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New chromium complexes with diphosphine ligands have been obtained by the reaction of chromium(III) hexahydrate and diphosphines in acetone. The structure of chromium(III) complex 4 containing water molecule and 1,2-bis(diphenylphosphino)benzene as ligands and that of two chromium(III) complexes (12 and 13) with 1,2-bis(diphenylphosphino)benzene ligands containing alkenyl substituents in the ortho-position of one of the phenyl groups at the phosphorous atom have been determined using X-ray diffraction analysis. The catalytic properties of the obtained complexes in the composition of catalytic systems for ethylene trimerization have been studied. It has been shown that the obtained series of catalytic systems manifests high activity in the process of ethylene trimerization to 1-hexene, with the process selectivity exceeding 94%. The highest value of productivity amongst known selective catalytic systems for trimerization was achieved using a chromium complex 13 bearing the 2-methylprop-1-enyl group at the ortho-position of one of the phenyl groups. The influence of temperature, pressure, the nature of the solvent and the composition of the catalytic system on the parameters of the process of ethylene trimerization to form 1-hexene has been determined.

The activity of the catalyst systems of a number of diphosphine ligands and chromium complexes based on 1,2-bis(diphenylphosphino)benzene in the ethylene oligomerization reaction has been studied. Structural modifications of diphosphine ligands have been performed to create selective catalyst systems for ethylene oligomerization. It has been shown that the introduction of ortho-functional groups into one of the phenyl substituents at the phosphorus atom in diphosphine ligands makes it possible to carry out the process of ethylene oligomerization to 1-hexene with the selectivity of 90 wt % and above. One of the complexes (chromium complex 15) with a functionalized diphosphine ligand has been characterized by X-ray structure analysis. The influence of the change in the amount of the activator and its type on the activity of the catalyst systems has been studied. It has been shown that the replacement of some organoaluminum activator, methylaluminoxane, by trimethylaluminum does not decrease the productivity and selectivity of the catalyst systems based on diphosphine chromium complexes.

Reactions of [ exo-nido -5,6,10-{Cl(Ph 3 P) 2 Ru}-5,6,10-(μ-H) 3 -10-H-7,8-R 2 -7,8-C 2 B 9 H 6 ] ( 1 , R = H; 2 , R = Me) with the chiral (2S,4S)-2,4-bis(diphenylphosphino)pentane ( 3 , S , S -bdpp) ligand proceed in benzene with replacement of both PPh 3 ligands on the metal center with the diphosphine affording the chelate exo-nido complexes [ exo-nido -5,6,10-{Cl( S , S -bdpp)Ru}-5,6,10-(μ-H) 3 -10-H-7,8-R 2 -7,8-C 2 B 9 H 6 ] ( 7 , R = H) and ( 8 , R = Me), respectively. A relatively fast and irreversible rearrangement of 7 into its closo isomer [ closo -3,3-( S , S -bdpp)-3-Cl-3-H-3,1,2-RuC 2 B 9 H 11 ] ( 4 ) occurs in solution already at room temperature. On the contrary, exo-nido -to- closo conversion of 8 proceeds in benzene (or much faster in toluene) only on heating and yields 17-electron paramagnetic complex [ closo -3,3-( S , S -bdpp)-3-Cl-1,2-Me 2 -3,1,2-RuC 2 B 9 H 9 ] ( 9 ). All exo-nido - and closo -ruthenacarboranes obtained were characterized by a combination of analytical, multinuclear NMR or EPR spectroscopic data and, in addition, by X-ray diffraction studies of both dimethylated complexes 8 and 9 .

Reactions of the [K]+ salts of the [nido-7,9-C2B9H12]- anion (2) and its C-phenylated derivative [7-Ph-nido-7,9-C2B9H11]- (4) with [OsCl2(PPh3)3] (3) proceed in benzene at ambient temperature with the formation of 16-electron chlorohydrido-Os(IV) exo-nido complexes, [exo-nido-10,11-{(Ph3P)2OsHCl}-10,11-(mu-H)2-7-R-7,9-C2B9H8] (5: R = H; 6: R = Ph), along with the small amounts of the charge-compensated nido-carboranes [nido-7,9-C2B9H11PPh3] (7) and [7-Ph-nido-7,9-C2B9H10PPh3] (8) as byproducts. However, when carried out under mild heating in ethanol, the reaction of 2 with 3 selectively afforded a 16-electron dihydrido-Os(IV) exo-nido complex [exo-nido-10,11-{(Ph3P)2OsH2}-10,11-(mu-H)2-7,9-C2B9H9] (9). Structures of both complexes 5 and 9 have been confirmed by single-crystal X-ray diffraction studies, which revealed that nido-carboranes in these species function as a bidentate dicarbollide ligands [7-R-nido-7,9-C2B9H10]2- linked to the Os(IV) center via two B-H...Os bonds involving adjacent B-H vertices in the upper CBCBB belt of the carborane cage. Thus, compounds 5 and 9 represent the first structurally characterized exo-nido-metallacarboranes based on meta-dicarbollide-type ligands. Variable-temperature 1H and 31P{1H} NMR experiments indicate that complex 9 is fluxional in solution and shows an unusual exchange between terminal Os-(H)2 and bridging {B-H}2...Os hydrogen atoms. Upon heating in d8-THF at 65 degrees C, complex 9 converts irreversibly to its closo isomer [2,2-(PPh3)2-2,2-H2-closo-2,1,7-OsC2B9H11] (13), which could thus be obtained as a pure crystalline solid. The structure of 13 has been established on the basis of analytical and multinuclear NMR data and a single-crystal X-ray diffraction study.