Synthesis, characterization, and x-ray crystal structure of a gallium monohydroxide and a hetero-bimetallic gallium zirconium oxide

Article abstract of DOI:10.1021/ic051769l

A monomeric hydroxide of gallium, LGa(Me)OH, containing terminal hydroxide and methyl groups was prepared by the hydrolysis of LGa(Me)Cl in the presence of N-heterocyclic carbene and water [L = HC{(CMe)(2,6-i-Pr₂C ₆H₃N)}₂] in high yield and in a pure form. LGa(Me)OH was used as a synthon to assemble the first hetero-bimetallic compound with a Ga-O-Zr core, [(LGaMe)-(Cp₂ZrMe)](μ-O).

Full text of DOI:10.1021/ic051769l

Inorg. Chem. 2006, 45, 949−951
Synthesis, Characterization, and X-ray Crystal Structure of a Gallium
Monohydroxide and a Hetero-bimetallic Gallium Zirconium Oxide
Sanjay Singh, Vojtech Jancik, Herbert W. Roesky,* and Regine Herbst-Irmer
Institut fu¨r Anorganische Chemie der Georg-August-UniVersita¨t Go¨ttingen, Tammannstrasse 4,
D-37077 Go¨ttingen, Germany
Received October 12, 2005
A monomeric hydroxide of gallium, LGa(Me)OH, containing terminal
hydroxide and methyl groups was prepared by the hydrolysis of
LGa(Me)Cl in the presence of N-heterocyclic carbene and water
locyanine,5 (2,6-Mes2C6H3)2GaOH;6 others contain hydroxy-
bridged [2,6-Mes2C6H3GaMe(µ-OH)]26 and [Ga(OH)(SO4)-
(terpy)(H2O)]‚H2O.7 Our long-standing interest in the synthesis
of group 13 hydroxides,1d,e,8 containing terminal -OH
groups, resulted in a series of compounds: LAl(OH)2,9a,10a
LGa(OH)2,9b LAl(Me)OH,11 and [LAlOH]2(µ-O)10b [L ) HC-
{(CMe)(2,6-i-Pr2C6H3N)}2]. A key factor in this successful
assembly has been the choice of an appropriate ligand
environment around the metal atom and a synthetic strategy
that allows product formation in a rational and predictable
manner.12 Recently, we have shown that the use of N-
heterocyclic carbene as a HCl scavenger has proven to be a
versatile method in hydrolysis and ammonolysis reactions.9
The isolation of LAl(Me)OH prompted us to look for a
similar gallium derivative. Another driving force was the
compound [(LAlMe)(Cp2ZrMe)](µ-O), which was a very
good catalyst for the polymerization of ethylene.11a Moreover,
LAl(Me)OH has been utilized to prepare a series of
aluminum lanthanide hetero-bimetallic complexes.11c
[L
form. LGa(Me)OH was used as a synthon to assemble the first
hetero-bimetallic compound with a Ga Zr core, [(LGaMe)-
(Cp2ZrMe)]( -O).
) HC{(CMe)(2,6-i-Pr2C6H3N)}2] in high yield and in a pure
−O−
µ
The controlled hydrolysis of compounds of group 13
metals has been a topic of wide interest for a long time,
particularly of those of aluminum alkyls and aryls.1 The
major interest has been the partial hydrolysis product of
trimethylaluminum, viz., methylalumoxane (MAO), an ex-
tremely potent cocatalyst in the polymerization of ethylene
and propylene.2 Presently, a wide range of terminal to
bridging and monomeric to oligomeric hydroxides of alu-
minum have been synthesized and structurally character-
ized.1,3 However, only a few hydroxides of gallium contain-
ing terminal -OH groups have been reported.3 In 1994,
Atwood et al. reported the preparation of the first gallium
dihydroxide stabilized by a bulky pincer-type ligand from
the corresponding dihydride and water.4 Monohydroxides of
gallium reported previously include hydroxygallium phtha-
A
methylgallium hydroxide, MeGa(OH)Pz2BMe2
[Pz2BMe2 ) bis(pyrazolyl)dimethylboron], was isolated by
(5) Yamasaki, K.; Okada, O.; Inami, K.; Oka, K.; Kotani, M.; Yamada,
H. J. Phy. Chem. B 1997, 101, 13-19.
(6) Wehmschulte, R. J.; Steele, J. M.; Khan, M. A. Organometallics 2003,
22, 4678-4684.
