Synthesis and X-ray crystal structure of [Et4N] [Co(NH2-CSNHNH2)3] [Mo8O26]·4Me2NCHO

Summary [Et₂N] [Co(NH₂CSNHNH₂)₃] [Mo₈O₂₆] ·4Me₂NCHO, obtained by reacting MoCl₅, CoCl₂, thiosemicarbazide and DMF in nonaqueous solvents under i.r. radiation, was characterized by spectroscopy and X-ray crystallography. It contains an octanuclear molydenum anion with two pentabridging oxygen atoms and a cobalt-centred cation bonded to nitrogen and sulphur ligands.     

The reaction of [Bu4N]2[Pd2Br6(Se2N2)] with [14]aneS4; an effective source of the diselenium dinitride unit

Reaction of [Bu(4)N](2)[Pd(2)Br(6)(Se(2)N(2))] with [14]aneS(4) results in eventual formation of Se(4)N(4); intermediates in this reaction include an air-sensitive insoluble material which reacts with [PtCl(2)(PMe(2)Ph)](2) to give the first example of a platinum adduct of Se(2)N(2) and with [Pd(2)Br(6)](2-) to regenerate the starting material.     

Darstellung von trans-[Mo6Cl8]Cl4Br22−ausgehend von kristallisierten [Mo6Cl8]Cl4(H2O)2 und die Kristallstruktur von [(C6H5)4As]2[Mo6Cl8]Cl4Br2

Preparation of trans-[Mo₆Cl₈]Cl₄Br₂^2? Starting from Crystalline [Mo₆Cl₈]Cl₄(H₂O)₂ and Crystal Structure of [(C₆H₅)₄As]₂[Mo₆Cl₈]Cl₄Br₂ The synthesis of the title compound is successful if the crystallized [(Mo₆Cl₈)Cl₄(H₂O)₂] containing the H₂O molecules in trans-position reacts with HBr + [(C₆H₅)₄As]Br in ethanol in a heterogeneous reaction. The X-ray structure investigation confirms the existence of discrete trans-Br-substituted cluster anions of composition [(Mo₆Cl₈)Cl₄Br₂]^2? in the crystal. The reaction in homogeneous solutions proceeds to Br-enriched compounds. [(C₆H₅)₄As]₂[(Mo₆Cl₈)Cl₄Br₂] crystallizes in the triclinic space group P¯1 with a = 11.071(2), b = 11.418(2), c = 12.813(2) Å, α = 116.10(2), β = 95.27(2) and γ = 94.41(2)° (?133°C). The crystal structure at ?133°C was determined from single crystal X-ray diffraction data (R₁ = 0.026). The [(Mo₆Cl₈)Cl₄Br₂]^2?-anions are not completely ordered but distributed statistically among the three positions which are possible within the limits of the ordered [Mo₆Cl₈]-cores (ratio 11:5:4). The frameworks of the anions consist of Mo₆ cluster units with (slightly distorted) octahedral arrangement of the metal atoms (d(Mo? Mo): 2.600(1) up to 2.614(1) Å), which are coordinated by the halogeno ligands in a square-pyramidal manner. The details of the structure will be discussed and compared with similar [(Mo₆X₈)Y₄] cluster units (X, Y ? Cl, Br).     

Dinitrogen Activation by Fryzuk’s [Nb(P2N2)] Complex and Comparison with the Laplaza–Cummins [Mo{N(R)Ar}3] and Schrock [Mo(N3N)] Systems

