Matrix isolation studies of the photochemistry of some pi-hydrocarbon metal-carbonyl and metal-carbonyl-nitrosyl complexes

Hitam, Ramli Bin (1984) Matrix isolation studies of the photochemistry of some pi-hydrocarbon metal-carbonyl and metal-carbonyl-nitrosyl complexes. University of Southampton, Doctoral Thesis.

Abstract

Photochemical studies have been carried out on some v-hydrocarbon transition metal carbonyl and mixed nitrosyl carbonyl complexes isolated infrozen gas matrices (CH 4,Ar,N2,CO,13CO doped CH4 and C2 H4 doped CH4) at cryogenic temperatures (ca. 12 K). Photochemically generated species have been characterised via their infrared active CO and NO stretching bands, isotopic (13 CO, C180 and N180) labelling, and CO-factored force-field fitting. Consequently, intermediates arising from a variety of photochemical pathways have been established. Photochemical reactions of matrix isolated [Fe(n4-polyene)(CO)3](polyene=C4H4, C 4 H 4 CO, C7H10 and CaH8), [V(n5-C5H5)(CO)4], [V(n5-C5H5)(CO)(NO)2], [M(n5-C5H5)(CO)2(NO)](M=Cr, Mo. W), [Mn(n1-C3H5)(CO)5], [Mn(CO)5(COCH3)] and (Fe(n5-C5H5)(CO)2(COCH3)] complexes have been investigated. In general, all the complexes undergo dissociative loss of CO as primary photochemical processes to form co-ordinatively unsaturated 16-electron species (e.g. [Fe(n4-polyene)(CO)2],[V(n5-C5H5)(CO)3], [M(n5-C5H5)(CO)(NO)], [Mn(CO)4(COCH3)] and [Fe(n5-C5H5)(CO)(COCH3)].In addition, other processes have been observed, e.g. partial dechelation of the polyene-Fe bonding (e.g. [Fe(n2-C4 H4)(CO)3] and [Fe(n2-C8H8)(CO)3]), ring-to-metal H migration (e.g. [Fe(n5-C7H9)(CO)2(H)]), changes in NO co-ordinationfrom being 3-electron donor to being 1-electron donor ligand (e.g. [V(n5-C5H5)(CO)(NO)(NO~)]), intramolecular CO attack at the N of a NO ligand to form isocyanato species (e.g. [VIN 5-C5H5)(CO)(NCO)) and [W(n5-C5H5)(NCO)I), andnl-C3H5 n3-C5 H5 conversion (e.g. [Mn(nl-C3H5)(CO)5] -a [Mn(n3-C3H5)(CO)4]). In the case of [Fe(n4-C4H4)(CO)3] the n2-species may have resulted in the generation of a metallocyclic intermediate, via vK_~ a rearrangement of the diene-Fe bonding, which has been proposed to be responsible for the CO insertioninto the C4H4 ring of [Fe(n4-C4H4)(CO)3J to form [Fe(n4-C4H4C0)(CO)3] in a CO matrix. In [Fe(n4-C8H8)(CO)3J the n2-species has been proposed as the intermediate for [Fe(tub-n4-C 8H8)(CO)3] -c-- [Fe(chair -n4-C8H8)(CO)3J conformational interconversion. The infrared v(CO) acetyl data have established that the acetyl ligands in the matrix isolated co-ordinatively unsaturated species [Mn(CO)4(COCH3)] and [Fe(n5-C5H5)(CO)(COCH3)] have a-acetyl type bonding.

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