Novel coordinatively unsaturated ruthenium complexes, (eta(5)-C5Me5)Ru(amidinate), were synthesized from [(eta(5)-C5Me5)Ru(OMe)](2) and lithium amidinates, which exist as monomers in both solution and solid states and are highly reactive toward two-electron ligands.
Reactions of Cp*Ru(kappa(2)-N(R)=C(R')NR) (1a; R = Pr-i, R' = Me, 1b; R = Bu-t, R' = Ph) with TCNE initially give dark green colored intermediary species, which are readily converted to brown colored "eta(2)-C" coordination complexes, Cp*Ru(kappa(2)-N(R)=C(R')NR)(eta(2)-TCNE) (3a; R = Pr-i, R' = Me, 3b; R = Bu-t, R' = Ph). These "eta C2-" complexes are characterized by spectroscopy and crystallography. A stable ruthenium amidinate having a kappa(1)-N ''-coordinated TCNE, Cp*Ru(kappa(2)-N(Bu-t)=C(Mes)(NBu)-Bu-t)(kappa(1)(N)-TCNE) (2c), is synthesized by treatment of Cp*Ru(kappa(2)-N(Bu-t)=C(Mes)(NBu)-Bu-t) (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 "kappa(1)-N" ruthenium amidinate, which is rearranged to the "eta(2)-C" complex 3b. (C) 2008 Elsevier B.V. All rights reserved.