%0 Journal Article
%A G. H. Hetterscheid, Dennis
%A Kaiser, Jasper
%A Reijerse, Eduard
%A P. J. Peters, Theo
%A Thewissen, Simone
%A Blok, Arno N. J.
%A M. M. Smits, Jan
%A de Gelder, René
%A Bruin, Bas de
%D 2005
%T IrII(ethene): Metal or Carbon Radical?
%U https://acs.figshare.com/articles/journal_contribution/Ir_sup_II_sup_ethene_Metal_or_Carbon_Radical_/3300925
%R 10.1021/ja0439470.s002
%2 https://ndownloader.figshare.com/files/5138659
%K MeCN
%K C 2 H 4
%K type addition reactions
%K CH
%K ethene ligand
%K NHC
%K DFT
%K III
%K II
%K tpa
%K Ir
%X One-electron oxidation of [(Mentpa)IrI(ethene)]+ complexes (Me3tpa = N,N,N-tri(6-methyl-2-pyridylmethyl)amine; Me2tpa = N-(2-pyridylmethyl)-N,N,-di[(6-methyl-2-pyridyl)methyl]-amine) results in
relatively stable, five-coordinate IrII−olefin species [(Mentpa)IrII(ethene)]2+ (12+: n = 3; 22+: n = 2). These
contain a “vacant site” at iridium and a “non-innocent” ethene fragment, allowing radical type addition
reactions at both the metal and the ethene ligand. The balance between metal- and ligand-centered radical
behavior is influenced by the donor capacity of the solvent. In weakly coordinating solvents, 12+ and 22+
behave as moderately reactive metallo-radicals. Radical coupling of 12+ with NO in acetone occurs at the
metal, resulting in dissociation of ethene and formation of the stable nitrosyl complex [(Me3tpa)Ir(NO)]2+
(62+). In the coordinating solvent MeCN, 12+ generates more reactive radicals; [(Me3tpa)Ir(MeCN)(ethene)]2+
(92+) by MeCN coordination, and [(Me3tpa)IrII(MeCN)]2+ (102+) by substitution of MeCN for ethene. Complex
102+ is a metallo-radical, like 12+ but more reactive. DFT calculations indicate that 92+ is intermediate between
the slipped-olefin IrII(CH2CH2) and ethyl radical IrIII−CH2−CH2· resonance structures, of which the latter
prevails. The ethyl radical character of 92+ allows radical type addition reactions at the ethene ligand.
Complex 22+ behaves similarly in MeCN. In the absence of further reagents, 12+ and 22+ convert to the
ethylene bridged species [(Mentpa)(MeCN)IrIII(μ2-C2H4)IrIII(MeCN)(Me3tpa)]4+ (n = 3: 34+; n = 2: 44+) in
MeCN. In the presence of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxo), formation of 34+ from 12+ in MeCN
is completely suppressed and only [(Me3tpa)IrIII(TEMPO-)(MeCN)]2+ (72+) is formed. This is thought to
proceed via radical coupling of TEMPO at the metal center of 102+. In the presence of water, hydrolysis of
the coordinated acetonitrile fragment of 72+ results in the acetamido complex [(Me3tpa)IrIII(NHC(O)CH3))(TEMPOH)]2+ (82+).
%I ACS Publications