Soluble Ring-Unsubstituted Phthalocyanine Zirconium(IV) and Niobium(V) cis-Alkoxides and Their Catalytic Activity Toward the Ring-Opening Polymerization of rac-Lactide.

A series of soluble ring-unsubstituted early-transition metallophthalocyanine (PcM) alkoxides with zirconium(IV) and niobium(V) metal centers was prepared via salt metathesis with PcM chlorides and a range of lithium or sodium alkoxides (NaOMe, NaOEt, LiOiPr, and NaOtBu); several examples were structurally characterized. Given their large ionic size, the metal centers protrude out of the Pc cavity, engendering cis-axial ligation of the alkoxides and thereby generating substantially improved solubility relative to the starting PcM chlorides. Seven-coordinate PcM(OR)3-type coordination spheres were typically observed, with lithium- or sodium-balanced "ate" species PcZr(OiPr)3Li(THF) and PcZr(OtBu)3Na(THF) isolated for PcZr(IV), compared to the neutral PcNb(OiPr)3. With the highly steric R = tBu the neutral six-coordinate PcZr(OtBu)2 was also structurally characterized. The catalytic activity of the PcZr(IV) and PcNb(V) alkoxides was probed toward the ring-opening polymerization (ROP) of rac-lactide, with PcZr(OiPr)3Li(THF) being the most active, while the PcNb(V) systems were either inactive or yielded oligomers.