Nickel, palladium, and platinum heteronuclear complexes and the platinum-mediated deoxygenation of phenols with carbon monoxide

Jinfeng Ni, Purdue University

Abstract

The reaction of Pd$\sb2$Cl$\sb2$(dmpm)$\sb2$ with Pt(PPh$\sb3$)$\sb2$C$\sb2$H$\sb4$ results in the first heterotrinuclear A-frame complex Pd$\sb2$($\mu$-Pt(PPh$\sb3$)$\sb2$) Cl$\sb2$(dmpm)$\sb2$, 1. Metalation of a dinickel(0) complex Ni$\sb2$(CNMe)$\sb3$(dppm)$\sb2$ with (M(CNMe)$\sb4$) (PF$\sb6$) $\sb2$ (M = Pd, Pt) leads to the formatin of heterotrinuclear complexes (Ni$\sb2$Pd(CNMe)$\sb6$(dppm)$\sb2$) (PF$\sb6$) $\sb2$, 2, and (Ni$\sb2$Pt(CNMe)$\sb5$(dppm)$\sb2$) (PF$\sb6$) $\sb2$, 3. Complex 2 exhibits a strictly linear Ni-Pd-Ni structure with the Ni-Pd bond distance of 2.6078 A$\sp\circ$. However, Complex 3 possesses a bent acyclic structure. Both of 2 and 3 display the unusual long distance phosphorus proton coupling. The metalated products 2 and 3 undergo a net elimination of a Ni(CNMe)$\sb{\rm n}$ (2, n = 3; 3, n = 2) fragment to afford the transmetalated products of Ni$\sb2$(CNMe)$\sb3$(dppm)$\sb2$: (NiPdCNMe)$\sb3$(dppm)$\sb2$) (PF$\sb6$) $\sb2$, 4, and (Ni$\sb2$Pt(CNMe)$\sb3$(dppm)$\sb2$) (PF$\sb6$) $\sb2$, 5. Complex 4 exists, in solution, in two conformational isomers A and B which have the approximate exchange rate constants 9 s$\sp{-1}$ (k$\sb{\rm AB}$) and 10 s$\sp{-1}$ (k$\sb{\rm BA}$) in MeCN at 25$\sp\circ$C. The conformational isomer A possesses a tetrahedral T-shaped structure with dative metal metal bond and the isomer B has a trigonal bipyramidal T-shaped structure with covalent metal metal bond. Complex 5, however, exists in solution in one conformation which has the trigonal bipyramidal T-shaped structure with covalent metal metal bond. Reaction of Pt(dppe)Cl$\sb2$ with NaOAr results in complexes Pt(dppe)(OAr)$\sb2$ (Ar = p-ClC$\sb6$H$\sb4$, p-MeSC$\sb6$H$\sb4$, C$\sb6$H$\sb5$, p-MeC$\sb6$H$\sb4$, p-Me$\sb2$NC$\sb6$H$\sb4$), which incorporate CO to yield complexes Pt(dppe)(COOAr)$\sb2$. In the case of ordinary phenoxy complex Pt(dppe)(OPh)$\sb2$, 6, which has been studied in detail, the CO incorporated product Pt(dppe)(COOPh)$\sb2$, 7, undergoes two competing reactions: (1) deoxygenation of the phenoxy ligand to produce phenylbenzoate, CO$\sb2$, and PT(dppe)(CO)$\sb2$, (2) elimination of PhOH to give Pt(dppe)(COOC$\sb6$H$\sb4$), 8. These two competing pathways can be controlled by the CO pressure. Complex 8, consisting of a central platinum atom coordinated by a bidentate diphosphine ligand and a bidentate organic ligand, is the first example of orthometallo-lacton. Complex 8 is thermochemically stable, but photochemically active to give complex Pt(dppe)(OC$\sb6$H$\sb4$CO). The mechanism for the deoxygenation of phenoxy ligand with CO involves a platinum benzyne complex.

Degree

Ph.D.

Advisors

Kubiak, Purdue University.

Subject Area

Chemistry

COinS