Redox routes to arenechromium complexes of two-, three- and four-electron alkynes; structure and bonding in paramagnetic [Cr(CO)L(η-RC
CR)(η-arene)]+
Abstract
X-Ray structural studies on the redox pair [Cr(CO)2(η-PhCCPh)(η-C6Me5H)]z
(z
= 0 and 1) show that one-electron
CR)(η-C6Me6)]+
(R = Ph or C6H4OMe-p) reacts with Lewis bases to give [Cr(CO)L(η-RC
CR)(η-C6Me6)]+
{L = CNXyl, P(OMe)3 and P(OCH2)3CEt}, X-ray studies on which show a rotation of the
CR)(η-C6Me6)]+ show delocalisation of the unpaired electron onto the
CR)(η-C6Me6)]+ undergo both one-electron reduction and oxidation, and chemical oxidation of [Cr(CO){P(OCH2)3CEt}(η-p-MeOC6H4C
CC6H4OMe-p)(η-C6Me6)]+ with AgPF6 gives the dication [Cr(CO){P(OCH2)3CEt}(η-p-MeOC6H4C
CC6H4OMe-p)(η-C6Me6)]2+. Thus the two-electron
CR)(η-C6Me6)] is converted into the four-electron
CR)(η-C6Me6)]2+ by an ECE (E = electrochemical, C = chemical) process in which all of the intermediates have been fully characterised.