N-Alkoxy-β-ketoiminate Complexes of Groups 4 and 5:  Synthesis and Characterization of the Complexes [(η⁵-C₅H₄R)M{CH₃C(O)CHC(NCH₂CHR‘O)CH₃}Cln] (M = Ti, n = 1; M = Nb, n = 2; R = H, Me; R‘ = H, Me), [Ti{CH₃C(O)CHC(NCH₂CHR‘O)CH₃}Cl₂(thf)], and [Ti{CH₃C(O)CHC(NCH₂CHR‘O)CH₃}₂]

The synthesis and characterization of a range of N -alkoxo β-ketoiminate complexes of groups 4 and 5 are reported. Reactions between the acylic N -hydroxyalkyl β-ketoimines CH 3 C(O)CH 2 C(NCH 2 CHR‘OH)CH 3 (R‘ = H, Me) and [(η 5 -C 5 H 4 R)TiCl 3 ] (R = H, Me) in the presence of triethylamine afford the monocyclopentadienyl derivatives [(η 5 -C 5 H 4 R)Ti{CH 3 C(O)CHC(NCH 2 CHR‘O)CH 3 }Cl] (R = H, R‘ = H, 2a; R = Me, R‘ = H, 2b; R = H, R‘ = Me, 2c; R = Me, R‘ = Me, 2d ). Complex 2a adopts a square pyramidal coordination geometry with the Cp occupying the apical site and the terdentate ketoiminate and chloride occupying basal positions. Upon standing in thf, solutions of 2a − d containing NEt 3 HCl deposit deep orange crystals of [Ti{CH 3 C(O)CHC(NCH 2 CHR‘O)CH 3 }Cl 2 (thf)] (R‘ = H, 3a; R‘ = Me, 3b ) via protonolysis of the Ti−Cp bond. Alternatively, compounds 3a and 3b can be prepared in near quantitative yield either from the reaction between [TiCl 4 (thf) 2 ] and the corresponding acylic N -hydroxyalkyl β-ketoimine, in the presence of NEt 3, or via a ligand exchange reaction between [Ti(OPr i ) 2 Cl 2 ] and the N -hydroxyalkyl β-ketoimine. Variable-temperature 1 H NMR studies of 3a and 3b have shown that stereoisomers of these complexes interchange via a dissociative dynamic process, involving the trigonal bypyramidal intermediate [Ti{CH 3 C(O)CHC(NCH 2 CHR‘O)CH 3 }Cl 2 ]. The free energy of activation associated with this exchange has been determined (Δ G ⧧ = 45.5 kJ mol - 1, 3a; Δ G ⧧ = 47.0 kJ mol - 1, 3b ). Surprisingly, treatment of [Ti(OPr i ) 4 ] with N -hydroxyalkyl β-ketoimine (1:1) results in complete alcoholysis to afford [Ti{CH 3 C(O)CHC(NCH 2 CHR‘O)CH 3 } 2 ] (R‘ = H, 4a; R‘ = Me, 4b ), which contain two meridianally coordinated terdentate ketoiminate ligands. The reactions between N -hydroxyalkyl β-ketoimine derivatives and [(η 5 -C 5 H 4 R)NbCl 4 ] afford [(η 5 -C 5 H 4 R)Nb{CH 3 C(O)CHC(NCH 2 CHR‘O)CH 3 }Cl 2 ] (R = H, R‘ = H, 5a; R = Me, R‘ = H, 5b; R = H, R‘ = Me, 5c; R = Me, R‘ = Me, 5d ). A single-crystal X-ray study of 5a revealed a structure based on an octahedral geometry, such that the nitrogen of the mer -terdentate ligand is trans to the Cp and the two chloro ligands mutually trans. The single-crystal X-ray structures of 2a, 3a, 3b, 4a · CH 2 Cl 2, and 5a are reported.