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

Room temperature photolysis of a triply‐bridged borylene complex, [(μ 3 ‐BH)(Cp*RuCO) 2 (μ‐CO)Fe(CO) 3 ] ( 1 a ; Cp*=C 5 Me 5 ), 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 {Fe 2 (CO) 5 }‐4‐Ph‐4,5‐C 2 BH 2 ] ( 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 11 B NMR chemical shifts accurately reflect the experimentally measured shifts. All the new compounds have been characterized in solution by mass spectrometry and IR, 1 H, 11 B, and 13 C NMR spectroscopies and the structural types were unequivocally established by crystallographic analysis of 2 , 5 a , and 5 b .