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

Abstract

The syntheses of mononuclear complexes cis-MoVOXL (X = Cl, Br, OMe, OEt, OPh, SPh, NCS, OSiMe3) and two binuclear complexes MoV 2O3L2 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 C i and C 1 point symmetries. C i -(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 C 1-(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. C i -(MoOL)2(μ-O)·thf features two cis,trans-MoVOXL centers with X = μ-O, while C 1-(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.

Synthesis, characterization and spectrochemical studies on a few binuclear µ-oxo molybdenum(V) complexes of pyrimidine derived Schiff base ligands

“…25 The Mo-Cl bond length of 2⋅51 Å shows that the chloride is loosely bound. 26 The bond lengths in the coordination sphere are not appreciably different from those in the previous dioxomolybdenum(VI) complex despite of the change in Mo oxidation state. Among the angles in A two-fold intermolecular H-bonding interaction is observed in the complex involving the hydrogen bound to the azomethine nitrogen and the chloride donors, i.e.…”

Toward modeling the high chloride, low pH form of sulfite oxidase: Ka-band ESEEM of equatorial chloro ligands in oxomolybdenum(V) complexes

“…In order to simulate such a small ESEEM amplitude (assuming the 10 MHz line comes from chlorine), one has to employ a rather weak hfi. Attempts to simulate this spectrum assuming a single remote chlorine nucleus (a iso = 0 and |T^| < 0.5 MHz, which corresponds to the Mo-Cl distance R > 2.5 Å , slightly greater than the Mo-Cl bond length for a coordinated chloride [42]) were unsuccessful, in that the calculated ESEEM amplitude was about five times smaller than the experimental one. The experimental ESEEM amplitude could only be reproduced if a iso 6 ¼ 0 was assumed (see dashed trace 3 in Fig.…”

Binding N2, N2H2, N2H4, and NH3 to Transition‐Metal Sulfur Sites: Modeling Potential Intermediates of Biological N2 Fixation

“…These doublets were assigned to the formation of further mononuclear diazene complexes 8 (Figure 3 The appearance of at least four different mononuclear diazene complexes 8, presumably with the identical formula [Ru(N 2 H 2 )(PiPr 3 )(−N 2 Me 2 S 2 ×)], is rationalized by the fact that 1) N 2 H 2 ligands in transition-metal thiolate complexes form comparably strong hydrogen bonds to the thiolate donors, which can result in a total hydrogen-bond energy of up to 21 kJ mol À1 , [13] 2) chiral cis,trans-[Ru(N 2 H 2 )-(PiPr 3 )(−N 2 Me 2 S 2 ×)] can form two different hydrogen-bond species I and II, which are diastereomers because the Ru center is stereogenic, [14] and 3) the [Ru(PiPr 3 )(−N 2 Me 2 S 2 ×)] fragment itself can also exist in the cis,cis configurations III and IV, which are diastereomeric both to each other and to the fragments in I and II (Scheme 2). [15] The two diastereom- However, cis,cis configuration of the −N 2 Me 2 S 2 × 2À ligand is usually not favored, unless sterical constraints enforce this less-common coordination mode. Diazene ligands, which are capable of forming strong hydrogen bridges to neighboring S(thiolate) functions (see above), can impose such steric constraints and therefore promote the formation of cis,cis-[Ru(N 2 H 2 )(PiPr 3 )(−N 2 Me 2 S 2 ×)] (8) complexes.…”