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(II) complex [(eta(1):eta(6):eta(1)-1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene) Rh][PF6](2), 6(+), in a two-legged 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 [(eta(1):eta(1)-1,4bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene)Rh(CO)(3)][PF6] (8), [(eta(1):eta(1)-1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene)Rh(CNC(CH3)(3))(2)][PF6] (10), and [(eta(1):eta(1)-1,4-bis[4-(diphenylphosphino)butyl]-2,3,5,6-tetramethylbenzene) Rh (CO)(CH3CN)][PF6] (11). The Rh(II) 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 [(eta(1):eta(6):eta(1)-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; P (1) over bar; a = 10.1587(7) Angstrom; b = 11.5228(8) Angstrom; c = 17.2381(12) Angstrom; alpha = 96.4379(13)degrees; beta = 91.1870(12)degrees; gamma = 106.1470(13)degrees; Z= 2. 6: triclinic; P (1) over bar; a = 11.1934(5) Angstrom; b = 12.4807(6) Angstrom; c = 16.1771-(7) Angstrom; alpha = 81.935(7)degrees; beta = 89.943(1)degrees; gamma = 78.292(1)degrees; Z = 2.6(+): monoclinic; P2(1)/n; a = 11.9371(18) Angstrom; b = 32.401(5) Angstrom; c 12.782(2) Angstrom; beta 102.890(3)degrees; Z = 4.11: triclinic; P (1) over bar; a = 13,5476(7) Angstrom; b = 13.8306(7) Angstrom; c = 14.9948(8) Angstrom; alpha = 74.551(1)degrees; beta 73.895(1)degrees; gamma= 66.046(1); Z = 2.