Organometallic chemistry of mononuclear tungsten aryloxide compounds
Abstract
Room temperature sodium amalgam reduction (4 Na/Hg) of ($\rm WCl\sb4$(OAr-2,6Ph$\sb2)\sb2$) in the presence of phosphine gives the bis cyclo-metallated compound, ($\rm W(OC\sb6H\sb3 Ph$-$\rm C\sb6H\sb4)\sb2(L)\sb2$) (L = $\rm PMe\sb2Ph, PMePh\sb2, PEtPh\sb2)$ which contains the W(IV) in an octahedral central coordination environment. Reaction of ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2(L)\sb2\rbrack$ with ethylene ($>$1atm) gives the corresponding olefin complex ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2 (L) (C\sb2H\sb4)$). The crystal structure confirms an octahedral arrangement about the metal and the presence of a metallacyclopropane ring. Reduction of either ($\rm W(OC\sb6H\sb3Ph\sb2 $-$\rm 2,6)\sb2Cl\sb4$) or ($\rm W(OC\sb6H\sb3Pr\sb2\sp{i}$-$\rm 2,6)\sb2Cl\sb4$) in toluene with sodium amalgam in the presence of alkynes (EtC$\equiv$CEt; PhC$\equiv$CPh; 4Me-PhC$\equiv$CPh-4Me) leads to a series of alkyne adducts of general formulae ((ArO)$\sb2$WCl$\sb2$(ac)) and ((ArO)$\sb2$W(ac)$\sb2$). The $\sp{13}$C NMR spectra of ((ArO)$\sb2$WCl$\sb2$(ac)) and ((ArO)$\sb2$W(ac)$\sb2$) show large downfield shifts for the alkyne carbon atoms. A single X-ray diffraction analysis shows five coordinate ((ArO)$\sb2$WCl$\sb2$(ac)) to adopt a square pyramidal geometry about tungsten with trans aryloxide ligands and an axial 3-hexyne. The solid state structure of ((ArO)$\sb2$W(ac)$\sb2$) shows a pseudo-tetrahedral environment about tungsten with two 3-hexyne ligands arranged parallel with each other. The bis-cyclometallated compounds ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2(L)\sb2\rbrack\ (L = PMe\sb2Ph, PMePh\sb2$ and py) react with alkyne to form a number of products. From the reaction with 3-hexyne, two new compounds of formula ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2 (C\sb4Et\sb4)$) and ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2(C\sb6Et\sb6)$) are produced. Structural studies of both complexes show them to contain metallacyclic rings formed by transfer of one of the W-C(metallated aryloxide) to an $\alpha$-carbon of an intermediate tungstacyclopenta-2,4-diene. The product ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2(C\sb4Et\sb4)$) contains a tungstacyclopenta-1,3-diene ring which can also add 3-hexyne to the tungsten-alkylidene bond to form ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2(C\sb6Et\sb6)$). Reaction of ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2(L)\sb2\rbrack\ (L = PMe\sb2Ph, PMePh\sb2)$ with various monodentate and bidentate pyridine complexes resulted in the substitution of both phosphines to form ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2 (py)\sb2$) or ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2 (py\sp2)$) (py = various monodentate pyridines) (py$\sp2$ = various bidentate pyridines). The paramagnetic compounds exhibited sharp contact shifted $\sp1$H NMR consistent with the spin density being transferred through the aromatic ring by a hyperconjugative mechanism. Structural studies of ($\rm W(OC\sb6H\sb3Ph$-$\rm C\sb6H\sb4)\sb2(C\sb5H\sb5N)\sb2$) shows an octahedral arrangement about the metal center with cis pyridines. Included in this study is the determination of hyperfine coupling constants, as well as the singlet-triplet energy gaps for the various compounds isolated, utilizing the Van Vleck equation.
Degree
Ph.D.
Advisors
Rothwell, Purdue University.
Subject Area
Chemistry
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