Synthesis, Structure, and Characterization of the Hydrogen-Substituted Imido Complex TiCl2(NH)(OPPh3)2

Full text of DOI:10.1021/ic960595s

5968
Inorg. Chem. 1996, 35, 5968-5969
Synthesis, Structure, and Characterization of the Hydrogen-Substituted Imido Complex
TiCl2(NH)(OPPh3)2
Peggy J. McKarns,1a Glenn P. A. Yap,1b Arnold L. Rheingold,1b and Charles H. Winter*,1a
Departments of Chemistry, Wayne State University, Detroit, Michigan 48202, and University of Delaware, Newark, Delaware 19716
ReceiVed May 22, 1996
The reaction of high-valent early transition metal halides or
alkylamides with ammonia represents one of the most common
routes to metal(III) nitride films.2,3 There has been considerable
speculation that metal imido complexes of the formula LnMNH
(L ) halide, NR2) are important intermediates in such film
deposition processes.4-6 For example, imido complexes bearing
TiNH groups have been suggested as intermediates along the
reaction path leading to titanium nitride films from titanium
tetrachloride and ammonia.4 Imido complexes of the formula
Ti(NH)(NR2)2 have been frequently proposed as intermediates
in the formation of titanium nitride films by ammonolysis of
Ti(NR2)4 (R ) Me, Et).5,6 We recently reported evidence that
alkylimido complexes are important gas phase species in the
deposition of titanium nitride,7 niobium nitride,8 and tantalum
nitride8 films from molecular precursors. In particular, mass
spectrometry studies of the niobium and tantalum nitride
deposition systems suggested that dealkylation of the alkylimido
ligand occurs to afford the hydrogen-substituted imido complex.8
Despite the relative abundance of group 4 and 5 alkylimido
complexes with monomeric linkages,9 there are only three
reported complexes bearing terminal hydrogen-substituted imido
groups in the group 5 metals10 and none in the group 4 metals.
As part of our program to explore coordination chemistry
relevant to film depositions, we sought to develop routes to
hydrogen-substituted imido complexes. Herein we report the
synthesis, structure, and properties of TiCl2(NH)(OPPh3)2, which
constitutes the first group 4 complex containing a terminal
hydrogen-substituted imido ligand.
11
Treatment of TiCl4(NH3)2 with sodium hydride (2 equiv)
in diethyl ether at ambient temperature led to rapid gas evolution
(complete in <10 min) with concomitant formation of an
orange-yellow suspension (eq 1). After 0.25 h, triphenylphos-
phine oxide (2 equiv) was added and the solution was refluxed
for 18 h, during which the color changed to lemon yellow.
Removal of the diethyl ether, extraction with dichloromethane,
filtration, and crystallization from dichloromethane/hexane
afforded TiCl2(NH)(OPPh3)2 (1, 73%) as large, well-formed
lemon yellow polygons.12 The formulation for 1 was based
upon spectral and analytical data, as well as on a crystal structure
1
determination (vide infra). The H NMR at 25 °C in chloro-
form-d or benzene-d6 showed resonances attributable only to
phenyl hydrogens; the imido proton was not detected. Low-
1
temperature H NMR spectra in chloroform-d (-55 to 0 °C)
were similar to the spectrum at 25 °C and did not reveal the
imido hydrogen. The imido hydrogen may be obscured by the
phenyl protons, or the resonance could be broad due to coupling
to 14N (I ) 1, 99.63%).13,14
(1) (a) Wayne State University. (b) University of Delaware.
(2) Kurtz, S. R.; Gordon, R. G. Thin Solid Films 1986, 140, 277.
Yokoyama, N.; Hinode, K.; Homma, Y. J. Electrochem. Soc. 1991,
138, 190. Buiting, M. J.; Otterloo, A. F.; Montree, A. H. J.
Electrochem. Soc. 1991, 138, 500.
(11) Winter, C. H.; Lewkebandara, T. S.; Proscia, J. W.; Rheingold, A. L.
(3) Oya, G.-I.; Onodera, Y. J. Appl. Phys. 1974, 45, 1389. Takahashi, T.;
Itoh, H.; Ozeki, S. J. Less-Common Met. 1977, 52, 29. Kieda, N.;
Mizutani, N.; Kato, M. Proc.sElectrochem. Soc. 1987, 87-88, 1203.
Nippon Kagaku Kaishi 1987, 1934.
(4) For leading references, see: Everhart, J. B.; Ault, B. S. Inorg. Chem.
