A new type of asymmetric tridentate pyrrolyl-linked pincer ligand and lts aluminum dihydride complexes

Article abstract of DOI:10.1021/ic9016189

The new pyrrolyl-linked pincer-type ligand, [C₄H ₂NH(2-CH₂NH^tBu)(5-CH₂NMe ₂)] (1), that has been employed conveniently in high yield by treatment of (2-t-butylaminomethyl)pyrrole with 1 equiv of formaldehyde and dimethylamine hydrochloride each in diethylether and its corresponding aluminum derivative, [C₄H₂N(2-CH₂NH^tBu)(5- CH₂NMe₂)]AlH₂ (2), that has been generated from Me₃N.AlH₃ using diethylether as a solvent are described. Furthermore, reactions of 2 with 2 equiv of either 1,3-diphenylpropane-1,3-dione in diethylether or phenyl thioisocyanate in dichloromethane interestingly formed [C₄H₂N(2-CH₂NH^tBu)(5-CH ₂NMe₂)]Al(PhCOCHCOPh)₂ (3) and [C ₄H₂N(2-CH₂NH^tBu)(5-CH ₂NMe₂)]Al(SCHNPh)₂ (4), respectively, following deprotonation or hydroalumination reaction kinetics under a dry nitrogen environment. All of the compounds have been subjected to the X-ray diffraction technique in the solid state as well as characterized by NMR spectra.

Full text of DOI:10.1021/ic9016189

136 Inorg. Chem. 2010, 49, 136–143
DOI: 10.1021/ic9016189
A New Type of Asymmetric Tridentate Pyrrolyl-Linked Pincer Ligand and
Its Aluminum Dihydride Complexes
Yu-Ling Lien,† Ya-Chi Chang,† Nien-Tsu Chuang,† Amitabha Datta,† Shau-Jiun Chen,† Ching-Han Hu,†
Wen-Yen Huang,† Chia-Her Lin,‡ and Jui-Hsien Huang*,†
†Department of Chemistry, National Changhua University of Education, Changhua, Taiwan 500 and
‡Department of Chemistry, Chung-Yuan Christian University, Chung-Li, Tau Yan, Taiwan
Received August 13, 2009
The new pyrrolyl-linked pincer-type ligand, [C4H2NH(2-CH2NHtBu)(5-CH2NMe2)] (1), that has been employed
conveniently in high yield by treatment of (2-t-butylaminomethyl)pyrrole with 1 equiv of formaldehyde and dimethyl-
amine hydrochloride each in diethylether and its corresponding aluminum derivative, [C4H2N(2-CH2NHtBu)-
(5-CH2NMe2)]AlH2 (2), that has been generated from Me3N AlH3 using diethylether as a solvent are described.
3
Furthermore, reactions of 2 with 2 equiv of either 1,3-diphenylpropane-1,3-dione in diethylether or phenyl
thioisocyanate in dichloromethane interestingly formed [C4H2N(2-CH2NHtBu)(5-CH2NMe2)]Al(PhCOCHCOPh)2
(3) and [C4H2N(2-CH2NHtBu)(5-CH2NMe2)]Al(SCHNPh)2 (4), respectively, following deprotonation or hydroalumi-
nation reaction kinetics under a dry nitrogen environment. All of the compounds have been subjected to the X-ray
diffraction technique in the solid state as well as characterized by NMR spectra.
Introduction
The different electronic properties of the phosphine and
amine ligands and the more labile coordination of the latter
in the case of late transition metal complexes5 can play
important roles in catalytic and stochiometric reactions, as
shown for complexes based on PNN-type ligands.6 The field
of aluminum hydride chemistry could be said to have been
inaugurated because of its diverse range of applications in the
solid state regarding some alane amine adducts showing
Organometallic pincer complexes containing tridentate
monoanionic ligands composed of an anionic aryl carbon atom
and two mutually trans-chelating donor sites at the 2,6 positions
of the aromatic ring have been attracting widespread interest in
catalysis and material science.1 Pincer compounds are a group
of species showing high thermal stability and unusual charac-
teristics of robustness that attract the continuous attention of
the chemistry community for multiple applications, this being
particularly true in the case of homogeneous catalysis.2
dimeric connectivities [(H3Al L)2]7 with five-coordinated
3
aluminum atoms and somewhat counterintuitive unsymme-
trical Al-H-Al bridges, while, on the other hand, others
seem to favor a monomeric mode with four-coordinated Al in
Transition metal complexes of bulky pincer-type ligands3
have found significant applications in synthesis, bond activa-
tion, and catalysis. Among those, complexes of the pyridine-
based bulky ligand tBuPNP (tBuPNP=2,6-(di-tert-butylphos-
phinomethyl) pyridine) have been explored in recent years.4
H3Al L.8 In this regard, hydroalumination reactions using
3
complex aluminum hydrides work extremely well for term-
inal alkenes and internal alkynes that result in an interesting
observation of the regeoselectivity involved in bis(dialkyl-
amino)alane.9 This group reported earlier the details of the
HAl(NR2)2 hydroalumination of alkenes10 and catalytic
*To whom correspondence should be addressed. E-mail: juihuang@
cc.ncue.edu.tw.
(1) (a) Albrecht, K.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750.
(b) Singleton, J. T. Tetrahedron 2003, 59, 1837. (c) Dupont, J.; Consorti, C. S.;
Spencer, J. Chem. Rev. 2005, 105, 2527.
(2) (a) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759.
(b) Morales-Morales, D. Rev. Soc. Quim. Mex. 2004, 48, 338. (c) Szabo, K. J.
Syn. Lett. 2006, 811.
(5) Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. 1994, 33, 497.
(6) (a) Choualeb, A.; Lough, A. J.; Gusev, D. G. Organometallics 2007,
26, 5224. (b) Gomez-Benitez, V.; Toscano, R. A.; Morales-Morales, D. Inorg.
Chem. Commun. 2007, 10, 1. (c) Poverenov, E.; Leitus, G.; Shimon, L. J. W.;
Milstein, D. Organometallics 2005, 24, 5937.
(3) (a) Jensen, C. M. Chem. Commun. 1999, 2443. (b) Vigalok, A.; Milstein,
D. Acc. Chem. Res. 2001, 34, 798. (c) Rybtchinski, B.; Milstein, D. Angew.
Chem., Int. Ed. 1999, 38, 870. (d) Milstein, D. Pure Appl. Chem. 2003, 75, 445.
(4) (a) Kawatsura, M.; Hartwig, J. F. Organometallics 2001, 20, 1960.
