Dizinc alkoxides and amides supported by binucleating bis(amidoamine) ligands

Article abstract of DOI:10.1021/ic051669f

Several new dizinc complexes that are supported by dianionic bis(amidoamine) ligands are reported. Reaction of N,N′-bis(2- dimethylaminoethyl)dibenzofuran-4,6-diamine (^MeLH₂) with 2 equiv of EtZn(OⁱPr) forms the dizinc bis-(alkoxide) ^MeLZn₂(OⁱPr)₂ (1), which was isolated in 76% yield. Similarly, ^MeLH₂ reacts cleanly with EtZn(OPh) and EtZn(OCHPh₂) to form ^MeLZn ₂(OPh)₂ (2) and ^MeLZn₂(OCHPh ₂)₂ (3), respectively. The solid-state structures of 1 and 2 feature puckered [Zn₂(μ-OR)₂]²⁺ cores, with short intermetal separations (2.81-2.88 A). Overall, the molecules have approximate (noncrystallographic) C_2v symmetry. The use of the more-hindered ⁱPr-substituted ligand N,N′-bis(2- diisopropylaminoethyl)dibenzofuran-4,6-diamine (^iPrLH₂) to prepare zinc alkoxides gave similar results. Thus, reaction of ^iPrLH₂ with 2 equiv of EtZn(OPh), EtZn(OMe), EtZn(OCHPh₂), and EtZn(OCH₂Ph) forms ^iPrLZn₂(OPh)₂ (4), ^iPrLZn ₂(OMe)₂ (5), ^iPrLZn₂(OCHPh ₂)₂ (6), and ^iPrLZn₂(OCH ₂Ph)₂ (7), respectively (isolated yields 48-63%). At 70°C, C₆D₆ solutions of 6 undergo β-hydride transfer with 2 equiv of benzaldehyde to form 7 and benzophenone in quantitative yield (according to ¹H NMR spectroscopy). Benzene solutions of 1 react with 1 equiv of trimethylsilyl trifluoromethanesulfonate (Me ₃SiOTf) to form ^MeLZn₂(OⁱPr)(OTf) (8) in 70% isolated yield. In the solid state, 8 features a bridging alkoxide donor as well as a 1,3-bridging triflate group. The previously reported dinuclear organozinc species ^MeLZn₂Ph₂ (9) reacts with 1 equiv of tert-butylamine to form the protonolysis product ^MeLZn₂(Ph)(NH^tBu) (10) in 66% isolated yield. The solid-state structure of 10 (two independent molecules) reveals a somewhat asymmetric [Zn₂(μ-Ph)(μ-NH^tBu)]²⁺ core with short Zn-Zn separations [2.6761(5) and 2.6518(5) A]. In CD ₂Cl₂ solution, the Ph bridge of 10 undergoes rapid reversible cleavage. Cleavage of this bridging interaction followed by rotation about the Zn-Ph bond and re-formation of the bridging interaction results in exchange of the inequivalent ortho (and meta) protons of the phenyl ligand. Variable-temperature ¹H NMR spectroscopic data indicate that this exchange occurs with ΔG^≠ = 12.7(1) kcal·mol ^-1 (-27°C). At 75°C, toluene solutions of ^MeLH₂ react with 2 equiv of EtZn-NH^tBu to form the dizinc bis(amido) product ^MeLZn₂(NH ^tBu)₂ (11) in 46% isolated yield. The solid-state structure of 11 (two independent molecules) features a puckered and fairly symmetric [Zn₂(μ-NH^tBu)₂]²⁺ core with short intermetal separations [2.775(1), 2.760(1) A].

Full text of DOI:10.1021/ic051669f

Inorg. Chem. 2006, 45, 1815−1822
Dizinc Alkoxides and Amides Supported by Binucleating
Bis(amidoamine) Ligands
Mark L. Hlavinka, Michael J. McNevin, Richard Shoemaker, and John R. Hagadorn*
Department of Chemistry and Biochemistry, UniVersity of Colorado,
Boulder, Colorado 80309-0215
Received September 28, 2005
Several new dizinc complexes that are supported by dianionic bis(amidoamine) ligands are reported. Reaction of
N,N′
-bis(2-dimethylaminoethyl)dibenzofuran-4,6-diamine (MeLH2) with 2 equiv of EtZn(OiPr) forms the dizinc bis-
(alkoxide) MeLZn2(OiPr)2 (1), which was isolated in 76% yield. Similarly, MeLH2 reacts cleanly with EtZn(OPh) and
EtZn(OCHPh2) to form MeLZn2(OPh)2 (2) and MeLZn2(OCHPh2)2 (3), respectively. The solid-state structures of 1 and
+
2 feature puckered [Zn2(
µ
-OR)2]2 cores, with short intermetal separations (2.81
−
2.88 Å). Overall, the molecules
i
have approximate (noncrystallographic) C2v symmetry. The use of the more-hindered Pr-substituted ligand N,N
′
-
bis(2-diisopropylaminoethyl)dibenzofuran-4,6-diamine (iPrLH2) to prepare zinc alkoxides gave similar results. Thus,
i
i
reaction of PrLH2 with 2 equiv of EtZn(OPh), EtZn(OMe), EtZn(OCHPh2), and EtZn(OCH2Ph) forms PrLZn2(OPh)2
i
i
i
(4), PrLZn2(OMe)2 (5), PrLZn2(OCHPh2)2 (6), and PrLZn2(OCH2Ph)2 (7), respectively (isolated yields 48
−63%). At
70
°
C, C6D6 solutions of 6 undergo
â
-hydride transfer with 2 equiv of benzaldehyde to form 7 and benzophenone
1
in quantitative yield (according to H NMR spectroscopy). Benzene solutions of 1 react with 1 equiv of trimethylsilyl
trifluoromethanesulfonate (Me3SiOTf) to form MeLZn2(OiPr)(OTf) (8) in 70% isolated yield. In the solid state, 8 features
a bridging alkoxide donor as well as a 1,3-bridging triflate group. The previously reported dinuclear organozinc
species MeLZn2Ph2 (9) reacts with 1 equiv of tert-butylamine to form the protonolysis product MeLZn2(Ph)(NHtBu)
(10) in 66% isolated yield. The solid-state structure of 10 (two independent molecules) reveals a somewhat asym-
+
metric [Zn2(
µ
-Ph)(µ
-NHtBu)]2 core with short Zn
−Zn separations [2.6761(5) and 2.6518(5) Å]. In CD2Cl2 solution,
the Ph bridge of 10 undergoes rapid reversible cleavage. Cleavage of this bridging interaction followed by rotation
about the Zn−Ph bond and re-formation of the bridging interaction results in exchange of the inequivalent ortho
(and meta) protons of the phenyl ligand. Variable-temperature 1H NMR spectroscopic data indicate that this exchange
1
occurs with
∆
Gq
)
12.7(1) kcal
‚
mol-
(−27
°
C). At 75
°
C, toluene solutions of MeLH2 react with 2 equiv of EtZn-
NHtBu to form the dizinc bis(amido) product MeLZn2(NHtBu)2 (11) in 46% isolated yield. The solid-state structure of
11 (two independent molecules) features a puckered and fairly symmetric [Zn2(µ
-NHtBu)2]2+ core with short intermetal
separations [2.775(1), 2.760(1) Å].
