Photochemistry of (η-cyclopentadienyl)nitrosylnickel in frozen gas matrices at 20 K. Infrared spectroscopic evidence for mono- and di-carbonyl(η-cyclopentadienyl)nickel in carbon monoxide matrices and for a species formed by photoionisation or photoelectron transfer in inert matrices

Abstract

Infrared evidence, including ¹³CO data, is presented for the formation of [Ni(η-C₅H₅)(CO)], [Ni(η-C₅H₅)(CO)₂], and ultimately [Ni(CO)₄] on the u.v. photolysis of [Ni(η-C₅H₅)(NO)] in CO or mixed CO and ‘inert’(nitrogen, argon) matrices at 20 K. Infrared evidence, including ¹⁵NO data, is also presented for the formation of a species [Ni(η-C₅H₅)(NO*)][the asterisk denotes a nitrosyl group with an unusually low value of ν(NO)] on photolysis of [Ni(η-C₅H₅)(NO)] in argon, methane, and nitrogen matrices at 20 K. The significance of the low value of ν(NO) for [Ni(η-C₅H₅)(NO*)] is discussed in terms of either photoionisation, i.e. formation of an ion pair [Ni(η-C₅H₅)]⁺NO^–, or photoelectron transfer, i.e. the nitrosyl group acting as a one- or two-electron ligand instead of a three-electron ligand. It is concluded that [Ni(η-C₅H₅)(NO*)] belongs to a class of complexes in which electron transfer from the metal to the nitrosyl ligand is particularly extensive and bending of the M–N–O group may be involved. A convenient photochemical synthesis of [Ni(η-C₅H₅)(¹⁵NO)] is described.