Niobium(III) monocyclopentadienyl isocyanide, acetylene, and diene complexes. X-ray crystal structures of Nb(.eta.5-C5Me5)Cl4(CN-2,6-Me2C6H3) and Nb(.eta.5-C5Me5)Cl2(CN-2,6-Me2C6H3)3.1/2MeC6H5

New Bis(silyl)cyclopentadienidoniobium and ‐tantalum Complexes:X‐ray Crystal Structures of [NbCp∧Cl4] and [NbCp∧Cl4(CNAr)][Cp∧ = η5‐C5H3(SiClMe2)(SiMe3); Ar = 2,6‐Me2C6H3]

“…The Cp∧ ring is bound to the niobium atom in a nearly symmetric η 5 ‐fashion with the distance between the metal and the centroid of the ring being 2.137 Å and with the two silicon atoms of the substituents Si(6) and Si(7) located 0.31 Å above the ring plane. The isocyanide ligand is linearly bound to the niobium atom, the values of the Nb–C(6) bond length and of the Nb–C(6)–N(1) and C(6)–N(1)–C(7) angles being 2.215(13) Å and 176.3(11)° and 175.2(13)°, respectively; the length of the N(1)–C(6) bond [1.192(15) Å] is in agreement with a triple bond 6,13. The coordination around the niobium atom is completed by four chlorine atoms with Nb–Cl bond lengths ranging from 2.412(3) to 2.442(3) Å.…”

Synthesis and Reactivity of Oxametallacyclic Niobium Compounds by Using α,β‐Unsaturated Carbonyl Ligands

“…[7,11,17] The MMA and MO ligands presented a supine coordination as expected for the disposition of the five-membered metallacycle folded through the O-C(1) vector, with a dihedral angle of about 103°, as in related oxametallacyclic tantalum compounds. A comparison of the O-C and C-C bond lengths of the coordinated MMA and MO ligands in complexes 1a, 2a, and 2c with the corresponding average bond lengths of vinyl ether and α,β-unsaturated carbonyl compounds (Table 1) [18] showed that the O-C and the internal C-C bond values are closer to a vinyl ether disposition (metallacycle), mainly for derivatives 1a and 2c, whereas the C(1)-C(2) bond lengths present values intermediate between these two situations.…”

“…The reduction of the niobium compound [NbCp*Cl 4 ] in toluene with Na/Hg amalgam in the presence of MMA has been reported previously, [7] and we have applied this method using the α,β-unsaturated carbonyl compounds CH 2 . The whole process can be considered as a reduction of the metal center followed by the oxidative coupling of the α,β-unsaturated carbonyl ligand.…”

“…induces an important modification on the butadiene ligand. [6][7][8][9][10][11] Functionalization with one oxygen atom provides an oxametallacyclic system, which consists of a cyclic enolate ligand. The study of enolate derivatives has attracted attention because they have been proposed as the active species for polymerization of polar monomers.…”

Insertion of Isocyanide into Metal−Carbon Bonds of Alkylchloro(pentamethylcyclopentadienyl)niobium- and -tantalum Complexes − X-ray Structure of [TaCp*Cl2(CH2CMe2Ph){η2-C(CH2CMe2Ph)=N(2,6-Me2C6H3)}] and Unexpected Decomposition of Alkyldichloro(η2-iminoacyl) Complexes of Tantalum

“…of isocyanide, a different sequence of reactions occurred leading to the diamagnetic pseudooctahedral niobium(III) complex NbCp*Cl 2 (CN-2,6-Me 2 C 6 H 3 ) 3 . We have isolated this complex previously [18] by reducing NbCp*Cl 4 with 2 equiv. of Na/Hg in the presence of a stoichiometric amount of isocyanide.…”