Reactions of the unsaturated methyl-bridged complexes [Mo 2 Cp 2 ( μ-CH 3 )( μ-P t Bu 2 )(CO) x ] (x=1, 2) towards transition metal carbonyls: convenient dehydrogenative route to heterometallic methylidyne-bridged clusters

The unsaturated dicarbonyl complex [Mo 2 Cp 2 ( mu-CH 3 )( mu-P t Bu 2 )(CO) 2 ] ( 1 ) reacted with [W(CO) 6 ] under photolytic conditions to give three isomers of formula [Mo 2 WCp 2 ( mu 3 -CH)( mu-P t Bu 2 )(CO) 7 ] ( cis -3, cis 3 ' and trans -3 in a ratio ca. 10:1:3), these differing in the relative disposition of the Cp, CO and methylidyne ligands, as inferred from the available spectroscopic data and the crystal structure of trans 3 (Mo -Mo = 2.8931(4) A). The cis isomers are thermally unstable species which could not be isolated as pure solids as they either decomposed upon manipulation ( cis -3 ') or rearranged into the corresponding trans isomer ( cis -3 ). In contrast, no reaction was observed between this compound and [W(THF)(CO) 5 ] in the absence of photochemical activation, yet a rapid reaction occurred between this fragment and the monocarbonyl [Mo 2 Cp 2 ( mu-CH 3 )( mu-P t Bu 2 )( mu-CO)] ( 2 ) to give the cis -3 isomer exclusively. The reaction of 2 with [Fe 2 (CO) 9 ] at room temperature led to a mixture of two trinuclear clusters: the 46-electron methylidyne-bridged [Mo 2 FeCp 2 ( mu 3 -CH)( mu-P t Bu 2 )(CO) 5 ] ( 4a ) and the acetyl-bridged [Mo 2 FeCp 2 { mu 3 - xe002;1 : xe003;2 : xe002;1 -C(O)CH 3 }( mu-P t Bu 2 )(CO) 5 ] ( 5 ) in a ca. 3:1 ratio. A symmetrical coordination of the methylidyne group is found in compound 4a , while the electronic unsaturation is mainly located at the Mo -Mo edge (2.667(1) A). In contrast, an asymmetric 5-electron donor coordination of the acetyl group is observed in compound 5 and, accordingly, the intermetallic lengths are consistent with the formulation of single bonds in a 48-electron trinuclear cluster (Mo -Mo = 2.8235(4) A and Mo -Fe ca. 2.76 A). Finally, the reaction of compound 2 with [Ru 3 (CO) 12 ] required photochemical activation and then led to the formation of the corresponding unsaturated methylidyne cluster [Mo 2 RuCp 2 ( mu 3 -CH)( mu-P t Bu 2 )(CO) 5 ] ( 4b ) in high yield.