Bidentate alkene-aminocarbene complexes of chromium. Synthesis and reactivity toward alkynes

Article abstract of DOI:10.1021/om00111a024

The reaction of the aminocarbene complex (CO)₅Cr=C(CH₃)NHCH₂CH=CH₂ (2) with lithium diisopropylamide (LDA) followed by methyl iodide led, at -60°C, to (CO)₅Cr=C(CH₃)N(CH₃)CH₂CH=CH ₂ (7) and, at 0°C, to (CO)₅Cr=C(CH₃)N(CH₃)CH=CH(CH₃) (8). Both complexes 7 and 8 gave upon coordination in refluxing toluene (CO)₄Cr=C(CH₃)N(CH₃)(η²-CH ₂CH=CH₂) (9). Complex 9 reacted with diphenylacetylene to give the insertion-cyclopropanation (arene) chromium tricarbonyl complex 10. In the case of the phenyl-substituted carbene complex (CO)₄Cr=C(Ph)NHCH₂CH=CH₂ (6) the reaction with alkynes led to the annulation products 11, 12, and 13 isolated as the (arene)chromium tricarbonyl complexes. The structures of complexes 8, 9, 10, and 12 were determined by X-ray crystallography. Crystals of 8 are monoclinic, space group Pn, with unit cell dimensions a = 6.240 (2) A?, b = 10.787 (1) A?, c = 10.262 (2) A?, α = 90°, β = 95.96 (2)°, and γ = 90°. Crystals of 9 are triclinic, space group P1, with a = 6.808 (3) A?, b = 6.952 (2) A?, c = 12.811 (2) A?, α = 93.73 (2)°, β = 100.05 (3)°, and γ = 102.45 (3)°. Crystals of 10 are monoclinic, space group P2₁/n, with a = 9.710 (2) A?, b = 19.278 (4) A?, c = 10.634 (4) A?, α = 90°, β = 103.24 (2)°, and γ = 90°. Crystals of 12 are monoclinic, space group C2/c, with a = 26.384 (14) A?, b = 6.398 (2) A?, c = 19.461 (4) A?, α = 90°, β = 115.27 (1)°, and γ = 90°. The structures were solved and refined to the following R and R_w values: 8, R = 0.0313, R_w = 0.0357, on 997 observed (I > 3σ(I)) data; 9, R = 0.0280, R_w = 0.0300, on 1666 data; 10, R = 0.0413, R_w = 0.0357, on 1858 data; 12, R = 0.0292, R_w = 0.0357, on 1858 data. The transformation of complex 8 into complex 9 provides the first example of the internal to terminal double-bond isomerization upon coordination of an alkene-carbene ligand.