NOVEL AND STABLE METAL METAL-BONDED DIRUTHENIUM(I) COMPLEXES CONTAINING TCNX(0)/BULLET- IN BOTH THE INNER AND THE OUTER COORDINATION SPHERE (TCNX = TCNE, TCNQ) - A COMBINED EPR/ENDOR-SPECTROSCOPIC, UV/VIS/NEAR-IR-SPECTROSCOPIC, AND IR-SPECTROSCOPIC AND ELECTROCHEMICAL INVESTIGATION

Reaction of the diphosphazane-bridged diruthenium derivatives Ru2(mu-CO)(CO)4[mu-(RO)2PN(Et)P(OR)2]2 (R = Me, (i)Pr) with the electron acceptors TCNX (X = Q, E) affords products of the type {Ru2(CO)5[mu-(RO)2PN(Et)P(OR)2]2(eta-1-TCNX)}TCNX) containing a TCNX radical anion in both the inner and outer coordination sphere of the cation. The contribution of the coordinated TCNX.- to the EPR/ENDOR and UV/vis/near-IR spectra of these salts is partly obscured by that of the external, completely dissociated D2h-symmetric TCNX.-, but the infrared vibrational spectra and, in particular, the cyclic voltammograms show clearly the presence of both coordinated and noncoordinated species. Four distinct and reversible waves appear in benzonitrile; two correspond to the TCNX0/- and TCNX-/2- couples of the external TCNX, while the other pair, shifted by ca. 0.3 V to more positive potentials because of rather weak Ru --> TCNX pi-back-donation, are readily assigned to the corresponding redox couples of the coordinated TCNX. The external TCNQ.- anion of the TCNQ salts is readily exchanged for the diamagnetic tetraphenylborate anion to give compounds of the type {RU2(CO)5[mu-(RO)2PN(Et)P(OR)2]2(eta-1-TCNQ)}(BPh4) (R = Me, (i)Pr), thus enabling UV/vis/near-IR, IR, and EPR spectra of the coordinated TCNQ.- to be recorded in CH2CI2 without interference from the external TCNQ.- anion; the IR and EPR data confirm the low symmetry of the eta-1-bound TCNQ.-. With the aid of HMO/McLachlan perturbation calculations and ENDOR measurements it proved possible, for the first time, to record and reproduce EPR spectra of a coordinated TCNQ.- anion; the H-1 and N-14 hyperfine coupling constants used to simulate the EPR spectra fit the pattern calculated for a TCNQ.- bonded in the eta-1-mode to one metal center. Replacement of the external TCNE.- in the TCNE salts by a diamagnetic anion could not be achieved, but since the external TCNE.- is more easily oxidized than bound TCNE.-, selective oxidation of the former in situ to diamagnetic neutral TCNE could be accomplished, thus allowing EPR spectra of the coordinated TCNE.- to be recorded in CH2Cl2 Without interference from external TCNE.-. Successful reproductions of the highly resolved EPR spectra showed that, like TCNQ.-, TCNE.- is bonded in the eta-1-mode to one metal center. In situ oxidation of {Ru2(CO)5[mu-(RO)2PN(Et)P(OR)2]2(eta-1-TCNX)}+ (R = Me, (i)Pr) affords the completely oxidized dications containing a neutral coordinated TCNX ligand; these dications, as well as the reduced species {Ru2(CO)5[mu-(iPrO)2PN(Et)P(OiPr)2]2(eta-1-TCNQ)}, were characterized by UV/vis/near-IR spectroscopy.