Unsymmetric d ⁸ –d ⁸ Ir and Rh Dinuclear Complexes Formed with a Linear Tetraphosphine under Thermodynamic Control

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.