Dimeric gallium oxide and sulfide species stabilized by a sterically encumbered β-diketiminate ligand

Article abstract of DOI:10.1021/ic015506c

Reaction of {HC(MeCDippN)₂}Ga: with N₂O or S₈ produces the compounds [{HC(MeCDippN)₂}GaE]₂ (E = O or S), which are unique examples of gallium oxide and sulfide dimers stabilized by a chelating ligand.

Full text of DOI:10.1021/ic015506c

2474
Inorg. Chem. 2001, 40, 2474-2475
Dimeric Gallium Oxide and Sulfide Species Stabilized by a Sterically Encumbered â-Diketiminate Ligand
Ned J. Hardman and Philip P. Power*
Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616
ReceiVed January 17, 2001
Table 1. Selected Bond Distances (Å) and Angles (deg) for
[{HC(MeCDippN)2}GaE]2 (E ) O (1), S (2))
Organo group 13 metal chalcogenides of formula (RME)n (R
) alkyl, aryl, or related group; M ) Al, Ga, or In; E ) O, S, Se,
or Te)1-22 can be synthesized by a variety of synthetic routes.
For the organometalloxanes (RMO)n, the most widely used
method involves the controlled hydrolysis of metal trialkyls
MR3.5,6 For the heavier chalocogenides, the direct reaction of
organo M(I) or M(III) precursors with the elemental chalco-
gens usually affords the (RME)n (E ) S, Se, or Te) conge-
ners.1-4,7-13,18-20 A common feature of these products is that they
are oligomeric, with n ) 4-8 as the most common association
numbers. In the lighter oxo derivatives, in particular those of
aluminum, relatively high degrees of association are often found,
even with fairly large organic groups such as t-Bu. Only in the
case of the very large substituent -C6H2-2,4,6-t-Bu3 (Mes*) was
a lower degree of aggregation (4) observed in the compound
(Mes*AlO)4,14 which has an unusual Al4O4 ring structure instead
of a three-dimensional cubane arrangement.21 In contrast, structur-
ally characterized (RGaO)n cages are limited to the silyl substi-
tuted species {(t-Bu)3SiGaO}4 which has an almost perfectly cubic
Ga4O4 core and an average Ga-O distance near 1.92 Å.22 It is
now shown that use of the sterically encumbering â-diketiminate
ligand [HC(MeCDippN)2]- (Dipp ) C6H3-2,6-i-Pr2)23 stabilizes
the first dimeric galloxane derivative [{HC(MeCDippN)2}GaO]2,
1
2
Ga-E(1)
1.8536(9)
1.8485(9)
1.970(1)
1.978(1)
2.5989(3)
2.2511(7)
2.2736(7)
1.986(2)
1.983(2)
3.0127(6)
Ga-E(1A)
Ga-N(1)
Ga-N(2)
Ga(1)‚‚‚Ga(1A)
Ga-E-Ga
E-Ga-E
N-Ga-N
88.18(4)
90.82(4)
94.96(4)
83.49(2)
96.51(2)
94.01(2)
1, as well as its sulfur analogue [{HC(MeCDippN)2}GaS]2, 2. In
addition, compound 1 was obtained by a facile route involving
the reaction of {HC(MeCDippN)2}Ga:24 with N2O.
Treatment of {HC(MeCDippN)2}Ga: with N2O or S8 in toluene
solution at room temperature produced compounds 1 or 2 as
colorless crystals that possess low solubility in hydrocarbon
solvents.25 The compounds were characterized by C, H, N
analysis, 1H NMR spectroscopy, and X-ray crystallography.26 The
structures of 1 and 2 may be illustrated by the thermal ellipsoid
plot of 1 in Figure 1. Selected bond lengths and angles are
provided in Table 1. Both compounds are dimeric, which can be
attributed to the large size and bidentate nature of the â-diketimi-
nate ligands. There is a center of symmetry in the middle of their
* To whom correspondence should be addressed. Fax: 530-752-8995.
E-mail: pppower@ucdavis.edu.
(1) Power, M. B.; Barron, A. R. Chem. Commun. 1991, 1315.