(7) Sofetis, A.; Papaefstatthiou, G. S.; Terzis, A.; Raptopoulou, C. P.;
Zafiropoulos, T. F. Z. Naturforsch. 2004, 59b, 291-297.
(8) Storre, J.; Klemp, A.; Roesky, H. W.; Fleischer, R.; Stalke, D.
Organometallics 1997, 16, 3074-3076.
(9) (a) Jancik, V.; Pineda, L. W.; Pinkas, J.; Roesky, H. W.; Neculai, D.;
Neculai, A. M.; Herbst-Irmer, R. Angew. Chem., Int. Ed. 2004, 43,
2142-2145. (b) Jancik, V.; Pineda, L. W.; Stu¨ckl, A. C.; Roesky, H.
W.; Herbst-Irmer, R. Organometallics 2005, 24, 1511-1515. (c)
Pineda, L. W.; Jancik, V.; Roesky, H. W.; Neculai, D.; Neculai, A.
M. Angew. Chem., Int. Ed. 2004, 43, 1419-1421.
(10) (a) Bai, G.; Peng, Y.; Roesky, H. W.; Li, J.; Schmidt, H.-G.;
Noltemeyer, M. Angew. Chem., Int. Ed. 2003, 42, 1132-1135. (b)
Bai, G.; Roesky, H. W.; Li, J.; Noltemeyer, M.; Schmidt, H.-G. Angew.
Chem., Int. Ed. 2003, 42, 5502-5506.
(11) (a) Bai, G.; Singh, S.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-
G. J. Am. Chem. Soc. 2005, 127, 3449-3455. (b) Singh, S.; Kumar,
S. S.; Chandrasekhar, V.; Ahn, H.-J.; Biadene, M.; Roesky, H. W.;
Hosmane, N. S.; Noltemeyer, M.; Schmidt, H.-G. Angew. Chem., Int.
Ed. 2004, 43, 4940-4943. (c) Chai, J. F.; Jancik, V.; Singh, S.; Zhu,
H. P.; He, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer, M.;
Hosmane, N. S. J. Am. Chem. Soc. 2005, 127, 7251-7258.
(12) Roesky, H. W.; Singh, S.; Jancik, V.; Chandrasekhar, V. Acc. Chem.
Res. 2004, 37, 969-981.
* To whom correspondence should be addressed. E-mail: hroesky@
gwdg.de. Fax: (+49)551-393373.
(1) Feng, T. L.; Gurian, P. L.; Healy, M. D.; Barron, A. R. Inorg. Chem.
1990, 29, 408-411. (b) Harlan, C. J.; Mason, M. R.; Barron, A. R.
Organometallics 1994, 13, 2957-2969. (c) Wehmschulte, R. J.;
Grigsby, W. J.; Schiemenz, B. R.; Bartlett, A.; Power, P. P. Inorg.
Chem. 1996, 35, 6694-6702. (d) Storre, J.; Klemp, A.; Roesky, H.
W.; Schmidt, H.-G.; Noltemeyer, M.; Fleischer, R.; Stalke, D. J. Am.
Chem. Soc. 1996, 118, 1380-1386. (e) Storre, J.; Schnitter, C.; Roesky,
H. W.; Schmidt, H.-G.; Noltemeyer, M.; Fleischer, R.; Stalke, D. J.
Am. Chem. Soc. 1997, 119, 7505-7513. (f) Koide, Y.; Barron, A. R.
