Abstract The 2.5-difurfurylpyrrole-O.N.O ligands 3a, b [R = CO2C2H5 (a). COCH, (b)] are obtained by reaction of the furanes l a , b with the 2,5-bis(chloromethyl)pyrrole 2 in the presence of SnCl4. Proton abstraction from 3a, b with NaH affords the sodium salts 4a-Na and 4b-Na. Exchange of the chlorine bridges in [μ-ClRh(Diol)]2 (5,5') (Diol = cyclooctadiene, norbornadiene) results in the formation of the 14-electron complexes (Diol)Rh(O.N.O) (6a,6'a). Addition of PPh3, yields the four-coordinated rhodium complexes (Diol)Rh(O.N.O)(PPh3) (7a,7'a). These compounds are also available in a reverse reaction sequence from 5,5', PPh3, and 4a-Na. The mononuclear rhodium complexes RhCl(Diol)(PPh3) (8,8') are isolated as intermediates. In 7a, 7'a the olefinic ligands are replaced by carbon monoxide to give the dicarbonyl rhodium complex (OC)2Rh(O.N.O)(PPh3) (9a) being detectable only in solution. The same result is achieved upon addition of CO to the compound (OC)Rh(O.N.O)(PPh,) (11a) which results bv the reaction of [μ-ClRh(CO)(PPh3)]2 (10) with 4a-Na. Oxidative addition of CH3I or H2 to 6a, 6 a, 7a, 7'a or 11a was not observed. 1H and 31P{1H} NMR investigations indicate that depending on the temperature the O.N.O ligand in the 14-electron rhodium complex 11a acts as tri- (11a-A), bi- (11a-B) and monodentate (IIa-C) ligands. respectively. 11a also reacts with PPh, to form the /ram-bis(phosphane)rhodium complex (PPh3)2Rh(CO)(O.N.O) (12a). 12a and the analogous complexes 12b and trans-(PMe3)2Rh(CO)(O,N.O) (14a) are obtained by action of ClRh(CO)L2 (13) (L = PPh3. PMe3) on 4a-Na and 4b-Na, respectively. The methylene bridges in the O.N.O ligand 3a are not oxidized, neither in the non-complexed (3a) nor in the complexed (12a) state. According to an X-ray structural analysis 14a crystallizes in the monoclinic space group P21/n with Z = 4. In 6a, 6'a, 7a, 7'a, 9a, 11a, 12a, b, and 14a the O.N.O ligand is always nitrogen bonded
