Tantalum complexes phosphines

Green et al. observed that the tantalum complex 101 is converted into the bicyclic complex 109 after prolonged exposure to sodium and trimethyl-phosphine.930 Two phosphine ligands of 101 are easily displaced by butadiene, affording the complex 110, while treatment of 109 with dihydrogen leads to the reduction of the metallic center. In both cases, the metallacycle remains intact.930... 

Addition of other nucleophiles or Lewis bases to neopentyltantalum complexes also generated alkylidene complexes, as shown in Scheme 13.2. Addition of slightly less than one molar equivalent of bis(neopentyl)zinc to tantalum pentachloride generated bis(neopentyl) tantalum trichloride, and addition of thalium cyclopentadienide to this intermediate generated the Cp-ligated tantalum alkylidene. Addition of dative ligands, such as THE, and monodentate or bidentate phosphines to the bis(neopentyl)tantalum complex generated the octahedral alkylidenes in Scheme 13.2. ... 

Hadi GAA, Fromm K, Blaurock S, Jelonek S, Hey-Hawkins E (1997) Organometallic tantalum complexes with phosphine, phosphanido and phosphinidene ligands. Syntheses... 

Phosphinate complexes of tantalum have been used as fillers for special purpose high temperature laminates. They are polymeric species of the stoichiometry [Ta(0PPh20)2(0H)3] .33... 

The tantalum-benzyne complex (130) is much less reactive than other early transition-metal aryne complexes. It shows no reaction with acetone, benzophenone, benzaldehyde, acetonitrile, 3-hexyne, or methanol. The lack of reactivity of 130 was attributed to nonlability of the PMe3 ligand. Indeed, no phosphine exchange was observed when 130 was mixed with an excess of PMe3-d9. Refluxing 129 in a mixture of methanol and toluene (3 10 v/v) leads to clean formation of 131. This presumably results from reaction of a 16-electron benzyne complex with the alcohol. 

Protactinium pentachloride (42) and pentabromide (43) form both 1 1 and 1 2 complexes with phosphine oxides, the former being analogous to those formed by niobium, tantalum, and uranium pentahalides (26, 42, 43). Unlike niobium and tantalum pentachloride (42, 64) however, they do not react with excess triphenylphosphine oxide (TPPO) to form... 

O)] and [TaCl3(OSiMe3)Cp ]. Terry, however, would not be thwarted, and he switched from looking at high-valent routes to exploring the potential for low-valent precursors. He was subsequently able to show to our surprise that the half-sandwich tertiary phosphine tantalum(iii) complex, [TaCl2(PMe3)2Cp ]... 

In turn, the tantalum phosphine complex 3(Ta) gives dibridged structures ll(Ta), which are accompanied, in some cases, by small amounts of monobridged complexes. ... 

Niobium pentoxide, Nb20s, acts as a smoke retarder for poly(vinyl chloride) but is less effective than V2O5. Tantalum pentoxide is even more limited and is unlikely to find application. Phosphinate complexes of tantalum have been used as fillers for special purpose high temperature laminates. They are polymeric species of the stoichiometry [Ta(0PPh20)2(0H)3] . ... 

Addition of a phosphine to a tantalum-methyl-mesityl complex (below) also leads to Y-elimination rather than a-elimination, which yields methane and a dimethyl-benzylidene complex.The a-bond-metathesis mechanism can again take this y-elimination into account... 

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