Organometallics 1995, 14, 4026-4029. (g) Veith, M.; Jarczyk, M.;
Huch, V. Angew. Chem., Int. Ed. 1998, 37, 105-108. (h) Schmitt,
W.; Baissa, E.; Mandel, A.; Anson, C. E.; Powell, A. K. Angew. Chem.,
Int. Ed. 2001, 40, 3577-3581. (i) Harlan, C. J.; Gillan, E. G.; Bott,
S. G.; Barron, A. R. Organometallics 1996, 15, 5479-5488.
(2) (a) Sinn, H.; Kaminsky, W.; Vollmer, H.-J.; Woldt, R. Angew. Chem.,
Int. Ed. Engl. 1980, 19, 390-392. (b) Chen, E. Y.-X.; Marks, T. J.
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2001, 34, 201-211.
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10.1021/ic051769l CCC: $33.50
Published on Web 01/04/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 3, 2006 949

COMMUNICATION
Scheme 1. Preparation of â-Diketiminate Methylgallium Hydroxide 2
Scheme 2. Preparation of the Hetero-bimetallic Gallium Zirconium
Oxide Compound 3
Figure 1. Molecular structure of 2. The hydrogen atoms of the C-H
bonds are omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ga(1)-O(1) 1.831(1), Ga(1)-N(1) 1.957(1), Ga(1)-N(2) 1.953(1),
Ga(1)-C(30) 1.949(2); O(1)-Ga(1)-N(1) 102.8(1), O(1)-Ga(1)-N(2)
105.4(1), N(1)-Ga(1)-N(2) 95.6(1), O(1)-Ga(1)-C(30) 119.5(1),
N(1)-Ga(1)-C(30) 116.0(1), N(2)-Ga(1)-C(30) 114.3(1).
Rettig and co-workers as a byproduct of the reaction between
Na[Me2BPz2] and Me2GaCl‚OEt2. The formation of MeGa-
(OH)Pz2BMe2 probably resulted from an accidental use of
wet solvent.13 Therefore, it was of interest to prepare a
molecule with similar functionalities with a much simpler
procedure that rationally allows the assembly of such
molecules. Herein we report on the high yield synthesis of
a monomeric terminal hydroxide of gallium, LGa(Me)OH
(2), and its reaction with Cp2ZrMe2 to prepare the hetero-
bimetallic compound [(LGaMe)(Cp2ZrMe)](µ-O) (3).
The hydrolysis of LGa(Me)Cl (1) with a stoichiometric
amount of water in the presence of 1,3-di-tert-butylimidazol-
2-ylidene as a hydrogen chloride acceptor results in the
formation of 2 in good yield (Scheme 1). The 1,3-di-tert-
butylimidazolium chloride formed can easily be separated
because of its insolubility in n-hexane and affords 2 in pure
form. Moreover, upon reduction with t-BuOK, 1,3-di-tert-
butylimidazol-2-ylidene was regenerated and recycled. Com-
pound 2 is a rare example of a monohydroxide of gallium
with a methyl group as a substituent on gallium.
The OH groups are one of the most important functional
groups for the immobilization of catalytically active metal
complexes and also for solid acid catalysts. Because of the
stability of the Ga-O bond, the proton of the GaO-H moiety
in 2 can be anticipated to be Bro¨nsted acidic. Therefore, the
reaction of 2 with Cp2ZrMe2 in toluene leads to methane
evolution and the formation of 3. Compound 3 represents
the first example of a X-ray-characterized molecule with a
Ga-O-Zr core (Scheme 2).
Figure 2. Molecular structure of 3. The hydrogen atoms of the C-H bonds
are omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ga(1)-O(1) 1.815(1), Ga(1)-N(1) 1.975(2), Ga(1)-N(2) 1.967(2),
Ga(1)-C(30) 1.971(2), Zr(1)-O(1) 1.926(1), Zr(1)-C(41) 2.301(3); O(1)-
Ga(1)-N(1) 109.0(1), O(1)-Ga(1)-N(2) 109.8(1), N(1)-Ga(1)-N(2) 96.1-
(1), O(1)-Ga(1)-C(30) 116.2(1), N(1)-Ga(1)-C(30) 112.3(1), N(2)-
Ga(1)-C(30) 111.7(1), Ga(1)-O(1)-Zr(1) 146.7(1), O(1)-Zr(1)-C(41)
102.0(1).
