Reactions of Substituted Zirconocene−Bis(trimethylsilyl)ethyne Complexes with Terminal Alkynes

The complexes [Zr(η²-Me<INF>3</INF>SiC&tbd1;CSiMe<INF>3</INF>)(η⁵-C<INF>5</INF>Me<INF>4</INF>R)<INF>2</INF>] (R = Me (<BO>5</BO>), H (<BO>6</BO>), SiMe<INF>3</INF> (<BO>7</BO>)) reacted smoothly with terminal alkynes HC&tbd1;CR‘ (R‘ = CMe<INF>3</INF>, SiMe<INF>3</INF>, ferrocenyl (Fc), Ph) to give the agostic alkenyl−alkynyl complexes [Zr(η¹-C&tbd1;CR‘){η³-C(SiMe<INF>3</INF>)&dbd;CH(SiMe<INF>3</INF>)}(η⁵-C<INF>5</INF>Me<INF>4</INF>R)<INF>2</INF>] (R/R‘ = Me/CMe<INF>3</INF> (<BO>5a</BO>), Me/SiMe<INF>3</INF> (<BO>5b</BO>), H/CMe<INF>3</INF> (<BO>6a</BO>), H/SiMe<INF>3</INF> (<BO>6b</BO>), H/Fc (<BO>6c</BO>), H/Ph (<BO>6d</BO>), SiMe<INF>3</INF>/CMe<INF>3</INF> (<BO>7a</BO>), SiMe<INF>3</INF>/Fc (<BO>7c</BO>)). Complex <BO>7a</BO>, formed in situ from <BO>7</BO> and HC&tbd1;CCMe<INF>3</INF>, dimerized tert-butylethyne exclusively to give the head-to-tail dimer Me<INF>3</INF>CC&tbd1;CC(CMe<INF>3</INF>)&dbd;CH<INF>2</INF>, and when all the terminal alkyne was consumed, <BO>7</BO> was restored. Complex <BO>7</BO> reacted similarly with 1-hexyne, phenylethyne, and (trimethylsilyl)ethyne, affording the respective alkenyl−alkynyl complexes, which also changed back to <BO>7</BO> on evaporation of the reaction solutions; none of these terminal alkynes was dimerized with <BO>5</BO>−<BO>7</BO>. Heating of complex <BO>6</BO> with LiC&tbd1;CSiMe<INF>3</INF> in toluene or THF yielded the diamagnetic zirconate complex Li[Zr(η¹-C&tbd1;CSiMe<INF>3</INF>)(η²-Me<INF>3</INF>SiC&tbd1;CSiMe<INF>3</INF>)(η⁵-C<INF>5</INF>HMe<INF>4</INF>)<INF>2</INF>] (<BO>6e</BO>) and its solvatomorph Li[Zr(η¹-C&tbd1;CSiMe<INF>3</INF>)(η²-Me<INF>3</INF>SiC&tbd1;CSiMe<INF>3</INF>)(η⁵-C<INF>5</INF>HMe<INF>4</INF>)<INF>2</INF>]·C<INF>4</INF>H<INF>8</INF>O (<BO>6f</BO>), respectively. The lithium cation in <BO>6e </BO>and<BO> 6f </BO>is placed in a position at the side of the alkynyl triple bond and close to C^β of the η²-Me<INF>3</INF>SiC&tbd1;CSiMe<INF>3</INF> ligand, apparently interacting with both moieties. All presented complexes were characterized by the standard spectral methods, and the structures of <BO>5a</BO>,<BO> 6a</BO>,<BO> 6c</BO>,<BO> 6d</BO>, and <BO>6e </BO>were determined by single-crystal X-ray diffraction.