1995, 34, 4379. Dekker, J. P.; van der Put, P. J.; Veringa, H. J.;
Schoonman, J. J. Electrochem. Soc. 1994, 141, 787. Saeki, Y.;
Matsuzaki, R.; Yajima, A.; Akiyama, M. Bull. Chem. Soc. Jpn. 1982,
55, 3193. Dunn, P. Aust. J. Chem. 1960, 13, 225. Cueilleron, J.;
Charret, M. Bull. Soc. Chim. Fr. 1956, 802. Antler, M.; Laubengayer,
A. W. J. Am. Chem. Soc. 1955, 77, 5250. Fowles, G. W. A.; Pollard,
F. H. J. Chem. Soc. 1953, 2588.
(5) Fix, R. M.; Gordon, R. G.; Hoffman, D. M. J. Am. Chem. Soc. 1990,
112, 7833. Chem. Mater. 1991, 3, 1138. See also: Hoffman, D. M.
Polyhedron 1994, 13, 1169.
(6) Weiller, B. H. Chem. Mater. 1995, 7, 1609. 1994, 6, 260. Dubois, L.
H.; Zegarski, B. R.; Girolami, G. S. J. Electrochem. Soc. 1992, 139,
3603. Prybyla, J. A.; Chiang, C.-M.; Dubois, L. H. J. Electrochem.
Soc. 1993, 140, 2695. Dubois, L. H. Polyhedron 1994, 13, 1329.
Intemann, A.; Koerner, H.; Koch, F. J. Electrochem. Soc. 1993, 140,
3215.
(7) Lewkebandara, T. S.; Sheridan, P. H.; Heeg, M. J.; Rheingold, A. L.;
Winter, C. H. Inorg. Chem. 1994, 33, 5879.
(8) Jayaratne, K. C.; Yap, G. P. A.; Haggerty, B. S.; Rheingold, A. L.;
Winter, C. H. Inorg. Chem. 1996, 35, 4910.
(9) For a recent comprehensive review, see: Wigley, D. E. Prog. Inorg.
Chem. 1994, 42, 239.
(10) Freundlich, J. S.; Schrock, R. R.; Cummins, C. C.; Davis, W. M. J.
Am. Chem. Soc. 1994, 116, 6476. Cummins, C. C.; Schrock, R. R.;
Davis, W. M. Inorg. Chem. 1994, 33, 1448. Parkin, G.; van Asselt,
A.; Leahy, D. J.; Whinnery, L.; Hua, N. G.; Quan, R. W.; Henling, L.
M.; Schaefer, W. P.; Santasiero, B. D.; Bercaw, J. E. Inorg. Chem.
1992, 31, 82.
Inorg. Chem. 1994, 33, 1227.
(12) Spectral and analytical data for 1: mp >300 °C; IR (Nujol, cm-1
)
3161 (w), 1591 (m), 1378 (m), 1312 (m), 1279 (w), 1190 (vs), 1165
(s), 1146 (s), 1122 (vs), 1095 (s), 1072 (s), 1060 (s), 1027 (m), 997
(s), 971 (w), 939 (w), 862 (w), 847 (w), 763 (s), 751 (s), 722 (vs),
1
699 (vs); H NMR (CDCl3, δ, 23 °C) 7.70-7.45 (m, 2 (C6H5)3PO);
13C{1H} NMR (CDCl3, ppm, 23 °C) 132.92 (s, ipso C of P-C6H5),
132.05 (d, JCP ) 9.0 Hz, ortho or meta C of P-C6H5), 131.88 (d, JCP
) 1.8 Hz, para C of P-C6H5), 128.44 (d, JCP ) 11.6 Hz, ortho or
meta C of P-C6H5); 31P{1H} NMR (CDCl3, ppm, 23 °C) 50.44 (s,
minor), 48.04 (s, minor), 42.38 (s, major), 28.51 (s, minor). Anal.
Calcd for C36H31Cl2NO2P2Ti: C, 62.63; H, 4.53. Found: C, 61.98;
H, 4.30.
(13) Further evidence for the imido hydrogen in 1 comes from the reaction
with triethylamine (1.1 equiv) in dichloromethane (48 h, 23 °C), which
afforded triethylammonium chloride (87% isolated yield, identified
by melting point, 1H NMR, and gravimetric analysis of chloride ion)
and unidentified, insoluble titanium complexes.
1
(14) Because the imido hydrogen could not be detected by H NMR, the
deuterated complex TiCl2(ND)(OPPh3)2 (1-d) was prepared as above
from TiCl4(ND3)2. Analysis of 1-d by 2H NMR did not show the imido
deuterium resonance. The infrared spectrum of 1-d was carefully
compared with that of 1. A very weak N-H stretch was tentatively
assigned in 1 at 3161 cm-1, while in 1-d this stretch came at 2345
cm-1. Examination of the fingerprint region showed six absorptions
that shifted to lower energy by a factor of 1.012-1.023 upon going
from 1 to 1-d: 1279 (1262), 1165 (1139), 1060 (1047), 1101 (1088),
1060 (1047), 939 (925), and 763 (754) cm-1. The bands that are
sensitive to isotope substitution are probably associated with combina-
tion stretches involving the imido ligand and with N-H wagging
modes: Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed.; Wiley-Interscience: New York,
1986; pp 191-205.
