Insertion of a metal nitride into carbon-carbon double bonds [16]

Full text of DOI:10.1021/ja992385v

9752
J. Am. Chem. Soc. 1999, 121, 9752-9753
apparently by initial trans f cis isomerization of the nitride
complex8 followed by reaction of the cis nitride.
Insertion of a Metal Nitride into Carbon-Carbon
Double Bonds
Seth N. Brown*
Department of Chemistry and Biochemistry
251 Nieuwland Science Hall, UniVersity of Notre Dame
Notre Dame, Indiana 46556-5670
ReceiVed July 9, 1999
Metal nitride complexes are receiving increasing attention in
reactions which form bonds to nitrogen. Reactions of electrophilic
nitrido groups with reagents such as phosphines,1 amine-N-
oxides,2 amines,3 azide,4 main group organometallics,5 and
isobenzofurans6 have all been reported recently. Nitride com-
pounds have also been used as starting materials for reactions
with less nucleophilic reagents such as alkenes.7 However, these
reactions invariably take place only after activation of the nitride
with a strong electrophile such as trifluoroacetic anhydride to form
a reactive imido complex. Here I describe the direct reaction of
the cationic nitrido complex cis-[(terpy)OsNCl2]PF68 with a variety
of aryl-substituted alkenes to form η2-azaallenium complexes. In
these reactions, the alkene carbon-carbon double bond is
completely ruptured, forming two new carbon-nitrogen bonds
and a new metal-carbon bond. The asymmetrically bonded
azaallenium adducts are formed with a high degree of regiose-
lectivity and can be further functionalized under either oxidative
or reductive conditions.
A variety of other aryl-substituted alkenes also react with 1 to
give analogous products (eq 1). p-Methoxy substitution of the
phenyl groups increases the rate of the reaction, with dimeth-
oxystilbene reacting ∼20 times faster than stilbene. trans-â-
Methylstyrene is the most reactive alkene, with its reaction going
to completion overnight at room temperature. Trisubstituted
alkenes such as 1-(4-methoxyphenyl)-2-methylpropene form
analogous products at rates only modestly slower than their
disubstituted counterparts. Styrene and other alkenes such as
norbornene or trans-5-decene that lack aryl substituents all react
with 1 but have so far failed to yield tractable products.
The bonding in these complexes is clarified by the X-ray crystal
structure of 2d, derived from 1,6-diphenyl-1,3,5-hexatriene (Figure
1).10 In compounds 2, the osmium-nitrogen triple bond has in-
serted into one carbon-carbon double bond of the organic sub-
strate. One carbon in the ruptured alkene in 2d is bonded to
osmium (dOs-C ) 2.182 (5) Å), while the other carbon forms a
double bond to the coordinated nitrogen (dCdN ) 1.293 (7) Å).
The original alkene has been completely cleaved; there is no sign
of residual bonding between the carbon atoms (dC‚‚‚C ) 2.484
Å). The osmium is bonded in an η2-(C,N) fashion to the new
organic fragment in what may be regarded as an osmium(II) aza-
allenium complex or an osmium(IV) azametallacyclopropane. The
metrical data of the organic fragment (C1-N1 ) 1.374 Å, C1-
N1-C2 ) 137.5°) lie between these two extreme forms.11 One
prior example of a structurally characterized η2-azaallenium
complex, CpMo(CO)2(η2-Tol2CdNdCTol2), has been reported.12
Though details are not available, the preliminary data for this
complex indicate that its structure is shifted more toward the
azametallacyclopropane canonical form (C-N ) 1.43 Å, C-N-C
) 128.3°),13 consistent with weaker back-bonding by Os(II) than
by Mo(0).
The cationic osmium(VI) nitrido complex cis-[(terpy)OsNCl2]-
PF6 (1; terpy ) 2,2′:6′,2′′-terpyridine) reacts with cis-stilbene in
acetonitrile overnight at 60 °C to give the blood-red air-stable
azaallenium complex cis-[(terpy)OsCl2(1,2-η2-PhCHdNdCHPh)]-
PF6 (2a, eq 1).9 trans-Stilbene gives the same product 2a, albeit
more slowly. The trans isomer of [(terpy)OsNCl2]PF6 also reacts
with either cis- or trans-stilbene to give the same cis product 2a,
(1) (a) Griffith, W. P.; Pawson, D. J. Chem. Soc., Dalton Trans. 1975,
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.
