Lai Yoong Goh

Determination of metalmetal bond energies in [CpCr(CO)2L]2 complexes [ L = CO, P(OMe)3] by NMR

Abstract A variable-temperature proton NMR study of the dimer-monomer equilibrium in the [CpCr(CO) 2 L] 2 complexes [( 1 ), L = CO; ( 2 ), L = P(OMe) 3 ] and application of vant Hoffs equation gave the following thermodynamic parameters: 1 , Δ H = 21.3±0.7 kcal mol −1 , Δ S = 50.7±2.2 cal mol −1 K −1 and Δ G 300 = 6.1 kcal mol −1 ; 2 , Δ H = 18.8±0.4 kcal mol −1 , Δ S = 69.0±1.5 cal mol −1 K −1 and Δ G 300 = −1.9 kcal mol −1 .

Sulphur chromium complexes: syntheses and crystal structures of (η5C5H5)2Cr2(CO)4S and (η5-C5H5)2Cr2(CO)5S2

The facile reaction of dicyclopentadienylhexacarbonyldichromium with stoicheiometric amounts of elemental sulphur in tetrahydrofuran or toluene at ambient temperature produces (η5-C5H5)2Cr2(CO)4S (1) and (η5-C5H5)2Cr2(CO)5S2(2) in isolated yields of 100 and 90%, respectively.

Isolation of pentamethylcyclopentadienylchromium tricarbonyl dimer by two methods. X-Ray crystal structural study of two polymorphs

The [(C5Me5)Cr(CO)3]2 dimer has been prepared by two methods, (i) oxidation of the anion [(C5Me5)Cr(CO)3]− by ferric ions in an aqueous acidic medium, and (ii) carbonylation of [(C5Me5)Cr(CO)2]2 under high CO pressure at elevated temperatures. The complex crystallises in the monoclinic system in two polymorphic forms (I and II). Crystal structure data: I: space group P21/c, a = 8.376(4), b = 19.397(6), c = 8.805(5) A, β = 117.40(3)°, U = 1269.8 A3, Z = 2, Dc = 1.419 g cm−3, and II: space group P21/n, a = 9.333(2), b = 8.998(1), c = 15.297(3) A, β = 95.86(2)°, U = 1277.9(1) A3, Z = 2, Dc = 1.37 g cm−3.

Chemistry of chromium-selenium complexes. Thermolytic degradation of Cp2Cr2(CO)4Se, and the crystal structures of the cubane-like clusters Cp4Cr4(μ3-CO)2(μ3-Se)2 and Cp4Cr4(μ3-O)2(μ3-Se)2

Abstract Thermolysis of Cp 2 Cr 2 (CO) 4 Se ( 1 ) solution gave initially Cp 4 Cr 4 (CO) 2 Se 3 ( 3 ), and a thermally labile unidentified species, which on further degradation afforded a mixture of products, from which more of 3 , and the cubane-like complexes Cp 4 Cr 4 (CO) 2 Se 2 ( 2 ) and Cp 4 Cr 4 O 2 Se 2 ( 4 ) were isolated. A more prolonged thermolysis in THF yielded Cp 4 Cr 4 Se 4 ( 5 ) as the main product. Crystal data: 2 , monoclinic, space group C 2/ c , a 17.656(5), b 8.232(1), c 18.079(6) A, β 126.15(2)°, Z = 4, R = 0.075 for 1499 observed Mo- K α data; 4 , monoclinic, space group P 2 1 / c , α 14.08(1), b 10.306(8), c 15.212(6) A, β 103.55(2)°, Z = 4, R = 0.082 for 1711 observed Mo- K α data. Both complexes possess a cubane-like structure with triply bridging Se and CO or O ligands at alternating corners of the cuboid.

1-Adamantylpentacyanocobaltate(III)

Abstract The preparation and properties of potassium 1-adamantylpentacyanocobaltate(III) trihydrate are described.

