Rh(II) and Rh(I) Two-Legged Piano-Stool Complexes: Structure, Reactivity, and Electronic Properties

The ligand 1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene, 3, was used to synthesize a mononuclear Rh(ll) complex [eta1:eta6:eta1-1, 4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene)Rh][PF6]2, 6, in a twolegged piano-stool geometry. The structural and electronic properties of this novel complex including a singlecrystal EPR analysis are reported. The complex can be cleanly interconverted with its Rh(l) form, allowing for a comparison of the structural properties and reactivity of both oxidation states. The Rh(l) form 6 reacts with CO, tert-butyl isocyanide, and acetonitrile to form a series of 15-membered mononuclear cyclophanes [(:-1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene)Rh(CO)3][PF6] (8), [(:-1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene)Rh(CNC(CH3)3)2][PF6] (10), and [(:-1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6tetramethylbenzene)Rh(CO)(CH3CN)][PF6] (11). The Rh(ll) complex 6 reacts with the same small molecules, but over shorter periods of time, to form the same Rh(l) products. In addition, a model two-legged piano-stool complex [eta1:eta6:eta1-1,4-bis[3-(diphenylphosphino)propoxy]-2,3,5,6-tetramethylbenzene)Rh][B(C6F5)4], 5, has been synthesized and characterized for comparison purposes. The solid-state structures of complexes 5, 6, 6, and 11 are reported. Structure data for 5: triclinic; PI; a = 10.1587(7) A; b == 11.5228(8) A; c = 17.2381(12) A; a = 96.4379(13)°; (beta) = 91.1870(12)°; y = 106.1470(13)°; Z= 2. 6: triclinic; PI; a = 11.1934(5) A; b= 12.4807(6) A; c= 16.1771(7) A; a = 81.935(7)°; (beta) = 89.943(1)°; y = 78.292(1)°; Z= 2. 6 monoclinic; P2(1)/n; a = 11.9371(18) A; b = 32.401(5) A; c = 12.782(2) A; (beta) - 102.890(3)°; Z= 4. 11: triclinic; PI; a = 13.5476(7) A; b = 13.8306(7) A; c = 14.9948(8) A; a - 74.551(1)°; (beta) = 73.895(1)°; ... - 66.046(1)°; Z= 2.