135929-06-5Relevant academic research and scientific papers
Synthesis and reactivity of bimetallic alkoxysilyl complexes. Crystal structure of [Fe(CO)3{μ-Si(OMe)2(OMe)}(μ-dppm)Rh(CO)] (dppm = Ph2PCH2PPh2): A complex with a μ2-η2-SiO bridge between iron and rhodium
Braunstein, Pierre,Knorr, Michael,Villarroya, Eva,DeCian, André,Fischer, Jean
, p. 3714 - 3722 (2008/10/08)
Bimetallic Fe-Rh complexes have been prepared from the (alkoxysilyl)iron derivatives [HFe(CO)3{Si-(OMe)3}(dppm-P)] or [HFe(CO)3{Si(OMe)3}(dppm-P)]-, the dppm ligand of which helps assembling and stabilizing the dinuclear unit The crystal structure of [Fe(CO)3{μ-Si(OMe)2(OMe)}(μ-dppm)Rh(CO)] (1a) has been determined: monoclinic, space group P21/n, a = 22.717 (5) A?, b = 11.348 (2) A?, c = 14.202 (2) A?, β = 94.47 (2)°, V = 3650.2 A?3, Z = 4, R = 0.033, Rw = 0.052 for 4531 reflections with I > 3σ(I). Complex 1a contains an unusual μ2-η2-SiO bridge between the Fe and Rh atoms (Fe-Rh = 2.6283 (7), Rh-O7 = 2.167 (3), 07-Si = 1.683 (3), Si-Fe = 2.249 (1) A?). Complex [Fe(CO)3{μ-Si(OMe)2(OMe)}(μ-dppm)Rh(PPh 3)] (2) reacts with P(OPh)3 to give [Fe(CO)3{μ-Si(OMe)2(OMe)}(μ-dpprn)RhiP(OPh) 3}] (3). Complex 1a reacts reversibly with CO with opening of the μ2-η2-SiO bridge to give [Fe(CO)3(Si(OMe)3](μ-dppm)Rh(CO)2] (4). Protonation of the Fe-Rh bond of 1a with HBF4 yields [Fe(CO)2{μ-Si(OMe 2(OMe)}(μ-dppm)(μ-H)μ-CO)Rh(PPh3)] [BF4] (5), which is isoelectronic with [Fe(CO)2{μ-Si(OMe) 2(OMe)}(μ-dppm)(μ-H)(μ-CO)-RhCl] (6a), prepared by the addition of [HFe(CO)3{Si(OMe)3}(dppm-P)] to a suspension of [Rh2(μ-Cl)2-(COD)2] in Et2O. Reaction of K[Fe(CO)3{Si(OMe)3}(dppm-P)] with [RhCl(CS)(PPh3)2] afforded [Fe-(CO)3{Si(OMe)3}μ-dppm)Rh(CS)(PPh3)] (8). The stronger Rh-CS interaction compared with the Rh-CO interaction accounts for the strengthening of its bonding to Rh, preventing the transformation of 8 into 2, and also of the Rh←PPh3 bond, which precludes formation of the Rh-CS analogue of 1a. In contrast to the rigid situation in 1a, the lability of the O→Rh bond in 2, 3, 5, and 6 accounts for the dynamic behavior of the alkoxysilyl ligand, evidenced by variable-temperature 1H NMR spectroscopy, which renders the methoxy protons equivalent. The observed increase in O→Rh bond lability parallels the increase in electron density at the Rh center. Attempts to isolate related Fe-Co or Fe-Ir complexes were unsuccessful. In the latter case, a redox reaction resulted in the formation of [Fe(CO)3(PPh3)(dppm-P)].
