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.