195628-68-3Relevant academic research and scientific papers
Synthesis and chemistry of titanacyclopentane and titanacyclopropane rings supported by aryloxide ligation
Thorn, Matthew G.,Hill, John E.,Waratuke, Steven A.,Johnson, Eric S.,Fanwick, Phillip E.,Rothwell, Ian P.
, p. 8630 - 8641 (1997)
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-cyclohexadiene. 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(OC6H-3Ph2-2,6)2(C4H6R2)] (R = Me, 5; Et, 6; Ph, 7) formed from α-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)2Cl2] (1) or [Ti(OC6HPh4-2,3,5,6)2Cl2] (2) with either sodium amalgam (2 Na per Ti) or 2 equiv of-Bu(n)Li in the presence of the substrate olefin. Using these conditions the titanabicyclic compounds [(ArO)2Ti{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 11 show an exclusive traits 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, ΔH = +18.7(5) kcal mol-1 and ΔS = -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-diphenyl 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(η2-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 a-olefin products, two isomers are detected by 1H, 13C, and 31P 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 (η2-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)CH2Ph}] (31) react with alkynes to produce the corresponding 2-azatitanacyclopent-4-ene which hydrolyze to produce a stoichiometric equivalent of alkylamine. Reaction of 30 with benzonitrile produces the 2,5-diazatitanacyclopent-2-ene [Ti(OC6H3Ph2-2,6)2(N=CPhCHPhNR)] (35) along with ethylene.
