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Bis(phosphinimino)methanide Borohydride Complexes of the Rare‐Earth Elements as Initiators for the Ring‐Opening Polymerization of ε‐Caprolactone: Combined Experimental and Computational Investigations
Author(s) -
Jenter Jelena,
Roesky Peter W.,
Ajellal Noureddine,
Guillaume Sophie M.,
Susperregui Nicolas,
Maron Laurent
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200903107
Subject(s) - caprolactone , borohydride , polymerization , rare earth , ring opening polymerization , ring (chemistry) , polymer chemistry , chemistry , materials science , catalysis , organic chemistry , mineralogy , polymer
Rare‐earth‐metal borohydrides are known to be efficient catalysts for the polymerization of apolar and polar monomers. The bis‐borohydrides [{CH(PPh 2 NSiMe 3 ) 2 }La(BH 4 ) 2 (THF)] and [{CH(PPh 2 NSiMe 3 ) 2 }Ln(BH 4 ) 2 ] (Ln=Y, Lu) have been synthesized by two different synthetic routes. The lanthanum and the lutetium complexes were prepared from [Ln(BH 4 ) 3 (THF) 3 ] and K{CH(PPh 2 NSiMe 3 ) 2 }, whereas the yttrium analogue was obtained from in situ prepared [{CH(PPh 2 NSiMe 3 ) 2 }YCl 2 ] 2 and NaBH 4 . All new compounds were characterized by standard analytical/spectroscopic techniques, and the solid‐state structures were established by single‐crystal X‐ray diffraction. The ring‐opening polymerization (ROP) of ε‐caprolactone initiated by [{CH(PPh 2 NSiMe 3 ) 2 }La(BH 4 ) 2 (THF)] and [{CH(PPh 2 NSiMe 3 ) 2 }Ln(BH 4 ) 2 ] (Ln=Y, Lu) was studied. At 0 °C the molar mass distributions determined were the narrowest values ( M̄ w / M̄ n =1.06–1.11) ever obtained for the ROP of ε‐caprolactone initiated by rare‐earth‐metal borohydride species. DFT investigations of the reaction mechanism indicate that this type of complex reacts in an unprecedented manner with the first BH activation being achieved within two steps. This particularity has been attributed to the metallic fragment based on the natural bond order analysis.