New Half-Sandwich Alkyl, Aryl, Aryloxide, and Propargyloxide Titanium(IV) Complexes Containing a Cyclopentadienyl Ligand with a Pendant Ether Substituent: Behavior and Influence in the Hydroamination of Alkynes of the Ether Group

The complex Cp O TiCl 3 ( 1; Cp O = C 5 H 4 CH 2 CH 2 OCH 3 ) reacts with 1.0, 2.0, and 3.0 equiv of MeMgCl to give Cp O TiMeCl 2 ( 2 ), Cp O TiMe 2 Cl ( 3 ), and Cp O TiMe 3 ( 4 ). In the solid state, the ether group of the pendant substituent of the cyclopentadienyl ligand is coordinated to the metal center ( d (Ti−O) = 2.3373(18) Å in 2 and 2.2818(10) Å in 3 ) disposed transoid to a methyl ligand. In solution the O-donor substituent is involved in a coordination−dissociation equilibrium (Δ H ° = 3.0 ± 0.7 kcal mol - 1 and Δ S ° = 12 ± 4 cal mol - 1 K - 1 for 2, Δ H ° = 4.3 ± 0.1 kcal mol - 1 and Δ S ° = 17.2 ± 0.1 cal mol - 1 K - 1 for 3, and Δ H ° = 2.3 ± 0.1 kcal mol - 1 and Δ S ° = 11.9 ± 0.3 cal mol - 1 K - 1 for 4 ). The reactions of 1 with 3.0 equiv of PhCH 2 MgCl, PhMgCl, and ( p -tolyl)MgBr lead to Cp O TiR 3 (R = PhCH 2 ( 5 ), Ph ( 6 ), p -tolyl ( 7 )) containing a free pendant ether group. The X-ray structure of 6 shows a β-agostic Ti−H interaction between the metal center and a phenyl group (Ti−C α −C β = 139.3(3) and 105.3(2)°). Complex 1 reacts with 1.0 equiv of Li(O-2,6- t Bu 2 -4-MeC 6 H 2 ) to give the six-coordinate aryloxide derivative Cp O Ti(O-2,6- t Bu 2 -4-MeC 6 H 2 )Cl 2 ( 8 ), which has been also characterized by X-ray diffraction analysis. The structure suggests a significant multiple bond character for the Ti−aryloxide bond (Ti−O−C = 151.31(14)°). The addition of 1.0 and 2.0 equiv of MeMgCl to 8 affords Cp O TiMe(O-2,6- t Bu 2 -4-MeC 6 H 2 )Cl ( 9 ) and Cp O TiMe 2 (O-2,6- t Bu 2 -4-MeC 6 H 2 ) ( 10 ). Treatment of 1 with 1.0, 2.0, and 3.0 equiv of Li(O-2,6- i Pr 2 C 6 H 3 ) gives rise to Cp O Ti(O-2,6- i Pr 2 C 6 H 3 )Cl 2 ( 11 ), Cp O Ti(O-2,6- i Pr 2 C 6 H 3 ) 2 Cl ( 12 ), and Cp O Ti(O-2,6- i Pr 2 C 6 H 3 ) 3 ( 13 ). Complex 11 reacts with 1.0 and 2.0 equiv of MeMgCl to afford Cp O TiMe(O-2,6- i Pr 2 C 6 H 3 )Cl ( 14 ) and Cp O TiMe 2 (O-2,6- i Pr 2 C 6 H 3 ) ( 15 ), whereas the reaction of 12 with 1.0 equiv of MeMgCl leads to Cp O TiMe(O-2,6- i Pr 2 C 6 H 3 ) 2 ( 16 ). Complexes 15 and 16 can be also obtained by addition of 1.0 and 2.0 equiv of 2,6-diisopropylphenol to 4 . Treatment of 4 with 1.0 and 2.0 equiv of 1,1-diphenyl-2-propyn-1-ol gives the propargyloxide derivatives Cp O TiMe 2 (OCPh 2 C⋮CH) ( 17 ) and Cp O TiMe(OCPh 2 C⋮CH) 2 ( 18 ). Like 5 − 7, complexes 8 − 18 contain a free pendant ether group. Complex 4 is a more efficient catalyst precursor than the related CpTiMe 3 ( 19 ) for the regioselective anti-Markovnikov hydroamination of phenylacetylene with cyclohexylamine, 2,6-dimethylaniline, tert -butylamine, and 2,6-diisopropylaniline and for the hydroamination of 1-phenylpropyne and diphenylacetylene with cyclohexylamine and 2,6-dimethylaniline.