Oxidative azavinylidene formation in the reaction of 1,3-diphenylisobenzofuran with osmium nitride complexes

Article abstract of DOI:10.1021/ic990815c

The cationic osmium nitrido complexes cis- and trans-[(terpy)OsNCl₂]PF₆ react with 1,3-diphenylisobenzofuran at room temperature to form azavinylidene complexes by oxidative ring opening of the isobenzofuran. The reaction involves ta

Full text of DOI:10.1021/ic990815c

378
Inorg. Chem. 2000, 39, 378-381
Notes
azirines,18 additions to vinylimido complexes,19 and R-depro-
tonation of imido complexes.20 The synthetic method described
here involves formation of the nitrogen-carbon bond of the
azavinylidene via a redox reaction with the metal nitride.
Oxidative Azavinylidene Formation in the
Reaction of 1,3-Diphenylisobenzofuran with
Osmium Nitride Complexes
Seth N. Brown
Experimental Section
Department of Chemistry and Biochemistry,
251 Nieuwland Science Hall, University of Notre Dame,
Notre Dame, Indiana 46556-5670
cis- and trans-[(terpy)OsNCl2]PF6 were prepared by the literature
methods.8 1,3-Diphenylisobenzofuran was purchased from Aldrich. All
solvents were used as received, and all manipulations were performed
on the benchtop without precautions to exclude air or moisture.
Reactions were carried out in the dark to avoid possible photodecom-
ReceiVed July 8, 1999
1
position of the diphenylisobenzofuran. H and 13C{1H} NMR spectra
Introduction
were obtained on a General Electric GN-300 NMR spectrometer at
300.49 and 75.56 MHz, respectively. IR spectra were measured on a
Perkin-Elmer PARAGON 1000 FT-IR spectrometer. Fast atom bom-
bardment mass spectra were obtained on a JEOL JMS-AX505HA mass
spectrometer using 3-nitrobenzyl alcohol as a matrix. Elemental analyses
were performed by M-H-W Laboratories (Phoenix, AZ).
Terminal metal nitride complexes present two complementary
types of reactivity. On one hand, the uncoordinated nitrogen
lone pair can act as a nucleophile, leading to Lewis acid adducts,
µ-nitrido complexes, or alkylation.1 On the other hand, a
growing number of studies have shown that nitrido complexes,
particularly those of osmium and ruthenium, can also display
electrophilic reactivity at nitrogen. Reagents as diverse as
phosphines,2 amine N-oxides,3 amines,4 azides,5 Grignard
reagents,6 and arylboranes7 have been reported to add to
osmium(VI) nitride complexes. Below is described the reaction
of the electrophilic nitrido complexes cis- and trans-[(terpy)-
OsNCl2]+ (cis- and trans-1)8 with 1,3-diphenylisobenzofuran
to form azavinylidene complexes. This novel azavinylidene
synthesis represents, formally at least, action of the nitride
nitrogen as both an electrophile and a nucleophile in the
formation of the new carbon-nitrogen double bond.
Azavinylidene complexes are known for transition metals
ranging from group IV through group IX. They are typically
prepared from precursors that already contain a carbon-nitrogen
bond, although condensation of metal amides with ketones has
also been used.9 Typical synthetic methods include oxidation
of coordinated amines,10 deprotonation of organic imines,11
reduction of oximes,12 reductive cleavage of azines,13 insertions
of nitriles into metal-hydrogen or metal-carbon bonds,14
protonation of nitriles,15 addition of nucleophiles to coordinated
nitriles,16 reductive coupling of nitriles,17 ring opening of
(11) (a) Farmery, K.; Kilner, M.; Midcalf, C. J. Chem. Soc. A 1970, 2279-
2285. (b) Kilner, M.; Midcalf, C. J. Chem. Soc. A 1971, 292-297.
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Latham, I. A.; Leigh, G. J.; Huttner, G.; Jibril, I. J. Chem. Soc., Dalton
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Organometallics 1994, 13, 3315-3323. (h) Daniel, T.; Werner, H. Z.
