Synthesis and characterization of HC{C(Me)N(C6H3-2,6-i-Pr2)}2 MX2 (M = Al, X = Cl, I; M = Ga, In, X = Me, Cl, I): Sterically encumbered β-diketiminate group 13 metal derivatives

Article abstract of DOI:10.1021/ic001311d

A series of group 13 metal complexes featuring the β-diketiminate ligand [{(C₆H₃-2,6-i-Pr₂)NC(Me)}₂CH] ^- (i.e., [Dipp₂nacnac]^-, Dipp = C₆H₃-2,6-i-Pr₂) have been prepared and spectroscopically and structurally characterized. The chloride derivatives Dipp₂nacnacMCl₂ (M = Al (3), Ga (5), In (8)) were isolated in good yield by the reaction of 1 equiv of Dipp₂nacnacLi·Et₂O (2) and the respective metal halides. The iodide derivatives Dipp₂nacnacMl₂ (M = Al (4), Ga (6), In (9)), which are useful for reduction to afford M(I) species, were made by a variety of routes. Thus, 4 was obtained by treatment of the previously reported Dipp₂nacnacAlMe₂ with I₂, whereas the gallium analogue 6 was obtained as a product of the reaction of GaI with Dipp₂nacnacLi·EtzO, and 9 was obtained by direct reaction of InI₃ and the lithium salt. The methyl derivatives Dipp₂nacnacMMe₂ (M = Ga (7), In (10)), which are analogous to the previously reported Dipp₂nacnacAlMe₂, were synthesized by the reaction of GaMe₃ with Dipp₂nacnacH (1) or by reaction of the indium chloride derivative 8 with 2 equiv of MeMgBr in diethyl ether. The compounds 3-10 exist as colorless, air- and moisture-sensitive crystalline solids. Their X-ray crystal structures feature nearly planar C₃N₂ arrays in the Dipp₂nacnac ligand backbone with short C-C and C-N distances that are consistent with a delocalized structure. However, there are large dihedral angles between the C₃N₂ plane and the N₂M metal coordination plane which have been attributed mainly to steric effects. The relatively short M-N distances are consistent with the coordination numbers of the metals and the normal/dative character of the nitrogen ligands. The compounds were also characterized by ¹H and ¹³C NMR spectroscopy. ¹H NMR data for 7 revealed equivalent methyl groups whereas the spectrum of 10 displayed two In-Me signals which indicated that ring wagging was slow on the ¹H NMR time scale.

Full text of DOI:10.1021/ic001311d

2794
Inorg. Chem. 2001, 40, 2794-2799
Synthesis and Characterization of HC{C(Me)N(C6H3-2,6-i-Pr2)}2MX2 (M ) Al, X ) Cl, I;
M ) Ga, In, X ) Me, Cl, I): Sterically Encumbered â-Diketiminate Group 13 Metal
Derivatives
Matthias Stender, Barrett E. Eichler, Ned J. Hardman, and Philip P. Power*
Department of Chemistry, University of California at Davis, One Shields Avenue,
Davis, California 95616
Jo1rg Prust, Mathias Noltemeyer, and Herbert W. Roesky
Institut fu¨r Anorganische Chemie der Universita¨t Go¨ttingen, Tammannstrasse 4,
D-37077 Go¨ttingen, Germany
ReceiVed NoVember 20, 2000
A series of group 13 metal complexes featuring the â-diketiminate ligand [{(C6H3-2,6-i-Pr2)NC(Me)}2CH]- (i.e.,
[Dipp2nacnac]-, Dipp ) C6H3-2,6-i-Pr2) have been prepared and spectroscopically and structurally characterized.
The chloride derivatives Dipp2nacnacMCl2 (M ) Al (3), Ga (5), In (8)) were isolated in good yield by the reaction
of 1 equiv of Dipp2nacnacLi‚Et2O (2) and the respective metal halides. The iodide derivatives Dipp2nacnacMI2
(M ) Al (4), Ga (6), In (9)), which are useful for reduction to afford M(I) species, were made by a variety of
routes. Thus, 4 was obtained by treatment of the previously reported Dipp2nacnacAlMe2 with I2, whereas the
gallium analogue 6 was obtained as a product of the reaction of “GaI” with Dipp2nacnacLi‚Et2O, and 9 was
obtained by direct reaction of InI3 and the lithium salt. The methyl derivatives Dipp2nacnacMMe2 (M ) Ga (7),
In (10)), which are analogous to the previously reported Dipp2nacnacAlMe2, were synthesized by the reaction of
GaMe3 with Dipp2nacnacH (1) or by reaction of the indium chloride derivative 8 with 2 equiv of MeMgBr in
diethyl ether. The compounds 3-10 exist as colorless, air- and moisture-sensitive crystalline solids. Their X-ray
crystal structures feature nearly planar C3N2 arrays in the Dipp2nacnac ligand backbone with short C-C and
C-N distances that are consistent with a delocalized structure. However, there are large dihedral angles between
the C3N2 plane and the N2M metal coordination plane which have been attributed mainly to steric effects. The
relatively short M-N distances are consistent with the coordination numbers of the metals and the normal/dative
character of the nitrogen ligands. The compounds were also characterized by 1H and 13C NMR spectroscopy. 1H
NMR data for 7 revealed equivalent methyl groups whereas the spectrum of 10 displayed two In-Me signals
1
which indicated that ring wagging was slow on the H NMR time scale.
Introduction
activity in the area subsequently waned,7 the last 5 years have
seen an impressive revival of interest. This is especially true
for the more sterically encumbered derivatives (i.e., R ) bulky
group, especially ortho-substituted aryl groups), which have
found use as either neutral8 or monoanionic9-20 ligands in a
The monoanionic, bidentate â-diketiminate ligands shown by
the formula are members of a fundamentally important class of
(7) For example, these ligands were not treated as a separate class in the
following: ComprehensiVe Coordination Chemistry; Wilkinson, G.,
Gillard, R. D., McCleverty, J. A., Eds.; Pergamon: Oxford, U.K., 1987;
Vol. 1. Rare examples of the use of nacnac ligands in the 1980s include
the following: Bercaw, J. E.; Davies, D. L.; Wolczanski, P. T.