Similarly, a peak at m/z 739 in 3 is due to [M+ - Me]. The
IR spectrum of 2 shows a sharp band at 3676 cm-1, which
1
can be attributed to the GaO-H stretch. The H NMR
spectrum of 2 shows two resonances (δ +0.08 and -0.57),
which can be attributed to the protons of OH and GaMe
groups, respectively. In much the same way, resonances (δ
-0.12 and -0.32) for 3 correspond to ZrMe and GaMe,
respectively. The other resonances for 2 and 3 are charac-
teristic of the â-diketiminate ligand L.
Single crystals of 2 and 3 suitable for X-ray structural
analysis were obtained from their n-hexane and toluene
solutions, respectively. The molecular structures of 2 and 3
are shown in Figures 1 and 2. Compounds 2 and 3 crystallize
in the monoclinic space groups P21/c and P21/n, respectively.
The X-ray crystal structure reveals 2 as a monomeric
gallium hydroxide (Figure 1). The Ga center exhibits a
distorted tetrahedral geometry with two nitrogen atoms of
the â-diketiminate ligand, one Me group, and an OH group.
The small N-Ga-N angle 95.6(1)° is the result of the
formation of the C3N2Ga six-membered ring. The Ga-OH
Compounds 2 and 3 have been unambiguously character-
ized by means of spectroscopic, spectrometric, and crystal-
lographic techniques. Both 2 and 3 are colorless crystalline
solids and are thermally quite stable. Compound 2 melts at
200 °C, while 3 melts with decomposition at 318 °C. The
electrospray ionization (EI) mass spectrum of 2 revealed that
the most intense peak appears at m/z 503 and corresponds
to the loss of one methyl group from the molecular ion.
(13) Rettig, S. J.; Sandercock, M.; Storr, A.; Trotter, J. Can. J. Chem. 1990,
68, 59-63.
950 Inorganic Chemistry, Vol. 45, No. 3, 2006

COMMUNICATION
bond length [1.831(1) Å] in 2 is considerably shorter than
that found in hydroxyl(methyl)gallium bis(pyrazolyl)di-
methylboron13 (2.033(5) Å) and in [(2,6-Mes2C6H3Ga(Me)-
(µ-OH)]2 (average 1.914 Å)6 but slightly longer than that
observed in (2,6-Mes2C6H3)2GaOH [1.783(2) Å].6 The
Ga-Me distance 1.949(2) Å in 2 is comparable to 1.957(8)
Å observed in hydroxyl(methyl)gallium bis(pyrazolyl)di-
methylboron and in [(2,6-Mes2C6H3Ga(Me)(µ-OH)]2 (aver-
age 1.947 Å).13
The molecular structure of 3 is shown in Figure 2. The
Ga atom exhibits a highly distorted tetrahedral geometry with
two nitrogen atoms of the â-diketiminate ligand, one Me
group, and one µ-O unit. The coordination sphere of Zr is
completed by two Cp ligands and one Me group. The Me
groups in 3 are bent out of the Ga-O-Zr plane in a trans
manner. The Ga-(µ-O) bond length [1.815(1) Å] in 3 is
slightly shorter than the Ga-O distance in 2 [1.831(1) Å]
and is shorter in other Ga-(µ-O) derivatives, for example,
8
1.910 Å in (MesGaO)9 and 1.898 Å in (Mes2GaOLi)2‚
4THF.1e The Ga-O-Zr angle [146.7(1)°] lies between the
Ga-O-Ga angle [91.9(1)° in (Mes2GaOLi)2‚4THF1e and
100.6(2)° in [(t-BuO)2GaH]214] and the Zr-O-Zr angle
[174.1(3)° in [Cp2Zr(Me)]2(µ-O)].15 The Zr-(µ-O) bond
length [1.926(1) Å] is slightly shorter than those exhibited
by compounds [(Cp2ZrCl)2(µ-O)] [1.945(3) Å],16 [(Cp2-
ZrMe)]2(µ-O) [1.948(1) Å],15 and [{(Cp2Zr)(µ-O)3]
[1.959(3) Å]17 but significantly shorter than the Zr-(µ-O)
or Zr-(µ-OH) bond lengths observed in the clusters [(Cp*Zr)6-
(µ4-O)(µ-O)4(µ-OH)8]‚2C7H8 (∼2.106 Å)18 and [{(Cp*ZrCl)-
(µ-OH)}3(µ3-OH)(µ3-O)]‚2THF [2.160(2) Å].19-23 The Zr-
Me bond length [2.301(3) Å] in 3 is longer than that found
in (Cp2ZrMe)2(µ-O) [2.276(9) Å].15
(14) Veith, M.; Faber, S.; Wolfgang, H.; Huch, V. Chem. Ber. 1996, 129,
381-384.
