On the insertion processes of unsaturated molecules into the Nb–X σ-bond of moieties (Cp′=η5-C5H4SiMe3; X=H, C, P)

Unusual Mechanism for the Reaction of a Niobocene Hydride Complex with Activated Alkynes. Experimental and DFT Studies

“…Reaction of Activated Alkynes with [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (H)(P(OMe) 3 )]. The complex [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (H)(P(OMe) 3 )] 6 (1) reacts with the electrophilic alkynes RO 2 CCCCO 2 R (R = Me, t Bu) to afford the corresponding alkenyl-containing species [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (C(CO 2 R)C(CO 2 R)H)(P(OMe) 3 …”

“…10 Concluding Remarks. The synthesis of new phosphitecontaining niobocene (E)-alkenyl complexes [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (C(CO 2 R)C(CO 2 R)H)(P(OMe) 3 )] (2) is described, where two parallel synperiplanar (2a sp ) or parallel antiperiplanar (2a ap ) conformers are possible. In the particular case of 2b (R = t Bu) interconversion between the two conformers is not observed.…”

“…In fact, a few years ago it was shown that, when an electron-rich ligand with one lone pair is present in some niobocene complexes, this type of attack was responsible for the interaction with the activated alkyne species, thus allowing the isolation of phosphorus alkenyl complexes (Scheme 2). 5 As a continuation of our studies on the complexes [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (H)(L)] (L = π-acid ligand), we report here the reaction of [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (H)(P(OMe) 3 )] with two activated alkynes. The results of DFT studies established that the nucleophilic attack of the niobium center on the CC bond promotes the formation of the final alkenyl-containing niobocenes 2.…”

Chemistry of CS2- and SCNPh-adducts of the pyramidal phosphinidene-bridged complex [Mo2Cp(μ–κ1:κ1,η5-PC5H4)(CO)2(η6-HMes*)(PMe3)]

“…2i, 9,10 In the case of 1, this event is unlikely to be occurring in a single step. Because of the strong nucleophilicity of 1 already noted, 8 it is more sensible to assume that these reactions are started by the nucleophilic attack of the P atom to the electrophilic carbon atom of the added organic molecule, to give an intermediate I1 with the newly formed PC bond placed in the Mo 2 P plane, according to the frontier orbitals of 1 (Scheme 2).…”

“…Methylation at the P site occurs preferentially when using a mild reagent as MeI; this reaction actually takes place rapidly at room temperature to give the phosphanyldithioformato derivative [Mo 2 Cp{- (9) in 80% yield. As expected, compound 9 was also obtained when reacting either 6a or 7a with the above oxonium salt (Scheme 4).…”