4622 Organometallics, Vol. 18, No. 22, 1999
Dagorne et al.
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filtration (0.970 g, 64%). H NMR (C6D6): δ 3.82 (septet, J )
donor ability of Me vs Cl. The Ga-N bond distances
in 3b are shorter than those in {PhC(NPh)2}GaMe2
(2.039(3) Å average)1a due to the stronger electron-donor
ability of alkyl vs Ph groups. The Ga-Cl bond distances
in 2b,c (2.156(1) Å average) are slightly longer than the
Ga-Cl distances in Ga2Cl6 (terminal Ga-Cl ) 2.06(2)
Å),8 while the Ga-Me distances in 3b (1.985(2) Å
average) are comparable to the Ga-Me bond distances
in GaMe3 (1.97(1) Å).9
3
6.5, 2H, CHMe2), 1.14 (d, J ) 6.2, 12H, CHMe2), 0.96 (s, 9H,
CMe3). 13C NMR (C6D6): δ 179.6 (NCN), 47.5 (CHMe2), 38.5
(Me3C), 28.6 (Me3C), 25.7(CHMe2). Anal. Calcd for C11H23Cl2-
GaN2: C, 40.78; H, 7.17; N, 8.65. Found: C, 40.45; H, 6.92; N,
8.57. EI-MS (m/z): 324 (M+, 5), 309 (M+ - CH3, 36), 287 (M+
- Cl, 1), 184 (8), 126 (75), 84 (100), 69 (5), 57 (26).
{tBu C(NCy)2}Ga Cl2 (2b). The procedure described for 2a
was followed using GaCl3 (0.840 g, 4.75 mmol) and Li[tBuC-
(NCy)2] (1.28 g, 4.75 mmol). Crystallization from Et2O at -78
°C for 18 h yielded pure {tBuC(NCy)2}GaCl2 as colorless
crystals that were collected by filtration (1.21 g, 63%). 1H NMR
(C6D6): δ 3.58 (br m, 2H, Cy), 1.96 (br d, 4H, Cy), 1.64-1.42
(br m, 10H, Cy), 1.07 (s, 9H, CMe3), 1.3-0.9 (br m, 6H, Cy).
In all of the {tBuC(NR′)2}GaX2 complexes, the {tBuC-
(NR′)2}Ga core forms a nearly planar metallacycle
(|(N-Ga-N-C torsion angles)| < 3.6°). The amidinate
carbon and nitrogen atoms exhibit distorted-trigonal-
planar coordination (sum of angles ca. 360°). The two
C-N distances (1.34(2) Å average) are very similar
within each molecule and consistent with fully delocal-
ized π-bonding within the amidinate unit.10
One important aspect of our work on cationic alumi-
num and gallium amidinate complexes is control of
steric crowding at the metal center.2a,4 Comparison of
key bond angles within the {tBuC(NR′)2}Ga core as a
function of the C-tBu and N-R′ substituents provides
insight into this issue (Figure 4). The tBu-N-Ga
angle in 2c (127.8(4)° average) is 6° smaller than the
Cy-N-Ga angles in 2b (133.7(7)° average) and 3b
(133.1(4)° average). For comparison, the Ph-N-Ga
angles in {PhC(NPh)2}GaMe2 (138.3(5)° average, Figure
4)1a are significantly larger than the R′-N-Ga angles
in 2b,c and 3b. Thus, changing the N-R′ group from
Cy to tBu decreases the R′-N-Ga angle, which projects
the N-R′ substituents more toward the metal center.
As described in detail elsewhere, this effect strongly
influences the structure of the cationic species formed
upon Me- abstraction from {RC(NR′)2}GaMe2.4
13C NMR (C6D6): δ 179.8 (s, NCN), 55.7 (d, J CH ) 138, Cy-
C1), 38.6 (s, CMe3), 36.9 (t, J CH ) 128, Cy), 28.7 (q, J CH
1
1
1
)
1
1
127, CMe3), 25.4 (t, J CH ) 127, Cy), 25.2 (t, J CH ) 126, Cy).
Anal. Calcd for C17H31Cl2GaN2: C, 50.52; H, 7.75; N, 6.93.
Found: C, 50.41; H, 7.85; N, 6.93. EI-MS (m/z): 404 (M+, 79),
361 (M+ - Cl, 84), 264 (45), 221 (27), 207 (14), 193 (8), 182
(61), 166 (100).
{tBu C(NtBu )2}Ga Cl2 (2c).
A
colorless solution of
tBuCdNdCtBu (2.00 g, 13.0 mmol) in Et2O (35 mL) was cooled
t
to 0 °C, and BuLi (7.62 mL of 1.7 M solution in pentane, 13.0
mmol) was added dropwise by syringe. The mixture was
warmed to room temperature and was stirred for 1 h, resulting
in a white slurry. The mixture was cooled to -78 °C, and a
colorless solution of GaCl3 (2.29 g, 13.0 mmol) in Et2O (10 mL),
which was also cooled to -78 °C, was added dropwise. The
resulting mixture was warmed to room temperature and was
stirred for 12 h, affording a slurry of a white solid in a pale
yellow solution. The mixture was filtered. The filtrate was
concentrated to 25 mL and cooled to -78 °C for 18 h to yield
pure {tBuC(NtBu)2}GaCl2 as colorless crystals that were col-
1
lected by filtration (0.710 g, 17%). H NMR (C6D6): δ 1.41 (s,
18H, NCMe3), 1.13 (s, 9H, CCMe3). 13C NMR (C6D6): δ 183.7
(NCN), 56.0 (NCMe3), 37.3 (CCMe3), 34.0 (NCMe3), 31.2
(CCMe3). Anal. Calcd for C13H27Cl2GaN2: C, 44.36; H, 7.75;
N, 7.96. Found: C, 44.43; H, 7.82; N, 7.70.
