Formation of Bonds to Carbon at Transition Metal Centers

The reactions of Cp2TiCH2Al(Me)2Cl 1, Cp2TiCH2C(R) = CR 2, and Cp2TiCH2CHRCH2 3 with organic carbonyl compounds are explored. 1 with carbonyl, in a Wittig-type reaction, exchanges methylene for oxygen and yields alkenes; no intermediates can be observed. When treated with carbonyl, 2a (R = Ø) inserts O = C into the Ti-CH2 bond, generating oxytitanacyclohexenes. Other metallacyclobutenes similarly insert carbonyl; or, if RC ≡ CR is labile, exchange methylene for oxygen, producing alkenes. 3a (R = t-butyl) with carbonyl compounds also exchanges methylene for oxygen, and the mechanism of this reaction is explored. 3a is in equilibrium with a titanocene-carbene-olefin complex 11, which is trapped by ketones. 11 is also in equilibrium with titanocene carbene 12 and free olefin; 12 is trapped by esters (as well as ketones}. The formation of 11 is rate-determining. Formation of 12 from 11, trapping of 11 by ketone, and the reverse reaction, formation of 3a from 11 are all competitive. Trapping of 12 by esters is competitive with the reverse reaction, formation of 11 from 12 and olefin. Relative rates of reaction of several ketones and esters are determined. A new platinum vinyl complex, L2Pt(CH = CH2) Me 3 (L = PMe2Ø) is prepared by treatment of the known L2Pt(CH = CH2)Cl with MeLi at low temperatures. Oxidative addition of MeI to the platinum (II) complex 3 generates L2Pt(CH = CH2)Me2I 4· The thermal decomposition of 4 is examined, and the relative amounts of ethane and propene formed lead to the conclusion that a vinyl group reductively eliminates twenty times faster than methyl. CpCr(NO)2Me is treated with various ligands in an attempt to see insertion of NO into the Cr-Me bond. A clean reaction is observed with PMe3. Instead of insertion, deoxygenation of NO by PMe3 generates O = PMe3 and, ultimately, CpCr(NO) (:NMe) - (PMe3) 5a· Similar reactions occur with CpCr(NO)2R, R = n-hexyl, isobutyl, Ø, Thermal decomposition of 5a or treatment with H+ generates CH4.