Donor properties of the vanadyl ion: reactions of vanadyl salicylaldimine beta-ketimine and acetylacetonato complexes with groups 14 and 15 Lewis acids.

Reactions of organosilicon, -germanium, -tin, -lead, -antimony, and -tin tetrahalide Lewis acids with VO(salen) [H(2)salen = N,N'-bis(salicylidene)ethane-1,2-diamine], related vanadyl salicylaldimines, VO(acacen) [H(2)acacen = N,N'-bis(acetylacetonato)ethane-1,2-diamine], and VO(acac)(2) (acac = acetylacetonato) have been investigated, revealing VO(salen) and VO(acacen) to be significantly stronger vanadyl donors than VO(acac)(2). The vanadyl donor strength of VO(salen) significantly diminishes with the introduction of electron-withdrawing substituents on the salicylaldimine ligand, and the introduction of methyl substituents on the imine carbon atoms can result in a preference for phenolic over vanadyl oxygen donation. Vanadyl donation results in an increase in the vanadyl bond length, while it leaves the distance of vanadium from the basal plane relatively unaffected. Coordination of water trans to a vanadyl oxygen that is involved in a donor bond to tin or lead has little or no effect on the vanadyl bond length but results in a marked movement of vanadium toward the basal plane and a decrease of the V=O-D (D = Sn or Pb) bond angle by as much as 13 degrees, the latter reflecting a loss of multiple bond character of the vanadyl bond. Formation of a vanadyl donor bond results in a decrease in both the vanadyl stretching frequency (infrared spectrum) and energy of the e(pi) <-- b(2) transition (electronic spectrum), the latter being intimately related to the strength of the vanadyl donor bond, while the shift of the b(1) <-- b(2) transition to higher or lower energy is relatively small for vanadyl salicylaldimine and beta-ketimine complexes. Donation through the phenolic oxygen atoms results in an increase in the vanadyl stretching frequency and energy of the e(pi) <-- b(2) transition, which can result in e(pi) <-- b(2)/b(1) <-- b(2) energy crossover.