Organometallics 1986, 5, 443. Richeson, D. S.; Mitchell, J. F.;
Theopold, K. H. Organometallics 1989, 8, 2570.
(8) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall, W. J.;
Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16, 1514.
(9) Lappert, M. F.; Liu, D.-S. J. Organomet. Chem. 1995, 500, 203.
(10) Rahim, M.; Taylor, N. J.; Xin, S.; Collins, S. Organometallics 1998,
17, 1315.
â-difunctional, uninegative, chelating ligands. Metal complexes
of these ligands were first synthesized more than four decades
ago,1 and they have been studied extensively for their unique
geometric and electronic properties.1-6 Although the level of
(11) Gibson, V. C.; Maddox, P. J.; Newton, C.; Redshaw, C.; Solan, G.
A.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 1651.
(12) Budzelaar, P. H. M.; de Gelder, R.; Gal, A. W. Organometallics 1998,
17, 4121.
(13) Kim, W.-K.; Fevola, M. J.; Liable-Sands, L. M.; Rheingold, A. L.;
Theopold, K. H. Organometallics 1998, 17, 4541.
(14) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485. Budzelaar, P. H. M.; Moonen, N. N. P.; de Gelder,
R.; Smits, J. M. M.; Gal, A. W. Eur. J. Inorg. Chem. 2000, 753.
(1) Bradley, W.; Wright, I. J. Chem. Soc. 1956, 640.
(2) Tsybina, N. M.; Vinokurov, V. G.; Protopova, T. V.; Skoldinov, A.
P. J. Gen. Chem. USSR 1966, 36, 1383.
(3) Parks, J. E.; Holm, R. H. Inorg. Chem. 1968, 7, 1408.
(4) Honeybourne, C. L.; Webb, G. A. J. Chem. Soc., Chem. Commun.
1968, 739.
(5) McGeachin, S. G. Can. J. Chem. 1968, 46, 1903.
(6) Holm, R. H.; O’Connor, M. J. Prog. Inorg. Chem. 1971, 14, 241.
10.1021/ic001311d CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/10/2001

HC{C(Me)N(C6H3-2,6-i-Pr2)}2MX2 Complexes
Inorganic Chemistry, Vol. 40, No. 12, 2001 2795
wide range of transition metal,8-21 main group element,22-31
and lanthanide32 complexes. These are of interest owing to their
behavior as olefin polymerization catalysts8,11,13,23,25 or as models
for active sites in metalloproteins.19,20 In addition, the ability
of these ligands to stabilize low coordination numbers, rare
coordination geometries, or low oxidation states has been
recognized.19,20,30,31 The bulky [Dipp2nacnac]- ligand8,33 (i.e.,
[{(Dipp)N(Me)C}2CH]-; Dipp ) C6H3-2,6-i-Pr2) has played a
leading role in these investigations. Our interest in this ligand
derives in part from its steric resemblance to the terphenyl ligand
2,6-Trip2H3C6 (Trip ) C6H2-2,4,6-i-Pr3) as shown. The latter
Trip2H3C6M: (M ) In or Tl).35 The unusual composition and
structure of the low-valent group 13 metal Dipp2nacnac
complexes requires that structural and spectroscopic data from
other group 13 derivatives be available for comparison. Cur-
rently, such data are scant and are available only for
Dipp2nacnacAlMe2 (and related less crowded derivatives),22
[Dipp2nacnacAlMe][B(C6F5)4],25 [{Dipp2nacnacAlMe}2{B(C6F5)3-
Me}],25 Dipp2nacnacAl(SeH)2,27 and {Dipp2nacnacAl(SeH)}2Se.27
Our objectives in this work were the preparation and charac-
terization of a range of Dipp2nacnacMX2 (M ) Al, Ga, or In,
X ) halogen or methyl) species and then to compare their
spectroscopic and structural properties with the new monovalent
metal derivatives in order to draw conclusions regarding the
bonding in the latter species.
Experimental Section
General Procedures. All manipulations were carried out by using
modified Schlenk techniques under an atmosphere of N2 or in a Vacuum
Atmospheres HE-43 drybox. All solvents were distilled from Na/K alloy
and degassed three times before use. The compounds Dipp2nacnacH
(1)8 and Dipp2nacnacLi‚OEt2 (2)27 were prepared as previously
described. Aluminum(III) chloride and iodide were sublimed prior to
use. High-purity GaCl3 (99.999%), InCl3, and InI3 (99.99%) were
purchased commercially and used as received. The compound “GaI”
was prepared in accordance with the literature procedure.36 1H and 13
NMR spectroscopic data were recorded on a Varian INOVA 400 MHz
spectrometer and referenced to the deuterated solvent.
C
has been demonstrated to be effective in the stabilization of a
wide variety of new compounds.34 Very recently, it has been
shown that the use of the Dipp2nacnac ligand can stabilize the
unusual monomeric M(I) species Dipp2nacnacM: (M ) Al or
Dipp2nacnacMCl2 (M ) Al (3), Ga (5), In (8)). For 3, A toluene
solution (20 mL) of Dipp2nacnacLi‚OEt2 (2) (1.92 g, 4.53 mmol) was
added dropwise to a chilled (ca. 0 °C) suspension of freshly sublimed
AlCl3 (0.63 g, 4.73 mmol) with rapid stirring. The mixture was allowed
to warm to room-temperature overnight, whereupon the solvents were
removed under reduced pressure. The crude product was extracted with
hexane (30 mL), and filtration produced a clear pale yellow solution
which, upon concentration and cooling, afforded the product 3 as
colorless crystals. The compounds 5 and 8 were prepared in a similar
manner. 3: yield 1.70 g (73%); mp 211-213 °C. Anal. Calcd for
C29H41AlCl2N2: C, 67.57; H, 8.00; N, 5.44. Found: C, 67.91; H, 8.11;
1
N, 5.61. H NMR (C6D6, 399.77 MHz, 25 °C): δ 1.10 (d, 12H, J )
6.8 Hz, CH(CH3)3, 1.42 (d, 12H, J ) 6.8 Hz, CH(CH3)3), 1.50 (s, 6H,
CH3), 3.43 (sept, 4H, J ) 6.8 Hz, CH(CH3)3), 4.91 (s, H, γ-CH), 7.1-
7.2 (br, 6H, Ar). 13C{1H}NMR (C6D6, 100.53 MHz, 25 °C): 24.7 (CH3),
24.9 (CH(CH3)2), 25.5 (CH(CH3)2), 28.8 (CH(CH3)2), 98.9 (γ-C), 124.9
(Ar), 138.2 (Ar), 144.8 (Ar), 172.3 (CN). 5: colorless crystals, yield:
2.21 g (87%); mp 183-184 °C. Anal. Calcd for C29H41Cl2GaN2: C,
Ga).30,31 These results parallel the recent finding that monomeric,
monovalent group 13 metal complexes can also be stabilized
by terphenyl ligands as exemplified by the compounds 2,6-
1
(15) Chen, M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 1998,
120, 11018.
