Spectroscopic study of dehydrochlorination and exchange with D{sub 2} in WH{sub 2}Cl{sub 2}(PMe{sub 2}Ph){sub 4}: Unexpected stereochemical rigidity of dodecahedra containing both hydride and chloride ligands. Crystal and molecular structure of W(H){sub 3}({eta}{sup 2}-C{sub 6}H{sub 4}PMe{sub 2})(PMe{sub 2}Ph){sub 3}