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M. A.; Lopez, A. M.; Oro, L. A. J. Organomet. Chem. 1996, 526,
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1987, 26, 248-250. (b) Werner, H.; Daniel, T.; Mu¨ller, M.; Mahr, N.
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Guedes da Silva, M. F. C.; Kukushkin, V. Y.; Frau´sto da Silva, J. J.
R.; Pombeiro, A. J. L. J. Chem. Soc., Dalton Trans. 1998, 325-326.
(13) Zippel, T.; Arndt, P.; Ohff, A.; Spannenberg, A.; Kempe, R.; Rosenthal,
U. Organometallics 1998, 17, 4429-4437.
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Chem., Int. Ed. Engl. 1984, 23, 68-69. (b) Fro¨mberg, W.; Erker, G.
J. Organomet. Chem. 1985, 280, 343-354. (c) Bercaw, J. E.; Davies,
D. L.; Wolczanski, P. T. Organometallics 1986, 5, 443-450.
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Chem. Commun. 1988, 1052-1053.
(16) (a) Feng, S. G.; Templeton, J. L. Organometallics 1992, 11, 1295-
1303. (b) Feng, S. G.; White, P. S.; Templeton, J. L. Organometallics
1993, 12, 2131-2139. (c) Feng, S. G.; White, P. S.; Templeton, J. L.
Organometallics 1993, 12, 1765-1774. (d) Knight, D. A.; Dewey,
M. A.; Stark, G. A.; Bennett, B. K.; Arif, A. M.; Gladysz, J. A.
Organometallics 1993, 12, 4523-4534. (e) Schollhammer, P.; Pichon,
M.; Muir, K. W.; Petillon, F. Y.; Pichon, R.; Talarmin, J. Eur J. Inorg.
Chem. 1999, 221-223.
(1) Dehnicke, K.; Stra¨hle, J. Angew. Chem., Int. Ed. Engl. 1992, 31, 955-
978.
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417-423. (b) Demadis, K. D.; Bakir, M.; Klesczewski, B. G.;
Williams, D. S.; White, P. S.; Meyer, T. J. Inorg. Chim. Acta 1998,
270, 511-526.
(3) Williams, D. S.; Meyer, T. J.; White, P. S. J. Am. Chem. Soc. 1995,
117, 823-824.
(4) Huynh, M. H. V.; El-Samanody, E.-S.; Demadis, K. D.; Meyer, T. J.;
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(10) (a) Adcock, P. A.; Keene, F. R.; Smythe, R. S.; Snow, M. R. Inorg.
Chem. 1984, 23, 2336-2343. (b) Gunnoe, T. B.; White, P. S.;
Templeton, J. L. J. Am. Chem. Soc. 1996, 118, 6916-6923.
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(18) Green, M.; Mercer, R. J.; Morton, C. E.; Orpen, A. G. Angew. Chem.,
Int. Ed. Engl. 1985, 24, 422-424.
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14, 5184-5192.
