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

Abstract

The (iminophosphoranyl)(thiophosphoranyl)methanide {CH(PPh2=NSiMe3)(PPh2=S)}(-) ligand has been used for the synthesis of divalent and trivalent rare-earth borohydride complexes. The salt metathesis of the potassium reagent [K{CH(PPh2=NSiMe3)(PPh2=S)}]2 with [Yb(BH4)2(THF)2] resulted in the divalent monoborohydride ytterbium complex [{CH(PPh2=NSiMe3)(PPh2=S)}Yb(BH4)(THF)2]. The 2D (31)P/(171)Yb HMQC-NMR spectrum clearly showed the coupling between both nuclei. The trivalent bisborohydrides [{CH(PPh2=NSiMe3)(PPh2=S)}Ln(BH4)2(THF)] (Ln = Y, Sm, Tb, Dy, Er, Yb and Lu) were obtained by reaction of [K{CH(PPh2=NSiMe3)(PPh2=S)}]2 with [Ln(BH4)3(THF)3]. All new compounds were characterized by single X-ray diffraction. The divalent and trivalent compounds were next used as initiators in the ring-opening polymerization (ROP) of ε-caprolactone (CL) and trimethylene carbonate (TMC). All complexes afforded a generally well-controlled ROP of both of these cyclic esters. High molar mass poly(ε-caprolactone) diols (Mn,NMR < 101,300 g mol(-1), ĐM = 1.44), and α,ω-dihydroxy and α-hydroxy,ω-formate telechelic poly(trimethylene carbonate)s (Mn,NMR < 20,000 g mol(-1), ĐM = 1.61) were thus synthesized under mild operating conditions.

η5–η1 Switch in Divalent Phosphaytterbocene Complexes with Neutral Iminophosphoranyl Pincer Ligands: Solid-State Structures and Solution NMR 1JYb–P Coupling Constants

“…One resonance is found at 29.4 ppm, a value that is very close to that found for the free ligand in thf- d 8 (δ P 25.6 ppm), and the other is found at 40.4 ppm and is attributed to the coordinated arm. This signal presents also additional satellites that are attributed to the 2 J Yb–P coupling with a value of 55.0 Hz, a value comparable to that obtained by Roesky et al in their iminophosphoranyl complexes of divalent ytterbium . This situation (at −80 °C) is in good agreement with that found in the solid state, which was described above.…”

“…This signal presents also additional satellites that are attributed to the 2 J Yb−P coupling with a value of 55.0 Hz, a value comparable to that obtained by Roesky et al in their iminophosphoranyl complexes of divalent ytterbium. 42 This situation (at −80 °C) is in good agreement with that found in the solid state, which was described above. Taken together, these data are in agreement with a fast dynamic exchange of the two iminophosphoranyl arms in solution, as shown in Scheme 1.…”

Yttrium Methanide and Methanediide Bis(silyl)amide Complexes

“…This likely results from the increased size of the N RR ligands in 4 and 5 , which give relatively long Y–N silylamide bond lengths (2.267(8) Å ( 4 ); 2.281(3) Å ( 5 )) and correspondingly shorter Y–C H‑BIPM distances. The latter interactions are longer than those normally found for yttrium complexes with H-BIPM; , however, similar distances have been previously observed for methanide heteroleptic Y­(H-BIPM)­(L) 2 compounds featuring relatively large donors, such as [Y­(H-BIPM)­{OC­(CH 2 SiMe 3 )­Ph 2 }­O­{(CPh 2 )­(OCPh)­C 6 H 4 }] (2.726(4) Å) . Comparatively, the Y–C cyclometalate interactions in 3 – 5 ( 3 , 2.404(6) Å; 4 , 2.394(10) Å; 5 , 2.352(6) Å) are all significantly shorter than their corresponding Y–C H‑BIPM bonds.…”

Rare Earth Starting Materials and Methodologies for Synthetic Chemistry

“…Divalent borohydrides have found application as salt metathesis precursors with various ligands, including BDIs ( 151-Ln ; Ln = Sm, Eu, Yb), bis-iminophosphorano-methanides, , tris-pyrazolylborate, substituted pyrrolyls, and cyclopentadienyls . Roesky and co-workers reacted K­(H-BIPM) with [Ln­(BH 4 ) 2 (THF) 2 ] (Ln = Eu, Yb) to give heteroleptic borohydride complexes of formula [Ln­(H-BIPM)­(BH 4 )­(THF) 2 ] ( 152-Ln ; Ln = Eu, Yb) (Scheme ).…”

“…442 Interestingly, the authors noted that comproportionation reaction between [Tm(BH 4 ) 3 (THF) 3 ] and Tm did not yield a reduced Tm(II) species. Divalent borohydrides have found application as salt metathesis precursors with various ligands, including BDIs (151-Ln; Ln = Sm, Eu, Yb), 443 bis-iminophosphoranomethanides, 441,444 tris-pyrazolylborate, 442 substituted pyrrolyls, 445 and cyclopentadienyls. 446 1959, but in their methodology they could only obtain partial conversion to mixed borohydride-chloride salts RE-(BH 4 ) 2 Cl.…”