POLYOXOMETALATE CATALYST PRECURSORS - IMPROVED SYNTHESIS, H-TITRATIONPROCEDURE, AND EVIDENCE FOR P-31 NMR AS A HIGHLY SENSITIVE SUPPORT-SITE INDICATOR FOR THE PROTOTYPE POLYOXOANION-ORGANOMETALLIC-SUPPORT SYSTEM [(ETA-C4H9)(4)N]9P2W15NB3O62()

An improved synthesis of the prototype polyoxoanion-organometallic-sup port system, P2W15Nb3O629-, as its organic solvent-soluble all-[(n-C4H 9)(4)N](+) salt is described. The improvements result in a 30% faster procedure which also provides a 60% increase in yield of [(n-C4H9)(4)N ]9P2W15Nb3O62, 2 One key improvement in this synthesis is a pH titrati on of protonated [(n-C4H9)(4)N]5H4P2W15Nb3O62, 1, using [(n-C4H9)(4)N] OH and phenolpthalein indicator, which leads to fully deprotonated 2-t he key synthon required for clean support of organometallic cations on to the P2W15Nb3O629- polyoxoanion's ''Nb3O93-'' cap. The material obta ined from this procedure is of the highest purity (greater than or equ al to 95%) seen to date as judged by P-31 NMR spectroscopy. [(n-C4H9)( 4)N]9P2W15Nb3O62 has been further characterized by H-1, C-13, O-17, an d W-183 NMR spectroscopy as well as IR spectroscopy and complete eleme ntal analysis. Also reported are control experiments that (i) confirm the identical reactivity of 2, obtained by either the procedure report ed herein or by our previously published accounts, with organometallic cations such as [Ir-I(1,5-COD)](+), [Rh-I(1,5-COD)](+) and [Rh-III(C( 5)Me(5))](2+), (ii) show that the pH titration employed herein may be used to cleanly deprotonate polyoxoanions containing varying degrees o f protonation, (iii) show that trace amounts of excess OH- present in P2W15Nb3O629- prevent clean organometallic cation-support reactions, a nd (iv) show that P-31 NMR titration of P2W15Nb3O629- using [(1,5-COD) Ir](+) is an effective and simple method of determining the purity of P2W15Nb3O629-.