Introduction
these ligands can prevent unwanted processes such as
fragmentation and oligomerization. Their design can also
useful for tailoring reactivity. In this context, we have been
developing new preorganized binucleating ligands that are
suitable for the preparation of main-group-metal bimetallics,
including a range of dialuminum and dizinc complexes
Bimetallic complexes play important roles in numerous
areas of chemistry, including metalloprotein modeling,
supramolecular chemistry, and catalysis.1 To control the
physical properties and chemical reactivities of this class of
compounds, it is necessary that a broad range of well-defined
binucleating ligands be developed.2 Generally, these ligands
feature multiple donor groups that are linked together with
some sort of unreactive spacer. When properly designed,
(1) Representative reviews on bimetallics in metalloenzyme models: (a)
Du Bois, J.; Mizoguchi, T. J.; Lippard, S. J. Coord. Chem. ReV. 2000,
200-202, 443. (b) Bosnich, B. Inorg. Chem. 1999, 38, 2554.
Supramolecular chemistry: (c) Leininger, S.; Olenyuk, B.; Stang, P.
J. Chem. ReV. 100, 853. Catalysis: (d) Catalysis by Di- and
Polynuclear Metal Cluster Complexes; Adams, R. D.; Cotton, F. A.,
Eds.; Wiley-VCH: New York, 1998. (e) Rowlands, G. J. Tetrahedron
2001, 57, 1865.
* To whom correspondence should be addressed. E-mail: hagadorn@
colorado.edu.
10.1021/ic051669f CCC: $33.50
Published on Web 12/31/2005
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 4, 2006 1815

Hlavinka et al.
1H NMR (C6D6): δ 7.51 (t, J ) 7.8 Hz, 2H), 7.39 (dd, J ) 1.0,
7.8 Hz, 2H), 6.76 (dd, J ) 1.0, 7.8 Hz, 2H), 4.06 (sept, J ) 6.0
Hz, 2H), 3.26 (t, J ) 5.5 Hz, 4H), 2.26 (t, J ) 5.5 Hz, 4H), 1.99
(s, 12H, NMe2) 0.98 (d, J ) 6.0 Hz, 12H). 13C{1H} NMR (C6D6):
δ 146.3, 144.2, 125.9, 125.0, 106.7, 104.6, 67.4, 62.1, 45.9, 43.8,
29.0. Anal. Calcd (found) for C26H40N4O3Zn2: C, 53.16 (53.56);
H, 6.86 (6.60); N, 9.54 (9.38).
supported by bis(amidinate)3,4 and bis(amidoamine)5 ligands.
Here, we present the preparation and characterization of a
series of dizinc alkoxide and amido derivatives supported
by bis(amidoamine) ligands. These results contribute to the
growing number of well-defined zinc alkoxides of low
nuclearity that have attracted significant interest as catalysts
for lactide polymerization6 and epoxide/CO2 copolymeriza-
tion reactions.7
MeLZn2(OPh)2 (2). The compound was prepared using a method
analogous to that described for 1 with the following differences:
Phenol was used in place of 2-propanol. The reaction mixture was
heated to 75 °C for 3 days and then filtered while hot into a warm
Schlenk tube. Colorless crystals of the product formed as the
solution slowly cooled to room temperature. Further cooling to 5
Experimental Section
General Considerations. Standard Schlenk-line and glovebox
i
techniques were used unless stated otherwise. MeLH2,5a,8 PrLH2,8
and MeLZn2Ph2
(9) were prepared as previously described.
5a,8b
1
°C yielded additional MeLZn2(OPh)2 (58% yield). H NMR (CD2-
2-Propanol, tert-butylamine, benzaldehyde, and methanol were
distilled from CaH2 under N2 prior to use. Phenol, benzhydrol,
benzyl alcohol, trimethylsilyl trifluoromethanesulfonate (Me3SiOTf),
and ZnEt2 were purchased from Sigma-Aldrich and were used as
received. Hexanes, Et2O, toluene, tetrahydrofuran (THF), and CH2-
Cl2 were passed through columns of activated alumina and sparged
with N2 prior to use. C6D6 and C7D8 were vacuum-transferred from
sodium benzophenone ketyl. CD2Cl2 and CDCl3 were vacuum-
transferred from CaH2. Elemental analyses were performed by
Desert Analytics and the University of Michigan elemental analysis
laboratory. Analytical data are provided for at least one representa-
tive of each type of compound reported.
MeLZn2(OiPr)2 (1). Toluene (10 mL) and ZnEt2 (1.19 mL, 11.6
mmol) were combined in a 100-mL round-bottomed flask. The
mixture was cooled to 0 °C, and 2-propanol (0.890 mL, 11.6 mmol)
was added. Gas evolution was observed. The colorless solution was
stirred for 30 min during which time it reached ambient temperature.
To the mixture was added MeLH2 (1.98 g, 5.80 mmol) in toluene
(15 mL) to form a colorless solution. The mixture was heated to
75 °C for 2 days. The removal of the volatiles under reduced
pressure afforded the crude product as a colorless solid. This was
purified by crystallization from Et2O at -40 °C (2.56 g, 75.6%).
Cl2): δ 7.07 (t, J ) 1.0, 7.8 Hz, 2H), 7.01 (t, J ) 7.6 Hz, 4H),
6.88 (d, J ) 7.6 Hz, 2H), 6.77 (d, J ) 8.0 Hz, 4H), 6.68 (t, J ) 7.6
Hz, 2H), 6.41 (d, J ) 8.0 Hz, 2H), 3.39 (t, J ) 5.6 Hz, 4H), 2.88
(t, J ) 5.6 Hz, 4H), 2.55 (s, 12H, NMe2). 13C{1H} NMR (CD2-
Cl2): δ 162.8, 145.9, 143.5, 130.1, 124.8, 124.5, 119.7, 119.6,
106.4, 103.8, 62.6, 46.3, 43.3. Anal. Calcd (found) for C32H36N4O3-
Zn2: C, 58.64 (58.35); H, 5.54 (5.34); N, 8.55 (8.30).
MeLZn2(OCHPh2)2 (3). The compound was prepared using a
method analogous to that described for 1 with the following
differences: Benzhydrol was used in place of 2-propanol. Colorless
crystals of the product formed in the reaction mixture at 75 °C.