(20) (a) Chatt, J.; Dosser, R. J.; King, F.; Leigh, G. J. J. Chem. Soc., Dalton
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10.1021/ic990815c CCC: $19.00 © 2000 American Chemical Society
Published on Web 12/31/1999

Notes
trans-[(terpy)OsCl2(dNdC[Ph][2-PhCOC6H4])]PF6 (trans-2). trans-
Inorganic Chemistry, Vol. 39, No. 2, 2000 379
Table 1. Crystallographic Data for
trans-[(terpy)OsCl2(dNdC[Ph][2-PhCOC6H4])]PF6‚CD3CN
[(terpy)OsNCl2]PF6 (trans-1, 54.9 mg, 0.0840 mmol), 1,3-diphenyl-
isobenzofuran (35.3 mg, 0.131 mmol, 1.55 equiv), and CH3CN (7 mL)
were placed in a 20 mL screw-cap vial. After the vial was capped, the
mixture was swirled to dissolve the solids and allowed to stand at room
temperature for 2 days. The solvent was evaporated under reduced
pressure and the residue washed several times with diethyl ether. The
highly fluorescent washes, containing unreacted isobenzofuran, were
discarded, and the ether-insoluble material was taken up in 3 mL of
dichloromethane. The orange CH2Cl2 solution, which rapidly began
depositing crystals, was layered with 3 mL of Et2O. After 5 h, the
glittery orange flakes were isolated by suction filtration, washed with
(trans-2‚CD3CN) and
cis-[(terpy)OsCl2(dNdC[Ph][2-PhCOC6H4])]PF6 (cis-2)
trans-2‚CD3CN
cis-2
empirical formula C37H25D3Cl2F6N5OOsP C35H25Cl2F6N4OOsP
fw
967.71
923.66
space group
a, Å
b, Å
P21/n, monoclinic
8.6941(7)
32.558(4)
13.696(2)
90
96.098(9)
90
3854.9(8)
4
1.667
P1h, triclinic
10.6798(13)
11.3589(9)
15.655(2)
71.483(8)
76.942(9)
79.747(8)
1742.6(3)
2
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
1
3 × 5 mL of Et2O, and air-dried. Yield: 64.3 mg (83%). H NMR
(CD3CN): δ 6.76 (tt, 7.5, 1 Hz, 1H; p-NdCPh), 6.86 (dd, 8, 1 Hz,
2H; o-NdCPh), 7.45 (t, 7.5 Hz, 2H; m-NdCPh), 7.52 (td, 7.5, 1.5 Hz,
1H; H-4, C6H4), 7.56 (t, 7.5 Hz, 2H; m-COPh), 7.61 (tt, 7.5, 1.5 Hz,
1H; p-COPh), 7.76 (m, 5H; H-3,5,6, C6H4 + o-COPh), 7.86 (td, 8, 1.5
Hz, 2H; terpy H-4,4′′), 7.90 (ddd, 8, 6, 1.5 Hz, 2H; terpy H-5,5′′),
8.19 (d, 8 Hz, 2H; terpy H-3′,5′), 8.31 (t, 8 Hz, 1H; terpy H-4′), 8.38
(m, 2H; terpy H-3,3′′), 8.87 (m, 2H; terpy H-6,6′′). 13C{1H} NMR
(acetone-d6): δ 113.0, 124.9, 126.3, 128.1, 129.2, 129.5, 131.5, 131.7,
132.0, 132.5, 133.1, 133.7, 134.3, 134.7, 137.7, 140.3, 141.0, 144.2,
145.9, 146.0, 152.2, 161.4, 161.6, 196.4. IR (evaporated film; cm-1):
3115, 3080, 2920 (w, νCH), 1652 (s, νCdO), 1600 (m), 1570 (m), 1474
(w), 1448 (s, νCdN), 1315 (m), 1279 (m), 1238 (m), 1184 (w), 1159
(w), 1056 (w), 1024 (w), 936 (w), 923 (w), 919 (w), 840 (vs, PF6-),
776 (s), 750 (w), 733 (w), 719 (w), 702 (s). FABMS: m/z ) 780 (M
+ H). Anal. Calcd for C35H25Cl2F6N4OOsP: C, 45.51; H, 2.73; N, 6.07.
Found: C, 45.39; H, 2.48; N, 6.22.
F
calc, g cm-3
λ, Å
1.760
0.710 73
21
0.710 73
21
T, °C
crystal size, mm
0.25 × 0.15 × 0.04
0.40 × 0.29 × 0.28
µ, mm-1
3.554
3.926
R1, I > 4σ(I)a
wR2, I > 4σ(I)b
GOF on F 2
0.0409
0.1001
1.055
0.0238
0.0627
1.095
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo2 - Fc2)2/∑w(Fo )2]1/2
.
2
for absorption and for Lorentz and polarization effects, 6751 unique
) 0.0405), of which 59 were suppressed
reflections were obtained (Rint
during least-squares refinement due to highly negative apparent values
of Fo. The space group was determined to be P21/n on the basis of
systematic absences. The osmium atom was located on a Patterson map,
and remaining non-hydrogen atoms were found in difference Fourier
syntheses. Hydrogens were placed in calculated positions. Final full-
matrix least-squares refinement of F2 converged at R1 ) 0.0409 for
5093 reflections with Fo > 4σ(Fo) and R1 ) 0.0693 for all data (wR2
) 0.1101 and 0.2232, respectively).
