REACTIONS OF ATOMIC AND DIATOMIC IRON WITH METHYLACETYLENE IN SOLID ARGON

The chemistry of atomic and diatomic iron with methylacetylene (MA) in argon matrices has been studied using Fourier transform infrared spec troscopy. Cocondensation of iron vapors with MA results in the formati on of atomic iron and diatomic iron complexes with MA. Vibrational spe ctra indicate that the atomic Fe(MA) complex is sigma bonding with one or more hydrogen atoms, whereas Fe-2(MA) exhibits a spectrum that is characteristic of a pi complex. Photolysis of the diiron-methylacetyle ne complex with low-energy visible Light (lambda > 670 nm) causes its isomerization into Fe-2(H2C=C=CH2). Upon exposure of the matrix to vis ible light (lambda > 500 nm), photoisomerization of methylacetylene in to allene with the subsequent C-H bond activation of allene is observe d. The photoproduct has been characterized as the metal atom insertion compound, propadienyliron hydride (HFeHC=C=CH2). Excitation of the Fe (MA) sigma complex with shorter wavelength visible light (lambda > 400 nm) leads to the activation of the acetylenic C-H bond via metal atom insertion and formation of 1-propynyliron hydride. Photolysis with ul traviolet light (280 MI < lambda < 360 nm) causes activation of one of the methyl C-H bonds as well as the carbon-carbon single bond of MA. The photoproducts have been identified as 3-propynyliron hydride and e thynylmethyliron, respectively. Experiments using various deuterated f orms of methylacetylene (CH3C equivalent to CD, CD3C equivalent to CH, CD3C equivalent to CD) support the characterization of these products and their vibrational mode assignments.