cationic Rhenium(VII) Oxo Imido Complexes and
Their Tunability Towards Oxygen Atom Transfer
Elon A. Ison,† Jeanette E. Cessarich, Nicholas E. Travia, Phillip E. Fanwick, and
Mahdi M. Abu-Omar*
Contribution from the Brown Laboratory, Department of Chemistry, Purdue UniVersity, 560
OVal DriVe, West Lafayette, Indiana 47907
Received August 1, 2006; E-mail: mabuomar@purdue.edu
Abstract: A facile method is described for the synthesis of cationic Re(VII) cis oxo imido complexes of the
form [Re(O)(NAr)(salpd)+] (salpd ) N,N′-propane-1,3-diylbis(salicylideneimine)), 4, [Re(O)(NAr)(saldach)+]
(saldach ) N,N′-cyclohexane-1,3-diylbis(salicylideneimine)), 5, and [Re(O)(NAr)(hoz)2+] (hoz ) 2-(2′-
hydroxyphenyl)-2-oxazoline) (Ar ) 2,4,6,-(Me)C6H2; 4-(OMe)C6H4; 4-(Me)C6H4; 4-(CF3)C6H4; 4-MeC6H4-
SO2), 6, from the reaction of oxorhenium(V) [(L)Re(O)(Solv)+] (1-3) and aryl azides under ambient
conditions. Unlike previously reported cationic Re(VII) dioxo complexes, these cationic oxo imido complexes
can be obtained on a preparative scale, and an X-ray crystal structure of [Re(O)(NMes)(saldach)+], 5a,
has been obtained. Despite the multiple stereoisomers that could arise from tetradentate ligation of
salen ligands to rhenium, one major isomer is observed and isolated in each instant. The electronic
rationalization for stereoselectivity is discussed. Investigation of the mechanism suggests that the reactions
of Re(V) with aryl azides proceed through an azido adduct similar to the group 5 complexes of Bergman
and Cummins. Treatment of the cationic oxo imido complexes with a reductant (PAr3, PhSMe, or PhSH)
results in oxygen atom transfer (OAT) and the formation of cationic Re(V) imido complexes. [(salpd)Re-
(NMes)(PPh3)+] (7) and [(hoz)2Re(NAr)(PPh3)+] (Ar ) m-OMe phenyl) (9) have been isolated on a
preparative scale and fully characterized including an X-ray single-crystal structure of 7. The kinetics of
OAT, monitored by stopped-flow spectroscopy, has revealed rate saturation for substrate dependences.
The different plateau values for different oxygen acceptors (Y) provide direct support for a previously
suggested mechanism in which the reductant forms a prior-equilibrium adduct with the rhenium oxo
(ReVII ) OrY). The second-order rate constants of OAT, which span more than 3 orders of magnitude
for a given substrate, are significantly affected by the electronics of the imido ancillary ligand with
electron-withdrawing imidos being most effective. However, the rate constant for the most active oxo imido
rhenium(VII) is 2 orders of magnitude slower than that observed for the known cationic dioxo Re(VII)
[(hoz)2Re(O)2+].
The use of heptavalent rhenium oxo complexes as oxidation
catalysts has been extensively developed during the past 15
years. Particularly noteworthy is the chemistry of methylrhenium
trioxide (MTO) which has found wide use in oxidation
catalysis.1 Because of the success of MTO, catalyst systems
derived from this molecule have been of interest for a wide
variety of transformations. Research activity in recent years has
focused on inorganic and/or organometallic derivatives of MTO
primarily possessing the LReO3 trioxo core (where L is an
anionic ligand).2 In contrast, less research has involved the use
of the cationic cis dioxo rhenium(VII) [L2ReO2+] framework.
In these complexes, the high oxidation state combined with the
cationic charge results in these species being very reactive. An
example of this enhanced reactivity can be seen in the chemistry
of the cis dioxo Re(VII) cations [{HB(pz)3Re(O)2R]+ (R ) Ph,
Et, or Bu; and HB(pz)3 ) tris(pyrazolyl)borate) where the first
example of the thermal migration of a ligand from a metal center
to an oxo ligand has been observed.3 We have also shown the
cationic Re(VII) dioxo complex [Re(O)2(hoz)2]+ (hoz ) 2-(2′-
hydroxyphenyl)-2-oxazoline) to be a catalyst for the reduction
of perchlorate via an oxygen atom transfer mechanism.4 These
two cases are the only reported examples of characterizable
cationic cis dioxo rhenium(VII) complexes, [L2Re(O)2+]. How-
ever, in both cases, the complexes were generated in situ and
not isolated.5
(2) Representative examples of the LReO3 motif: (a) Toganoh, M.; Ikeda, S.;
Furuta, H. Chem. Commun. 2005, 4589-4591. (b) Hegetschweiler, K.; Egli,
A.; Herdtweck, E.; Herrmann, W. A.; Alberto, R.; Gramlich, V. HelV. Chim.
Acta 2005, 88, 426-434. (c) Shan, X.; Ellern, A.; Espenson, J. H. Angew.
Chem., Int. Ed. 2002, 41, 3807-2809. (d) Deubel, D. V.; Frenking, G. J.
Am. Chem. Soc. 1999, 121, 2021-2031. (e) Herrmann, W. A.; Ding, H.;
Kuehn, F. E.; Scherer, W. Organometallics 1998, 17, 2751-2757. (f) Gable,
K. P.; Juliette, J. J. J.; Li, C.; Nolan, S. P. Organometallics 1996, 15, 5250-
5251. (g) Paulo, A.; Domingos, A.; Marcalo, J.; Pires de Matos, A.; Santos,
I. Inorg. Chem. 1995, 34, 2113-2120.
† Present address: Department of Chemistry, North Carolina State
University, Campus Box 8204, Raleigh, NC 27695.
(1) (a) Ramao, C. C.; Kuhn, F. E.; Hermann, W. A.; Chem. ReV. 1997, 97,
3197-3246 and references therein. (b) Espenson, J. H. Chem. Commun.
1999, 479-488. (c) Owens, G. S.; Arias, J.; Abu-Omar, M. M. Catal. Today
2000, 55, 317-363.
(3) Brown, S. N.; Mayer, J. M. J. Am. Chem. Soc. 1996, 118, 12119-12133.
(4) McPherson, L. D.; Drees, M.; Khan, S. I.; Strassner, T.; Abu-Omar, M.
M. Inorg. Chem. 2004, 43, 4036-4050.
9
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J. AM. CHEM. SOC. 2007, 129, 1167-1178
1167

A R T I C L E S
Ison et al.
is believed to involve an organo-azido intermediate, and in two
cases metal-azido complexes have been isolated.8 Recently, we
reported yet another mechanism for the reaction of organic
azides with Mn(III) corroles that does not involve organo-azido
intermediates; rather, the metal complex reacts with a transitory
triplet nitrene generated upon thermolytic or photolytic activation
of selected aryl azides.9 The use of aryl azides to generate
transition metal imidos is of interest because metal imides have
been implicated as active intermediates in group transfer
catalysis.11
As part of our continuing studies on the interactions of
transition metals with organic azides, we investigated the
reactions of the cationic oxorhenium salen complexes, [(salpd)-
Re(O)(Solv)][B(C6F5)4] (1),12 and [(saldach)Re(O)(Solv)]-
[B(C6F5)4] (2),12 and the mono-oxo oxazoline complex [(hoz)2Re-
(O)(Solv)][B(C6F5)4] (3)13 (Figure 1). Herein we report the
synthesis and full characterization of novel cationic rhenium-
(VII) oxo-imido complexes obtained from reactions with aryl
azides under ambient conditions. We also examine the effect
that systematic variation of the electronic properties of the imido
ligand has on the oxidizing ability of these complexes. The
reaction rates for oxygen atom transfer (OAT) from [ReVII(O)-
(NR)+] to acceptor substrates have been measured and compared
to those of the isoelectronic dioxo complex [(hoz)2Re(O)2+].
This study illustrates the ancillary ligand effect of imido [NR]
vs oxo [O] on OAT reactions.
Figure 1. Cationic oxorhenium salen and oxazoline complexes 1-3.
Results and Discussion
Synthesis of Cationic Rhenium(VII) Oxo Imido Com-
plexes. Treatment of the cationic oxorhenium complexes 1-3
with 1 equiv of an aryl azide results in an immediate color
change from green to red and the formation of the cationic oxo
1
imido rhenium complexes 4-6 (Scheme 1). H and 13C NMR
Figure 2. X-ray single-crystal structure of [(saldach)Re(O)(NMes)]-
[B(C6F5)4], 5a. Thermal ellipsoids are 50%. Hydrogens and the anion
[B(C6F5)4-] have been removed for clarity. Selected bond distances (Å)
and angles (deg). Re-O, 1.714(3) Å; Re-O1, 2.052(3); Re-O22, 1.914-
(3); Re-N8, 2.070(4); Re-N15, 2.192(4); Re-N30, 1.751(4); N30-C31-
Re, 164.7(3); O-Re-N30, 100.9(2); O-Re-O22, 102.0(2); N30-Re-
O22, 103.3(2); O-Re-O1, 163.4(1); N30-Re-O1, 93.5(2); O22-Re-
O1, 82.5(1); O-Re-N8, 90.0(2); N30-Re-N8, 94.0(2); O22-Re-N8,
156.5(2); O1-Re-N8, 80.6(1); O-Re-N15, 82.3(2); N30-Re-N15,
168.0(2); O22-Re-N15, 87.2(1); O1-Re-N15, 81.9(1); N8-Re-N15,
74.3(1).
spectra are consistent with a cis orientation of the imido and
oxo ligands. The 2,4,6-trimethyl phenyl (mesityl) imido com-
plexes with the salen-type ancillary liagnds, 4 and 5a, feature
equivalent ortho-methyl groups in their 1H spectra (δ 2.6, 6H),
indicative of free rotation in solution about the N-CAr bond.
