Synthesis, characterization, and activity of yttrium(III) nitrate complexes bearing tripodal phosphine oxide and mixed phosphine-phosphine oxide ligands

摘要

A series of four tripodal phosphine oxide ligands, (OPR _2) _2CHCH _2POR _2 (1a-1d), and four mixed phosphine-phosphine oxide ligands, (OPR _2) _2CHCH _2PR _2 (3a-3d), were synthesized and coordinated to yttrium to produce Y(NO _3) _3[(OPR _2) _2CHCH _2POR _2] (2a-2d) and Y(NO _3) _3[(OPR _2) _2CHCH _2PR _2](OPPh _3) (4a-4d) complexes. The previously reported ligand 1a and unknown phosphine oxide ligands 1b-1d were generated in an unprecedented trisubstitution reaction of bromoacetaldehyde diethyl acetal, while the novel partially reduced ligands _3a-3d were synthesized from 1a-1d according to a known literature protocol for the selective monoreduction of bisphosphine oxides. The neutral yttrium complexes _2a-2d are nine-coordinate and display a tricapped trigonal-prismatic geometry. Complexes 4a-4d are also neutral, nine-coordinate species and have a pendant phosphine functionality, which provides the potential to form bimetallic early-late transition-metal complexes. Additionally, yttrium complexes _2a-2d were activated with base and tested for the ring-opening polymerization of ε-caprolactone, but the results showed that base by itself was significantly more effective than the yttrium species investigated.