After being cooled to ambient temperature, they were isolated and
dried under reduced pressure to give MeLZn2(OCHPh2)2 in 68%
1
yield. H NMR (CD2Cl2): δ 7.20-7.05 (m, 22H, ArH), 7.01 (dd,
J ) 1.2, 7.6 Hz, 2H), 6.30 (d, J ) 7.6 Hz, 2H), 5.99 (s, 2H,
OCHPh2), 2.77 (t, J ) 5.6 Hz, 4H), 1.81 (s, 12H), 1.64 (t, J ) 5.6
Hz, 4H). 13C{1H} NMR (CD2Cl2): δ 147.2, 145.9, 144.5, 128.5,
128.2, 127.5, 125.1, 124.6, 105.8, 102.5, 80.5 (OCHPh2), 60.8, 45.6,
43.1. Anal. Calcd (found) for C46H48N4O3Zn2: C, 66.11 (66.40);
H, 5.79 (5.88); N, 6.70 (6.66).
i
PrLZn2(OPh)2 (4). The compound was prepared using a method
analogous to that described for 1 with the following differences:
i
Benzene, phenol, and PrLH2 were used in place of toluene,
(2) Selected reviews: (a) Gavrilova, A. L.; Bosnich, B. Chem. ReV. 2004,
104, 349. (b) Vigato, P. S.; Tamburini, S.; Fenton, D. E. Coord. Chem.
ReV. 1990, 106, 25. (c) Kaden, T. A. Coord. Chem. ReV. 1999, 190-
192, 371. (d) Suzuki, M.; Furutachi, H.; Okawa, H. Coord. Chem.
ReV. 2000, 200-202, 105.
2-propanol, and MeLH2, respectively. The reaction mixture was
heated to 75 °C for 3 days. Colorless crystals of the product formed
upon cooling of the reaction solution to ambient temperature. The
solution was then cooled to 5 °C overnight, and the product was
(3) Clare, B. C.; Sarker, N.; Shoemaker, R.; Hagadorn, J. R. Inorg. Chem.
2004, 43, 1159.
1
isolated and dried under reduced pressure (56% yield). H NMR
(CD2Cl2): δ 7.08 (t, J ) 7.8 Hz, 2H), 6.91-6.96 (m, 6H), 6.63-
6.70 (m, 6H), 6.33 (dd, J ) 1.0, 7.8 Hz, 2H), 3.39 (sept, J ) 6.8
Hz, 4H), 3.27 (t, J ) 5.8 Hz, 4H), 3.02 (t, J ) 5.8 Hz, 4H), 1.37
(d, J ) 6.4 Hz, 12H), 1.09 (d, 6.8 Hz, 12H). 13C{1H} NMR (CD2-
Cl2): δ 162.2, 145.5, 143.6, 129.7, 124.9, 124.4, 121.2, 120.0,
106.2, 103.5, 53.3, 52.2, 45.9, 21.5, 21.2.
(4) Selected other bis(amidinates): (a) Babcock, J. R.; Incarvito, C.;
Rheingold, A. L.; Fettinger, J. C.; Sita, L. R. Organometallics 1999,
18, 5729. (b) Whitener, G. D.; Hagadorn, J. R.; Arnold, J. J. Chem.
Soc., Dalton Trans. 1999, 1249. (b) Chen, C. T.; Rees, L. H.; Cowley,
A. R.; Green, M. L. H. J. Chem. Soc., Dalton Trans. 2001, 1761. (c)
Bambirra, S.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics
2001, 20, 782. (d) Appel, S.; Weller, F.; Dehnicke, K. Z. Anorg. Allg.
Chem. 1990, 583, 7.
i
PrLZn2(OMe)2 (5). The compound was prepared using a method
(5) (a) Hlavinka, M. L.; Hagadorn, J. R. Organometallics 2005, 24, 4116.
(b) Greco, J. F.; McNevin, M. J.; Hagadorn, J. R. Organometallics
2005, 24, 5167-5171.
analogous to that described for 1 with the following differences:
iPr
Methanol and LH2 were used in place of 2-propanol and MeLH2,
(6) (a) O’Keefe, B. J.; Hillmyer, M. A.; Tolman, W. B. J. Chem. Soc.,
Dalton Trans. 2001, 2215. (b) Cheng, M.; Attygalle, A. B.; Lobkovsky,
E. B.; Coates, G. W. J. Am. Chem. Soc. 1999, 121, 11583. (c)
Chamberlain, B. M.; Cheng, M.; Moore, D. R.; Ovitt, T. M.;
Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 3229.
(7) (a) Darensbourg, D. J.; Holtcamp, M. W. Coord. Chem. ReV. 1996,
153, 155. (b) Super, M. S.; Beckman, E. J. Trends Polym. Sci. 1997,
5, 236. (c) Chamberlain, B. M.; Cheng, M.; Moore, D. R.; Ovitt, T.
M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123,
8738. (d) Moore, D. R.; Cheng, M.; Lobskovsky, E. B.; Coates, G.
W. J. Am. Chem. Soc. 2003, 125, 11911, (e) Lee, B. Y.; Kwon, H.
Y.; Lee, S. Y.; Na, S. J.; Han, S.; Yun, H.; Lee, H.; Park, Y. J. Am.
Chem. Soc. 2005, 127, 3031.
respectively. The reaction mixture was heated to 100 °C for 3 days.
Colorless crystals of the product formed as the solution was cooled
to ambient temperature. The solution was then cooled to 5 °C
overnight, and the product was isolated and dried under reduced
1
pressure (63% yield). H NMR (C6D6): δ 7.55 (t, J ) 7.8 Hz,
2H), 7.43 (dd, J ) 1.0, 7.6 Hz, 2H), 6.81 (dd, J ) 1.0, 7.8 Hz,
2H), 3.44 (s, 6H, OMe), 3.33 (t, J ) 5.8 Hz, 4H), 3.06 (sept, J )
6.6 Hz, 4H), 3.60 (t, J ) 5.8 Hz, 4H), 0.98 (d, J ) 6.8 Hz, 12H),
0.96 (d, J ) 6.4 Hz, 12H). 13C{1H} NMR (C6D6): δ 146.9, 144.8,
125.6, 124.9, 106.5, 104.5, 55.1, 51.1, 49.2, 45.0, 20.5, 20.3.