In contrast, the mesityl imido complex of oxazoline, 6a, displays
1
two ortho-methyl peaks in the H spectrum (δ 3.04, 3H and
2.80, 3H) at room temperature. The two methyl peaks coalesce
in the VT-NMR experiment at 80 °C. The synthesis of
complexes 4-6 from aryl azides is attractive because (1) the
A natural complement to this class of compounds is com-
plexes possessing the oxo-imido framework [L2Re(O)(NR)+].6
The tunable electronic properties of the imido ligand combined
with the ability to vary its steric bulk are expected to provide
complexes that are interesting to study in the context of atom
transfer reactions. However, the synthesis and reactivity of these
complexes until now have not been reported.
One common approach for the synthesis of imido complexes
involves the decomposition of organic azides with the formation
of dinitrogen as a byproduct.7 The mechanism for these reactions
(8) (a) Proulx, G.; Bergman, R. G. Organometallics 1996, 15, 684-692. (b)
Proulx, G.; Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 6382-6383. (c)
Fickes, M. G.; Davis, W. M.; Cummins, C. C. J. Am. Chem. Soc. 1995,
117, 6384-6385.
(9) Abu-Omar, M. M.; Shields, C. E.; Edwards, N. E.; Eikey, R. A. Angew.
Chem., Int. Ed. 2005, 44, 6203-6207.
(10) (a) Groves, J. T.; Takahashi, T. J. Am. Chem. Soc. 1983, 105, 2073-2074.
(b) Eikey, R. A.; Abu-Omar, M. M. Coord. Chem. ReV. 2003, 243, 83-
124.
(11) Examples of the reactions of organic azides with transition metals: (a)
Hu, X.; Mayer, K. J. Am. Chem. Soc. 2004, 126, 16322-16323. (b) Brown,
S. D.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2003, 125, 322-323.
(c) Walstrom, A.; Pink, M.; Yang, X.; Tomaszewski, J.; Baik, M.-H.;
Caulton, K. G. J. Am. Chem. Soc. 2005, 127, 5330-5331. (d) Lucas, R.
L.; Powell, D. R.; Borovik, A. S. J. Am. Chem. Soc. 2005, 127, 11596-
11597. (e) Jenkins, D. M.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc.
2002, 124, 11238-11239. (f) Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem.
Soc. 2001, 123, 4623-4624. (g) Mindiola, D. J.; Hillhouse, G. L. Chem.
Commun. 2002, 1840-1841.
(12) Ison, E. A.; Cessarich, J. E.; Du, G.; Fanwick, P. E.; Abu-Omar, M. M.
Inorg. Chem. 2006, 45, 2385-2387.
(13) (a) Ison, E. A.; Corbin, R. A.; Abu-Omar, M. M. J. Am. Chem. Soc. 2005,
127, 11938-11939. (b) Ison, E. A.; Trivedi, R. E.; Corbin, R. A.; Abu-
Omar, M. M. J. Am. Chem. Soc. 2005, 127, 15374-15375.
(5) A search of the Cambridge Structural Database (CSD) of rhenium dioxo
complexes yielded 413 hits of which 25 are rhenium(VII) dioxo and none
of the 25 structures is cationic.
(6) A search of the Cambridge Structural Database (CSD) of rhenium oxo imido
complexes afforded only four structures of rhenium(VII): Herrmann, W.
A.; Ding, H.; Kuhn, F. E.; Scherer, W. Organometallics 1998, 17, 2751.
(b) Guiterrez, A.; Wilkinson, G.; Hussain-Bates, B.; Hursthouse, M. B.
Polyhedron 1990, 9, 2081. (c) Roesky, H. W.; Hesse, D.; Bohra, R.;
Noltemeyer, M. Chem. Ber. 1991, 124, 1913.
(7) (a) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds; Wiley:
New York, 1988. (b) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239.
9
1168 J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007

Cationic Re(VII) Oxo Imido Complexes
A R T I C L E S
Scheme 1
Scheme 2
reaction proceeds cleanly at ambient conditions requiring no
thermal or photochemical activation of the organic azide, (2)
the reactions proceed with moderate to high yields (70-90%),
and (3) the only byproduct is molecular nitrogen (N2), which
simplifies isolation and purification as there are no organic side
products to separate from the rhenium complexes.
X-ray Molecular Structure of [(saldach)Re(O)(NMes)]-
[B(C6F5)4]. Suitable crystals were obtained for X-ray diffraction
by vapor diffusion of pentane into a concentrated methylene
chloride solution of 5a at room temperature (Figure 2). Complex
5a adopts a distorted octahedral geometry with the angles around
Re ranging from 74° to 168°. The Re imido bond is linear Re-
N30-C31 (164.7(3)°) and the Re imido, Re-N30 (1.751(4)
Å) and Re oxo, Re-O (1.714(3) Å) bond lengths are within
normal range for Re-(heteroatom) multiple bonds.1,6,7 The Re
oxo bond length is similar to that of the starting cationic oxo
Re(V) complex 2.12 Bonds trans to multiply bonded ligands
are significantly lengthened (Re-O1 (2.052(3) Å) trans to oxo
and Re-N15 (2.192(4) Å) trans to imido) per the trans influence
expected for multiply bonded ligands.
only example to our knowledge of a structurally characterized
cationic cis oxo-imido Re(VII) complex. Its synthesis allows
us to compare its reaction chemistry directly to the cis
dioxo complex [(hoz)2Re(O)2+] previously generated in our
laboratory.4
Synthesis of Cationic Rhenium(V) Imido Complexes and
X-ray Molecular Structure of [(salpd)Re(NMes)(PPh3)]-
[B(C6F5)]. Treatment of the red oxo-imido Re(VII) complexes
4-6 with excess PPh3 results in an immediate color change to
green and the formation of the cationic imido complexes 7-9
and triphenyl phosphine oxide (Scheme 2).
(14) Neutral cis Re(VII) oxo-imido: (a) Gisdakis, P.; Rosch, N.; Bencze, E.;
Mink, J.; Goncalves, I. S.; Kuhn, F. E. Eur. J. Inorg. Chem. 2001, 981-
991. (b) Hermann, W. A.; Ding, H.; Kuhn, F. E.; Scherer, W. Organome-
tallics 1998, 17, 2751-2757. Neutral cis Re(VII) dioxo: (c) Wang, W.-
D.; Ellern, A.; Guzei, I. A.; Espenson, J. H. Organometallics 2002, 21,
5576-5582. (d) Espenson, J. H.; Shan, X.;; Wang, Y.; Huang, R.; Lahti,
D. W.; Dixon, J.; Lente, G.; Ellern, A.; Guzei, I. A. Inorg. Chem. 2002,
41, 2583-2591. (e) Cai, S.; Hoffmann, D. M.; Wierda, D. A. Organome-
tallics 1988, 7, 2069-2070. Cationic trioxo Re(VII): (f) Weighart, K.;
Pomp, C.; Nuber, B.; Weiss, J. Inorg. Chem. 1986, 25, 1659-1661. Cationic
cis dioxo Re(V): (g) Che, C.-M.; Cheng, J. Y. K.; Cheung, K.-K.; Wong,
K.-Y. J. Chem. Soc., Dalton Trans. 1997, 2347-2350. Neutral trans dioxo
Re(V): (h) Paulo, A.; Reddy, K. R.; Domingos, A.; Santos, I. Inorg. Chem.
1998, 37, 6807-6813. (i) Kuckmann, T. I.; Abram, U. Inorg. Chem. 2004,
43, 7068-7074. Re(VII) dioxo alkylidene: (j) Cai, S.; Hoffman, D. M.;
Wierda, D. A. Organometallics 1996, 15, 1023-1032. Oxo-imido com-
plexes of other metals: (k) Gibson, V. C.; Graham, A. J.; Jolly, M.; Mitchell,
J. P. J. Chem. Soc., Dalton Trans. 2003, 4457-4465. (l) Montilla, F.; Pastor,
A.; Galindo, A. J. Organomet. Chem. 1999, 590, 202-207.
While there have been many structural examples of tris-oxo,
tris-imido, bis-oxo imido, and bis-imido oxo congeners of
MTO,14 examples of cis dioxo Re(VII) and their oxo imido or
bis-imido analogues are rare.15 Hence, cationic derivatives of
these complexes have not been isolated and structurally
characterized. In fact, only two examples of cationic Re(VII)
dioxo complexes have been generated and detected in situ but
have not been structurally characterized.3,4 Complex 5 is the
(15) A search of the Cambridge Structural Database (CSD) of rhenium diimido
complexes yielded only 17 structures of rhenium(VII) complexes that did
not include a third multiply bonded ligand, and out of the 17 structures
only one is cationic: Cheng, J. Y. K.; Cheung, K.-K.; Chan, M. C. W.;
Wong, K.-Y.; Che, C.-M. Inorg. Chim. Acta 1998, 272, 176.
9
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A R T I C L E S
Ison et al.
