Transformations of aryl isocyanide on guanidinate-supported organozirconium complexes to yield terminal imido, iminoacyl, and enediamido ligands

Article abstract of DOI:10.1021/om0108548

Reactions of aryl isocyanide with bis(guanidinate) Zr(IV) hydrocarbyl complexes are presented. With 1 equiv of Ar′NC the ultimate products are the terminal Zr imido complexes [{(R′NR″)C(NR)₂} ₂ZrN(2,6-Me₂C₆H₃)] (3, R=R′ = ⁱPr, R″ = H; 5, R.= ⁱPr, R′ = R″ = Me), which are derived via a unique transformation from intermediate η²-iminoacyl species. With 2 equiv ofAr′NC, [{(Me ₂N)C(NⁱPr)₂}₂Zr(η²- Ar′N-CMe)₂](6) was isolated. Mild thermolysis of 6 generates an enediamido complex via intramolecular coupling of the iminoacyl groups.

Full text of DOI:10.1021/om0108548

© Copyright 2002
Volume 21, Number 1, January 7, 2002
American Chemical Society
Communications
Tr a n sfor m a tion s of Ar yl Isocya n id e on
Gu a n id in a te-Su p p or ted Or ga n ozir con iu m Com p lexes To
Yield Ter m in a l Im id o, Im in oa cyl, a n d En ed ia m id o
Liga n d s
Tiow-Gan Ong, Dayna Wood, Glenn P. A. Yap, and Darrin S. Richeson*
Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
Received October 1, 2001
Summary: Reactions of aryl isocyanide with bis(guani-
dinate) Zr(IV) hydrocarbyl complexes are presented. With
1 equiv of Ar′NC the ultimate products are the terminal
Zr imido complexes [{(R′NR′′)C(NR)2}2ZrN(2,6-Me2C6H3)]
(3, R ) R′ ) Pr, R′′ ) H; 5, R ) Pr, R′ ) R′′ ) Me),
which are derived via a unique transformation from
intermediate η2-iminoacyl species. With 2 equiv of Ar′NC,
[{(Me2N)C(NiPr)2}2Zr(η2-Ar′NdCMe)2] (6) was isolated.
Mild thermolysis of 6 generates an enediamido complex
via intramolecular coupling of the iminoacyl groups.
Guanidinate anions, [R′R′′NC(NR)2]-, exhibit versa-
tile and flexible coordination properties and have re-
ceived increasing attention as ancillary ligands for both
main-group and transition-metal complexes.1-3 These
species offer several patterns of substitution, and we are
particularly interested in those with either one or two
organic substituents on the tertiary N(R′)R′′ center (e.g.
N(H)R′ or NR2′). Most of the efforts in this area have
been in the development of new guanidinate complexes,
with fewer examples of reactivity studies involving
small-molecule activation by complexes supported by
guanidinate ligands. Insertion reactions represent a
fundamental reaction type in organometallic chemistry,
and isocyanides are among the common substrates of
such reactions.4 We report a sequence of reactions of
isocyanide with two bis(guanidinate) Zr(IV) hydrocarbyl
complexes that proceed beyond insertion to form new
C-C bonds. One of these transformations gives rise to
the terminal Zr imido complexes [{(R′NR′′)C(NR)2}2ZrN-
(2,6-Me2C6H3)] (R ) R′ ) iPr, R′′ ) H; R ) iPr, R′ ) R′′
) Me) through a novel reaction pathway. A change in
reaction stoichiometry produced an enediamido complex
via intramolecular coupling of iminoacyl groups. These
reactions exemplify the ability of group 4 guanidinate
complexes to undergo migratory insertion and to exhibit
noteworthy reactivity.
i
i
The direct reaction of a 1:2 molar ratio of Zr(Bz)4
and N,N′,N′′-triisopropylguanidine, (iPrN)dC(NHiPr)2,
in toluene at room temperature proceeds via proton
transfer and toluene elimination to yield the new species
[{(iPrNH)C(NiPr)2}2ZrBz2] (1) in 88% isolated yield. The
i
1H and 13C NMR spectra of 1 display two sets of Pr
signals in a 2:1 ratio and a single methylene resonance,
suggesting a pseudo-octahedral Zr center with freely
rotating, cis-oriented benzyl groups. An X-ray crystal-
lographic analysis confirms this hypothesis.5
(1) Bailey, P. J .; Pace, S. Coord. Chem. Rev. 2001, 214, 91 and
references therein.