(8) Hlavinka, M. L.; Hagadorn, J. R. Chem. Commun. 2003, 2686. (b)
Hlavinka, M. L.; Hagadorn, J. R. Organometallics 2005, 24, 5335-
5341.
i
PrLZn2(OCHPh2)2 (6). The compound was prepared using a
method analogous to that described for 1 with the following
1816 Inorganic Chemistry, Vol. 45, No. 4, 2006

Dizinc Alkoxides and Amides Supported by Binucleating Ligands
iPr
differences: Benzhydrol and LH2 were used in place of 2-propanol
Schlenk tube, which was slowly cooled to 5 °C. The product was
isolated as colorless crystals (0.418 g, 46.4%). 1H NMR (CDCl3):
δ 7.12 (t, J ) 7.6 Hz, 2H), 6.86 (dd, J ) 1.2, 7.6 Hz, 2H), 6.37
(dd, J ) 1.2, 7.6 Hz, 2H), 3.41 (t, J ) 5.6 Hz, 4H), 2.88 (t, J ) 5.6
Hz, 4H), 2.54 (s, 12H, NMe2), 0.97 (s, 18H, NtBu), 0.22 (s, 2H,
NH). 13C{1H} NMR (CDCl3): δ 144.5, 144.1, 125.0, 123.9, 104.7,
102.2, 61.7, 51.0, 47.0, 44.0, 35.8. Anal. Calcd (found) for
and MeLH2, respectively. Colorless crystals of the product formed
upon cooling of the reaction solution to ambient temperature. Vapor
diffusion of hexanes into the mixture afforded additional product
(48%). 1H NMR (C6D6): δ 7.63 (t, J ) 7.6 Hz, 2H), 7.55 (dd, J )
0.8, 7.6 Hz, 2H), 7.11-7.16 (m, 8H, ArH), 6.88-6.93 (m, 12H,
ArH), 6.64 (dd, J ) 0.8, 7.6 Hz, 2H), 6.20 (s, 2H, OCHPh2), 2.79
(t, J ) 5.6 Hz, 4H), 2.69 (sept, J ) 6.8 Hz, 4H), 1.77 (t, J ) 5.6
Hz, 4H), 0.90 (br, 24H). 13C{1H} NMR (C6D6): δ 147.0, 146.3,
144.5, 129.4, 127.9, 127.3, 126.0, 125.4, 107.2, 104.3, 81.9
(OCHPh2), 53.5, 52.2, 45.6, 21.8.
C30.3H48.7N6OZn2 [11‚(toluene)0.33]: C, 56.56 (56.31); H, 7.61
(7.38); N, 13.04 (12.87).
NMR Spectroscopy. NMR spectra were measured on a Varian
1
Inova-400 NMR spectrometer, at an H observation frequency of
i
400.16 MHz. Chemical shifts (δ) for 1H NMR (400 MHz) spectra
are given relative to residual protium in the deuterated solvent at
7.16, 5.32, 7.27, and 2.09 ppm for C6D6, CD2Cl2, CDCl3, and C7D8,
respectively. Sample temperatures for variable-temperature NMR
experiments were calibrated using 100% methanol by measuring
the chemical shift between the OH resonance and the CH3 resonance
and using the temperature calibration utility in the VNMR 6.1C
software. Variable-temperature NMR spectra were simulated, and
exchange rate constants were determined using the DNMR3 utilities
within the SpinWorks 2.4 software.9
PrLZn2(OCH2Ph)2 (7). The compound was prepared using a
method analogous to that described for 1 with the following
differences: Benzyl alcohol and PrLH2 were used in place of
i
2-propanol and MeLH2, respectively. The product was isolated as
colorless crystals following the cooling of the reaction solution to
-40 °C (63%). 1H NMR (C6D6): δ 7.60 (t, J ) 7.6 Hz, 2H), 7.48
(dd, J ) 1.0, 7.6 Hz, 2H), 7.06-7.30 (m, 10H), 6.82 (dd, J ) 1.0,
7.6 Hz, 2H), 4.70 (s, 4H, OCH2Ph), 3.21 (t, J ) 6.0 Hz, 4H), 2.86
(sept, J ) 6.8 Hz, 4H), 2.20 (t, J ) 6.0 Hz, 4H), 0.95 (d, J ) 6.8
Hz, 12H), 0.80 (d, J ) 7.8 Hz, 12H). 13C{1H} NMR (C6D6): δ
146.8, 144.9, 144.7, 129.6, 128.3, 127.3, 125.8, 125.2, 106.7, 104.5,
70.0 (OCH2Ph), 51.4, 50.0, 45.2, 21.2, 20.6.
Reduction of PhCHO with 6. Benzaldehyde (10.0 µL, 98.2
µmol) was added to a C6D6 solution (0.5 mL) of 6 (46.5 mg, 49.1
µmol) in the presence of an internal standard (1,3,5-trimethoxy-
benzene). The clear colorless solution was allowed to stand at
X-ray Crystallography. Table 1 summarizes crystal data and
collection parameters for all crystallographically characterized
compounds. Table 2 lists selected bond lengths and angles for the
core atoms. Additional data are presented as Supporting Information.
General Procedure. A crystal of appropriate size was mounted
on a glass fiber using hydrocarbon oil (Paratone-N), transferred to
a Siemens SMART diffractometer/CCD area detector, centered in
the beam (Mo KR, λ ) 0.71073 Å, graphite monochromator), and
cooled to -125 ( 10 °C by a nitrogen low-temperature apparatus.
Preliminary orientation matrix and cell constants were determined
by collection of 60 frames, followed by spot integration and least-
squares refinement. A minimum of a hemisphere of data was
collected using 0.3° ω scans. The raw data were integrated, and
the unit cell parameters were refined using SAINT. Data analysis
was performed using XPREP. Absorption correction was applied
using SADABS. The data were corrected for Lorentz and polariza-
tion effects, but no correction for crystal decay was applied.
Structure solutions and refinements were performed (SHELXTL-
Plus V5.1) on F2.10 Notable details of each data collection and
refinement are described below.
Structure of MeLZn2(OiPr)2‚Et2O (1‚Et2O). Crystals suitable
for X-ray diffraction studies were grown from Et2O at -40 °C.
Preliminary data indicated a triclinic cell. Choice of the centric space
group was confirmed by the successful solution and refinement of
the structure. The asymmetric unit contains two independent
molecules of 1 and two cocrystallized Et2O. Analysis using
PLATON did not reveal any missed symmetry, and an attempt to
solve the structure in space group C2/m failed. One of the µ-OiPr
groups is disordered over two positions (C47-C49, C47A-C49A)
with 67% and 33% occupancies. These atoms were refined
isotropically. All other non-H atoms were refined anisotropically.
Hydrogens were placed in idealized positions and were included
in structure factor calculations but were not refined.
1
ambient temperature for 6 d. Analysis by H NMR spectroscopy
indicated 80% conversion to 7 and benzophenone. The solution
was heated to 70 °C for 12 h, after which NMR spectroscopy
indicated complete conversion to the aforementioned products.
