CO₂ Insertion Chemistry as a Probe of Organosamarium Allyl Reactivity

Abstract

CO2 reacts with (C5Me5)2Sm(η3-CH2CHCH2), 1, in toluene at room temperature and with (C5Me5)2Sm(η3-CH2CHCHR) (R = Me (2), Et (3)) in toluene at −78 °C to form [(C5Me5)2Sm(μ-O2CCH2CHCHR)]2 (R = H (4), Me (5) Et (6)) in >90% yield. In THF, 4−6 exist as solvated monometallic species, (C5Me5)2Sm(μ2-O2CCH2CHCHR)(THF). Crystallization of 4 from hexanes gives a bimetallic complex which contains an eight membered ring. CS2 reacts with 1 to form (C5Me5)2Sm(η2-S2CCH2CHCH2), 7, which isomerizes to (C5Me5)2Sm(η2-S2CCHCHCH3), 8, in less than 48 h. COS reacts with 1 to form (C5Me5)2Sm(η2-OSCCH2CHCH2), 9. Both 8 and 9 exist as monometallic species in THF, benzene, and toluene. Crystallization of 8 from toluene/phthalan gives a monometallic structure which contains a four-membered ring. CO2 also reacts with (C5Me5)2Sm(C6H5) in toluene to form [(C5Me5)2Sm(μ-O2CC6H5)]2, 10, which is dimeric in toluene and exists as a solvated monomer in THF. 10 can also be made by the reduction of benzoic acid by (C5Me5)2Sm(THF)2 in THF. Similarly, reduction of terephthalic acid with 2 equiv of (C5Me5)2Sm(THF)2 produces [(C5Me5)2Sm(THF)]2[μ-η2,η2-(O2C)2C6H4], 11, which contains a single bridging [(O2C)2C6H4]2- unit and two four-membered rings. X-ray crystal structures were obtained for 4, 8, 10, and 11.

Synthesis and structure of samarium benzyl complex supported by bridged bis(guanidinate) ligand and its reactivity toward nitriles and phenyl isocyanate

“…The benzyl ligand adopts an h 1 -coordination mode. The bond angle of C(25)eC(24)eSm(1) is 136.8 (7) , which is comparable with that in (C 5 Me 5 ) 2 Sm(h 1 -CH 2 C 6 H 5 )(THF) [36] but much larger than those found in the complexes with a h 3 -or a h 2 -benzyl group: {(Me 3 Si) 2 NC(NCy) 2 } 2 Ln(h 3 -CH 2 C 6 H 5 ) (Cy ¼ C 6 H 11 ) [37] and {HC-(MeCNAr) 2 }La(h 2 -CH 2 C 6 H 5 ) 2 (THF) (Ar ¼ 2,6-iPr 2 C 6 H 3 ) [38]. The distance of Sm(1)/C(25) is 3.687(8) A, indicative of no interaction between Sm(1) and C (25).…”

Reactivity of Bulky Formamidinatosamarium(II or III) Complexes with C═O and C═S Bonds

“…These values are somewhat shorter than those of related [Cp* 2 Sm-(κ(S,S′)-S 2 CCHCHCH 3 )] (S−C bond lengths, 1.693(13) and 1.703(12) Å). 39 As obtained from XRD data of good quality (Table 1) present structure, electron delocalization in the S1C1S2 and S3C2S4 units is clear and S2−C2 is a single bond. However, the overall pattern of bond lengths in both structures is the same, and in particular the Sm−S distance in the Sm−C(S) chelate is shorter than those of the Sm−S 2 chelate (Figure 3).…”

On the Initiation Mechanism of Syndiospecific Styrene Polymerization Catalyzed by Single‐Component ansa‐Lanthanidocenes

“…Another interesting finding of this computational study is that, in all cases, insertion of styrene proceeds directly in the h 3 -coordinated allyl group; in other words, there is no need for an h 3 to h 1 haptotropic change in coordination, as might have been hypothesized. [28] Also, the up/ down orientation of the monomer during the insertion reaction has been underlined, with the styrene phenyl ring pointing (down) toward the Cp' ligand found at the DFT level to be the most thermodynamically and kinetically favorable one. The dramatic influence of the nature of the ancillary ligand bridge and of the "active" R (allyl or alkyl) group on the initiation process of styrene polymerization catalyzed by such ansa-lanthanidocene systems has been highlighted and rationalized.…”