Orange blocks of cis-2 formed after diffusion of benzene into a
solution of the complex in acetone. A 0.40 × 0.29 × 0.28 mm orange
block was treated as described for the trans isomer. A triclinic unit
cell (P1h) was determined on the basis of 25 accurately centered
reflections with 16° < θ < 17°. A total of 6369 reflections were
measured (6125 unique, Rint ) 0.0255) in the hemisphere (h,(k,-l.
Decay was negligible. Data analysis and structure solution proceeded
as described above for the trans isomer, converging at R1 ) 0.0238
for 5884 reflections with Fo > 4σ(Fo) and R1 ) 0.0252 for all data
(wR2 ) 0.0627 and 0.0637, respectively). All calculations used
SHELXTL (Bruker Analytical X-ray Systems), with scattering factors
and anomalous dispersion terms taken from the literature.21 Other
crystallographic details are summarized in Table 1.
cis-[(terpy)OsCl2(dNdC[Ph][2-PhCOC6H4])]PF6 (cis-2). cis-
[(terpy)OsNCl2]PF6 (83.3 mg, 0.127 mmol) and 1,3-diphenylisoben-
zofuran (50.4 mg, 0.186 mmol, 1.5 equiv) were dissolved in 10 mL of
CH3CN in a 25 mL round-bottom flask. After standing at room
temperature for 2 h, the solution was filtered through a plug of cotton
wool. The solvent was then removed on the rotary evaporator and the
residue washed several times with diethyl ether. The ether-insoluble
oil was taken up in 4 mL of CH2Cl2, and the solution was layered with
1 mL of Et2O. After 1 h, the orange needles that had deposited were
filtered off onto a glass frit, washed with 4 mL of CH2Cl2 and then 3
1
× 10 mL of Et2O, and air-dried to yield 111.5 mg of cis-2 (95%). H
NMR (CD3CN): δ 6.37 (d, 7.5 Hz, 2H; o-NdCPh), 6.39 (t, 7.5 Hz,
1H; p-NdCPh), 6.82 (dd, 7.5, 1 Hz, 1H; H-3, C6H4), 7.35 (m, 4H; o-
and m-COPh), 7.41 (td, 7.5, 1 Hz, 1H; H-5, C6H4), 7.48 (t, 7.5 Hz,
2H; m-NdCPh), 7.53 (m, 2H; p-COPh + H-4, C6H4), 7.62 (dd, 7.5, 1
Hz, 1H; H-6, C6H4), 8.0-8.2 (m, 7H; terpy H-4,5,3′,4′,5′,4′′,5′′), 8.27
(dd, 7, 2 Hz, 2H; terpy H-3,3′′), 9.13 (dd, 5, 2 Hz, 2H; terpy H-6,6′′).
13C{1H} NMR (CD3CN): δ 109.5, 111.7, 125.0, 125.4, 127.5, 129.4,
130.6, 130.8, 132.1, 132.4, 132.7, 134.4, 134.5, 136.0, 137.5, 139.1,
140.8, 144.1, 145.6, 157.6, 160.3, 162.7, 163.1, 195.0. IR (evaporated
film; cm-1): 3080 (m, νCH), 1657 (s, νCdO), 1597 (s), 1568 (m), 1474
(m), 1452 (s), 1314 (m), 1274 (s), 1165 (w), 1101 (w), 1055 (w), 1026
(m), 935 (w), 911 (w), 840 (vs, PF6-), 771 (s), 749 (m), 704 (m), 656
(m), 634 (m), 558 (s). FABMS: m/z ) 780 (M + H). Anal. Calcd for
C35H25Cl2F6N4OOsP: C, 45.51; H, 2.73; N, 6.07. Found: C, 45.36; H,
2.90; N, 6.11.
