Putting on the Crown: Synthesis and Reactivity of Trimethyltitanium

Abstract

The trimethyltitanium complex (Me 3 TACN)TiMe 3 (Me 3 TACN = 1,4,7-Me 3 -1,4,7-triazacyclononane) is obtained by reacting (Me 3 TACN)TiCl 3 with methyllithium in the cold. The isolation of pure (Me 3 TACN)TiMe 3 was achieved via direct crystallization from the filtered reaction mixture or by extraction of the reaction residue with toluene. A similar reaction with neosilyllithium comes to a halt at the bis(alkyl) complex (Me 3 TACN)TiCl(CH 2 SiMe 3 ) 2 . Treatment of (Me 3 TACN)TiMe 3 with ClSiMe 3 or TfOSiMe 3 gives mixed ligand complexes (Me 3 TACN)TiMe 2 Cl, (Me 3 TACN)TiMe 2 (OTf), and (Me 3 TACN)TiMe(OTf) 2 in good yields. The reaction of (Me 3 TACN)-TiMe 3 with trimethylaluminum in THF leads to the ion-separated compound [(Me 3 TACN)TiMe 2 (THF)][AlMe 4 ], while salt-metathetical exchange of (Me 3 TACN)TiMe 2 Cl with LiAlMe 4 affords chlorido-bridged [{(Me 3 TACN)TiMe 2 } 2 (μ-Cl)][AlMe 4 ]. Treatment of (Me 3 TACN)-TiMe 3 with HAlMe 2 gives access to the reduced hydride species [{(Me 3 TACN)Ti(μ-H) 2 AlMe 2 } 2 (μ-H)][AlMe 4 ]. Monomeric alkoxides (Me 3 TACN)Ti(OR) 3 (R = Me, Et) are obtained via the protonolysis of (Me 3 TACN)TiMe 3 with stoichiometric amounts of methanol and ethanol, respectively. The crystal structure of (Me 3 TACN)Ti(OMe) 3 is compared to the scandium congener (Me 3 TACN)Sc(OMe) 3 (δ( 45 Sc) = 140.6 ppm), which was synthesized from (Me 3 TACN)ScMe 3 and methanol.Article pubs.acs.org/Organometallics

Reactivity of a Neutral Yttrium(III) Trimethyl Complex toward Brønsted and Lewis Acids

“…Protonolysis of the YÀ CH 3 moieties under methane elimination seemed the most immediate transformation to study, [22] since the reaction of [(Me 3 TACN)ScMe 3 ] with methanol has been shown to afford [(Me 3 TACN)Sc(OMe) 3 ] in decent yield. [17] Probing both a considerably less Brønsted acidic and sterically more demanding proligand, we examined silylamine HN(SiHMe 2 ) 2 . The latter has been previously successfully applied to convert amorphous unsolvated [YMe 3 ] n into homoleptic silylamide [Y {N(SiHMe 2 ) 2 } 3 ] 2 .…”

“…More recently, the crystal structures of [(Me 3 TACN)LnMe 3 ] (Ln=Sc, Y, Yb, Lu) have been elucidated [14–16] . Previous reactivity studies also include the redox transformation of the ytterbium congener in the presence of AlMe 3 and GaMe 3 , [16] the controlled ClSiMe 3 ‐promoted Me/Cl exchange at the yttrium center, [15] as well as the exhaustive protonolysis of the scandium congener with methanol [17] . It was also revealed that the 89 Y nucleus ( I =$${{ 1/2 }}$$ , natural abundance=100 %) [18] is a useful complementing probe for assessing the alkylation degree/substitution pattern at the rare‐earth‐metal center and any involved decomposition reactions, via heteronuclear NMR spectroscopy [15,19–21] …”

“…[14][15][16] Previous reactivity studies also include the redox transformation of the ytterbium congener in the presence of AlMe 3 and GaMe 3 , [16] the controlled ClSiMe 3 -promoted Me/Cl exchange at the yttrium center, [15] as well as the exhaustive protonolysis of the scandium congener with methanol. [17] It was also revealed that the 89 Y nucleus (I = 1 = 2 , natural abundance = 100 %) [18] is a useful complementing probe for assessing the alkylation degree/substitution pattern at the rare-earth-metal center and any involved decomposition reactions, via heteronuclear NMR spectroscopy. [15,[19][20][21] To further deepen the knowledge of such donor-stabilized trimethyl complexes, the reactivity of [(Me 3 TACN)YMe 3 ] [15] has been systematically expanded toward Brønsted acids and group 13 Lewis acids.…”