Synthesis of compounds with C–P–P and CP–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 Ph2CP–PtBu2 (2) and (fluorenyl)CP–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(CO)Ph}] (8) and in parallel to phosphanylphosphaalkene (Ph)MeCP–PtBu2 (9) and 5. The reactions of 1 with cyclic ketones (cyclopentanone and cyclohexanone) lead to Ti(III) complexes [{(ArNC(Me)CHC(Me)NAr)((CH2)4CO)}Ti(Cl){PtBu2–P(SiMe3)((CH2)4CO)}] (10) and [{(ArNC(Me)CHC(Me)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)4CP–PtBu2 (10a) and (CH2)5CP–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(CO)(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.