(b) Stambuli, J. P.; Stauffer, S. R.; Shaughnessy, K. H.; Hartwig, J. F. J. Am.
Chem. Soc. 2001, 123, 2677. (c) Gibson, D. H.; Pariya, C.; Mashuta, M. S.
Organometallics 2004, 23, 2510. (d) Kloek, S. M.; Heinekey, D. M.; Goldberg,
K. I. Organometallics 2006, 25, 3007.
(7) (a) Atwood, J. L.; Bennett, F. R.; Elms, F. M.; Jones, C.; Raston,
C. L.; Robinson, K. D. J. Am. Chem. Soc. 1991, 113, 8183. (b) Andrews, P. C.;
Gardiner, M. G.; Raston, C. L.; Tolhurst, V. A. Inorg. Chim. Acta 1997, 259, 249.
(8) (a) Lobkovski, E. B.; Semenenko, K. N. Zh. Strukt. Khim 1975, 16, 50.
(b) Atwood, J. L.; Butz, K. W.; Gardiner, M. G.; Jones, C.; Koutsantonis, G. A.;
Raston, C. L.; Robinson, K. D. Inorg. Chem. 1993, 32, 3482.
(9) Ashby, E. C.; Noding, S. A. J. Org. Chem. 1980, 45, 1035.
(10) Ashby, E. C.; Noding, S. A. J. Org. Chem. 1979, 44, 4364.
r
pubs.acs.org/IC
Published on Web 12/01/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 1, 2010 137
Scheme 1
Scheme 2
A schematic drawing of the pincer-type ligands is shown in
Scheme 1 where types A and B are formed from aromatic
rings of phenyl or pyridine and type C represents donor atom
linkages.19-21 The D1 and D2 of the pincer-type ligands are
donating atoms such as N, P, As, O, S, and so forth.
activities of bis(dialkylamino)alanes to olefins and alkynes.
Furthermore, it is a convenient phenomenon related to
aluminum hydrogen bonds because of its well-known modu-
lations, and the topics relating to their applications have been
reviewed periodically.11 However, the tendency for the hy-
dride to bridge two metal atoms allows the aluminum hydride
compounds to aggregate as dimers12 or oligomers.13 The
aggregated aluminum compounds may show less reactivity in
comparison to those of monomeric14 ones presumably be-
cause of the modulation for breaking the Al-H-M (where
M = Al, Li, etc.) bond.15 Organic ligands containing bulky
groups bound to an aluminum center not only take part in
increasing the solubility of organoaluminum hydride com-
pounds in organic solvents but also are very consistent in
preventing the aggregation of aluminum hydride.16 There-
fore, ligand design participates in a well-known criterion in
organometallic chemistry and activates not only an increase
in the stability of these compounds but also the reactivity as
well, both sterically and electronically.17 Multidentate pincer-
type ligands containing rigid and nonrigid linker have raised
much attention in the past decade because of their multiple-
bonding modes and versatility of coordinating groups.18
In addition to the aromatic-linked tridentate pincer ligands,
pyrrolyl-linked anionic tridentate pincer ligands are also used
in many groups as supporting ligands to bind metals.22,23
Some of the pyrrolyl ligand systems are shown in Scheme 2,
where all of these ligands exhibit symmetrical manners. To be
concise about the chemistry of the pyrrolyl-based system,
reactions of aluminum hydride complexes with ketones
generating aluminum alkoxide complexes via hydride insertion
have been reported previosuly,24 and we also showed the
reactivity of monomeric aluminum hydride compounds with
pyrrolyl ligands25 reflecting insertion and a C-C coupling
mechanistic pathway. In the present contribution, we have
developed a new typeofasymmetricalpyrrolyl-linkedanionic
tridentate pincer ligand, [C4H2NH(2-CH2NHtBu)(5-CH2-
NMe2)] (1), and its corresponding aluminum derivative,
[C4H2N(2-CH2NHtBu)(5-CH2NMe2)]AlH2 (2), that moder-
ately undergoes further reaction to [C4H2N(2-CH2NHtBu)-
(5-CH2NMe2)]Al(PhCOCHCOPh)2 (3) and [C4H2N(2-CH2-
NHtBu)(5-CH2NMe2)]Al(SCHNPh)2 (4), to explore the
reactivity via deprotonation or hydroalumination reactions.
All of the compounds are well characterized by single-crystal
X-ray diffraction analysis and NMR spectra.
(11) (a) Gardiner, M. G.; Raston, C. L. Coord. Chem. Rev. 1997, 166, 1.
(b) Jones, C.; Koutsantonis, G. A.; Raston, C. R. Polyhedron 1993, 12, 1829.
(c) Cowley, A. H.; Gabbaï, F. P.; Isom, H. S.; Decken, A. J. Organomet. Chem. 1995,
500, 81. (d) Downs, A. J. Coord. Chem. Rev. 1999, 189, 59. (e) Wehmschulte, R. J.;
Power, P. P. Polyhedron 2000, 19, 1649.
Results and Discussion
Preparation of Asymmetrical Ligand 1 and Aluminum
Dihydride Compound 2. A rational design and synthetic
(12) (a) Jones, C.; Waugh, M. Dalton Trans. 2004, 1971. (b) Janik, J. F.;
Wells, R. L.; Rheingold, A. L.; Guzei, I. A. Polyhedron 1998, 17, 4101. (c) Bauer,
T.; Schulz, S.; Nieger, M.; Kessler, U. Organometallics 2003, 22, 3134.
(d) Gorrell, I. B.; Hitchcock, P. B.; Smith, J. D. Chem. Commun. 1993, 189.
(13) (a) Veith, M.; Freres, J.; Huch, V.; Zimmer, M. Organometallics
2006, 25, 1875. (b) Noth, H.; Schlegel, A.; Knizek, J.; Krossing, I.; Schwenk, H.
Angew. Chem., Int. Ed 1997, 36, 2640. (c) Etkin, N.; Hoskin, A. J.; Stephan,
D. W. J. Am. Chem. Soc. 1997, 119, 11420.
(14) (a) Brazeau, A. L.; Wang, Z.; Rowley, C. N.; Barry, S. T. Inorg.
Chem. 2006, 45, 2276. (b) Knizek, J.; Noth, H.; Schlegel, A. Eur. J. Inorg. Chem.
2001, 181. (c) Luo, B.; Kucera, B. E.; Gladfelter, W. L. Dalton Trans. 2006, 4491.
(d) Kuhn, N.; Fuchs, S.; Steimann, M. Z. Anorg. Allg. Chem. 2000, 626, 1387.
