Zirconium Tetraisopropoxide


[2171-98-4]  · C12H28O4Zr  · Zirconium Tetraisopropoxide  · (MW 327.62) (.i-PrOH)

[50939-84-9]  · C15H36O5Zr  · Zirconium Tetraisopropoxide-Isopropanol  · (MW 387.73)

(hydrogenation catalyst; Meerwein-Ponndorf-Verley reduction; Oppenauer oxidation; ester synthesis; diketopiperazine synthesis)

Physical Data: Zr(O-i-Pr)4: bp 160 °C/0.1 mmHg; Zr(O-i-Pr)4.i-PrOH: mp 138-141 °C.1

Solubility: Zr(O-i-Pr)4 readily sol organic solvents; Zr(O-i-Pr)4.i-PrOH sparingly sol isopropanol.

Form Supplied in: Zr(O-i-Pr)4.i-PrOH: white solid.

Purification: Zr(O-i-Pr)4.i-PrOH: crystallization from isopropanol followed by drying at rt/0.5 mmHg. Zr(O-i-Pr)4: heating of Zr(O-i-Pr)4.i-PrOH at 90-120 °C/1 mmHg to remove isopropanol followed by distillation.1

Handling, Storage, and Precautions: moisture sensitive; irritating to eyes, respiratory system, and skin. Use in a fume hood.

Preparation of ClZr(O-i-Pr)3.

Zr(O-i-Pr)4 is a good substrate for the preparation of ClZr(O-i-Pr)3 (eq 1),2-4 which is a useful reagent for further conversion to other organozirconium reagents (RZr(O-i-Pr)3) by organolithium or Grignard derivatives as described for the titanium analogs (see Titanium Tetraisopropoxide).5

Meerwein-Ponndorf-Verley Reduction and Oppenauer Oxidation.

The zirconate reagent in the Meerwein-Ponndorf-Verley reduction is known to show high functional group selectivity due to both steric and electronic effects. Thus aldehydes are reduced in preference to ketones, and selective reduction of the carbonyl group occurs in a,b-unsaturated carbonyl compounds.2,6 The sensitivity to electronic effects was demonstrated in a study of the reduction of benzaldehydes: the efficiency and rate of the aldehyde conversion to the benzyl alcohol was dependent on the electron-withdrawing properties of the p-substituent.2,6 In the dihydro formation of 5-halo-2-pyrimidinones, regioselective formation of the 3,4-dihydro isomer predominates whereas the 3,6-dihydro isomer is formed with Lithium Tri-t-butoxyaluminum Hydride.7

In the reverse reaction, the Oppenauer oxidation, studies on the oxidation of secondary alcohols with Chloral as the hydride acceptor again demonstrate the sensitive nature of Zr(O-i-Pr)4 to electronic and steric effects (eqs 2 and 3).2

Zr(O-i-Pr)4 is not a good catalyst for the oxidation of allylic alcohols to a,b-unsaturated aldehydes, in contrast to Cp2Zr(O-i-Pr)2 and Bis(h5-cyclopentadienyl)dihydridozirconium.8

Michael-Aldol Reaction.

In an intramolecular Michael-aldol reaction, the n-propoxide Zr(O-n-Pr)4 was far superior to the isopropoxide Zr(O-i-Pr)4.9

Ester Synthesis.

Isopropoxide groups in Zr(O-i-Pr)4 are readily exchanged by other alkoxy groups,1 and by aryloxy and iminoxy (oxime) groups.10 In salicylaldehyde the initial ester exchange at room temperature is succeeded by a Meerwein-Ponndorf-Verley reduction of the formyl group on heating the zirconium phenoxide in benzene.11

Zirconates, like titanates,2 should be useful reagents for esterification or reesterification, especially when either or both of the ester components are acid or base sensitive. In carbonylation reactions with aryl, vinyl, or alkyl bromides and rhodium or palladium catalysis, good yields of the corresponding esters are formed in the presence of zirconates or titanates.12 In another esterification and catalysis process, ketenes react with aldehydes and ketones in the presence of titanium or zirconium alkoxides to form essentially b-hydroxy esters.13 Zr(O-i-Pr)4, although giving 83% yield in the above reaction, was not in any way superior but only complementary to Zr(O-n-Bu)4, Zr(O-n-Pr)4, Zr(OEt)4, Ti(O-t-Bu)4, Ti(O-n-Bu)4, Ti(O-n-Pr)4, and Ti(OEt)4.

Diketopiperazine Synthesis.

Zirconates are water absorbents. Thus Zr(O-i-Pr)4 effects dimerization of amino acids (glycine, alanine) to the corresponding diketopiperazines (eq 4).14 The reaction proceeds in a similar fashion if the corresponding titanium reagent is employed.

1. Bradley, D. C.; Wardlaw, W. JCS 1951, 280.
2. Weidmann, B.; Seebach, D. AG 1983, 95, 12; AG(E) 1983, 22, 31.
3. Dijkgraaf, C.; Rousseau, J. P. G. Spectrochim. Acta, Part A 1968, 24, 1213.
4. Bürger, H.; Neese, H.-J. Z. Anorg. Allg. Chem. 1969, 370, 275.
5. Gmelin Handbuch der Anorganischen Chemie, 8th ed.; Springer: Berlin, 1977-1980; System Number 40, Sections 1 and 2.
6. Seebach, D.; Weidmann, B.; Widler, L. Mod. Synth. Methods 1983, 3, 217.
7. Høseggen, T.; Rise., F.; Undheim, K. JCS(P1) 1986, 849.
8. Nakano, T.; Ishii, Y.; Ogawa, M. JOC 1987, 52, 4855.
9. Attah-Poku, S. K.; Chau, F.; Yadav, V. K.; Fallis, A. G. JOC 1985, 50, 3418.
10. Singh, A.; Rai, A. K.; Mehrotra, R. C. ICA 1973, 7, 450.
11. Mehrotra, R. C.; Gupta, V. D.; Bharara, P. C. IJC 1973, 11, 814.
12. Woell, J. B.; Fergusson, S. B.; Alper, H. JOC 1985, 50, 2134.
13. Hofer, R.; Evard, D.; Jacot-Guillarmod, A. HCA 1985, 68, 969.
14. Yoshino, N.; Yoshino, T. BCJ 1973, 46, 2899.

Lise-Lotte Gundersen

Norwegian College of Pharmacy, Oslo, Norway

Frode Rise & Kjell Undheim

University of Oslo, Norway

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