Stereochemistry of Oxo-Imido and Imido-Phosphine com-
plexes. The oxo-imido complexes 4-5 and the imido complexes
7-8 feature tetradentate salen ligands. For complexes incor-
porating these ligands in an octahedral environment, three
geometric isomers are possible (trans, cis-R, and cis-â) as
depicted in (Scheme 3).18 In the cis-R isomer the phenoxide
ligands of salen are trans to each other, while in the cis-â isomer
both the phenoxides and imines are cis. In addition, two isomers
of the cis-â structure are possible with the imido ligand trans
to phenoxide or trans to the imine nitrogen. The synthesis of
complexes 4-6 is stereoselective for the cis-â isomer (by NMR
spectroscopy and X-ray crystallography). However, the current
data do not rule out the possibility of rearrangement from the
cis-â isomer to the cis-R isomer in solution.
Tetradentate salen-type ligands preferentially adopt a planar
trans geometry, but this geometric isomer is precluded on an
electronic basis for both types of complexes reported herein.
In the oxo-imido complexes, π donation by the imido and oxo
ligands is maximized through the cis configuration of these two
ligands. In contrast, the trans isomer would force the multiply
bonded ligands to compete for one of the dπ orbitals.
Figure 3. X-ray single-crystal structure of [(salpd)Re(NMes)(PPh3)]-
[B(C6F5)4], 7. Thermal ellipsoids are 50%. Hydrogens and the anion
[B(C6F5)4-] have been removed for clarity. Selected bond distances (Å)
and angles (deg). Re1-N120, 1.755(4); Re1-O119, 1.986(4); Re1-O11,
2.027(3); Re1-N112, 2.091(4); Re1-N18, 2.126(4); Re1-P130, 2.464-
(4); C121-N120-Re1, 173.1(4); N120-Re1-O119, 178.9(2); N120-
Re1-O11, 100.3(2); O119-Re1-O11, 80.9(1); N120-Re1-N112, 162.6-
(12); O119-Re1-N112, 82.3(2); O11-Re1-N112, 162.6(2); N120-Re1-
N18, 91.4(2); O119-Re1-N18, 88.4(2); O11-Re1-N18, 89.2(2); N112-
Re1-N18, 85.8(1); N120-Re1-P130, 94.4(1); O119-Re1-P130, 85.8(1);
O11-Re1-P130, 85.5(1); N112-Re1-P130, 97.8(1); N18-Re1-P130,
172.8(1).
In the case of the phosphine complexes 7-8, the π-acceptor
ligand (PPh3) favors occupying a cis position relative to the
multiply bonded imido ligand in order to align (overlap) σ* on
PPh3 with d2xy. Thus the stereoselectivity realized in the
synthesis of complexes 4-6 and 7-9 can be rationalized on
the basis of electronics, which is minimize π competition among
π donating ligands (4-6) and maximize overlap between dx2y
and σ* orbitals of PPh3 (7-9). Similar electronic arguments
can be invoked to rationalize the preference for cis-â over cis-
R. In d0 oxo-imido complexes, the cis-R isomer forces the π
donating phenoxide ligands trans to each other, and they would
be competing for donation into the same d orbital. In the cis-R
isomer of imido-phosphine complexes 7-9, the phenoxide
ligands reside in the same plane as the filled dxy orbital.
From the X-ray crystal structures for 5a and 7, there also
appears to be a stereoselective preference for the cis-â isomer
with imido trans to the imine group of the saldach ligand in 5a
and trans to the phenoxy group in 7. Again this stereochemical
preference can be rationalized based on the need to minimize
π-donor competition. In the d0 oxo-imido complexes, a strong
π donor (oxo or imido) must be trans to a π-donating phenoxide
ligand in either of the cis-â geometric isomers. The isomer
with the oxo ligand trans to phenoxide is favored because the
imido ligand is a stronger π donor than the oxo ligand, and
such arrangement allows the stronger π donor (imido) to
maximize its π interactions. As mentioned above, an occupied
molecular orbital (d2xy) occurs in the plane formed by
the saldach nitrogens and one phenoxide ligand in the Re(V)
imido-phosphine complexes. As a result, the strongly π-donating
imido ligand is not likely to occupy the fourth position in the
equatorial plane because such arrangement would result in
filled-filled interactions between d2xy and a lone pair on the
imido nitrogen.
Complexes 7-9 all feature cis (to imido) coordination of
triphenyl phosphine. In all complexes, the chemical shifts of
the triphenyl phosphine ligand are shifted upfield (-4 to -18
ppm) in the 31P spectra relative to free triphenyl phosphine. The
product of oxygen atom transfer from 4 was isolated on a
preparative scale, and suitable crystals were obtained for X-ray
diffraction by vapor diffusion of pentane into a concentrated
methylene chloride solution of 7 at room temperature
(Figure 3).
Complex 7 adopts a distorted octahedral geometry with the
angles around Re ranging from 82° to 173°. The Re imido bond
C121-N120-Re1 is linear (173.1(4)°), and the Re imido bond
length (1.755(4) Å) is within normal range and similar to that
of the Re(VII) oxo-imido complex described above. The Re
phosphorus bond length, Re-P130 (2.464(1) Å), is within
normal range.16 The Re oxygen bond cis to the imido ligand,
Re1-O11, (2.027(3) Å), is significantly lengthened (cf. to Re1-
O22 in 5a, 1.914(3) Å). The lengthening of this bond results
from a repulsive interaction between the lone pairs on the
alkoxide ligand and the dxy electrons in this d2 metal center. As
a result, the Re oxygen bonds cis (2.027(3) Å) and trans (1.986-
(4) Å) to the imido ligand have similar bond lengths. This is
unexpected given the strong trans influence of the imido ligand.
Examples of filled-filled interactions between transition metal
orbitals and lone pairs on ancillary ligands have been observed
in other d2 metal systems.17
Similar arguments have been advanced for the stereochemical
preferences in oxo-imido salen complexes involving other
(17) (a) Mills, R. C.; Wang, S. W. S.; Abboud, K. A.; Boncella, J. M. Inorg.
Chem. 2001, 40, 5077-5082. (b) Cammeron, T. M.; Abboud, K. A.;
Boncella, J. M. Chem. Commun. 2001, 13, 1224-1225. (c) Ison, E. A.;
Abboud, K. A.; Boncella, J. M. Organometallics 2006, 25, 1557-1564.
(18) Knight, P. D.; Scott, P. Coord. Chem. ReV. 2003, 242, 125-143.
(16) Chakraborty, I.; Panda, B. K.; Gangopadhyay, J.; Chakravorty, A. Inorg.
Chem. 2005, 44, 1054-1060.
9
1170 J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007

Cationic Re(VII) Oxo Imido Complexes
A R T I C L E S
Scheme 3
metals. For example, the cis-â isomer with the imido trans to
the imine ligand has been recently observed in [Mo(O)NtBu)-
{(3,5-tBu2)2salpd}], and this geometry was rationalized based
on the relative π donor strengths of the oxo and imido ligands.19
However, the observation of the opposite arrangement (imido
trans to phenoxide) in [Mo(O)(N-2,6-iPr2C6H3){(7-Me)2salen}]
by the same authors suggests that caution should be exercised
when applying qualitative “back of the envelope” electronic
arguments, as other factors may be responsible for the geometric
preference.
Scheme 4
An interesting feature of the stereochemistry of the oxo-imido
and imido-phosphine complexes described here is the fact that
the stereochemistry changes as a result of OAT and the imido
ligand switches form trans to imine (oxo-imido) to trans to
phenoxide (imido-phosphine). The mechanistic implications of
this change in geometry will be the subject of a future
publication.
Mechanism of Oxo-imido Formation. To date two mech-
anisms have been postulated for the interaction of aryl azides
with transition metals. Both the Bergman and Cummins
laboratories have isolated azido adducts of tantalum and
vanadium, respectively, and observed their thermal decomposi-
tion to imido complexes with the evolution of N2.8 Recently,
we have proposed a different mechanism for the reaction of
Mn(III) corrole with aryl azides in which the azide is activated
thermally or photochemically to afford a nitrene intermediate
that is subsequently trapped by the manganese corrole.9 Ad-
ditionally ortho substituents on the aryl azide are necessary, and
the reaction exhibits complex dependencies on Mn with a zeroth-
order dependence for a significant portion of the reaction.9
In contrast, the formation of complexes 4-6 does not require
thermal or photochemical activation, and the reaction is not
restricted to aryl azides containing ortho substituents. The
reaction reported herein is quite versatile and proceeds with both
electron rich and electron deficient azides (Scheme 1). In light
of these observations it is apparent that the formation of
complexes 4-6 does not proceed via nitrene capture. The
kinetics of the formation of 5d from 2 and p-CF3 phenyl azide
were studied in detail by monitoring product formation in the
19F spectra at ambient conditions. As shown in Figure 4, the
reaction exhibits first-order dependencies on complex 2 (time
profile) and p-CF3 phenyl azide (inset).