(16) Lee, L. W. M.; Piers, W. E.; Elsegood, M. R. J.; Clegg, W.; Parvez,
M. Organometallics 1999, 18, 2947.
(17) Qian, B.; Scanlon, W. J.; Smith, M. R., III.; Motry, D. H. Organo-
metallics 1999, 18, 1693.
62.40; H, 7.39; N, 5.02. Found: C, 62.1; H, 7.12; N, 4.78. H NMR
(C6D6, 399.77 MHz, 25 °C): δ 1.13 (d, J ) 6.8 Hz, 12H, CH(CH3)2),
1.43 (d, J ) 6.8 Hz, 12H, CH(CH3)2), 1.58 (s, 6H, CH3), 3.42 (sept, J
) 6.8 Hz, 4H, CH(CH3)2), 4.7 (s, 1H, CH), 7.10 (m, 6H, ArH). 13C-
{1H}NMR (C6D6, 100.53 MHz, 25 °C): δ 24.6 (CH3), 25.2 (CH(CH3)2),
29.0 (CH(CH3)), 98.4 (γ-C), 124.19 (Ar), 138.5 (Ar), 144.9 (Ar), 172.9
(CN). 8: colorless crystals, yield: 2.40 g (ca. 80%); mp 140 °C, dec
216 °C. 1H NMR (C6D6, 399.77 MHz, 25 °C): δ 1.07 (d, J ) 6.8 Hz,
(18) Kakaliou, L.; Scanlon, W. J., IV.; Qian, B.; Baek, S. W.; Smith, M.
R., III; Motry, D. H. Inorg. Chem. 1999, 38, 5964.
(19) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 1999, 121, 7270.
(20) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 2000, 122, 6331.
(21) Closely related, neutral R-diimine ligands have also been recently
employed in transition complexes that act as catalysts for olefin
polymerization; see: Johnson, L. K.; Killian, C. M.; Brookhart, M. J.
Am. Chem. Soc. 1995, 117, 6414. Tempel, D. J.; Johnson, L. K.; Huff,
R. L.; White, R. S.; Brookhart, M. J. Am. Chem. Soc. 2000, 122, 6686.
(22) Qian, B.; Ward, D. L.; Smith, M. R., III. Organometallics 1998, 17,
3070.
(23) Radzewich, C. E.; Coles, M. P.; Jordan, R. F. J. Am. Chem. Soc. 1998,
120, 9384.
(24) Kuchta, M. C.; Parkin, G. T. New J. Chem. 1998, 22, 523.
(25) Radzewich, C. E.; Guzei, I. A.; Jordan, R. F. J. Am. Chem. Soc. 1999,
121, 8673.
(29) Gibson, V. C.; Segal, J. A.; White, A. J. P.; Williams, D. J. J. Am.
Chem. Soc. 2000, 122, 7120.
(30) Hardman, N. J.; Eichler, B. E.; Power, P. P. Chem. Commun. 2000,
1491.
(31) Cui, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer, M.; Hao, H.;
Cimpoesu, F. Angew. Chem., Int. Ed.Engl. 2000, 39, 4274.
(32) Driess, D.; Magull, J. Z. Anorg. Allg. Chem. 1994, 620, 814.
(33) The designation [nacnac]- for the unsubstituted species
[HC{CMeNH}2]- by analogy with [acac]- for [HC{C(Me)O}2]-,
which was first proposed by Theopold and co-workers,13 is used here.
(34) Twamley, B.; Haubrich, S. T.; Power, P. P. AdV. Organomet. Chem.
1999, 44, 1.
(35) Haubrich, S. T.; Power, P. P. J. Am. Chem. Soc. 1998, 120, 2202.
Niemeyer, M.; Power, P. P. Angew. Chem., Int. Ed. Engl. 1998, 37,
1277.
(36) Green, M. L. H.; Mountford, P.; Smart, G. J.; Speel, S. R. Polyhedron
1990, 9, 2763.
(26) Qian, B.; Baek, S. W.; Smith, M. R., III. Polyhedron 1999, 18, 2405.
(27) Cui, C.; Roesky, H. W.; Hao, H.; Schmidt, H.-G.; Noltemeyer, M.
Angew. Chem., Int. Ed. Engl. 2000, 39, 1815.
(28) Bailey, P. J.; Dick, C. M. E.; Fabre, S.; Parsons, S. Dalton Trans.
2000, 1655.

2796 Inorganic Chemistry, Vol. 40, No. 12, 2001
Stender et al.
12H, CH(CH3)2), 1.41 (d, J ) 6.8 Hz, 12H, CH(CH3)2), 1.57 (s, 6H,
CH3), 3.15 (sept, J ) 6.8 Hz, 4H, CH(CH3)2), 3.84 (sept, J ) 6.8 Hz,
4H, CH(CH3)2), 4.79 (s, 1H, CH), 7.13 (m, 6H, ArH). 13C{1H}NMR
(C6D6, 100.53 MHz, 25 °C): δ 24.5 (CH3), 25.0 (CH(CH3)2), 25.3 (s),
28.6 (CH(CH3)2), 98.9 (γ-C), 124.64 (Ar), 138.1 (Ar), 144.8 (Ar), 172.7
(CN).
