Pentacarbonyl(cyclobutenylidene)chromium complexes - Synthesis, structure and nonlinear optical properties

The pentacarbonyl(vinylidene)chromium complexes [(CO)(5)Cr=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)(5)Cr=C=C(Me)=C(NEt2)=C(R)R'] (2a-d). The analogous reaction of [(CO)(5)Cr=C=C(Ph)H] with MeC=CNEt2 affords via cycloaddition and formal [1,3]-H shift the complex [(CO)(5)Cr=C=C(Ph)=C(NEt2)=C(Me)H] (3). The cycloadditions of Me2NC=CNMe2 and MeC=COEt to 1b give [(CO)(5)Cr=C=C(NMe2)=C(NMe2)=C(CH2)(5)] (4) and [(CO)(5)Cr=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)(5)Cr=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 beta of 2b was determined by hyper-Rayleigh scattering (beta=22 x 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 pi-system [(CO)(5)Cr=C=C=C=N].