Relative Reactivity of the Metal−Amido versus Metal−Imido Bond in Linked Cp-Amido and Half-Sandwich Complexes of Vanadium

Abstract

Treatment of (η5-C5H4C2H4NR)V(N-t-Bu)Me (R = Me, i-Pr) and CpV(N-p-Tol)(N-i-Pr2)Me (Cp = η5-C5H5) with B(C6F5)3 or [Ph3C][B(C6F5)4] results in formation of the corresponding cations, [(η5-C5H4C2H4NR)V(N-t-Bu)]+ and [CpV(N-p-Tol)(N-i-Pr2)]+. The latter could also be generated as its N,N-dimethylaniline adduct by treatment of the methyl complex with [PhNMe2H][BAr4] (Ar = Ph, C6F5). Instead, the analogous reaction with the linked Cp-amido precursor results in protonation of the imido-nitrogen atom. Sequential cyclometalation of the amide substituents gave cationic imine complexes [(η5-C5H4C2H4NCR′2)V(NH-t-Bu)]+ (R′ = H, Me) and methane. Reaction of cationic [(η5-C5H4C2H4NR)V(N-t-Bu)]+ with olefins affords the corresponding olefin adducts, whereas treatment with 1 or 2 equiv of 2-butyne results in insertion of the alkyne into the vanadium−nitrogen single bond, affording the mono- and bis-insertion products [(η5-C5H4C2H4N(i-Pr)C2Me2)V(N-t-Bu)]+ and [(η5-C5H4C2H4N(i-Pr)C4Me4)V(N-t-Bu)]+. The same reaction with the half-sandwich compound [CpV(N-p-Tol)(N-i-Pr2)]+ results in a paramagnetic compound that, upon alcoholysis, affords sec-butylidene-p-tolylamine, suggesting an initial [2+2] cycloaddition reaction. The difference in reactivity between the V−N bond versus the VN bond was further studied using computational methods. Results were compared to the isoelectronic titanium system CpTi(NH)(NH2). These studies indicate that the kinetic product in each system is derived from a [2+2] cycloaddition reaction. For titanium, this was found as the thermodynamic product as well, whereas the insertion reaction was found to be thermodynamically more favorable in the case of vanadium.

Ligand assisted carbon dioxide activation and hydrogenation using molybdenum and tungsten amides

“…26 Hessen and coworkers demonstrated an example of a thermodynamically favored insertion of alkynes into the V-amide bond of cationic amido imido vanadium complexes rather than a 2 + 2 cycloaddition reaction. 27 Therefore, an insertion reaction of CO 2 across the M-amide bond could alternatively be envisaged. Nevertheless, this CO 2 activation product is unique in its structure and is therefore in its way of formation presumed to be distinct from the insertion reactions of early transition M-N bonds.…”

Organoaluminum-Assisted Formation of Rare-Earth Metal Imide Complexes

“…Metal imido (MNR) moieties engage in a multitude of chemical transformations, as evidenced for C–H bond activation, metathesis of carbonyl and carbodiimide functionalities, catalytic imine metathesis, hydroamination of alkynes, and metallacycle formation with alkenes and alkynes. , Moreover, imido ligands were utilized as ancillaries in transition metal alkylidene complexes to promote stereoselective olefin metathesis and polymerization . In contrast to the numerous examples of transition metal and actinide imide complexes, lanthanide congeners remained scarce (Chart : A – H feature lanthanide imide complexes structurally authenticated by X-ray crystallography along with the synthesis protocols) .…”

Vanadium, niobium and tantalum

“…[CpV(dmpe)SiHPh 2 ] and [CpV(dmpe)SiH 2 Mes] were synthesised. 43 45 The N,N-dimethylaniline adducts of the cations were also synthesised. Alkenes bind reversibly to the cations with measureable equilibrium constants.…”

“…75 [CpV(N-pTol)(N i Pr)][MeB(C 6 F 5 ) 3 ] was used as a hydroamination catalyst. 45 V(salen) complexes derived from C 2 -and C 1 -symmetric diamines were used for the synthesis of asymmetric cyanohydrins. 76 Chiral V(salen) complexes were also utilised in the enantioselective cyanoformylation of aldehydes.…”