1048985-04-1Relevant articles and documents
Relative reactivity of the metal - Amido versus metal - Imido bond in linked Cp-amido and half-sandwich complexes of vanadium
Bouwkamp, Marco W.,Batinas, Aurora A.,Witte, Peter T.,Hubregtse, Ton,Dam, Jeroen,Meetsma, Auke,Teuben, Jan H.,Hessen, Bart
, p. 4071 - 4082 (2009/02/06)
Treatment of (η5-C5H4C 2H4NR)V(N-te-Bu)Me (R = Me, i-Pr) and C pV(N-p-Tol)(N-/-Pr2)Me (Cp = η5-C 5H5) with B(C6F5)3 or [Ph3C][B(C6F5)4] results in formation of the corresponding cations, [(η5-C5H 4C2H4NR)V(N-NBu)+ 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, C6F 5). Instead, the analogous reaction with the linked Cp-amido precursor results in protonation of the imidonitrogen atom. Sequential cyclometalation of the amide substituents gave cationic imine complexes [(η5- C5H4C2H 4NCR′2)V(NH-i-Bu)]+ (R′ = H, Me) and methane. Reaction of cationic [(η5-C5H 4C2H4NR)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 monoand bis-insertion products [(η5-C 5H4C2H4N(i-Pr)C2 Me 2)V(N-t-Bu)]+)and [(η5-C5H 4C2H4N(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.
