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heterobimetallic species is calculated to perform the PNPDPP
hydrolysis at 35 times the uncatalyzed reaction. These bimetallic
complexes of 1L are comparable to the fastest known metal-based
catalysts for PNPDPP hydrolysis. Complexes of the ester ligand
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between 4 to 10 times greater than that of (TMEDA)CuCl2 under
identical conditions. The best results were obtained for the Zn- and
3 H. Morales-Rojas and R. A. Moss, Chem. Rev., 1992, 92, 1729–1743.
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6 A Zn–Pb heterobimetallic complex stoichiometrically hydrolyzes
tris(p-nitrophenyl) phosphate: M. Yamami, H. Furutachi,
¯
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7 Comparisons were made to non-micellular systems.
8 V. McKee, M. Zvagulis, J. V. Dagdgian, M. G. Patch and C. A. Reed,
J. Am. Chem. Soc., 1984, 106, 4765–4772.
2
2
2
Cu-containing complexes L?Zn2, L?Cu2, and L?Zn?Cu (entries
14, 16, and 18), which catalyze the hydrolysis of PNPDPP at a rate
ca. 200 times faster than the uncatalyzed reaction.
As described above, the rate of PNPDPP hydrolysis catalyzed
by the bimetallic complexes occurs with pseudo-first-order
dependence on PNPDPP concentration. The reaction order in
1
catalyst was also of interest. This was determined for L?Zn2 by
analysis of the hydrolysis rate as
a function of catalyst
concentration. Reaction rates were determined using nine different
catalyst concentrations between 0.0125 mM and 0.125 mM. A plot
of 2log(kobs) versus 2log([1L?Zn2]) was found to be linear with a
slope of 1.3. Thus, the reaction is approximately first-order in
catalyst concentration. Repeating the experiment with 2L?Zn2
indicated a reaction order of 1.1 for the more active, toluoyl-ester-
modified catalyst.
For comparison, the mononucleating ligands 3L and 4L
(Scheme 1) were prepared and used to support catalysts for
PNPDPP hydrolyses. As shown in entries 20–25, complexes
prepared with MCl2 (M = Zn, Co, Cu) were effective catalysts for
PNPDPP hydrolysis. These displayed activities similar (at equal
1
metal concentrations) to those of bimetallic derivatives of L, but
2
far less than those of derivatives of L.
In summary, homo- and heterobimetallic Cu(II), Zn(II), and
Co(II) complexes of N,N,N9,N9-tetrakis[(2-benzimidazoyl)-
methyl]-2-hydroxy-1,3-diaminopropane (1L) and its toluoyl ester
derivative (2L) were found to be excellent catalysts for the
hydrolysis of PNPDPP under mild conditions. The hydrolysis
rates of these complexes were found to approach and/or surpass
the best reported metal-based catalysts, with the 2L-based
bimetallic complexes being more active than the analogous 1L
complexes. We are currently exploring the effects of modifying
these and related ligands to maximize reactivity and gain more
detailed mechanistic insight. Additionally, these and related
catalysts are being incorporated onto solid nanostructured
supports to aid in catalyst recovery and to potentially amplify
reactivity.
9 (a) Y. Dong, S. Me´nage, B. A. Brennan, T. E. Elgren, H. G. Jang,
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Notes and references
{ See ESI{ for details of syntheses and catalytic studies.
§ Crystal data for 1L?Zn2?2EtOH?2H2O: C39H50Cl4N10O5Zn2,
¯
M 5 1011.43, space group P1 (No. 2), triclinic, a 5 12.3747(4),
b 5 13.7692(5), c 5 14.0177(5) s, a 5 93.140(1), b 5 111.015(1),
c 5 93.478(1)u, V 5 2218.0(1) s3, Z 5 2, T 5 152 K, m 5 1.376 mm21
,
10 L. Yin, P. Cheng, S. Yan, X. Fu, J. Li, D. Liao and Z. Jiang, J. Chem.
Soc., Dalton Trans., 2001, 1398–1400.
17620 reflections measured, 10150 independent reflections (Rint 5 0.0527),
R1 (for Fo . 4sFo) 5 0.0799, wR2 (all data) 5 0.2252, GOF 5 1.021 for
541 parameters. Crystal data for 2L?Zn2?2EtOH: C47H52Cl4N10O4Zn2,
M 5 1093.53, space group P2(1)/c (No. 14), monoclinic, a 5 17.5457(4),
b 5 12.8691(4), c 5 23.3783(8) s, b 5 104.362(1)u, V 5 5113.9(3) s3, Z 5 4,
T 5 147 K, m 5 1.199 mm21, 40729 reflections measured, 12192
independent reflections (Rint 5 0.1076), R1 (for Fo . 4sFo) 5 0.0676, wR2
(all data) 5 0.1766, GOF 5 1.020 for 606 parameters. CCDC 290488 and
290489. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b602769e
11 Solution structures of complexes of 1L and 2L are unknown. Preliminary
NMR and UV-Vis data indicate that each ligand reacts with ca. two
equiv of MCl2 (M = Cu, Co, Zn) to form a single product.
12 R. A. Moss, S. Bose, K. G. Ragunathan, N. Jayasuriya and T. J. Emge,
Tetrahedron Lett., 1998, 39, 347–350 and references therein.
13 Meaningful comparisons of catalyst activities can only be made between
systems using identical phosphorus ester substrates.
14 Micellar Cu(diamine) catalysts show enhanced activity. Ref. 4a–c.
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