MeLZn2(OiPr)(OTf) (8). Me3SiOTf (0.188 mL, 1.04 mmol) was
added to a benzene solution (100 mL) of 1 (0.608 g, 1.04 mmol)
to form a clear, colorless solution. The solution was allowed to
stand for 30 h during which time colorless crystals of product
1
formed (0.490 g, 69.6%). H NMR (CD2Cl2): δ 7.11 (t, J ) 7.6
Hz, 2H), 6.93 (dd, J ) 1.2, 7.6 Hz, 2H), 6.45 (dd, J ) 1.2, 7.6 Hz,
2H), 4.27 (sept, J ) 6.0 Hz, 2H, ZnOCHMe2), 3.39 (m, 4H), 3.04
(m, 2H), 2.84 (m, 2H), 2.60 (s, 6H), 2.57 (s, 6H), 1.24 (d, J ) 6.0
Hz, 6H, ZnOCHMe2). 13C{1H} NMR (CD2Cl2): δ 145.7, 143.5,
125.1, 124.5, 106.8, 103.8, 71.0, 61.8, 46.5, 46.1, 44.2, 28.2. 19F
NMR (CD2Cl2) δ -78.2 (s). Anal. Calcd (found) for C25.5H34.5F3-
N4O5SZn2 [8‚(benzene)0.25]: C, 43.93 (43.63); H, 4.99 (5.17); N,
8.04 (7.66).
MeLZn2(Ph)(NHtBu) (10). Toluene (20 mL) was added to
MeLZn2Ph2 (9) (0.362 g, 0.581 mmol). To the colorless suspension
was added tert-butylamine (61.0 µL, 0.581 mmol). The solution
was stirred for 24 h at ambient temperature. Cooling the solution
to 5 °C yielded the product as colorless crystals (0.212 g, 66.2%).
1H NMR (CD2Cl2): δ 7.1-7.7 (br, 5H, ZnPh), 7.06 (t, J ) 7.8
Hz, 2H), 6.48 (dd, J ) 1.0, 7.6 Hz, 2H), 6.29 (dd, J ) 1.0, 7.6 Hz,
2H), 3.30 (m, 2H), 3.11 (m, 4H), 2.56 (s, 6H), 2.43 (m, 2H), 1.40
(s, 6H), 1.38 (s, 1H, NH), 1.20 (s, 9H, NtBu). 13C{1H} NMR (CD2-
Cl2): δ 145.6, 144.5, 144.3 (ipso Zn-Ph), 131.4, 128.1 (br), 124.6,
124.4, 105.2, 102.4, 61.3, 51.5, 47.4, 44.1, 42.1, 35.2. Anal. Calcd
(found) for C30H41N5OZn2: C, 58.26 (58.23); H, 6.68 (6.43); N,
11.32 (11.32).
Structure of MeLZn2(OPh)2‚(Toluene)0.5 [2‚(Toluene)0.5]. Crys-
tals suitable for X-ray diffraction studies were grown from toluene
at ambient temperature. Preliminary data indicated a primitive
monoclinic cell. Systematic absences indicated space group P21/n
(No. 14). This choice was confirmed by the successful solution
MeLZn2(NHtBu)2 (11). ZnEt2 (0.302 mL, 2.94 mmol), tert-
butylamine (0.307 mL, 2.94 mmol), and toluene (125 mL) were
combined in a 250-mL round-bottomed flask. The colorless solution
was heated to 75 °C for 24 h. At ambient temperature, MeLH2 (0.501
g, 1.47 mmol) was added, and the resulting colorless solution was
heated to 75 °C for 24 h. The hot solution was filtered into a warm
(9) Software by Kirk Marat at the University of Manitoba. For more
information, see http://www.umanitoba.ca/chemistry/nmr/spinworks.
(10) Sheldrick, G. M. SHELXTL-Plus: A Program for Crystal Structure
Determination, version 5.1, Bruker AXS: Madison WI, 1998.
Inorganic Chemistry, Vol. 45, No. 4, 2006 1817

Hlavinka et al.
Table 1. Crystallographic Data and Collection Parameters
1‚Et2O
2‚(toluene)0.5
4
formula
formula wt (g‚mol-1
space group
temp (K)
a (Å)
C30H50N4O4Zn2
661.48
P1h (No. 2)
140(2)
10.1422(4)
16.8789(8)
19.4637(9)
82.1670(10)
75.3130(10)
89.6530(10)
4
3191.6(2)
1.377
2.35-29.23
1.542
0.40 × 0.15 × 0.15
21682
C35.5H40N4O3Zn2
701.46
P21/n (No. 14)
142(2)
10.2097(4)
12.0692(5)
26.8683(10)
90
90.7290
90
4
3310.5(2)
1.407
2.27-31.47
1.490
C40H52N4O3Zn2
767.60
)
P21/n (No. 14)
150(2)
12.2365(4)
19.4966(6)
15.2313(5)
90
92.6670(10)
90
4
3629.8(2)
1.405
2.34-31.22
1.365
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
Z
V (Å3)
d
calc (g‚cm-3
)
θ range (deg)
µ (mm-1
)
crystal size (mm)
0.36 × 0.34 × 0.30
25413
0.40 × 0.30 × 0.20
23855
reflections collected
data/restraints/parameters
R1 (for Fo > 4sFo)
R1, wR2 (all data)
GOF
15019/0/741
0.0649
0.1250, 0.1811
0.958
7594/13/438
0.0700
0.1330, 0.1470
1.009
10103/0/450
0.0548
0.0865, 0.1428
1.016
largest peak, hole (e‚Å-3
)
0.71, -1.00
0.69, -0.76
0.70, -0.82
8‚benzene
10
11‚(toluene)0.25
formula
C30H39F3N4O5SZn2
755.45
P1h (No. 2)
156(2)
9.5997(10)
15.5502(10)
22.370(2)
89.489(2)
79.351(2)
87.199(3)
4
C30H41N5OZn2
618.42
Pbca (No. 61)
154(2)
18.5586(5)
18.7571(6)
33.5543(9)
90
C28H46N6OZn2
613.45
P21/n (No. 14)
152(2)
20.4807(9)
15.6023(7)
20.6304(9)
90
109.5000(10)
90
formula wt (g‚mol-1
space group
temp (K)
a (Å)
)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
Z
90
90
16
8
V (Å3)
3278.0(6)
1.531
2.19-26.42
1.588
11680.4(6)
1.407
2.39-27.46
1.674
6214.2(5)
1.311
2.39-18.96
1.573
d
calc (g‚cm-3
)
θ range (deg)
µ (mm-1)
crystal size (mm)
reflections collected
0.35 × 0.20 × 0.10
26694
0.50 × 0.20 × 0.15
89337
0.20 × 0.10 × 0.10
50031
data/restraints/parameters
R1 (for Fo > 4sFo)
R1, wR2 (all data)
GOF
15613/0/823
0.0969
0.1899, 0.2607
0.970
13932/0/707
0.0466
0.0978, 0.1125
0.999
14810/0/667
0.0866
0.2267, 0.2046
0.886
largest peak, hole (e‚Å-3
)
2.64, -2.05
0.46, -0.43
0.69, -0.62
and refinement of the structure. The asymmetric unit contains one
molecule of 2 and a disordered, half-occupancy toluene located on
a crystallographic inversion center. All non-H atoms were refined
anisotropically. Hydrogens were placed in idealized positions and
were included in structure factor calculations but were not refined.
anisotropically. Hydrogens were placed in idealized positions and
were included in structure factor calculations but were not refined.