(2) Lu, Z.; Yap, G. P. A.; Richeson, D. S. Organometallics 2001, 20,
706. Foley, S. R.; Yap, G. P. A.; Richeson, D. S. Chem. Commun. 2000,
1515. Thirupathi, N.; Yap, G. P. A.; Richeson, D. S. Organometallics
2000, 19, 2573. Thirupathi, N.; Yap, G. P. A.; Richeson, D. S. Chem.
Commun. 1999, 2483.
(3) Duncan, A. P.; Mullins, S. M.; Arnold, J .; Bergman, R. G.
Organometallics 2001, 20, 1808.
(4) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059 and
references therein.
10.1021/om0108548 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 12/06/2001

2
Organometallics, Vol. 21, No. 1, 2002
Communications
Sch em e 1
Complex 1 reacts rapidly with 1 equiv of 2,6-dimethyl-
ligand and the appearance of new signals in the olefinic
region of the H NMR spectrum (multiplet, δ 6.2-6.4).
1
phenyl isocyanide, as indicated by a color change from
yellow to dark orange to generate compound 2 (Scheme
1). The identity of 2 as the monoinsertion product was
indicated by the relative intensity of the aromatic
methyl signals and appearance of two equal-intensity
The olefin byproduct of this reaction was determined
to be trans-2-benzylstyrene by comparison of MS and
NMR data with literature values.7 The Zr-containing
product exhibited two isopropyl signals in a ratio of 2:1
as well as resonances attributed to a single 2,6-Me2C6H3
group. On the basis of these observations, we were
able to assign the formula of 3 as [{(iPrNH)C(NiPr)2}2-
ZrdN(2,6-Me2C6H3)] and to suggest the C2-symmetric
structure depicted in Scheme 1. Compound 3 could be
prepared directly by allowing the reaction of 1 and
isocyanide to proceed at room temperature for 1 day.
The level of aggregation for 3 was confirmed through
structural analysis, which revealed it to be a novel
terminal imido complex.8 Terminal imido complexes of
Zr have been isolated and structurally characterized
with amido, tetraaza macrocycle, cyclopentadienyl, and
aryloxido ligation.9 Complex 3 is the first example of
this moiety supported by guanidinate or amidinate
ligation. The geometry of 3 is derived from a trigonal
1
resonances for the benzyl methylene protons in the H
NMR spectrum at 2.41 ppm (Zr-CH2Ph) and 4.06 ppm
(Zr-η2-Ar′NdCCH2Ph). A characteristic resonance for
the iminoacyl C appeared at δ 252.86.4
The molecular structure of 2 confirmed the connectiv-
ity of this species and was consistent with our spectro-
scopic observations (Scheme 1).6 The Zr(IV) coordina-
tion environment consists of two chelating, bidentate
guanidinate monoanions, a benzyl ligand, and an η2-
iminoacyl ligand derived from the insertion of the aryl
isocyanide into a Zr-Bz bond. Although formally seven-
coordinate, the geometry of 2 can be considered distorted
octahedral if the η2-CdN is assigned a single coordina-
tion site. The N(7)-C(35) bond length of 1.292(3) Å is
consistent with double-bond formation. This moiety is
symmetrically bonded to the Zr center (Zr-C(35) )
2.295(3) Å, Zr-N(7) ) 2.242 (2) Å). The guanidinate
ligands exhibit bonding parameters similar to those of
related complexes.1,3
(7) Moreno-Man˜as, M.; Pajuelo, F.; Pleixats, R. J . Org. Chem. 1995,
60, 2396. Uozumi, Y.; Danjo, H.; Hagashi, T. J . Org. Chem. 1999, 64,
3384.
(8) Crystal data: empirical formula C28H53N7Zr, T ) 203(2) K, λ )
0.710 73 Å, space group P41212, a ) b ) 9.8146(13) Å, c ) 33.688(5) Å,
R ) â ) γ ) 90°, V ) 3245.1(8) Å3, Z ) 4, R indices (I > 2σ(I)) R1 )
0.0347 and wR2 ) 0.0983.
(9) (a) Thorman, J . L.; Guzei, I. A.; Young, V. G., J r.; Woo, L. K.
Inorg. Chem. 1999, 38, 3814. (b) Krska, S. W.; Zuckerman, R. L.;
Bergman, R. G. J . Am. Chem. Soc. 1998, 120, 11828. (c) Fryzuk. M.
