Frustrated Lewis Pair Behavior of [Cp₂ZrOCR₂CH₂PPh₂]⁺ Cations

Abstract

Reactions of Cp 2 ZrMe 2 with 1 equiv of 2-diphenylphosphino-substituted alcohols Ph 2 PCH 2 CR 2 OH (R = H, CH 3 ) gave the neutral monomethyl zirconocene alkoxy complexes Cp 2 Zr(Me)OCR 2 CH 2 PPh 2 (7) by means of methane elimination. Treatment of the complexes 7 with the alkyl abstraction reagent [Ph 3 C] + [B(C 6 F 5 ) 4 ] − resulted in the formation of the cationic complexes 8. X-ray crystal structure analysis shows that 8a (R = H) is a doubly oxygen bridged dimer and 8b (R = CH 3 ) is a monomer with P−Zr coordination. Complexes 8 show some typical Zr + /P FLP reactivity. For example, complex 8a undergoes selective 1,4-addition to chalcone to produce the nine-membered metallacyclic product 13. Complex 8b reacts with benzaldehyde and an ynone reagent to form the respective Zr + /P addition products 14 and 15. Complex 8b also adds to the NO functionality of nitrosobenzene with formation of 20. Treatment of 8b with NO gave the six-membered metallaheterocycle 21 by oxidation of the phosphane. The reaction of compound 8b with 0.5 mol equiv of nitrobenzene afforded a mixture of complexes 20 and 21 in a 1:1 molar ratio.

Insertion Reactions of Neutral Phosphidozirconocene Complexes as a Convenient Entry into Frustrated Lewis Pair Territory

“…Regardless of the solution structure of 9a – 11a in coordinating solvents, such as [D 5 ]pyridine and [D 8 ]THF, their slow decomposition in CD 2 Cl 2 shows that they are probably in equilibrium with minute amounts of monomeric Zr + /P FLPs in this solvent (see below). Similar behaviour was observed for complex D , which exhibited typical FLP reactivity, despite its O‐bridged dimeric structure …”

“…However, the main feature is the presence of a weak interaction between Zr and P, as evidenced by the Zr−P distance of 2.876(1) Å . One of us recently reported a similar structure for {[Cp 2 Zr(OCH 2 CH 2 PPh 2 )][B(C 6 F 5 ) 4 ]} 2 ( D ); in this case, the Zr−P distance was found to be slightly longer at 2.956(1) Å . The sum of angles around O (ΣO ZrZrC 359.4°) indicates trigonal planar geometry and, as a result, C11, O1, Zr1, C11a, O1a and Zr1a are in the same plane.…”

“…In the meantime, frustrated Lewis pairs (FLPs) have emerged as a useful tool in small‐molecule activation and catalysis . Since the Lewis acidity of zirconocene cations is well known, their use in FLPs is a logical development; indeed a number of Zr + ‐based FLPs have now been reported, notably systems in which the Lewis base is a tertiary phosphane (Scheme ) –,…”

“…Until recently, intramolecular Zr + /P FLPs were synthesised by the following methods: 1) protonolysis of a Zr−Me bond with a functionalised phosphane followed by Zr + formation with a suitable electrophile [Scheme , Eq. (1)];–, or 2) insertion of a phosphaalkyne into the Zr−Me bond of a zirconocene cation [Scheme , Eq. (2)] ,,.…”

Early–Late Heterometallic Complexes of Gold and Zirconium: Photoluminescence and Reactivity

“…[31] In previous investigations,E rker et al showedt hat phosphines linked to aZ r IV centre via an alkoxide bridge are suitable candidates for frustrated Lewis pairs (FLPs), which can react with nitrobenzene or activate small molecules. [32] The synthesis of OH-functionalized phosphines is described in the literature and can be easily conducted on multigram scale through palladium-catalysed P-Cc oupling of iodophenolsa nd diphenylphosphine in dimethylacetamide (Scheme 1). [33][34][35] The synthesis of the metalloligands was achieved by the treatment of dimethyl zirconocene with [X-(diphenylphosphine)phenol] (X = 2, 3, 4) I, II,a nd III in toluene at room temperature.…”