Conjugated Polyunsaturated Oxacyclic Carbene Complexes : Synthesis, Structure, and Properties

Abstract

The reaction of [(CO)5M(thf)] with but-3-yn-1-ols in the presence of NEt3 offers a convenient route to 2-oxacyclopentylidene complexes [(CO)5M=C-O-CH2CH2CH2] (M = Cr (1a), W (1b)) in yields up to 96%. Furthermore, the reaction of 1 with ω-(dimethylamino)- substituted enals, Me2N-(CH=CH)n-C(=O)H, activated by Me3SiCl/NEt3 or POCl3/NEt3 gives via aldol condensation the unsaturated oxacyclic push-pull carbene complexes [(CO)5M=C-O-CH2CH2C{=CH-(CH=CH)n-NMe2}] (n = 0 (2), 1 (3), 2 (4), 3 (5)). In 2-5, the amino group acts as an electron-donor unit and the oxacyclic carbene pentacarbonyl moiety as an electron acceptor. The aminometallaenes 2-5 have been characterized spectroscopically, the chromium complexes 2a-5a additionally by X-ray structure analysis. For some complexes, their nonlinear optical properties (second harmonic generation) have been studied and β values up to 58 × 10-30 esu have been determined. The results of DFT calculations on chromium complexes 2a-5a show that on lengthening of the unsaturated chain the influence of the carbonyl-metal fragment on the polyunsaturated chain strongly decreases.