Homoleptic Phosphoraneiminato Complexes of Rare Earth Elements as Initiators for Ring-Opening Polymerization of Lactones

Abstract

As cyclopentadienide equivalents, the first homoleptic phosphoraneiminato complexes of rare earth elements with the very small coordination number four (see, for example, the ytterbium compound shown) are excellent initiators for the ring‐opening polymerization of lactones.

Ring-Opening Polymerization ofɛ-Caprolactone by Phosphorane Iminato and Cyclopentadienyl Complexes of Rare Earth Elements

“…[La 2 (NPPh 3 ) 4 (l-NPPh 3 ) 2 (l-THF)] [5] (1), [Yb(NPPh 3 ) 3 ] 2 [5] (2), and [Cp 3 Dy 2 (NPPh 3 ) 3 ] [8] (5) complexes were prepared under argon using Schlenk tube, vacuum line, and glove box techniques according to the reported procedures. [5,8] Complexes La(C 5 H 5 ) 3 (3) and Yb(C 5 H 5 ) 3 (4) were obtained from Aldrich and used as received.…”

“…[5,8] Complexes La(C 5 H 5 ) 3 (3) and Yb(C 5 H 5 ) 3 (4) were obtained from Aldrich and used as received.…”

“…The crystal structure of 5 is shown in Figure 4 which compares well to the crystal structure of 1 and 2. The molecular structure of 5 allows directly to compare the steric situation and the bonding [5] B) 2, [5] C) 3, [14] D) 4, [15] E) 5. [8] Table 3.…”

“…[4] We have introduced Ln complexes with phosphorane iminato (PI) ligands, which are of particular interest due to w-isolobal analogy of these PI ligands to g 5 -cyclopentadienyl (CP) ligands. [3,5,6] Homoleptic LnCP complexes have not been used as initiator for ROP of CL to the best of our knowledge but Evans et al reported on Sm(C 5 Me 5 ) 3 as initiator for ROP of CL. [7] Recently, we have reported on homoleptic di(tris(triphenylphosphorane iminato)lanthanum)-THF complex ([La 2 (NPPh 3 ) 4 (l-NPPh 3 ) 2 (l-THF)]) (1) and quasi-homoleptic tris(triphenylphosphorane iminato)ytterbium [Yb(NPPh 3 ) 3 ] 2 (2) complex as initiator for ROP of CL and compared these complexes briefly to corresponding CP complexes of lanthanum and ytterbium.…”

“…[7] Recently, we have reported on homoleptic di(tris(triphenylphosphorane iminato)lanthanum)-THF complex ([La 2 (NPPh 3 ) 4 (l-NPPh 3 ) 2 (l-THF)]) (1) and quasi-homoleptic tris(triphenylphosphorane iminato)ytterbium [Yb(NPPh 3 ) 3 ] 2 (2) complex as initiator for ROP of CL and compared these complexes briefly to corresponding CP complexes of lanthanum and ytterbium. [5] In this paper we wish to report in detail on the ROP of lactones using the complexes 1, 2 as initiators and for comparison on ROP of CL using corresponding CP complexes. In addition, we wish to report on ROP of lactones using heteroleptic dysprosium complexes with PI and CP ligands.…”