The reaction profile of N₂ with Fryzuk’s [Nb(P₂N₂)] (P₂N₂=PhP(CH₂SiMe₂NSiMe₂CH₂)₂PPh) complex is explored by density functional calculations on the model [Nb(PH₃)₂(NH₂)₂] system. The effects of ligand constraints, coordination number, metal and ligand donor atom on the reaction energetics are examined and compared to the analogous reactions of N₂ with the three‐coordinate Laplaza‐Cummins [Mo{N(R)Ar}₃] and four‐coordinate Schrock [Mo(N₃N)] (N₃N=[(RNCH₂CH₂)₃N]^3?) systems. When the model system is constrained to reflect the geometry of the P₂N₂ macrocycle, the N? N bond cleavage step, via a N₂‐bridged dimer intermediate, is calculated to be endothermic by 345 kJ mol^?1. In comparison, formation of the single‐N‐bridged species is calculated to be exothermic by 119 kJ mol^?1, and consequently is the thermodynamically favoured product, in agreement with experiment. The orientation of the amide and phosphine ligands has a significant effect on the overall reaction enthalpy and also the N? N bond cleavage step. When the ligand constraints are relaxed, the overall reaction enthalpy increases by 240 kJ mol^?1, but the N₂ cleavage step remains endothermic by 35 kJ mol^?1. Changing the phosphine ligands to amine donors has a dramatic effect, increasing the overall reaction exothermicity by 190 kJ mol^?1 and that of the N? N bond cleavage step by 85 kJ mol^?1, making it a favourable process. Replacing Nb^II with Mo^III has the opposite effect, resulting in a reduction in the overall reaction exothermicity by over 160 kJ mol^?1. The reaction profile for the model [Nb(P₂N₂)] system is compared to those calculated for the model Laplaza and Cummins [Mo{N(R)Ar}₃] and Schrock [Mo(N₃N)] systems. For both [Mo(N₃N)] and [Nb(P₂N₂)], the intermediate dimer is calculated to lie lower in energy than the products, although the final N? N cleavage step is much less endothermic for [Mo(N₃N)]. In contrast, every step of the reaction is favourable and the overall exothermicity is greatest for [Mo{N(R)Ar}₃], and therefore this system is predicted to be most suitable for dinitrogen cleavage.     

Hydroboration of the Amino(imino)borane [Me3C(Me3Si)N]B[N(CMe3)]

The formation of four products of the type Me₃C(Me₃Si)N=BH–N(CMe₃)=BR'₂ [BR'₂ = B(CHMeiPr)₂ ( 1 ), B(c‐C₆H₁₁)₂ ( 2 ), B(C₈H₁₄) ( 3 ), B(O₂C₆H₄) ( 4 )] from the iminoborane Me₃C(Me₃Si)N–···B=···N(CMe₃) and the hydroboranes (R'₂BH)₂ is described. Crystal structure analysis reveals the molecule 1 to have an N=B–N=B backbone with two orthogonal N=B bond planes and, hence, no conjugation between the two B–N double bonds.     

Characterization of Diastereoisomeric [Ni(Me8[14]ane)]2+ Cations

The isomeric Me₈[l4]anes, designated by L_A, L_B and L_C, on reaction with nickel(II) acetate tetrahydrate and subsequent addition of LiClO₄·3HO yield yellow or orange-yellow square planar [NiL](ClO₄)₂ diastereoisomers. It has been possible to isolate two N-chiral diastereoisomers for each ligand and these give distinct infrared and ¹H NMR spectra. The structures of these isomers have been assigned mainly on the basis of their ¹H NMR spectra. One structure, namely [NiL_Bα ](ClO₄)₂, has been confirmed by x-ray crystallography.     

ESR-Untersuchungen an μ-Dichloro-bis[chloro-bis(N,N-diäthyldiselenocarbamato)molybdän(V)]-dichlorid, [Mo2CI4(däsc)4]CI2

EPR-Investigations of α-Dichloro-bis[chloro?bis(N,N?diethyldiselenocarbamato)molybdänum(V)] dichloride, [Mo₂Cl₄(däsc)₄]Cl₂. Preparation and bonding properties of the coordination sphere of [Mo₂Cl₄(däsc)₄]Cl₂ studied by EPR, are reported. The EPR-spectrum at 77°K can be described by an axial symmetric spin-HAMILTONian, the parameters of which are g| = 2.046, g|= 1.996, A| = 53.5 · 10^?4 cm^?1, and A| = 22.8 · 10^?4 cm^?1. No ⁷⁷Se-ligand hyperfine structure could be observed. The very high g-values are explained as being caused by strong ligand spin-orbit interaction, CT-contributions and a high degree of co valency of tho Mo? Se bond. Using an MO-model of the symmetry C_4v, the bonding parameters of the first coordination sphere have been calculated.