Synthesis and chemistry of titanacyclopentane and titanacyclopropane rings supported by aryloxide ligation

Treatment of the titanacyclopentadiene compound [Ti(OC6H3Ph2-2,6)(2)(C4Et4)] (3) (OC6H3Ph2-2,6 = 2,6-diphenylphenoxide) with olefins leads to the formation of a variety of stable titanacyclopentane derivatives along with one equivalent of substituted 1,3-cydohexadiene. The structural and spectroscopic properties of the ethylene product [Ti(OC6H3Ph2-2,6)(2)(CH2)(4)] (4) show a ground state titanacyclopentane structure, but facile fragmentation on the NMR time scale to form a bis(ethylene) complex has been detected. The substituted products [Ti(OC6H3Ph2-2,6)(2)(C4H6R2)] (R = Me, 5; Et, 6; Ph, 7) formed from alpha-olefins RCH=CH2 exist as a mixture of regio- and stereoisomers in hydrocarbon solution. Analysis of a crystal obtained from solutions of 7 showed a trans-2,5-diphenyl-titanacyclopentane ring to be present in the solid state. Alternative routes to the titanacyclopentane compounds involve treatment of the dichlorides [Ti(OC6H3Ph2-2,6)(2)Cl-2] (1) or [Ti(OC6HPh4-2,3,5,6)(2)Cl-2] (2) with either sodium amalgam (2 Na per Ti) or 2 equiv of (BuLi)-Li-n in the presence of the substrate olefin. Using these conditions the titanabicyclic compounds [(ArO)(2)Ti{CH2CH(C4H8)CHCH2}](ArO = OC6H3Ph2-2,6, 10; OC6HPh4-2,3,5,6, 11) can be obtained by intramolecular coupling of 1,7-octadiene. The spectroscopic properties of 10 and 11 as well as a single-crystal X-ray diffraction analysis of la show an exclusive trans stereochemistry is present. Thermolysis of 10 or 11 in the presence of excess 1,7-octadiene leads to the catalytic formation of 2-(methylmethylene)cyclohexane (80%) along with E,Z isomers of 2,6-octadiene (20%). A kinetic study shows the reaction to be zero order in diene with activation parameters, Delta H double dagger = +18.7(5) kcal mol(-1) and Delta S double dagger = -26(5) eu. The diphenyltitanacyclopentane 7 will catalyze the dimerization of styrene to trans-1,3-diphenylbut-1-ene followed by isomerization to 1,3-diphenylbut-2-ene. This result shows that although a 2,5-dipheuyl regiochemistry was observed in the solid state, styrene dimerization occurs via the 2,4-diphenyltitanacyclopentane intermediate. The facile fragmentation of these titanacyclopentane compounds accounts for the products observed in a number of reactions. Addition of phosphine donor ligands (L) leads to a series of titanacyclopropane compounds [Ti(OC6H3Ph2-2,6)(2)(eta(2)-CHR=CH2)(L)] (R = H, 14; Me, 15; Et, 16; Ph, 17) along with 1 equiv of olefin. The solid-state structure of the ethylene complex 14 shows the C2H4 unit lies approximately coplanar with the Ti-PMe3 bond. This structure is not only maintained in solution but slow olefin rotation is observed on the NMR time scale. In the case of the alpha-olefin products, two isomers are detected by H-1, C-13, and P-31 NMR spectroscopy. Addition of Ph2C=O or PhCH=NR (R=Ph, CH2Ph) to the titanacyclopentane and titanacyclopropane compounds leads to different products depending upon the reagent and reaction conditions. These can be classified as 2-oxa(aza)titanacycloheptanes, 2-oxa(aza)titanacyclopentanes, 2,5-dioxa(diaza)titanacyclopentanes, and examples of 2-oxatitanacyclopropane (eta(2)-ketone) and 2,7-dioxatitanacycloheptane compounds. The 2-azatitanacyclopentane compounds [Ti(OC6H3Ph2-2,6)(2){(PhCH2)NCH(Ph)CH2CH2}] (30) and trans-[Ti(OC6H3Ph2-2,6)(2){(Ph)NCH(Ph)CH2CH(Ph)}] (31) react with alkynes to produce the corresponding 2-azatitanacyclopent-4-ene which hydrolyze to produce a stoichiometric equivalent of allylamine. Reaction of 30 with benzonitrile produces the 2,5-diazatitanacyclopent-2-ene [Ti(OC6H3Ph2-2,6)(2)(N=CPhCHPhNR)] (35) along with ethylene.