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.