{1H}NMR (100.53 MHz, 25 °C): δ -8.8 (InCH3), 1.6 (InCH3), 24.2
(CH(CH3)2), 24.7 (CH(CH3)2), 28.3 (CH(CH3)2), 95.6 (γ-C), 124.2,
143.2, 143.8 (Ar), 168.3 (s, CN).
X-ray Crystallographic Studies. Crystals of 3 and 5-10 were
removed from the Schlenk tube under a stream of N2 and immediately
covered with a layer of hydrocarbon oil. A suitable crystal was selected,
attached to a glass fiber, and quickly placed in the low-temperature
nitrogen stream.37 The data were recorded near 90 K using a Bruker
SMART 1000 (Mo KR radiation and a CCD area detector). The
SHELXTL version 5.03 program package was used for the structure
solutions and refinements.38 Absorption corrections were applied using
the SADABS program.39 The crystal structures were solved by direct
methods and refined by full-matrix least-squares procedures. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
included in the refinement at calculated positions using a riding model
included in the SHELXTL program. The structure of 8 included 50%
Br occupancy (as a result of Br contamination by an in situ preparation
of LinacnacDipp2 using halide-rich LiMe) at one of the Cl positions
and refined satisfactorily. For 4, data were obtained on a crystal mounted
in a capillary tube at room temperature. Some details of the data
collection and refinement are given in Table 1. Further details are
provided in the Supporting Information.
Dipp2nacnacMI2 (M ) Al (4), Ga (6), In (9)). The synthesis and
spectroscopic characterization of 4 has been given previously in ref
27. For 6, solid 2 (2.5 g, 5 mmol) was added to a rapidly stirred slurry
of “GaI” (1.5 g, 7.6 mmol)36 of toluene (30 mL) with cooling in a dry
ice/acetone bath. The mixture was allowed to come to room-temperature
overnight, and the volume was reduced to ca. 10 mL. The solution
was then placed in a ca. -20 °C freezer for 48 h to give yellow crystals
of Dipp2nacnacGa in ca. 40% yield. The supernatant liquid was
separated and pumped to dryness and washed with hexane. The
remaining, almost colorless solid was recrystallized from the minimum
volume of hot toluene (ca. 5 mL) with cooling in a -20 °C freezer to
give 6 as colorless crystals. Yield: 0.70 g (26%), mp 246-248 °C.
Anal. Calcd for C29H41GaI2N: C, 47.00; H, 5.56; N, 3.79. Found: C,
47.61; H, 5.79; N, 3.38. 1H NMR (C6D6, 399.77 MHz, 25 °C): δ 1.10
(d, J ) 6.3 Hz, 12H, CH(CH3)2), 1.43 (d, J ) 6.6 Hz, 12H, CH(CH3)2),
1.50 (s, 6H, CH3), 3.56 (sept, J ) 6.6 Hz, 4H, CH(CH3)2), 4.92 (s, H,
λ-CH), 7.11 (m, br, 6H, ArH). 13C{1H}NMR (C6H6, 100.53 MHz, 25
°C): δ 24.5 (CH(CH3)2), 24.7 (CCH3), 27.0 (CH(CH3)2), 29.3 (CH-
(CH3)2), 98.5 (γ-C), 125.0 (m-C), 127.3 (p-C), 139.3 (o-C), 144.8
(C(CH3)), 170.8 (CN). For 9, a diethyl ether solution (20 mL) of 2
(1.24 g, 2.48 mmol) was added dropwise to a stirred solution of InI3
(1.23 g, 2.48 mmol) in diethyl ether (20 mL) with cooling in a dry
ice/acetone bath. The cooling bath was then removed, and the solution
was allowed to come to room temperature and stirred for a further 24
h. The solvent was removed under reduced pressure, and the crude
product was dissolved in hexane (30 mL). Filtration through Celite
followed by cooling in a ca. -20 °C freezer afforded the product 9 as
very pale yellow needles. Yield: 1.69 g (87%). Mp: 168-171 °C.
Anal. Calcd for C29H41I2InN2: C, 44.3; H, 5.24; N, 3.56. Found: C,
43.71; H, 5.01; N, 3.46. 1H NMR (C6D6, 399.77 MHz, 25 °C): δ 1.11
(d, 12H, J ) 6.8 Hz, CH(CH3)2), 1.40 (d, 12H, J ) 6.8 Hz, CH(CH3)2),
1.50 (s, 6H, CH3), 3.48 (sept, 4H, J ) 6.8 Hz), 4.73 (s, 1H, γ-CH),
7.1-7.2 (br, 6H, Ar). 13C{1H}NMR (C6D6, 100.53 MHz, 25 °C): δ
24.3, 24.6 (CH(CH3)2), 25.5 (CH(CH3)2), 28.7 (CH(CH3)2), 97.0 (γ-
C), 124.6, 137.7, 143.7 (Ar), 171.8 (CN).
Results and Discussion
Synthesis. A number of Al(III) nacnac derivatives have been
previously synthesized and structurally characterized. These
include the cation [Dipp2nacnacAlMe]+,25 the chloride (p-
tolyl)2nacnacAlCl2,22 and the dimethyl derivative Dipp2-
nacnacAlMe2.22,25 The latter species was prepared independently
by two different groups22,25 via the reaction of AlMe3 with
21
Dipp2nacnacH. The chloride (p-tolyl)2nacnacAlCl2 was syn-
thesized by the reaction of AlCl3 with (p-tolyl)2nacnacLi, and
it was also shown that either one or both chlorides in this
compound could be replaced by methyl groups.22 In a similar
manner, the aluminum, gallium, and indium chloride derivatives
3, 5, and 8 were prepared in 73-87% yield by the straight-
27
forward reaction of Dipp2nacnacLi‚OEt2 with the respective
trihalides in accordance with eq 1.