(2) Cowley, A. H.; Jones, R. A.; Harris, P. R.; Atwood, D. A.; Contreras,
L.; Burek, C. J. Angew. Chem., Int. Ed. Engl. 1991, 30, 1143.
(3) Power, M. B.; Ziller, J. W.; Tyler, A. N.; Barron, A. R. Organometallics
1992, 11, 1055.
(4) Power, M. B.; Ziller, J. W.; Barron, A. R. Organometallics 1992, 11,
2783.
(5) Mason, M. K.; Smith, J. M.; Bott, S. G.; Barron, A. R. J. Am. Chem.
Soc. 1993, 115, 4971.
(6) Barron, A. R. Comments Inorg. Chem. 1993, 14, 123.
(7) Harlan, C. J.; Mason, M. R.; Barron, A. R. Organometallics 1994, 13,
2957.
(23) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall, W. J.; Calabrese,
J. C.; Arthur, S. D. Organometallics 1997, 16, 1514.
(24) Hardman, N. J.; Eichler, B. E.; Power, P. P. Chem. Commun. 2000, 1991.
(25) All manipulations were carried out under anaerobic and anhydrous
conditions. A toluene solution (63 mL) of {HC(MeCDippN)2}Ga: (0.805
g, 1.65 mmol) was added dropwise under slightly positive pressure to a
septum-capped, 100 mL Schlenk tube that had been flushed with N2O
and vented with a needle. A white precipitate formed immediately. Upon
completion of the addition, stirring was continued for 1 h, whereupon
the mixture was heated to redissolve the precipitate. Cooling to room
temperature afforded the product 1 as large colorless crystals. Yield:
0.52 g, 62%. Mp: 246-249 °C. Anal. Calcd for C29H41GaN2O: C, 69.19;
(8) Roesky, H. W.; Haming, L.; Kuhn, A.; Herbst-Irmer, R. Organometallics
1994, 13, 4004.
1
H, 8.21; N, 5.57. Found: C, 69.91; H, 8.34; N, 5.12. H NMR (C7D8,
(9) Uhl, W.; Graupner, R.; Layh, M.; Schu¨tz, U. J. Organomet. Chem. 1995,
493, C1.
(10) Uhl, W.; Graupner, R.; Pohlmann, M.; Pohl, S.; Saak, W. Chem. Ber.
1996, 129, 143.
(11) Harlan, C. J.; Gillan, E. G.; Bott, S. G.; Barron, A. R. Organometallics
1996, 15, 5479.
(12) App, U.; Merzweiler, K. Z. Anorg. Allg. Chem. 1997, 623, 478.
(13) Stoll, S. L.; Bott, S. G.; Barron, A. R. Dalton Trans. 1997, 1315.
(14) Wehmschulte, R. J.; Power, P. P. J. Am. Chem. Soc. 1997, 119, 8387.
(15) Wehmschulte, R. J.; Power, P. P. Chem. Commun. 1998, 335.
(16) Uhl. W.; Pohlmann, M. Chem. Commun. 1998, 451.
(17) Linti, G.; Bu¨hler, M.; Urban, H. Z. Anorg. Allg. Chem. 1998, 624, 517.
(18) Uhl, W.; Jantschak, A. W. J. Organomet. Chem. 1998, 555, 263.
(19) Uhl, W.; Benter, W.; Saak, W.; Jones, P. G. Z. Anorg. Allg. Chem. 1998,
824, 1622.