Results and Discussion
The violet osmium(VI) nitrido complex trans-[(terpy)OsNCl2]-
8
PF6 (trans-1; terpy ) 2,2′:6′,2′′-terpyridine) reacts with 1,3-
diphenylisobenzofuran over the course of 1.5 days at room
temperature to form the orange azavinylidene complex trans-
[(terpy)OsCl2(dNdC[Ph][2-PhCOC6H4])]PF6 (trans-2), which
can be isolated in 83% yield (eq 1). The isomeric nitrido
X-ray Structure Determinations of trans-[(terpy)OsCl2(dNd
C[Ph][2-PhCOC6H4])]PF6‚CD3CN (trans-2‚CD3CN) and cis-[(terpy)-
OsCl2(dNdC[Ph][2-PhCOC6H4])]PF6 (cis-2). Orange plates of trans-2
were deposited after slow diffusion of ether into a solution of the
complex in CD3CN. A 0.25 × 0.12 × 0.04 mm crystal was glued to
the tip of a glass fiber in the air and examined at 20 °C on an Enraf-
Nonius CAD4 diffractometer using Mo KR radiation with a graphite
monochromator (λ ) 0.710 37 Å). The crystal was monoclinic, and its
unit cell was determined on the basis of 25 reflections with 13.4° < θ
< 16°. A total of 7215 reflections in two octants (hkl, hkhl) with 2θ
< 50° were collected. Crystal quality was monitored by recording three
standard reflections approximately every 160 reflections measured;
decay was negligible. The large size of the unit cell resulted in a small
amount of overlap in reflections; this was treated by correcting the
backgrounds of reflections with highly unsymmetrical backgrounds by
setting both backgrounds equal to the smaller one. After corrections
8
complex cis-[(terpy)OsNCl2]PF6 (cis-1) reacts to give the
analogous azavinylidene complex cis-2 in 95% yield. The cis
isomer reacts over an order of magnitude more rapidly than the
trans, with the reaction going to completion in less than 1 h.
The observed spectral data for compounds 2 agree with the
above formulation. The reaction generates a free organic
carbonyl group, as indicated by characteristic absorptions in the
infrared (1657 and 1652 cm-1 for cis- and trans-2, respectively;
cf. ν ) 1660 cm-1 for benzophenone) and by peaks at ∼δ 195
(21) International Tables of Crystallography; Kluwer Academic Publish-
ers: Dordrecht, The Netherlands, 1992; Vol. C.

380 Inorganic Chemistry, Vol. 39, No. 2, 2000
Notes
(1)
ppm in the 13C NMR. The NMR resonances of 2 are sharp and
unshifted, indicating that the compounds are diamagnetic. The
ortho and para hydrogens of the phenyl group bonded to the
1
azavinylidene carbon resonate in the H NMR significantly
upfield of the other resonances, suggesting a rather electron-
rich azavinylidene ligand. The para resonance, integrating to
1H, clearly demonstrates that the C2V symmetry of the isoben-
zofuran has been lost upon reaction with the osmium nitride.
The bonding in the molecules is confirmed by X-ray
diffraction studies of trans-2 (Figure 1) and cis-2 (Figure 2).
Apart from the disposition of the chloride ligands, the two
complexes are quite similar (Table 2). The azavinylidene
moieties are linear (175.5(6) and 168.2(3)° for the trans and
cis isomers, respectively) and have short OsdN (1.812(6),
1.806(3) Å) and CdN bonds (1.273(9), 1.264(4) Å). These
features are similar to those reported for osmium(II) azavi-
nylidene complexes12a,b as well as those of the isoelectronic
ruthenium(IV) complex [(bipy)(terpy)Ru(dNdCMe2)](ClO4)3.10a
The short OsdN distance and diamagnetism of the octahedral
d4 complex indicate that the azavinylidene group forms a single
strong π bond, giving an overall Os-N bond order of 2. In
both complexes, the orientation adopted in the crystal requires
that the π donor orbital on the azavinylidene22 interact with an
empty dπ orbital on osmium that could otherwise be involved
in back-bonding to the central pyridine of the terpyridine ligand.