When 2 is treated with 1 equiv of p-CF3 phenyl azide at
-80 °C in CD2Cl2, in addition to signals for the organic azide
(-62.2 ppm) and 5d (-63.5 ppm), an additional peak is
observed at -63.8 ppm in the 19F spectrum in the integral ratios
of 13:6:1, respectively. When the temperature was raised to
-30 °C, the azide signal (-62.2 ppm) and the signal at -63.8
ppm converted slowly to 5d. These results suggest that the
reaction of complexes 1-3 with aryl azides proceeds through
a mechanism analogous to that proposed by Bergman for the
reaction of organic azides with Cp2TaMe(PMe3); i.e., an
organoazido adduct of rhenium is initially formed followed by
its decomposition to give the Re(VII) oxo imido complex and
N2. A consensus mechanism is depicted in Scheme 4 along with
(19) Ramnauth, R.; Al-Juaid, S.; Motevalli, M.; Parkin, B. C.; Sullivan, A. C.
Inorg. Chem. 2004, 43, 4072-4079.
9
J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007 1171

A R T I C L E S
Ison et al.
Figure 4. A typical time profile for the reaction of 2 with p-CF3 phenyl
azide. The signal for the product 5d at δ -63.5 was monitored by 19F NMR
spectroscopy. Conditions: 20.8 mM 2, 8.0 M CH3CN, 0.10-0.65 M p-CF3
phenyl azide in C6D6 at 298 K. The data are shown for 0.20 M p-CF3 phenyl
azide. The fit is to single-exponential first-order equation [5d]t ) [2][1 -
exp(-kψt)]. Inset: Dependence on p-CF3 phenyl azide. Linear fit gives a
second-order rate constant (9.4 ( 0.8) × 10-3 M-1 s-1 (R2 ) 0.977).
Figure 5. PAr3 dependences for the reaction of [(saldach)Re(O)(NMes)]-
[B(C6F5)4] , 5a, with PAr3 (Ar ) phenyl, p-OMe phenyl, or p-CF3 phenyl)
monitored at 500 nm. Conditions: [5a] ) 50 µM and [PPh3] ) 0.625-
50.0 mM, [P(p-CF3Ph)3] ) 0.313-100 mM, or [P(p-OMePh)3] ) 0.313-
5.0 mM in CH3CN at 298 K. The fits are to eq 2 for PPh3 and P(p-CF3Ph)3
and to a linear equation for P(p-OMePh)3.
According to eq 1, K1k2 ) slope × [NCCH3]; K1k2 ) 0.075 ( 0.006 s-1
.
its corresponding rate law in eq 1, assuming a prior equilibrium
for the formation of the organoazido adduct/intermediate.
The observed reactivity is consistent with the fact that Re-
(V) complexes used here are easier to oxidize than Mn(III) and
therefore do not require thermal or photochemical activation
of the azide. Such reactivity is consistent with the periodic trend
that second and third row transition metals stabilize higher
oxidation states and thus tend to be more reducing than their
first row counterparts.
Oxygen Atom Transfer Reactions of Rhenium(VII) Oxo-
Imido Complexes. The reactions of 5 with PPh3 were inves-
tigated under pseudo-first-order conditions using stopped-flow
spectroscopy. The progress of the reaction was monitored at
500 nm, where the cationic rhenium(VII) oxo-imido complex
[(saldach)Re(NAr)(O)][B(C6F5)4], 5, absorbs but the rhenium-
(V) imido product [(saldach)Re(NAr)(OPPh3)][B(C6F5)4], 10,
does not. The disappearance of 5 monitored at 500 nm displayed
clean first-order kinetics in Re (Figure S1). A plot of kψ versus
[PPh3] revealed saturation kinetics for the dependence on PPh3
(Figure 5). The plateau value was not affected by the addition
of excess triphenyl phosphine oxide. Furthermore, when the
reaction of 5 with triphenyl phosphine was monitored by 31P
NMR spectroscopy a triphenyl phosphine oxide adduct (δ 41.0),
10, was observed prior to the formation of the phosphine
adduct 8 (isolated product). These results suggest that the
reduction of 5 occurs at a different rate than the formation of
8; i.e., the substitution of triphenyl phosphine oxide by free
triphenyl phosphine is slower than the reduction of 5 to the
rhenium(V) imido phosphine oxide adduct, [(saldach)Re(NAr)-
(OPPh3)+] (10).
for our complexes suggests that mechanisms involving rate-
determining attack of PPh3 on the metal oxo can be ruled out.
The data presented here appear to be in agreement with three
kinetically indistinguishable schemes. The oxo-imido complex
reacts with PPh3 to form, in a prior equilibrium step, an adduct
preceding OAT (Scheme 5A, eq 2). In this adduct initial attack
of the PPh3 ligand results in an intermediate that resembles
[Re(VII)dO---PPh3] more than [Re(V)rOdPPh3]. By analogy to
Taube’s inner-sphere electron transfer, the intermediate in
Scheme 5A is the precursor complex and the product the
successor complex. Although intermediates of this form have
not been directly isolated, similar intermediates have been
proposed in the reaction of bis(arylimido)oxorhenium(VII)
complexes,22 oxorhenium(V) complexes,23 and arylimido ru-
thenium(IV) complexes24 with organic phosphines. Alterna-
tively, the oxo-imido complex isomerizes to an active steady-
state intermediate where the stereochemistry of the imido ligand
switches from trans to imine to trans to phenoxy (most likely
via the cis-R isomer). The resulting intermediate then subse-
quently reacts with PPh3 (Scheme 5B, eq 3). Another mechanism
along the same lines is separation of the ion pair
[LReVII(O)(NAr)+][B(C6F5)4-] (Scheme 5C, eq 4). This last
pathway is unlikely because the reactions were carried out in a
polar medium (acetonitrile) where the ions are expected to be
well separated.
In order to interrogate these mechanisms further, we compared
the kinetic behavior of three different triarylphosphines, PAr3
(Ar ) phenyl, p-CF3 phenyl, or p-OMe phenyl). Changing the
phosphine substrate would have an effect on the saturation value
in Scheme 5A, as the saturation value is governed by k4.
Metal oxo complexes are known to oxidize organic phos-
phines, and the mechanism for this reaction has been extensively
discussed and is generally believed to proceed through a direct
attack of the phosphine on the metal oxo.20 Usually these
reactions exhibit bimolecular kinetics, and saturation kinetics
is not observed.21 The observed kinetic saturation in [phosphine]
(21) (a) Pietsch, M. A.; Hall, M. B. Inorg. Chem. 1996, 35, 1273-1278. (b)
Tucci, G. C.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 1998, 37, 1602-
1608.
(22) Wang, W.-D.; Guzei, I. A.; Espenson, J. H. Organometallics 2001, 20,
148-156.
(23) Li, M.; Ellern, A.; Espenson, J. H. J. Am. Chem. Soc. 2005, 127, 10436-
10447.
(24) Leung, W.-H.; Hun, T. S. M.; Hou, H.-W.; Wong, K.-Y. J. Chem. Soc.,
Dalton Trans. 1997, 237-243.
(20) Seymore, S. B.; Brown, S. N. Inorg. Chem. 2000, 39, 325-332.
9
1172 J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007

Cationic Re(VII) Oxo Imido Complexes
A R T I C L E S
Scheme 5
structural changes were observed to accompany OAT of the
Re(V) oxazoline complex 3 to the Re(VII) dioxo complex
[(hoz)2Re(O)2+] (11).4 The Re(V) complex, 3, begins with a
solvent molecule (water or acetonitrile) in a trans configuration
with respect to the oxo ligand, and as a result of oxygen atom
transfer the two oxo ligands in the Re(VII) dioxo complex, 11,
are arranged cis. These structural changes were proposed to
occur as a result of substitution of the solvent molecule in 3,
with an oxo donor substrate that enters cis to the oxo ligand.
As a result of the cis entry of the oxo donor substrate, the
oxazoline ligand in 3 undergoes a geometrical change to
accommodate the incoming oxo donor ligand and facilitate OAT.
Similar geometric changes associated with ligand substitution
reactions have also been suggested for dithiolate Re(V) com-
plexes.25 Thus a reasonable mechanism for substitution of
triphenyl phosphine oxide via a solvent adduct is depicted in
Scheme 6, which accounts for the change in imido ligand from
trans to imine to trans to phenoxide. The details of the
mechanism of substitution of OPPh3 and the geometric changes
associated with this substitution, however, are beyond the scope
of this article.
Comparison of Oxygen Atom Transfer (OAT) Reactivity.
The synthesis of oxo-imido complexes 4-6 allows us to
compare directly the chemistry of these complexes with the
cationic cis dioxo complex [(hoz)2Re(O)2+] (11). This complex
has been shown to be an effective catalyst for the reduction of
perchlorate at room temperature, and it has been demonstrated
that oxygen atom transfer is the operational mechanism during
this catalysis.4 Unlike, complexes 4-6, which are stable to air
and moisture and isolable on a preparative scale, 11 could only
be prepared in situ and could not be isolated. In addition, in
complexes 4-6, the sterics and electronics of the substituents
on the imido ligands can be varied in order to tune their
reactivity.
First, we examined the effect changing the electronics of the
imido substituent has on the rate of OAT to PPh3 by measuring
the rates for a series of complexes at 500 nm in CH3CN by
stopped-flow spectroscopy. All complexes displayed first-order
dependencies on Re and saturation kinetics on PPh3. The rate
and equilibrium constants in accordance with Scheme 5A and
eq 2 are summarized in Table 1. From Table 1, two features of
this system are readily apparent. The oxazoline complex 6a is
somewhat less reactive (ca. 0.25 times) than the corresponding
saldach complex 5a (second-order rate constants 1.1 × 104 vs
4.3 × 104 M-1 s-1). Second, the rate of oxygen atom transfer
reactions is influenced greatly by the electronics of the ancillary
imido ligand such that the rate increases dramatically as the
imido ligand becomes more electron-deficient. The tosyl
substituted imido 5e reacts faster than the stopped-flow dead
time, and the p-CF3 phenyl substituted oxo imido complex 5d
is approximately 13 times more reactive than the corresponding
mesityl imido complex 5a. Thus a general order of reactivity
for the imido ligand substituent is Tos > p-CF3 phenyl > Mes.
