REACTIONS OF THE ELECTRON-RICH TRIPLY BONDED DIRHENIUM(II) COMPLEXES RE2X4-MU-DPPM)2 (X = CL, BR) WITH DIOXYGEN .1. MULTIELECTRON REDOX CHEMISTRY WITH PRESERVATION OF THE RE2X4(DPPM)2 UNIT
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The dirhenium(II) complexes Re2X4(-dppm)2 (1a, X = Cl; 1b, X = Br; dppm = Ph2PCH2PPh2), which contain an electron-rich Re-Re triple bond, react with dioxygen in a variety of solvents to afford Re2(-O)(-X)(O)X3(-dppm)2 (2a, X = Cl; 2b, X = Br) and Re2(-O)(O)2X4(-dppm)2 (3a, X = Cl; 3b, X = Br) in which the Re2X4(-dppm)2 entity is preserved and net 4- and 6-electron oxidations of the dirhenium unit have occurred. The complexes of type 2, which are weakly paramagnetic and possess Knight-shifted NMR spectra, have edge-sharing bioctahedral structures as shown by a single-crystal X-ray structure determination on a crystal of composition Re2(-O)(-Cl)(O)Cl3(-dppm)2(CH3)2CO (2a(CH3)2CO). The structure solution was complicated by a disorder involving the terminal oxo ligand and the syn terminal chloro ligand on the adjacent Re atom. The ReRe distance is very long (3.363(2) ). Crystal data for 2a(CH3)2CO (+23 C): triclinic space group P1 (No. 2), a = 16.069(6) , b = 16.540(5) , c = 12.214(2) , = 109.18(2), = 99.09(3), = 101.01(3), V = 2923(2) 3, and Z = 2. The structure was refined to R = 0.068 (Rw = 0.082) for 6553 data with I > 3.0(I). Complex 2a can be derivatized by reaction with isocyanide ligands (RNC; R = C6H3-2,6-Me2 (xylyl), CHMe2, CMe3, C6H11) and acetonitrile to give complexes of the type Re2(-O)(O)Cl4(-dppm)2(L) (4, L = RNC; 5, L = MeCN) which like 2a are weakly paramagnetic and have Knight-shifted NMR spectra. The structure of crystals of composition Re2(-O)(O)Cl4(-dppm)2(CNxyl)CH2Cl2H2O (4a) has been established by X-ray crystallography. The structure is an unsymmetrical corner-sharing bioctahedron Cl3Re(-O)(-dppm)2Re(O)Cl(CNxyl), in which the rhenium centers can formally be represented as Re(III)-Re(V), i.e. ReIII0RevO. Crystal data for 4a (+20 C): triclinic space group P1 (No. 2), a = 14.316(3) , b = 14.818(2) , c = 16.840(2) , = 99.60(1), = 106.38(1), = 97.26(1), V = 3322(2) 3, and Z = 2. The structure was refined to R = 0.056 (Rw = 0.082) for 5978 data with I > 3.0(I). The compounds of type 4 have been oxidized by [(5-C5H5)2Fe]PF6 to afford the mixed-valence paramagnetic complexes [Re2(-O)(O)Cl4(-dppm)(CNR)]PF6 (6; R = C6H3-2,6-Me2, CHMe2, CMe3). The dirhenium(V) complexes Re2(-O)(O)2X4(-dppm)2 (3), which are the final products of the oxygenation of 1 and 2, have a centrosymmetric corner-sharing bioctahedral structure. The structures of two different crystals of 3a (X = Cl), which contain either two molecules of lattice acetone (3a(CH3)2CO) or two molecules of dichloromethane (3aCH2Cl2), have been determined. Crystal data for 3aCH3)2CO (+23 C): triclinic space group P1 (No. 2), a = 11.193(2) , b= 12.882(2) , c = 10.892(2) , = 101.95(1), = 113.30(1), = 75.52(1), V= 1386.3(4) , and Z = 1. The structure was refined to R = 0.029 (Rw = 0.058) for 4209 data with I > 3.0(I). Crystal data for 3aCH2Cl2 (+20 C): triclinic space group P1 (No. 2), a = 11.264(4) , b = 11.317(4) , c = 12.966(7) , = 103.86(4), = 104.24(4), = 113.54(3), V= 1358(3) 3, and Z = 1. The structure was refined to R = 0.052 (Rw = 0.072) for 3538 data with I > 3.0(I). 1993, American Chemical Society. All rights reserved.
