β-Diketiminate Rare Earth Borohydride Complexes: Synthesis, Structure, and Catalytic Activity in the Ring-Opening Polymerization of ε-Caprolactone and Trimethylene Carbonate

Abstract

International audienceThe synthesis of a series of divalent and trivalent β-diketiminate borohydrides [(dipp)2NacNacLn(BH4)(THF)2] ((dipp)2NacNac = (2,6-C6H3iPr2)NC(Me)CHC(Me)N(2,6-C6H3iPr2); Ln = Sm, Eu, Yb) and [(dipp)2NacNacLn(BH4)2(THF)] (Ln = Sc, Sm, Dy, Yb, Lu) is reported. All compounds were obtained by salt metathesis in THF from [(dipp)2NacNacK] and the corresponding homoleptic divalent and trivalent borohydrides [Ln(BH4)2(THF)2] (Ln = Sm, Eu, Yb), [Sc(BH4)3(THF)2], and [Ln(BH4)3(THF)3] (Ln = Sm, Dy, Yb, Lu), respectively. The complexes were fully characterized, and their solid-state structures were established by single-crystal X-ray diffraction. In both the divalent and trivalent compounds, the BH4– groups coordinate in a κ3(H) mode to the metal. Only in the lutetium complex [(dipp)2NacNacLu(BH4)2(THF)] does one BH4– group coordinate in a κ3(H) mode, whereas the other one coordinates as κ2(H). This kind of mixed κ2/κ3(H) coordination mode is rare. The application of the divalent and trivalent compounds as initiators in the ring-opening polymerization (ROP) of ε-caprolactone (CL) and trimethylene carbonate (TMC) was investigated. All complexes afforded a generally well-controlled ROP of both of these cyclic esters. High molar mass poly(ε-caprolactone) diols (Mn,NMR < 92 700 g mol–1, ĐM = 1.51) and α-hydroxy,ω-formate telechelic poly(trimethylene carbonate)s (Mn,NMR < 16 000 g mol–1, ĐM = 1.59) were thus synthesized under mild operating conditions

(Iminophosphoranyl)(thiophosphoranyl)methane rare-earth borohydride complexes: synthesis, structures and polymerization catalysis

“…In contrast to the polymerization of CL (Table 2), quantitative TMC consumption was not reached within 10-30 min (Table 3), but rather in 120 min (entry 5). 66 As previously reported, 66 (Table 2), a trend common in the ROP of these two classes of cyclic esters, namely lactones and carbonates 63 and suggesting undesirable transcarbonatation reactions, which are also often encountered in the ROP of cyclic carbonates. In these experiments, the theoretical molar mass values have been calculated from the initial concentration in rare-earth complexes assuming one growing polymer chain for each BH 4 − unit, i.e.…”

Mono‐ and Dinuclear Rare‐Earth Chlorides Ligated by a Mesityl‐Substituted β‐Diketiminate

“…In recent years, increasing attention has been paid to the monoanionic β‐diketiminato or “nacnac” ancillary ligands R′NC(R)CHC(R)NR′ in coordination and organometallic chemistry of main‐group and transition metals, as well as of rare‐earth elements . The application of β‐diketiminates as an isoelectronic alternative to cyclopentadienyl ligands for supporting lanthanides is caused by a number of attractive features of nacnac.…”

“…A broad range of lanthanide complexes of general formula LLnX 2 supported by the β‐diketiminato ligands has been reported . N ‐Aryl‐substituted nacnac ligands ArNC(Me)CHC(Me)NAr are easily prepared on a large scale starting from commercially available reagents.…”

“…N ‐Aryl‐substituted nacnac ligands ArNC(Me)CHC(Me)NAr are easily prepared on a large scale starting from commercially available reagents. Mainly, the derivative with Ar = 2,6‐ i Pr 2 C 6 H 3 has been used for the preparation of a large variety of rare‐earth metal compounds . Other β‐diketiminato ligands of this class remain less explored.…”

High activity of an indium alkoxide complex toward ring opening polymerization of cyclic esters

“…Similarly to the phosphinimine indium chloride analogue previously reported by us, 22 a long In-Fe distance (3.98 Å) and a staggered configuration of the Cp rings were apparent. Elongation of the In-heteroatom distances compared to other compounds, such as (salen)InCl (salen = N,N ' -bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine (rac-or (R,R)-H2(ONNO))) 9 and (phosfen)In(OPh) (phosfen = 1,1'-di(2-tert-butyl-6-diphenylphosphiniminophenoxy)ferrocene), 22 30 and organocatalysts. 29 The polymerization of ε-caprolactone was particularly impressive.…”