67619-17-4Relevant academic research and scientific papers
Mixed chloride/amine complexes of dimolybdenum(II,II). 6. Stepwise substitution of amines by tertiary phosphines and vice versa: Stereochemical hysteresis
Cotton, F. Albert,Dikarev, Evgeny V.,Herrero, Santiago
, p. 609 - 616 (2008/10/08)
The substitution reactions of primary amines by tertiary phosphines in quadruply bonded, dimolybdenum(II,II) complexes Mo2Cl4(NH2R)4 have been studied. The exchange reaction has been shown to result at room temperature in disubstituted species Mo2Cl4(NH2R)2(PR3)2 (PR3 = PMe3, NH2R = NH2Pr(n) (1a), NH2Bu(t) (2a), NH2Cy (3a); PR3 = PMe2Ph, NH2R = NH2CY (4a)), while heating is needed to obtain fully substituted complexes Mo2Cl4-(PR3)4. The crystal structure of disubstituted products has been investigated by X-ray crystallography and revealed that they all belong to the α-isomer, having both phosphine groups at the same Mo atom. Crystal data are as follows: for 1a, tetragonal space group I41/a with a = 17.737(2) A, c = 15.6915(6) A, and Z = 8; for 3a, monoclinic space group P21 with a = 10.963(3) A, b = 10.117(2) A, c = 13.323(4) A, β = 90.05(2)°, and Z = 2; for 4a, triclinic space group P1 with a = 9.329(3) A, b = 10.206(2) A, c = 18.975(3) A, α = 85.45(2)°, β = 87.10(1)°, γ = 80.88(1)°, and Z = 2. The substitution processes for the direct and reverse reactions have been monitored by 31P NMR. They both proceed in a stepwise manner; however, a stereochemical hysteresis is taking place, i.e., the back reaction, the substitution of phosphines by amines, goes through another isomer of Mo2Cl4-(NH2R)2(PR3)2, having phosphine ligands on different Mo atoms. This β-isomer is more thermodynamically stable and can be obtained by thermal conversion of the α-form. All chemical equilibria studied in the paper have been explained as governed by a higher trans effect of PR3 groups compared to NH2R groups.
Structures of Mo2(CH3)4(PR3)4 molecules: Constancy of covalent radius of molybdenum in these and other Mo2X4(PR3)4 molecules
Cotton, F. Albert,Wiesinger, Kenneth J.
, p. 2594 - 2599 (2008/10/08)
The crystal and molecular structures of authentic, pure samples of Mo2Cl3(CH2C6H5)(PMe 3)4 (1), Mo2(CH3)4(PMe3)4 (2), and Mo2(CH3)4(PMe2Ph)4 (3) are reported. Special care was exercised in the preparation of 2 and 3 to exclude chloride and thus obviate the presence of chloride-containing contaminants. A previously reported structure for what was thought to be 2 is thus shown to be invalid owing to serious contamination by Cl--containing impurities. The Mo-C distances in 1 and 2 are then compared to those in other Mo2X4(PR3)4 compounds, and it is shown that the molybdenum atom in such compounds displays an essentially constant covalent radius of 1.40 ± 0.02 A?. Crystal data for 1-3 are as follows. 1: space group P21/c with a = 14.319 (5) A?, b = 10.612 (1) A?, c = 21.004 (5) A?, β = 106.62 (6)°, V = 3058 (4) A?3, and Z = 4. 2: space group C2/c with a = 18.464 (4) A?, b = 9.453 (2) A?, c = 17.477 (4) A?, β = 116.33 (1)°, V = 2734 (2) A?3, and Z = 4. 3: space group P2/c with a = 18.478 (4) A?, b = 11.820 (2) A?, c = 18.567 (8) A?, β = 109.89 (2)°, V = 3813 (4) A?3, and Z = 4. For 1, the Mo-Mo, Mo-C, average Mo-Cl, and Mo-P distances are 2.1382 (3), 2.248 (3), 2.431 [2], and 2.56 [1] A?. The average Mo-Mo, Mo-C, and Mo-P distances in 2 and 3, respectively, are 2.1489 (4) and 2.164 [1] A?, 2.244 [4] and 2.242 [8] A?, and 2.504 [1] and 2.534 [2] A?.
