Cp2Zr L

Recently, Oshima et al. developed the conversion of acid chlorides into the corresponding homoallylic alcohols catalyzed by in r(/ -prepared hydridozirconium allyl reagents (Scheme 41),147 147a The proposed mechanism suggests an initial hydride transfer from the zirconocene crotyl hydride species, in equlibrium with its Cp2Zr(l-alkene),147a to the acid chloride with subsequent allylation to afford the corresponding homoallylic alcohols. 

Scheme 1.1. Alkene- and alkyne-ZrCp2 complexes (1 and 2), and 3 as an example of a Cp2Zr(l 11) complex.

Guram AS, Jordan RF. Alkene and alkyne insertion reactions of cationic Cp2Zr (l] -pyridy])(L) complexes. Zirconium-mediated functionalization of pyridines. Organometallics. 1991 10 3470-3479. 

AUylzirconium complexes are conveniently obtained by the regio- and stereoselective hydrozirconation of allene [127-133] and can be, for example, used subsequently for the MAO-catalyzed allylzirconation of alkynes to prepare enyne derivatives [132]. Alternatively, the preparation of (E)-l,3-dienes from aldehydes and the appropriate allylstannane zirconocene derivative (R = SnBu,) is accomplished (Scheme 8-17) [131], Note that addition of [Cp2Zr(H)Cl[n (1) on the aUenyl reagent with the... 

Cp2Zr(H)(Cl) (8). The apparent record for catalyzed double bond movement is on 9-decene-l-ol to decanal (nine positions) using Fe3(CO)i2 (9). However, 30 mol % was required, which means that nearly a mole of metal was used per mole of alkenol. Herein we expand upon our initial report (10) of a very active catalyst (1) which has been shown to move a double bond over 30 positions. Catalyst 1 appears to have an intriguing and useful mode of action, in which the pendant base ligand performs proton transfer on coordinated alkene and Ti-allyl intermediates in a stereoselective fashion. 

Zr compounds are also useful as Lewis acids for oxidation and reduction reactions. Cp2ZrH2 or Cp2Zr(0 Pr)2 catalyze the Meerwein-Ponndorf-Verley-type reduction and Oppenauer-type oxidation simultaneously in the presence of an allylic alcohol and benzaldehyde (Scheme 40).170 Zr(C)1 Bu)4 in the presence of excess l-(4-dimethylaminophenyl) ethanol is also an effective catalyst for the Meerwein-Ponndorf-Verley-type reduction.1 1 Similarly, Zr(0R)4 catalyze Oppenauer-type oxidation from benzylic alcohols to aldehydes or ketones in the presence of hydroperoxide.172,173... 

Representative procedure for the synthesis of (Z)-a-selenenylvinylstannanes [34] A mixture of Cp2Zr(H)Cl (1.1 mmol) and (3-methoxy-l-propynyl)tributylstannane (1.0 mmol) in THF (5 mL) was stirred at room temperature for 20 min. A solution of PhSeBr (1.0 mmol) in THF (4 mL) (prepared in situ) was then injected into the resulting solution and the mixture was stirred at room temperature for 30 min. It was then diluted with light petroleum and stirred for a further 5 min., after which the supernatant was filtered through a short plug of silica gel. After evaporation of the solvent from the filtrate, the residue was purified by preparative TLC on silica gel to yield (lZ)-tributyl-[3-methoxy-l-(phenylse-leno) -1 -propenyl] stannane (60 %). 

Cationic r 2-acylzirconocenes [Cp2Zr(COR)(L)+] have been reported to show attractive reactivity [39]. A cationic r 2-acylzirconocene can be generated in quantitative yield by treating a cationic zirconocene complex [Cp2Zr(R)(L)+] (R = alkyl or alkenyl) with carbon monoxide (<23 °C, 1 atm) (Scheme 5.36). The cationic acylzirconocene complexes undergo regiose-... 

The first example of a stable 1,1-bidentate Lewis acid based on boron and zirconium has been reported [35]. The synthesis of 22 is outlined in Scheme 7.12. Treatment of hex-l-yne with HBBr2 Me2S followed by conversion of the dibromoboronic ester to the corresponding alkenyl boronic acid and esterification with propane-1,3-diol provided the alkenyl boronic ester. Hydrozirconation of this compound with 3 equivalents of the Schwartz reagent, Cp2Zr(H)Cl [57], afforded the desired product 22 in 86% yield. 

Hydrozirconation of 1-alkynyl pinacolboronates with Cp2Zr(H)Cl provides gem-boriozirco-nocenes 45. Treatment of 45 with CuBr gives the homocoupled (1 fc, 3fc)-2,3-dibora-l,3-dienes 46 in good yield (Scheme 7.15) [92]. The zirconocene-induced coupling was studied using a series of 1-alkynyl pinacolboronates 47. In this case, two regioisomers 48 and 49 were detected (Scheme 7.15). 

As representatives of this class of compounds, one hindered and one non-hindered gem-boriozirconocene alkene were prepared [54]. Hydrozirconation of a 1-alkynyldioxaborolane with Cp2Zr(H)Cl in either 1,4-dioxane or THF proceeded readily by a syn addition to give the essentially pure ( )-l,l-bis-metallic boriozirconocene 45 [12]. This bis-metallic complex 45 was also reacted with various electrophiles, thereby generating the alkenylboron derivatives 53—57 as shown in Scheme 7.17. 

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