Organometallic chemistry of group 4 metals containing nitrogen ligands

Cesar H. A Zambrano, Purdue University

Abstract

The room-temperature carbonylation (600-1000 psi) of solutions containing (ArO)$\sb2$-MR$\sb2,$ (ArO = 2,6-di-tert-butylphenoxide; M=Zr, Hf; R = methyl, benzyl) in the presence of pyridines (1 equiv.) leads to the formation of a series of $\alpha,\alpha\sp\prime$-disubstituted-2,6-pyridinedimethoxide compounds of formula (ArO)$\sb2$M (OCH(R)-pyr-CH(R)O), (pyr = $\rm NC\sb5H\sb3, NC\sb5H\sb2$-4Me, $\rm NC\sb5H\sb2$-4Ph). NMR studies of the latter show an approximate 50/50 mixture of the diastereomers meso and threo to be present. The mechanism for the reaction appears to involve sequential nucleophilic attack on the ortho-position of a pyridine ligand by an $\eta\sp2$-acyl group, initially formed by migratory insertion of CO into the metal-alkyl bond. Hydrolysis of these compounds allows the isolation of the corresponding $\alpha\alpha\sp\prime$-disubstituted pyridinedimethanols in good yields. The arylamido complexes (ArO)$\sb2$Zr$\rm (NHC\sb6H\sb4$-4X)$\sb2$ and M(NHAr$\sp\prime)\sb4,$ (M=Zr, Hf; X=H, F, CH$\sb3,$ OCH$\sb3,$ Br; Ar$\sp\prime$=2,6-diisopropylphenyl) were also prepared by reactions of (ArO)$\sb2$M(CH$\sb3)\sb2$ and M(CH$\sb2$Ph)$\sb4$ with the corresponding arylamines. The arylamido compounds can be readily converted into five-coordinate terminal imido derivatives by pyridine induced elimination of arylamine. In formation of the phenyl-imidos (ArO)$\sb2$Zr(=NC$\sb6$H$\sb4$-4X)(py)$\sb2$ from (ArO)$\sb2$Zr(NHC$\sb6$H$\sb4$-4X)$\sb2,$ four possible mechanisms were proposed in which the initial step is the formation of a the five-coordinate monopyridine adduct (ArO)$\sb2$M(NHAr$\sp{\rm X})\sb2$(py). Addition of more basic pyridines, as well as using electron withdrawing substituents on the phenyl rings of the arylamido precursors, favor the formation of the arylimido products.

Degree

Ph.D.

Advisors

Rothwell, Purdue University.

Subject Area

Chemistry

COinS