(15) Hunter, W. E.; Hrncir, D. C.; Bynum, R. V.; Penttila, R. A.; Atwood,
J. L. Organometallics 1983, 2, 750-755.
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft and the Go¨ttinger Akad-
emie der Wissenschaften.
(16) Clarke, J. F.; Drew, M. G. B. Acta Crystallogr. 1974, B30, 2267-
2269.
(17) Fachinetti, G.; Floriani, C.; Chiesi-Villa, A.; Guastino, C. J. Am. Chem.
Soc. 1979, 101, 1767-1175.
Supporting Information Available: Full details of the crystal
structure determination for 2 (CCDC 280865) and 3 (CCDC
280866) (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
(18) Bai, G.; Roesky, H. W.; Li, J.; Labahn, T.; Cimpoesu, F.; Magull, J.
Organometallics 2003, 22, 3034-3038.
(19) Babcok, L. M.; Day, V. W.; Klemperer, W. G. J. Chem. Soc., Chem.
Commun. 1988, 519-520.
(20) (a) To a solution of 1,3-di-tert-butylimidazol-2-ylidene (0.45 g, 2.50
mmol) and LGa(Me)Cl (1.34 g, 2.50 mmol) in toluene (50 mL) was
added slowly with vigorous stirring over a period of 30 min degassed
and distilled water (45 µL, 2.50 mmol). The mixture was stirred for
another 15 min. After removal of all volatiles, the product was
extracted with n-hexane (60 mL). The final solution was concentrated
(15 mL) and stored at -20 °C for 2 days to afford colorless crys-
tals. Yield: 1.00 g (76 %). Mp: 198-200 °C. Anal. Calcd for
C30H45GaN2O (519.41): C, 69.37; H, 8.73, N, 5.39. Found: C, 69.46;
IC051769L
(21) (a) Crystal data for compound 2 (C30H45GaN2O): Mw ) 519.40,
monoclinic, P21/c, a ) 8.943(2) Å, b ) 9.752(2) Å, c ) 33.182(4)
Å, â ) 92.09(2)°, V ) 2892(1) Å3, Z ) 4, Dcalcd ) 1.193 Mg‚m-3, T
) 100(2) K, λ(Cu KR) ) 1.541 78 Å, µ ) 1.462 mm-1. Out of 19 318
collected reflections, 4120 were independent (Rint ) 0.0268). The
final refinements converged at R1 ) 0.0268 for [I > 2σ(I)], wR2 )
0.0671 for all data, CCDC 280865. (b) Crystal data for compound 3
(C41H57GaN2OZr): Mw ) 754.83, monoclinic, P21/n, a ) 10.056(2)
Å, b ) 18.586(3) Å, c ) 20.013(3) Å, â ) 90.20(1)°, V ) 3740(1)
Å3, Z ) 4, Dcalcd ) 1.340 Mg‚m-3, T ) 100(2) K, λ(Cu KR) ) 1.54178
Å, µ ) 3.407 mm-1. Out of 17 776 collected reflections, 4956 were
independent (Rint ) 0.0195). The final refinements converged at R1
) 0.0199 for [I > 2σ(I)], wR2 ) 0.0477 for all data, CCDC 280866.
