Article abstract of DOI:10.1016/S0022-328X(97)00075-2

The pentacarbonyl(vinylidene)chromium complexes [(CO)₅Cr=C=C(R)R′] (1) [C(R)R′ = CPh₂ (a), C(CH₂)₅ (b), CMe₂, (c), C(Me)H (d)] react with 1-diethylamino-1-propyne, MeC≡CNEt₂, by regiospecific addition of the C≡C bond of the alkyne to the C≡C bond of the vinylidene ligand to form the cyclobutenylidene complexes [(CO)₅Cr=C=C(Me)=C(NEt₂)=C(R)R′] (2a-d). The analogous reaction of [(CO)₅Cr=C=C(Ph)H] with MeC≡CNEt₂ affords via cycloaddition and formal [1,3]-H shift the complex [(CQ)₅Cr=C=C(Ph)=C(NEt₂)=C(Me)H] (3). The cycloadditions of Me₂NC≡CNMe₂ and MeC≡COEt to 1b give [(CO)₅Cr=C=C(NMe₂)=C(NMe₂)=C(CH₂)₅] (4) and [(CO)₅Cr=C=C(Me)=C(OEt)=C(CH₂)₅] (5) respectively. The addition of (S)-2-methoxymethyl(N-1-propynyl)pyrrolidine (6) and (R)-methyl(1-propynyl)(1-phenylethyl)amine (8) with 1a-c leads to E/Z mixtures of [(CO)₅Cr=C=C(Me)=C(R*)=C(R)R′] [R* = (S)-2-methoxymethyl pyrrolidinyl (7a-c), R* = (R)-N(Me)[CH(Me)Ph] (9a-c)]. In the reactions of 1a-c with 6 predominantly the E isomer, in the reactions of 1a-c with 8 predominantly the Z isomer is formed. All 3-amino substituted complexes exhibit a considerable solvatochromic behavior. The first hyperpolarizability β of 2b was determined by hyper-Rayleigh scattering ( β = 22 × 10^-30 esu). The Kurtz powder method was used to investigate the effectiveness in second harmonic generation of 2d, 3, 7a, 7b, and 9c. Their efficiencies range from 4 to 35 times that of urea. The structures of 2b and Z-9b were established by X-ray structural analyses. Together with the results of spectroscopic investigations, they reveal a strongly delocalized π-system [(CO)₅Cr=C=C=C=N].