Group 4 and group 9 transition metal chemistry of 2-(6-methylpyridyl)methyl and similar ligands

Diego Elias Chebi, Purdue University

Abstract

The synthesis of Cp$\sb2$Hf(Cl)CH$\sb2$-py-6Me (CH$\sb2$-py-6Me=2-(6-methylpyridyl)methyl) was accomplished by thermolysis of a mixture of Cp$\sb2$HfCl$\sb2$ and Cp$\sb2$Hf (CH$\sb2$-py-6Me)$\sb2$ in benzene carrying out a ligand redistribution reaction. Other related compounds such as Cp$\sb2$Hf(Cl)CHR-py-5R$\sp\prime$ ((a) R=ph, R$\sp\prime$=H; (b) R=H, R$\sp\prime$=Me; (c) R=H, R$\sp\prime$=H) were prepared by metathesis of Cp$\sb2$HfCl$\sb2$ and LiCHR-py-5R$\sp\prime$ at room temperature. All the 2-methylpyridyl ligands were not nitrogen-bound to the hafnium in these products. The aryl isocyanide migratory insertion into the Hf-C bonds of the above hafnium compounds was studied, and the expected $\eta\sp2$-iminoacyls were initially obtained in most cases. The solid structure of Cp$\sb2$Hf(Cl)($\eta\sp2$-xyNCCH(Ph)-py) showed the proximal configuration for the iminoacyl. No rearrangements for this product were observed. The rest of the $\eta\sp2$-iminoacyls underwent a facile (1,2) -hydrogen shift to yield the vinylamido products (Cp$\sb2$Hf(Cl)((Ar)NC(H)-py-R) with the olefin in a trans configuration. The scope, kinetics and isotope effect of this rearrangement were studied, and a mechanistic pathway was proposed. The 2-(6-methylpyridyl) methyl ligand were shown to bridge Rh(I) and Ir(I) binuclear complexes containing 1,5-cyclooctadiene (COD) forming eight-membered "boat-like" rings with the metals. The metal-metal distances were longer than the normal bond length between these metals, as shown in their crystal structure. These products were reacted with bis-(diphenylphosphino)methane (dppm) to yield (dppm)M(dppm-H) (M=Ir, Rh) (dppm-H=bis-(diphenylphosphino)methanide) which was structurally characterized in the case of rhodium. Reaction of the iridium dimer with tertiary phosphines split the C-N bridge and generated the five-coordinated (COD)Ir(CH$\sb2$-py-6Me)(PR$\sb3$)$\sb2$. The 2,6-diphenylphenoxide ligand (O-Ar-2,6Ph$\sb2$) reacted with (Rh(CO)$\sb2$($\mu$-Cl)) $\sb2$ to form (Rh(CO)$\sb2$($\mu$-O-Ar-2,6Ph$\sb2$)) $\sb2$, bridging through the oxygen. On the other hand its reaction with (IrCOD($\mu$-Cl)) $\sb2$ yielded ((COD)Ir(O-Ar-2,6Ph$\sb2$)$\sb2$) $\sp-$ ((COD)Ir($\eta\sp5$-Ar-2,6Ph$\sb2$)) $\sp+$, featuring the metal pentacoordinated to the phenolic ring in the case of the cation.

Degree

Ph.D.

Advisors

Rothwell, Purdue University.

Subject Area

Organic chemistry|Chemistry

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