Structure of MeLZn2(Ph)(NHtBu) (10). Crystals suitable for
X-ray diffraction studies were grown from toluene at 5 °C.
Preliminary data indicated a primitive orthorhombic cell. Systematic
absences indicated space group Pbca (No. 61). This choice was
confirmed by the successful solution and refinement of the structure.
The asymmetric unit contains two independent molecules of 10.
Analysis using PLATON did not reveal any missed symmetry. All
non-H atoms were refined anisotropically. Hydrogens were placed
in idealized positions and were included in structure factor
calculations but were not refined.
Structure of MeLZn2(NHtBu)2‚(Toluene)0.25 [11‚(Toluene)0.25].
Crystals suitable for X-ray diffraction studies were grown from hot
toluene. Preliminary data indicated a primitive monoclinic cell.
Systematic absences indicated space group P21/n (No. 14). This
choice was confirmed by the successful solution and refinement
of the structure. The asymmetric unit contains two independent
molecules of 11 and a cocrystallized toluene molecule located on
a crystallographic inversion center. Analysis using PLATON did
not reveal any missed symmetry. Attempts to model the disordered
toluene molecule gave unacceptable metrical parameters. The data
i
Structure of PrLZn2(OPh)2 (4). Crystals suitable for X-ray
diffraction studies were grown from C6D6 at ambient temperature.
Preliminary data indicated a primitive monoclinic cell. Systematic
absences indicated space group P21/n (No. 14). This choice was
confirmed by the successful solution and refinement of the structure.
The asymmetric unit contains only one molecule of 4. All non-H
atoms were refined anisotropically. Hydrogens were placed in
idealized positions and were included in structure factor calculations
but were not refined.
Structure of MeLZn2(OiPr)(OTf)‚Benzene (8‚Benzene). Needle-
shaped crystals suitable for X-ray diffraction studies were grown
from benzene at ambient temperature. Preliminary data indicated
a triclinic cell. Choice of the centric space group was confirmed
by the successful solution and refinement of the structure. The
asymmetric unit contains two independent molecules of 8 and two
cocrystallized benzene molecules. Analysis using PLATON did not
reveal any missed symmetry. All non-H atoms were refined
1818 Inorganic Chemistry, Vol. 45, No. 4, 2006

Dizinc Alkoxides and Amides Supported by Binucleating Ligands
Table 2. Core Bond Lengths and Angles for Dizinc Species
(a)
Zn-X
(Å)
(b)
Zn-Y
(Å)
(c)
Zn-Namido
(Å)
(d)
Zn-Namine
(Å)
(a)
X-Zn-Y
(deg)
(b)
N-Zn-N
(deg)
Zn‚‚‚Zn
(Å)
compound (X, Y)
MeLZn2(OiPr)2 (1)
1.982(3)
1.971(3)
1.986(3)
1.960(3)
1.972(3)
2.001(3)
1.995(2)
2.005(2)
1.891(5)
1.906(5)
1.921(5)
1.910(6)
2.212(4)
2.130(4)
2.211(4)
2.135(4)
2.041(6)
2.017(6)
2.024(6)
2.055(6)
1.957(3)
1.970(3)
1.956(3)
1.973(3)
1.996(3)
1.955(3)
1.993(2)
1.988(2)
2.082(5)
2.122(6)
2.112(5)
2.082(6)
2.003(3)
2.032(3)
2.003(3)
2.031(3)
2.066(6)
2.030(6)
2.038(6)
2.025(6)
1.941(4)
1.939(4)
1.942(4)
1.932(4)
1.917(4)
1.925(3)
1.926(2)
1.914(2)
1.895(7)
1.889(6)
1.908(6)
1.893(7)
1.944(3)
1.962(3)
1.950(3)
1.960(3)
1.914(7)
1.939(6)
1.938(6)
1.938(6)
2.116(4)
2.129(4)
2.123(4)
2.134(4)
2.087(3)
2.090(3)
2.143(3)
2.131(2)
2.107(7)
2.104(7)
2.128(7)
2.121(6)
2.153(3)
2.184(3)
2.139(3)
2.151(3)
2.198(6)
2.161(7)
2.167(6)
2.158(6)
83.3(1)
83.2(1)
83.3(1)
83.6(1)
80.5(1)
80.8(1)
79.69(8)
79.57(8)
97.8(2)
97.4(2)
94.5(2)
100.4(2)
91.4(1)
93.0(1)
92.5(1)
94.0(1)
86.4(3)
88.0(2)
88.7(2)
88.2(2)
86.3(2)
85.5(2)
86.1(2)
85.5(2)
87.3(1)
87.2(1)
87.1(1)
88.2(1)
87.8(3)
88.5(3)
87.2(3)
88.7(3)
84.5(1)
83.3(1)
83.9(1)
84.2(1)
83.5(3)
85.7(3)
84.2(3)
85.3(2)
2.8185(7)
2.8048(7)
2.8771(6)
2.9435(5)
3.270(1)
3.274(1)
2.6761(5)
2.6518(5)
2.775(1)
2.760(1)
(OiPr, OiPr)
two molecules
MeLZn2(OPh)2 (2)
(Oph, OPh)
iPrLZn2(OPh)2 (4)
(Oph, OPh)
MeLZn2(OiPr)(OTf) (8)
(OiPr, OTf)
two molecules
MeLZn2(Ph)(NHtBu) (10)
(Ph, NHtBu)
two molecules
MeLZn2(NHtBu)2 (11)
(NHtBu, NHtBu)
two molecules
Chart 1
Scheme 1
were corrected for the disordered solvent using PLATON/
SQUEEZE. This gave a calculated potential solvent area of 360.0
Å (5.8% total volume) containing 108 electrons, which is consistent
with ca. 2.2 molecules of toluene in the unit cell. The R1 value
improved from 0.0985 to 0.0866 after the correction, and refinement
of the model gave acceptable convergence. All non-H atoms were
refined anisotropically. Hydrogens were placed in idealized posi-
tions and were included in structure factor calculations but were
not refined.
Also, the two isopropoxide ligands are equivalent, with the
methine protons being observed as a septet at δ 4.06 ppm
and the methyls as a doublet at δ 0.98 ppm. These data are
consistent with 1 having a pair of bridging isopropoxide
ligands. Alternatively, C2V symmetry could also be observed
for a structure without any bridging alkoxides, but this is
quite unlikely given the general preference of Zn2+ for a
coordination number of four instead of three. H NMR
spectroscopic data for both 2 and 3 (in CD2Cl2) similarly
reveal C2V-symmetric solution structures.
