d-Orbital effects in silicon substituted π-electron systems. Part XII. Some spectroscopic properties of alkyl and silyl acetylenes and polyacetylenes

Abstract

Vertical ionization energies, characteristic vibrational frequencies, l H n.m.r. signals, and electronic transitions are reported for acetylenes X-[C=C];X ( n = 1, 2, 3; X = H, CMe,, CH,-SiMe,. SiMe,). Comparison with the corresponding data of ethylene and butadiene derivatives indicates stronger electron back-donation to silicone Si C , which is interpreted as being due to interactions with both of the perpendicular acetylene n-components. The inductive polarization +/(SiR,) =-+/(CR,) can be estimated from the substituent effect of CH,*SiR, groups. ALTHOUGH numerous silylacetylenes have been synthesized in recent years,2 very little is known about their spectroscopic properties. Most of the work originates from Zeil and his co-workers who determined the bond distances in acetylene derivatives like Me,X*C-C-Y or Me,X*C-C-XMe, (X = C, Si, Ge, Sn, P b ; Y = H, Cl)by microwave spectroscopy and electron diffraction, and recorded their infrared, Raman, and nuclear quadrupole resonance spectra. Strong evidence for ($ fd)= bonding was, for instance, deduced from the shorter bond-length d(C-C1) in the silyl chloroacetylene and from the fact that the calculated force constants f(C-C) are smaller andf(C-C1) are larger than for the corresponding t-butyl derivative, which also shows a higher 35Cl n.q.r. coupling constant. Bond distances have been evaluated from the rotational constants of ethynylsilane, H,Si*C-C*H, by Muenter and Laurie; a complete analysis of the vibrational spectrum was given by

Dimetallapoly‐yn‐diylidynes: LnM≡C−(C≡C)x−C≡MLn (x=0–4)

“…This is in concert with Bock's early observations on the ionisation and transition (*) energies of poly-ynes Me3Si-(C≡C)nSiMe3 (n = 1, 2, 3). [23] Notably, the molar absorptivities of both types of absorption increase monotonically with increasing chain length as has also been noted for silyl-capped poly-ynes. [6,23] Cyclic voltammetry indicates that with the exception of WC2W which is insufficiently soluble for study, each of the series has two oxidation events that are remarkably insensitive to the carbon chain length.…”

“…[23] Notably, the molar absorptivities of both types of absorption increase monotonically with increasing chain length as has also been noted for silyl-capped poly-ynes. [6,23] Cyclic voltammetry indicates that with the exception of WC2W which is insufficiently soluble for study, each of the series has two oxidation events that are remarkably insensitive to the carbon chain length. This may be attributed to the essential invariance of the energy of the HOMO which is associated with metal-carbonyl bonding rather than being intimately involved with the WCxW chain.…”

Single‐Electron Oxidation of Tungsten Acetylide Complexes [(η5‐C5H5)(CO)(NO)W–C≡C–R]Li

“…In the IR spectrum, the signal for the $\tilde {\nu}$ (C≡C) stretch of 9c at 1820 cm –1 and similar IR bands for complexes 9a (1847 cm –1 ) and 9b (1852 cm –1 ) are in accordance with the related absorptions of the zirconocene complexes [(RCp) 2 Zr] 2 (μ‐C≡C–R) 2 5a,5c (1770–1820 cm –1 ) and the bimetallic tungsten–iron complexes{[(η 5 ‐C 5 H 5 )‐μ‐(CO)(NO)W][(η 5 ‐C 5 H 5 )(CO)Fe–C≡C–R]}(1861–1908 cm –1 ) 8. The decrease in the $\tilde {\nu}$ (C≡C) stretching frequency of 9c is a result of the strong electron back‐donation Si←C π 9. Additionally, the IR spectra of complexes 9a – c show for the nitrosyl ligand, as expected, a strong and broad signal in the 1553–1560 cm –1 region.…”

Über den Einfluss nichtpolarer Lösungsmittel auf Lage und Intensität von Absorptionsbanden in den Elektronenspektren apolarer Molekeln: II. Polyacetylene

“…2). Die allen Spektren eigene Vibrationsfeinstruktur, deren Aufspaltung von etwa 2000 cm-l der CK-Streckschwingung zugeschrieben wird [3], erlaubt infolge der Bandenscharfe eine genaue Messung der Absorptionsfrequenzen v1 bis v5. In Fig.…”