Coordination of Cp2Cr2(CO)4(μ-η2P2) to metal carbonyl fragments and crystal structure of Cp2Cr2(CO)4− (μ-η2-P2)[Cr(CO)5]2

Cp2Cr2(CO4(μ-η2-P2) (I) reacts with 2 mole equivalents of M(CO)5THF to give Cp2Cr2(CO)4(μ-η2-P2)[M(CO)5]2 (M = Cr, II; Mo, III; W, IV) in 65–70% yields. The reaction with 1 mole equivalent of Cr(CO)5THF gave the mono-metallated complex Cp2Cr2(CO)4(μ-η2-P2[Cr(CO)5] (V) in 60% yield along with II in 18% yield. In the presence of stoichiometric amount of PPh3 as a Cr(CO)5 scavenger, II was converted into V and I. X-ray analysis showed that II has C2 molecular symmetry; the Crue5f8Cr′ and Pue5f8P′ bond distances in the tetrahedral Cr2P2 core are 3.003(1) and 2.063(1) A, respectively.

Linkage of a pentacarbonylchromium fragment to a (μ-η2-P2)Cr2 core. Crystal structure of Cp2Cr2(CO)4)(μ-η2-P2)[Cr(CO5)]

Abstract The complex Cp2Cr2(CO)4(μ-η2-P2)[Cr(CO)5] (2) formed in the reaction of Cp2Cr2(CO)4(μ-η2-P2) (1) with one molar proportion of Cr(CO)5(THF), has been structurally characterized. Crystal data: triclinic, space group P 1 , a 7.859(4), b 9.948(5), c 16.209(8) A, α 104.29(3), β 97.30(3), γ 108.90(3)°, and Z = 2. The molecular geometry of 2 is compared with those of 1 and Cp2Cr2(CO)4(μ-η2-P2)[Cr(CO)5]2 (3).

A new type of polycyclophosphidochromium cluster, [(Cp)Cr(CO)2]5P10(Cp =η5-C5H5). First observation of polycylic P-to-M coordination

The co-thermolysis of [(Cp)Cr(CO)3]2(Cp =η5-C5H5) with P4 forms [(Cp)Cr(CO)2]5P10, a new paramagnetic structure with a P10 core, which represents the first example of polycyclic phosphorus-to-metal coordination.

Equilibrium studies on metalmetal bond dissociation in the [(C5Me5)Cr(CO)3]2 dimer by use of NMR spectroscopy

The thermodynamics of metalue5f8metal bond dissociation in the [(C5Me5)Cr(CO)3]2 dimer was studied by variable-temperature room NMR study in toluene-d8. Dissociation constants and proton isotropic shifts at various temperatures were obtained. Application of the van ′ Hoff equation gives the following thermodynamic parameters: ΔH = 18.3 (±0.6) kcal mol−1; ΔS = 54.8 (±2.2) cal mol−1 K−1 (ΔG = 1.9 kcal mol−1 at 300 K). These parameters were compared with those of the [(C5H5)Cr(CO)3]2 dimer. The most likely spin delocalization mechanism for the methyl protons is believed to be a combination of σ and π spin delocalization. The ESR spectrum in toluene (g0 = 2.004±0.001) or at below 273 K is consistent with a non-degenerate ground state of the monomer.

The kinetics of the step-wise aquation of the oxalatobis(ethylenediamine) chromium(III) ion in acid solution

Abstract Four stages in the aquation of the Cr en2ox+ ion have been studied in the hydrogen ion concentration range 1·0-0·1 M The stages followed with the corresponding rate constants, × 107/sec−1, 298 K, H+ = 1·0 M, and activation parameters, ΔH ‡ / cal. K −1 mole −1 are ase as follows: Cr en2ox+ → Cr en(enH)ox(H)2O)2+, 190 ± 5, 19·7 ± 0·4, −14 ± 1; Cr en(enH)ox(H2O)2+ → Cr en ox(H2O)2+, 184 ± 8, 20·1 ± 1·0, −13 ± 1; Cr en ox(H2O)2+ → Cr(enH)ox(H2O)32+, 63 ± 3, 19·5 ± 0·3, −17 ± 1; Cr(enH)ox(H2O)32+ → Cr ox(H2O)4+, 25 ± 1, 22·1 ± 0·1, −10 ± 1. ∗ Mathematical analysis of the overall absorbance changes suggests that isomerization reactions are involved in the aquation of the Cr en2ox+ ion. A comparison is made of kinetic data now known for a number of complexes which show labilization of chromium-nitrogen bonds.