This trend is indicative of electrophilic oxo transfer from the
oxo-imido complexes to the substrate.
However, changing the phosphine would not affect the saturation
values k5 and k7 according to Schemes 5B and C. Furthermore,
the observation of saturation kinetics permits the separation of
the “apparent” second-order rate constant to its components,
an equilibrium constant for formation of the phosphine adduct
and a first-order rate constant for the redox atom transfer reaction
in which the RedO bond is cleaved and the PdO bond is
formed.
Plots of kψ versus [PAr3] for all three phosphine substrates
are shown in Figure 5. The kinetic data clearly favor the
mechanism presented in Scheme 5A because the plateau values
are substrate specific. P(p-OMePh)3 does not exhibit saturation
within the measurement limits of stopped-flow. Nevertheless,
all three phosphine substrates give second-order rate constants
that follow a Hammett correlation with a negative reaction
constant, F ) -0.6 ( 0.1 (Figure S2).
A significant structural change occurs along the oxygen atom
transfer reaction pathway from the Re(VII) oxo-imido complex
to the Re(V) imido phosphine complex. The imido ligand in
complexes 4-6 is trans to the imine group of the saldach ligand
and becomes trans to the phenoxide group of the saldach ligand
in the isolated products 7-9. Previously, in our labs similar
In order to compare the rates of OAT directly with the cis
dioxo complex, we examined the rates of OAT to other
substrates because OAT to PPh3 from [(hoz)2Re(O)2+] (11) was
(25) Lahti, D. W.; Espenson, J. H. J. Am. Chem. Soc. 2001, 123, 6014-6024.
9
J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007 1173

A R T I C L E S
Ison et al.
a
Table 1. Comparison of Rate and Equilibrium Constants for the Reaction of Select Oxo-Imido Complexes with PPh3
a Values are obtained from a nonlinear fit to the equation (-d[LRe(O)(NAr)+])/dt ) (k4[LRe(O)(NAr)+][PPh3])/(1/K3 + [PPh3]). b This rate was not
observed because it is faster than the dead time of the stopped-flow analyzer (2 ms).
Scheme 6
too fast to measure by stopped-flow. The second-order rate
constants for these reactions are gathered in Table 2.
The higher reactivity of the dioxo complex in comparison to
the electron-withdrawing tosyl imido complex (entry 1 vs 2) is
a direct demonstration of the enhanced electron donation exerted
by the imido ligand, which stabilizes rhenium(VII) more
effectively than a terminal oxo.
As expected for electrophilic oxygen atom transfer, aryl
sulfides are less reactive than aryl thiols,26 which are less
reactive than PPh3 (entries 3-5). The rate of OAT from
[(hoz)2Re(O)2+] has been determined and can be directly
compared with our isoelectronic cationic rhenium(VII) oxo-
imido complexes. From Table 2, a dramatic effect on the rates
of OAT is seen as the imido substituent is varied. While the
p-CF3 phenyl substituted oxo-imido complex is 105 times less
reactive than the dioxo, changing the imido substituent to the
more electron-withdrawing tosyl group leads to a 1000-fold
improvement in the rate of OAT (entries 2 and 3), and this tosyl
imido complex is now only 300 times less reactive than the
dioxo complex. This is a clear demonstration of the tunabilty
of these oxo-imido complexes toward atom transfer reactions.
Summary and Conclusions
The development of methods for the synthesis of transition
metal imido complexes is of interest because of their implication
in catalysis, particularly, in [NR] group transfer chemistry. We
have demonstrated a facile method for the synthesis of cationic
Re(VII) cis oxo-imido complexes from aryl azides under
ambient conditions without the need for thermal or photochemi-
cal activation of the organic azide. Mechanistic interrogation
suggests the reactions of Re(V) with aryl azides proceed through
an azido adduct similar to the group 5 complexes of Bergman
and Cummins.8 The only byproduct from the organic azide is
N2; thus the method presented in this paper does not require
(26) For an example of thiols oxidation to disulfides with rhenium oxo, see:
Abu-Omar, M. M.; Khan, S. I. Inorg. Chem. 1998, 37, 4979-4985.
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Cationic Re(VII) Oxo Imido Complexes
A R T I C L E S
Table 2. Second-Order Rate Constants for the Following OAT Reaction: LReVII(O)(E)+ + Y f LReV(E)+ + YO; E ) O or NAr, and L ) hoz
or Saldacha
a Apparent second-order rate constant ) K3k4 obtained from a nonlinear fit to the equation (-d[LRe(O)(NAr)+])/dt ) (k4[LRe(O)(NAr)+][Y])/(1/K3 +
[Y]). b Obtained from ref 4. c Obtained from a linear fit because the data for this substrate did not show saturation within the stopped-flow time scale.
tedious chromatography to separate organic byproducts. Fur-
thermore, the synthesis of imido complexes from aryl azides in
high yield has allowed us to characterize crystallographically
the first example of a cationic Re(VII) oxo-imido complex.
Unlike the previously reported cationic Re(VII) dioxo com-
plexes, which have been observed in situ but not isolated,3,4
the cationic oxo-imido complexes are obtained on a preparative
scale. In addition, the chemistry of these complexes toward
oxygen atom transfer (OAT) reactions can be compared directly
with the cationic dioxo complex [(hoz)2Re(O)2+], which was
previously shown to be an effective OAT catalyst.4 Rates of
OAT reactions are significantly affected by the electronics of
the imido ancillary ligand with electron-withdrawing imidos
being most effective. For example, the tosyl substituted imido
complex is more reactive (ca. 103 times) than the p-CF3 phenyl
imido complex, which in turn is an order of magnitude more
reactive than the mesityl imido complex. However, the most
reactive tosyl imido complex remains 300 times slower in OAT
reactions than the dioxo analogue. Consistent with the observed
trend is the rate sensitivity toward the oxygen acceptor. Aryl
phosphines are more reactive than thiophenol (PhSH), which
is more reactive than thioanisole (PhSMe). Also within the
family of aryl phosphines, electron-donating substituents are
more reactive than electron-withdrawing substituents affording
a negative Hammett reaction constant. These reactivity trends
confirm electrophilic oxygen atom transfer from Re(VII) oxo-
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J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007 1175

A R T I C L E S
Ison et al.
[(saldach)Re(O)(NAr)][B(C6F5)4], Ar ) p-OMe Phenyl (5b).
[(saldach)Re(O)(Solv)][B(C6F5)4], 2, (0.100 g, 0.080 mmol) in CH2-
Cl2 was added to p-OMe phenyl azide (0.0125 g, 0.084 mmol). 5b
imido complexes. The ability to tune the reactivity of cationic
rhenium(VII) imido complexes should have a bearing on the
intelligent design of catalysts for [NR] group transfer from
organic azides, an appealing methodology because its only waste
is molecular nitrogen (N2). Work is currently being undertaken
in our laboratory toward the development of suitable complexes
for such group transfer catalysis.
1
was obtained in 63% (0.084 g) yield. H NMR (200 MHz, CD3CN):
δ 8.58 (s, 1H, CdNsH), 8.51 (s, 1H, CdNsH), 7.84-7.82 (1H,
overlapping aromatic), 7.77-7.69 (2H, overlapping aromatic), 7.50-
7.47 (1H, overlapping aromatic), 7.30-7.27 (2H, overlapping aromatic),
7.05-6.98 (2H, overlapping aromatic), 6.90-6.86 (2H, overlapping
aromatic), 6.76-6.72 (2H, overlapping aromatic), 4.31 (m, 1H, saldach
CH2), 4.02 (s, 3H, p-CH3), 3.15 (m, 1H, saldach CH2), 3.69 (m, 1H,
saldach CH2), 2.51-2.48 (m, 1H, saldach CH2), 2.17-2.14 (m, 3H,
saldach CH2), 1.65-1.44 (m, 3H, saldach CH2). 13C NMR (200 MHz,
CD3CN): δ 167.7, 164.5, 162.0, 157.3, 150.0, 147.4, 145.2, 139.2,
138.1, 137.1, 135.9, 135.3, 133.2, 125.7, 123.5, 120.3, 118.8, 117.2,
114.3, 79.2, 73.5, 56.9, 31.2, 29.4, 24.8, 24.1. Elemental Analysis Calcd
for C51H27BF20N3O4Re: C, 46.3; H, 2.06; N, 3.18. Found: C, 46.6; H,
2.16; N, 3.03.
Experimental Section
Materials and Methods. Reactions were performed in a nitrogen-
filled glovebox or open to the environment as stated. Solvents were
degassed and purified with a solvent purification system (Anhydrous
Engineering INC.) prior to use. Thiols, sulfides, and aryl phosphines
were purchased from Aldrich and used as received. The cationic
rhenium mono-oxo salen complexes, [(salpd)Re(O)(Solv)][B(C6F5)4]
(1) and [(saldach)Re(O)(Solv)][B(C6F5)4] (2), and the mono-oxo
oxazoline complex [(hoz)2Re(O)(Solv)][B(C6F5)4] (3) were synthesized
according to published procedures.4,12 NMR spectra were recorded on
Varian Inova300 instruments. Mass spectrometry was performed by
the Purdue University Campus Wide Mass Spectrometry Center. UV-
vis spectra were recorded on a Shimadzu UV-2501 spectrophotometer.