+ MCl3 Et O8
2
Dipp2nacnacMMe2 (M ) Ga (7), In (10)). For 7, a toluene (15
mL) solution of GaMe3 (0.59 g, 5.17 mmol) was treated dropwise with
a diethyl ether solution (30 mL) of 1 (2.58 g, 5.17 mmol) with cooling
in a dry ice/acetone bath. The solution was then allowed to warm to
room temperature and refluxed for 48 h. The solvents were removed
under reduced pressure, and the residue was extracted with hexane (30
mL) and filtered. Concentration to ca. 10 mL and storage in ca. -20
°C freezer for 5 d afforded the product 7 as colorless crystals. Yield:
2.27 g (85%). Mp: 156-158 °C. Anal. Calcd for C31H47GaN2: C,
71.95; H, 9.16; N, 5.42. Found: C, 72.41; H, 9.00; N, 5.01. 1H NMR
(C6D6, 399.77 MHz, 25 °C): δ -0.18 (s, 6H, Ga(CH3)2), 1.15 (d, J )
6.8 Hz, 12H, CH(CH3)2), 1.30 (d, J ) 6.8 Hz, 12H, CH(CH3)2), 1.58
(s, 6H, CH3), 3.43 (sept, J ) 6.8 Hz, 4H, CH(CH3)2), 4.80 (s, 1H,
CH), 7.12 (br, m, 6H, ArH). 13C{1H}NMR (C6D6, 100.53 MHz, 25
°C): δ 24.3 (CH(CH3)2), 24.5 (CH(CH3)2), 28.5 (CH(CH3)2), 95.91
(γ-C), 124.2 (s), 125.7, 126.6, 142.0, 142.6, 144.03 (Ar), 172.2 (CN).
For 10, methylmagnesium bromide (3.6 mmol, 1.2 mL of 3M solution)
in diethyl ether was added to a rapidly stirred diethyl ether (30 mL)
solution of 8 (1.00 g, 1.66 mmol) with cooling in a dry ice/acetone
bath. The bath was then removed, and the solution was allowed to
come to room temperature, whereupon it was stirred for a further 12
h. The solvent was removed under reduced pressure, and the residue
was extracted with hexane (30 mL) and filtered. Concentration to ca.
5 mL and storage in a ca. -20 °C freezer for 2 d afforded the product
10 as colorless crystals. Yield: 0.86 g (92%). Mp: 154-157 °C. Anal.
Calcd for C31H47InN2: C, 66.18; H, 8.42; N, 4.98. Found: C, 65.48;
Dipp nacnacLi‚Et O
2
2
2
Dipp2nacnacMCl2
+ LiCl (1)
M ) Al (3), Ga (5), In (8)
Although chloride compounds are generally the most acces-
sible, least expensive halide derivatives to prepare, the corre-
sponding iodide species possess advantages as precursors. An
example is the synthesis of the M(I) species Dipp2nacnacAl:
where the reaction of potassium with Dipp2nacnacAlI2 affords
Dipp2nacnacAl in accordance with eq 2.30,31 In contrast, the
corresponding reaction using the Dipp2nacnacAlCl2 was unsuc-
cessful.
Dipp2nacnacAlI2 + 2K f Dipp2nacnacAl + 2KI (2)
4
4,31
The compound Dipp2nacnacAlI2
was synthesized, eq 3,
by the direct reaction of I2 with the methyl derivative Dipp2-
nacnacAlMe2.22 This approach avoids product separation prob-
lems encountered in the more direct route involving the reaction
of 2 with AlI3. The reaction of “GaI”36 with the lithium
derivative 2 produces Dipp2nacnacGaI2 (6) in addition to Dipp2-
1
H, 8.01; N, 4.71. H NMR (C6D6, 399.77 MHz, 25 °C): δ -0.02 (s,
(37) Hope, H. Progr. Inorg. Chem. 1995, 41, 1.
3H, InCH3), 0.34 (s, 3H, InCH3), 1.23 (d, 12H, J ) 6.9 Hz, CH(CH3)2),
1.32 (d, 12H, J ) 6.9 Hz, CH(CH3)2), 1.66 (s, 6H, Me), 3.48 (sept,
4H, J ) 6.9 Hz), 4.79 (s, 1H, γ-CH), 7.1-7.2 (br, m, 6H, ArH). 13C-
(38) SHELXL, version 5.1; Bruker AXS: Madison, WI.
(39) SADABS an empirical absorption correction program part of the
SAINTPlus NT Version 5.0 package; Bruker AXS: Madison, WI, 1998.

HC{C(Me)N(C6H3-2,6-i-Pr2)}2MX2 Complexes
Inorganic Chemistry, Vol. 40, No. 12, 2001 2797
Table 1. Data Collection Parameters for Compounds 3-10a
3
4
5
6
formula
fw
cryst system
space group
a (Å)
b (Å)
c (Å)
C29H41AlCl2N2
515.2
monoclinic
P21/c
17.9413(7)
9.9216(4)
17.1167(7)
C29H41AlI2N2
698.42
monoclinic
P21/n
18.927(10)
8.690(5)
20.137(15)
C29H41Cl2GaN2
558.26
monoclinic
P21/c
17.071(1)
13.095(1)
13.736(1)
C29H41GaI2N2
741.11
monoclinic
P21/n
18.8237(7)
8.6190(3)
20.0720(7)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
108.842(1)
113.45(4)
108.432(2)
113.388(1)
2883.6(2)
4
0.275
90
3038(3)
4
2.118
300
2912.9(4)
4
1.147
90
2989.0(2)
4
3.759
90
µ(Mo KR) (mm-1
T/K
)
R1
wR2
0.0326
0.0896
0.0248
0.0608
0.040
0.1025
0.0185
0.0528
7
8
9
10
formula
fw
cryst system
space group
a (Å)
b (Å)
c (Å)
C31H47GaN2
517.43
monoclinic
P21/n
12.6644(5)
19.3511(8)
13.3291(5)
C29H41Br0.50Cl1.50 InN2
625.59
monoclinic
P21/c
17.942(2)
10.1655(9)
17.4672(15)
C29H41I2InN2
786.26
monoclinic
P21/n
18.7802(8)
8.6647(4)
20.3412(8)
C31H47InN2
562.53
triclinic
P1h
10.3346(4)
12.5671(5)
12.9080(5)
69.829(1)
76.852(1)
74.993(1)
1502.2(1)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
107.02(1)
108.984(2)
113.0306(1)
2910.5(2)
4
0.965
90
0.0431
0.0696
3012.6(4)
4
1.599
90
0.0323
0.0810
3046.1(2)
4
2.822
90
0.0211
0.0434
µ(Mo KR) (mm-1
)
0.806
90
0.0215
0.0562
T/K
R1
wR2
a R1 ) Σ||Fo| - |Fc||/|Fo|. wR2 ) [Σw(Fo - Fc2)2/Σ[w(Fo ]]1/2
.
