Synthesis and structure of a chelated manganese carbene-alkene complex

Article abstract of DOI:10.1021/om00131a006

Reaction of (η⁵-C₅H₄(CH₃))Mn(CO) ₂(≡CC₆H₅)][BCl₄] with excess allylamine generated (η⁵-C₅H₄(CH₃))Mn(CO) ₂[C(C₆H₅)(NHCH₂CH=CH₂)], 1, as a 2.8:1.0 mixture of isomers. Isomers of 1 exist as a consequence of restricted carbene carbon-nitrogen bond rotation. High-temperature NMR studies on (η⁵-C₅H₄(CH₃))Mn(CO) ₂[C(C₆H₅)(N(CH₃)₂)] establish a minimum barrier to rotation around the C-N bond of 21 kcal/mol for this complex. Low-temperature photolysis of 1 resulted in the formation of (η⁵-C₅H₄(CH₃))Mn(CO)[C(C ₆H₅)(η²-NHCH₂CH=CH ₂)], 2. Infrared and ¹H and ¹³C NMR data are reported for both 1 and 2. The X-ray crystal structure of 2 shows a roughly octahedral arrangement of the ligands in which the carbene is cis and approximately parallel to the olefin. The compound crystallizes in the space group P2₁/c with four molecules per unit cell (a = 7.936 (2) A?, b = 14.593 (5) A?, c = 12.569 (5) A?, β = 99.08 (3)°, V = 1437.4 A?³, ρ(calcd) = 1.420 g/cm³). Full-matrix least-squares refinement of 121 parameters using 866 data with I ≥ 2σ(I) converged with R = 0.074 and R₂ = 0.052. The geometry of this first-row transition-metal carbene-alkene complex is compared to the geometry reported by Casey and co-workers for the analogous chelating carbene-alkene linkage in a tungsten derivative, (CO)₄W[C(tolyl)(η²-NHCH₂CH=CH ₂)].