The radical alkylation of tetraethylammonium pentacarbonyl(cyano)chromate 1 yielded the halogenated ethyl isocyanide complexes [(CO)5Cr(CN-CClX-CClYF)] 3 (a, X= Cl, Y= F; b, X = F, Y= F and c, X=Y= Cl). Dehalogenation of 3 using zinc in diethyl ether gave [(CO)5Cr(CN-CX=CFY)] 4. The compounds 4a, b reacted with various nucleophiles exclusively at the difluoromethylene group. The unstable phosphorane 5, which is formed on reaction of 4b with trimethylphosphane, decomposed thermally and on hydrolysis yielding pentacarbonyl(1,2-difluoroethenyl isocyanide)chromium (6). The cyano substituent can be introduced in the beta position of the isocyanide function by reaction of 4a, b with potassium cyanide, leading to the formation of [(CO)5Cr(CN-CX=CF-CN)] (7). Reactions of 4a, b with organolithium or organomagnesium compounds yielded [(CO)5Cr(CN-CX=CF-R)] (8) and [(CO)5Cr(CN-CF=CF-C...C-CF=CF-NC)Cr(CO)5] (10). The trimethylsilyl group in 8a, b, d could be removed by a solution of potassium carbonate in methanol leading to [(CO)5Cr(CN-CX=CF-Cn-H)] (11) (n=2,4). Octacarbonyldicobalt reacted with 8e under coordination of the C-C triple bond to the hexacarbonyldicobalt fragment, resulting in the cluster compound 12. The crystal and molecular structure of 8i, 11 a, b, and 12 were elucidated by X-ray crystallography. The alkenyl and alkynyl isocyanides CN-CCl=CF2 (13a), CN-CF=CF2 (13b), CN-CCl=CClF (13c), CN-CF=CFH (14), CN-CC-H (15), CN-CC-CN (16), and CN-CCl=CF-CN (17) were obtained by flash vacuum pyrolysis of 4a, 4b, 4c, 6, and 7a, respectively.

Rotational transitions of the linear molecule 3-isocyano-2-propynenitrile, NCCCNC, have been measured in the frequency range from 75 up to 120 GHz and assigned to the excited vibrational bending states (upsilon(6) upsilon(7) upsilon(8) upsilon(9)) = (0002), (0003), (0004), (0011), and (0020). The analysis of the spectrum extends the spectroscopic data for NCCCNC by adding various newly determined rotational and rovibrational constants. (C) 2000 Elsevier Science B.V. All rights reserved.

The millimetre-wave spectrum of 2-isocyano-3-propynenitrile, NC3NC, was observed in the vibrational ground state (0000) and in the excited bending states (v6v7v8v9)=(1000), (0100), (0010), and (0001). Pure rotational transitions J+1←J were recorded in the ranges 40–120 and 240–315 GHz. The analysis of the spectra, aided greatly by accompanying ab initio calculations, yielded precisely determined rotational, centrifugal distortion, and l-type doubling constants. They are in excellent agreement with the results of coupled-cluster calculations. Wavenumbers and infrared (IR) intensities of various stretching vibrational transitions were calculated variationally. Good agreement with results from high-resolution IR spectroscopy is observed for the highest fundamentals ν1–ν3, with deviations amounting to 15.4 cm−1 (ν1), 1.2 cm−1 (ν2), and 7.0 cm−1 (ν3).

Nach Vakuumpyrolyse des gezielt synthetisierten Komplexes [(CO)5Cr(CN−CCl=CF-CN)] gelingt die Isolierung und molekülspektroskopische Strukturbestimmung des nach Ab-initio-Rechnungen um 109 kJ mol−1 instabileren Isomers 1 des schon lange bekannten N≡C−C≡C−C≡N. Von 1 konnte unter Verwendung gemischt experimentell/theoretischer Methoden die genaue Gleichgewichtsstruktur ermittelt werden.

Vacuum pyrolysis of the precursor complex [(CO)5 Cr(CN-CCl=CF-CN)] resulted in the isolation and structure elucidation by molecular spectroscopy of isomer 1. According to ab initio calculations 1 is 109 kJ mol-1 less stable than NC-C≡C-CN, which has been known for some time. An accurate equilibrium structure for 1 has been determined with mixed experimental and theoretical methods.