[Cp2V] Migration along an Octatetrayne Chain: From the Monometallic Complex [Cp2V(3-4η-tBuC≡C−C2−C≡CC≡CtBu)] to the Dimetallic Complex [(Cp2V)2(1-2η:7-8η-tBuC2−C≡CC≡C−C2tBu)]
Abstract:The oxidative addition of one equivalent of [Cp2V] (4) to the tetrayne ligand tBuC triple bond CC triple bond CC triple bond CC triple bond CtBu (5) gives the monometallic complex [Cp2V(3-4eta-tBuC triple bond C-C2-C triple bond CC triple bond CtBu)] (7). Compound 7 reacts further with a second equivalent of [Cp2V] to give the dimetallic complex [(Cp2V)2(1-2eta:7-8eta-tBuC2-C triple bond CC triple bond C-C2tBu)] (8), which involves a shift of the first coordinated [Cp2V] unit from the internal C3-C4 to the ext… Show more
“…Choukroun and co-workers reported η 2 -vanadocene complexes of tetraynes. 4 They isolated 3 and 5 and determined their molecular structures (Scheme 2). They observed the transformation from 3 to 5 by addition of vanadocene and vice versa by adding one more equivalent of tetrayne.…”
Section: ■ Introductionmentioning
confidence: 99%
“…Choukroun and co-workers reported η 2 -vanadocene complexes of tetraynes . They isolated 3 and 5 and determined their molecular structures (Scheme ).…”
Zirconium complexes of some [5]cumulene derivatives were studied for their variable coordination modes and haptotropic shifts. Some [5]cumulene compounds reacted with zirconocene(II) species to afford 1-zirconacyclopent-3-yne complexes that have five-membered cycloalkyne structures. Only a few [5]cumulene compounds afforded η 2 -coordinated complexes in the presence of neutral ligands such as trimethylphosphine and tert-butyl isocyanide. Interconversion between the five-membered structure and the η 2 -complex was observed. Investigation of [5]cumulene derivatives of various cycloalkylidene moieties indicated that the η 2 -complex was preferred when the [5]cumulene has bulkier substituents. A [5]cumulene with 2,2,6,6-tetramethylcyclohexylidene groups much preferred the 1-zirconacyclopent-3-yne structure to η 2 -coordination. In sharp contrast, the η 2 -coordinated complex was favored for a [5]cumulene with 2,2,7,7-tetramethylcycloheptylidene groups in the presence of PMe 3 . Small differences in steric environments caused totally different reactivity in [5]cumulene complexes. DFT calculations on the formation enthalpy were consistent with the experimental results, although that cannot fully rationalize the difference.
“…Choukroun and co-workers reported η 2 -vanadocene complexes of tetraynes. 4 They isolated 3 and 5 and determined their molecular structures (Scheme 2). They observed the transformation from 3 to 5 by addition of vanadocene and vice versa by adding one more equivalent of tetrayne.…”
Section: ■ Introductionmentioning
confidence: 99%
“…Choukroun and co-workers reported η 2 -vanadocene complexes of tetraynes . They isolated 3 and 5 and determined their molecular structures (Scheme ).…”
Zirconium complexes of some [5]cumulene derivatives were studied for their variable coordination modes and haptotropic shifts. Some [5]cumulene compounds reacted with zirconocene(II) species to afford 1-zirconacyclopent-3-yne complexes that have five-membered cycloalkyne structures. Only a few [5]cumulene compounds afforded η 2 -coordinated complexes in the presence of neutral ligands such as trimethylphosphine and tert-butyl isocyanide. Interconversion between the five-membered structure and the η 2 -complex was observed. Investigation of [5]cumulene derivatives of various cycloalkylidene moieties indicated that the η 2 -complex was preferred when the [5]cumulene has bulkier substituents. A [5]cumulene with 2,2,6,6-tetramethylcyclohexylidene groups much preferred the 1-zirconacyclopent-3-yne structure to η 2 -coordination. In sharp contrast, the η 2 -coordinated complex was favored for a [5]cumulene with 2,2,7,7-tetramethylcycloheptylidene groups in the presence of PMe 3 . Small differences in steric environments caused totally different reactivity in [5]cumulene complexes. DFT calculations on the formation enthalpy were consistent with the experimental results, although that cannot fully rationalize the difference.
“…We conclude that magnetic ordering in the sample exists at this temperature. The ferromagnetism of 6 may arise from the planarity of the TCNQ molecule, which may serve as an adequate superexchange mediator between the orbitals of the two metallic ions. 7b, 4 Magnetic behavior for 6 recorded at 2 K (magnetization vs applied magnetic field). The inset represents an enlargement between −600 and +600 G and −15 and +15 emu mol -1 .…”
The TCNX ligands TCNE and TCNQ reacted in
toluene with Cp2V in the presence of B(C6F5)3 to yield,
depending on the stoichiometry, the divanadium(III) complexes
[(Cp2V)2{(C6F5)3B·(μ4-TCNX)·B(C6F5)3}] (X = Q (3), E (4))
or the vanadium(IV) dimers [Cp2V{(C6F5)3B·(μ4-TCNX)·B(C6F5)3}]2 (X = E (5), Q (6)), all containing [TCNX]2- ligands
σ-bonded to vanadium through a nitrile nitrogen, as revealed
by crystallographic (for 3−5) and magnetic studies (for 3−6).
“…As part of an ongoing study of vanadium complexes with various supporting ligand environments, − we recently described the synthesis and molecular structure of the new terminal imido complex [V(NAr)Cl 2 (NHMe 2 ) 2 ] (Ar = 2,6- i -Pr 2 C 6 H 3 ),10a one of the very few Cp-free vanadium(IV) terminal imido compounds that have been structurally characterized, ,, and we embarked on the coordination chemistry of these new compounds toward neutral N-donor ligands (pyridine, bipyridine, tmeda) 10b. In addition, early transition metal species in their high oxidation states containing phosphine ligands are uncommon, and consequently information on vanadium(IV) phosphine adducts are still scarce; as a typical example, a common feature of all reactions of VCl 4 with phosphines is reduction of vanadium from V(IV) to V(III) .…”
The reaction of the imido precursor [V(NAr)Cl(2)](n)() (1) (Ar = 2,6-i-Pr(2)C(6)H(3)) with 3 equiv of PMe(2)Ph yields the monomeric complex [V(=NAr)Cl(2)(PMe(2)Ph)(2)] (2). Reacting 1 with 1.5 equiv of dmpe or 1 equiv of dppm affords the dimeric complexes [V(=NAr)Cl(2)(dmpe)](2)(mu-P,P'-dmpe) (3) and [V(=NAr)Cl(2)(dppm)](2) (4), respectively. Complexes 2-4 have been fully characterized by spectroscopic methods, magnetism studies, and X-ray crystallography.
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