The solid-phase structures of 1 and 2 were determined by
single-crystal X-ray diffraction. Thermal ellipsoid drawings
are shown in Figure 1. Compound 1 crystallizes with two
independent molecules in the asymmetric unit. The two
molecules feature similar coordination geometries. Each
distorted tetrahedral Zn center is coordinated to one bidentate
bis(amidoamine) and two bridging isopropoxide ligands. The
puckered Zn2(µ-OiPr)22+ cores feature Zn-O bonds that vary
between 1.956 and 1.986 Å, which are comparable to
reported values.11 The alkoxide oxygens are significantly
pyramidalized [∑(angles at O)avg ) 338°] consistent with
Results and Discussion
The bis(diaminoethane) ligands MeLH2 and iPrLH2, shown
in Chart 1, readily undergo protonolysis with zinc(alkoxy)-
alkyl reagents. The products of these reactions are zinc
alkoxide derivatives of the general formula LZn2(OR′)2
(R′ ) alkyl, aryl). For example, a toluene solution of MeLH2
reacted with 2 equiv of EtZnOiPr, generated in situ from
ZnEt2 and 2-propanol, over 2 days at 75 °C to form
MeLZn2(OiPr)2 (1) (Scheme 1). The product was isolated in
76% yield as colorless crystals following Et2O workup.
Repeating the reaction using phenol and benzhydrol in place
of 2-propanol formed the closely related species MeLZn2-
(OPh)2 (2) and MeLZn2(OCHPh2)2 (3), respectively. Com-
plexes 2 and 3 were isolated as colorless crystals in moderate
to good yields from toluene solutions. The 1H NMR spectrum
of 1 (in C6D6) indicates that the molecule has overall C2V
symmetry in solution. Thus, the four Me groups of the MeL2-
ligand are equivalent and appear as a singlet at δ 1.99 ppm.
1
(11) Melnik, M.; Gyo¨ryova´, K.; Skorsepa, J.; Holloway, C. E. J. Coord.
Chem. 1995, 35, 179.
Inorganic Chemistry, Vol. 45, No. 4, 2006 1819

Hlavinka et al.
Figure 1. Molecular structures of all crystallographically characterized complexes drawn with 50% thermal ellipsoids. Hydrogens are omitted except for
the N-H groups of the tert-butyl amido ligands of 11. Only one of two molecules in the asymmetric unit is shown for structures 1, 8, 10, and 11. Cocrystallized
solvent molecules are omitted for 1, 2, 8, and 11.
the expected lack of π bonding with the d10 metal centers.
The structural features of 2 are very similar to those of 1,
although the phenolate oxygens are less pyramidalized
[∑(angles at O) ) 343.7, 349.5°] and the Zn-N bonds are
slightly shorter.
of the isopropyl groups. This suggests that the coordinated
diisopropylamine donors undergo reversible dissociation
followed by inversion at nitrogen to exchange the methyls
of each isopropyl group. It is likely that this process is
observed for only 6 because this molecule features a
combination of the most hindered ligands used in this study.
The solid-state structures of 4 and 6 were determined by
single-crystal X-ray diffraction. The structure of 6 is not
included here because of the low quality of the data, but its
overall structural features are related to those of 4. Compound
4 features a symmetric and puckered [Zn2(µ-OPh)2]2+ core
that is similar to that of 2, which is supported by the less-
A series of dizinc alkoxides supported by the isopropyl-
iPr
substituted ligand LH2 were studied to evaluate the effect
of increased steric bulk on both structure and reactivity.
Complexes 4-7 (Scheme 1) were prepared in a fashion
similar to that used for the preparation of 1-3. The
complexes were all isolated in moderate to good yields as
colorless crystals from benzene or toluene solutions and were
characterized by a combination of NMR spectroscopy,
combustion analysis, and single-crystal X-ray diffraction. The
1H NMR spectra of 4, 5, and 7 are all fundamentally similar,
so only that of 5 will be discussed. Analogous to what was
observed for compounds 1-3, compound 5 features C2V
symmetry in C6D6 solution. The bridging methoxides are
observed as a singlet at δ 3.44 ppm, and the methine protons
of the isopropyl groups are equivalent and appear as a septet
at δ 3.06 ppm. The two methyls of each isopropyl group
are inequivalent and are observed as doublets at δ 0.98 and
0.96 ppm. 13C{1H} NMR spectroscopic data confirm the
inequivalence of the methyls (δ 20.5 and 20.3 ppm). These
data indicate that the two methyls of each isopropyl group
do not exchange on the NMR spectroscopic time scale. This
suggests that the diisopropylamine donors remain coordinated
to the Zn centers. In contrast, NMR spectroscopic data for 6
reveals some distinct behavior, which is a consequence of
the bulky diphenylmethoxy ligands. The 1H NMR spectrum
of 6 (C6D6) features a single broad resonance at δ 0.90 ppm
with an integrated intensity of 24 hydrogens for the methyls
hindered Me 2- ligand. The effect of the isopropyl substitution
L
of the bis(amidoamine) ligand is evident in several structural
perturbations relative to compound 2. First, for 4, the Zn-
Zn distance [2.9435(5) Å] is 0.066 Å longer and its
O-Zn-O angles [79.57(8), 79.69(8)°] are about 1° smaller
than the related parameters of 2. Steric repulsions between
the isopropyl groups and the metal center also result in an
average 0.05 Å increase in the Zn-Namine distances relative
to those of 2.
Zinc alkoxides have been shown to catalyze the oxidation
of alcohols to aldehydes and ketones12 in a fashion similar
to that of the Zn-containing enzyme liver alcohol dehydro-
genase (LADH).13 We examined whether iPrLZn2(OCHPh2)2
(12) (a) Bergquist, C.; Parkin, G. Inorg. Chem. 1999, 38, 422. (b) Walz,
R.; Vahrenkamp, H. Inorg. Chim. Acta 2001, 314, 58.
(13) (a) Holm, R. H.; Kennepohl, P.; Solomon, E. I. Chem. ReV. 1996, 96,
2239. (b) Lipscomb, W. N.; Strater, N. Chem. ReV. 1996, 96, 2239.
(c) Berreau, L. M.; Makowska-Grzyska, M. M.; Arif, A. M. Inorg.
Chem. 2001, 40, 2212. (d) Kimura, E.; Shionoya, M.; Hoshino, A.;
Ikeda, T.; Yamada, Y. J. Am. Chem. Soc. 1992, 114, 10134. (e) Cronin,
L.; Walton, P. H. Chem. Commun. 2003, 1572.
1820 Inorganic Chemistry, Vol. 45, No. 4, 2006

Dizinc Alkoxides and Amides Supported by Binucleating Ligands
Scheme 2
Scheme 4
Scheme 3
prepared in the interest of comparing its properties to those
of MeLZn2(Ph)(OCHPh2), which was recently shown to
feature a bridging phenyl group that undergoes reversible
cleavage in solution with ∆Gq ) 11.5(1) kcal‚mol-1 (-50
°C).8b Compound 10 was formed by reaction of 1 equiv of
tert-butylamine with MeLZn2Ph2 (9) in toluene solution
(Scheme 4). Cooling the solution to 5 °C afforded the product
as colorless crystals in 66% yield. The structure of 10 was
determined. One of the two independent molecules in the
asymmetric unit is shown in Figure 1. Overall, the structure
of 10 is quite similar to that of MeLZn2(Ph)(OCHPh2). It
features a dizinc core with bridging amido and phenyl groups.