(e) Glore, J. D.; Hall, R. E.; Schram, E. P. Inorg. Chem. 1972, 11, 550.
(15) (a) Aldridge, S.; Blake, A. J.; Downs, A. J.; Gould, R. O.; Parsons, S.;
Pulham, C. R. J. Chem. Soc., Dalton Trans. 1997, 1007. (b) Veith, M.; Konig,
P.; Rammo, A.; Huch, V. Angew. Chem., Int. Ed. 2005, 44, 5968. (c) Girolami,
G. S.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M. B. J. Am. Chem. Soc.
1983, 105, 6752. (d) Bruno, J. W.; Huffman, J. C.; Caulton, K. G. J. Am. Chem.
Soc. 1984, 106, 444.
(16) (a) Leung, W.-P.; So, C.-W.; Chong, K.-H.; Kan, K.-W.; Chan,
H.-S.; Mak, T. C. W. Organometallics 2006, 25, 2851. (b) Zhu, H.; Chai, J.;
Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G.; Vidovic, D.; Magull, J. Eur. J.
Inorg. Chem. 2003, 3113. (c) Carey, D. T.; Mair, F. S.; Pritchard, R. G.; Warren,
J. E.; Woods, R. J. Dalton Trans. 2003, 3792.
(17) (a) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283.
(b) Dechy-Cabaret, O.; Martin-Vaca, B.; Bourissou, D. Chem. Rev. 2004, 104,
6147. (c) Park, S.; Han, Y.; Kim, S. K.; Lee, J.; Kim, H. K.; Do, Y. J. Organomet.
Chem. 2004, 689, 4263.
(19) (a) Abbenhuis, H. C. L.; Feiken, N.; Grove, D. M.; Jastrzebski, J. T.
B. H.; Kooi’man, H.; van der Sluis, P.; Smeets, W. J. J.; Spek, A. L.;
van Koten, G. J. Am. Chem. Soc. 1992, 114, 9773. (b) Gupta, M.; Hagen, C.;
Kaska, W. C.; Cramer, R. E.; Jensen, C. M. J. Am. Chem. Soc. 1997, 119, 840.
(c) Gerisch, M.; Krumper, J. R.; Bergman, R. G.; Tilley, T. D. J. Am. Chem. Soc.
2001, 123, 5818.
(20) (a) Baratta, W.; Ballico, M.; Chelucci, G.; Siega, K.; Rigo, P. Angew.
Chem., Int. Ed. 2008, 47, 4362. (b) Pugh, D.; Wright, J. A.; Freeman, S.;
Danopoulos, A. A. Dalton Trans. 2006, 775. (c) Vuzman, D.; Poverenov, E.;
Shimon, L. J. W.; Diskin-Posner, Y.; Milstein, D. Organometallics 2008, 27,
~
2627. (d) Castarlenas, R.; Esteruelas, M. A.; Onate, E. Organometallics 2007, 26,
3082.
(21) (a) Nuzzo, R. G.; Haynie, S. L.; Wilson, M. E.; Whitesides, G. M.
J. Org. Chem. 1981, 46, 2861. (b) Cerrada, E.; Falvello, L. R.; Hursthouse, M. B.;
Laguna, M.; Luquín, A.; Pozo-Gonzalo, C. Eur. J. Inorg. Chem. 2002, 826.
€
(22) (a) Mazet, C.; Gade, L. H. Chem.;Eur. J. 2003, 9, 1759. (b) Broring,
M.; Prikhodovski, S.; Brandt, C. D. Inorg. Chim. Acta 2004, 357, 1733.
(c) Tsurugi, H.; Matsuo, Y.; Yamagata, T.; Mashima, K. Organometallics 2004,
23, 2797. (d) Mazet, C.; Gade, L. H. Organometallics 2001, 20, 4144.
(23) (a) Li, Y.; Banerjee, S.; Odom, A. L. Organometallics 2005, 24, 3272.
(b) Kuo, P.-C.; Chang, J.-C.; Lee, W.-Y.; Lee, H. M.; Huang, J.-H. J. Organomet.
Chem. 2005, 690, 4168. (c) Kuo, P.-C.; Huang, J.-H.; Hung, C.-H.; Lee, G.-H.;
Peng, S.-M. Eur. J. Inorg. Chem. 2003, 1440. (d) Chang, J.-C.; Hung, C.-H.;
Huang, J.-H. Organometallics 2001, 20, 4445. (e) Huang, J.-H.; Chen, H.-J.;
Chang, J.-C.; Zhou, C.-C.; Lee, G.-H.; Peng, S.-M. Organometallics 2001, 20,
2647.
(24) (a) Yu, Z.; Wittbrodt, J. M.; Xia, A.; Heeg, M. J.; Schlegel, H. B.;
Winter, C. H. Organometallics 2001, 20, 4301. (b) Lansbury, P. T.; Rogozinski,
J. R.; Coblentz, F. L. J. Org. Chem. 1961, 26, 2277.
(25) Lin, C.-Y.; Tsai, C.-F.; Chen, H.-J.; Hung, C.-H.; Yu, R.-C.; Kuo,
P.-C.; Lee, H. M.; Huang, J.-H. Chem.;Eur. J. 2006, 12, 3067.
(18) (a) Benito-Garagorri, D.; Kirchner, K. Acc. Chem. Res. 2008, 41, 201.
(b) Nishiyama, H. Chem. Soc. Rev. 2007, 36, 1133. (c) Slagt, M. Q.; van Zwieten,
D. A. P.; Moerkerk, A. J. C. M.; Gebbink, R. J. M. K.; van Koten, G. Coord.
Chem. Rev. 2004, 248, 2275.

138 Inorganic Chemistry, Vol. 49, No. 1, 2010
Lien et al.
Scheme 3
procedure of the pyrrolyl-linked tridentate ligand 1 and
its aluminum dihydride compound 2 is shown in Scheme 3.
