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 (CpTiCl3)-Ti-O (1; Cp-O = C5H4CH2CH2OCH3) reacts with 1.0, 2.0, and 3.0 equiv of MeMgCl to give (CpTiMeCl2)-Ti-O (2), (CpTiMe2Cl)-Ti-O (3), and (CpTiMe3)-Ti-O (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) angstrom in 2 and 2.2818(10) angstrom in 3) disposed transoid to a methyl ligand. In solution the O-donor substituent is involved in a coordination-dissociation equilibrium (Delta H-o = 3.0 +/- 0.7 kcal mol(-1) and Delta S-o = 12 +/- 4 cal mol(-1) K-1 for 2, Delta H-o = 4.3 +/- 0.1 kcal mol(-1) and Delta S-o = 17.2 +/- 0.1 cal mol(-1) K-1 for 3, and Delta H-o = 2.3 +/- 0.1 kcal mol(-1) and Delta S-o 11.9 +/- 0.3 cal mol(-1) K-1 for 4). The reactions of 1 with 3.0 equiv of PhCH2MgCl, PhMgCl, and (p-tolyl)MgBr lead to CpOTiR3 (R = PhCH2 (5), Ph (6), p-tolyl (7)) containing a free pendant ether group. The X-ray structure of 6 shows a beta-agostic Ti-H interaction between the metal center and a phenyl group (Ti-C-alpha-C-beta = 139.3(3) and 105.3(2)degrees). Complex 1 reacts with 1.0 equiv of Li(0-2,6-Bu-t(2)-4-MeC6H2) to give the six-coordinate aryloxide derivative (CpTi)-Ti-O(O-2,6-Bu-t(2)-4-MeC6H2)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)degrees). The addition of 1.0 and 2.0 equiv of MeMgCl to 8 affords (CpTiMe)-Ti-O(O-2,6-Bu-t(2)-4-MeC6H2)Cl (9) and (CpTiMe2)-Ti-O(O-2,6-Bu-t(2)-4-MeC6H2) (10). Treatment of 1 with 1.0, 2.0, and 3.0 equiv of Li(O-2,6-(Pr2C6H3)-Pr-i) gives rise to (CpTi)-Ti-O(O-2,6-(Pr2C6H3)-Pr-i)Cl-2 (11), (CpTi)-Ti-O(O-2,6-(Pr2C6H3)-Pr-i)(2)Cl (12), and (CpTi)-Ti-O(O-2,6-(Pr2C6H3)-Pr-i)(3) (13). Complex 11 reacts with 1.0 and 2.0 equiv of MeMgCl to afford (CpTiMe)-Ti-O(O-2,6-(Pr2C6H3)-Pr-i)Cl (14) and CpOTiMe2(O-2,6-(Pr2C6H3)-Pr-i) (15), whereas the reaction of 12 with 1.0 equiv of MeMgCl leads to (CpTiMe)-Ti-O(O-2,6-(Pr2C6H3)-Pr-i)(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 (CpTiMe2)-Ti-O(OCPh2C CH) (17) and CpOTiMe(OCPh2C=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 CpTiMe3 (19) for the regioselective anti-Markovnikov hydroamination of phenylacetylene with cyclohexylamine, 2,6-dimethylaniline, tert-butylamine, and 2,6-diisopropylaniline an for the hydroamination of 1-phenylpropyne and diphenylacetylene with cyclohexylamine and 2,6dimethylaniline.