Characterization and coordination chemistry of low valent vanadium complexes incorporating anionic oxygen donor ligands

Low valent vanadium complexes featuring either novel coordination geometry or nuclearity have been synthesized and characterized.; The crystal structure of [(dme)Li(mu-tbdmpd)V(mu-tbdmpd)Li(dme)] (tbdmpdH2, 3,3'-di-tert-butyl-5,5 ',6,6'-tetramethyl-1,1'-biphenyl-2,2 '-diol) shows the metal center to be four-coordinate exhibiting a distorted tetrahedral coordination geometry---unprecedented for vanadium(II). Reactivity of this coordinatively unsaturated complex with CO and tert-butylisocyanide was observed. Reaction with diphenylhydrazine and oxygen resulted in the isolation of [V(tbdmpd)2] and trinuclear [V3Li2(mu-tbdmpd)3(mu-O)7(mu-OTF){lcub}Li(thf){rcub} 2{lcub}Li(Et2O){rcub}2] respectively. The species [(dme)Li(mu-tbdmpd)V(mu-tbdmpd)Li(dme)] and [V(tbdmpd)2] are also interesting as rare examples of bis-biphenolate complexes.; Tetranuclear examples of vanadium(II) were discovered and structurally characterized. These complexes represent a significant and important advance in multinuclear low valent early transition metal chemistry. [V4(mu 3-Cl)2(mu-Cl)2(mu-tfa)4(thf) 6] was prepared via a unique outer sphere ZnCl+ abstraction reaction from [(thf)3V(mu-Cl)(mu-tfa)2V(thf) 3][ZnCl3(thf)] using potassium hydrotris(3,5-dimethylpyrazolyl)borate (KTpb*). Further treatment of [V4(mu3-Cl)2(mu-Cl) 2(mu-tfa)4(thf)6] with two equivalents of KTpb* yielded the novel asymmetric binuclear product [(Tpb*)V(mu-Cl)(mu-tfa) 2V(thf)3]. Selected reactivity of these complexes is discussed. The reaction of [(thf)3V(mu-X)3V(thf)3] + (X = Cl and Br) starting materials with sodium tetrahydrofuran-2-methoxide (Nathffa) yielded species containing cuboidal cores, namely [V4(mu-thffa) 8{lcub}ZnX2{rcub}2] (X = Cl and Br).; A number of low valent vanadium acetylacetonate compounds were prepared and studied. Binuclear species [V2E2(m-XBA) 2(thf)2] (E = Cl and Br) (m-XBAH2, (3,3'-[1,3-phenylenebis(methylene)]bis(2,4-pentanedione)), contain six-coordinate VIII centers, and display an intriguing 'cage-like' structural type new to low valent vanadium chemistry and the m-XBA2- ligand system. Reduction of [V2Cl2(m-XBA)2(thf) 2] in the presence of TMEDA (N,N,N', N'-tetramethylethylenediamine) formed the complex [V2(m-XBA)2(tmeda)2] which has been crystallographically characterized. In [V(acac)2(tmeda)], a six-coordinate, nearly octahedral VII atom is present. These are the first examples of structurally characterized bis(acetylacetonate) ligated complexes of vanadium(II).