A series of d 8 –d 8 unsymmetric dinuclear Ir and Rh complexes with 32 valence electrons, Ir (XylNC) 3 M (XylNC) (meso ‐dpmppp) 2+ (2aIrM: M = Ir, Rh), Rh (RNC) 2 Rh (RNC) 2 (meso ‐dpmppp) 2+ (3a, bRh 2: R = Xyl (a), t Bu (b) ), and M 1 (CO) 2 M 2 Cl (CO) (meso ‐dpmppp) + (4cM 1 M 2: M 1 M 2 = Ir 2, IrRh, Rh 2), were synthesized using meso ‐Ph 2 PCH 2 P (Ph) (CH 2) 3 P (Ph) CH 2 PPh 2 (meso ‐dpmppp). Two distinct structural motifs were characterized: the (4: 4) face‐to‐face arrangement without metal–metal bonding and the (5: 3) configuration with a M 1 →M 2 bond. Experimental and theoretical results suggested that the structural motifs appeared as the most thermodynamically stable species depending on the combination of metal elements and terminal ligands. The (4: 4) complexes displayed a characteristic absorption band around 494–525 nm. Reactions of 4cRh 2 with RNC yielded 3a, bRh 2 through Rh (XylNC) 2 Rh (CO) Cl (meso ‐dpmppp) + (6Rh 2) and that of 4cIrRh with XylNC gave 2aIrRh. In contrast, reactions of 4cIr 2 with RNC afforded d 8 –d 8 Ir 2 complexes with 34 valence electrons, Ir (XylNC) 2 (μ−CO) Ir (XylNC) 2 (meso ‐dpmppp) 2+ (7aIr 2 ’) and Ir (t BuNC) 3 Ir (CO) (t BuNC) (meso ‐dpmppp) 2+ (8bIr 2), possessing the (4. 5: 4. 5) structure with Ir (μ‐CO) Ir 3c/2e interactions and the (5: 4) configuration with an Ir→Ir polarized bond, respectively. Selective formation occurred thermodynamically under the decisive influence of RNC ligands. These results revealed that the structure and reactivity of unsymmetric d 8 –d 8 Ir/Rh complexes can be thermodynamically controlled by choosing the metals and terminal ligands, providing useful information for dimetal catalytic systems.
Nakajima et al. (Thu,) studied this question.