| Description: |
A series of lanthanide monoborohydrido complexes {C 6 H 4 ‐1,2‐[NC(R)NR′] 2 }Ln(BH 4 )(L) n (Ln = Y, Nd, Sm; R = t Bu, Ph; R′ = 2,6‐Me 2 C 6 H 3 , SiMe 3 ; L = dme = dimethoxyethane, n = 1; L = thf, n = 2), in which lanthanides are coordinated by bulky ansa ‐bis(amidinato) ligand systems with a conformationally rigid o ‐phenylene linker ({C 6 H 4 ‐1,2‐[NC(R)NR′] 2 } 2– ), were synthesized by the salt metathesis reactions of equimolar amounts of Ln(BH 4 ) 3 (thf) 3 and {C 6 H 4 ‐1,2‐[NC(R)NR′] 2 }X 2 (thf) n (X = Li, Na) in thf. X‐ray diffraction studies revealed that the complexes are monomeric. Depending on the denticity of the donor ligand (L = dme or thf), the terminal borohydrido ligand coordinated to the metal ion can be located in either an equatorial (L = thf) or an apical (L = dme) position. All complexes are efficient catalysts for the ring‐opening polymerization of rac ‐lactide, which allows to convert up to 1000 equiv. of monomer into a polymer at room temperature within 10–150 min and affords atactic polylactides with high molecular weights and moderate molecular‐weight distributions (1.28–2.16). Yttrium–borohydrido complexes coordinated by the {C 6 H 4 ‐1,2‐[NC( t Bu)N(2,6‐Me 2 C 6 H 3 )] 2 } 2– ligand system showed enhanced catalytic activity compared to that of the analogue complexes containing the {C 6 H 4 ‐1,2‐[NC(Ph)NSiMe 3 ] 2 } 2– ligand. The obtained borohydrido complexes catalyze the hydrophosphonylation of benzaldehyde at room temperature with good reaction rates. |