Previous difficulties in rationalizing the relative trans effect and trans influence of alkyl groups in organocobalt complexes, including organocobalt B12 species (i.e. organocobalamins), are resolved by using a modified dual-substituent-parameter (DSP) approach. In contrast to some previous studies, in which the entire alkyl axial ligand (R) was treated as the substituent, the new approach involves treating R groups with a methylene group bound to Co as a CH2Y species, where Y is the substituent. This approach is tested in depth in cobaloxime compounds of the type LCo(DH)2CH2Y (where DH = monoanion of dimethylglyoxime). It was found that when L = 4-cyanopyridine (4-CNpy) and Y = N02, CN, CF3, I, C02Me, Br, COMe, Cl, H, SiMe3, Ph, Me, and OMe, the 4-CNpy dissociation rate increased by a factor of more than 106 and that the log of the first-order rate constant could be linearly correlated with the equation log k = + + in which , and + are organic-inductive and resonance-substituent constants and pl and pR are the respective coefficients. With use of and + = 0 for Y = Me (i.e. R = CH2Me), the linear correlation coefficient (lcc) was 0.9963 for 13 points and the goodness of fit (J) was excellent (0.093). A similar study with L = anisidine (without Y = N02) gave even better results (lcc = 0.9978 and / = 0.073). In contrast, the use of the substituent constant * for the entire R group gave no clear relationship, especially for R = CH2OMe. Thus, previous usage of * for quantitative analysis of data for organocobalt systems is questioned. Likewise, the modified DSP approach works well for 13C NMR shifts when the resonance parameter employed is °. These findings can be explained by invoking -* conjugation involving nonbonded electron pairs on the alkyl group and the polarizable Co-C bond. Since R = CH2OMe is a key alkyl group in our analysis and since no structural data are available to assess the structural trans influence of CH2OMe, several structural studies of PhNH2Co(DH)2R compounds were performed. Structural results for three compounds, (1) R = CH2Me, (2) R = CFI2OMe, and (3) R = t'-Pr, are reported. Crystallographic details follow: (1) C16H26CoN504-H20, P2l/n, a = 10.998 (1) A, b = 8.417 (2) A, c = 21.859 (2) A, 0 = 96.81 (1)°, Z)calcd = 1.42 g cm™3, Z = 4, R = 0.042 for 3006 independent reflections. (2) C16H26CoN505-H20, P2^c, a = 8.351 (3) A, b = 27.038 (8) A, c = 9.893 (2) A, ß = 107.37 (2)°, Z)calcd = 1.39 g cm™3, Z = 4, R = 0.046 for 2909 independent reflections. (3) C17H28CoN504-H20, P2l/C, a = 8.335 (1) A, b = 27.046 (5) A, c = 9.829 (1) A, ß = 106.71 (2)°, Z)ca,cd = 1.39 g cm™3, Z = 4, R = 0.043 for 3523 independent reflections. The structure of 2 reveals a trans influence for CH2OMe between that of CFI2Me and i'-Pr and no unusual steric effect of CH2OMe to account for its large trans effect or trans influence. Therefore, we conclude that the high position of CH2OMe in the trans effect/influence series is electronic and not steric in nature. Previous treatment of substituent effects of R groups demonstrate...

We have redetermined the known structures of (i) methylthiourea (MTU) and (ii) 1,1-dimethylthiourea (1,1-DMTU), and investigated the structure of 1,3-dimethylthiourea (1,3-DMTU), which was however severely disordered. We report the structures of crystalline adducts of (iii) MTU with morpholine (1:1), (iv) 1,1-DMTU with 1,4-dioxane (2:1) and (v) 1,3-DMTU with 1,4-dioxane (2:1). Finally, (vi) we determined the structure of tetramethylthiourea (TetMTU). (i) In both independent molecules of MTU, the methyl group is trans to the C=S group across the C-N bond. The two molecules are connected to form an R2(2)(8) dimer by mutual N-H...S=C interactions. The packing involves six N-H...S=C interactions and is three-dimensional. (ii) The packing of the MTU-morpholine adduct is a layer structure, within which both molecules form linear aggregates parallel to the b axis. (iii) The packing of 1,1-DMTU involves N-H...S=C hydrogen bonds forming a corrugated layer structure. (iv) In the 2:1 adduct between 1,1-DMTU and 1,4-dioxane, the DMTU molecule occupies a general position whereas the dioxane molecule lies across an inversion centre. The crystal packing involves chains of alternating 1,1-DMTU R2(2)(8) dimers and dioxanes, both across inversion centres. (v) In the 2:1 adduct between 1,3-DMTU and dioxane, the 1,3-DMTU molecule occupies a general position, while the dioxane molecule lies across an inversion centre. One methyl group of the DMTU is trans and one cis to the sulfur across the corresponding C-N bond. The molecules form chains of alternating 1,3-DMTU R2(2)(8) dimers and dioxanes, both across inversion centres. Crystals of the 2:1 adduct between 1,3-DMTU and morpholine were also obtained, and were isotypic with the dioxane adduct. The morpholine molecule is disordered across the inversion centre. (vi) The molecule of TetMTU displays crystallographic twofold symmetry. Significant distortions reflect the steric pressure between methyl groups trans to sulfur. The packing of TetMTU involves only a weak hydrogen bond, C-Hmethyl...S, which connects the molecules to form layers.

The solvents 1,4-dioxane and morpholine have been employed to synthesize solvates of urea and thiourea.The structures confirm the tendency of urea to form more rigid systems of hydrogen bonds in the plane of the N 2 CLO moiety, thus forming layer structures with close complementarity of the donors and acceptors, whereas the more flexible sulfur acceptor of thiourea can also accept hydrogen bonds from donors that lie far from the N 2 CLS plane, forming three-dimensional packing patterns with much more variable parameters. A database investigation confirms these tendencies. The solvate urea : morpholine (1 : 1) crystallizes in Pbcm with Z = 4. The complete urea molecule lies in the mirror plane, as do the heteroatoms of the morpholine molecule. The molecular packing is a layer structure. The solvate urea : 1,4-dioxane (1 : 1) crystallizes in P2/c with Z = 2. The CLO bond of the urea molecule lies along a twofold axis, whereas the dioxane molecule lies across an inversion centre. The molecules form a layer structure analogous to that of the morpholine solvate. The thiourea solvates are more complex, and both involve a more irregular hydrogen bonding geometry at sulfur. The solvate thiourea : morpholine (4 : 3) crystallizes in P2 1 /c with Z = 2. The asymmetric unit contains two independent molecules of thiourea, one morpholine on a general position, and one morpholine disordered over an inversion centre. The thiourea molecules combine to form an open framework with a series of channels, in which the morpholine molecules are attached. The solvate thiourea : 1,4-dioxane (4 : 1) crystallizes in P2 1 /n with Z = 2. The asymmetric unit contains two independent molecules of thiourea and one molecule of dioxane across an inversion centre. One thiourea molecule and the dioxane combine to form a layer structure. The second thiourea molecule links these layers in the third dimension.

Previous difficulties in rationalizing the relative trans effect and trans influence of alkyl groups in organocobalt complexes including organocobalt B12 species (i.e.