Syntheses and characterization of new vinyl-borylene complexes by the hydroboration of alkynes with [(μ₃-BH)(Cp*RuCO)₂(μ-CO)Fe(CO)₃]

Abstract

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.