S0020-1669(96)00595-2 CCC: $12.00 © 1996 American Chemical Society

Communications
Inorganic Chemistry, Vol. 35, No. 21, 1996 5969
and 88.1° for the cis ligands and between 146.7 and 156.9°
for the trans ligands. The titanium-oxygen-phosphorus
angles are suprisingly obtuse at 148.7(5)° (Ti-O(1)-P(1))
and 162.2(5)° (Ti-O(2)-P(2)). These large angles are probably
the result of steric interactions involving the phenyl groups,
rather than multiple bonding between titanium and oxygen.
In summary, deprotonation of TiCl4(NH3)2 with sodium
hydride, followed by addition of triphenylphosphine oxide,
provides the hydrogen-substituted imido complex 1 in good
yield. The formation of 1 presumably proceeds by elimination
of ammonia from TiCl2(NH2)2 to afford the imido species [TiCl2-
(NH)]n, which is then trapped by triphenylphosphine oxide to
give 1. The diethyl ether solvent probably coordinates weakly
to [TiCl2(NH)]n, thereby stabilizing it and facilitating its
formation. Complex 1 represents a base-stabilized structural
model for a species that may play an important role in the
formation of titanium nitride films. Moreover, the vibrational
spectroscopy analysis presented herein14 serves as a valuable
benchmark for in situ infrared studies of film deposition
processes6 and may allow for definitive characterization of
hydrogen-substituted imido species in such systems. Finally,
the successful synthesis of 1 suggests that deprotonation of
ammonia adducts of other high-valent early transition metal
chlorides17 should also provide hydrogen-substituted imido
complexes. The synthesis of such species, as well as the study
of their role in the deposition of metal nitride films, is being
pursued in our laboratory.
Figure 1. Perspective view of C36H31Cl2NO2P2Ti (1) with thermal
ellipsoids at the 35% probability level. Selected bond lengths (Å) and
angles (deg): Ti-N 1.627(8), Ti-Cl(1) 2.374(4), Ti-Cl(2) 2.355(4),
Ti-O(1) 2.009(7), Ti-O(2) 2.023(8); N-Ti-Cl(1) 107.9(3), N-Ti-
Cl(2) 105.4(3), N-Ti-O(1) 102.3(4), N-Ti-O(2) 100.7(4), Cl(1)-
Ti-O(1) 86.9(2), Cl(1)-Ti-O(2) 84.7(2), Cl(2)-Ti-O(1) 87.2(2),
Cl(2)-Ti-O(2) 88.1(2), Cl(1)-Ti-Cl(2) 146.7(2), O(1)-Ti-O(2)
156.9(3).
Figure 1 shows a perspective view of 1 along with selected
bond lengths and angles.15 The complex adopts approximately
square pyramidal geometry, with nitrogen at the apex and trans-
triphenylphosphine oxide ligands and trans-chloride ligands at
the base. The titanium-nitrogen bond length (1.627(8) Å) is
very short, while the titanium-chlorine bond lengths are typical
at 2.355(4) and 2.374(4) Å. The titanium-oxygen bond lengths
are 2.023(8) and 2.009(7) Å. These values are close to those
expected for titanium-oxygen single bonds16 and do not indicate
significant multiple-bond character. The angles associated with
the apical nitrogen range between 100.7 and 107.9°, which
indicate that a “flat” square pyramid is formed. The angles
associated with the base of the pyramid range between 84.7
Acknowledgment. We are grateful to the National Science
Foundation (Grant CHE-9510712 to C.H.W.) for support of this
research.
Supporting Information Available: Tables S1-S7, listing full
experimental details for data collection and refinement, atomic coor-
dinates, bond lengths, bond angles, and thermal parameters, for 1, text
giving preparative details for new compounds, and figures showing IR
spectra for 1 and 1-d (11 pages). An X-ray crystallographic file, in
CIF format, is available. Access and ordering information is given on
any current masthead page.
(15) For C36H31Cl2NO2P2Ti: monoclinic, P21/c, a ) 17.341(6) Å, b )
18.390(6) Å, c ) 11.308(5) Å, â ) 98.37(3)°, V ) 3568(2) Å3, Z )
4, T ) 298 K, Dcalc ) 1.285 g cm-3, R(F) ) 8.50% for 2178 observed
independent reflections (4° e 2θ e 45°). Carbon and nitrogen atoms
were refined isotropically. Hydrogen atoms were refined as idealized
contributions. All other atoms were refined anisotropically. Phenyl
rings were refined as rigid bodies.
IC960595S
(17) For leading references, see: Yajima, A.; Segawa, Y.; Matsuzaki, R.;
Saeki, Y. Bull. Chem. Soc. Jpn. 1983, 56, 2638. Fowles, G. W. A.
Prog. Inorg. Chem. 1964, 6, 1. Nicholls, D. Coord. Chem. ReV. 1966,
1, 379.
(16) Winter, C. H.; Sheridan, P. H.; Heeg, M. J. Inorg. Chem. 1991, 30,
1962.