Synthesis of compounds with C-P-P and C[double bond, length as m-dash]P-P bond systems based on the phospha-Wittig reaction.

Abstract

A reactivity study of a β-diketiminate titanium(iii) phosphanylphosphido complex [MeNacNacTi(Cl){η2-P(SiMe3)-PtBu2}] (1) towards ketones such as benzophenone, 9-fluorenone, acetophenone, cyclopentanone, cyclohexanone and cycloheptanone is reported. The reactions of 1 with aromatic ketones (without α-protons) directly lead to the Ti(iii) complex [MeNacNacTi(μ2-Cl)(OSiMe3)] (5) and Ti(iv) complexes with the pinacol condensation product [MeNacNacTi(OSiMe3)(η2-pinacolate)] (3), and phosphanylphosphaalkenes Ph2C[double bond, length as m-dash]P-PtBu2 (2) and (fluorenyl)C[double bond, length as m-dash]P-PtBu2 (6), respectively. The reaction with acetophenone leads to the titanium(iii) complex with the aldol condensation product as ligand [MeNacNacTi(Cl){OC{Me(Ph)}CH2(C[double bond, length as m-dash]O)Ph}] (8) and in parallel to phosphanylphosphaalkene (Ph)MeC[double bond, length as m-dash]P-PtBu2 (9) and 5. The reactions of 1 with cyclic ketones (cyclopentanone and cyclohexanone) lead to Ti(iii) complexes [{(ArN[double bond, length as m-dash]C(Me)CHC(Me)[double bond, length as m-dash]NAr)((CH2)4CO)}Ti(Cl){PtBu2-P(SiMe3)((CH2)4CO)}] (10) and [{(ArN[double bond, length as m-dash]C(Me)CHC(Me)[double bond, length as m-dash]NAr)((CH2)5CO)}Ti(Cl){PtBu2-P(SiMe3)((CH2)5CO)}] (11), which are formed via the successive insertion of two molecules of ketone to one molecule of 1. The stability investigation of complexes 10 and 11 in a polar solvent (THF) revealed that under these conditions, the complexes decompose, resulting in titanium(iii) complexes with aldol condensation products and the expected phosphanylphosphaalkenes (CH2)4C[double bond, length as m-dash]P-PtBu2 (10a) and (CH2)5C[double bond, length as m-dash]P-PtBu2 (11a). In the reaction of 1 with cycloheptanone, only the Ti(iii) complex with the aldol condensation product [MeNacNacTi(Cl){OC(CH2)6}CH(C[double bond, length as m-dash]O)(CH2)5] (12) was isolated. The structures 3, 5, 8, 10, 11, 11b and 12 were characterized by X-ray spectroscopy, while all the phosphanylphosphaalkenes were characterized by NMR spectroscopy.