D.; Love, J . B.; Rettig, S. J . Organometallics 1998, 17, 846. (d) Blake,
A. J .; Mountford, P.; Nikonov, G. I.; Swallow, D. J . Chem. Soc., Chem.
Commun. 1996, 1835. (e) Breen, T. L.; Stephan, D. W. J . Am. Chem.
Soc. 1995, 117, 11914. (f) Zambrano, C. H.; Profilet, R. D.; Hill, J . E.;
Fanwick, P. E.; Rothwell, I. P. Polyhedron 1993, 12, 689. (g) Walsh, P.
J .; Hollander, F. J .; Bergman, R. G. Organometallics 1993, 12, 3705.
(h) Bai, Y.; Roesky, H. W.; Noltemeyer, M.; Witt, M. Chem. Ber. 1992,
125, 825. (i) Arney, D. J .; Bruck, M. A.; Huber, S. R.; Wigley, D. E.
Solutions of 2 underwent a transformation at room
temperature over several hours, as indicated by the
disappearance of the signals attributed to the benzyl
(5) The single-crystal X-ray structures for compounds 1, 5, and 6
have been determined. Thermal ellipsoid plots for these complexes can
be found in the Supporting Information. Full structural details will
be reported in a future paper.
(6) Crystal data: empirical formula C43H67N7Zr, T ) 203(2) K, λ )
0.710 73 Å, space group P21/c, a ) 10.8273(8) Å, b ) 16.3749(12) Å,
c ) 24.2102(17) Å, R ) γ ) 90°, â ) 90.2690°, V ) 4292.3(5) Å3,
Z ) 4, R indices (I > 2σ(I)) R1 ) 0.0469 and wR2 ) 0.1063.

Communications
Organometallics, Vol. 21, No. 1, 2002
3
Sch em e 2
iminoacyl) compound 6 was produced (Scheme 1).
Perhaps the clearest spectroscopic indications for 6
are the 13C NMR resonance at δ 252.19 assigned to
the η2-iminoacyl moieties and the relative integration
intensities for the methyl groups in this species.5
The intramolecular coupling between two η2-imino-
acyl groups to yield enediamido ligands has been
extensively studied by Rothwell et al. for bis(aryloxy)
bis(η2-iminoacyl) group 4 complexes.12 Coupling re-
actions have also been observed for group 4 tropo-
coronand-10 and calix[4]arene-supported complexes.13
A
recent theoretical treatment of this reaction has also
recently appeared.14 Compound 6 produces the enedi-
amido complex 7 upon mild thermolysis. The clearest
spectroscopic evidence for 7 is the appearance of a new
carbon signal at δ 112.0, which was assigned to the
CdC carbon centers.
Complex 7 was characterized by crystallographic
analysis.15 The Zr center exhibits a distorted pseudo-
octahedral geometry with substantial distortions due to
the limitations of the guanidinate bite angles (approx-
imately 58°). The enediamido group has a typical bite
angle of 82.96(15)°. The Zr-N(1) and Zr-N(2) bond
distances (2.090(4) and 2.108(4) Å) are consistent with
Zr amido linkages and are shorter than the average
Zr-Nguanidinate distance of 2.28 Å. The C(9)-C(11)
distance (1.358(6) Å) corresponds to a CdC bond, while
the N(1)-C(9) and N(2)-C(11) distances (1.427(6) and
1.415(6) Å) are consistent with single bonds between
sp2-hybridized C and N. As is commonly observed for
such species, there is a significant fold angle between
the N-Zr-N and N-CdC-N planes of 44.8°.12,13,16
We have shown that the bis(guanidinate) frame-
work offers a scaffold for interesting reactivity. We are
currently exploring the generality of these reactions
with isocyanates and related small molecules as well
as the further reactivity of 3 and 5 with various
unsaturated substrates.
bipyramid, with the imido ligand occupying an equa-
torial site. Structural and theoretical analysis of five-
coordinate Zr imido species along with the Zr-N bond
length of 1.863(3) Å and the linearity of the aryl imido
group (180.0(2)°) suggest that the Z-N(4) interaction
is best viewed as a triple bond.9f
The transformation of the η2-iminoacyl group of 2
to the terminal imido group of 3 is unique.10 The
formation of trans-2-benzylstyrene as the byproduct in
this reaction suggests a retro 2 + 2 cycloaddition from
an azametallacyclobutane as a route to this species. We
propose the formation of this metallacycle via the mech-
anism outlined in Scheme 2. First, 2 forms a metal-
laaziridine complex that undergoes a â-H elimination
reaction to yield a transient metal-hydride and a vinyl
amido ligand similar to an intermediate in the for-
mation of [(Ar′O)2Ta(dNAr′){N(Ar′)(CH2CH2Ph)}].11 An
insertion step could produce an azametallacyclobutane,
which can proceed to 3 by elimination of observed olefin.
