Cationic rare-earth metal bis(tetrahydridoborato) complexes: direct synthesis, structure and ring-opening polymerisation activity toward cyclic esters

Abstract

Rare-earth metal tris(borohydrides) [Ln(BH4)3(thf)3] (Ln = Y, La, Nd, Sm) are converted with one equivalent of the Brønsted acid [NEt3H]+[BPh4]- in thf into the monocationic bis(borohydride) complexes [Ln(BH4)2(thf)5]+[BPh4]-. They efficiently initiate the ring-opening polymerisation of epsilon-caprolactone.

Mixed Allyl Rare‐Earth Borohydride Complexes: Synthesis, Structure, and Application in (Co‐)Polymerization Catalysis of Cyclic Esters

“…However, the longer Y−B bond length revealed a likely dihapto terminal mode, as encountered in [Y(BH 4 ) 3 (thf) 3 ], which marks here a clear difference between the yttrium and lanthanum complexes. For both complexes, the borohydride groups are almost in trans position to each other, showing a nearly linear setup (B1‐La‐B2=172.4 and B1‐Y‐B2=173.2°), like in the homoleptic Y(BH 4 ) 3 , [Y(BH 4 ) 3 (thf) 3 ], and the cationic [Y(BH 4 ) 2 (thf) 5 ] + , despite the presence of the allyl ligand. In contrast, much tighter B1‐RE‐B2 angles were found in the bulky η 3 ‐supported −(NPCN), −(NCCCN), and −(NCN) monosubstituted bisborohydrido rare‐earth complexes.…”

Synthesis, Structures and Magnetic Properties of two Heteroleptic Dy3+ Borohydride Complexes

“…Whereas 1 is a cationic [Dy(THF) 5 (BH 4 ) 2 ] + complex, the electroneutrality being ensured by a [BPh 4 ] − moiety, [Dy( t Bu 4 Carb)(BH 4 ) 2 (THF)] 2 compound is neutral (Figure 1). 1 appears to be isostructural to the previously reported Y 3+ , La 3+ , Nd 3+ and Sm 3+ analogues [13b] . The coordination sphere of the Dy 3+ ion in 1 is composed by five THF in the equatorial plane and two κ 3 ‐borohydride in the apical positions.…”

Rationalizing the Reactivity of Mixed Allyl Rare-Earth Borohydride Complexes with DFT Studies

“…of Ph2CO to a THF-D8 solution of RE(BH4)2(C3H5)(THF)x (RE = La, Y, Sc), we found by 1 H NMR that benzophenone reacts exclusively with the RE-(allyl) moiety, leading to the corresponding allyldiphenylalkoxide compound (Scheme 2, path a). Furthermore, the addition of one equivalent of substituted cyclopentadiene (C5Me4RH, R = H or Et) to Nd(BH4)2(C3H5)(THF)x afforded the immediate formation of the corresponding halfsandwich of the formula (C5Me4R)Nd(BH4)2 (Scheme 2, path b) [24], as unambiguously observed by 1 [25,26]. These two latter examples show that the allyl group is also more reactive than the borohydride one toward protic reagents.…”