Stopped-flow kinetics was collected on an Applied Photophysics
SX.18MV stopped-flow reaction analyzer. Data fitting was done using
KaleidaGraph 3.0 software.
[(saldach)Re(O)(NAr)][B(C6F5)4], Ar ) p-Me Phenyl (5c).
[(saldach)Re(O)(Solv)][B(C6F5)4], 2, (0.101 g, 0.080 mmol) in CH2-
Cl2 was added to p-Me phenyl azide (10.5 µL, 0.084 mmol). 5c was
obtained in 81% (0.089 g) yield. 1H NMR (300 MHz, CD2Cl2): δ 8.60
(s, 1H, CdNsH), 8.55 (s, 1H, CdNsH), 7.88-7.83 (1H, overlapping
aromatic), 7.79-7.72 (2H, overlapping aromatic), 7.49-7.44 (1H,
overlapping aromatic), 7.34-7.27 (4H, overlapping aromatic), 7.05-
6.99 (2H, overlapping aromatic), 6.65-6.62 (d, 2H, J ) 8.20 Hz,
aromatic CH), 4.34-4.28 (m, 1H, saldach CH2), 3.18-3.12 (m, 1H,
saldach CH2), 2.89 (s, 3H, p-CH3), 2.77-2.69 (m, 2H, saldach CH2),
2.52-2.45 (m, 2H, saldach CH2), 1.91-1.76 (m, 2H, saldach CH2),
1.57-1.44 (m, 2H, saldach CH2). 13C NMR (300 MHz, CD3CN): 165.4,
162.8, 150.7, 145.9, 140.3, 136.5, 134.0, 132.0, 129.5, 124.6, 121.3,
120.8, 119.6, 80.1, 74.1, 32.0, 30.2, 25.5, 24.8, 22.2. Elemental Analysis
Calcd for C51H27BF20N3O3Re: C, 46.9; H, 2.08; N, 3.22. Found: C,
47.2; H, 2.40; N, 2.92.
Synthesis of Cationic Re(VII) Oxo-Imido Complexes. [(salpd)-
Re(O)(NMes)][B(C6F5)4] (4). (Typical Procedure). [(salpd)Re(O)-
(Solv)][B(C6F5)4], 1, (0.200 g, 0.167 mmol) was dissolved in CH2Cl2.
To this solution was added 2,4,6-trimethyl phenyl azide (0.027 g, 0.167
mmol). The solution changed color from green to red and was stirred
overnight. The solvent was removed under a vacuum, and the residue
dissolved in a minimal amount of CH2Cl2. Pentane was added until a
red powder precipitated. The red powder was washed several times
1
with pentane to yield 4 in 66% (0.231 g) yield. H NMR (300 MHz,
[(saldach)Re(O)(NAr)][B(C6F5)4], Ar ) p-CF3 Phenyl (5d).
[(saldach)Re(O)(Solv)][B(C6F5)4], 2, (0.102 g, 0.085 mmol) in CH2-
Cl2 was added to p-CF3 phenyl azide (13.0 µL, 0.092 mmol). 5d was
obtained in 69% (0.079 g) yield. 1H NMR (300 MHz, CD2Cl2): δ 8.65
(s, 2H, CdNsH), 7.93-7.88, (1H, overlapping aromatic), 7.80-7.74
(4H, overlapping aromatic), 7.50-7.47 (1H, overlapping aromatic),
7.39-7.29 (2H, overlapping aromatic), 7.06-7.00 (2H, overlapping
aromatic), 6.86-6.83 (d, 2H, J ) 8.20 Hz, aromatic CH), 4.36 (m,
1H, saldach CH2), 3.18 (m, 1H, saldach CH2), 2.74-2.70 (m, 1H,
saldach CH2), 2.55 (m, 1H, saldach CH2), 2.17-2.13 (m, 3H, saldach
CH2), 1.63-1.54 (m, 3H, saldach CH2). 19F NMR (300 MHz, CD2-
Cl2): δ -63.7 (s, 3F, p-CF3), -133.1 (s, 8F, B(C6F5)4-), -163.5 (t,
4F, J ) 19.9 Hz, B(C6F5)4-), -167.3 (s, 8F, B(C6F5)4-). Elemental
Analysis Calcd for C51H23BF23N3O3Re: C, 45.0; H, 1.78; N, 3.09.
Found: C, 44.7; H, 2.05; N, 2.90.
CD2Cl2): δ 8.45 (s, 1H, CdNsH), 8.34 (s, 1H, CdNsH), 7.79-7.73
(m, 1H, overlapping aromatic), 7.60-7.52 (m, 2H, overlapping
aromatic), 7.35-7.33 (m, 1H, overlapping aromatic), 7.24-7.19 (m,
1H, overlapping aromatic), 7.14-7.12 (d, 1H, J ) 8.20 Hz, aromatic
CH), 7.08 (s, 2H, overlapping aromatic), 6.96-6.91 (m, 1H, overlapping
aromatic), 6.71-6.68 (d, 1H, J ) 8.79, aromatic CH), 4.66-4.51 (m,
3H, salpd CH2), 4.10-4.04 (m, 1H, salpd CH2), 3.01 (s, 3H, p-CH3),
2.64 (s, 6H, CH3), 2.15-2.13 (m, 2H, salpd CH2). 13C NMR (300 MHz,
CD3CN): δ 168.5, 166.6, 163.4, 158.9, 154.5, 151.4, 149.7, 148.7,
146.5, 139.7, 137.1, 134.7, 133.7, 128.3, 123.8, 121.5, 121.0,
120.2, 66.9, 59.7, 31.0, 21.3, 17.8. Elemental Analysis Calcd for
C50H27BF20N3O3Re: C, 46.4; H, 2.10; N, 3.25. Found: C, 46.5; H,
2.47; N, 2.86.
[(saldach)Re(O)(NMes)][B(C6F5)4] (5a). [(saldach)Re(O)(Solv)]-
[B(C6F5)4], 2, (0.100 g, 0.080 mmol) was dissolved in CH2Cl2. To this
solution was added 2,4,6-trimethyl phenyl azide (0.0158 g, 0.099 mmol).
The solution changed color from green to red and was stirred overnight.
The solvent was removed under a vacuum, and the residue was
dissolved in a minimal amount of CH2Cl2. Pentane was added until a
red powder precipitated. The red powder was washed several times
with pentane to yield 5a in 66% (0.0737 g) yield. 1H NMR (300 MHz,
CD2Cl2): δ 8.77 (s, 1H, CdNsH), 8.75 (s, 1H, CdNsH), 7.85-7.81
(2H, overlapping aromatic), 7.57-7.51 (2H, overlapping aromatic),
7.32-7.26 (2H, overlapping aromatic), 7.09-6.99 (2H, overlapping
aromatic), 6.91-6.83 (2H, overlapping aromatic), 4.40-4.33 (m, 1H,
saldach CH2), 3.13-3.25 (m, 1H, saldach CH2), 2.77 (s, 3H, p-CH3),
2.68 (s, 6H, CH3), 2.58-2.47 (m, 2H, saldach CH2), 2.05 (m, 2H,
saldach CH2) 1.87-1.78 (m, 2H, saldach CH2), 1.60-1.40 (m, 2H,
saldach CH2). 13C NMR (300 MHz, CD3CN): δ 164.7, 161.8, 150.1,
145.4, 143.2, 139.2, 137.2, 135.8, 133.5, 127.7, 124.1, 120.5, 120.2,
79.8, 73.7, 31.5, 29.8, 25.0, 24.3, 21.1, 17.8. Elemental Analysis Calcd
for C53H31BF20N3O3Re: C, 47.7; H, 2.34; N, 3.15. Found: C, 47.7; H,
2.34; N, 2.92.
[(saldach)Re(O)(NAr)][B(C6F5)4], Ar ) p-Tolyl Sulfonyl (5e).
[(saldach)Re(O)(Solv)][B(C6F5)4], 2, (0.0500 g, 0.042 mmol) was
dissolved in CH2Cl2. To this solution was added p-tolyl sulfonyl (tosyl)
azide (6.5 µL, 0.042 mmol). The solution changed color from green to
red and was stirred overnight. The solvent was removed under a
vacuum, and the residue was dissolved in a minimal amount of CH2-
Cl2. Pentane was added until a light red/brown powder precipitated.
The powder was quickly washed several times with pentane to yield
5e in 82% (0.0472 g) yield. Complex 5e is very unstable and
decomposes quickly in both the solid state and in solution. As a result
complex 5e could only be isolated in low purity. 1H NMR (300 MHz,
CD2Cl2): δ 8.97 (s, 1H, CdNsH), 8.60 (s, 1H, CdNsH), 8.01-7.96
(m, 1H, aromatic), 7.78-7.73 (m, 3H, overlapping aromatic), 7.59-
7.56 (d, 2H, J ) 8.8 Hz, aromatic CH), 7.45-7.31 (m, 5H, overlapping
aromatic), 6.80-6.77 (d, 1H, J ) 8.20 Hz, aromatic CH), 4.38-4.30
(m, 1H, saldach CH2), 3.43 (s, 3H, p-CH3), 3.11-3.03 (m, 1H, saldach
CH2), 2.64-2.62 (m, 2H, saldach CH2), 2.43 (s, 2H, CH2), 2.30-2.14
(m, 2H, saldach CH2), 1.88-1.75 (m, 2H, saldach CH2). Elemental
9
1176 J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007

Cationic Re(VII) Oxo Imido Complexes
A R T I C L E S
Analysis Calcd for C53H31BCl4F20N3O5ReS (with two molecules of CH2-
Cl2): C, 41.32; H, 2.03; N, 2.73. Found: C, 40.64; H, 2.60; N, 2.39.
