SUBSTITUENT INTERACTIONS IN ETA-6-ARENE COMPLEXES .1. SYSTEMATIC X-RAY CRYSTALLOGRAPHIC STUDY OF THE STRUCTURAL MANIFESTATIONS OF PI-DONOR AND PI-ACCEPTOR SUBSTITUENT EFFECTS IN SUBSTITUTED (ETA-6-ARENE)CR(CO)3 COMPLEXES

The new X-ray crystal structures of five (eta(6)-arene)Cr(CO)3 complexes having one or two pi-donor or pi-acceptor substituents on their benzene rings are reported and are compared with the structures of the related (eta(6)-arene)Cr(CO)3 complexes reported in the literature. It is found that the pi-donor substituents and the ipso-carbon atoms to which they are attached are bent away from the Cr(CO)3 fragments while the pi-acceptor substituents and the ipsi-carbon atoms to which they are attached are approximately in the arene plane or are bent slightly toward the Cr(CO)3 fragments. The magnitudes and directions of these distortions of the arene planarity are found not to be dependent on the steric bulk of the substituent for any but the most bulky substituents. Rather, these distortions appear to be due primarily to electronic effects and a model is proposed to explain these distortions in terms of the pi-donor and/or pi-acceptor character of the arene substituents. The new X-ray structures reported are those of (eta(6)-C6H5(NH2))Cr(CO)3 (C9H7CrNO3: a = 7.0425 (12) angstrom, b = 9.572 (4) angstrom, c = 7.4694 (11) angstrom, beta = 110.798 (12)-degrees, V = 470.7 (2) angstrom 3; monoclinic; P2(1)/m; Z = 2), (eta(6)-C6H5(OMe))Cr(CO)3 (C10H8CrO4: a = 7.2485 (6) angstrom, b = 11.6331 (12) angstrom, c = 12.0276 (10) angstrom, V = 1014.20 (14) angstrom 3; orthorhombic; P2(1)2(1)2(1); Z = 4), (eta(6)-1,4-C6H4(NMe2)2)Cr(CO)3 (C13H16CrN2O3: a = 8.2210 (16) angstrom, b = 16.7202 (13) angstrom, c = 9.1900 (19) angstrom, beta = 90.879 (10)-degrees, V = 1263.1 (4) angstrom 3; monoclinic; P2(1)/n; Z = 4), (eta(6)-1,4-C6H4(OMe)2)Cr(CO)3 (C11H10CrO5: a = 7.859 (3) angstrom, b = 8.140 (9) angstrom, c = 19.014 (7) angstrom, beta = 98.930 (20)-degrees, V = 1216.5 (7) angstrom 3; monoclinic; P2(1)/c; Z = 4), and (eta(6)-1,4-C6H4(CO2Me)2)Cr(CO)3 (C13H10CrO7: a = 8.8537 (14) angstrom, b = 20.2488 (11) angstrom, c = 7.5823 (12) angstrom, beta = 92.724 (8)-degrees, V = 1357.8 (3) angstrom 3; monoclinic; P2(1)/c; Z = 4).