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)C(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)C(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)C(Mes)NtBu)(κ1(N)-TCNE) (2c), is synthesized by treatment of Cp∗Ru(κ2-N(tBu)C(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.

A stable ruthenium amidinate having a “κ1-N”-coordinated TCNE, Cp∗Ru(κ2-N(tBu)C(Mes)NtBu)(κ1(N)-TCNE) (2c), is synthesized by treatment of Cp∗Ru(κ2-N(tBu)C(Mes)NtBu) (1c) with TCNE, and the charge transfer nature is supported by ESR analysis. Close analogy in IR and UV–Vis spectroscopy of 2c with the intermediary species formed from the Ph analogue of 1c suggests that this intermediary product is “κ1-N TCNE” ruthenium amidinate, which is rearranged to the “η2-C TCNE” complex.Figure optionsDownload as PowerPoint slide