Ta-X bonds

The broken bonds (boldface=dissociated atom) BDEs (boldface = recommended data reference in parentheses) Methods (reference in  

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The reactivity of a remarkable electronically unsaturated tantalum methyli-dene complex, [p-MeCgH4C(NSiMe3)2]2Ta( = CH2)CH3, has been investigated. Electrophilic addition and olefination reactions of the Ta = CH2 functionality were reported. The alkylidene complex participates in group-transfer reactions not observed in sterically similar but electronically saturated analogs. Reactions with substrates containing unsaturated C-X (X = C, N, O) bonds yield [Ta] = X compounds and vinylated organic products. Scheme 117 shows the reaction with pyridine N-oxide, which leads to formation of a tantalum 0x0 complex. ... 

The data for these compounds can be found in Tables 27 and 28 173). The frequencies for TI3MX4, where M is V, Nb or Ta and X is S or Se, can readily be taken from Table 22. In every case the chalcogen-metal vibrations are markedly decreased. The compounds such as CU3MX4 where M is V, Nb or Ta and X is S or Se form a three dimensional crosslinked network due to strong Cu—X bonding. The coppermetaUates crystallize in the sulvanite form. 

Alkilidine tantalum complexes have also been utilized for the preparation of ni-trido Tav. Reaction of ammonia with 31 or 32 afforded nitride 33 in moderate yields [14]. The structure of 33 has been determined by single-crystal X-ray crystallography and shown to consist of a pentameric complex, as depicted in Eq. (9). All of the Ta-N bond lengths are equivalent (2.00 A), suggesting a structure with extensive delocalization of the multiple bonds. 

A mononuclear tantalum-benzyne complex (121) has been prepared by thermolysis of 120 [Eq. (20)].14 An X-ray crystal structure was reported for 121. Bond lengths for the benzyne unit are given in Table III. Complex 121 exhibits a rich insertion chemistry similar to that of Ti, Zr, and Ru benzyne complexes. Insertion reactions of 121 with ethylene, 2-butyne, acetonitrile, and carbon dioxide give 122, 123, 124, and 125, respectively (Scheme 15). Diphenylacetylene does not couple with 121, presumably because of steric constraints. Reagents with acidic protons such as methanol or terminal alkynes cleave the Ta—C bond to give butyl isocyanide and carbon monoxide, but... 

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