Zirconoxycarbenes

The hydride donor ability of ZrH2(C5Me5)2 was demonstrated convincingly in a separate study (88b) when it reacted with (C5H5)2W(CO) to yield the zirconoxycarbene compound of structure (17b). 

The zirconoxycarbene complexes undergo a variety of typical Fischer-carbene reactions. Typically, unsaturated nine-membered zirconoxycarbene complexes such as 103 are readily deprotonated in the a-position to the carbene carbon atom. The stereochemistry of the subsequent alkylation reaction is very efficiently controlled by the remote stereogenic center at C2, resulting in an effective 1,5-asymmetric induction113 (Scheme 34, Fig. 10). 

Fig. 10. Molecular structure of the zirconoxycarbene tungsten complex 104 obtained by diastereoselective alkylation of 103.

The carbene-carbon monoxide coupling was suggested as a potential elementary C—C coupling step in catalytic carbon monoxide reduction systems based on the observation of the reaction product (r -C5(CH3)5)2ZrH 2(p-OCH=CHO) [31]. The zirconoxycarbene complex 3 was found to react with carbon monoxide at room temperature to afford a zirconium-coordinated ketene complex 4 in 30% isolated yield (reaction 8.18). The X-ray structures of both 3 and 4 were determined [32]. 

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