This orientation may be favored because of steric interactions
or because of maximum favorable π donation from the chloride
ligands; the loss of back-bonding is unlikely to be significant
in this relatively high-valent complex. Since twisting of the aryl
groups around their bonds to C1 renders the two sides of the
terpyridine ligand equivalent, the (symmetrical) NMR spectra
of the complexes do not offer any information about barriers
to rotation in solution. The facts that the bond to the central
N21 of the terpyridine ligand is slightly longer in the trans
isomer than in the cis isomer and that the Os-Cl bonds in
trans-2 are shorter than the Os-Cl bond trans to the azavi-
nylidene ligand in cis-2 indicate that the azavinylidene exerts a
small trans influence of ∼0.03 Å (compared to a trans influence
of ∼0.17 Å in the parent nitride23). The distortions from
octahedral geometry due to constraints in the terpy ligand
(relatively acute trans N11-Os-N31 angle ) 159.0° (average);
central Os-N21 bond shorter than outer Os-N11/N31 bonds
by 0.052 Å in trans-2 and 0.088 Å in cis-2) are typical (in 137
structures in the Cambridge Crystallographic Database, avg.
trans angle ) 155 ( 10° and average ∆d ) 0.09 ( 0.05 Å).24
Formation of the azavinylidene ligand is presumably initiated
by nucleophilic attack of isobenzofuran at the nitrogen atom of
Figure 1. Molecular structure of the cation of trans-[(terpy)OsCl2(d
NdC[Ph][2-PhCOC6H4])]PF6‚CD3CN (trans-2‚CD3CN), with thermal
ellipsoids shown at the 30% probability level.
Figure 2. Molecular structure of the cation of cis-[(terpy)OsCl2(d
NdC[Ph][2-PhCOC6H4])]PF6 (cis-2), with thermal ellipsoids shown at
the 30% probability level.
the metal nitride (Scheme 1). This is congruent with the known
propensity of isobenzofurans to act as nucleophiles25 and of the
cationic nitrides 1 to react as electrophiles at nitrogen.2b,3-5
Initiation of the reaction sequence by outer-sphere electron
transfer is unlikely because the enormous difference in redox
potentials of the two reagents (E° ≈ +0.75 V vs SCE26 for
(22) Feng, S. G.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1994,
116, 8613-8620.
(23) Pipes, D. W.; Bakir, M.; Vitols, S. E.; Hodgson, D. J.; Meyer, T. J. J.
Am. Chem. Soc. 1990, 112, 5507-5514.
(25) Friedrichsen, W. AdV. Heterocycl. Chem. 1980, 26, 135-241.
(26) (a) Zweig, A.; Metzler, G.; Maurer, A.; Roberts, B. G. J. Am. Chem.
Soc. 1967, 89, 4091-4098. (b) Fehlhammer, W. P.; Moinet, C. J.
Electroanal. Chem. Interfacial Electrochem. 1983, 158, 187-191.
(24) Indicated error limits refer to the standard deviation of the mean of
the 171 crystallographically inequivalent examples in the 137 struc-
tures.

Notes
Inorganic Chemistry, Vol. 39, No. 2, 2000 381
Table 2. Selected Bond Distances (Å) and Angles (deg) for
trans-[(terpy)OsCl2(dNdC[Ph][2-PhCOC6H4])]PF6‚CD3CN
(trans-2‚CD3CN) and
the second carbon-nitrogen bond. It should be noted that free
organic nitrenes have also been observed to react with 1,3-
diphenylisobenzofuran to give imines of 2-benzoylbenzophe-
none in a reaction presumed to involve initial aziridination.28
Initial aziridination by 1 prior to formation of the open structure
shown in Scheme 1 cannot be ruled out but seems unlikely in
view of the lack of precedent for aziridine formation from nitrido
complexes and the unusual reactivity of the isobenzofuran. In
contrast to the reactions of free nitrenes, which react readily
with a variety of furans,28 trans-1 does not react with furan,
2,5-dimethylfuran, or vinylene carbonate, even upon heating at
65 °C for several days.