Exp er im en ta l Section
{tBu C(NiP r )2}Ga Me2 (3a ). {tBuC(NiPr)2}GaCl2 (2a ) was
generated in situ in Et2O (50 mL) as described above. The
resulting mixture was cooled to -78 °C, and 2 equiv of CH3-
MgCl (6.34 mL of a 3.0 M solution in THF, 19.1 mmol) was
added dropwise by syringe. The reaction mixture was warmed
to room temperature and was stirred for 15 h. The volatiles
were removed under reduced pressure, affording a pale yellow
solid that was extracted with hexanes (70 mL). The extract
was concentrated to 15 mL and cooled to -78 °C for 18 h to
yield pure {tBuC(NiPr)2}GaMe2 as colorless crystals which
Gen er a l P r oced u r es. All experiments were carried out
under N2 using standard Schlenk techniques or in a Vacuum
Atmospheres glovebox. Hexanes and diethyl ether were dis-
tilled from Na/benzophenone and stored under N2 prior to use.
Li[tBuC(NiPr)2] and Li[tBuC(NCy)2] were prepared according
to a literature procedure.2a All other chemicals were purchased
from Aldrich and used as received.
1H and 13C NMR spectra were obtained on a Bruker AMX-
360 spectrometer, in Teflon-valved or flame-sealed tubes, at
ambient probe temperature (25 °C). 1H and 13C chemical shifts
are reported versus SiMe4 and were determined by reference
to the residual solvent peaks. All coupling constants are
reported in Hz. Mass spectra were obtained using the direct
insertion probe (DIP) method, on a VG Analytical Trio I
instrument operating at 70 eV. Elemental analyses were
performed by Desert Analytics Laboratory.
{tBu C(NiP r )2}Ga Cl2 (2a ). A colorless solution of GaCl3
(0.840 g, 4.75 mmol) in Et2O (10 mL) was cooled to -78 °C
and added dropwise to a slurry of Li[tBuC(NiPr)2] (0.904 g,
4.75 mmol) in Et2O (40 mL), also at -78 °C. The mixture was
warmed to room temperature and was stirred for 12 h,
affording a slurry of a white solid in a pale yellow solution.
The mixture was filtered, and the filtrate was concentrated
to 30 mL and cooled at -78 °C for 18 h to yield pure {tBuC-
(NiPr)2}GaCl2 as colorless crystals that were collected by
1
were collected by filtration (1.36 g, 51%). H NMR (C6D6): δ
4.10 (septet, 3J ) 6.1, 2H, CHMe2), 1.21 (s, 9H, CMe3), 1.12
(d, 3J ) 6.1, 12H, CHMe2), 0.24 (s, 6H, GaMe2). 13C NMR
1
(C6D6): δ 173.9 (s, NCN), 46.3 (d, J CH ) 139, CHMe2), 39.3
1
1
(s, CMe3), 29.6 (q, J CH ) 127, CHMe2), 26.2 (q, J CH ) 125,
1
CMe3), -4.7 (q, J CH ) 123, GaMe2). Anal. Calcd for C13H29
-
GaN2: C, 55.14; H, 10.34; N, 9.89. Found: C, 55.18; H, 10.44;
N, 9.90. EI-MS (m/z): 282 (M+ - H, 1), 267 (M+ - CH3, 45),
126 (38), 99 (3), 84 (100), 69 (5), 57 (46).
{tBu C(NCy)2}Ga Me2 (3b). {tBuC(NCy)2}GaCl2 (2b) was
generated in situ in Et2O (50 mL) as described above. The
mixture was cooled to -78 °C, and 2 equiv of CH3MgCl (6.34
mL of a 3.0 M solution in THF, 19.1 mmol) was added dropwise
by syringe. The reaction mixture was warmed to room tem-
perature and was stirred for 15 h. The volatiles were removed
under reduced pressure, affording a pale yellow solid that was
extracted with hexanes (70 mL). The extract was concentrated
to 15 mL and cooled to -78 °C for 18 h to yield pure {tBuC-
(NCy)2}GaMe2 as large colorless crystals which were collected
(8) Wallwork, S. C.; et al. J . Chem. Soc. 1965, 1816.
(9) Beagley, B.; Schmidling, D. G.; Steer, I. A. J . Mol. Struct. 1974,
21, 437.
(10) The C-N distance of 1.34 Å is intermediate between the normal
CdNimine double-bond distance (1.29 Å) and the normal C(sp2)sN
single-bond distance (1.47 Å).
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by filtration (1.81 g, 53%). H NMR (C6D6): δ 3.72 (br m, 2H,
Cy), 2.00-1.95 (br m, 4H, Cy), 1.74-1.70 (br m, 4H, Cy), 1.61-
1.57 (br m, 2H, Cy), 1.30-1.00 (br m, 10H, Cy), 1.29 (s, 9H,
Dagorne, Samuel