(2) Williams, D. S.; Meyer, T. J.; White, P. S. J. Am. Chem. Soc. 1995,
117, 823-824.
(3) Huynh, M. H. V.; El-Samanody, E.-S.; Demadis, K. D.; Meyer, T. J.;
White, P. S. J. Am. Chem. Soc. 1999, 121, 1403-1404.
(4) Demadis, K. D.; Meyer, T. J.; White, P. S. Inorg. Chem. 1998, 37,
3610-3619.
(5) (a) Crevier, T. J.; Mayer, J. M. J. Am. Chem. Soc. 1998, 120, 5595-
5596. (b) Crevier, T. J.; Mayer, J. M. Angew. Chem., Int. Ed. 1998, 37, 1891-
1893.
(6) Brown, S. N. Inorg. Chem., manuscript submitted for publication.
(7) (a) Groves, J. T.; Takahashi, T. J. Am. Chem. Soc. 1983, 105, 2073-
2074. (b) Du Bois, J.; Tomooka, C. S.; Hong, J.; Carreira, E. M. Acc. Chem.
Res. 1997, 30, 364-372.
(8) Williams, D. S.; Coia, G. M.; Meyer, T. J. Inorg. Chem. 1995, 34,
586-592.
(9) Partial spectroscopic data for selected compounds (for full experimental
details, see the Supporting Information): 2a: 1H NMR (CD3CN) δ 5.48 (d,
8 Hz, 1H; ortho OsCHPh); 6.49 (t, 7.5 Hz, 1H; m-OsCHPh), 6.62 (d, 2 Hz,
1H; OsCHPh), 6.72 (d, 7.5 Hz, 1H; ortho′ OsCHPh), 7.02 (t, 7.5 Hz, 1H;
m′-OsCHPh), 7.19 (tt, 7.5, 1 Hz, 1H; para OsCHPh), 7.32 (t, 7.5 Hz, 2H;
m-NdCHPh), 7.43 (m, 3H; o,p-NdCHPh), 8.21 (d, 2 Hz, 1H; NdCHPh),
9.09 (dd, 5.5, 1 Hz; terpy H-6), 9.15 (dt, 5.5, 1 Hz; terpy H-6′′). 13C{1H}
NMR (CD3CN) δ 44.75 (OsCH), 163.12 (CHdN). FABMS 689 (M+). 2c:
1H NMR (CD3CN) δ 5.58 (br d, 8 Hz, 1H; o-OsCHPh), 6.23 (d, 2 Hz, 1H;
OsCHPh), 6.62 (br t, 7.5 Hz, 1H; m-OsCHPh), 6.68 (br d, 8 Hz, 1H; o′-
OsCHPh), 6.79 (dd, 16, 10 Hz, 1H; NdCH-CH)CHPh), 6.99 (br t, 8 Hz,
1H; m′-OsCHPh), 7.23 (tt, 7.5, 1 Hz, 1H; p-OsCHPh), 7.27 (d, 16 Hz, 1H;
NdCH-CHdCHPh), 7.33 (m, 3H; m,p-N)CH-CHdCHPh), 7.39 (m, 2H;
o-N)CH-CHdCHPh), 7.86 (dd, 9, 2 Hz, 1H; NdCH-CHdCHPh), 9.12
(dd, 5, 1 Hz, 1H; terpy H-6), 9.18 (dt, 5.5, 1 Hz, 1H; terpy H-6′′). 13C{1H}
NMR (CD3CN) δ 44.73 (OsCHPh), 122.98 (N)CH-CH)CHPh), 149.13
(N)CH-CH)CHPh), 162.99 (N)CH-CHdCHPh). FABMS 715 (M+).
2e: 1H NMR (CD3CN) δ 2.38 (dd, 5.4, 1.5 Hz, 3H; NdCHCH3), 5.56 (br d,
7 Hz, 1H; ortho), 6.29 (sl br, 1H; OsCHPh), 6.67 (br m, 2H, meta, ortho′),
6.96 (br t, 7 Hz, 1H; meta′), 7.24 (tt, 7, 1 Hz, 1H; para), 7.40 (qd, 5.4, 2.5
Hz, 1H; NdCHCH3), 9.10 (ddd, 5.5, 1.5, 0.5 Hz, 1H; terpy H-6), 9.13 (ddd,
5.5, 2, 1 Hz; terpy H-6′′). 13C{1H} NMR (CD3CN) δ 23.75 (CH3), 42.35
(OsCHPh), 168.57 (N)CHCH3). FABMS: 627 (M+).