Ligand 1 was obtained from the reaction of [C4H3-
NH(2-CH2NHtBu)]26 with 1 equiv each of formaldehyde
and Me2NH HCl in a diethyl ether/water biphase solu-
3
tion. The 1H NMR spectrum of 1 shows two singlets at δ
1.11 and 2.18 for the methyl protons of tBuNH and Me2N
with a ratio of 3:2. A broad triplet for the amino proton of
tBuNH was observed at ca. δ 2.14, which partly over-
lapped with the methyl protons of NMe2. We have tried to
employ an alternative method to synthesize 1 from
[C4H3NH(2-CH2NMe2)], formaldehyde, and BuNH
t
3
HCl, and several compounds along with 1 have been
retrieved from the reaction mixture. However, we were
unable to separate 1 from other unidentified products
using simple trap-to-trap distillation. Ligand 1, obtained
after appropriate workup of the reaction, appears as a
sticky liquid at room temperature and is difficult to
solidify. However, a few colorless crystals were obtained
suitable for X-ray diffraction from a trap-to-trap distilla-
tion following a purification procedure. The molecular
structure of 1 and selected bond lengths and angles are
represented in Figure 1 and Table 1, respectively. The
asymmetrical ligand 1 exhibits a dimeric form where two
units of molecules bind together through intermolecular
hydrogen bonding. The distances of N(3)-N(5) and
Figure 1. Molecular structure of 1. The thermal ellipsoids are shown at
the 30% probability level. All of the hydrogen atoms (except NH) are
omitted for clarity.
amino proton of tBuNH results in the methylene protons of
tBuNHCH2 changing from doublet to singlet, which further
t
confirms the existence of the amino proton of BuNH.
Basically, the 1H NMR spectra of 2-D and 2 are the same
except for a broad signal observed at δ 4.29 for 2, but which
is absent in 2-D, that corresponds to the AlH2 protons. The
evidence for the existence of hydride for 2 can also be
established by means of correlating the IR stretching fre-
quency of Al-H appearing at 1813 cm-1, which is not
observed for 2-D. Compound 2 is highly moisture-sensitive
and decomposes to form unidentified products while being
exposed to the air for a short period. Considering the
coordinating nature of 1, it can be treated either as a mono
anionic ligand system by removing the pyrrolyl NH proton
or as a dianionic form executed by removal of an additional
amino proton of tBuNH. In this regard, 2 has been heated in
C6D6 at 90 °C in a J. Young NMR tube over 24 h in an
attempt to eliminate 1 equiv of hydrogen molecules, how-
ever, resulting in unidentified products.
˚
N(2)-N(6) are 3.142 and 3.168 A, respectively, confirming
the existence of hydrogen bonding of tBuNH NMe2.27
3 3 3
During an overnight reaction between
1 and
AlH3 NMe3,28 obtained from the reaction of LiAlH4
3
with Me3N HCl, in diethyl ether at 0 °C, an aluminum
3
dihydride compound 2, [C4H2N(2-CH2NHtBu)(5-CH2N-
Me2)]AlH2, was moderately yielded. A similar isotopic
compound 2-D, [C4H2N(2-CH2NHtBu)(5-CH2NMe2)]-
AlD2, was obtained using AlD3 NMe3, following the same
3
synthetic route mentioned above for 2. Compound 2 is
soluble in most of the organic solvents such as toluene,
diethyl ether, methylene chloride, and tetrahydrofuran but
only slightly soluble in hydrocarbon-like solvents such as
heptane. The 1H NMR spectra of 2 show one singlet at δ
2.18 for the Me2N and one broad triplet at δ 2.14 for the
amino proton of tBuNH. A homonuclear decoupling of the
A colorless crystal of 2 suitable for X-ray crystallogra-
phy was obtained at -20 °C from a diethyl ether solution.
Figure 2 shows a perspective drawing of the molecule 2
and the selective atomic labeling, and the necessary bond
lengths and angles are presented in Table 2. The mole-
cular structure of 2 is quite similar to that of [C4H2N-
(CH2NMe2)2-2,5]AlH2,23d considering the Al-N (pyrrolyl-N
and N-Me2 fragments) bond distances, 1.8487(10) and
(26) Chen, Y.-C.; Lin, C.-Y.; Li, C.-Y.; Huang, J.-H.; Chang, L.-C.; Lee,
T.-Y. Chem.;Eur. J. 2008, 14, 9747.
(27) (a) Gallagher, J. F.; Goswami, S.; Chatterjee, B.; Janab, S.; Dutta, K.
Acta Crystallogr. 2004, C60, o229. (b) Gallagher, J. F.; Briody, J. M.; Cantwell,
B. P. Acta Crystallogr. 1998, C54, 1331.
(28) Ruff, J. K.; Hawthorne, M. F. J. Am. Chem. Soc. 1960, 82, 2141.

Article
Inorganic Chemistry, Vol. 49, No. 1, 2010 139
Table 1
1
2
3
4
formula
fw
T, K
C
418.67
150(2)
24H46N6
C12H24AlN3
237.32
150(2)
C45.5H47.5AlN3O4
727.34
150(2)
C56H78Al2N10S4
1089.48
150(2)
cryst syst
space group
monoclinic
C2/c
27.1751(8)
16.7898(7)
12.3090(4)
90
monoclinic
C2/c
22.9553(16)
6.5478(4)
19.3734(12)
90
triclinic
P1
9.426(3)
12.260(4)
18.019(5)
75.317(6)
82.890(6)
83.565(6)
1991.9(10)
2
monoclinic
P2(1)/n
9.2065(3)
23.2457(8)
14.1390(6)
90
˚
a, A
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
105.747(2)
90
103.110(2)
90
108.7240(10)
90
3
˚
V, A
5405.4(3)
8
1.029
0.063
1856
2836.1(3)
8
1.112
0.124
1040
2865.76(18)
2
1.263
0.245
1164
Z
dcalcd, Mg/m3
μ, mm-1
F(000)
1.213
0.097
773
0.28 Â 0.19 Â 0.18
cryst size
˚
0.31 Â 0.22 Â 0.15
0.28 Â 0.17 Â 0.12
0.25 Â 0.17 Â 0.16
λ, A
no. of reflns collected
ind reflns
0.71073
21796
0.71073
18114
0.71073
29794
0.71073
23122
6529 (Rint =0.0272)
6529/0/297
1.067
R1 =0.0543
wR2 =0.1469
R1 =0.0823
wR2 =0.1620
0.616 and -0.224
3422 (Rint =0.0282)
3422/0/162
1.078
R1 =0.0327
wR2 =0.0907
R1 =0.0428
wR2 =0.0949
0.248 and -0.196
9529 (Rint =0.0926)
9592/0/497
0.994
R1 =0.0674
wR2 =0.1689
R1 =0.1508
wR2 =0.2164
0.390 and -0.423
6784 (Rint =0.0263)
6784/0/346
1.074
R1 =0.0377
wR2 =0.0956
R1 =0.0517
wR2 =0.1046
0.507 and -0.491
data/restraints/params
goodness-of-fit on F2
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
3
largest diff peak, hole (e/A )
˚
˚
2.2543(10) A, respectively, well comparable to those of
the previously reported structure, 1.8381(14), 2.2264(15),
˚
and 2.2461(16) A. It can be described as a distorted
trigonal bipyramidal where the nitrogen atoms of tBuNH
and Me2N fragments occupy the axial positions with a
corresponding bond angle of N(1)-Al(1)-N(3) at
˚
155.61(4)°. The bond length of Al(1)-N(1) (2.203(1) A)
˚
is slightly shorter than that of Al(1)-N(3) (2.254(1) A);
presumably, the Al atom has less congestion with the
t
smaller BuNH than with Me2N. The pyrrolyl nitrogen
atom in combining with two hydride atoms forms a
trigonal plane where the entire angle for the three indivi-
dual plane angles (N(2)-Al(1)-H(13), N(2)-Al(1)-
H(15), and H(15)-Al(1)-H(13)) is close to 360°. The
˚
bond length of Al(1)-N(2), 1.8487(9) A, belongs in the
normal range of the pyrrolyl nitrogen linked aluminum
atom, as reported in the literature.23b-d Again, the Al-H
bond lengths (1.51 A) are well comparable, belonging in
Figure 2. Molecular structure of 2. The thermal ellipsoids are shown at
the 30% probability level. All of the hydrogen atoms are omitted for
clarity.
