Dihaptoacyls

Table in. Infrared Vibrational Spectroscopic Data for Organoactinide Dihaptoacyls.a... 

Thus, the reaction of (Th[(CH3>5C5]2 2 2 (JJL) with the organoactinide dihaptoacyls was investigated to learn whether the inserted carbon monoxide was susceptible to any unusual modes of hydride reduction. In particular, analogues to the well-known insertion of carbenes into metal and metalloid hydride bonds (59,60) would offer a means to functionalize the acyl carbon atom. 

The mechanism of this catalytic dihaptoacyl isomerization is proposed to involve initial insertion of the acyl carbon atom into the Th-H bond, followed by -hydride elimination. This process is illustrated in eq. (11). There is precedent in recent transition metal chemistry for the formation of stable MOC(R)HM species analogous to 13. from MH and M (r -cOR) precursors (61). 

Further support for the proposed mechanism of hydride-catalyzed dihaptoacyl isomerization is derived from deuterium labelling studies. When the reaction is conducted with an excess of Th[(( 3)505]2 2)2 the enolate product is selectively deuterated at the H position (Figure 3b) as expected from eq.(12). Furthermore, nmr studies confirm the production of... 

This article reviews recent results on the chemical, spectral and structural properties of bis(pentamethylcyclopentadienyl) thorium and uranium dihaptoacyl complexes produced by migratory insertion of carbon monoxide into actinide-carbon sigma bonds. 

The product isolated from the reaction of a 1 1 stoichiometric amount of CO with the lutetium complex was characterized as a monoinsertion product, an acyl. From spectroscopic data, a dihaptoacyl structure involving significant Lu-0 interaction was postulated. With excess CO, a dimeric complex was isolated in which four CO molecules were coupled via one C=C double bond and two C—C single bonds to form an enedionediolate moiety. The condensation of these four CO molecules can be rationalized based on the carbenoid character of the dihaptoacyl carbon atom. This multiple coupling of CO has precedent in early transition metal... 

CP2MR2 organoctinides also display a rich CO migratory insertion chemistry [54,55]. The pivotal precursors in this chemistry are carbene-like (i.e., behaving as anchored Fischer carbene complexes) dihaptoacyl complexes An example of such a compound is shown in... 

The CO insertion mode regarding early transition metals and f-elements is different from that of late transition metals. Thus, carbene-like dihaptoacyl bonding mode is observed with these acyl complexes formed in the first CO insertion. The subsequent course of the reaction with the second CO may differ considerably from that of late transition metals. " ... 

On the basis oflabeling experiments, the formation of the dionediolate complex 35 from 33 was explained by the rapid dimerization of a transient ketene complex 34, a product of coupling of the carbenelike dihaptoacyl complex 33 with carbon monoxide (reaction 8.56) [91]. 

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