Syntheses of & beta;,& beta;& PRIME;-Disubstituted Tungstacyclopentanes from Terminal Olefins and Their Conversions to Alkylidenes

& beta;,& beta;& PRIME;-Disubstitutedtungstacyclopentanecomplexeshave been prepared through addition of propylene, 1-heptene, 1,6-heptadiene,1,7-octadiene, or diallylaniline to unsubstituted tungstacyclopentanecomplexes, W(NR)(OR & PRIME;)(2)(C4H8); tungstabicycloalkanes are formed from the dienes. Several tungstacyclopentaneshave been prepared from W(NR)(OR & PRIME;)(2)Cl-2 complexes through alkylation and reduction with diethylzinc in thepresence of the olefin. The synthesized complexes include those inwhich NR = NPh, NCPh3, or N-2,6-i-Pr2C6H3 and OR & PRIME; = OSiPh3 or OCMe2(CF3). The tungstacyclopentane complexesare stable in the dark, but upon exposure to violet (405 & lambda;(max)) or blue (445 nm & lambda;(max)) LED light, theyform alkylidenes, largely through & alpha; hydrogen abstraction; ring-contractionto give a tungstacyclobutane is a minor reaction pathway only forthe & beta;,& beta;& PRIME;-dimethyltungstacyclopentane. PreliminaryDFT calculations suggest that one electron is promoted from the HOMO(composed of the two W-C & sigma; bonds) into an empty d( xy ) orbital to give what could be viewed asa W(V)CH2CHRCHRCH2 & BULL; complex. Abstractionof an H-& alpha; by the radical chain end yields an alkylidene,while abstraction of an H-& gamma; leads to ring-contractionto give a tungstacyclobutane. The rates of the photochemical reactionsfor the & beta;,& beta;& PRIME;-disubstituted tungstacyclopentanesdo not vary dramatically with solvent (toluene, THF, CDCl3). Twelve compounds were characterized through single crystal X-raydiffraction studies.

Automated summary

β, β'-disubstituted tungstacyclopentane complexes were prepared by adding propylene, 1-heptene, 1,6-heptadiene, 1,7-octadiene, or diallylaniline to unsubstituted tungstacyclopentane complexes, resulting in the formation of tungstabicycloalkanes from the dienes. Tungstacyclopentane complexes were also synthesized through alkylation and reduction reactions with diethylzinc in the presence of olefin. The photochemical reactions of the β, β'-disubstituted tungstacyclopentanes were studied and twelve compounds were characterized through X-ray crystallography.