Differing Reactivities of Zirconium and Titanium Alkoxides with Phenyl Isocyanate: An Experimental and Computational Study

Abstract

The insertion reaction of 1 and 2 equiv of PhNCO (2) into Ti(OnBu)4 (1aTi) and Zr(OnBu)4 (1aZr) results in the formation of a carbamate ligand (PhNCOOnBu) referred to as a monoinsertion ligand (MIL). Reaction of metal n-butoxide (1a) with more than 2 equiv of PhNCO leads to the competitive insertion of PhNCO into the M−N bond of metal carbamate or into the M−O bond of the alkoxide. The ligand formed by the insertion of PhNCO into a metal carbamate is an allophanate ligand (PhNCONPhCOOnBu), referred to as a double insertion ligand (DIL). The complexes containing these ligands were hydrolyzed, and the organic products 5 (from MIL) and 6 (from DIL) were spectroscopically characterized. The reactivity of Ti(OnBu)4 is very similar to the reactivity of Ti(OiPr)4 reported earlier by us. The formation of DIL over MIL is clearly favored in the case of Ti(OnBu)4, whereas the formation of DIL is less favored with Zr(OnBu)4. At −80 °C, Zr(OnBu)4 gives only MIL, and so only 5 is isolated on hydrolysis. In contrast, Ti...