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Mononuclear and Binuclear Molybdenum(V) Complexes of the Ligand N,N‘-Dimethyl-N,N‘-bis(2-mercaptophenyl)ethylenediamine:  Geometric Isomers

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journal contribution
posted on 12.02.1997, 00:00 by Keith R. Barnard, Michael Bruck, Susan Huber, Carina Grittini, John H. Enemark, Robert W. Gable, Anthony G. Wedd
The syntheses of mononuclear complexes cis-MoVOXL (X = Cl, Br, OMe, OEt, OPh, SPh, NCS, OSiMe3) and two binuclear complexes MoV2O3L2 of the title ligand LH2 are reported. Two forms of MoOClL, with cis oxo and chloro ligands, were crystallized, one in space group P21/n, with a = 10.440(2) Å, b = 14.260(2) Å, c = 12.041(2) Å, β = 102.76(2)°, V = 1748(1) Å3, and Z = 4, and the other in P21/c, with a = 13.564(4) Å, b = 7.172(2) Å, c = 18.242(6) Å, β = 95.19(1)°, V = 1767(2) Å3, and Z = 4. MoO(OSiMe3)L crystallizes in space group P21/c, with a = 15.923(3) Å, b = 11.141(2) Å, c = 14.186(2) Å, β = 112.64(2)°, V = 2323(1) Å3, and Z = 4, while MoO(NCS)L crystallizes in Pna21, with a = 22.471(2) Å, b = 12.136(2) Å, c = 7.138(1) Å, V = 1947(1) Å3, and Z = 4. The four structures reveal two possible conformations for ligand L:  one with trans S atoms (cis,trans-MoOClL and -MoO(OSiMe3)L) and one with cis S atoms (cis,cis-MoOClL and -MoO(NCS)L). The cis,cis isomers are converted to the cis,trans forms under reflux in MeCN at 80 °C. Only the cis,trans forms could be isolated for bulkier ligands X (OPh, SPh, OSiMe3). A short H3C···X interaction is present in the cis,cis forms:  C···Cl = 3.07 Å and C···N = 2.93 Å, for X = Cl and NCS, respectively. Infrared and electronic spectral data provide unambiguous identification of the stereochemistry of ligand L in mononuclear complexes MoOXL. Effective removal of ligand X = OR from cis,cis-MoO(OR)L (R = Me, Et) led to two binuclear complexes (MoVOL)2(μ-O) of Ci and C1 point symmetries. Ci-(MoOL)2(μ-O)·thf crystallizes in space group P21/c, with a = 8.5650(5) Å, b = 15.1862(9) Å, c = 16.8038(9) Å, β = 100.183(1)°, V = 2157.1(8) Å3, and Z = 2, while C1-(MoOL)2(μ-O)·CH2Cl2 crystallizes in space group P21/c, with a = 12.5250(5) Å, b = 24.673(1) Å, c = 12.7253(6) Å, β = 108.070(4)°, V = 3738.6(3) Å3, and Z = 4. Ci-(MoOL)2(μ-O)·thf features two cis,trans-MoVOXL centers with X = μ-O, while C1-(MoOL)2(μ-O)·CH2Cl2 contains a cis,trans and a cis,cis center. In the latter, the Mo−O−Mo link is asymmetric, allowing relief of steric crowding on the cis,cis side of the molecule.

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