400 MHz): δ 7.13. 7.10 (m, 6H, aromatic H of Ar group), 4.77 (s, 1H,
methane CH), 3.18 (sept, 3JHH ) 7.2 Hz, 4H, CHMe2), 1.32 (s, 6H, CMe),
3
3
1.24 (d, JHH ) 6.8 Hz, 12H, CHMe2), 1.12 (d, JHH ) 7.2 Hz, 12H,
CHMe2). 2: A toluene solution (50 mL) of {HC(MeCDippN)2}Ga: (0.42
g, 0.803 mmol) was added to sulfur (0.04 g, 1.25 mmol) with rapid
stirring and cooling in an ice bath. The solution was allowed to come to
room temperature and stirred for a further 12 h. The resultant white
precipitate was redissolved by heating. Cooling the solution to room
temperature over a 2 h period produced 2 as colorless crystals. Yield:
0.15 g, 34%. Mp: decomposes slowly above 280 °C. Anal. Calcd for
C29H41GaN2S: C, 67.05; H, 7.96; N, 5.39. Found: C, 67.91; H, 7.76; N,
5.01. 1H NMR (C7D8, 300 MHz): δ 7.10 (br, s, 6H, aromatic H’s of Ar
3
group), 4.73 (s, 1H, methane CH), 3.25 (sept, JHH ) 6.9 Hz, 4H,
3
CHMe2), 1.61 (s, 6H, CMe), 1.28 (d, JHH ) 6.9 Hz, 12H, CHMe2),
3
1.10 (d, JHH ) 6.9 Hz, 12H, CHMe2).
(20) Fahlman, B. D.; Barron, A. R. Organometallics 1998, 17, 510.
(21) Besides (Mes*AlO)4 (ref 14), the only other structurally characterized
tetrameric group 13 metal (RMO)4 species are {(Me3Si)3CInO}4 (ref 16)
and {(t-Bu)3SiGaO}4 (ref 22) both of which have cubane structures.
(22) Wiberg, N.; Amelunxen, K.; Lerner, H.-W.; No¨th, H.; Ponikwar, W.;
Schwenk, H. J. Organomet. Chem. 1999, 574, 246. Also, the species
(t-BuGaO)9 has been spectroscopically characterized. The data suggest
that it has a structure derived from two parallel Ga3O3 rings linked by
three GaO units (ref 4).
(26) Crystal data at 90 K with Mo KR (λ ) 0.710 73 Å) radiation: 1, C29H41-
GaN2O, fw ) 503.36, colorless parallelepipeds, a ) 13.7132(7) Å, b )
13.7585(7) Å, c ) 14.2230(7) Å, â ) 107.278(1)°, monoclinic, space
group P21/n, V ) 2562.4(2) Å3, Z ) 4, Fcalc ) 1.305 Mg m-3, µ )
1.098 mm-1, R1 ) 0.0285 for 6739 (I > 2 σ(I)) data; 2, C29H41GaN2S,
fw ) 519.42, colorless parallelepipeds, a ) 22.4257(9) Å, b )
14.7953(6) Å, c ) 16.3518(6) Å, â ) 90.368(1)°, monoclinic, space
group C2/c, Z ) 8, Fcalc ) 1.272 Mg m-3, µ ) 1.110 mm-1, R1 ) 0.0503
for 5887 (I > 2 σ(I)) data.
10.1021/ic015506c CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/26/2001

Communications
Inorganic Chemistry, Vol. 40, No. 11, 2001 2475
three-coordinate gallium bound to two-coordinate oxygen. The
slightly longer Ga-O bond in 1 can be attributed to the higher
(4) coordination of the metal in this species.
The sulfur derivative 2 also has a bridged dimeric structure32
which is analogous to that of 1. The Ga2S2 core is planar and has
an average Ga-S bond length of 2.26(1) Å. This distance is just
within the currently known range (2.20-2.27 Å) for low-
coordinate Ga-S species.4,33-35 Unlike the almost square core
geometry in 1, the ring angle at sulfur 83.49(2)° differs consider-
ably from the 96.51(2)° at gallium. Despite the narrower sulfur
angle, the Ga‚‚‚Ga separation is 3.0127(3) Å, which is similar to
the Ga‚‚‚Ga separation of 3.099(6) Å in (t-BuGaS)4.2 Although
no dimeric gallium structures are available for comparison, the
structure of the organoaluminum sulfide dimer (Mes*AlS)2 (Mes*
) C6H2-2,4,6-t-Bu3) was described recently.15 It is notable that
this compound shows similar angular distortions in its core in
that the angle at sulfur (Al-S-Al
)
78.09(3)°)
is also narrower than the angle at the metal (S-Al-S )
101.91(3)°). In contrast, the oxygen analogue (Mes*AlO)4 is a
tetramer with a unique, planar Al4O4 ring structure in which the
Al-O-Al angle is a wide 151.32(13)°. It was argued that the
reluctance of the sulfur atom to hybridize led to narrower angles
which resulted in greater steric congestion and a lower degree of
aggregation for that molecule. These findings suggest that there
is considerable strain in the structure of 1 and that dissociation
to monomeric species featuring formal GaO multiple bonding may
be possible with suitable ligand modification.36
Figure 1. Thermal ellipsoid (30%) drawing of 1. H atoms are not shown.