˚
the range of previously published Al-H bond lengths in
neutral and anionic aluminum hydride compounds.16,23d
Deprotonation and Insertion Reactions of 2. The alumi-
num hydride of compound 2 may react with organic
compounds via hydroalumination or deprotonation, as
shown in Scheme 4, depending on the relative acidity of
organic molecules and the hydrides. The reactions of 2
with 1,3-diphenylpropane-1,3-dione and phenyl thioiso-
cyanate are shown in Scheme 5. Reacting 2 with 2 equiv of
1,3-diphenylpropane-1,3-dione in diethyl ether results in
a deprotonation of the methylene proton of the propane
backbone to generate diphenylacetonate aluminum com-
pound 3, [C4H2N(2-CH2NHtBu)(5-CH2NMe2)]Al(PhCO-
CHCOPh)2, in 64% yield. The compound can be fur-
ther purified via recrystallization from a toluene solution
at -20 °C to yield yellowish orange crystals. The presence of
and 4.64 for the methylene protons of the Me2NCH2,
representing the diasterotopic geometry of the two methy-
lene protons. The methylene protons of tBuNHCH2, how-
ever, show two more complicated multiplets at δ 3.64 and
4.03. Presumably, the strong steric congestion of the bulky
t-butyl amino group with the phenyl ring of the acetylace-
tonate ligands blocks the C-N bond rotation to resolve the
slow limit of methylene protons in the NMR spectroscopy.
Two singlets appearing at δ6.88 and 7.07 were assigned due
to the methine protons of the two acetylacetonate back-
bone, which further confirms the asymmetrical manner of 3.
Reacting 2 with 2 equiv of PhNCS in a diethyl ether
solution results in a double hydroaluminumation gener-
ating compound 4, [C4H2N(2-CH2NHtBu)(5-CH2NMe2)]-
Al(SCHNPh)2, in 57% yield. A similar reaction of 2-D with
PhNCS affords deuterium-inserted compound 4-D, [C4H2-
N(2-CH2NHtBu)(5-CH2NMe2)]Al(SCDNPh)2. The 1H NMR
1
a small amount of toluene is observed in the H and 13C
NMR spectra. Compound 3 shows two doublets at δ 3.58

140 Inorganic Chemistry, Vol. 49, No. 1, 2010
Lien et al.
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) for Compounds 1-4
1
C(1)-N(1)
1.376(2)
1.370(2)
122.43(16)
121.53(15)
C(1)-C(2)
1.365(3)
1.365(2)
114.24(14)
C(4)-N(1)
C(3)-C(4)
N(1)-C(1)-C(5)
N(1)-C(4)-C(8)
N(2)-C(5)-C(1)
2
Al(1)-N(1)
2.2030(10) Al(1)-N(2)
2.2543(10) C(1)-N(1)
1.8487(10)
1.5108(14)
77.68(4)
Al(1)-N(3)
N(2)-Al(1)-N(1)
N(1)-Al(1)-N(3) 155.62(4)
C(5)-N(1)-Al(1) 110.50(7)
78.04(4)
N(2)-Al(1)-N(3)
C(1)-N(1)-Al(1)
C(10)-N(3)-Al(1) 106.79(7)
119.87(7)
3
Al(1)-O(4)
1.859(2)
1.883(2)
1.931(2)
92.50(10)
88.32(9)
85.52(9)
97.36(10)
92.87(9)
175.32(10)
96.99(9)
80.86(10)
Al(1)-O(1)
1.881(2)
Al(1)-O(2)
Al(1)-O(3)
1.891(2)
2.111(3)
87.40(9)
Al(1)-N(1)
Al(1)-N(3)
O(4)-Al(1)-O(1)
O(1)-Al(1)-O(2)
O(1)-Al(1)-O(3)
O(4)-Al(1)-N(1)
O(2)-Al(1)-N(1)
O(4)-Al(1)-N(3)
O(2)-Al(1)-N(3)
N(1)-Al(1)-N(3)
O(4)-Al(1)-O(2)
O(4)-Al(1)-O(3)
O(2)-Al(1)-O(3)
O(1)-Al(1)-N(1)
O(3)-Al(1)-N(1)
O(1)-Al(1)-N(3)
O(3)-Al(1)-N(3)
89.74(9)
173.09(10)
170.11(10)
93.74(10)
89.25(10)
86.07(9)
4
Al(1)-N(1)
1.9021(13) Al(1)-N(4)
2.0207(14) Al(1)-N(2)
1.9837(14)
2.1206(14)
2.5184(6)
Figure 3. Molecular structure of 3. The thermal ellipsoids are shown at
the 30% probability level. All of the toluene and hydrogen atoms are
omitted for clarity.
