Cooperative Metal−Boron Interactions in the Reaction of <i>n</i><i>ido</i>-1,2-(Cp*RuH)₂B₃H₇, Cp* = η⁵-C₅Me₅, with HC⋮CPh

Products of the reaction of nido-1,2-(Cp*RuH)2B3H7, 1, and phenylacetylene demonstrate the ways in which cluster metal and main group fragments can combine with an alkyne. Observed at 22 °C are (a) reduction to μ-alkylidene Ru−B bridges (isomers nido-1,2-(Cp*Ru)2(1,5-μ-C{Ph}Me)B3H7, 2, and nido-1,2-(Cp*Ru)2(1,5-μ-C{CH2Ph}H)B3H7, 3), (b) reduction to exo-cluster alkyl substituents on boron (nido-1,2-(Cp*RuH)2-3-CH2CH2Ph-B3H6, 4), (c) cluster insertion with extrusion of a BH2 fragment into an exo-cluster bridge (nido-1,2-(Cp*Ru)2(μ-H)(μ-BH2)-4-or-5-Ph-4,5-C2B2H5, 5), (d) combined insertion with BH2 extrusion and reduction (nido-1,2-(Cp*Ru)2(μ-H)(μ-BH2)-3-CH2CH2Ph-5-Ph-4,5-C2B2H4, 6), (e) insertion and loss of borane with and without reduction (nido-1,2-(Cp*Ru)2-5-Ph-4,5-C2B2H7, 7, and isomers nido-1,2-(Cp*Ru)2-3-CH2CH2Ph-4-(and-5-)Ph-C2B2H6, 8 and 9), and (f) insertion and borane loss plus reduction (nido-1,2-(Cp*Ru)2-3-(trans-CHCHPh)-5-Ph-4,5-C2B2H6, 10). Along with 7, 8, and 10, the reaction at 90 °C generates products of insertion and nido- to closo-cluster closure (closo-4-Ph-1,2-(Cp*RuH)2-4,6-C2B2H3, 11, closo-1,2-(Cp*RuH)2-3-CH2CH2Ph-5-Ph-7-CH2CH2Ph-4,5-C2B3H2, 12, closo-1,2-(Cp*RuH)2-5-Ph-4,5-C2B3H4, 13, and isomers closo-1,2-(Cp*RuH)2-3-and-7-CH2CH2Ph-5-Ph-4,5-C2B3H3, 14 and 15). The clusters with an exo-cluster bridging BH2 groups are shown to be intermediates by demonstrating that the major products 5 and 6 rearrange to 13 and convert to 14, respectively. 14 then isomerizes to 15, thus connecting low- and high-temperature products. Finally, all available information shows that the high reactivity of 1 with alkynes can be associated with the “extra” two Ru−H hydrides on the framework of 1 which are required to meet the nido-cluster electron count.