Synthesis and reactivity of cyclometalated triamidophosphine complexes of niobium and tantalum

Martin's Phosphino-Triol Revisited: Unexpected P-C Bond Cleavage Reactions and Their Suppression via Complexation of Al3+ and Sc3

A revised synthesis of Martin's phosphino-triols (two derivatives) is reported. Once isolated, these thermally sensitive triols were shown to disassemble selectively via an unexpected P-C bond cleavage reaction. This degradation pathway was effectively suppressed via complexation of Al³⁺ and Sc³⁺. In the resulting half-cage complexes, the ligand scaffold is bound to each metal (Al³⁺ and Sc³⁺, respectively) via all four donor atoms. So far, this κ⁴-P,O,O',O″-coordination mode has not been observed for any other phosphino-triol.

Tantalum(iv) pyrazolate: new wine in the old wineskin

Homoleptic binuclear Ta(iv) pyrazolate [Ta₂(pz)₈] with Ta–Ta distance of 3.1895(7) Å was obtained in a reaction of Ta(NMe₂)₅ with unsubstituted pyrazole Hpz.

Synthesis and characterization of crystalline niobium and tantalum carbonyl complexes at room temperature

A variety of homoleptic transition metal carbonyl complexes are known as bulk compounds for group 7-12 metals. These metals typically feature a maximum of 6 CO ligands to form complexes with 18 valence electrons. In contrast, group 3-5 metals, with fewer valence electrons, have been shown to form highly coordinated heptacarbonyl and octacarbonyl complexes-although they were only identified by gas-phase mass spectrometry and/or matrix isolation spectroscopy work. Now we have prepared heptacarbonyl cations of niobium and tantalum as crystalline salts that are stable at room temperature. The [M(CO)₇]⁺ (M = Nb or Ta) complexes were formed by the oxidation of [M(CO)₆]^- with 2Ag⁺[Al(OR^F)₄]^- (R^F, C(CF₃)₃) under a CO atmosphere; their experimental characterization was supported by density functional theory calculations. Other unusual carbonyl compounds were also synthesized: two isostructural salts that contained the 84-valence-electron cluster cation [Ag₆{Nb(CO)₆}₄]²⁺, the piano-stool complexes [(1,2-F₂C₆H₄)M(CO)₄]⁺ and two polymorphs of neutral Ta₂(CO)₁₂ with a long, unsupported Ta-Ta bond.

C–F sp2 bond functionalization mediated by niobium complexes

The functionalization of fluorobenzene is described via insertion of isocyanide after the oxidative addition of the C–F bond.