2
2
nacnacGa:. The diiodide 6 also undergoes reduction with
potassium to give Dipp2nacnacGa:.30 Dipp2nacnacInI2 (9) was
synthesized by the direct reaction of Dipp2nacnacLi‚OEt2 with
InI3. Thus, the three iodides 4, 6, and 9 were each synthesized
by a different method. The gallium methyl compound 7 was
synthesized in a manner very similar to that of its aluminum
analogue. However, the indium methyl species 10 was made
by the reaction of 2 equiv of the Grignard MeMgBr with the
chloride 8 in diethyl ether solution.
Dipp2nacnacAlMe2 + 2I2 f Dipp2nacnacAlI2 + 2MeI (3)
4
1
All compounds afforded simple H and 13C NMR spectra.
There are only minor differences in the observed chemical shifts
for the Dipp2nacnac ligand in compounds 3-10. However, the
1H NMR shifts of the â-Me and γ-H hydrogens of the lower
valent Dipp2nacnacM: derivatives (M ) Al or Ga) are ca. 0.05
Figure 1. Thermal ellipsoid plot (30%) of 3. H atoms are not shown
for clarity. Structural data are given in Table 2.
1
and 0.2 ppm further downfield. The H NMR metal methyl
Selected bond distances and angles are listed in Table 2. The
structures have several features in common: (a) The C3N2 ring
fragment is planar or close to planar in each molecule. (b) The
metals lie significantly out of the C3N2 planes such that there
are considerable dihedral angles between the C3N2 and MN2
arrays. (c) The ring C-C and C-N distances lie within the
narrow ranges 1.387(6)-1.418(3) and 1.320(2)-1.353(2) Å,
which are indicative of considerable multiple character in these
bonds. (d) Within the C3N2M (M ) Al, Ga or In) rings the
N-M-N angle is invariably the narrowest (usually e100°)
whereas the other angles are all g117° with widest angle (130-
((3)°) observed at the C(2) carbon position.
resonances of compounds 7 and 10 were found at upfield shifts.
The gallium methyl signal was observed as a single peak like
its aluminum counterpart,21,22 despite the puckering of the ring
which renders distinct environments to the two metal methyl
groups in the solid state. The solid state structures are likely to
be maintained in solution, so that methyl site exchange must
be rapid on the NMR time scale. For 10, however, two distinct
methyl signals are observed suggesting that the exchange is quite
slow. It is possible that the rate of exchange observed for 10 is
connected to the puckering of the ring which is the largest of
any compound in the series 3-10 (vide infra).
Structural Data. The structures of compounds 3-10 are
represented by the thermal ellipsoid plots in Figures 1-3.
One of the most noticeable aspects of the structures is the
presence of a dihedral angle between the N(1)C(1)C(2)C(3)N-

2798 Inorganic Chemistry, Vol. 40, No. 12, 2001
Stender et al.
Table 2. Selected Bond Distances (Å) and Angles (deg) for 3-10
3
4
Al(1)-N(1)
Al(1)-N(2)
Al(1)-Cl(1)
Al(1)-Cl(2)
N(1)-C(1)
N(2)-C(3)
C(1)-C(2)
C(2)-C(3)
1.8843(9) Al(1)-N(1)
1.8663(9) Al(1)-N(2)
2.1344(4) Al(1)-I(1)
2.1185(4) Al(1)-I(2)
1.872(2)
1.893(3)
2.501(1)
2.541(1)
1.338(3)
1.340(3)
1.391(4)
1.394(4)
1.341(1)
1.348(1)
1.405(1)
1.396(1)
N(1)-C(1)
N(2)-C(2)
C(1)-C(2)
C(2)-C(3)
N(1)-Al(1)-N(2)
99.36(4)
N(1)-Al(1)-N(2) 99.9(1)
Cl(1)-Al(1)-Cl(2) 108.02(2) I(1)-Al(1)-I(2)
108.40(5)
118.2(2)
Al(1)-N(1)-Cl(1)
Al(1)-N(2)-C(3)
N(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-N(2)
119.33(7) Al(1)-N(1)-I(1)
119.73(7) Al(1)-N(2)-C(3) 117.7(2)
120.76(9) N(1)-C(1)-C(2)
127.7(1)
123.1(2)
128.1(2)
123.8(2)
Figure 2. Thermal ellipsoid plot (30%) of 7. H atoms are not shown
for clarity. Structural data are given in Table 2.
