Two coordination modes of TCNE in the ruthenium amidinates: The first example providing experimental evidence for κ1-N to η2-C rearrangement

Reactions of Cp∗Ru(κ2-N(R)double bond; length as m-dashC(R′)NR) (1a; R = iPr, R′ = Me, 1b; R = tBu, R′ = Ph) with TCNE initially give dark green colored intermediary species, which are readily converted to brown colored “η2-C” coordination complexes, Cp∗Ru(κ2-N(R)double bond; length as m-dashC(R′)NR)(η2-TCNE) (3a; R = iPr, R′ = Me, 3b; R = tBu, R′ = Ph). These “η2-C” complexes are characterized by spectroscopy and crystallography. A stable ruthenium amidinate having a “κ1-N”-coordinated TCNE, Cp∗Ru(κ2-N(tBu)double bond; length as m-dashC(Mes)NtBu)(κ1(N)-TCNE) (2c), is synthesized by treatment of Cp∗Ru(κ2-N(tBu)double bond; length as m-dashC(Mes)NtBu) (1c) with TCNE, the structure of which is unequivocally confirmed by X-ray structure determination and the charge transfer nature is supported by ESR analysis. Close analogy in IR and UV–Vis spectroscopy of 2c with the dark green colored intermediary species formed from 1b suggests that this is “κ1-N” ruthenium amidinate, which is rearranged to the “η2-C” complex 3b.