Nonchelated Phosphoniomethylidene Complexes of Scandium and Lutetium

Abstract

The first phosphoniomethylidene complexes of scandium and lutetium, [LLn(CHPPh)X] (L = [MeC(NDIPP)CHC(NDIPP)Me]; Ln = Sc, X = Me, I, TfO; Ln = Lu, X = CHSiMe), have been synthesized and fully characterized. DFT calculations clearly demonstrate the presence of an allylic Ln, C, P π-type interaction in these complexes. X-ray diffraction indicates that the scandium iodide complex has the shortest Sc-C bond length to date (2.044(5) Å). These phosphoniomethylidene complexes readily convert into the ylide complexes, and the reactivity is affected by both X anion and Ln ion. The reaction of lutetium complex with imine shows a rapid insertion of imine into the Lu-C(alkylidene) bond. DFT calculations indicate that, although the bonding situation seems similar to that of the scandium analog, the strong negative charge at the alkylidene carbon is not sufficiently screened by one hydrogen in the lutetium complex because of a more ionic bonding, and therefore, the reactivity of the lutetium complex is much higher.

Potential Precursors for Terminal Methylidene Rare‐Earth‐Metal Complexes Supported by a Superbulky Tris(pyrazolyl)borato Ligand

“…Recent advances in the latter areas are represented by the syntheses of the first bridged bis-alkylidene scandium complex, [10] an on-pincer-type monometallic phosphinoalkylidene scandium complex, [11] and silyl-thiophosphinoyl alkylidene as well as phosphinomethylidener are-earth-metal compounds. [12] By nature, higher-valentt ransition-metal chemistry draws upon alternative approaches to access terminal alkylidenes. For example,i n2 017, Mindiola and co-workersi solated the first terminal titanium methylidene complex [(PN) 2 Ti(= CH 2 )] by treating [(PN) 2 Ti(CH 3 )(OTf)] (I,P N = (N-(2-(diisopropylphosphino)-4methylphenyl)-2,4,6-trimethylanilide)) with the Wittig reagent H 2 CPPh 3 .T his protocoli nvolves the abstraction of the weakly coordinating OTfg roup (OTf = trifluoromethanesulfonato, also triflato or SO 3 CF 3 )a nd formation of the reactive Ti=CH 2 moiety (Scheme 1, path A).…”

Are Sc—C and Sc—P Bonds Reactive in Scandium Phosphinoalkylidene Complex? Insights on a Versatile Reactivity

“…In 10 (Figure 3), the Sc-C36 bond length (2.148(5) Å) is longer than that in the phosphinoalkylidene complex 1 (2.089(3) Å), but much shorter than the Sc-C alkyl bond length (2.292(4) Å) in the phosphinoalkyl complex [LSc{CH(SiMe 3 )-PPh 2 }Me]; [7] the C36-P bond length (1.675(5) Å) is close to that in a reported scandium phosphoniomethylidene complex [{MeC-(NDIPP)CHC(NDIPP)Me}Sc(CHPPh 3 )Me] (1.673(2) Å). [12] In order to check the general aspect of this reactivity, the reaction of 1 with a conjugated enone, 2-cyclohexen-1-one, was carried out. A Sc-P 1,2-addition product 11 was obtained whereas no Sc-P 1,4-addition product was observed.…”

The high reactive site and the unusually short Sc‐C bond of the scandium phosphinoalkylidene complex, an explanation from first‐principles calculation

“…These novel RE metal complexes show rich chemical reactivity, for example activating alkene, nitrile, isonitrile, PhCHO, and so on . Among these complexes, the RE metal alkylidene/carbene complexes rose puzzling questions concerning the chemical bonding of Sc‐C for their unusually short Sc‐C bond lengths (2.044‐2.113 Å) as determined by X‐ray diffraction method . On the other hand, the high reactivity of the first scandium phosphinoalkylidene complex [L{ScC(SiMe 3 )PPh 2 }THF] (LScPT) with a new β‐diketiminato‐based bidentate nitrogen ligand (L = [MeC(NDIPP)CHC(NDIPP)Me]) is also interesting in synthetic chemistry because it can activate pyridine, 4‐dimethylamino pyridine, 1, 3‐dimethylpyrazole, and H 2 under mild conditions.…”

“…The earlier theoretical work focused on the possible reaction paths for the C‐H and H‐H bonds activation, while left the important high reactivity of LScPT and the unusually short Sc‐C bond unexplained. In addition, a three center π interaction between Sc, C, and P atoms was proposed for the HOMO without atomic orbital resolved quantitative analyses …”

“…[8,16] Among these complexes, the RE metal alkylidene/carbene complexes rose puzzling questions concerning the chemical bonding of Sc-C for their unusually short Sc-C bond lengths (2.044-2.113 Å) as determined by X-ray diffraction method. [17][18][19] On the other hand, the high reactivity of the first scandium phosphinoalkylidene complex [L{ScC(SiMe 3 )PPh 2 }THF] (LScPT) with a new β-diketiminato-based bidentate nitrogen ligand (L = [MeC(NDIPP)CHC (NDIPP)Me]) is also interesting in synthetic chemistry [18] because it can activate pyridine, 4-dimethylamino pyridine, 1, 3-dimethylpyrazole, and H 2 under mild conditions. The earlier theoretical work focused on the possible reaction paths for the C-H and H-H bonds activation, while left the important high reactivity of LScPT and the unusually short Sc-C bond unexplained.…”