SYNTHESIS AND REACTIVITY OF TRIRUTHENIUM CARBONYL CLUSTERS CONTAINING BIS(DIPHENYLPHOSPHINO)METHANE AND THE FACE-BRIDGING LIGAND 2-AMIDO-6-METHYLPYRIDINE

The compounds [Ru3(mu-H)(mu-3-ampy)(CO)9] (1) and [Ru3(mu-H)2(mu-3-ampy)(CO)9]BF4 (2) (Hampy = 2-amino-6-methylpyridine) react with bis(diphenylphosphino)methane (dppm) to give [Ru3(mu-H)(mu-3-ampy)(CO)7(dppm)] (3) and [Ru3(mu-H)2(mu-3-ampy)(CO)7(dppm)]BF4 (4), respectively. In complex 3 the two P atoms of the dppm ligand are cis to both the hydride and the amido-fragment of the bridging ampy ligand, whereas in complex 4 each P atom is trans to a hydride. Protonation of complex 3 with HBF4.OEt2 affords [Ru3(mu-H)2(mu-3-ampy)(CO)7(dppm)]BF4 (5), which is an isomer of complex 4; in fact, 5 can also be obtained by refluxing a solution of complex 4 in tetrahydrofuran. Complex 5 undergoes deprotonation upon reaction with potassium methoxide or triethylamine, giving 3; however, the reaction of 4 with potassium methoxide produces the methoxycarbonyl derivative [Ru3(mu-H)2(mu-3-ampy)(CO2Me)(CO)6(dppm)] (6), which contains the CO2Me group in an equatorial position on the Ru atom bonded to the two hydrides.