Iodo- and hydridotantalum(III) complexes of dialkylacetylenes

Niobocene Alkyne Complexes: Synthesis and Characterization of Neutral and Cationic d2Metal Alkyne Derivatives. X-ray Crystal Structure of [Nb(η5-C5H4SiMe3)2(η2(C,C)-HC⋮CPh)(CH2Ph)]

“…The ORTEP drawing of 11e is given in Figure , and selected bond lengths and angles are presented in Table . The structure is typical of bent metallocenes and is closely related to those reported earlier for niobocene alkyne complexes. 2e,f,4a The alkyne unit adopts an exo conformation with respect to the benzyl group, and this is the only isomer formed in the synthesis of this compound. The exo geometry for some of the other nonsymmetrical alkyl−alkyne complexes was assigned by NOE studies ( 9e and 12e , see Experimental Section).…”

“…The structure showed that the alkyne unit adopts an endo configuration with respect to the nitrile ligand (the methoxycarbonyl group is in a cis disposition with respect to the acetonitrile ligand). The angles and the bond distance of the alkyne carbon atoms shows them to be almost sp 2 -hybridized, the distance being slightly shorter than in a typical carbon−carbon double bond. 2e,f,4a Both crystallographic and 13 C NMR data (vide supra) indicate that the alkyne ligand in the cationic niobocene complexes behaves as a two-electron ligand …”

Successive Insertion of Alkynes into a Tantalum−Alkynyl Bond: Implications for the Coordination Polymerization of Alkynes

“…The choice of ancillary ligand system (L n ) for complexes of type A is critical since metallacyclopentadiene compounds can result from the coupling of alkynes, impeding the coordination insertion process. For instance, η 2 -alkyne complexes are obtained with bis(cyclopentadienyl) templates (e.g., Cp 2 Ta(η 2 -RC⋮CR)X) − and mono(pentamethylcyclopentadienyl) ligation (e.g., Cp * Ta(η 2 -RC⋮CR)X 2 ), − while less coordinatively saturating alkoxide ligands yield metallacycles (e.g., (DIPP) 3 Ta(C 4 Et 4 ), DIPP = 2,6-diisopropylphenoxide) …”

New Niobocene Alkyne Complexes: Synthesis and Characterization of Neutral and Cationic Niobium Complexes with Functionalized Alkynes. X-ray Crystal Structure of [Nb(η5-C5H4SiMe3)2(Cl)(η2(C,C)-R1C⋮CR2)] (R1= C⋮CPh, R2= Ph (2b); R1= CH2CHC(CH3)2, R2= Ph (3b))

“…However, the alkylation of diyne− and enyne−niobocene complexes does not always lead to the expected alkyl complexes, and instead, a mixture of intractable products is sometimes observed (for instance, this occurs in the reaction of 3a with Mg(CH 3 ) 2 and in the reactions of both 2a and 3b with Mg(CH 2 Ph) 2 (THF) 2 ). Some niobocene alkyl−alkyne complexes have previously been synthesized. 2f,4f …”

“…The chemistry of d-block transition metals with alkyne ligands has been well-documented . However, while η 2 -alkyne compounds of group 6 metals are extensively known, the range of alkyne complexes of group 5 metals is much less developed and, in the majority of the complexes described, cyclopentadienyl or aryloxide ligands are also present . Certain niobium or tantalum complexes enable the polymerization and cyclization of alkynes, and hence it is important to prepare and study the reactivity of new alkyne-containing complexes of these metals in order to better understand the mechanisms involved in such processes, especially as alkyne complexes of low oxidation state are likely to be intermediates.…”