C(1)-C(2)-C(3)
122.78(9) C(2)-C(3)-N(2)
5
6
Ga(1)-N(1)
Ga(1)-N(2)
Ga(1)-Cl(1)
Ga(1)-Cl(2)
N(1)-C(1)
N(2)-C(3)
C(1)-C(2)
C(2)-C(3)
1.926(3)
1.906(3)
2.228(1)
2.218(1)
1.337(5)
1.353(2)
1.403(6)
1.387(6)
Ga(1)-N(1)
Ga(1)-N(2)
Ga(1)-I(1)
Ga(1)-I(2)
N(1)-C(1)
N(2)-C(3)
C(1)-C(2)
C(2)-C(3)
1.924(1)
1.948(1)
2.5528(2)
2.5082(2)
1.340(2)
1.337(2)
1.400(2)
1.401(2)
N(1)-Ga(1)-N(2)
100.2(1)
N(1)-Ga(1)-N(2) 99.25(5)
109.413(7)
Ga(1)-N(1)-C(1) 118.0(1)
Ga(1)-N(2)-C(3) 117.4(1)
Cl(1)-Ga(1)-Cl(2) 110.20(4) I(1)-Ga(1)-I(2)
Ga(1)-N(1)-C(1)
Ga(1)-N(2)-C(3)
N(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-N(2)
118.3(3)
117.6(3)
123.4(4)
129.6(4)
123.7(4)
N(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-N(2)
123.6(1)
129.1(1)
124.2(1)
Figure 3. Thermal ellipsoid plot (30%) of 9. H atoms are not shown
for clarity. Structural data are given in Table 2.
(2) and N(1)MN(2) (M ) Al, Ga or In) arrays. This is also
found in many other derivatives of these ligands from different
groups of the periodic table.10-18,22-29 The folding of the rings
in 3-10 can be expressed by either the angle between the planes
or the distance of the metal from the averaged extended plane
formed by the N(1)C(1)C(2)C(3)N(2) array. These data are listed
in Table 3. It can be seen that the deviation from planarity of
the chloride and iodide derivatives is similar, whereas the values
for the methyl derivatives are considerably greater. There is also
some correlation between the NMN angles and the degree of
ring folding; the narrower the N-M-N angle is, the greater
the folding. However, the monomeric aluminum and gallium
species Dipp2nacnacM: (M ) Al or Ga),30,31 which have planar
C3N2M arrays, have narrower angles of 89.36(8) and 87.53-
(5)°. It seems probable that more highly charged and polarizing
metal cations such as Al3+, Ga3+, or In3+ result in shorter M-N
bonds and greater steric interactions involving the Dipp and
metal substituents which results in folding of the ring for steric
reasons. The planar geometries observed for Dipp2nacnacM: (M
) Al or Ga) molecules are consistent with this argument since
the M-N bonds in these molecules are long and the metals are
unsubstituted by other groups so that steric crowding is much
lower. A ring geometry, which is much closer to planarity, is
also observed for [Dipp2nacnacAlMe][B(C6F5)4]25 which, al-
though it has shorter Al-N distances, features a less crowding,
essentially three coordinate environment at aluminum.
7
8
Ga(1)-N(1)
Ga(1)-N(2)
Ga(1)-C(30)
Ga(1)-C(31)
N(1)-C(1)
N(2)-C(3)
C(1)-C(2)
C(2)-C(3)
1.979(2)
2.001(2)
1.970(2)
1.979(2)
1.333(3)
1.325(2)
1.400(3)
1.415(3)
In(1)-N(1)
In(1)-N(2)
In(1)-Cl(1)
In(1)-Cl(2)
In(1)-Br(1)
N(1)-C(1)
N(2)-C(3)
C(1)-C(2)
C(2)-C(3)
2.123(3)
2.111(3)
2.3872(9)
2.404(3)
2.546(1)
1.335(4)
1.332(4)
1.406(5)
1.400(5)
N(1)-Ga(1)-N(2)
C(30)-Ga(1)-C(31) 122.44(9) Cl(1)-In(1)-Cl(2) 108.99(8)
Ga(1)-N(1)-C(1)
Ga(1)-N(2)-C(3)
N(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-N(2)
93.92(7)
N(1)-In(1)-N(2)
92.5(1)
118.5(1)
118.5(1)
123.3(2)
127.7(2)
123.8(2)
In(1)-N(1)-C(1)
In(1)-N(2)-C(3)
N(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-N(2)
120.0(2)
120.5(2)
124.8(3)
131.2(3)
124.7(3)
9
10
In(1)-N(1)
In(1)-N(2)
In(1)-I(1)
In(1)-I(2)
N(1)-C(1)
N(2)-C(3)
C(1)-C(2)
C(2)-C(3)
2.121(2)
In(1)-N(1)
In(1)-N(2)
In(1)-C(30)
In(1)-C(31)
N(1)-C(1)
N(2)-C(3)
C(1)-C(2)
C(2)-C(3)
2.190(1)
2.204(1)
2.148(1)
2.168(1)
1.332(2)
1.320(2)
1.403(2)
1.418(2)
2.147(1)
2.7008(2)
2.6050(2)
1.338(2)
1.333(2)
1.401(2)
1.405(2)
N(1)-In(1)-N(2) 92.42(5)
I(1)-In(1)-I(2)
N(1)-In(1)-N(2)
111.748(6) C(30)-In(1)-C(31) 130.94(6)
86.76(4)
The aluminum chloride and iodide derivatives 3 and 4 bear
a very close structural resemblance. Inspection of the data in
Table 2 shows that the Al-N bonds in 3 and 4 have an average
distance of 1.88(1) Å and nearly equal N(1)-Al(1)-N(2) angles
of 99.36(4) and 99.8(1)°. The angles between the halogens are
also very close, having the values 108.02(2) and 108.40(5)°.
The Al-N bond lengths are similar to those observed for
terminal Al-N bonds in aluminum amides having four coor-
In(1)-N(1)-C(1) 118.9(1)
In(1)-N(2)-C(3) 118.9(1)
N(1)-C(1)-C(2) 125.0(2)
In(1)-N(1)-C(1)
In(1)-N(2)-C(3)
N(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-N(2)
119.35(7)
120.08(8)
124.5(1)
129.6(1)
124.3(1)
C(1)-C(2)-C(3)
C(2)-C(3)-N(2) 125.1(2)
131.3(2)
dinate aluminum,40 although they are shorter than those values
(1.922(2) and 1.935(2) Å) recently reported for Dipp2-

HC{C(Me)N(C6H3-2,6-i-Pr2)}2MX2 Complexes
Inorganic Chemistry, Vol. 40, No. 12, 2001 2799
Table 3. Folding Parameters for the C3N2 and MN2 Arrays of
Compounds 3-10
amidinate gallium chloride and methyl derivatives the Ga-N
bonds average 1.941(5) and 1.986(5) Å. The difference between
these values is similar to that between the Ga-N distances in
5 and 7. The (Me)2ATI and related ligands46 also resemble
nacnac ligands in that they are uninegative bidentate dimine
donors. In {(Me)2ATI}2GaI the Ga-N bond lengths average
1.968(14) Å, which is not significantly different from the 1.936-
(12) Å average Ga-N distance in the iodide 6. However, the
Ga-I distance in {(Me)2ATI}2GaI is 2.7178(5) Å, which is ca.