Al(1)-N(5)
Al(1)-S(2)
2.4822(6)
97.79(6)
99.74(6)
99.31(6)
97.15(4)
68.56(4)
Al(1)-S(1)
N(1)-Al(1)-N(4)
N(4)-Al(1)-N(5)
N(4)-Al(1)-N(2)
N(1)-Al(1)-S(2)
N(5)-Al(1)-S(2)
N(1)-Al(1)-N(5) 100.24(6)
N(1)-Al(1)-N(2) 85.07(6)
N(5)-Al(1)-N(2) 159.31(6)
N(4)-Al(1)-S(2) 162.49(5)
N(2)-Al(1)-S(2)
N(4)-Al(1)-S(1)
N(2)-Al(1)-S(1)
91.02(4)
68.18(4)
89.79(4)
N(1)-Al(1)-S(1) 164.11(5)
N(5)-Al(1)-S(1)
S(2)-Al(1)-S(1)
89.84(4)
97.97(2)
Scheme 4
Scheme 5
Figure 4. Molecular structure of 4. The thermal ellipsoids are shown at
the 30% probability level. All of the diethyl ether and hydrogen atoms are
omitted for clarity.
spectra of 4 showed two singlets at δ 9.09 and 9.48 for the
methine protons of the two SCHNPh fragments. In addi-
tion, the 13C NMR spectra of 4-D show two triplets at δ
1
184.7 and 188.9 with the JC-D of both at 26 Hz, further
confirming the existence of the two SCDNPh fragments.29
The methylene protons of 4 for the two asymmetric side
arms, tBuNHCH2 and Me2NCH2, are all exhibiting stereo-
specific differentiation where four doublets are observed.
Presumably, the bulky tBuNH and Me2N fragments block
the C-N bond rotation of the methylene carbon and amino
nitrogen atom.
(29) (a) Monsted, L.; Monsted, O. Inorg. Chem. 2005, 44, 1950. (b) Casey,
C. P.; Strotman, N. A. J. Am. Chem. Soc. 2004, 126, 1699.

Article
Inorganic Chemistry, Vol. 49, No. 1, 2010 141
Scheme 6
showing sp2 hybridization for the carbon atom of the
NCS.
Scheme 7
Geometry Optimization of the Bonding Modes of the
Pincer Ligand. As we mentioned earlier, the pincer
ligands can bind metal atoms in various modes such as
tridentate NtBu-Npy-NMe2-bound, bidentate NtBu
-
Npy-bound. and Npy-NMe2-bound, and monodentate
Npy-bound, as shown in Scheme 6. The molecular struc-
tures of 2, 3, and 4, adopted directly from X-ray crystal
data, show the aforementioned bound nature that
has been represented as NtBu-Npy-NMe2-bound 2,
Npy-NMe2-bound 3, and Npy-NMe2-bound 4, shown in
Scheme 7. The factor influencing the molecular geome-
tries of these compounds is mainly the steric congestion.
This is further verified and established by density func-
tional theory, that is, B3LYP/6-31G*.31 The relative
energies of species with respect to that of the X-ray
resolved isomers of 2 and 3 (enthalpy at 298 K) are shown
X-ray-quality crystals of 3 and 4 were obtained from
in Scheme 7. The enthalpies in regard to Npy-NMe2
-
saturated solutions of toluene and methylene chloride,
respectively, at -20 °C. The data collections and selected
bond lengths and angles of 3 and 4 are listed in Tables 1
and 2, respectively. The molecular structure of 3 (Figure 3)
contains a toluene molecule and exhibits a distorted octahe-
dral geometry where the bond angles of the three axes
are close to linearity [O(2)-Al(1)-O(3), 173.09(10)°;
O(4)-Al(1)-N(3), 175.32(10)°; and O(1)-Al(1)-N(1),
170.11(10)°]. The corresponding bond lengths between alu-
minum and oxygen of diphenylactetylacetonate are rela-
tively shorter and smaller in biting angles in comparison to
those of the oxygen atoms of the acetylacetonate. The
pincer-type pyrrolyl ligand binds to the aluminum atom
only through the nitrogen atoms of pyrrole and Me2N
groups, leaving the tBuNH fragment outside the coordinat-
ing sphere. The bond lengths of Al-N are rather similar to
those of earlier reported aluminum pyrrolyl compounds.23d,e
The crystal of 4 contains one unit each of the aluminum
molecule and diethyl ether. One of the carbon atoms of
the diethyl ether is disordered and splits into two parts
with a 50:50 ratio. The molecular structure of 4 (Figure 4)
can be described as a distorted octahedral considering
the bond angles of the three axes being close to linea-
rity [N(1)-Al(1)-S(1), 164.11(5)°; N(4)-Al(1)-S(2),
162.49(5)°; and N(2)-Al(1)-N(5), 159.31(6)°]. The
bonding mode of the phenyl thioisocyanates to the alu-
minum atom is relatively similar to that described in the
literature30 by Jordan et al., where the thioisocyanate
bound 2 and NtBu-Npy-bound 2 are 9.6 and 8.8 kcal/
mol, respectively, higher than NtBu-Npy-NMe2-bound 2.
Similarly, NtBu-Npy-bound 3 is 0.2 kcal/mol, higher in
energy than Npy-NMe2-bound 3. Even the energy differ-
ence is small from our (gas-phase) computations; only the
crystals of Npy-NMe2-bound 3 can be generated. Vari-
1
able-temperature H NMR spectra of 3 show that the
activation energy (ΔG‡) of fast exchange between
Npy-NMe2-bound 3 and NtBu-Npy-bound 3 is estimated
at ca. 62.8 kJ/mol (15.0 kcal/mol).
Again, the relative energy profiles concerning the pos-
sible geometries of 4 were investigated. The correspond-
ing geometric isomers of 4 and their relative energy are
presented in Scheme 8. The theoretical computation
indicates that the crystal geometry of 4, that is, the
Npy-NMe2-bound 4, is the lowest-energy isomer. In con-
trast, isomers consisting of rotation of one or two phenyl
thiocyanate fragments are higher in energy.
Conclusion
In summary, we are able to synthesize a new type of
asymmetrical pyrrolyl-linked anionic tridentate pincer ligand
that further reacts with alane to form an asymmetrical
aluminum dihydride compound. The aluminum dihydride
compound shows high reactivity toward small organic mo-
lecules such as diphenyl acetylacetone and phenyl thioiso-
cyanate undergoing deprotonating or insertion reactions.
Future work will explore the mechanistic pathway and
modification that corresponds to several applications in
organic synthesis of the highly reactive asymmetrical alumi-
num dihydride compound, 2. In addition, the development of
an asymmetrical pyrrolyl-linked anionic tridentate pincer
˚
exhibits a NdC double bond [N(4)-C(19), 1.309(2) A;
˚
N(5)-C(26), 1.303(2) A] and a C-S single bond
˚
˚
[C(19)-S(1), 1.7006(17) A; C(26)-S(2), 1.6983(17) A].
