Syntheses and Characterization of New Vinyl-Borylene Complexes by the Hydroboration of Alkynes with [(μ3-BH)(Cp*RuCO)2(μ-CO)Fe(CO)3].

Room temperature photolysis of a triply-bridged borylene complex, [(μ₃-BH)(Cp*RuCO)₂(μ-CO)Fe(CO)₃] ( 1 a; Cp*=C₅Me₅), in the presence of a series of alkynes, 1,2-diphenylethyne, 1-phenyl-1-propyne, and 2-butyne led to the isolation of unprecedented vinyl-borylene complexes ( Z)-[(Cp*RuCO)₂(μ-CO)B(CR)(CHR′)] ( 2: R, R′=Ph; 3: R=Me, R′=Ph; 4: R, R′=Me). This reaction permits a hydroboration of alkyne through an anti -Markovnikov addition. In stark contrast, in the presence of phenylacetylene, a metallacarborane, closo-[1,2-(Cp*Ru)₂(μ-CO)₂{Fe₂(CO)₅}-4-Ph-4,5-C₂BH₂] ( 5 a), is formed. A plausible mechanism has been proposed for the formation of vinyl-borylene complexes, which is supported by density functional theory (DFT) methods. Furthermore, the calculated ¹¹B NMR chemical shifts accurately reflect the experimentally measured shifts. All the new compounds have been characterized in solution by mass spectrometry and IR, ¹H, ¹¹B, and ¹³C NMR spectroscopies and the structural types were unequivocally established by crystallographic analysis of 2, 5 a, and 5 b. [ABSTRACT FROM AUTHOR]