The observation of only trans olefin requires stereo-
specific formation of the metallacycle and of the retro-
cycloaddition reaction. The closely related conversion
of an η2-imine complex, [Zr(tropocoronand){η2-Ar′NC-
(Bz)2}] (Ar′ ) 2,6-Me2C6H3), to yield a µ-imido species
apparently proceeds via elimination of a carbene group.10
Support for our proposal as well as evidence of
the generality of this reaction is provided by the
formation of the analogous imido species [{(Me2N)C-
(iPrN)2}2ZrdN(Me2C6H3)] (5) from the reaction of the
tetrasubstituted alkylguanidinate complex [{(Me2N)-
C(iPrN)2}2ZrMe2] (4)3 with CN(2,6-Me2C6H3), as de-
picted in Scheme 1. An equimolar reaction of these
reagents yields 5 over 1 day at room temperature.
Furthermore, as would be expected from our proposed
mechanism, propene evolution accompanied formation
of 5. The NMR spectra of 5 were similar to those of
1 with appropriate replacements, and the molecular
geometry of 5 is similar to that of 3.5
Ack n ow led gm en t. This work was supported by the
Natural Sciences and Engineering Research Council of
Canada.
Su p p or tin g In for m a tion Ava ila ble: Text giving experi-
mental details for compounds 1-3 and 5-7, figures giving
thermal ellipsoid plots of compounds 1, 5, and 6, and tables of
crystal data and structure solution and refinement details,
atomic coordinates, bond lengths and angles, and anisotropic
thermal parameters for compounds 1, 3, and 7. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM0108548
(12) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobriger, L.
M.; Latesky, S. L.; McMullen, A. K.; Steffey, B. D.; Rothwell, I. P.;
Folting, K.; Huffman, J . C. J . Am. Chem. Soc. 1987, 109, 6068. Durfee,
L. D.; McMullen, A. K.; Rothwell, I. P. J . Am. Chem. Soc. 1988, 110,
1463.
(13) Giannini, L.; Caselli, A.; Solari, E.; Floriani, C.; Chiesi-Villa,
A.; Rizzoli, C.; Re, N.; Sgamellotti, A. J . Am. Chem. Soc. 1997, 119,
9709.
Complex 4 also reacts with CN(2,6-Me2C6H3) in a
(14) Hardesty, J . H.; Albright, T. A.; Kahlal, S. Organometallics
2000, 19, 4159.
1:2 stoichiometric ratio. In this case the new bis(η2-
(15) Crystal data: empirical formula C38H64N8Zr, T ) 203(2) K, λ )
0.710 73 Å, space group P1h, a ) 10.9082(18) Å, b ) 111.226 76(18) Å,
c ) 18.699(3) Å, R ) 73.361(3)°, â ) 86.806(3)°, γ ) 61.590(3)°,
V ) 1921.0(5) Å3, Z ) 2, R indices (I > 2σ(I)) R1 ) 0.0520 and
wR2 ) 0.0815.
(16) Berg, F. J .; Peterson, J . L. Organometallics 1991, 10, 1599 and
references therein. Berg, F. J .; Peterson, J . L. Organometallics 1989,
8, 2461.
Inorg. Chem. 1992, 31, 3749. (j) Profilet, R. D.; Zambrano, C. H.;
Fanwick, P. E.; Nash, J . J .; Rothwell, I. P. Inorg. Chem. 1990, 29, 4362.
(k) Walsh, P. J .; Hollander, F. J .; Bergman, R. G. J . Am. Chem. Soc.
1988, 110, 8729.
(10) Scott, M. J .; Lippard, S. J . Organometallics 1997, 16, 5857.
(11) Chamberlain, L. R.; Steffey, B. D.; Rothwell, I. P.; Huffman,
J . C. Polyhedron 1989, 8, 341.