[(hoz)2Re(O)(NMes)][B(C6F5)4] (6a). A round-bottom flask equipped
with a magnetic stir bar was charged with [(hoz)2Re(O)(Solv)]-
[B(C6F5)4], 3, (0.182 g, 0.146 mmol) dissolved in CH2Cl2. To this
solution was added 2,4,6-trimethyl phenyl azide (0.0235 g, 0.147 mmol).
The reaction flask was capped, and the solution was stirred for 2 h as
it changed color from green to deep red. The solution was concentrated
under a vacuum to an approximate volume of 5 mL. With stirring 100
mL of pentane was added. Microcrystalline red/brown solid precipitated.
The precipitate was isolated by filtration, washed with pentane, and
After an hour a green film was deposited inside the flask. The light
green supernatant was removed, and the film redissolved in 10 mL of
CH2Cl2. Pentane was added until a green microcrystalline solid was
observed. The precipitate was isolated by suction filtration, washed
with pentane, and dried under a vacuum to yield 9 in 27% (0.060 g)
yield. 1H NMR (300 MHz, CD2Cl2): δ 7.87 (d, 1H, J ) 8.2 Hz), 7.56-
7.20 (18H, overlapping aromatic), 7.06 (d, 2H, J ) 5.3 Hz), 6.84 (t,
1H, J ) 7.6 Hz), 6.73 (t, 1H, J ) 7.3 Hz), 6.62 (dd, 1H, J ) 7.6 Hz,
J′ ) 2.9 Hz), 6.22 (m, 1H), 6.11 (s, 1H), 4.76-4.64 (3H, overlapping
hoz CH2), 4.46-4.29 (2H, overlapping hoz CH2), 4.16-3.99 (2H,
overlapping hoz CH2), 3.63-3.54 (4H, overlapping hoz CH2 and
m-OCH3). 31P NMR (200 MHz, CD2Cl2): δ -10.97 (s). Elemental
Analysis Calcd for C67H38BF20N3O5PRe: C, 51.2; H, 2.43; N, 2.67.
Found: C, 51.5; H, 2.44; N, 2.43.
1
dried under a vacuum to give 6a in 27% (0.031 g) yield. H NMR
(300 MHz, CD3NO2): δ 7.82 (d, 1H, J ) 8.2 Hz), 7.78 (d, 1H, J )
8.2 Hz), 7.41 (s, 1H, imido aromatic), 7.32-7.28 (2H, overlapping hoz
aromatic), 7.26 (s, 1H, imido aromatic), 6.91 (t, 1H, J ) 8.2 Hz), 6.80
(t, 1H, J ) 8.2 Hz), 6.33 (d, 1H, J ) 8.2 Hz), 6.20 (d, 1H, J ) 8.2
Hz), 5.01-4.80 (m, 5H, overlapping hoz CH2), 4.54-4.45 (m, 2H,
overlapping hoz CH2), 4.29-4.13 (m, 1H, hoz CH2), 3.29 (s, 3H), 3.04
(s, 3H), 2.80 (s, 3H).
Stopped-Flow Kinetics. Equal volumes of solutions of 4-6 in
acetonitrile (0.10 mM) and the reductant (PPh3, PhSMe, or PhSH in
excess concentrations 0.02 - 2.0 M) were mixed in the stopped-flow
analyzer at 298 K to give reaction solutions with half the loaded
concentrations (50 µM in Re and 0.01-1.0 M in the reducing substrate).
The decrease in absorbance of the Re(VII) oxo-imido species was
monitored at 500 nm under these pseudo-first-order conditions. The
kψ values were obtained by nonlinear fitting of Abs500 versus time to
the equation: Abst ) Abs∞ + (Abs0 - Abs∞) exp(-kψt). Plots of kψ
versus [reductant] showed saturation kinetics. Fits of the data to the
appropriate rate law, (-d[LRe(O)(NAr)+])/dt ) (k4[LRe(O)(NAr)+]-
[Y])/(1/K3 + [Y]) (where Y ) PAr3, PhSMe, or PhSH), yielded a first-
order rate constant (k4) and an equilibrium constant (K3) for each of
the reducing substrates.
[(hoz)2Re(O)(NAr)][B(C6F5)4], Ar ) (p-OMe)Ph, (6b). A round-
bottom flask equipped with a magnetic stir bar was charged with
[(hoz)2Re(O)(Solv)][B(C6F5)4], 3, (0.182 g, 0.146 mmol) dissolved in
CH2Cl2. To this solution was added 1 equiv of p-methoxy phenyl azide
(0.0219 g, 0.147 mmol). The solution was covered and allowed to stir
for at least 2 h as it changed color from green to red-orange. The
solution was concentrated to approximately 10 mL, and with stirring,
200 mL of pentane were added. A large microcrystalline brown solid
appeared. The precipitate was isolated by suction filtration, washed
with pentane, and dried under a vacuum to give 6b in 75% (0.145 g)
yield. 1H NMR (300 MHz, CD2Cl2): δ 7.75 (d, 2H, J ) 8.0 Hz), 7.64
(d, 2H, J ) 9.1 Hz), 7.32-7.21 (2H, overlapping hoz aromatic), 7.09
(d, 2H, J ) 9.1 Hz), 6.90-6.78 (2H, overlapping hoz aromatic), 6.29
(d, 1H, J ) 8.4 Hz, hoz aromatic), 6.18 (d, 1H, J ) 8.5 Hz, hoz
aromatic), 4.97-4.77 (4H, overlapping hoz CH2), 4.45-4.16 (4H,
overlapping hoz CH2), 4.13 (s, 3H, p-OCH3). 13C NMR (200 MHz,
CD2Cl2): δ 170.8, 170.3, 168.8,165.2, 163.8, 150.2, 146.6, 145.4, 142.4,
140.4, 138.2, 136.8, 135.6, 133.6, 130.4, 129.4, 128.9, 121.3, 120.3,
120.1, 119.8, 115.0, 110.7, 110.2, 71.4, 71.0, 58.4, 57.3, 55.7. Elemental
Analysis Calcd for C49H23BF20N3O6Re: C, 44.36; H, 1.75; N, 3.17.
Found: C, 44.09; H, 1.54; N, 2.92.
19F NMR Kinetics with 5d. Solutions of 2 (16.6 mM) containing a
constant acetonitrile concentration (8.0 M) were prepared in C6D6 (1.00
mL), sealed in an NMR tube, and the tube was allowed to equilibrate
in the NMR probe at 298 K for at least 10 min. The aromatic azide,
p-CF3 phenyl azide, was then added in excess concentration (0.10-
0.65 M) to achieve pseudo-first-order conditions. The growth in the
intergral for the CF3 signals of the product 5d (δ -63.5) was monitored
over time. Concentrations were determined relative to the 19F signals
-
of the B(C6F5)4 anion, which was used as an internal standard. The
kψ values were obtained by nonlinear fitting of the data of [5d] versus
time to the equation Abst ) (Abs0 - Abs∞)[1 - exp(-kψt)]. A plot of
the pseudo-first-order rate constant (kψ) versus [p-CF3 phenyl azide]
was linear, and the slope afforded an apparent second-order rate
constant.
Syntheses of Cationic Re(V) Imido Complexes. [(salpd)Re-
(NMes)(PPh3)][B(C6F5)4] (7). [(salpd)Re(O)(NMes)][B(C6F5)4], 4,
(0.100 g, 0.077 mmol) was dissolved in CH2Cl2. To this solution was
added PPh3 (0.203 g, 0.77 mmol). The solution changed color from
red to green and was stirred overnight. The solvent was removed under
a vacuum, and the residue dissolved in a minimal amount of CH2Cl2.
Pentane was added until a green powder precipitated. The green powder
was washed several times with pentane to yield 7 in 56% (0.066 g)
yield. 1H NMR (300 MHz, CD2Cl2): δ 8.09-8.06 (d, 1H, CdNsH),
7.69 (s, 1H, CdNsH), 7.58-7.55 (2H, overlapping aromatic), 7.42-
7.2 (16H, overlapping aromatic) 6.95-6.82 (4H, overlapping aromatic),
6.62-6.55 (4H, overlapping aromatic), 4.66-4.63 (1H, saldach CH2),
4.37-4.36 (m, 1H, saldach CH2), 4.01-3.98 (m, 1H, saldach CH2),
3.84 (m, 1H, saldach CH2), 2.28 (s, 3H, CH3), 2.15 (s, 6H, CH3), 1.91
(s, 2H, saldach CH2). 31P (300 MHz, CD2Cl2): δ -3.97. Elemental
Analysis Calcd for C68H42BF20N3O2PRe: C, 53.0; H, 2.75; N, 2.73.
Found: C, 52.9; H, 2.72; N, 2.89.
X-ray Structure Determination for 5a. A red dark plate of
C29H31N3O3Re,C24BF20 having approximate dimensions of 0.44 × 0.38
× 0.13 mm3 was mounted on a glass fiber in a random orientation.
