THE MO(CO)(3) FRAGMENT AS AN ORGANOMETALLIC PROTECTION GROUP IN THE SYNTHESIS OF FUNCTIONALIZED TRIPODAL PHOSPHINE-LIGANDS

Treatment of Mo(CO)(6) with lphosphino)-1,3,5-tris(methoxycarbonyl)cyc lohexane (tdp-pcyme) (L) at elevated temperatures gives Mo(CO)(3)(tdpp cyme) (1) in high yield. The ester groups in complex 1 are saponed to carboxylic acid groups by lithium n-propyl mercaptide in DMF and reduc ed to alcoholic groups by lithium aluminum hydride in THF to yield the carboxylic acid complex 2 and hydroxymethyl complex 4, respectively. Treatment of 1 with ethylenediamine and NaH results in the formation o f the carboxamide 3. The methoxymethyl complex 5 is formed from 4 in a phase transfer reaction (THF/aqueous NaOH) with dimethyl sulfate as t he methylating agent. Deprotonation of compound 4 with NaH in THF resu lts in the formation of the corresponding trisodium alcoholate which o n treatment with chloromethyl methyl ether, 1-methoxy-2-[p-tolylsulfon yl)oxy]ethane, and allyl bromide leads to the corresponding complexes 6-8, respectively. The acid catalyzed addition of the hydroxyl functio n to 5,6-dihydro-4H-pyran yields the acetal 9. The modified functional ized tripodal phosphines 2a and 5a-9a can be liberated by irradiating solutions of the corresponding molybdenum carbonyl complexes in the pr esence of pyridine N-oxide or N2O, respectively. No oxidation of the p hosphines is observed; MoO3 and CO are obtained. Single-crystal X-ray structure determinations were performed on complexes 3 and 5.