Deuterium hydrozirconation

Hydrozirconation is useful for regiospecific and/or stereospecific deuterium labeling [177]. Formation of diastereomerically pure dideuterated 3,3-dimethyl-butylzirconium(IV) complexes by successive hydrozirconation sequences showed... 

Cleavage of Zr—C a bonds occurs readily on treatment with H20 or dilute acids, while the Zr—Cp bond usually survives mild protonolysis conditions. The use of D20 or DC1/D20 permits the replacement of Zr with D. Deuterolysis provides a generally reliable method for establishing the presence of Zr—C bonds. Protonolysis or deuterolysis of Zr—Csp bonds proceeds with retention of configuration [97]. In the hydrozirconation of terminal alkynes, deuterium can be introduced at any of the three positions in the vinyl group in a completely regio- and stereoselective manner, as shown in Scheme 1.18. Although relatively little is known about the mechanistic details, the experimental results appear to be consistent with concerted c-bond metathesis (Pattern 13) between C—Zr and H— X bonds. 

Treatment of the optically active gem-borazirconocene alkanes with deuterium oxide followed by alkaline oxidation affords the corresponding optically active 1-deuterio primary alcohols. The enantiomeric excess of the resulting primary alcohols represents the diaster-eoselectivity of the asymmetric hydrozirconation (Scheme 7.13). Based on the cost and availability of optically active ligands, three types were explored monoterpenes, 1,2-diols, and 1,2-amino alcohols. Hydrozirconation of optically pure 1-alkenyl boranes 39 provided optically active 1,1-bimetallics 40. 

Perhaps the most useful application of the hydrozirconation/protodezirconation sequence is for specific introduction of deuterium label some examples were presented in the previous section. Although most such work indicates that deuterium incorporation is essentially complete, Svenson and coworkers have found that around 20% of the alkane thus obtained from simple alkenes is undeuterated. The amount of alkane-reaction times, so transfer of hydrogen to give alkane prior to hydrolysis is probably responsible. This in situ hydrogenation was found to be even more pronounced for a,p-unsaturated carboxylic acid oxazolines, giving 70% of the undeuterated saturated product. ... 

Hydrozirconation occurs by cis addition of Zr and hydrogen to terminal alkenes . Both the (E) and (Z) diastereomers of l-deuterio-3,3-dimethylbutene react with ( -Cp)2ZrHCl to give primary alkylzirconiums characterized by deuterium-decoupled NMR ... 

Regiospecific deuterium labeling can be achieved by quenching organozir-conocenes with D2O or by using Cp2ZrDCl for hydrozirconation. A nice demonstration of this concept is the synthesis of three deuterium-substituted analogues of dimethyl hept-l,6-dienyl-4,4-dicarboxylate [42] (Scheme 6). These compounds were used for the study of the mechanism of the transition metal-... 

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