(c) The structures were solved by direct methods (SHELXS-97)21 and
refined against all data by full-matrix least squares on F 2.22 All of
the C-H hydrogen atoms except H(3A) were included in geometrically
idealized positions and refined with the riding model. Localization of
the H(3A) hydrogen from the electron density map in both structures
proved to be more accurate than its fixing in the idealized position
and led to lowering of the R1 and wR2 values. The hydrogen atom
from the OH in 2 was localized from the difference electron density
map and refined isotropically. (d) Compound 3 crystallizes as a pseudo-
merohedral twin emulating orthorhombic crystal system. The twin law
was determined as -1 0 0 0 -1 0 0 0 1, and the ratio of the domains
was refined as 0.33/0.67.
H, 8.62; N, 5.42. MS (EI): m/z (%) 518 (6) [M+], 503 (100) [M+
-
Me], 485 (44) [M+ - Me - 3H]. IR (Nujol): ν˜ 3676, 1558, 1527,
1442, 1384, 1319, 1262, 1178, 1105, 1056, 1023, 936, 869, 804, 757,
603, 571 cm-1
.
1H NMR (200 MHz, C6D6): δ 7.12-7.03 (m, Ar),
3
4.80 (s, 1 H, γ-CH), 3.79 (sept, JHH ) 6.8 Hz, 2 H, CHMe2), 3.20
(sept, 3JHH ) 6.5 Hz, 2 H, CHMe2), 1.57 (s, 6 H, CMe), 1.34 (d, 3JHH
) 6.6 Hz, 6 H, CHMe2), 1.24 (dd, 12 H, CHMe2), 1.08 (d, 3JHH ) 6.6
Hz, 6 H, CHMe2), 0.08 (s, 1 H, GaOH), -0.57 (s, 3 H, GaMe). (b)
Toluene (60 mL) was added at 0 °C to the mixture of 2 (0.52 g, 1.00
mmol) and Cp2ZrMe2 (0.25 g, 1.00 mmol). The resulting solution was
stirred for 2 h at room temperature and then continuously for 24 h at
100 °C. The colorless solution was kept at room temperature for 48
h to isolate colorless crystals of 3 (0.52 g). An additional crop of 3
(0.18 g) was obtained at 0 °C. Yield: 0.70 g (93%). Mp: 318 °C
(dec). Anal. Calcd for C41H57GaN2OZr (754.85): C, 65.24; H, 7.61;
N, 3.71. Found: C, 65.28; H, 7.58; N, 3.73. MS (EI): m/z (%): 739
(48) [M+ - Me], 501 (100) [M+ - 2Me - 2H - ZrCp2], 485 (16)
[M+ - 2Me - 2H - O - ZrCp2]. IR (Nujol): ν˜ 1554, 1526, 1438,
1316, 1384, 1264, 1253, 1179, 1120, 1100, 1023, 934, 791, 769, 703,
637, 620, 552, 449 cm-1. 1H NMR (200 MHz, CDCl3): δ 7.25-7.24
(m, Ar), 5.29 (s, 10 H, C5H5), 4.87 (s, 1 H, γ-CH), 3.15 (sept, 3JHH
)
(22) Sheldrick, G. M. SHELXS-90, Program for Structure Solution. Acta
Crytallogr., Sect. A 1990, 46, 467-473.
(23) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refine-
ment; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997.
6.8 Hz, 4 H, CHMe2), 1.74 (s, 6 H, CMe) 1.38, 1.35 (dd, 3JHH ) 6.8
3
3
Hz, 12 H, CHMe2), 1.25 (d, JHH ) 6.8, 6 H, CHMe2), 1.08 (d, JHH
) 6.8, 6 H, CHMe2), -0.12 (s, 3 H, ZrMe), -0.32 (s, 3 H, GaMe).
Inorganic Chemistry, Vol. 45, No. 3, 2006 951