The bond angles of N(4)-C(19)-S(1) and N(5)-C-
(26)-S(2) are 116.07(12) and 116.78(12)°, respectively,
(30) Coles, M. P.; Swenson, D. C.; Jordan, R. F. Organometallics 1998,
17, 4042.
(31) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, W.;
Parr, R. G. Phys. Rev. B 1988, 37, 785.

142 Inorganic Chemistry, Vol. 49, No. 1, 2010
Lien et al.
Scheme 8
ligand with a late transition metal is under progress in res-
ponse to growing interest as well.
ether (15 mL) solution of 1 (4.380 g, 20.90 mmol). The solution
was stirred at room temperature for 12 h, and the volatiles were
removed in vacuo to generate 3.770 g of a white solid (76%
yield). Colorless crystals suitable for X-ray analysis were ob-
tained from a diethyl ether solution at -20 °C. 1H NMR (C6D6):
1.02 (s, 9H, NCMe3), 2.14 (t, 1H, NHCMe3), 2.18 (s, 6H,
NMe2), 3.37 (s, 2H, CH2NMe2), 3.46 (d, JHH = 8.4 Hz, 2H,
CH2NHCMe3), 4.29 (br, 2H, Al-H), 6.27 (s, 1H, pyrrolyl CH),
6.33 (s, 1H, pyrrolyl CH). 13C (C6D6): 27.7 (q, JCH = 124 Hz,
Experimental Section
General Procedure. All of the reactions were performed using
standard Schlenk techniques in an atmosphere of high-purity
nitrogen or in a glovebox. Diethyl ether was dried by refluxing
over sodium benzophenone ketyl. CH2Cl2 was dried over P2O5.
All solvents were distilled and stored in solvent reservoirs which
NCMe3), 41.9 (t, JCH =138 Hz, CH2NHCMe3), 46.9 (q, JCH =
135 Hz, NMe2), 53.5 (s, NCMe3), 59.8 (t, JCH = 138 Hz,
CH2NMe2), 104.0 (d, JCH = 164 Hz, pyrrolyl CH), 105.5 (d,
˚
contained 4 A molecular sieves and were purged with nitrogen.
CDCl3 and C6D6 were degassed by using freeze-and-thaw cycles
1
and dried over 4 A molecular sieves. H and 13C NMR spectra
˚
J
CH = 164 Hz, pyrrolyl CH), 130.0 (s, pyrrolyl Cipso), 131.9 (s,
pyrrolyl Cipso). IR (KBr): 1813 cm-1 (υAl-H). Anal. Calcd for
C12H24AlN3: C, 60.73; H, 10.19; N, 17.71. Found: C, 60.38; H,
10.37; N, 17.70.
were measured on a Bruker avance 300 MHz NMR spectro-
meter at room temperature. Chemical shifts for 1H and 13C
spectra were recorded in parts per million relative to the residual
proton and 13C of CDCl3 (δ 7.24, 77.0) and C6D6 (δ 7.15, 128.0).
IR spectra were obtained as KBr pellets using a Shimadzu
FTIR-8100 spectrophotometer. Elemental analysis was per-
formed on a Perkin-Elmer CHN-2400 or Heraeus CHN-OS
Rapid.
[C4H2N(2-CH2NHtBu)(5-CH2NMe2)]Al(PhCOCHCOPh)2 (3).
A 100 mL Schlenk flask charged with 2 (0.5 g, 2.107 mmol)
and 30 mL of diethyl ether was cooled to 0 °C and a diethyl ether
(30 mL) solution of 1,3-diphenyl-1,3-propanedione (0.9642 g,
4.214 mmol) was added. The mixture was stirred at 0 °C for 10 min,
and volatiles were removed under a vacuum. The residue was
purified from a toluene solution at -20 °C to generate 0.925 g of
[C4H2NH(2-CH2NHtBu)(5-CH2NMe2)] (1). A round-bot-
tom flask charged with Me2NH HCl (5.410 g, 65.70 mmol)
3
1
was cooled to 0 °C and 37% formaldehyde (5.330 g, 65.70 mmol)
was added. The mixture was stirred for 30 min and a diethyl
ether solution of [C4H3NH(2-CH2NHtBu)] (10.000 g, 65.70 mmol)
was added slowly. The biphase solution was stirred for 24 h and
then was neutralized with a 20% NaOH solution. The solution
was extracted three times with diethyl ether in 20 mL portions.
The diethyl ether extraction was dried over MgSO4, and the
volatiles were removed in vacuo to yield a yellowish final
orange crystals in 64% yield. H NMR (CDCl3): 0.81 (s, 9H,
NCMe3), 1.17 (s, 1H, NHCMe3), 2.33 (s, 3H, NMe2), 2.38 (s,
toluene Me), 2.72 (s, 3H, NMe2), 3.58 (d, 1H, CH2NMe2), 3.64
(m, 1H, CH2NHCMe3), 4.03 (m, 1H, CH2NHCMe3), 4.64 (d,
1H, CH2NMe2), 5.99 (s, 1H, pyrrolyl CH), 6.10 (s, 1H, pyrrolyl
CH), 6.88 (s, 1H, PhCOCHCOPh), 7.07 (s, 1H, PhCOCHCO-
Ph), 7.19-7.59 (m, 17H, phenyl CH and toluene CH), 7.92-8.16
(m, 8H, phenyl CH). 13C (CDCl3): 21.4 (q, JCH = 126 Hz,
1
product in 74.5% yield (10.250 g). H NMR (CDCl3): 1.11 (s,
9H, NCMe3), 2.14 (br, 7H, NMe2, NHCMe3), 3.31 (s, 2H,
CH2NMe2), 3.67 (s, 2H, CH2NHCMe3), 5.85 (s, 2H, pyrrolyl
toluene Me), 28.9 (q, JCH = 125 Hz, NCMe3), 42.1 (t, JCH
133 Hz, CH2NHCMe3), 46.6 (q, JCH=140 Hz, NMe2), 47.5 (q,
CH =137 Hz, NMe2), 49.7 (s, NCMe3), 60.7 (t, JCH =135 Hz,
=
J
CH), 9.07 (s, 1H, pyrrolyl NH). 13C (CDCl3): 28.9 (q, JCH
=
CH2NMe2), 93.7 (d, JCH = 160 Hz, PhCOCHCOPh), 94.3 (d,
JCH = 160 Hz, PhCOCHCOPh), 101.4 (d, JCH = 164 Hz,
pyrrolyl CH), 103.3 (d, JCH = 162 Hz, pyrrolyl CH), 125.2,
127.5, 127.6, 127.7, 127.8, 127.9, 128.1, 128.2, 128.4, 128.5,
128.9, 131.5, 131.7, 131.8, 132.0, 132.2, 137.3, 137.5, 137.6,
138.4, 138.5 (phenyl and pyrrolyl), 184.1 (s, PhCOCH), 184.2
(s, PhCOCH), 185.6 (s, PhCOCH), 185.7 (s, PhCOCH). Anal.
