C O M M U N I C A T I O N S
excess Me3SiCl in toluene at room temperature for several weeks.
On a preparative scale, 5 was isolated as colorless crystals in good
yield. Finally, addition of 4 equiv of PhCH2MgCl to 5 gave the
corresponding dibenzyl complex 1, which could be readily sepa-
rated.
This study demonstrates a synthetic cycle having relevance to
F-T chemistry, wherein zirconium alkyl complexes of the [LR]
ligands serve to transform H2 and CO into corresponding allenes
via alkylidene intermediates. This transformation involves the
activation of H2, formation of C-C, C-H bonds, C-O bond
cleavage, and deoxygenative recycling of the oxo-bridging zirco-
nium complexes. All of the preceding reactions are spectroscopically
quantitative under mild conditions. Thus, there is much potential
for yield optimization, including the combination of consecutive
steps.
Acknowledgment. We acknowledge the Institute for Molecular
Science and the Ministry of Education, Culture, Sports, Science
and Technology, Japan, for financial support for this research.
Supporting Information Available: Experimental procedures and
the CIF file for 2a. This material is available free of charge via the
Figure 1. 13C{1H} NMR monitoring of the reaction of 2a with 13CO in
C6D6 at room temperature; ketene intermediates (b), phenylallene (0), and
free 13CO (∆).
References
Scheme 3. Proposed Mechanism for the Carbonylation of 2
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CdO)(µ-CH2O) via double migration of two hydride groups
followed by formaldehyde-ketene coupling and deoxygenation.
Following a recent protocol of Figueroa and Cummins,10
treatment of 3 with trifluoromethanesulfonic anhydride (Tf2O) in
C6D6 led to clean conversion to {[LR]Zr(OTf)}2(µ-O) (4). Complex
4 did not react with excess Tf2O due to the reduced nucleophilicity
of the remaining oxo ligand in 4. Next we examined the reactions
of 3 with trimethylsilylated reagents, because the use of the
trimethylsilyl moiety in the deoxygenation of oxo complexes could
allow for favorable thermodynamic release of (Me3Si)2O. The
reaction of 3 with 2 equiv of trimethylsilyltrifluoromethanesulfonate
(Me3SiOTf) in C6D6 quantitatively gave the oxo-OTf complex 4
along with (Me3Si)2O according to NMR spectroscopy, while
increasing the amount of Me3SiOTf resulted in a complicated
mixture of products. When Me3SiCl was used as a mild silylating
reagent instead of Me3SiOTf, we found that 4 could be slowly
transformed into {[LR]ZrCl}2(µ-OTf)2 (5) upon treatment with
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