Crystalline Adducts of Tetrakis(triphenylacetato)dichromium(II) with Benzene, Pyridine, and Diethyl Ether. Benzene as a Multiple ? Donor

Article abstract of DOI:10.1021/ja00217a019

Three crystalline compounds, Cr2(O2CCPh3)4*C6H6 (1), Cr2(O2CCPh3)4*Py (2), and Cr2(O2CCPh3)4*2Et2O (3), have been prepared and structurally characterized.Compound 1 is obtained by reaction of (η⁵-C5H5)2Cr with Ph3CCO2H in toluene/benzene, and the others are derived by recrystallization in the presence of pyridine and Et2O, respectively.Crystallographic parameters are as follows.Compound 1: tetragonal space group P4/ncc; a=b=20.787(4) Angstroem, c=17.710(3) Angstroem, V=7653(3) Angstroem³, and Z=4.Compound 2: tetragonal space group <*>, a=b=18.268(4) Angstroem, c=10.919(2) Angstroem, V=3644(2) Angstroem³, and Z=2.Compound 3: monoclinic space group C2/c; a=21.535(5) Angstroem, b=17.065(5) Angstroem, c=20.498(4) Angstroem, β=90.65(3)^o, V=7532(3) Angstroem³, and Z=4.The Cr2(O2CCPh3)4 molecules pack in ways that are heavily influenced by the requirements of the CPh3 groups, and this leaves holes of intermediate size in the axial regions of the Cr2(O2CR)4 molecules.In 1 there is a benzene molecule centered in each hole so that the center of the benzene ring is 3.30 Angstroem from each adjacent Cr atom, with the ring plane perpendicular to the Cr2 axes.Calculations by the Xα-SW-SCF method show that the e_1u orbitals of the benzene molecules donate appreciable electron density to the ?^* orbitals of the Cr2 units, thus weakening the Cr-Cr bond, which has a lenght of 2.256(4) Angstroem.In the pyridine compound 2 the size of the cavity available allows only one pyridine molecule and also enforces a tilt relative to the Cr-Cr axis.The Cr-N distance is 2.31(4) Angstroem, and the Cr-Cr distance is 2.383(4) Angstroem.Each pyridine molecule is disordered systematically over four positions.In the ether-containing compound, two ether molecules are accommodated in each cavity, and thus each dichromium molecule has an axial Cr-O bond, 2.30(1) Angstroem, at each end and a Cr-Cr distance of 2.303(4) Angstroem.