124 Hz, NCMe3), 40.0 (t, JCH=134 Hz, CH2NHCMe3), 45.0 (q,
JCH =132 Hz, NMe2), 50.4 (s, NCMe3), 56.6 (t, JCH =135 Hz,
CH2NMe2), 105.0 (d, JCH = 170 Hz, pyrrolyl CH), 107.3 (d,
JCH = 171 Hz, pyrrolyl CH), 128.4 (s, pyrrolyl Cipso), 131.3 (s,
pyrrolyl Cipso). Anal. Calcd for C12H23N3: C, 68.85; H, 11.07; N,
20.07. Found: C, 69.07; H, 11.19; N, 20.23%.
[C4H2N(2-CH2NHtBu)(5-CH2NMe2)]AlH2 (2). A flask char-
ged with a diethyl ether (20 mL) solution of Me3N HCl (2.000 g,
Calcd for C42H44AlN3O4 0.25C6H5CH3: C, 74.55; H, 6.58; N,
3
5.96. Found: C, 74.47; H, 6.91; N, 5.83.
3
[C4H2N(2-CH2NHtBu)(5-CH2NMe2)]Al(SCHNPh)2 (4). A
methylene chloride (30 mL) solution of 2 (0.50 g, 2.107 mmol)
was treated dropwise with a methylene chloride (30 mL) solu-
tion of PhNCS (0.581 g, 4.214 mmol) at -78 °C. The solution
20.90 mmol) was cooled to 0 °C and a diethyl ether (20 mL)
suspension of LiAlH4 (0.950 g, 25.10 mmol) was added slowly.
The mixture was stirred at room temperature for 2 h and filtered
through Celite. To this filtrate was added dropwise a diethyl

Article
Inorganic Chemistry, Vol. 49, No. 1, 2010 143
was then allowed to warm to room temperature and was stirred
for another 10 min. The solvent was removed under reduced
pressure to yield pale orange powder. The powder was redis-
solved in a mixed diethyl ether and methylene chloride solution
and stored at -20 °C. Colorless crystals of 4 were obtained in
57.1% yield (0.61 g). 1H NMR (CDCl3): 0.38 (s, 9H, NCMe3),
0.51 (s, 1H, NHCMe3), 1.19 (t, OCH2CH3), 2.52 (s, 3H, NMe2),
2.66 (d, 1H, CH2NMe2), 2.81 (s, 3H, NMe2), 3.14 (d, 1H, CH2-
NMe2), 3.46 (q, OCH2CH3), 3.57 (d, 1H, CH2NHCMe3), 4.14
(d, 1H, CH2NHCMe3), 6.01 (s, 1H, pyrrolyl CH), 6.06 (s, 1H,
pyrrolyl CH), 6.37-7.27 (phenyl CH), 9.09 (s, 1H, NCHS), 9.48
(s, 1H, NCHS). 13C (CDCl3): 15.2 (q, JCH = 126 Hz, NCMe3),
28.3 (q, OCH2CH3), 43.6 (t, JCH=131 Hz, CH2NHCMe3), 46.5
and treated as riding where the H atom displacement parameter
was calculated from the equivalent isotropic displacement para-
meter of the bound atom. The structures of both complexes were
determined by direct methods procedures in SHELXS32 and
refined by full-matrix least-squares methods, on F2’s, in
SHELXL.33 All of the relevant crystallographic data and struc-
ture refinement parameters for 1 and 2 are summarized in
Table 1. For all of the structures, the hydrogen atoms on Al(1)
and N(1) in compound 2 and N(1), N(3), N(4), and N(6) in
compound 1 were found on the difference Fourier maps and
refined isotropically. The other hydrogen atom positions were
calculated, and they were constrained to idealized geometries
and treated as riding where the H atom displacement parameter
was calculated from the equivalent isotropic displacement para-
meter of the bound atom.
(q, JCH=137 Hz, NMe2), 49.1 (s, CH2NHCMe3), 49.8 (q, JCH=
137 Hz, NMe2), 60.6 (t, JCH = 140 Hz, CH2NMe2), 65.8 (t,
OCH2CH3), 104.6 (d, JCH = 165 Hz, pyrrolyl CH), 106.1 (d,
J
CH = 165 Hz, pyrrolyl CH), 120.9, 121.4, 126.1, 129.2, 130.8,
Acknowledgment. The authors express their appreciation to
the National Science Council of Taiwan for financial assistance.
We would also like to thank the National Changhua University
of Education for supporting the X-ray diffractometer and NMR
spectrometer.
138.3, 144.9, 146.2 (phenyl and pyrrolyl), 185.1 (d, JCH = 181
Hz, NCHS), 189.2 (d, JCH = 178 Hz, NCHS). Anal. Calcd for
C26H34AlN5S2: C, 61.51; H, 6.75; N, 13.79. Found: C, 60.98; H,
7.06; N, 13.50.
Crystallographic Structure Determination of 1-4. All of the
crystals were mounted on a glass fiber using epoxy resin and
transferred to a goniostat. Data collections were performed at
150 K under liquid nitrogen vapor for complexes 1-4. Data
were collected on a Bruker SMART CCD diffractometer with
graphite monochromated Mo KR radiation. Crystal data were
collected at 150 K with an Oxford Cryosystems Cryostream. No
significant crystal decay was found. Data were corrected for
absorption empirically by means of ψ scans. All non-hydrogen
atoms were refined with anisotropic displacement parameters.
For all of the structures, the hydrogen atom positions were
calculated, and they were constrained to idealized geometries
Supporting Information Available: Crystallographic data in
CIF file format for compounds 1-4 and Cartesian coordinates
of stationary points for all compounds 1-4 and their possible
geometries. This material is available free of charge via the
Internet at http://pubs.acs.org.
(32) Sheldrick, G. M. SHELX97 - Programs for Crystal Structure
€
Analysis: Structure Determination (SHELXS); University of Gottingen:
€
Gottingen, Germany, 1997.
(33) Sheldrick, G. M. SHELX97 - Programsfor Crystal StructureAnalysis:
€
€
Refinement (SHELXL); University of Gottingen: Gottingen, Germany, 1997.