The NMR spectra of the diamagnetic complexes 2 are
consistent with retention of the crystallographically determined
structure in solution. The two termini of the original double bond
are in very different chemical environments, as judged by 1H (δ
6.62 vs 8.21 ppm for 2a) and 13C (δ 44.75 vs 163.12 ppm for
2a) NMR spectroscopy. These differences are consistent with η2-
(C,N) coordination, with the metal-bonded CH group showing
upfield shifts and the iminium-like methine group shifting
(10) Crystallographic data for 2d‚(CD3)2C)O: C36H27D6Cl2F6N4OOsP, dark
red blocks grown from acetone-d6/Et2O, triclinic, space group P1h, a )
11.7391 (12) Å, b ) 13.2219 (10) Å, c ) 14.1111 (12) Å, R ) 94.154 (6)°,
â ) 113.610 (7)°, γ ) 111.576 (7)°, V ) 1803.2 (3) Å3, Z ) 2, R1 ) 0.0490,
wR2 ) 0.0774, GOF ) 1.045.
(11) Cf. d(CdN) for 1,3-ditolyl-2-azaallenium ion ) 1.258 Å. Bo¨ttger,
G.; Geisler, A.; Fro¨lich, R.; Wu¨rthwein, E.-U. J. Org. Chem. 1997, 62, 6407-
6411.
(12) Keable, H. R.; Kilner, M. J. Chem. Soc., Dalton Trans. 1972, 1535-
1540.
(13) Kilner, M. AdV. Organomet. Chem. 1972, 10, 115-198.
10.1021/ja992385v CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/29/1999

Communications to the Editor
J. Am. Chem. Soc., Vol. 121, No. 41, 1999 9753
Scheme 1
confirming that formation of the azaallenium fragment is in-
tramolecular.
The azaallenium fragments bonded to osmium retain consider-
able electrophilicity and can be synthetically modified by a variety
of nucleophilic reagents (Scheme 1). For example, the diphenyl
compound 2a reacts with trimethylamine-N-oxide to split off 1
equiv of benzaldehyde (detected by 1H NMR) and form the dark
purple, insoluble benzonitrile complex cis-(terpy)OsCl2(NCPh)
(3, νCN ) 2181 cm-1; cf. νCN ) 2204 cm-1 in the trans isomer4).15
Presumably the nitrile in 3 arises by deprotonation of a cationic
azavinylidene complex16 formed after loss of benzaldehyde and
trimethylamine. Curiously, the complete regioselectivity in azaal-
lenium formation does not translate into complete regioselectivity
in this reaction: the diphenylbutadiene-derived product cis-
[(terpy)OsCl2(1,2-η2-PhCHdNdCHCHdCHPh)]PF6 (2c) gives
a 2:1 mixture of cinnamaldehyde and benzaldehyde on treatment
with Me3NO at room temperature. The azaallenium complexes
can also be reduced. Complex 2a reacts instantly with sodium
borohydride in acetonitrile to give primarily dark blue cis-(terpy)-
OsCl2(η1-PhCHdNCH2Ph) (4) and traces of the doubly reduced
violet dibenzylamine complex cis-(terpy)OsCl2(NH[CH2Ph]2) (5).
Figure 1. Thermal ellipsoid plot of the cation of cis-[(terpy)OsCl2(1,2-
η2-PhCHdNdCHCHdCHCHdCHPh)]PF6‚(CD3)2CdO (2d‚(CD3)2-
CdO). Selected bond lengths (Å) and angles (deg): Os-N1, 2.006 (4);
Os-C1, 2.182 (5); C1-N1, 1.374 (7); C2-N1, 1.293 (7); N1-Os-C1,
38.0 (2); C1-N1-C2, 137.3 (5).
downfield. The presence of two sharp sets of signals indicates
that the two ends of the azaallenium group do not exchange on
the NMR time scale. As in free allenes,14 long-range proton-
proton couplings are observed through the unsaturated framework
5
(4JHH ) 2 Hz and JHH ) 1-2 Hz in 2a-f). All compounds 2
1
The H NMR spectrum of 4 indicates that it has a mirror plane,
1
show eleven separate resonances in the H NMR and fifteen in
implying that the imine is bonded only through nitrogen.
Reactions that cleave carbon-carbon double bonds are rare,
due to the strength and nonpolar nature of the alkene linkage.