0.2 Å longer than that in 6. Clearly, the different coordination
numbers and steric environment have very large effects on the
Ga-I distance in these compounds, and this is also consistent
with the data for the aluminum compounds.47 The Ga-C
distances in 7, average 1.975(5) Å are well within the range ca.
1.94-2.03 Å for Ga-C bonds.47
metal dist
from the
dihedral angle between
the C3N2 and
compd
C3N2 plane (Å)
MN2 arrays (deg)
Dipp2nacnacAlCl2 (3)
Dipp2nacnacAlI2 (4)
Dipp2nacnacAlMe2
0.525
0.571
0.72
155.0
152.5
a
Dipp2nacnacGaCl2 (5)
Dipp2nacnacGaI2 (6)
Dipp2nacnacGaMe2 (7)
Dipp2nacnacInBr0.5Cl1.5 (8)
Dipp2nacnacInI2 (9)
0.507
0.568
0.76
0.551
0.643
0.892
156.2
153.7
146.8
158.3
154.7
146.7
Dipp2nacnacInMe2 (10)
a Reference 22.
nacnacAlMe2.22 The difference is probably due to the increased
positive charge on the metals in 3 and 4 (and a stronger ionic
Al-N bonding component) as a result of their bonding to
halides. This argument is supported by the fact that even shorter
Al-N bonds (average 1.826(1) Å) were observed in the complex
[Dipp2nacnacAlMe][B(C6F5)4].25 Nonetheless, the Al-N dis-
tances are marginally longer than the 1.850(2) Å bond length
in [HC{C(Me)N(C6H4-4-Me)}2]AlCl2,21 possibly as a result of
the greater steric hindrance in 3 and 4. The aluminum chlorine
distances in 3 (average 2.126(1) Å) are slightly longer than Al-
Cl distances (2.106(4) Å) in {Cl2Al(µ-NMe2)}2.41 The Al-I
bonds (average 2.52(2) Å) in 4 are essentially the same as the
average Al-I bond of 2.49(1) Å in {I2Al(µ-NMe2)}2 although
it is considerably shorter than the 2.704(1) Å measured for
(pyridine)(I)Al(2,2,6,6-tetramethylpiperidino)2.42 In the latter
species the very crowded four-coordinate aluminum environment
may cause lengthening of the Al-N bond. The steric argument
is supported by the observation of a much shorter Al-I bond
(ca. 2.57 Å) in the less crowded (pyridine)(I)2Al(2,2,6,6-
tetramethylpiperidino) molecule.42
The Ga-N bond lengths for the gallium compounds 5-7
follow a pattern similar to that for the aluminum species 3 and
4 and their methyl analogue Dipp2nacnacAlMe2, presumably
for similar reasons. For the pair of compounds 5 and 6, the
average Ga-N distances 1.916(10) and 1.936(12) Å are
essentially equal. These distances are significantly shorter than
the average of 1.990(11) Å observed for the methyl derivative
7. The compounds most closely related to 5-7 are the amidinate
species {PhC(NPh)2}GaMe2,43 {t-BuC(NCy)2}GaCl2,44 and {t-
BuC(NCy)2}GaMe244 and the N-methyl-2-(methyamino)tropon-
imininate [(Me)2ATI]- derivative {(Me)2ATI}2GaI.45 In the
The indium halide compounds 8 and 9 have similar In-N
bond lengths in the narrow range 2.111(3)-2.147(1) Å, whereas
those of the methyl derivative have a somewhat longer average
In-N distance of ca. 2.197(7) Å. This is, of course, similar to
the pattern observed for both the aluminum and gallium series.
The In-N bond lengths in 8-10 are very similar to the average
of 2.145(3) Å (In-N(eq) and 2.171(4) Å (In-N(ax)) observed
in the species {(Me)2ATI}2InCl42 despite the higher indium
coordination number. The In-Cl distance in {(Me)2ATI}2InCl,
2.4174(9) Å, is also very similar to the value, 2.3872(9) Å,
observed for 8. The similarity in these metal chloride bonds is
in sharp contrast to the large differences between the Ga-I
distances in the corresponding pair of gallium iodide derivatives
6 and {(Me)2ATI}2GaI. Structural data for the five coordinate
In-I species phthalocyaninatoindium(III) iodide48 and the tris-
(3,5-di-tert-butylpyrazolyborato)diiodoindium(III)49 also show
that their In-I distances of 2.672(1)45 and 2.743(20) Å46 are
similar to the 2.6050(2) and 2.7008(2) Å observed in 9. Perhaps,
the larger size of indium in comparison to gallium renders steric
effects less important in the heavier element compounds. The
In-C distances, ca. 2.16 Å, lie within the range for indium
terminally bound to carbon.47
Acknowledgment. We are grateful to the National Science
Foundation and the Alexander von Humboldt Stiftung for the
award of a fellowship to P.P.P. H.W.R. thanks the Deutsche
Forschungsgemeinschaft for support of this work.
Supporting Information Available: Eight X-ray files in CIF
format. This material is available free of charge via the Internet at
http://pubs.acs.org.
IC001311D
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(45) Dias, H. V. R.; Jin, W. Inorg. Chem. 1996, 35, 6546.
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(47) Starowieski, K. B. In Chemistry of Aluminum, Gallium, Indium and
Thallium; Downs, A. J., Ed.; Blackie/Chapman-Hall: London, 1993;
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