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 beta-ketoiminate complexes of groups 4 and 5 are reported. Reactions between the acylic N-hydroxyalkyl beta-ketoimines CH3C(O)CH2C(NCH2CHR ' OH)CH3 (R ' = H, Me) and [(eta(5)-C5H4R)TiCl3] (R = H, Me) in the presence of triethylamine afford the monocyclopentadienyl derivatives [(eta(5)-C5H4R)Ti-{CH3C(O)CHC(NCH2CHR ' O)CH3}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 NEt3HCl deposit deep orange crystals of [Ti{CH3C(O)CHC(NCH2CHR ' O)CH3)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 [TiCL4(thf)(2)] and the corresponding acylic N-hydroxyalkyl beta-ketoimine, in the presence of NEt3, or via a ligand exchange reaction between [Ti(OPri)(2)Cl-2] and the N-hydroxyalkyl beta-ketoimine. Variable-temperature H-1 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{CH3C(O)CHC(NCH2CHR ' O)CH3}Cl-2]. The free energy of activation associated with this exchange has been determined (Delta G(double dagger) = 45.5 kJ mol(-1), 3a; Delta G(double dagger) = 47.0 kJ mol(-1), 3b). Surprisingly, treatment of [Ti(OPri)al with N-hydroxyalkyl beta-ketoimine (1:1) results in complete alcoholysis to afford [Ti{CH3C(O)CHC(NCH2CHR ' O)CH3}(2)] (R ' = H, 4a; R ' = Me, 4b), which contain two meridianally coordinated terdentate ketoiminate ligands. The reactions between N-hydroxyalkyl beta-ketoimine derivatives and [(eta(5)-C5H4R)NbCl4] afford [(eta(5)-C5H4R)Nb{CH3C(O)CHC(NCH2CHR ' O)CH3}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 . CH2Cl2, and 5a are reported.