Each phenyl group bridges two Zn centers in an unsym-
metrical fashion, with one short [Zn2-C21, 2.130(4) Å;
Zn4-C51, 2.135(4) Å] and one long [Zn1-C21, 2.212(4)
Å; Zn3-C51, 2.211(4) Å] Zn-Ph interaction. The zinc
centers (e.g., Zn2) that form the shorter bonds to the phenyl
donors are, on average, 1.04 Å out of the calculated phenyl
group planes. In contrast, the zincs involved in the longer
Zn-Ph bonds are, on average, 1.60 Å out of the calculated
phenyl planes. These latter Zn centers are expected to have
less overlap with the in-plane donor orbital.
was compatible with the reduction of organic carbonyls. As
shown in Scheme 2, a C6D6 solution of 6 and 2 equiv of
benzaldehyde showed 80% conversion (1H NMR spectros-
copy) to 7 and benzophenone over 6 days. Heating of the
solution to 70 °C overnight gave quantitative conversion to
the products. The reaction occurs by the formal hydride
transfer from the diphenylmethoxy ligand to benzaldehyde.
A single isopropoxide ligand of 1 can be selectively
substituted using Si-based reagents. Thus, the addition of 1
equiv of Me3SiOTf (OTf ) O3SCF3) to a benzene solution
of 1 formed the mixed-ligand complex MeLZn2(OiPr)(OTf)
(8; Scheme 3), which crystallized from the reaction solution
in 70% yield. The 1H NMR spectrum of 8 dissolved in CD2-
Cl2 indicates overall Cs symmetry, with the mirror plane of
symmetry oriented perpendicular to the intermetal axis and
passing through the bridging triflate and alkoxide ligands.
Thus, the two methyls of each dimethylamino donor are
inequivalent, and they are observed as two sharp singlets at
δ 2.60 and 2.57 ppm. There is also a distinct septet at δ
4.27 ppm (1H) that is assigned to the methine of the
isopropoxide ligand. The presence of the triflate ligand was
confirmed by a single fluorine resonance in the 19F NMR
spectrum (δ -78.2 ppm). The molecular structure of 8 was
determined by single-crystal X-ray diffraction. There are two
independent molecules in the asymmetric unit. They are
essentially identical with the exception of some minor
variations (j1%) in metrical parameters. Each complex
features a [Zn2(1,3-µ-OTf)(µ-OiPr)]2+ core with bridging
isopropoxide and triflate ligands. The triflate anion forms a
three-atom bridge between the two Zn centers with Zn-O
bonds formed to two of the three sulfonate oxygens. As
expected, the Zn-alkoxide bonds (avg 1.907 Å) are much
shorter than the Zn-OTf bonds (avg 2.100 Å). It is also
notable that the Zn-OiPr bonds of 8 are, on average, 0.07
Å shorter than the related bonds of the bis(isopropoxide)
derivative 1. This is expected because the triflate ligand is a
much poorer donor than the alkoxide. It is likely that the
weakly basic triflate ligand is susceptible to displacement
by added Lewis bases, but we have not yet explored these
reactions.
The 1H NMR spectrum of 10 in CD2Cl2 indicates overall
Cs symmetry, with the mirror plane of symmetry oriented
perpendicular to the Zn‚‚‚Zn internuclear axis. The Me
groups of the dimethylamino donors are observed as two
sharp singlets at δ 2.56 and 1.40 ppm. Resonances at δ 1.38
t
(1H) and 1.20 (9H) ppm were assigned to the NH and Bu
groups of the bridging amido ligand, respectively. The ortho
and meta hydrogens of the Zn-Ph group were observed as
two very broad overlapping resonances between δ 7.1 and
7.7 ppm. These sharpen into two distinct resonances at
elevated temperatures. The equivalence of the ortho protons
at elevated temperatures is consistent with a dynamic process
in which the bridging Ph group is cleaved to form a species
with a terminal Zn-Ph group.8b Rotation about the Zn-Ph
bond prior to reformation of the Ph bridge would lead to
exchange of the two ortho (and meta) protons. Consistent
with this mechanism, 1H NMR spectroscopic data acquired
at -70 °C reveal five distinct resonances for the Zn-Ph
group (ortho, δ 7.67 and 7.14 ppm; meta, δ 7.35 and 7.03
ppm; para, δ 7.25 ppm), consistent with an intact Ph bridge
under these conditions. Analysis of the temperature depen-
dence of these data indicates that the exchange occurs with
In addition to the aforementioned zinc alkoxide derivatives,
we have also prepared some related zinc amido derivatives.
The first of these complexes, MeLZn2(Ph)(NHtBu) (10), was
Inorganic Chemistry, Vol. 45, No. 4, 2006 1821

Hlavinka et al.
∆Gq ) 12.7(1) kcal‚mol-1 (-27 °C). These data show that
the phenyl bridge in complex 10 is slightly more robust than
that of MeLZn2(Ph)(OCHPh2).
four-membered ring. The Zn-N bond lengths average 2.04
Å, but the individual bonds vary from 2.017(6) to 2.066(6)
Å.
Dizinc bis(amido) derivatives can be prepared analogously
to the bis(alkoxides)described earlier. For example, a toluene
solution of EtZn(NHtBu), prepared in situ from ZnEt2 and
tert-butylamine, reacted with MeLH2 at 75 °C to form
MeLZn2(NHtBu)2 (11). Cooling the solution to 5 °C afforded
the product as colorless crystals in 46% yield. The same
product can be formed in high yield by reaction of 10 with
1 equiv of tert-butylamine in toluene at 70 °C. The 1H NMR
spectrum of 11 (CDCl3) indicates a highly symmetric (C2V)
structure. The solid-state structure of 11 was determined by
single-crystal X-ray diffraction. Two independent molecules
are present in the asymmetric unit. Each molecule features
a pair of pseudo-tetrahedral Zn centers coordinated to the
bis(amidoamine) ligand and two bridging amido ligands. The
[Zn2(µ-NHtBu)2]2+ cores are moderately puckered. The core
atoms of each molecule form a slightly asymmetric Zn2N2
In conclusion, we have reported a new series of dizinc
alkoxide and amido derivatives supported by preorganized
bis(amidoamine) ligands. Reactivity studies of these and
related derivatives are currently being pursued.
Acknowledgment. We thank the Petroleum Research
Fund (38046-G3), administered by the ACS, for funding.
NMR instrumentation used in this work was supported in
part by the National Science Foundation CRIF program,
Award CHE-0131003.
Supporting Information Available: Crystallographic informa-
tion files (CIF) are provided for compounds 1, 2, 4, 8, 10, and 11.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC051669F
1822 Inorganic Chemistry, Vol. 45, No. 4, 2006