consistent with the proposed structure, notably the return to C, symmetry. The addition of a second rhodium dicarbonyl fragment and formation of 6 causes this Soret-like band to shift still further to the red, to about 500 nm. The structures of 5b-CI and 6a (Fig. 1 and2, respectively) are similar to those of [{Rh(CO),},(OEP)][91 and [{Rh(CO),},(NMC)] (NMC = N-methylcorrole)lloI in that each metal center bridges an imine and an amine nitrogen atom. The Rh-N distances range from 2.061(4) to 2.081(4) A, the Ir-N distances from 2.064(5) to 2.091(6) A. The general geometry around the metal atoms is thus approximately square-planar, with the metal planes at an angle of roughly 47" to the plane of the sapphyrin. The sapphyrin plane is considerably ruffled, with the pyrrole rings distorted in such a way that the nitrogen atoms N1 and N2 are bent towards Rh(a) and Ir and the nitrogen atoms N4 and N5 are bent towards Rh(b). Maximum and average deviations from the N,C,, plane are -0.425 and 0.26410.054 A, respectively, for Rh and -0.398(6) and 0.765(8)/0.206 A, respectively, for Ir.
All of the sapphyrin complexes discussed here, with the exception of 2a and 4a,I6] show remarkable stability. The relatively high v(C0) values indicate that at least one of the carbonyl groups bound to the rhodium center in either 4 or 6 should be easily displaced. To date, however, we have not seen any indication of either photolytic or thermal loss of CO from either 4 or 6. Also, all of the coordination compounds reported here display much lower reactivity under oxidizing conditions (e.g., methyl iodide or acetic anhydride)." Reagents such as HCI cleave the metals to form protonated sapphyrins (9). Iodine reacts only slowly with 6 or 7, removing one of the metal carbonyl moieties to afford 3 and 5 b, respectively. Furthermore, in preliminary studies we have found that complex 6 acts as an efficient homogeneous catalyst for the hydrogenation of alkenes.1'21 Experimental Procedure 5b: Sapphyrin 1 b (50 mg, 0.08 mmol) was dissolved in dichloromethane (1 5 mL) containing triethylamine (0.5 mL). [IrCl(CO),(py)] (30 mg, 0.08 mmol) was added and the solution stirred at room temperature for 12 h. The solvent was removed in vacuo and the residue taken up in dichloromethane. Filtration through Celite. followed by chromatographic purification on silica gel using dichloromethaneimethanol (9: 1) as the eluent, gave the cationic iridium complex 5 b (62 mg) in 81 O h yield. Recrystallization from dichloromethane-metha-no1 then gave analytically pure product (73% recovery). 'H NMR (300 MHz,