Other reactions involving CdC bond cleavage, such as ozonoly-
sis17 and olefin metathesis,18 have proven exceptionally useful in
organic synthesis. Studies are in progress to further develop the
reactivity of the azaallenium fragment, as well as to probe the
mechanism of this remarkable transformation.
the 13C{1H} NMR due to the terpyridine ligands, indicating that
they have C1 symmetry in solution, consistent with static binding
to one face of the CdN double bond.
The phenyl group on C-1 is held close to the terpyridine ligand,
on average 3.49 Å from its least-squares plane in 2d. As a result,
exactly one aryl group in each compound 2 cannot rotate freely
about the Cipso-COs bond and shows inequivalent ortho and meta
hydrogens in the 1H NMR (e.g., δ 5.48 and 6.72 ortho, 6.49 and
7.02 meta for 2a). Slight broadening of the ortho and meta (but
not para) resonances indicates that rotation is not quite frozen
out on the NMR time scale at room temperature, with the rotation
rates inversely related to the size of the substituent on the imine
carbon (krot < 3 s-1 for 2a-b, ≈ 18 s-1 for 2c-d, ≈ 23 s-1 for
2e). The upfield shifts suggest that this phenyl group is being
held in the shielding cone of the terpyridine, consistent with reten-
tion of the crystallographically observed orientation in solution.
Remarkably, one upfield-shifted, nonrotating aryl group is
observed in every compound 2, indicating that the insertion
reaction is completely regioselective, with an aryl group always
bonded to C-1. No sign of alternate isomers with alkenyl or alkyl
groups in this position can be detected when the reaction mixtures
are monitored by NMR, nor is there any sign of reaction with
the internal alkene of 1,6-diphenyl-1,3,5-hexatriene rather than
the terminal one. The regioselectivity is clearly counter-steric,
since the aryl substituent is larger than methyl or vinyl and is
placed in the most crowded position in the molecule. When two
different aryl groups are available, mixtures result. For example,
4-methoxystilbene gives a 4:1 mixture of the 1,2- and 2,3-isomers
of cis-[(terpy)OsCl2(PhCHdNdCHC6H4OMe)]PF6. Neither 2a
nor 2b is formed in the reaction of the monomethoxystilbene,
Acknowledgment. I thank Dr. Maoyu Shang for his assistance in
determining the X-ray crystal structure of 2d‚(CD3)2CdO and Professor
Xavier Creary for a generous gift of 1-(4-methoxyphenyl)-2-methylpro-
pene. Financial support from the Camille and Henry Dreyfus Foundation
(New Faculty Award), from a DuPont Young Professor award, and from
the National Science Foundation (Grant CHE97-33321-CAREER) are
gratefully acknowledged.
Supporting Information Available: Descriptions of synthetic pro-
cedures and spectroscopic data for compounds 2a-f and 3-5; tables of
crystallographic parameters, atomic coordinates, bond lengths and angles,
anisotropic thermal parameters, and hydrogen coordinates for 2d‚
(CD3)2CdO (PDF). This material is available free of charge via the
Internet at http://pubs.acs.org.
JA992385V
(15) The transformation alkene f nitrile + aldehyde has previously been
15a
achieved using Me3SiN3 and Pb(OAc)4 or PhI(OAc)215b: (a) Zbiral, E.;
Nestler, G.; Kischka, K. Tetrahedron 1970, 26, 1427-1434. (b) Zbiral, E.;
Nestler, G. Tetrahedron 1970, 26, 2945-2953.
(16) Pombeiro, A. J. L.; Hughes, D. L.; Richards, R. L. J. Chem. Soc.,
Chem. Commun. 1988, 1052-1053.
(17) (a) Lee, D. G.; Chen, T. In ComprehensiVe Organic Synthesis; Trost,
B. M., Ed.; Pergamon Press: Oxford, 1991; Vol. 7, pp 541-591. (b) Haines,
A. H. Methods for the Oxidation of Organic Compounds; Academic Press:
London, 1985; pp 117-132.
(18) (a) Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413-4450. (b)
Armstrong, S. K. J. Chem. Soc., Perkin Trans. 1 1998, 371-388. (c) Schuster,
M.; Blechert, S. Angew. Chem., Int. Ed. Engl. 1997, 36, 2037-2056.
(14) Runge, W. In The Chemistry of the Allenes; Landor, S. R., Ed.;
Academic Press: New York, 1982; Vol. 3, pp 775-884.