Preliminary examination and data collection were performed with Mo
KR radiation (λ ) 0.710 73 Å) on a Nonius KappaCCD equipped with
a graphite crystal, incident beam monochromator. Cell constants for
data collection were obtained from least-squares refinement, using the
setting angles of 29 085 reflections in the range 2° < θ < 27°. The
triclinic cell parameters and calculated volume are as follows: a )
12.3585(8) Å, b ) 13.2595(5) Å, c ) 16.1042(11) Å, R ) 106.938-
(3)°, â )103.032(3)°, γ ) 90.219(3)°, V ) 2452.6(2) Å3. For Z ) 2
and FW ) 1334.84 the calculated density is 1.81 g/cm3. The refined
mosaicity from DENZO/SCALEPACK27 was 0.52° indicating moderate
crystal quality. The space group was determined by the program
XPREP.28 There were no systematic absences; the space group was
determined to be P1h(#2). The data were collected at a temperature of
150(1) K. Data were collected to a maximum 2θ of 55.0°. A total of
29 085 reflections were collected, of which 11 059 were unique. Frames
were integrated with DENZO-SMN.27 Lorentz and polarization cor-
rections were applied to the data. The linear absorption coefficient is
26.3 /cm for Mo KR radiation. An empirical absorption correction using
[(hoz)2Re(NAr)(PPh3)][B(C6F5)4], Ar ) m-MeO Phenyl, (9). In a
typical procedure, a flask equipped with a magnetic stir bar was charged
with 3 (0.174 g, 0.139 mmol) dissolved in CH2Cl2. To this solution
was added approximately 1 equiv of m-methoxy phenyl azide (0.024
g, 0.158 mmol). The solution was covered and allowed to stir overnight
as it changed color from green to red/orange. To this solution was added
triphenylphosphine (0.394 g, 1.50 mmol). After being stirred for 12 h,
the solution became bright green in color. The solution was concentrated
to approximately 10 mL. 200 mL pentane were added with stirring.
(27) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(28) McArdle, P. C. J. Appl. Crystallogr. 1996, 29, 306.
9
J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007 1177

A R T I C L E S
Ison et al.
SCALEPACK27 was applied. Transmission coefficients ranged from
0.642 to 0.720. Intensities of equivalent reflections were averaged. The
agreement factor for the averaging was 5.6% based on intensity. The
structure was solved using the structure solution program PATTY in
DIRDIF99.29 The remaining atoms were located in succeeding differ-
ence Fourier syntheses. Hydrogen atoms were included in the refinement
but restrained to ride on the atom to which they are bonded. The
structure was refined in full-matrix least-squares where the function
Table 3. Crystal Data and Data Collection Parameters for
[(saldach)Re(O)(NMes)][B(C6F5)4], 5a, and
[(salpd)Re(NMes)(PPh3)][B(C6F5)4], 7
5a
7
formula
formula weight 1334.84
C53H31BF20N3O3Re
C69.43H44.87BCl2.87F20N3O2PRe
1662.86
space group
a, Å
b, Å
P1h (no. 2)
12.3585(8)
13.2595(5)
16.1042(11)
106.032(3)
103.032(3)
90.219(3)
2452.6(2)
2
P1h (no. 2)
18.1716(3)
19.4058(3)
22.1180(3)
72.3473(11)
76.3375(8)
65.7914(7)
6722.33(18)
4
2
2
minimized was Σw(|Fo| - |Fc| )2 and the weight w is defined as 1/[σ2-
c, Å
(Fo ) + (0.0501P)2 + 0.0000P] where P ) (Fo + 2Fc2)/3. Scattering
factors were taken from the “International Tables for Crystallography.”30
11 059 reflections were used in the refinements. However, only the
2
2
R, deg
â, deg
γ, deg
V, Å3
Z
2
2
7982 reflections with Fo > 2σ(Fo ) were used in calculating R1. The
final cycle of refinement included 733 variable parameters and
converged (largest parameter shift was <0.01 times its sd) with
unweighted and weighted agreement factors of R1 ) Σ |Fo - Fc|/Σ Fo
F
calc, g cm-3
1.807
150.
1.643
150.
temp, K
radiation
(wavelength)
R
Mo KR (0.710 73 Å) Mo KR (0.710 73 Å)
2
2
) 0.045 and R2 ) SQRT(Σ w(Fo - Fc2)2/Σ w(Fo )2) ) 0.091. The
standard deviation of an observation of unit weight was 1.01. The
highest peak in the final difference Fourier had a height of 2.10 e/A3.
The minimum negative peak had a height of -1.83 e/A3. Refinement
was performed on a LINUX PC using SHELX-97.31 Crystallographic
drawings were done using programs ORTEP32 and PLUTON.33
X-Ray Structure Determination for 7. A brown plate of C44H42N3O2-
PRe,1.434(CH2Cl2),C24BF20 having approximate dimensions of 0.50 ×
0.35 × 0.18 mm3 was mounted on a glass fiber in a random orientation.
Preliminary examination and data collection were performed with Mo
KR radiation (λ ) 0.710 73 Å) on a Nonius KappaCCD equipped with
a graphite crystal, incident beam monochromator. Cell constants for
data collection were obtained from least-squares refinement, using the
setting angles of 82 148 reflections in the range 2° < θ < 27°. The
triclinic cell parameters and calculated volume are as follows: a )
18.1716(3) Å, b ) 19.4058(3) Å, c ) 22.1180(3) Å, R ) 72.3473-
(11)°, â ) 76.3375(8)°, γ ) 65.7914(7)°, V ) 6722.33(18) Å3. For Z
) 4 and FW ) 1662.86 the calculated density is 1.64 g/cm3. The refined
mosaicity from DENZO/SCALEPACK27 was 0.46° indicating good
crystal quality. The space group was determined by the program
XPREP.28 There were no systematic absences; the space group was
determined to be P1h(#2). The data were collected at a temperature of
150(1) K. Data were collected to a maximum 2θ of 55.0°. A total of
82 148 reflections were collected, of which 30 634 were unique. Frames
were integrated with DENZO-SMN.27 Lorentz and polarization cor-
rections were applied to the data. The linear absorption coefficient is
20.7 /cm for Mo KR radiation. An empirical absorption correction using
SCALEPACK27 was applied. Transmission coefficients ranged from
0.580 to 0.696. Intensities of equivalent reflections were averaged. The
agreement factor for the averaging was 4.9% based on intensity. The
0.045
0.091
0.053
0.124
RW
structure was solved using the structure solution program PATTY in
DIRDIF99.29 The remaining atoms were located in succeeding differ-
ence Fourier syntheses. Hydrogen atoms were included in the refinement
but restrained to ride on the atom to which they are bonded. The
structure was refined in full-matrix least-squares where the function
minimized was Σw(|Fo| - |Fc| )2 and the weight w is defined as 1/[σ2-
2
2
(Fo ) + (0.0684P)2 + 0.0000P] where P ) (Fo + 2Fc2)/3. Scattering
factors were taken from the “International Tables for Crystallography.”30
30634 reflections were used in the refinements. However, only the
2
2
2
2
17 576 reflections with Fo > 2σ(Fo ) were used in calculating R1.
The final cycle of refinement included 1847 variable parameters and
converged (largest parameter shift was <0.01 times its sd) with
unweighted and weighted agreement factors of R1 ) Σ |Fo - Fc|/Σ Fo
) 0.053 and R2 ) SQRT(Σ w(Fo - Fc2)2/Σ w(Fo )2) ) 0.124. The
standard deviation of an observation of unit weight was 1.00. The
highest peak in the final difference Fourier had a height of 4.03 e/A3.
The minimum negative peak had a height of -2.73 e/A3. Refinement
was performed on an LINUX PC using SHELX-97.31 Crystallographic
2
2
drawings were done using programs ORTEP32 and PLUTON.33
A
summary of the crystallographic parameters for complexes 5a and 7 is
depicted in Table 3.
Acknowledgment. Support of this work was provided by the
Chemical Sciences Division, Office of Basic Energy Sciences,
U.S. Department of Energy (Grant No. DE-FG02-06ER15794).
Supporting Information Available: Crystallographic tables
for atomic coordinates and equivalent isotropic parameters, bond
lengths, and angles for 5a and 7 (CIF); kinetic profiles, substrate
(PAr3, PhSMe, and PhSH) dependencies for OAT reactions from
complexes 4-6, and Hammett analysis for aryl phosphines
(PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
(29) Beurskens, P. T.; Beurskens, G.; Garcia-Granda, R. de G.; Gould, R. O.;
Israel, R.; Smits, J. M. M. The DIRDIF-99 Program System. Crystallography
Laboratory: University of Nijmegen, The Netherlands, 1999.
(30) International Tables for Crystallography; Kluwer Academic Publishers:
Utrecht, The Netherlands, 1992; Vol. C, Tables 4.2.6.8 and 6.1.1.4.
(31) Sheldrick, G. M. SHELXL97. A Program for Crystal Structure Refinement;
University of Gottingen: Germany, 1997.
(32) Johnson, C. K. ORTEPII, Report ORNL-5138; Oak Ridge National
Laboratory: Tennessee, USA, 1976.
(33) Spek, A. L. PLUTON. Molecular Graphics Program; University of
Ultrecht: The Netherlands, 1991.
JA065551P
9
1178 J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007