Bis(alkyne) complexes of niobium(I), containing the alkyne as a three-electron donating ligand

Niobium and Tantalum

“…[CpNbCl(u-Cl)(CO) 2 ] 2 is also a precursor to an alkyne cyclotrimerization catalyst which cyclizes HC=CPh to form primarily l,3,5-C 6 H 3 Ph 3 . 57 406 Catalytic amounts of the niobium butadiene complexes of the type CpNb(butadiene)Cl 2 , CpNb(butadiene) 2 , and [CpNb(butadiene)(u-Cl)] 2 are reported to a f f o r d both 1 , 3 , 5 -and 1,2,4-C 6 Et 3 H 3 upon cyclizing EtC=CH. 477 Upon treatment o f NbCl 5 with alkynes, a cyclotrimerization catalyst is generated (in C C 1 4 ) after a long induction period which the authors proposed to be an Nb m alkyne complex.…”

Amine−Phenolate Ligands in Niobium Chemistry: π-Interactions Probed by an Ancillary Alkyne Ligand

“…The 13 C chemical shifts of the metal-bound alkyne carbons have been correlated to the electron donation ability of the alkyne. , Typically, δ > 200 is characteristic of “four-electron” (4e)-donor alkynes, 185 > δ > 165 describes formally (3e)-donor alkynes, whereas conventional (2e)-donor alkynes are characterized by δ ≈ 120. It must be emphasized that the formal (3e)-donor description strictly applies to bis(alkyne) complexes where there is no metal orbital of appropriate symmetry to interact with the symmetric linear combination of alkynes π ⊥ orbitals . Nonetheless, the chemical shifts for all isomers of 4a , b indicate competition between alkyne and phenoxy π-type orbitals for an available Nb d orbital, the phenoxy being a good π-donor.…”

Synthesis and structure of an alkyne-tetrabromoniobate(1-)

“…N (11) 4113( 13 -607 (7) 68(5) C( 24) 6338( 16) 8493 (10) -405 (8) 100 (7) Table II. Selected Bond Lengths and Bond Angles for Niobium is displaced out of this plane by 0.325(6) A toward the alkyne.…”