Ga2O2 or Ga2S2 cores. The Ga2O2 array is almost perfectly square
with angles within ca. 0.8° of 90° and Ga-O distances that differ
by only 0.005 Å. The Ga‚‚‚Ga separation is 2.5989(3) Å, which
is just slightly longer than double the covalent radius of gallium
and shorter than Ga‚‚‚Ga distances of 2.7052(9)-2.7188(7) Å in
{(t-Bu)3SiGaO}4.22 However, owing to the electronegative nature
of the nitrogen and oxygen ligand atoms, the gallium center has
considerable ionic character which decreases its effective radius.
Thus, significant Ga‚‚‚Ga interaction is probably small. The
Ga-N distances are both ca. 0.07 Å shorter than the
2.054(2) Å average value seen in the Ga(I) precursor {HC(Me-
CDippN)2}Ga:.24 This is most probably a result of the change in
oxidation state from Ga(I) in the precursor to Ga(III) in 1.27 The
Ga-O distance, av 1.851(3) Å, may be compared to the
1.821(3), 1.822(3), or 1.831(4) Å observed in the low-coordinate
species t-Bu2GaOC6H2-2,6-t-Bu2-4-Me,28 (2,2,6,6-tetramethyl-
Acknowledgment. We are grateful to the National Science
Foundation for financial support.
Supporting Information Available: Two X-ray files in CIF format.
This material is available free of charge via the Internet at http://pubs.acs.org.
IC015506C
(31) Cowley, A. H.; Decken, A.; Olazabal, C.; Norman, N. C. Inorg. Chem.
1994, 33, 3435.
(32) The lowest degree of aggregation known for a (RGaS)n species is a
monomer (n ) 1) having Ga-S multiple bond character, which was
stabilized by a bulky tridendate pyrazolylborate ligand. Kuchta, M. C.;
Parkin, G. Dalton Trans. 1998, 2278. For further discussion of this
compound class see the following. Kuchta, M. C.; Parkin, G. Coord.
Chem. ReV. 1998, 176, 323.
(33) Ruhlandt-Senge, K.; Power, P. P. Inorg. Chem. 1993, 32, 3478.
(34) Wehmschulte, R. J.; Ruhlandt-Senge, K.; Power, P. P. Inorg. Chem. 1995,
34, 2593.
(35) Uhl, W.; Gerding, R.; Hahn, I.; Pohl, S.; Saak, W.; Reuter, H. Polyhedron
1996, 15, 3987.
(36) There are no stable molecules having formal (as distinct from dative)
multiple bonding between oxygen and group 13 elements. Power, P. P.
Chem. ReV. 1999, 99, 3463.
piperidino)2GaOPh,29 or t-Bu2GaOCPh3 in addition to the
30
1.79(1) Å observed in the dimetalloxane O{Ga(Mes*)Mn(CO)5}2
(Mes* ) C6H2-2,4,6-t-Bu3).31 All of these compounds feature
(27) In the compounds {HC(MeCDippN)2}GaX2 (X ) Cl or I), the Ga(III)-N
distances are in the range 1.906(3)-1.948(1) Å. See: Stender, M.;
Eichler, B. E.; Hardman, N. J.; Power, P. P.; Prust, J.; Noltemeyer, M.;
Roesky, H. W. Inorg. Chem., in press.
(28) Petrie, M. A.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1991,
113, 8704.
(29) Linti, G.; Frey, R.; Polborn, K. Chem. Ber. 1994, 127, 1387.
(30) Cleaver, W. M.; Barron, A. R. Organometallics 1993, 12, 1001.