cis-[(terpy)OsCl2(dNdC[Ph][2-PhCOC6H4])]PF6 (cis-2)
trans-2
cis-2
Os-N1
Os-N21
Os-N11
Os-N31
Os-Cl1
Os-Cl2
N1-C1
1.812(6)
2.028(7)
2.078(6)
2.081(6)
2.341(2)
2.331(2)
1.273(9)
1.806(3)
1.991(3)
2.090(3)
2.069(3)
2.3571(10)
2.3688(10)
1.264(4)
N1-Os-N21
N1-Os-N11
N21-Os-N11
N1-Os-N31
N21-Os-N31
N11-Os-N31
N1-Os-Cl2
N21-Os-Cl2
N11-Os-Cl2
N31-Os-Cl2
N1-Os-Cl1
N21-Os-Cl1
N11-Os-Cl1
N31-Os-Cl1
Cl2-Os-Cl1
C1-N1-Os
178.1(2)
99.9(3)
79.6(3)
101.6(3)
78.8(3)
158.5(3)
98.8(2)
83.1(2)
88.9(2)
88.3(2)
95.1(2)
83.1(2)
89.3(2)
88.4(2)
166.14(8)
175.5(6)
121.7(7)
116.8(7)
91.38(12)
88.53(12)
80.03(13)
94.90(13)
79.71(14)
159.52(13)
173.35(9)
83.33(9)
86.59(9)
88.14(9)
95.84(9)
172.67(9)
98.87(9)
100.84(10)
89.38(4)
168.2(3)
120.9(3)
115.7(3)
Thus, azavinylidene formation appears to take place by initial
action of the nitride as an electrophile, followed by the action
of the (newly electron-rich) nitrogen as a nucleophile. This
pattern of successive electrophilic/nucleophilic reactivity seems
to be typical of electrophilic osmium nitrido complexes. A very
close analogy exists for the reaction of 1 with the nucleophilic
oxidant Me3NO,3 which presumably involves initial bond
formation between oxygen and the nitride followed by expulsion
of Me3N concurrent with formation of the nitrosyl N-O
multiple bond. The reaction of 1 with azide5 is likely analogous,
and the Grignard addition/protonation sequence used to make
amides from nitrides6 also exhibits this sequence. The only other
example where azavinylidene complexes have been prepared
from nitrides uses a two-step sequence in which the order of
reactivity is reversed. Shapley has prepared a methyleneamido
complex of osmium by initial methylation of CpOsN(CH2-
N1-C1-C51
N1-C1-C41
Scheme 1
29
SiMe3)2 followed by deprotonation of the resulting cationic
methylimido complex.30 The possibility of still other sequencess
for example, reactions where nucleophilic and electrophilic
bond-forming steps are concertedsis currently being explored.
Acknowledgment. I thank Dr. Maoyu Shang for his as-
sistance in determining the X-ray crystal structures of trans-2‚
CD3CN and cis-2. Financial support from the Camille and Henry
Dreyfus Foundation (New Faculty Award), from the National
Science Foundation, and from a DuPont Young Professor Award
is gratefully acknowledged.
Supporting Information Available: Tables listing crystallographic
parameters, atomic coordinates, bond lengths and angles, anisotropic
thermal parameters, and hydrogen coordinates and U(eq) values for
trans-2‚CD3CN and cis-2. This material is available free of charge via
the Internet at http://pubs.acs.org.
1,3-diphenylisobenzofuran and E° ≈ -0.36 V vs SCE27 for
[(terpy)OsNCl2]+) makes one-electron transfer too endoergic
to account for the observed rates. Formation of the first carbon-
nitrogen bond restores the aromaticity of the benzene ring of
the isobenzofuran and generates a superb leaving group, a diaryl
ketone. Its departure allows the lone pair on nitrogen to form
IC990815C
(28) Jones, D. W. J. Chem. Soc., Perkin Trans. 1 1972, 2728-2751.
(29) Marshman, R. W.; Shusta, J. M.; Wilson, S. R.; Shapley, P. A.
Organometallics 1991, 10, 1671-1676.
(30) Shapley, P. A.; Shusta, J. M.; Hunt, J. L. Organometallics 1996, 15,
1622-1629.
(27) Demadis, K. D.; El-Samanody, E.-S.; Coia, G.; Meyer, T. J. J. Am.
Chem. Soc. 1999, 121, 535-544.