Reactions of the 17-Electron Iron-Centered Radicals {η5-C5Ph5}Fe(CO)2•and {η5-C5Ph4(p-tolyl)}Fe(CO)2•with Organic Halides and Lewis Bases

The 18-electron dimers [Cp‘Fe(CO) 2 ] 2 (Cp‘ = η 5 -C 5 Ph 5, η 5 -C 5 Ph 4 ( p -tolyl)), which undergo only very slight thermal dissociation to the corresponding 17-electron monomers Cp‘Fe(CO) 2 •, nonetheless exhibit reactivity patterns which reflect the chemistry of the monomers. Thus, reactions with several organic halides RX give Cp‘Fe(CO) 2 R and Cp‘Fe(CO) 2 X, consistent with initial halogen atom abstraction by Cp‘Fe(CO) 2 • followed by coupling of the resulting carbon-centered radical with a second molecule of Cp‘Fe(CO) 2 • . Reactions of [(η 5 -C 5 Ph 4 ( p -tolyl)}Fe(CO) 2 ] 2 with small phosphines L result in displacement of η 5 -C 5 Ph 4 ( p -tolyl) radicals rather than formation of isolable 17-electron compounds [{η 5 -C 5 Ph 4 ( p -tolyl)}Fe(CO)L •, while reaction with the isonitrile t -BuNC results in disproportionation to the salt [{η 5 -C 5 Ph 4 ( p -tolyl)}Fe( t -BuNC) 3 ][{η 5 -C 5 Ph 4 ( p -tolyl)}Fe(CO) 2 ], possibly via the substituted species (η 5 -C 5 Ph 4 ( p -tolyl)Fe(CO)( t -BuNC) • . Reactions of [{η 5 -C 5 Ph 4 ( p -tolyl)}Fe(CO) 2 ] 2 with phosphites P(OR) 3 do give the substituted radical species {η 5 -C 5 Ph 4 ( p -tolyl)}Fe(CO){P(OR) 3 } •, but Arbuzov products such as {η 5 -C 5 Ph 4 ( p -tolyl)}Fe(CO) 2 Me, {η 5 -C 5 Ph 4 ( p -tolyl)}Fe(CO) 2 {P( O)(OMe) 2 }, and {η 5 -C 5 Ph 4 ( p -tolyl)}Fe(CO){P(OMe) 3 }{P( O)(OMe) 2 } are the major products formed when R = Me and, to a lesser extent, Et. The Arbuzov reaction is hindered when R is large, and the compound {η 5 -C 5 Ph 4 ( p -tolyl)}Fe(CO){P(O- i -Pr) 3 } • is a persistent radical which has been characterized by, inter alia, EPR spectroscopy. The EPR spectrum of a frozen solution in benzene can be analyzed in terms of a uniaxial g matrix ( g ∥ = 1.993, g ⊥ = 2.103) with isotropic 31 P hyperfine coupling of 37 G (3.7 mT), typical of d 7 organometallic radicals in which the unpaired electron is essentially confined to a metal d z 2 orbital.